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Selection on the timing of migration and breeding: A neglected aspect of fishing-induced evolution and trait change
Abstract
Fishing can drive changes in important phenotypic traits through plastic and evolutionary pathways. Size-selective harvest is a primary driver of such trait change, has received much attention in the literature and is now commonly considered in fisheries management. The potential for selection on behavioural traits has received less study, but mounting evidence suggests that aggression, foraging behaviour and linked traits can also be affected by fishing. An important phenomenon that has received much less attention is selection on reproductive phenology (i.e., the timing of breeding). The potential for this type of “temporal selection” is widespread because there is often substantial variability in reproductive phenology within fish populations, and fisheries management strategies or fishermen's behaviours can cause fishing effort to vary greatly over time. For example, seasonal closures may expose only early or late breeding individuals to harvest as observed in a range of marine and freshwater fisheries. Such selection may induce evolutionary responses in phenological traits, but can also have demographic impacts such as shortened breeding seasons and reduced phenotypic diversity. These changes can in turn influence productivity, reduce the efficacy of management, exacerbate ongoing climate-driven changes in phenology and reduce resilience to environmental change. In this essay, we describe how fisheries management can cause temporal variability in harvest, and describe the types of selection on temporal traits that can result. We then summarize the likely biological consequences of temporally selective fishing on populations and population complexes and conclude by identifying areas for future research.
... Temporal selection is likely to occur in many fisheries, particularly for salmon (Tillotson and Quinn 2018), and several mechanisms may lead to phenological shifts in response to such selection. The clearest example of FIE of timing is when, within a single population, fisheries disproportionately target early or late portions of a run and thus impose directional selection (Harvey et al. 2017). ...
... Fisheries should be explicitly considered as a source of bias in the data and as a causal mechanism. Virtually, all salmon populations are fished, often heavily, in coastal waters and during upriver migration, and many if not most fisheries are selective on timing, either by regulation or common practice (Tillotson and Quinn 2018). If the salmon are counted after some or all the fishing has taken place, those counted will not represent the whole population's timing, just as they often do not represent the true size distribution (e.g., Kendall and Quinn 2012) or sex ratio (Kendall and Quinn 2013) either. ...
... Temporal patterns of fishing effort under several common fishing/management strategies and their selective influence on salmon migration timing. Adapted fromTillotson and Quinn (2018). ...
Migration timing has evolved in many animals, allowing them to maximize breeding and feeding success by matching seasonal changes in abiotic conditions and resource pulses. These seasonal changes can shift with the climate, resulting in mismatches between migrations and resource availability unless the populations respond through phenotypic plasticity or evolutionary adaptation. It is common, however, for factors unrelated to climate to affect phenology. Salmon are an exceptionally well-studied group of fishes whose breeding migrations can serve as a template to consider the complex factors affecting migration phenology. In this paper, hypotheses for explaining changes in adult salmon migration phenology are reviewed. Pathways through which climate change may influence migration timing are first summarized, including shifting migration cues, limiting freshwater conditions, changes in distribution and conditions at sea, and alterations in embryo development. Alternative causes of phenological change in salmon are then explored including anthropogenic modifications of river habitat, demographic effects, hatcheries, and fisheries. The effects of these factors on phenology can mimic and mask climate effects, making it challenging to disentangle the causal basis of observed patterns. Instead of inferring shifts from trends in timing data (as is often done), it is suggested that specific mechanistic hypotheses be proposed and tested rigorously, and alternative causes systematically ruled out. Overall, it is challenging to attribute causation to phenological change, but salmon exemplify the many ways in which migration timing can change, including shifts due to climate and other processes.
... Siegel et al. (2018) attributed younger maturation in certain Alaskan Chinook salmon to faster growth in the second ocean year, with both genetic and environmental drivers. Climate change might select for later upstream migration timing in Snake River fall Chinook (Plumb 2018), although selective fishing can depresses heterogeneity in run timing and thus reduce resilience to climate change (Tillotson and Quinn 2018). There is some evidence of recent biological and human adaptation to climate change (Miller et al. 2018), but mostly papers documented historical adaptations to climate. ...
... A substantial body of research has focused on potential fisheries selection for earlier age at maturation. However, Tillotson and Quinn (2018) point out that selection on migration and spawn timing may also be an important impact of fisheries. There is substantial potential for such selection because exploitation of returning adults is often temporally disproportionate. ...
... There is substantial potential for such selection because exploitation of returning adults is often temporally disproportionate. Tillotson and Quinn (2018) describe how temporally selective fishing practices can ultimately limit breeding periods and reduce phenotypic diversity, thus depressing productivity and resilience to climate change. ...
A summary of the literature most relevant to the future impacts of climate change on Pacific Salmon from the year 2018
... Fishery-induced selection could change the timing of migration and breeding in commercially exploited fishes (Tillotson and Quinn 2018). Both selective fishing towards later migrants of Alaskan sockeye salmon (Oncorhynchus nerka) and shifts for earlier migration timing over the last quarter of the 20th century were demonstrated by Quinn et al. (2007). ...
... Both selective fishing towards later migrants of Alaskan sockeye salmon (Oncorhynchus nerka) and shifts for earlier migration timing over the last quarter of the 20th century were demonstrated by Quinn et al. (2007). However, the direction of fishery-induced selection on the timing of migration and breeding is likely to differ, depending on the way in which each fishery occurs (Tillotson and Quinn 2018). If so, it may not be possible to explain the general tendency towards temporally advanced migration in salmonids. ...
... As the timings of migration and breeding are highly heritable, potential exists for fisheries-induced evolution (Tillotson and Quinn 2018). In most salmon fisheries, fishing occurs in coastal areas rather than on spawning grounds, so it is important to know the timing of arrival of each breeding line to the coast to be fished, and whether any lag exists between the timing of coastal arrival and upstream migration. ...
Recent studies reporting shifts in the timing of salmonid migrations have suggested global warming to be a cause. However, the specific mechanisms underlining the evolution of earlier-migration timing in salmonid fishes are unknown. In this paper, I present a hypothesis by which fishery-induced selection works to advance the timing of salmonid migration, given the timing of migration and breeding are genetically controlled heritable traits. Although late-spawning salmon brood lines enter rivers after early spawning brood lines, there is evidence that all brood lines arrive in coastal fishing grounds at similar times. As such, late-spawning brood lines would be fished for longer periods of time, with their increased harvest rate imposing directional selection on earlier-spawning brood lines. Thus, fisheries-induced evolution could favor the earlier timing of river entry to escape coastal fisheries. Should earlier migration timing not be an adaptation to global warmingshould it be a maladaptation to fisheries-induced selection insteadthen it will have a negative impact on the sustainability of salmonid resources.
... Shifts in population size and demographics through restoration and management activities can also act to confound phenological responses due to changes in the sizes and ages of fish in the population (Tillotson and Quinn 2018). For example, passage was restored in the Acushnet River through the removal of three barriers, which resulted in the annual number of fish moving through this system increasing from 395 (prior to 2007) to 10,144 fish (in 2014). ...
... Run initiation and peak metrics were earlier when minimum winter SST was warmer and winter duration was shorter (either through later fall transition dates during the previous year or earlier spring transition dates). Run initiation was also earlier when run sizes were larger, indicating that changes in abundance and population restoration may confound climate-induced signals of phenology (Tillotson and Quinn 2018). Peak run timing was influenced by changes in the GSI and is consistent with prior studies in the region showing that fish population distributions are sensitive to changes in bottom water temperatures (Nye et al. 2011). ...
The timing of biological events in plants and animals, such as migration and reproduction, is shifting due to climate change. Anadromous fishes are particularly susceptible to these shifts as they are subject to strong seasonal cycles when transitioning between marine and freshwater habitats to spawn. We used linear models to determine the extent of phenological shifts in adult Alewife Alosa pseudoharengus as they migrated from ocean to freshwater environments during spring to spawn at 12 sites along the northeastern USA. We also evaluated broadscale oceanic and atmospheric drivers that trigger their movements from offshore to inland habitats, including sea surface temperature, North Atlantic Oscillation index, and Gulf Stream index. Run timing metrics of initiation, median (an indicator of peak run timing), end, and duration were found to vary among sites. Although most sites showed negligible shifts towards earlier timing, statistically significant changes were detected in three systems. Overall, winter sea surface temperature, spring and fall transition dates, and annual run size were the strongest predictors of run initiation and median dates, while a combination of within‐season and seasonal‐lag effects influenced run end and duration timing. Disparate results observed across the 12 spawning runs suggest that regional environmental processes were not consistent drivers of phenology and local environmental and ecological conditions may be more important. Additional years of data to extend time series and monitoring of Alewife timing and movements in nearshore habitats may provide important information about staging behaviors just before adults transition between ocean and freshwater habitats.
... All coho salmon released since the late 1990s from most large hatcheries in southern British Columbia, Washington, and Oregon have been visually marked with an adipose fin clip to facilitate mark-selective fisheries intended to target hatchery salmon and spare naturally spawned (unclipped) individuals. Not only does the presence of life history variation in hatchery fish impact the economic benefit derived from their harvest, but also selective harvest practices can in turn lead to altered life history and phenology in exploited populations (Hard et al., 2008;Tillotson & Quinn, 2018). Therefore, evaluation of life history variation among and within hatchery populations can facilitate both selection of populations well suited for harvest augmentation and evaluation of the subsequent impacts of exploitation rates on the populations under enhancement. ...
... The strong genetic basis for, and existence of both genetic and phenotypic correlations among, life history traits in salmonids makes the outcome of hatchery broodstock-selective efforts unpredictable, especially when combined with selective fishery forces that may be poorly characterized (Tillotson & Quinn, 2018). Broodstock manipulation within hatchery populations should be approached with caution and on an experimental basis until greater understanding of consequences is gained. ...
Abstract In salmonid parentage‐based tagging (PBT) applications, entire hatchery broodstocks are genotyped, and subsequently, progeny can be nonlethally sampled and assigned back to their parents using parentage analysis, thus identifying their hatchery of origin and brood year (i.e., age). Inter‐ and intrapopulation variability in migration patterns, life history traits, and fishery contributions can be determined from PBT analysis of samples derived from both fisheries and escapements (portion of a salmon population that does not get caught in fisheries and returns to its natal river to spawn). In the current study of southern British Columbia coho salmon (Oncorhynchus kisutch) populations, PBT analysis provided novel information on intrapopulation heterogeneity among males in the total number of progeny identified in fisheries and escapements, the proportion of progeny sampled from fisheries versus escapement, the proportion of two‐year‐old progeny (jacks) produced, and the within‐season return time of progeny. Fishery recoveries of coho salmon revealed heterogeneity in migration patterns among and within populations, with recoveries from north and central coast fisheries distinguishing “northern migrating” from “resident” populations. In northern migrating populations, the mean distance between fishery captures of sibs (brothers and sisters) was significantly less than the mean distance between nonsibs, indicating the possible presence of intrapopulation genetic heterogeneity for migration pattern. Variation among populations in productivity and within populations in fish catchability indicated that population selection and broodstock management can be implemented to optimize harvest benefits from hatcheries. Application of PBT provided valuable information for assessment and management of hatchery‐origin coho salmon in British Columbia.
... In addition to the pure effect of removals on age structure, there is potential for evolutionary change in spawner age structure through selection for maturation at earlier age or smaller size (reviewed in Wright & Trippel, 2009). Depending on the sensitivity of spawn timing to demography, demographic change could decouple spawn timing and larval first feeding from temperature-driven changes in the phenology of other spring events such as phytoplankton blooms and zooplankton production (Tillotson & Quinn, 2018). Furthermore, demography-induced reductions in spawning duration could increase the risk of a mismatch as firstfeeding larvae are delivered into the environment over a contracted period, which can increase variation in recruitment (McGilliard, Punt, Hilborn, & Essington, 2017;Mertz & Myers, 1994). ...
... For pollock, increased fishing mortality is projected to shift spawn timing to later in the season, on average, as well as contract the spawning season to a shorter time period. It is unknown to what extent spawn timing may have evolved or be evolving due to selection from fisheries (seeTillotson & Quinn, 2018), but fishing-induced shifts ...
Shifts in phenology are a well‐documented ecological response to changes in climate, which may or may not be adaptive for a species depending on the climate sensitivity of other ecosystem processes. Furthermore, phenology may be affected by factors in addition to climate, which may accentuate or dampen climate‐driven phenological responses. In this study, we investigate how climate and population demographic structure jointly affect spawning phenology of a fish species of major commercial importance: walleye pollock (Gadus chalcogrammus). We use 32 years of data from ichthyoplankton surveys to reconstruct timing of pollock reproduction in the Gulf of Alaska and find that the mean date of spawning has varied by over 3 weeks throughout the last >3 decades. Climate clearly drives variation in spawn timing, with warmer temperatures leading to an earlier and more protracted spawning period, consistent with expectations of advanced spring phenology under warming. However, the effects of temperature were nonlinear, such that additional warming above a threshold value had no additional effect on phenology. Population demographics were equally as important as temperature: An older and more age‐diverse spawning stock tended to spawn earlier and over a longer duration than a younger stock. Our models suggest that demographic shifts associated with sustainable harvest rates could shift the mean spawning date 7 days later and shorten the spawning season by 9 days relative to an unfished population, independent of thermal conditions. Projections under climate change suggest that spawn timing will become more stable for walleye pollock in the future, but it is unknown what the consequences of this stabilization will be for the synchrony of first‐feeding larvae with production of zooplankton prey in spring. With ongoing warming in the world’s oceans, knowledge of the mechanisms underlying reproductive phenology can improve our ability to monitor and manage species under changing climate conditions.
... Our findings further highlight that phenology can be particularly sensitive to inadvertent selection in hatcheries (see also Quinn et al., 2002;McLean et al., 2005;Ford et al., 2006). As with selection on timing in fisheries (Tillotson & Quinn, 2018), selection on timing in hatcheries can result from a number of processes including the natural tendency to spawn the first arriving fish, leaving those at the end to be released into the river if the capacity of the hatchery is filled. In addition, and more germane in the present case, river conditions favor the trapping of early arriving salmon more than those coming later, and thus, the progeny of the early fish is given the benefit of the higher survival rate during incubation in the hatchery. ...
... In addition, and more germane in the present case, river conditions favor the trapping of early arriving salmon more than those coming later, and thus, the progeny of the early fish is given the benefit of the higher survival rate during incubation in the hatchery. Because the timing of migration and reproduction is a key component of salmon diversity, the management of fisheries and hatcheries should strive to maintain the natural variation in these traits (Tillotson & Quinn, 2018). ...
The timing of breeding migration and reproduction links generations and substantially influences individual fitness. In salmonid fishes, such phenological events (seasonal return to fresh water and spawning) vary among populations but are consistent among years, indicating local adaptation in these traits to prevailing environmental conditions. Changing reproductive phenology has been observed in many populations of Atlantic and Pacific salmon, and is sometimes attributed to adaptive responses to climate change. The sockeye salmon spawning in the Cedar River near Seattle, Washington, USA have displayed dramatic changes in spawning timing over the past 50 years, trending later through the early 1990s, and becoming earlier since then. We explored the patterns and drivers of these changes using generalized linear models and mathematical simulations to identify possible environmental correlates of the changes, and test the alternative hypothesis that hatchery propagation caused inadvertent selection on timing. The trend toward later spawning prior to 1993 was partially explained by environmental changes, but the rapid advance in spawning since was not. Instead, since its initiation in 1991 the hatchery has, on average, selected for earlier spawning, and, depending on trait heritability, could have advanced spawning by 1‐3 weeks over this period. We estimated heritability of spawning date to be high (h²˜ 0.8; 95% CI: 0.5‐1.1), so the upper end of this range is not improbable, though at lower heritabilities a smaller effect would be expected. The lower reproductive success of early spawners and relatively low survival of early emerging juveniles observed in recent years suggest that artificial and natural selection are acting in opposite directions. The fitness costs of early spawning may be exacerbated by future warming, thus the artificially advanced phenology could reduce the population's productivity. Such artificial selection is known in many salmon hatcheries, so there are broad consequences for the productivity of wild populations comingled with hatchery produced fish.
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... Fishing that is limited in time or season, or that exploits the migratory behaviours of populations, could select for shifts in spawning phenology, spatial use patterns, or other related life history decisions and behaviours (Tillotson and Quinn, 2017). In Norway, the timing of fishing during the upstream migration of Atlantic salmon Salmo salar was identified as being a directional evolutionary pressure acting on the population (Harvey et al., 2017). ...
... For some species, there are seasonal closures in place to protect populations during spawning, but fishers might still exploit the tail ends of spawning windows given the year-to-year variability in climate conditions (Tillotson and Quinn, 2017). Such seasonal exploitation could select for altered timing of spawning. ...
Fisheries are selective, capturing fish based on their body size, behaviour, life stage, or location. Over time, if harvest pressure is strong enough and variation in traits heritable, evolution can occur that affects key aspects of the ecology of fish stocks. Most compelling examples of rapid evolution in response to harvest have come from marine systems. Here, we review the state of knowledge on fisheries-induced evolution (FIE) in the Laurentian Great Lakes where subsistence, commercial, and recreational fisheries have operated for centuries. We conclude that stocks experienced harvest rates high enough and for long enough to undergo evolution. While historical fisheries exploited more juveniles, some contemporary Great Lakes fisheries target primarily adult size-classes thus reducing current selection for earlier maturation; however, other traits and behaviours could evolve (e.g., growth, timing of spawning, boldness). While commercial harvest previously dominated, recreational fishing is now expected to be a strong contributor to harvest selection in the Great Lakes. Environmental variation, density-dependence, invasive species, and the genetic legacy of population bottlenecks and stocking interact with, and make it more challenging to detect, FIE in the Great Lakes than in marine systems. Case studies are presented for Great Lakes stocks of yellow perch Perca flavescens and lake whitefish Coregonus clupeaformis for which FIE has been investigated. The evidence for FIE in the Great Lakes is currently sparse, potentially because of the low research focus on this topic or because of the interacting influence of environmental variation and anthropogenic stressors.
... Reproduction in fish can be broadly classified into two categories: semelparous (a single reproductive event during lifetime) and iteroparous (multiple reproductive events). Semelparous fish are thought to be more prone to loss of genetic diversity as they rely on a singular reproductive event, so reproductive output is dependent on the available partner at the time of reproduction, as well as offspring survival being dependent on the temporality of reproduction [96]. For example, reproduction may coincide with an environmental stressor or indeed an intense fishery event. ...
Overfishing drives population decline, which in turn drives loss of genetic diversity. Many studies provide evidence of declines in genetic diversity; however, controversy exists within the literature, as some studies show evidence of no change in genetic diversity despite decades of overharvesting. The apparent discrepancy in the literature should therefore be examined to understand what biological and ecological processes are driving the differences in results. Here, we assess how different factors contribute to fisheries-induced susceptibility to declines in genetic diversity by first focusing on the different roles of genetic markers. Second, we assess how habitat type and conditions contribute to loss of genetic diversity. Third, we assess how life history and physiology affects catchability and loss of genetic diversity. Finally, we discuss how coinciding abiotic and biotic factors influence the intensity of genetic loss. We find a multitude of these factors could be interacting to influence how results are perceived and how intense the loss of genetic diversity can be. Future studies should carefully consider the methodology of genetic analysis used, as well as considerations of life history and ecology of the target species.
... Furthermore, exceeding optimal water temperature conditions has been found to negatively impact the physiological performance of Chinook salmon, affecting their migration and survival during spawning (Van Wert et al. 2023). Conversely, optimal water flow and temperature regimes likely influence the upstream migration timing of mature adults, exerting selection pressures and higher reproductive success (e.g., Ritcher and Kolmes 2005, Plumb 2018, Tillotson and Quinn 2018. In invaded systems, a better understanding of these environmental cues is crucial for the prediction of successful reproduction and growth of Chinook salmon populations. ...
Chinook salmon (Oncorhynchus tshawytscha) is invading South America. Both the high plasticity and genetic diversity of introduced propagules have been hypothesized to be responsible for the success of this species’ invasion. Yet, the influence of environmental variability on the expressed phenology of the adult spawning migration has been overlooked in this region. Here, we examined the consistency in timing, duration, and relative abundance of adult salmon migrants and their associations with environmental river conditions and surrounding ocean in a regulated river system in Patagonia. We conducted monthly long-term snorkeling fish surveys (2010–2019) and collected associated environmental information from the river and ocean. We observed a recent increase in duration of the spawning migration and a decline in the relative abundance of adult migrants. A warming phase of the Southern Pacific Ocean (during the two previous years) was associated to an extended migration season, whereas a colder river in fall was associated to a lower number of adult migrants. Collectively, our findings suggest that rapid phenological shifts could occur in a recently established salmon population (circa 1980). This process could be explained by novel selective pressures and expression of life history traits in response to novel environmental regimes. Further long-term surveys of introduced salmon can aid in parsing the relationships between environmental regimes and the biology and persistence of these self-sustained populations.
... Preserving diversity in the timing of reproduction may be required for adaptation to global climate change (Tillotson and Quinn 2018). As climate change is expected advance the annual timing of optimal juvenile rearing conditions (Visser and Both 2005), selection for earlier spawn timing may lead to changes in mean trait values over time (Crozier et al. 2008). ...
Life history diversity is generated and maintained in part by density‐dependent fitness tradeoffs that inhibit a single trait value from reaching fixation. While central to our understanding of evolution, demonstrating density dependence in the strength of fitness tradeoffs is difficult in natural systems. The timing of reproduction is a key life history trait that determines access to breeding habitat and exposure of offspring to competitive interactions and environmental conditions. Understanding the processes underlying diversity in reproductive timing will aid efforts to increase adaptive capacity under global environmental change. Here, we used detailed field studies, genetic parentage assignment, and simulation modeling to evaluate the fitness tradeoffs associated with the timing of reproduction for Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri in groundwater‐dominated tributaries to the upper Snake River, Wyoming, USA. We conducted our study across two years to understand how the strength of tradeoffs changes with population density. We found that early breeders experienced reduced reproductive success relative to later breeders due to the negative impact of nest superimposition (where later breeders construct nests overlapping those constructed previously) on embryo survival. However, as the risk of superimposition declined in the low‐density year and early breeders experienced fewer losses, reproductive success became more similar among individuals breeding at different times. Further, in the spring following the critical period for growth and survival, offspring of early breeders had experienced longer growing seasons, attained larger body sizes, and were equally abundant relative to those of later breeders, suggesting that fitness losses due to superimposition may be offset by size‐dependent competitive ability and overwinter survival. Our results illustrate a mechanism underlying diversity in the timing of reproduction for salmonids. This type of life history diversity will help to ensure the resilience and stability of salmonid populations attempting to adapt to changing local stressors associated with global climate change.
... Changing population size can affect observations of first and last phenological events in a year, such as animal migrations and plant flowering (Fig. 2) (Tryjanowski and Sparks 2001;Tryjanowski et al. 2005;Miller-Rushing et al. 2008a;Koleček et al. 2020;Dalton et al. 2022). Because of variation in phenology within populations, first events tend to occur earlier and last events tend to occur later as population sizes increase, regardless of changes in the average timing of the events (de Keyzer et al. 2017;Tillotson and Quinn 2018). The reverse happens when populations decline (Miller-Rushing et al. 2008b). ...
The number and diversity of phenological studies has increased rapidly in recent years. Innovative experiments, field studies, citizen science projects, and analyses of newly available historical data are contributing insights that advance our understanding of ecological and evolutionary responses to the environment, particularly climate change. However, many phenological data sets have peculiarities that are not immediately obvious and can lead to mistakes in analyses and interpretation of results. This paper aims to help researchers, especially those new to the field of phenology, understand challenges and practices that are crucial for effective studies. For example, researchers may fail to account for sampling biases in phenological data, struggle to choose or design a volunteer data collection strategy that adequately fits their project's needs, or combine data sets in inappropriate ways. We describe ten best practices for designing studies of plant and animal phenology, evaluating data quality, and analyzing data. Practices include accounting for common biases in data, using effective citizen or community science methods, and employing appropriate data when investigating phenological mismatches. We present these best practices to help researchers entering the field take full advantage of the wealth of available data and approaches to advance our understanding of phenology and its implications for ecology.
... Fishing can exert selective pressures on targeted populations, affecting biologically important traits such as size and age at maturity (Conover et al. 2009;Sharpe and Hendry 2009;Monk et al. 2021), growth rate (Biro and Post 2008;Enberg et al. 2012;Therkildsen et al. 2019), and seasonal timing of reproduction (Tillotson and Quinn 2018). Fisheries that employ hookand-line angling can even exact selection on behavioral traits such as boldness, ultimately giving rise 1 3 ...
Fish that exhibit high foraging activity or bold behavior can be particularly vulnerable to angling. If these traits are heritable, selection through harvest can drive phenotypic change, eventually rendering a target population less vulnerable to angling and consequently impacting the quality of the fishery. In this study, we used parental-based tags to investigate whether vulnerability to angling might be heritable in steelhead trout (Oncorhynchus mykiss) spawned at a hatchery in western Oregon, USA. We found modest evidence to support the hypothesis that vulnerability to angling is a heritable trait in steelhead. However, our data unexpectedly revealed that steelhead collected with in-river traps produced nearly twice as many adult offspring as steelhead collected by anglers. This difference in adult-to-adult production is explained in part through lower egg-to-fry survival of steelhead produced with angler-caught broodstock, possibly related to collection stress and greater time in captivity experienced by angler-caught broodstock. Our findings suggest that managers could improve broodstock fitness and program efficiencies by preferentially spawning fish collected with traps, and limiting use of broodstock collected by anglers. Additional research is needed to identify mechanisms contributing to higher juvenile mortality of steelhead produced with angler-caught broodstock.
... Run timing diversity has also decreased, with fish arriving to the river later (up to two months) and within a shorter time range than they did historically (McMillan et al., 2022). This is important because constricted genetic and run-time diversity (Tillotson & Quinn, 2018) degrade the resilience of steelhead populations. A 2018 assessment indicated that the number of adults produced by each adult spawner (i.e., adult-to-adult productivity) for Southwest Washington and Olympic Peninsula steelhead populations was consistently less than one, meaning that populations are in decline prior to fisheries occurring (Cram et al., 2018). ...
Dear Chairs, I am writing to provide you with the Washington Department of Fish and Wildlife's report to the legislature titled the Coastal Steelhead Proviso Implementation Plan (CSPIP). Funding and the proviso language requires a report to the relevant committees of the legislature per language in the 2021-23 operating budget proviso (37), which reads as follows: (37) $200,000 of the general fund-state appropriation for fiscal year 2022 and $100,000 of the general fund-state appropriation for fiscal year 2023 are provided solely for the department to develop a plan to protect native and hatchery produced steelhead for each river system of Grays harbor, Willapa bay, and coastal Olympic peninsula. The plan must adequately protect those fisheries for healthy runs year-after-year as well as provide reasonable fishing opportunities. The plan must include active stakeholder input and include an outreach strategy sufficient to keep conservation and angler interests well informed of proposed changes in advance of annual fishing seasons. The plan must be reported to the appropriate committees of the legislature by December 1, 2022. Declines in coastal steelhead population abundance and associated reductions in angling opportunity have highlighted the need to design and fund fisheries management strategies that provide sustainable angling opportunities and support the long-term viability of steelhead populations through science-based conservation objectives. In pursuit of that goal, the Washington Department of Fish and Wildlife (WDFW) has developed the CSPIP, which advances steelhead fishery management in the river systems of Grays Harbor, Willapa Bay, and the coastal Olympic Peninsula. The CSPIP aligns with and facilitates the implementation of existing policy in the Statewide Steelhead Management Plan (SSMP), the Anadromous Salmon and Steelhead Hatchery Policy C-3624 (2021), and Joint Comanager Hatchery Policy, which is currently under development. Although the state engaged tribal co-managers and Olympic National Park in the development of this plan, the CSPIP only applies to state steelhead management on Washington's Pacific coast. The science based CSPIP incorporates ecological knowledge of the target species while considering the history of harvest and management, state and federal mandates, and socioeconomic implications that underpin coastal steelhead management. The Plan lays out an adaptive management strategy that assigns appropriate management actions pertaining to monitoring and evaluation, fisheries regulations, hatchery operations based on steelhead population viability and the level of monitoring that is available to inform management. The CSPIP also provides guidelines pertaining to habitat, human dimensions and public communications and includes an implementation timeline with benchmarks, budget projections, critical research needs, and a vision for next steps. To this point, limited resources have resulted in a lack of crucial data needed to inform steelhead management decisions. Data gaps cause uncertainty around fishery impacts and in some cases lead to fishery closures when managers do not have enough information to ensure that angling opportunities remain within sustainable impact limits. Increased monitoring and research would address those problems, not only by enabling sustainable angling opportunity through high-precision sport fishery monitoring, but also by collecting the data required to evaluate and update long-term management strategies and conservation objectives. Thus, the CSPIP creates a win-win situation for multiple stakeholder groups and steelhead-related interests. WDFW aims to increase the two-way flow of information between those steelhead stakeholders and resource managers by providing accurate and consistent information about coastal steelhead, strengthening community partnerships, and increasing opportunities for the public to engage in the fisheries management process. Implementing the CSPIP requires an estimated biennial budget of $5.9 million (including indirect costs) above current appropriations, with most of this amount dedicated to freshwater sport fishery monitoring. WDFW intends to implement the CSPIP during the 2023-2025 biennium budget period. Among other implications, failure to fund this Plan would: (1) result in continued uncertainty regarding coastal steelhead fishery impacts, which could lead to fishery closures, (2) hinder the development of long-term steelhead management strategies and conservation objectives and (3) slow the pace of critical scientific research needed to inform fishery management. In accordance with the CSPIP, adaptive management, community engagement, and the refinement of quantitative tools will persist in perpetuity, with the understanding that reevaluation and adaptation are inherent elements of this new paradigm.
... In the same way, resiliency of a population can be related to behavioural polymorphisms, facilitating the adaptability of the species to changes that may occur in the environment (Schindler et al., 2010). Therefore, ignoring behavioural strategies when designing MPAs may reduce population variability, fostering resident individuals, and thus decreasing population resilience (Petitgas et al., 2010;Tillotson and Quinn, 2018;Maggs et al., 2019). ...
Marine protected areas (MPAs), and specially no-take areas (NTAs), play an important role in protecting target populations from fisheries. When developing spatial conservation and management tools, the design has mainly focused on population-level measures of fish home ranges, spawning and feeding areas, and migration routes. Intraspecific differences in fish behaviour, however, are often not accounted for, even though they could influence the level of realized protection. In this study, we investigated the intraspecific variation in spatial behaviour of a harvested fish, Diplodus sargus, and how it impacts the degree of protection granted by a NTA in the south of Portugal. We identified four behavioural types according to their spatial behaviour: residents, commuters, seasonal visitors, and single users. Time at risk (i.e. outside the NTA) greatly varied among the four groups, but also over the year for the seasonal and the single users. Our study shows how acoustic telemetry can assist spatial conservation and fisheries management and provides novel insight regarding the role of individual variation in behaviour to understand protection granted by MPAs to harvested species. It also suggests that incorporating such information into all stages of MPA design and implementation can result in increased resilience of the protected populations.
... For example, land-use practices can alter habitat quality and quantity, resulting in changes to river flows and temperatures and reducing abundance or even extirpating populations (Healey, 2009). Fisheries may alter the age structure, size structure, and migration timing of populations through selective harvest (Charbonneau et al., 2019;Ohlberger et al., 2018;Tillotson & Quinn, 2018) or, when multiple populations are exposed to fisheries, overfish less productive ones (Hilborn et al., 2015;Hilborn & Walters, 1992;Link, 2017;Ricker, 1958). The resulting reductions in population diversity can then lead to ecosystems and communities that are more vulnerable to environmental change (Chapin III et al., 2000;Elmqvist et al., 2003;Stier et al., 2020). ...
Variation among populations in life history and intrinsic population characteristics (i.e., population diversity) helps maintain resilience to environmental change and dampen interannual variability in ecosystem services. As a result, ecological variation, and the processes that generate it, are considered central to strategies for managing risks to ecosystems in an increasingly variable and uncertain world. However, characterizing population diversity is difficult, particularly in large and remote regions, which often prevents its formal consideration in management advice. We combined genetic stock identification of archived scale and tissue samples with state‐space run‐reconstruction models to estimate migration timing and annual return abundance for eight geographically and genetically distinct Chinook salmon populations within the Canadian portion of the Yukon River. We found that among‐population variation in migration timing and return abundances resulted in aggregate return migrations that were 2.1 times longer, and 1.4 times more stable, than if they comprised a single homogenous population. We then fit state‐space spawner‐recruitment models to the annual return abundances to characterize among‐population diversity in intrinsic productivity and population size and their consequences for the fisheries they support. Productivity and carrying capacity varied among‐populations by approximately 2.4‐fold (2.9 to 6.9 recruits‐per‐spawner) and 3‐fold (8,800 to 27,000 spawners), respectively. This diversity implies an equilibrium trade‐off between harvesting the population aggregate and conservation of individual populations whereby the harvest rate predicted to maximize aggregate harvests comes at the cost of overfishing ~ 40% of the populations but with a relatively low risk of extirpating the weakest ones. Our findings illustrate how population diversity in one of the largest salmon producing river basins in the world contributes to fisheries stability and food security in a region where salmon have high cultural and subsistence value. More generally our work demonstrates the utility of molecular analyses of archived biological material to characterize diversity in biological systems, and its benefits and consequences for trade‐offs in decision making.
... The unimodal upriver migration of green sturgeon into the Sacramento River during the spring months, peaking during the month of March, resembled observations of the nDPS green sturgeon in Oregon (Benson et al., 2007). The discrete period of spring migrations was consistent with selection pressures related to offspring development and survival (Tillotson & Quinn, 2018;Wright & Trippel, 2009). Reproductive success of fish migrating long distances from their home ranges to spawning grounds (such as sDPS green sturgeon migrating to California from areas near Vancouver Island; Lindley et al., 2008) may be under selection to ensure that arrival coincides with that of potential mates and optimal conditions for offspring development (Forsythe et al., 2012). ...
Understanding movement patterns of anadromous fishes is critical to conservation and management of declining wild populations and preservation of habitats. Yet, the duration of observations for individual animals can constrain accurate descriptions of movements. In this study, we synthesized over a decade (2006–2018) of acoustic telemetry tracking observations of green sturgeon (Acipenser medirostris) in the Sacramento River system to describe major anadromous movement patterns. We observed that green sturgeon exhibited a unimodal in‐migration during the spring months but had a bimodal distribution of out‐migration timing, split between an “early” out‐migration (32%) group during May–June, or, alternatively, holding in the river until a “late” out‐migration (68%), November–January. Focusing on these out‐migration groups, we found that river discharge, but not water temperature, may cue the timing of migration and that fish showed a tendency to maintain out‐migration timing between subsequent spawning migration events. We recommend that life history descriptions of green sturgeon in this region reflect the distinct out‐migration periods described here. Furthermore, we encourage the continued use of biotelemetry to describe migration timing and life history variation, in not only this population but also other green sturgeon populations and other species.
... There is good reason to believe that the costs of sea migration for Atlantic salmon have changed as a result of human activity. Where either directly or indirectly, human activity imposes additional costs to the expression of traits in a species, then an ecological change and an evolutionary response in that species is to be expected (see Allendorf & Hard, 2009;Tillotson & Quinn, 2018 and references therein). ...
There are strong signals that the selection forces favouring the expression of long-distance sea migration by Atlantic salmon (Salmo salar) are changing. Unlike many other behavioural traits, the costs of migration are incurred before any fitness benefits become apparent to the migrant. The expression of this behaviour has thus been shaped by selection forces over multiple generations and cannot respond to short interval (within a single generation) environmental change as many other behavioural traits can. Here we provide a framework to examine the evolutionary and ecological consequences of a sustained increase in migration cost. We argue that Atlantic salmon may have entered an evolutionary trap, where long-distance sea migration has become maladaptive because of shifting environmental conditions. We predict that if higher migration costs (affecting survivorship and ultimately fitness) persist, then shifting selection pressures will result in continuing declines in population size. We suggest, however, that in some populations there is demonstrable capacity for evolutionary rescue responses within the species which is to be found in the variation in the expression of migration. Under a scenario of low to moderate change in the selection forces that previously promoted migration, we argue that disruptive, sex-based selection would result in partial migration, where females retain sea migration but with anadromy loss predominantly in males. With more acute selection forces, anadromy may be strongly selected against, under these conditions both sexes may become freshwater resident. We suggest that as the migration costs appear to be higher in catchments with standing waters, then this outcome is more likely in such systems. We also speculate that as a result of the genetic structuring in this species, not all populations may have the capacity to respond adequately to change. The consequences of this for the species and its management are discussed.
... The timing of seasonal activities (i.e., phenology) such as migration and reproduction of fishes are demonstrated to be indirectly controlled by the quality of riverine habitats (Poff 1997;Huijbers et al. 2012;Tillotson and Quinn 2018). Fish synchronise their activities with physical cues (Wenger et al. 2011;Paumier et al. 2019), directly and indirectly relying with temporally and spatially limited resources (Cushing 1990;McNamara and Houston 2008;Chevillot et al. 2017). ...
This PhD takes place in a context of climate change (IPCC 2018) and a general decline in fish species. The objective of this PhD thesis was to define environmental control over the reproduction of the allis shad. Using 4 main studies with several modelling tools (Manly index, BRT model, HoOS model and flirtyShadBrain model), we studied this environmental control and assessed the future impact of climate change.The first step in assessing the impact of habitat changes was to test the influence of environmental factors on shad reproduction (paper #1, paper #2 and the flirtyShadBrain model). We first explored the influence of temperature, then tested several environmental factors on shad reproduction. In practice, we evaluate that the shad is a photoperiodic species. Day length may be the seasonal data that triggers migration, and temperature and flow are used for short-term decisions (final choice to reproduce with social benchmarks). We used this knowledge to explore the potential impact of climate change. According to our multifactorial projections, it would appear that allis shad spawners will not be affected by future global warming for the RCP 2.6 scenario, and that even in the worst case scenario (RCP 8.5), habitat favorability should even increase, although with an earlier favourable period. Thus, climate change does not appear to be a major threat to this species.
... Climate change is likely to affect the reproductive success of marine fishes through changes to the biological and physical environments, affecting resource availability, temperature, and bioenergetics (Hilborn et al. 1995, Harvey et al. 2011, Pankhurst & Munday 2011, Lowerre-Barbieri et al. 2017). However, size-dependent fecundity relationships currently used in population models to assess the health and status of fish populations are often treated as static through time and unaffected by environmental change (Lambert 2008), even as a growing body of evidence suggests that changes in the ocean environment, such as temperature and food availability, drive variability in life history traits (Narimatsu et al. 2010, Tillotson & Quinn 2018. Classic life history theory states that tradeoffs exist under limiting resources, leading to predictable shifts in energy allocation affecting growth, maturity, and reproductive effort (Stearns 1992). ...
Patterns of reproduction, such as size-fecundity relationships used in models to assess fish populations, are generally treated as static through time and invariant to environmental change. However, growing evidence suggests that changes in ocean conditions, such as warming water temperatures and reduced primary productivity, affect life history traits, including reproduction. Under controlled experimental conditions, we documented reproductive plasticity in the live-bearing rosy rockfish Sebastes rosaceus in response to different temperature and feeding regimes, with maternal size as a covariate. Rosy rockfish occur throughout the California Current, a highly dynamic ecosystem for which increased environmental variability is predicted with climate change. Females produced 0-5 larval broods annually. Larger females had disproportionately higher fecundity than smaller females by producing larger-sized broods and a greater number of annual broods. Warmer water temperature decreased the time interval between brood releases, likely reflecting faster egg and larval development. However, warmer temperature did not increase the total number of broods, potentially reflecting a tradeoff with increased metabolic demand. Well-fed females had better body condition and higher annual fecundity compared to poorly fed females, primarily due to a greater number of broods. Conversely, females with poor body condition at the start of the reproductive season did not reproduce, providing possible evidence of delayed maturation at smaller sizes or skipped spawning at larger sizes. Reproductive plasticity (in terms of whether and how many broods are produced per year) in response to the environment likely contributes to high inter-annual variation in population larval production. Understanding the causes and consequences of reproductive plasticity is critical to developing sustainable management strategies and predicting population response to changing climate conditions.
... However, species whose reproductive timing has a strong genetic basis and is driven by consistent environmental stimuli such as day length may also be vulnerable to climate change because of a reduced ability to shift reproductive timing in response to changing thermal conditions. Current fishery management practices [65] as well as global climate change [66] may irrevocably reduce genetic diversity in Pacific herring before its significance is fully recognized, thereby reducing the ability of species to adapt to future environmental conditions. Given that forage fishes like Pacific herring are foundational to coastal food webs [58], fisheries, and the livelihoods and cultures of coastal indigenous communities [25,26], diversity loss will have far-reaching consequences for associated social-ecological systems [67]. ...
The timing of reproduction influences key evolutionary and ecological processes in wild populations. Variation in reproductive timing may be an especially important evolutionary driver in the marine environment, where the high mobility of many species and few physical barriers to migration provide limited opportunities for spatial divergence to arise. Using genomic data collected from spawning aggregations of Pacific herring ( Clupea pallasii ) across 1600 km of coastline, we show that reproductive timing drives population structure in these pelagic fish. Within a specific spawning season, we observed isolation by distance, indicating that gene flow is also geographically limited over our study area. These results emphasize the importance of considering both seasonal and spatial variation in spawning when delineating management units for herring. On several chromosomes, we detected linkage disequilibrium extending over multiple Mb, suggesting the presence of chromosomal rearrangements. Spawning phenology was highly correlated with polymorphisms in several genes, in particular SYNE2 , which influences the development of retinal photoreceptors in vertebrates. SYNE2 is probably within a chromosomal rearrangement in Pacific herring and is also associated with spawn timing in Atlantic herring ( Clupea harengus ). The observed genetic diversity probably underlies resource waves provided by spawning herring. Given the ecological, economic and cultural significance of herring, our results support that conserving intraspecific genetic diversity is important for maintaining current and future ecosystem processes.
... Variation in the timing of spawning migration is also influenced by factors other than hatchery transplantations, including environmental factors (e.g., water flow: Jonsson 1991;Quinn et al. 1997, climate change: Kovach et al. 2013) and fishing activities (e.g., Tillotson and Quinn 2018). Based on these factors, the timing of spawning migration may show interannual variability. ...
The timing of migration and breeding is an important aspect in the study of the migratory ecology of fishes. This timing in fish is generally determined by both genetic and environmental factors but is also subject to anthropogenic selection. Hatchery transplantation practices, where hatchery fish are produced from returned adult salmon and then transplanted into several rivers, have been going on for over 30 years in the southern part of Hokkaido Island, Japan. In this study, I compared the inter-river variation in timing of spawning migration in chum salmon to examine the effects of hatchery transplantation on the timing of migration. There was less inter-river variation in the timing of spawning migration in transplanted rivers than in non-transplanted rivers. This result suggests that hatchery transplantation homogenizes the timing of spawning migration in chum salmon. Changes to other resource management tools, such as promoting natural spawning and/or hatchery releases using local fishes, may be important to preserve diversity in the timing of migration.
... The CT threshold of Coreius guichenoti, which is in the same genus as C. heterodon, ranges from 16.0°C to 19.0°C in the tributaries of the Yangtze River (Zhang et al., 2018). The discrepancy could be explained by differences in the geographical locations and fish species, and by varying tolerance and plasticity dynamics in the organisms (Rogers and Dougherty, 2019;Tillotson and Quinn, 2017). The time of achievement of the CT threshold is closely associated with spawning activities. ...
Dam operations considerably influence water temperature regimes in rivers, which affects fish spawning activities. Previous studies have focused on the effects of critical temperature (CT) alterations during the spawning period, and largely ignored the effects of accumulated temperature (AT) alterations on gonadal development. Successful spawning relies on the simultaneous achievement of the two thermal requirements at appropriate times. River damming may cause a mismatch between the times of achieving CT and AT thresholds, and in turn influence fish reproduction. In the present study, spawning events of Coreius heterodon (C. heterodon) from 2009 to 2015 in the upper reaches of the Yangtze River, which are under the influence of cascade dams, were analysed based on the times of achievement of CT and AT thresholds. The CT and AT thresholds for C. heterodon spawning were 18.4 °C and 1324.9 °C·d, respectively. Under pre-impoundment conditions, the time of achievement of the AT threshold was 23 d on average later than that under post-impoundment conditions; however, the time of achievement of the CT threshold was similar under both conditions. The time of achievement of the AT threshold was 10 d earlier than that of achievement of the CT threshold in post-impoundment conditions. Earlier achievement of AT thresholds was followed by reduced spawning. The alteration of temperature rhythm caused by reservoir operations could be the major factor decreasing spawning abundance after river damming. The results of the present study could facilitate sustainable reservoir operations with regards to water temperature management, and thereby improve the conservation of fish resources.
... In addition, modelling and empirical studies show that recreational fishing can also induce evolutionary changes of behavioural Martorell-Barceló et al., 2018;Tillotson & Quinn, 2018;Uusi-Heikkilä et al., 2015), metabolic (Hessenauer et al., 2015) and life-history traits (Arlinghaus et al., 2009;Ayllón et al., 2018;Edeline et al., 2007;Matsumura et al., 2011;Thériault et al., 2008;Uusi-Heikkilä et al., 2015). If fisheries-induced trait selection opposes the direction of trait selection by EC, then local adaptation will be limited and surplus production will be reduced even further, threatening the sustainability of the fishery. ...
Climate change is impacting the composition and functioning of virtually every ecosystem on Earth, and disrupting the productivity of exploited ones. Species are rapidly adjusting to their changing environments through evolutionary and/or plastic phenotypic changes in behavioural, physiological, phenological and life‐history traits. Size‐selective harvest produces severe demographic impacts on exploited populations and induces individual phenotypic changes in many of the same fitness‐related traits as climate change and thus can impair local adaptation and acclimation. We addressed in the context of inland recreational fisheries two interrelated questions: (1) Will fisheries‐induced phenotypic changes operate at different rates and direction than those induced by climate change, and thus hinder local adaptation and acclimation, threatening population persistence?; (2) which harvest regulations most likely lead to overexploitation of populations under the new environmental conditions?
We used an eco‐genetic individual‐based model to simulate the consequences of size‐selective fishing for a cold‐water fish species brown trout Salmo trutta across a range of regulatory (defined by exploitation rate and size‐based limits) and environmental scenarios (warming vs. concurrent warming and streamflow reduction) in a Mediterranean system. We ran 1,620 combinations of fishing and environmental scenarios and analysed results using artificial neural networks.
In our simulations, (a) climate change and size‐selective fishing both led to a reduced, truncated population, with increased juvenile but decreased adult growth and earlier maturation at smaller size, but fisheries‐induced changes were stronger than those produced by climate change; (b) their effects were additive or dampened but rarely synergistic and (c) phenotypic changes in fitness‐related traits resulted from both evolutionary and plastic processes.
Synthesis and applications . Our model‐based analyses highlight that any size‐selective fishing regime would lead to the overexploitation of cold‐water freshwater fish populations if climate warming is accompanied by streamflow reduction—as projected in Mediterranean fisheries. Even if we assumed no future streamflow regime changes, only a limited range of size‐based harvest regulations may provide an acceptable balance between conservation and fishery objectives. Thus, recreational fisheries of cold‐water fish in Mediterranean climates might be more sustainably managed under climate change if conservation‐oriented strategies based on harvest bans (e.g. catch‐and‐release fishing) were implemented.
... The potential for fisheries to alter the behavioural composition in fish populations has not been fully explored (Uusi-Heikkilä et al., 2008;Heino et al., 2015;Arlinghaus et al., 2017;Tillotson and Quinn, 2018) despite the publication of the first observations and hypotheses in the mid-1950s (Miller, 1957). Recent developments in fish personality research (e.g. ...
In a landscape of fear, humans are altering key behaviors expressed by wild-living animals, including those related to foraging, reproduction and survival. When exposed to potentially lethal human actions, such as hunting or fishing, fish and wildlife is expected to behaviorally respond by becoming more timid, but proving such responses underwater in the wild has been challenging. Using a rich dataset collected in situ , we provide evidence of spearfishing-induced behavioral effects in five coastal fish species using the flight initiation distance (FID) as a proxy of predator avoidance and boldness. We document that spearfishing promotes a timidity syndrome (i.e., an increase of the average timidity of harvested populations) and that the wariness of prey’s wariness is influenced by individual size, level of protection offered through marine protected areas and the ability to recognize the risk posed by underwater human predators. In particular, we show that changes in the appearance of the observer (spearfisher vs . snorkeler) modulate the risk perception among the exploited species, and these differences are more evident outside marine protected areas where spearfishing is allowed. We also detected a positive correlation between FID and fish size, with larger specimens (that are more likely targets of spearfishers) revealing larger FID. The behavioral effects were most clearly expressed in the most heavily exploited species and declined towards the less desired and less targeted ones, which may be a result of learning mechanisms and plasticity and/or fisheries-induced evolution of timidity. Our study reveals a trade-off where intensive spearfishing negatively affects future spearfishing success through behavior-based alteration of catchability. Either rotating harvest or implementation of mosaics of protected and exploited areas might be needed to manage spearfishing-induced timidity in exploited stocks.
... This is especially pronounced in crustaceans where voraciousness is observed in fastgrowing males (less in females), whose size also increases the chances of successful mating (Biro and Sampson 2015). In addition to behavioural traits, other individual characteristics that would lead to increased susceptibility to capture have been less explored, such as different physiological traits (see Hollins et al. 2018) or timing of breeding (Tillotson and Quinn 2018). This can offer additional insights into the impact of fisheries-induced alterations. ...
Overexploitation is still a leading problem of many commercially targeted fish species. In addition to the high harvest rates and increasing biomass removals, harvested marine ecosystems have become a stage for the dynamic interplay of evolutionary and ecological processes. Removal through size selective fishing gear can cause negative pervasive effects on individual as well as population level. Observations of the individual phenotypic traits show a general trend of decreasing size and age at maturity that can have further negative effects on fecundity and population productivity. As these phenotypic changes become heritable (i.e., fisheries-induced evolution or FIE), this can further diminish the fish available to fisheries and render future fishing yields unsustainable.
Current management requires additional measures to include avoidance and detection of evolutionary changes. In order to understand which fishing objectives precede evolutionary change in individual traits, in my thesis I explored how different fishing strategies of the European hake (Merluccius merluccius) fishery reflect on ecological and evolutionary processes. While management focusing on the protection of juvenile fish can minimise the negative ecological impact of fishing, it increases the potential for evolutionary change in fish phenotypic traits. In contrary to this, fishing mortality targeting a wider range of age–size classes avoids evolutionary shifts in individual traits, however such fishing strategy demonstrates higher biomass removals.
In the wild, fisheries continuously interact with other predators, such as marine mammals, which can prey upon the same fish species or stock. The impact of these direct and indirect biological interactions between the marine mammals and fisheries is harder to detect and quantify, especially in synergy with other natural or anthropogenic stressors. In the context of fisheries-induced evolution, changes observed on an individual and population level caused by fisheries will also affect the prey size selectivity and prey availability to natural predators. My synthesis of recent research and findings on marine mammal–fisheries biological interactions demonstrates the need for improvement on data regarding marine mammal dietary and energetic requirements as well as their representation in model-based approaches. Moreover, combining different sources of knowledge about marine mammal–fisheries competition can aid to better quantify fish mortality caused by predation. Subsequently, this information would improve the fish stock assessments and provide insight on a sustainable window of opportunity to catch fish for fisheries and natural predators.
Thus far, attempts to quantify predation and fish availability for fisheries and natural predators exist through studies using mainly ecosystem and fisheries models. To explore how predation and fisheries shape and direct individual as well as population parameters, I have used an individual-based model to simulate hake
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growth trajectories with regards to its own biological characteristics. As an individual grows, its life history is formed by ecological and evolutionary processes which also take into account the reproductive cost of survival and sexual size dimorphism (SSD). With co-evolved interactions between hake and the bottlenose dolphin (Tursiops truncatus) as the predator, fishing is introduced through a limited time period in order to observe prey recovery and resilience on an individual and population level. Although different types of predation give insight to discrepancies in the intensity of predation mortality, mere presence or absence of predation determines the projected values reached by prey individual and population parameters. Moreover, the joint effect of predation and fishing reveal contra-intuitive trends in hake individual traits and population parameters. The combination of duration and intensity of both size-selective removals, predation type and SSD determine the potential for persistent phenotypic and demographic changes after a period of overexploitation. Additionally, not all individual traits are equally susceptible to fisheries-induced evolution where the accountability of SSD and predation type can play a critical role. While fisheries remain the most detrimental source of mortality and size-selective removal for the harvested species, the indirect effects of fishing intensity diminish predator survival, thus having direct implications for top predator conservation. In conclusion, increasing the biological realism of the targeted species and incorporating different predation types with respect to evolutionary processes provide a more holistic approach to fisheries management: as it helps to avoid potential FIE and an overestimation of fish available to fisheries that can prevent top predator collapse. This will, ultimately, lead to a more ecosystem-based management with sustainable harvest rates and optimised fishing effort as well as the minimal cascading effects of size-selective removals.
... Conover and Munsch 2002;Hauser et al. 2002, Kuparinen and Merila 2007, Heino et al. 2015, Uusi-Heikkila et al. 2017, Therkildsen et al. 2019. While a full treatment of this topic is outside the scope of this review, readers are referred to the studies cited above as well as several recent reviews (Kuparinen et al. 2017;Tillotson et al. 2018;Palkovacs et al. 2018). ...
Many of the world’s major cities are located in coastal zones, resulting in urban and industrial impacts on adjacent marine ecosystems. These pressures, which include pollutants, sewage, runoff and debris, temperature increases, hardened shorelines/structures, and light and acoustic pollution, have resulted in new evolutionary landscapes for coastal marine organisms. Marine environmental changes influenced by urbanization may create new selective regimes, or may influence neutral evolution via impacts on gene flow or partitioning of genetic diversity across seascapes. While some urban selective pressures, such as hardened surfaces, are similar to those experienced by terrestrial species, others, such as oxidative stress, are specific to aquatic environments. Moreover, spatial and temporal scales of evolutionary responses may differ in the ocean due to the spatial extent of selective pressures and greater capacity for dispersal/gene flow. Here we present a conceptual framework and synthesis of current research on evolutionary responses of marine organisms to urban pressures. We review urban impacts on genetic diversity and gene flow, and examine evidence that marine species are adapting, or are predicted to adapt, to urbanization over rapid evolutionary timeframes. Our findings indicate that in the majority of studies, urban stressors are correlated with reduced genetic diversity. Genetic structure is often increased in urbanized settings, but artificial structures can also act as stepping stones for some hard‐surface specialists, promoting range expansion. Most evidence for rapid adaptation to urban stressors comes from studies of heritable tolerance to pollutants in a relatively small number of species; however, the majority of marine ecotoxicology studies do not test directly for heritability. Finally, we highlight current gaps in our understanding of evolutionary processes in marine urban environments, and present a framework for future research to address these gaps.
... While several fishway designs may work well for target species, it is increasingly apparent that they work poorly for others (Bunt et al., 2012;Foulds and Lucas, 2013), or fail to provide adequate community-level migration and dispersal solutions (Hall et al., 2012). Human actions such as fisheries can act as natural selection filters, resulting in anthropogenic induced evolutionary change (Edeline et al., 2007;Tillotson and Quinn, 2018); dams and fishways can also operate in this way (Haugen et al., 2008;Volpato et al., 2009). There is evidence that shows genetic changes within, and divergence between, populations that are partially or wholly split by barriers (Stamford and Talyor, 2005;Gouskov et al., 2016;Wilkes et al., 2018;Van Leeuwen et al., 2018). ...
Fishways are commonly employed to improve river connectivity for fishes, but the extent to which they cater for natural phenotypic diversity has been insufficiently addressed. We measured differential upstream passage success of three wild brown trout (Salmo trutta) phenotypes (anadromous, freshwater-resident adult and parr-marked), encompassing a range of sizes and both sexes, at a Larinier superactive baffle fishway adjacent to a flow-gauging weir, using PIT telemetry (n = 160) and radio telemetry (n = 53, double tagged with PIT tags). Fish were captured and tagged downstream of the weir in the autumn pre-spawning period, 2017, in a tributary of the River Wear, England, where over 95% of tributary spawning habitat was available upstream of the weir. Of 57 trout that approached the weir-fishway complex, freshwater-resident adult and parr-marked phenotypes were less successful in passing than anadromous trout (25%, 36%, and 63% passage efficiency, respectively). Seventy-one percent of anadromous trout that passed upstream traversed the weir directly. Although the fishway facilitated upstream passage, it was poor in attracting fish of all phenotypes (overall attraction efficiency, 22.8%). A higher proportion (68.2%) of parr-marked trout that approached the weir were male and included sexually mature individuals, compared with that of freshwater-resident (37.8%) and anadromous trout (37.0%). The greater passage success of anadromous trout was likely due to their greater size and locomotory performance compared to the other phenotypes. Barriers and fishways can act as selection filters, likely the case in this study, and greater consideration needs to be given to supporting natural diversity in populations when proposing fishway designs to mitigate river connectivity problems.
... For example, catch-and-release fisheries or fishing closures are used to restrict angling to cool temperature periods. Such practices mitigate the interaction between handling and temperature stress [234], but run the risk of accidentally selecting on run timing [235] and other traits [236,237]. Consideration of how all anthropogenic factors exacerbate or possibly mitigate for climate stressors is much needed [238]. ...
Major ecological realignments are already occurring in response to climate change. To be successful, conservation strategies now need to account for geographical patterns in traits sensitive to climate change, as well as climate threats to species-level diversity. As part of an effort to provide such information, we conducted a climate vulnerability assessment that included all anadromous Pacific salmon and steelhead (Oncorhynchus spp.) population units listed under the U.S. Endangered Species Act. Using an expert-based scoring system, we ranked 20 attributes for the 28 listed units and 5 additional units. Attributes captured biological sensitivity, or the strength of linkages between each listing unit and the present climate ; climate exposure, or the magnitude of projected change in local environmental conditions; and adaptive capacity, or the ability to modify phenotypes to cope with new climatic conditions. Each listing unit was then assigned one of four vulnerability categories. Units ranked most vulnerable overall were Chinook (O. tshawytscha) in the California Central Valley, coho (O. kisutch) in California and southern Oregon, sockeye (O. nerka) in the Snake River Basin, and spring-run Chinook in the interior Columbia and Willamette River Basins. We identified units with similar vulnerability profiles using a hierarchical cluster analysis. Life history characteristics, especially freshwater and estuary residence times, inter-played with gradations in exposure from south to north and from coastal to interior regions to generate landscape-level patterns within each species. Nearly all listing units faced high
exposures to projected increases in stream temperature, sea surface temperature, and
ocean acidification, but other aspects of exposure peaked in particular regions. Anthropogenic factors, especially migration barriers, habitat degradation, and hatchery influence, have reduced the adaptive capacity of most steelhead and salmon populations. Enhancing adaptive capacity is essential to mitigate for the increasing threat of climate change. Collectively, these results provide a framework to support recovery planning that considers climate impacts on the majority of West Coast anadromous salmonids.
... In addition, fish may form dense aggregations that are attractive targets for fishers (Claydon, 2004;Domeier, 2012;Sadovy de Mitcheson & Erisman, 2012). As the distribution of fishing effort is rarely homogeneous, there is the potential for selection that could impact the reproductive phenology of a population (Tillotson & Quinn, 2018). Management systems that lead to bias in fishing effort towards a specific period in the spawning season could potentially be problematic. ...
Lumpfish, Cyclopterus lumpus L., has an extended ovary development period and a relatively long spawning season. It therefore seems unlikely that individuals spawning later in the season would be able to recover from spawning and develop their gonads in time to spawn during the early part of the season the following year. The hypothesis that individuals spawning early or late in a spawning season would spawn early or late the following year was tested using fish tagged in Iceland between 2008 and 2017. The tagging date and recapture date the following year were positively correlated with an average of 356 days at large (DAL). Fish sampled from the fishery indicate that tagging/recapture date gives an indication of spawning time. From this, it was concluded that spawning time in the current year can be used to predict spawning time the following year. As fishing effort was greatest at the end of April/beginning of May, it seems likely that fish that come to spawn at this time will be subject to a higher fishing mortality. Therefore, they will be less likely to spawn successfully than fish spawning earlier or later in the year. If spawning time is under genetic control, then this could have consequences for the spawning phenology of lumpfish.
... The suite of factors underlying temporal variation in migration traits is not fully understood for amphidromous species, but this variation needs to be considered in the management of amphidromous fisheries. Fishing pressure can vary over time owing to constraints on fishing effort through management, behaviour of fishers or environmental conditions, and fishery-related mortality can be selective regarding important temporal traits such as spawning and migration date (Scharf, Craig, & Smith, 2017;Tillotson & Quinn, 2018 maculatus, which maximizes yields for fishers while also placing increased fishing pressure on this species. The population consequences of this current fisheries management regime are unknown. ...
Amphidromy is the most prevalent type of diadromous migration. Despite this, the conservation and management of amphidromous species is exceptionally challenging because this life history type, with larval development in a pelagic habitat (usually marine) and adult development in fresh water, is poorly resolved.
The chronological properties of otoliths, together with a spatial and temporal analysis of post‐larval migration traits and adult reproductive traits, were used to reconstruct the life history of a widespread, yet declining amphidromous galaxiid, Galaxias maculatus , and to explore relationships between marine and freshwater life phases.
A wide range of post‐larval migration traits were observed over the peak migratory period. Post‐larvae were smaller and younger at inward migration late in the migration season (November) and were derived from winter spawning events. Earlier migrants (September) were larger, older and derived from autumn spawning events.
Age estimates confirmed that G. maculatus is largely an annual species, but back‐calculated hatch dates showed that spawning times are more extensive than previously known.
Growth reconstructions revealed that winter‐hatched larvae were faster growing during marine and freshwater life and attained sexual maturity at a younger age than autumn‐hatched fish. However, no differences in body size or reproductive investment were detected between autumn‐ and winter‐hatched larvae.
The first 50 days of marine growth were inter‐dependent, indicating that early larval growth may be the critical link to understanding intra‐ and inter‐annual recruitment variations of inward migrating post‐larvae. Furthermore, growth after 60 days of larval life propagated through to adult freshwater development, highlighting linkages between late marine and adult freshwater life.
This study highlights the value of studying the marine and freshwater life phases of amphidromous species in tandem. This interconnected understanding must ultimately be achieved for the conservation and management of species with this poorly understood life history type.
... Selection for earlier age of maturity, run timing and time of spawning. Czorlich et al., 2018;Hollins et al., 2018;Kallio-Nyberg et al., 2018;Koeck et al., 2018;Syrjanen et al., 2018;Thériault et al., 2008;Tillotson & Quinn, 2018 Climate change. Changes in river flows and water temperature influencing feeding, migration timing, spawning and juvenile survival. ...
Brown trout Salmo trutta is endemic to Europe, western Asia and north-western Africa; it is a prominent member of freshwater and coastal marine fish faunas. The species shows two resident (river resident, lake-resident) and three main facultative migratory life histories (downstream–upstream within a river system, fluvial–adfluvial potamodromous; to and from a lake, lacustrine–adfluvial (inlet) or allacustrine (outlet) potamodromous; to and from an estuary or brackish water (semi anadromous); to and from the sea, anadromous). River-residency v. migration is a balance between enhanced feeding and thus growth advantages of migration to a particular habitat v. the costs of potentially greater mortality and energy expenditure. Fluvial–adfluvial migration usually has less feeding improvement, but less mortality risk, than lacustrine–adfluvial or allacustrine and anadromous, but the latter vary among catchments as to which is favoured. Indirect evidence suggests that around
50% of the variability in S. trutta migration v. residency, among individuals within a population, is due to genetic variance. This dichotomous decision can best be explained by the threshold-trait model of quantitative genetics. Thus, an individual’s physiological condition (e.g., energy status) as regulated by environmental factors,
genes and non-genetic parental effects, acts as the cue. The magnitude of this cue relative to a genetically predetermined individual threshold, governs whether it will migrate or sexually mature as a river-resident. This decision threshold occurs early in life and, if the choice is to migrate, a second threshold probably follows determining the age and timing of migration. Migration destination (mainstem river, lake, estuary, or sea) also appears to be genetically programmed. Decisions to migrate and ultimate destination
result in a number of subsequent consequential changes such as parr–smolt transformation, sexual maturity and return migration. Strong associations with one or a few genes have been found for most aspects of the migratory syndrome and indirect evidence supports genetic involvement in all aspects. Thus, migratory and resident
life histories potentially evolve as a result of natural and anthropogenic environmental changes, which alter relative survival and reproduction. Knowledge of genetic determinants of the various components of migration in S. trutta lags substantially behind that of Oncorhynchus mykiss and other salmonines. Identification of genetic
markers linked to migration components and especially to the migration–residency decision, is a prerequisite for facilitating detailed empirical studies. In order to predict effectively, through modelling, the effects of environmental changes, quantification of the relative fitness of different migratory traits and of their heritabilities, across a
range of environmental conditions, is also urgently required in the face of the increasing pace of such changes.
See general non-specialist summary - Anadromy potamodromy and residency in brown trout_General summary.pdf
Also available at: http://www.qub.ac.uk/Research/GRI/TheInstituteforGlobalFoodSecurity/institute-for-global-security-news/ShouldIstayorshouldIgoNewlightshedonmigratorybehaviourofbrowntrout.html
... Variation in population size and structure (size, age, sex) due to natural fluctuations, fishing mortality, or conservation efforts may confound detection of phenological shifts (Tillotson & Quinn, 2018). ...
The timing of recurring biological and seasonal environmental events is changing on a global scale relative to temperature and other climate drivers. This study considers the Gulf of Maine ecosystem, a region of high social and ecological importance in the Northwest Atlantic Ocean and synthesizes current knowledge of (a) key seasonal processes, patterns, and events; (b) direct evidence for shifts in timing; (c) implications of phenological responses for linked ecological‐human systems; and (d) potential phenology‐focused adaptation strategies and actions. Twenty studies demonstrated shifts in timing of regional marine organisms and seasonal environmental events. The most common response was earlier timing, observed in spring onset, spring and winter hydrology, zooplankton abundance, occurrence of several larval fishes, and diadromous fish migrations. Later timing was documented for fall onset, reproduction and fledging in Atlantic puffins, spring and fall phytoplankton blooms, and occurrence of additional larval fishes. Changes in event duration generally increased and were detected in zooplankton peak abundance, early life history periods of macro‐invertebrates, and lobster fishery landings. Reduced duration was observed in winter–spring ice‐affected stream flows. Two studies projected phenological changes, both finding diapause duration would decrease in zooplankton under future climate scenarios. Phenological responses were species‐specific and varied depending on the environmental driver, spatial, and temporal scales evaluated. Overall, a wide range of baseline phenology and relevant modeling studies exist, yet surprisingly few document long‐term shifts. Results reveal a need for increased emphasis on phenological shifts in the Gulf of Maine and identify opportunities for future research and consideration of phenological changes in adaptation efforts.
... Reproductive success drives population stock structure and phenology, with selection over evolutionary time scales determining an animal's physiological environmental constraints (Rangel et al., 2018), movement attributes, and thus population distributions. Because fitness occurs at the individual scale, and animals exhibit movement-related syndromes (Spiegel et al., 2017), fishing mortality can select for particular movement attributes (Andersen et al., 2018;Tillotson and Quinn, 2018). ...
Although movement has always played an important role in fisheries science, movement patterns are changing with changing ocean conditions. This affects availability to capture, the spatial scale of needed governance, and our food supply. Technological advances make it possible to track marine fish (and fishermen) in ways not previously possible and tracking data is expected to grow exponentially over the next ten years - the bio-logging decade. In this article, we identify fisheries management data needs that tracking data can help fill, ranging from: improved estimates of natural mortality and abundance to providing the basis for short-term fisheries closures (i.e. dynamic closures) and conservation of biodiversity hotspots and migratory corridors. However, the sheer size of the oceans, lack of GPS capability, and aspects of marine fish life history traits (e.g., adult/offspring size ratios, high mortality rates) create challenges to obtaining this data. We address these challenges and forecast how they will be met in the next 10 years through increased use of drones and sensor networks, decreasing tag size with increased sensor capacity trends, the ICARUS initiative to increase satellite tracking capacity, and improved connectivity between marine and terrestrial movement researchers and databases. © International Council for the Exploration of the Sea 2019. All rights reserved.
... Fishing is a strong, selective evolutionary factor which could lead to unwanted changes in fish stocks (e.g. Hard et al., 2008;Laugen et al., 2014;Tillotson & Quinn, 2017). Selective fishing mortality in migratory routes or in nonbreeding areas could severely affect fish population lifehistory diversity by decreasing the number of migrating individuals (Syrjänen & Valkeajärvi, 2010;Thériault, Dunlop, Dieckmann, Bernatchez, & Dodson, 2008). ...
We estimated the proportions of anadromous and freshwater‐resident brown trout (Salmo trutta) in different parts of the subarctic River Näätämöjoki/Neidenelva system (Finland and Norway) using carbon, nitrogen and hydrogen stable isotope analyses of archived scales as identifiers of migration strategy. Our results showed that carbon stable isotope values were the best predictor of migration strategy. Most individuals fell into two clearly distinct groups representing anadromous (47%) or freshwater‐resident (42%) individuals, but some fish had intermediate carbon values suggesting repeated movement between freshwater and the sea. The proportion of anadromous individuals decreased steadily with distance from the sea forming a spatial continuum in migration strategies which is probably maintained by the combination of several factors such as divergent availability of food resources, variable migration costs and genetic differences. These within‐catchment differences in migration strategies should be taken into account in fisheries management practices.
... The potential for fisheries to alter the behavioural composition in fish populations has not been fully explored (Uusi-Heikkilä et al., 2008;Heino et al., 2015;Arlinghaus et al., 2017;Tillotson and Quinn, 2018) despite the publication of the first observations and hypotheses in the mid-1950s (Miller, 1957). Recent developments in fish personality research (e.g. ...
In a landscape of fear, humans are altering key behaviours of wild-living animals, including those related to foraging, reproduction, and survival. When exposed to potentially lethal human actions, such as hunting or fishing, fish, and wildlife are expected to behaviourally respond by becoming shyer and learning when to be cautious. Using a rich dataset collected in temperate rocky reefs, we provide evidence of spearfishing-induced behavioural changes in five coastal fish taxa, exposed to different levels of spearfishing exploitation, by using flight initiation distance (FID) as a proxy of predator avoidance. We detected a significant increase of mean and size effects of FID when the observer was equipped with a speargun. Such effects were more evident outside marine protected areas where spearfishing was allowed and was commensurate to the historically spearfishing pressure of each investigated taxon. Our results demonstrate the ability of fish to develop finetuned antipredator responses and to recognize the risks posed by spearfishers as human predators. This capacity is likely acquired by learning, but harvest-induced truncation of the behavioural diversity and fisheries-induced evolution may also play a role and help to explain the increased timidity shown by the exploited fishes in our study.
... Surprisingly, behavioural traits that determine timing have been poorly considered in the context of the selective properties of fishing. Recently, Tillotson & Quinn (2017) proposed the timing of migration or breeding as candidate traits that are targeted by fisheries selection. Both the timing of migration and the timing of the breeding season have strong impacts on population dynamics (Lowerre- Barbieri et al., 2017), and selection imposed by these traits would strongly impact the long-term trajectory of the fish stocks. ...
The selective properties of fishing that influence behavioural traits have recently gained interest. Recent acoustic tracking experiments have revealed between-individual differences in the circadian behavioural traits of marine free-living fish; these differences are consistent across time and ecological contexts and generate different chronotypes. Here, we hypothesised that the directional selection resulting from fishing influences the wild circadian behavioural variation and affects differently to individuals in the same population differing in certain traits such as awakening time or rest onset time. We developed a spatially explicit social-ecological individual-based model (IBM) to test this hypothesis. The parametrisation of our IBM was fully based on empirical data; which represent a fishery formed by patchily distributed diurnal resident fish that are exploited by a fleet of mobile boats (mostly bottom fisheries). We ran our IBM with and without the observed circadian behavioural variation and estimated selection gradients as a quantitative measure of trait change. Our simulations revealed significant and strong selection gradients against early-riser chronotypes when compared with other behavioural and life-history traits. Significant selection gradients were consistent across a wide range of fishing effort scenarios. Our theoretical findings enhance our understanding of the selective properties of fishing by bridging the gaps among three traditionally separated fields: fisheries science, behavioural ecology and chronobiology. We derive some general predictions from our theoretical findings and outline a list of empirical research needs that are required to further understand the causes and consequences of circadian behavioural variation in marine fish.
... Importantly, exploitation, such as harvesting, exerts selection on other traits besides body size and age at maturity, but the impacts of these effects are only recently coming to light (Tillotson & Quinn, 2017). For example, the creation of marine reserves may generate selection on fish home range size (and correlated traits, such as personality) if individuals with small home ranges remain inside the reserve, while those with large home ranges spend more time outside the reserve (Villegas-Rios, Moland, & Olsen, 2017). ...
Aquatic ecosystems are facing escalating threats from urbanization, habitat loss and projected impacts of climate change, which both individually and in combination have the potential to fundamentally alter ecosystem functioning. While it is well established that habitat disturbances can affect the composition and diversity of aquatic communities, only recently have studies considered whether such impacts result in changes in species’ functional traits. We consider how functional traits of freshwater and marine fishes respond to environmental change, and how shifts in the expression of these traits can impact community dynamics and key ecological processes, including trophic interactions and nutrient transfer. We find that a multitude of functional traits, including behavioural and sensory traits, is sensitive to habitat disturbances. We demonstrate how these trait changes can be used to reveal hidden “ecological diversity” as well as serving as early indicators of environmental perturbation. We conclude that management strategies that consider the fundamental biological responses of fishes to habitat disturbance will be particularly effective in determining causal relationships within the ecological network. While detailed information on trait function is often lacking, even some general understanding of trait function and importance will facilitate targeted and efficient ecosystem management. We urge fisheries biologists and aquatic ecosystem managers to consider the role of functional traits in facilitating effective habitat restoration and management.
Earlier spring warming and anadromous fish migrations prompted by climate change are linked to shorter freshwater residency. Impacts of phenological change on anadromous fish populations are poorly understood with limited studies focused on iteroparous non-salmonids. We assessed freshwater residence time and reproductive success in an iteroparous clupeid, alewife (Alosa pseudoharengus) using a pedigree analysis and otolith-based spawning dates from captured juveniles. The primary objectives were to 1) estimate adult spawning duration in a freshwater pond (freshwater residence time) and 2) evaluate adult freshwater residence time, arrival date, length, sex, and reproductive success across two years in one system. Estimated freshwater residence times varied widely (1-64 days), and longer residence times were associated with earlier arrival dates, higher reproductive success, and more mating events. Longer freshwater residence times may allow alewife to spawn with more mates, produce more gametes, and experience a range of spawning and nursery conditions. Plasticity in alewife freshwater residence time could support earlier and shorter migration periods, but may result in lower reproductive output if adults spend less time in freshwater ponds.
Understanding variability in distributions and habitat-use among populations of anadromous salmonids is essential for their sustainable management. Arctic char (Salvelinus alpinus) is an important cultural and socioeconomic species, however, knowledge of their spatio-temporal habitat-use during the marine phase is limited. Here, a large-scale acoustic telemetry array was used to determine intraspecific variation in Arctic char summer marine habitat-use tied to overwintering lake occurrence in the Amundsen Gulf. Arctic char tagged in the ocean migrated to two main overwintering lakes, corresponding to distinct migration corridors and separate patterns of marine habitat-use, with one individual exhibiting among the longest recorded char marine migration to date (~330km). Arctic char that undertook longer migration distances initiated travel in the ocean towards freshwater 11 days earlier than those completing shorter migration distances; mean departure days (±SD) 2nd August (±8.1 days) and 13th August (±6.8 days), corresponding to migration distances of 252 and 131 km respectively. These findings identify that Arctic char from different populations can occupy distinct marine foraging grounds within a region, with consequences for variable interactions with fisheries.
Climate change is leading to shifts in not only the average timing of phenological events, but also their variance and predictability. Increasing phenological variability creates a stochastic environment that is critically understudied, particularly in aquatic ecosystems. We provide a perspective on the possible implications for increasingly unpredictable aquatic habitats, including more frequent trophic asynchronies and altered hydrologic regimes, focusing on ice-off phenology in lakes. Increasingly frequent phenological extremes may limit the ability of organisms to optimize traits required to adapt to a warming environment. Using a unique, long-term ecological dataset on Escanaba Lake, WI, USA as a case study, we show that the average date of ice-off is shifting earlier and becoming more variable, thus altering limnological conditions and yielding uncoupled food web responses with ramifications for fish spawn timing and recruitment success. A genes-to-ecosystems understanding of the responses of aquatic communities to increasingly variable phenology is needed. Our perspective suggests that management for diversity, at the intra- and inter-specific levels, will become paramount for conserving resilient aquatic ecosystems.
Background
Understanding movement patterns of anadromous fishes is critical to conservation management of declining wild populations and preservation of habitats. Yet, infrequent observations of individual animals fundamentally constrain accurate descriptions of movement dynamics.
Methods
In this study, we synthesized over a decade (2006–2018) of acoustic telemetry tracking observations of green sturgeon ( Acipenser medirostris ) in the Sacramento River system to describe major anadromous movement patterns.
Results
We observed that green sturgeon exhibited a unimodal in-migration during the spring months but had a bimodal distribution of out-migration timing, split between an ‘early’ out-migration (32%) group during May - June, or alternatively, holding in the river until a ‘late’ out-migration (68%), November - January. Focusing on these out-migration groups, we found that river discharge, but not water temperature, may cue the timing of migration, and that fish showed a tendency to maintain out-migration timing between subsequent spawning migration events.
Conclusions
We recommend that life history descriptions of green sturgeon in this region reflect the distinct out-migration periods described here. Furthermore, we encourage the continued use of biotelemetry to describe migration timing and life history variation, not only this population but other green sturgeon populations and other species.
We analyzed multiple historical data sources (circa 1948‐1960) to estimate Olympic Peninsula Winter Steelhead Oncorhynchus mykiss migration timing and abundance in the Quillayute, Hoh, Queets, and Quinault rivers, WA, to provide context for contemporary (circa 1980‐2017) population trends. Contemporary wild Winter Steelhead migrations peak one to two months later than historical migrations and migration timing breadth has contracted by up to 26 days (a 37% reduction of the interquartile range of the migration timing distribution). Migration timing changes coincide with an era of peak industrial forestry and introductions of early‐migrating hatchery Winter Steelhead stocks. We estimate that contemporary mean wild Winter Steelhead abundance has declined by 55% across populations compared to circa 1948‐1960 historical means, with 1920s records suggesting declines up to 77% in the Queets River. Migration timing shifts and the magnitude of population declines are not evident in modern fisheries monitoring records, which began around 1980. Our results demonstrate how modest extensions of the period of record (e.g., 30 yr) increase the power to identify population changes not readily apparent from contemporary fisheries monitoring programs. Historical fisheries data can help managers avoid the shifting baseline syndrome and provide important reference points for rebuilding population diversity and abundance.
Understanding and quantifying migration phenology of commercially harvested Pacific salmon (Oncorhynchus spp.) is a cornerstone for managing sustainable populations. Here, we use a multi-decadal data timeseries together with a hypothesis driven framework to evaluate migration phenology in adult fall and winter ecotype chum salmon (O. keta) in a poorly studied but highly managed system – the South Puget Sound (SPS) of Washington State, USA. Using generalized additive mixed models that accounted for temporal autoregressive dynamics, we examined the effect of commercial harvest, climate variation, intraspecific density dependence, and predator buffering on migration timing and run duration. SPS chum salmon are migrating earlier over time, especially the winter ecotype that showed the strongest temporal shift from historical timing. Migration timing shifts were closely associated with regional-scale marine climate regimes, local-scale freshwater availability, and statewide pinniped abundance. In conclusion, there is potential for the winter ecotype migration converging with that of the fall ecotype, and that directional change in migration phenology may be driven by a unique combination of ecosystem factors.
An essential management objective of the Yukon Delta and Koyukuk National Wildlife Refuges in Alaska is to conserve fish and wildlife populations and habitats in their natural diversity. In keeping with this objective, the U.S. Fish and Wildlife Service installed weirs in two tributaries of the Yukon River, the East Fork Andreafsky and Gisasa rivers, in 1994 to collect information on salmon populations that used them. The weirs have been in operation for over 23 years. Chinook Oncorhynchus tshawytscha and summer Chum Salmon O. keta were counted and sampled for various demographic data each year as they migrated through the weirs to upstream spawning areas. Here we examine this record of population data to describe and compare long-term variation in run abundance, run timing, length and age structure, sex composition, and production for these salmon populations. Because fishery managers often look to multiple monitoring projects in-season seeking corroboration of observed run qualities, we also considered whether Yukon River main-stem indicators of abundance were correlated with these tributary escapements. Our analyses suggest long-term stability of these populations despite large annual variations in most metrics we examined. Annual escapements have varied by factors of 3-5 for Chinook Salmon and over 23 for summer Chum Salmon, yet only the Chinook Salmon population in the Gisasa River appears to be declining. Main-stem abundance indicators were not correlated with Chinook Salmon escapements but were strongly correlated with summer Chum Salmon escapements. Run timing has varied annually by as much as a week earlier or later than average for all four populations with no trend over time. Mean age of the Chinook Salmon populations declined over time but remained stable for the summer Chum Salmon populations. Chinook Salmon populations in the East Fork Andreafsky and Gisasa rivers averaged 35% and 28% female, respectively. Both summer Chum Salmon populations averaged close to 50% female. Length at age has been stable or slightly declining for all four populations. Production over time was strongly correlated within species for populations in the two rivers, and averaged greater than one recruit per spawner for all populations except Chinook Salmon from the Gisasa River. We discuss these findings in the context of major changes in the fishery and the environments these populations experience.
Fisheries‐Induced Evolution (FIE) can result when harvest imposes artificial selection on variation in heritable phenotypic traits. While there is evidence for FIE, it remains difficult to disentangle the contributions of within‐generation demographic adjustment, phenotypic plasticity, and genetic adaption to observed changes in life history traits. We present evidence for FIE using dozens of Coho salmon (Oncorhynchus kisutch) populations in which males adopt one of two age‐invariant, heritable life history tactics: most mature as large three‐year‐old “hooknose” and typically fight for spawning opportunities, while some mature as small two‐year‐old “jacks” and fertilise eggs through sneaking. The closure of a fishery targeting three‐year‐old fish provided an experimental test of the prediction that fishery‐imposed selection against hooknose males drives an evolutionary increase in the proportion of males adopting the jack tactic. The data support the prediction: 43 of 46 populations had higher jack proportions during than after the fishery. The data further suggest that changes in jack proportion were not solely the result of demographic adjustments to harvest. We suggest that systems where fisheries differentially exploit phenotypically discrete, age‐invariant life histories provide excellent opportunities for detecting FIE.
Disruption of movement patterns due to alterations in habitat connectivity is a pervasive effect of humans on animal populations. In many terrestrial and aquatic systems there is increasing tension between the need to simultaneously allow passage of some species while blocking the passage of other species. We explore the ecological basis for selective fragmentation of riverine systems where the need to restrict movements of invasive species conflicts with the need to allow passage of species of commercial, recreational, or conservation concern. We develop a trait‐based framework for selective fish passage based on understanding the types of movements displayed by fishes and the role of ecological filters in determining the spatial distributions of fishes. We then synthesize information on trait‐based mechanisms involved with these filters to create a multi‐dimensional niche space based on attributes such as physical capabilities, body morphology, sensory capabilities, behavior, and movement phenology. Following this, we review how these mechanisms have been applied to achieve selective fish passage across anthropogenic barriers. To date, trap‐and‐sort or capture‐translocation efforts provide the best options for movement filters that are completely species selective, but these methods are hampered by the continual, high cost of manual sorting. Other less effective methods of selective passage risk collateral damage in the form of lower or higher than desired levels of passage. Fruitful areas for future work include using combinations of ecological and behavioral traits to passively segregate species; using taxon‐specific chemical or auditory cues to direct unwanted species away from passageways and into physical or ecological traps while attracting desirable species to passageways; and developing automated sorting mechanisms based on fish recognition systems. The trait‐based approach proposed for fish could serve as a template for selective fragmentation in other ecological systems. This article is protected by copyright. All rights reserved.
Current fisheries management pays little attention to fisheries‐induced evolution. Methods of exploitation that have benefits in the short term while ameliorating selection in the longer term would therefore be advantageous. Balanced harvesting is a potential candidate. This tries to bring fishing more in line with natural production, and some short‐term benefits for conservation of aquatic ecosystems and for biomass yield have already been documented. It is also predicted to be relatively benign as a selective force on fish stocks, because it keeps the overall distribution of mortality relatively close to natural mortality. We test this prediction, coupling an ecological model of marine, size‐spectrum dynamics to an adaptive dynamics model of life history evolution. The evolutionary variable is the reproductive schedule, set by the maximum body mass and the mass at maturation. The prediction is supported by our numerical analysis: Directional selection under balanced harvesting is approximately an order of magnitude weaker than in a standard fishery in which fish experience a fixed rate of fishing mortality after recruitment. The benefit of balanced harvesting follows from relatively little fishing on large fish, due to the low somatic production rates the big fish have. These results therefore support the general argument for protecting big, old fish, both for ecological and for evolutionary reasons. Slot fisheries that protect large fish share some qualitative features with balanced harvesting and show similar evolutionary benefits.
Time of spawning of Atlantic salmon (Salmo salar) in the River Dee in northeast Scotland was assessed from cumulative counts of redds made in five areas of the river system. Spawning occurred earliest at high altitude sites in the upper reaches of the river and progressively later at sites further downstream. The period of spawning at each location varied between 18 and 48 days and was more protracted at low altitude sites. Hatch occurred earlier in ova from redds in the lower altitude sites. Differences in the timing of spawning and hatch are considered in relation to water temperature. It is suggested that variation in the time of spawning is of adaptive significance and that it relates to the optimal timing of fry emergence in different parts of the river system.
Commercial and recreational harvests create selection pressures for fitness-related phenotypic traits that are partly under genetic control. Consequently, harvesting can drive evolution in targeted traits. However, the quantification of harvest-induced evolutionary life history and phenotypic changes is challenging, because both density-dependent feedback and environmental changes may also affect these changes through phenotypic plasticity. Here, we synthesize current knowledge and uncertainties on six key points: (i) whether or not harvest-induced evolution is happening, (ii) whether or not it is beneficial, (iii) how it shapes biological systems, (iv) how it could be avoided, (v) its importance relative to other drivers of phenotypic changes, and (vi) whether or not it should be explicitly accounted for in management. We do this by reviewing findings from aquatic systems exposed to fishing and terrestrial systems targeted by hunting. Evidence from aquatic systems emphasizes evolutionary effects on age and size at maturity, while in terrestrial systems changes are seen in weapon size and date of parturition. We suggest that while harvest-induced evolution is likely to occur and negatively affect populations, the rate of evolutionary changes and their ecological implications can be managed efficiently by simply reducing harvest intensity.
This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences'.
Selective harvest may lead to rapid evolutionary change. For large herbivores, trophy hunting removes males with large horns. That artificial selection, operating in opposition to sexual selection, can lead to undesirable consequences for management and conservation. There have been no comparisons of long-term changes in trophy size under contrasting harvest pressures. We analyzed horn measurements of Stone's rams (Ovis dalli stonei) harvested over 37 years in two large regions of British Columbia, Canada, with marked differences in hunting pressure to identify when selective hunting may cause a long-term decrease in horn growth. Under strong selective harvest, horn growth early in life and the number of males harvested declined by 12% and 45%, respectively, over the study period. Horn shape also changed over time: horn length became shorter for a given base circumference, likely because horn base is not a direct target of hunter selection. In contrast, under relatively lower hunting pressure, there were no detectable temporal trends in early horn growth, number of males harvested, or horn length relative to base circumference. Trophy hunting is an important recreational activity and can generate substantial revenues for conservation. By providing a reproductive advantage to males with smaller horns and reducing the availability of desirable trophies, however, excessive harvest may have the undesirable long-term consequences of reducing both the harvest and the horn size of rams. These consequences can be avoided by limiting offtake.
Many marine fishes mate in massive and spectacular gatherings at predictable times and places. These spawning aggregations
are often attractive targets of fisheries. Many commercially important fish species exhibit aggregation spawning, and many
have undergone serious declines from overfishing. It is timely to explore whether the exploitation of spawning aggregations
makes species particularly susceptible to overfishing; if so, why and how we can better manage these species. I present evidence
that aggregate fish spawners are especially vulnerable because of both increased catchability (lethal effects) and biological
factors (nonlethal effects). For these species to continue contributing to food security and livelihoods while retaining their
ecosystem function, a truly precautionary approach is essential to reduce the risk of declines, particularly in the case of
small-scale commercial fisheries of low-productivity species and where management and monitoring are lacking. There is a pressing
need to mainstream spawning aggregations into marine resource management.
In several groups of anadromous fishes, but especially the salmonids, some populations migrate from the ocean to fresh water many months prior to spawning. This "premature migration" reduces growth opportunities at sea, compels them to occupy much less productive freshwater habitats, and exposes them to extremes of flow and temperature, disease, and predation. We first review migration in salmonids and find great variation in timing patterns among and within species, relative to the timing of reproduction. Premature migration is widely distributed among species but not in all populations, and we propose two hypotheses to explain it. First, the fish may be making "the best of a bad situation" by entering early because access to suitable breeding sites is constrained seasonally by flow or temperature regimes, so they sacrifice growing opportunities at sea. Alternatively or additionally, some populations may be "balancing risks and benefits" as they trade off the benefits of growth at sea against the risk of mortality there. In this model, the reduced risk of mortality at sea must be balanced against the risk of mortality in freshwater habitats from thermal stress, disease, and predators. Premature migration may be favored where temperatures and flows are moderate or where lakes provide safety from predators and reduce energetic expenditure. Consistent with this hypothesis, early return is characteristic of larger, older salmonids (that would benefit less from additional time at sea to grow than would smaller fish). Finally, we consider the vulnerability of premature migrants to climate change and selective fisheries. Migration timing is an important part of the portfolio of phenotypic diversity that conveys resilience to species, population complexes, and the fisheries that depend on them. The premature migrants are often especially valued in fisheries and also often of particular conservation concern, and the phenomenon merits further research.
Significance
In terrestrial ecosystems, earlier phenology (i.e., seasonal timing) is a hallmark organismal response to global warming. Less is known about marine phenological responses to climate change, especially in Eastern Boundary Current Upwelling (EBCU) ecosystems that generate >20% of fish catch. The phenology of 43 EBCU fish species was examined over 58 years; 39% of phenological events occurred earlier in recent decades, with faster changes than many terrestrial ecosystems. Zooplankton did not shift their phenology synchronously with most fishes. Fishes that aren’t changing their phenology synchronously with zooplankton may be subject to mismatches with prey, potentially leading to reduced recruitment to fisheries. Adjusting the timing of seasonal management tactics (e.g., fishery closures, hatchery releases) may help ensure that management remains effective.
The value of big old fat fecund female fish (BOFFFFs) in fostering stock productivity and stability has long been underappreciated
by conventional fisheries science and management, although Hjort (1914) indirectly alluded to the importance of maternal effects. Compared with smaller mature females, BOFFFFs in a broad variety
of marine and freshwater teleosts produce far more and often larger eggs that may develop into larvae that grow faster and
withstand starvation better. As (if not more) importantly, BOFFFFs in batch-spawning species tend to have earlier and longer
spawning seasons and may spawn in different locations than smaller females. Such features indicate that BOFFFFs are major
agents of bet-hedging strategies that help to ensure individual reproductive success in environments that vary tremendously
in time and space. Even if all else were equal, BOFFFFs can outlive periods that are unfavourable for successful reproduction
and be ready to spawn profusely and enhance recruitment when favourable conditions return (the storage effect). Fishing differentially
removes BOFFFFs, typically resulting in severe truncation of the size and age structure of the population. In the worst cases,
fishing mortality acts as a powerful selective agent that inhibits reversal of size and age truncation, even if fishing intensity
is later reduced. Age truncation is now known to destabilize fished populations, increasing their susceptibility to collapse.
Although some fisheries models are beginning to incorporate maternal and other old-growth effects, most continue to treat
all spawning-stock biomass as identical: many small young females are assumed to contribute the same to stock productivity
as an equivalent mass of BOFFFFs. A growing body of knowledge dictates that fisheries productivity and stability would be
enhanced if management conserved old-growth age structure in fished stocks, be it by limiting exploitation rates, by implementing
slot limits, or by establishing marine reserves, which are now known to seed surrounding fished areas via larval dispersal.
Networks of marine reserves are likely to be the most effective means of ensuring that pockets of old-growth age structure
survive throughout the geographic range of demersal species.
Loher, T. 2011. Analysis of match–mismatch between commercial fishing periods and spawning ecology of Pacific halibut (Hippoglossus stenolepis), based on winter surveys and behavioural data from electronic archival tags. – ICES Journal of Marine Science, 68: 2240–2251.
The fishery for halibut (Hippoglossus stenolepis) in the eastern Pacific is closed during the boreal winter, roughly corresponding to the seasonal spawning of the species. Opening and closing dates for each season are stipulated annually based on economics and biology. Historical surveys and data from electronic tags are analysed to assess the extent to which recent closures have encompassed the annual spawning cycle of the species, as defined by migration to offshore spawning sites, active spawning, and return to feeding areas. These were assessed by calculating mean maximum daily depth profiles for fish exhibiting seasonal migration, calculating the date-specific proportions of the tagged population either migrating to or resident on their feeding or spawning grounds, and examining the temporal distribution of spent and running fish in historical surveys along with evidence of spawning contained in high-resolution tag data. The data indicate that fishery closures over the past 20 years have been consistently too short to protect the entirety of a migration period that begins as early as September and is not substantially completed until May. Additionally, some recent season openings have encroached on the active spawning season. Failure to fully protect spawning migrations may allow seasonal interception fisheries, and the selective removal of early and late spawners could cause changes in stock demographics, restrict effective spawning, and influence long-term stock productivity, especially in the face of environmental variability.
While fishery closures during the spawning season are commonplace, direct evidence for their benefit is mainly restricted to species forming large spawning aggregations. This paper analyses the conditions under which spawning closures could contribute to sustainable fisheries management by reviewing how fishing during spawning may affect the physiology, behaviour and ecology of individuals and how this may influence the dynamics and the genetics of the population. We distinguish between the effects of fishing activities in relation to mortality, disturbance of spawning activity, and impact on spawning habitat. Spawning closures may be of benefit it they: (1) reduce the fishing mortality of the large and older spawners; (2) avoid negative effects on spawning habitats; (3) reduce the risk of over-exploitation in species which form large spawning aggregations; (4) reduce the evolutionary effects on maturation and reproductive investment; and (5) reduce the risk of over-exploitation of specific spawning components. The contribution of spawning closures to sustainable fisheries will differ among species and depends on the complexity of the spawning system, the level of aggregation during spawning and the vulnerability of the spawning habitat. The importance of these closures depends on the degree of population depletion but does not cease when populations are ‘healthy’ (i.e. no sign that recruitment is impaired).
Ability to understand and predict fish recruitment is a key goal of fishery management agencies in both freshwater and marine ecosystems. Toward this end, an increasing amount of recruitment-oriented research focused on the effects of physical processes on the early life stages of fish (e.g., eggs, larvae), as physical processes have been shown to directly and indirectly influence early life early life growth, survival, and future recruitment to the fishery. However, the majority of this research has been conducted in marine ecosystems when compared to freshwater systems, despite these ecosystems having similar physical processes and economically important fishes with life-history characteristics equally vulnerable to physical controls. Herein, we review the physical processes common to large lakes that may impact freshwater fish recruitment and address the current state of coupled physical-biological research for predicting fish recruitment in freshwater systems. Examples emphasizing the importance of physical forcing in regulating fish recruitment in the Laurentian Great Lakes are provided. Given the similarities in physical and biological components between ecosystems, we argue that understanding, predicting, and managing recruitment variation in the large freshwater lakes of the world will require coupled physical-biological research and modeling approaches that are more typical of marine studies.
Anderson, S. C., Branch, T. A., Ricard, D., and Lotze, H. K. 2012. Assessing global marine fishery status with a revised dynamic catch-based method and stock-assessment reference points. – ICES Journal of Marine Science, 69: .
The assessment of fishery status is essential for management, yet fishery-independent estimates of abundance are lacking for most fisheries. Methods exist to infer fishery status from catches, but the most commonly used method is biased towards classifying fisheries as overexploited or collapsed through time and does not account for still-developing fisheries. We introduce a revised method that overcomes these deficiencies by smoothing catch series iteratively, declaring fisheries developing within three years of peak catch, and calibrating thresholds to biological reference points. Compared with status obtained from stock-assessment reference points for 210 stocks, our approach provides a more realistic assessment than the original method, but cannot be perfect because catches are influenced by factors other than biomass. Applied to FAO catches, our method suggests in 2006 32% of global fisheries were developing, 27% fully exploited, 25% overexploited, and 16% collapsed or closed. Although less dire than previous assessments, this still indicates substantial numbers of overexploited stocks. Probably because median exploitation rate decreased since 1992, our catch-based results do not reflect recent stabilization of assessed-stock biomass. Whether this outlook also applies to unassessed stocks can only be revealed with increased or more representative collection of biomass- and exploitation-rate trends.
Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely from competition) combined with adaptive microevolution (decreased PMRNs) have produced the observed life-history patterns. PMRNs did not decrease in all populations, and we documented differences in magnitude and consistency of size selection and exploitation rates among populations. Incorporating evolutionary considerations and tracking further changes in life-history traits can support continued sustainable exploitation and productivity in these and other exploited natural resources.
The physical and ecological 'fingerprints' of anthropogenic climate change over the past century are now well documented in many environments and taxa. We reviewed the evidence for phenotypic responses to recent climate change in fish. Changes in the timing of migration and reproduction, age at maturity, age at juvenile migration, growth, survival and fecundity were associated primarily with changes in temperature. Although these traits can evolve rapidly, only two studies attributed phenotypic changes formally to evolutionary mechanisms. The correlation-based methods most frequently employed point largely to 'fine-grained' population responses to environmental variability (i.e. rapid phenotypic changes relative to generation time), consistent with plastic mechanisms. Ultimately, many species will likely adapt to long-term warming trends overlaid on natural climate oscillations. Considering the strong plasticity in all traits studied, we recommend development and expanded use of methods capable of detecting evolutionary change, such as the long term study of selection coefficients and temporal shifts in reaction norms, and increased attention to forecasting adaptive change in response to the synergistic interactions of the multiple selection pressures likely to be associated with climate change.
Global climate change will affect the abundance, distribution, and life history timing of many exploited marine populations, but specific changes are difficult to predict. Management systems in which harvest strategies and tactics are flexible in responding to unpredictable biological changes are more likely to succeed in maintaining productive populations. We explore the adaptability of fisheries management systems in relation to oceanic warming rates by asking how two important management characteristics vary with temperature changes for >500 stocks. (1) Harvest control rules, a framework for altering fishing pressure in response to changes in the abundance of targeted species (primarily due to fishing), may provide the capacity for harvest policies to change in response to climate-driven abundance declines also. (2) Seasonal openings with flexible dates that involve in-season monitoring may allow managers to better respond to possible changes in the timing of life-history periods like spawning to prevent fishing seasons falling out of sync with species’ phenology. Harvest control rules were widely used across industrialized fisheries including in regions that experienced relatively high oceanic warming rates, but after controlling for regional factors we found no association between ocean warming and the use of harvest control rules. Flexible-date seasonal openings were rare compared to fixed-date seasonal openings, but tended to occur in areas with the greatest warming rates while fisheries without seasonal closures tended to occur in areas with the least observed temperature changes. We found no consistent evidence of recent ocean warming effects on the current biomass or exploitation rates relative to management targets of 241 assessed marine populations. Together, these results suggest that the oceanic areas expected to have the greatest climate impacts on populations do at least tend to contain fisheries that demonstrate the potential for adaptability to unpredictable climate impacts.
The peak of spawning runs of American shad (Alvsa sapidissima) into rivers at various latitudes on the Atlantic and Pacific coasts of North America takes place when water temperatures are near 18.5°C. At the Bonneville Dam, Columbia River, Wash., 90% of the run as a rule takes place when river temperatures are between 16.0° and 19.5°C. At the fish ladder of the Holyoke Water Power Company on the Connecticut River, the temperature at the peak of the shad run averaged 111.5°C for 15 years. In the St. Johns River, Fla., peak movement occurs in December and January at the time of the annual minimum water temperatures, or 14.0 0 to 20.0°C. Migrations of shad in the Atlantic Ocean follow paths associated with approximately the same range of temperatures (13.0 0 -18.0°C). Annual cycles of ocean warming cause shad to move into the Gulf of Maine in the summer, to the middle Atlantic in the winter, and to the south in the early spring. Juvenile shad move downstream in the fall, coin ciding with a decline in the temperature of each stream to below 15.5°C. A path of migration for shad in the Pacific Ocean is hypothesized from the known seasonal changes in ocean temperature. The potential effects of artificial warming of streams on timing and survival of shad runs in northern and southern latitudes is discussed. The American shad (Alosa sapidissima), in spite of declines in abundance on the Atlantic coast of the United States caused by obstruction of spawning runs by dams, by water pollution, and by overfishing, continues to provide a catch each year of some 8 million pounds valued at slightly more than one million dollars to the fish ermen (Walburg and Nichols, 1967). There is as yet no rationally based manage ment scheme to prevent overfishing of shad, and dams and pollution continue to increase. Recent changes in the environment for shad have been brought about by the greatly increased heating of the water by steam-electric generating sta tions. There will be a further increase in the construction of these facilities; thus the Federal Power Commission in 1960 estimated that by 1980 the generating capacity of hydroelectric power stations would double-some accom plished by construction of dams and some by ad ding capacity at existjng dams-but at the same time, steam-electric capacity would triple (Fed eral Power Commission, 1960). Other experts
We examined interannual variability in the timing of spawning of female cod Gadus morhua from 1947 to 1992 in 3 regions off Newfoundland, Canada, in the northwest Atlantic. Maturity data, assessed by visual examination of dissected gonads of cod collected by research trawls, were analysed with probit regressions to identify the day of each year on which 50 % of females had ceased spawning (which we ref er to as spawning time) on northern [Northwest Atlantic Fisheries Organisation (NAFO) Division 3L] and southern (3NO) Grand Bank and on St. Pierre Bank (3Ps). We minimized the bias in our estimates by separating sampling variability and interannual variation in age structure from true interannual variability in reproduction. Among regions, average spawning time (mean +/- SD) varied from Days 157 +/- 18 (June 6) and 139 +/- 16 (May 19) on northern and southern Grand Bank, respectively, to Day 135 +/- 24 (May 15) on St. Pierre Bank. Interannual differences in spawning time were significant within 3L (1948-1991), 3NO (1947-1992), and 3Ps (1953-1987) (likelihood ratio tests; p < 0.001). Interannual variation in spawning time was significantly associated with variation in water temperature prior to spawning in 3L and in 3Ps although the signs of the associations differed between regions, casting doubt on the hypothesis that the timing of cod reproduction represents an adaptive response to temperature change. The negative correlation between temperature and spawning time in 3L can be explained by the positive influence of temperature on gonad development. In 3Ps, we attribute the early spawning dates in years characterized by cold bank temperatures to (1) a thermal barrier imposed by sub-zero temperatures on spawning migrations from the continental slope to the shelf, and to (2) increased rates of gonad development, and an earlier readiness to spawn, experienced by cod 'forced' to prolong their residence in warm slope waters. Our analyses indicate that cod spawning time varies significantly among years, demonstrate how the effects of temperature on cod reproduction depend on regional hydrography, and underscore the importance of separating variation in sampling protocol and age structure from true interannual variability in spawning time.
We use an individual-based eco-genetic model to examine the demographic and evolutionary consequences of selective mortality on a species with parental care, the smallmouth bass Micropterus dolomieu. Our analyses are grounded in a long-term (1936-2003) empirical study of the dynamics of two populations that differ widely in both density and life history. The model we construct extends previous approaches by including phenotypic plasticity in age and size at maturation, by permitting density-dependent somatic growth, and by analyzing how costs associated with parental care alter model predictions. We show that, first, additional mortality on age-0 individuals applied for 100 years causes reduced population abundance and biomass, faster somatic growth rates, and phenotypic plasticity toward slightly larger sizes at maturation. Second, mortality on individuals above a minimum size limit, also applied for 100 years, has a small influence on population abundance and somatic growth, causes a reduction of biomass, and substantial evolution of the probabilistic maturation reaction norm, leading to younger ages and smaller sizes at maturation. Third, the incorporation of body-size-dependent survival costs associated with parental care (i.e., by reducing the number of small breeding adults at high population densities, increasing the mortality of parents that breed at small body sizes, or increasing the mortality of offspring originating from small-sized parents) reduces the amount of evolution predicted to occur within 100 years. Together, these results underscore that selective harvest can cause both phenotypically plastic responses and rapid evolution; however, the rate and magnitude of the evolved changes are sensitive to a species' life history characteristics.
Using mark-recovery data obtained from 1982 to 1987, we estimated rates of dispersal from release locations and mortality for mature male and female lingcod Ophiodon elongatus in the Strait of Georgia, British Columbia. Under the assumption of random dispersal from release locations, and incorporating sport-fishery effort data obtained by an independent creel survey, we determined from sport-fishery tag recoveries that male lingcod dispersed at a mean rate of 500 m/d (95% confidence interval, 400–600 m/d) and females dispersed at 1,040 m/d (900–1,180 m/d). In an unbounded environment, this can be interpreted as 95% of tagged males remaining within 17 km and 95% of females within 34 km of the release location after 1 year at large, In the confines of the Strait of Georgia, actual dispersal would be less. Males dispersed significantly (P < 0.01) more slowly than females, and they had a higher annual instantaneous total (fishing plus natural) mortality rate (95% confidence intervals 0.72–1.25 for males and 0.29–0.77 for females) after adjustments for tag loss. Our mortality estimates were consistent with our understanding of the history and current status of the commercial and sport fisheries for lingcod in the Strait of Georgia, but our movement rate estimates were greater than those suggested by previous studies. We argue that the sport fishery is likely becoming the main human cause of a continuing decline in lingcod landings, and that, in recent years, natural mortality, particularly for males and small females, has included increased predation by marine mammals. Movements appeared extensive enough for us to propose that the lingcod population within the Strait of Georgia be considered a stock unit.
The eastern Pacific halibut (Hippoglossus stenolepis ) fishery is prosecuted over a nine-month season with a provision to cease harvests if stock declines to historically-observed minimum spawn- ing biomass. The industry has requested to extend fishing into winter, but little information exists regarding potential impacts on spawning aggregations or effective spawning biomass. A strictly an- nual spawning cycle is presumed, but some adults fail to undertake the offshore migration associated with continental slope spawning. We examined depth records of halibut tagged with Pop-up Archival Transmitting (PAT) tags for evidence of offshore seasonal migration (n = 72). For tags that were physically recovered (n = 16) we identified the occurrence of abrupt (~100 m) mid-winter ascents, believed to be egg release. The active spawning season, defined by occurrence of these rises, lasted from 27 December-8 March, at bottom depths of 278-594 m. Eighteen percent of tagged halibut remained onshore. Thirty-one percent of fish with detailed archival records did not exhibit spawning rises, including all fish that remained onshore. Correcting for the possibility that some were likely immature, the data suggest that ~10% of the mature fish do not participate in the spawning migration and 10-15% that migrate to deep water may not actively spawn. The data suggest that opening the commercial fishery in early spring would likely subject actively spawning fish to fishing mortality, and could truncate the effective spawning period. Natural rates of skip-spawning and fisheries-in- duced reduction of the spawning period relative to suitable larval rearing conditions could introduce temporal and regional variance into levels of effective spawning biomass and warrant further inves- tigation.
Maturation rates (measured as the change in the gonosomatic index (GSI) with time) over the last month of the annual maturation cycle were estimated for male and female herring in British Columbia, between 1982–87. The data were analyzed to determine interannual and interregional differences in the maturation rate and its influence on spawning time. The data also indicated that in some areas herring spawned in discrete waves — the largest fish tended to spawn first and the smaller fish in subsequent waves. Each spawning wave lasted about 5–6 d and the interwave interval varied from 8–26 d in the Strait of Georgia. General equations were developed to describe gonadal growth over the entire maturation cycle. These equations accounted for the observed differences in: (1) the maturation rates between the sexes (males initially mature faster), (2) the interregional and interannual variation in the timing of spawning (herring tend to spawn later at higher latitudes, and earlier than normal when its warmer), and (3) provide an explanation for spawning waves. All of these phenomena derive from the fact that the instantaneous rate at which the gonad grows during the maturation cycle in both sexes depends on the weight of the fish, and the daily sea temperature.
Pacific herring Clupea harengus pallasi are winter-spring spawners which exhibit a S-N latitudinal cline in spawning time. Atlantic herring Clupea h. harengus consist of both winter-spring and summer-autumn spawning groups characterized in the NE Atlantic by oceanic, shelf, and coastal populations. The oceanic group are large migratory fish spawning off the coasts of Norway and Iceland. The shelf group includes the various locally migratory North Sea populations adjacent to the British Isles. The coastal groups consist of smaller fish restricted to the Baltic and White seas. In the NW Atlantic, spawning occurs from N Labrador to Virginia with spring spawners predominating in the north and fall spawners in the south. Temperature is one of the factors that determine when spawning occurs. The Atlantic herring exhibits sexual dimorphism in the spawning act with only the female interacting with the spawning substrate. Both sexes of the Pacific herring make physical contact with the substrate on which the adhesive eggs are deposited. Spawning grounds are located in high-energy environments, either nearshore for spring spawners or in tidally active areas for fall spawners. Spawn is deposited on marine vegetation or on bottom substrate, such as gravel, which is free from silting. The eggs are tolerant to temperatures in the range of 5-14oC and salinities in the range of 3-33per mille. Egg mortality results mostly from suffocation due to high egg densities and silting, predation, and, in intertidal spawn, from stresses imposed by exposure to air and from egg loss by wave action.-from Authors
The optimum spawning stock size for a Ricker stock recruitment curve was shown to be accurately approximated by the equation Ps = Pr(0.5–0.07a) when 0 < a < 3. A simple modification was also shown to incorporate stochastic variation about the stock recruitment curve into calculations of optimum stock size.
When several stocks of differing productivities are fished together and combined for stock recruitment analysis, the estimated productivity and size of the stock depends strongly on the previous exploitation history. As a mixed stock is harvested harder, it appears smaller in total size but more productive per individual. I analysed the mechanism behind this change. Passive feedback management policies perform well on mixed stocks, when starting from unexploited conditions. When starting from an overexploited condition, passive feedback management will fail to allow the less productive stocks to recover and will maintain overexploitation. This is also true in the presence of straying between stocks. Since few salmon fisheries operate on single stocks, stock recruitment analyses will usually underestimate the optimum escapement and overestimate the optimum harvest rate when mixed stocks are treated as a single stock. These conclusions will be true for any mixed stock fishery with different productivities of the stocks.
Each population of Atlantic herring (Clupea harengus harengus) has its own seasonally fixed spawning period of a few weeks duration, but the mean spawning times of different populations differ substantially. The extant theory explains the population-specific timing of spawning relative to the plankton production blooms in the inferred larval distributional area. Support of this theory is evaluated, and found lacking, in the light of a recent "stock" hypothesis involving larval retention. The new hypothesis involves two constraints. First, the larvae of a discrete herring population develop within, and are thus adapted to, the specific oceanographic conditions of their larval retention area. Second, metamorphosis from the larval to juvenile form occurs primarily within a restricted period of the year (April to October). Given these two constraints, it is hypothesized that the timing of spawning of a herring population is a function of the time necessary to complete the larval phase and yet metamorphose within the acceptable seasonal envelope. Populations that have "good" larval retention areas can spawn in the spring and still metamorphose within the seasonal envelope. Populations with larval retention areas that are less "good" for larval growth have to spawn earlier to satisfy the two constraints. The implications of the hypothesis on the "match–mismatch" theory are briefly discussed.
Optimal harvest rates for mixed stocks of fish are calculated using stochastic dynamic programming. This technique is shown to be superior to the best methods currently described in the literature. The Ricker stock recruitment curve is assumed for two stocks harvested by the same fishery. The optimal harvest rates are calculated as a function of the size of each stock, for a series of possible parameter values. The dynamic programming solution is similar to the fixed escapement policy only when the two stocks have similar Ricker parameters, or when the two stocks are of equal size. Normally, one should harvest harder than calculated from fixed escapement analysis.
Recent research has highlighted the importance of interpopulation diversity in fostering the stability of population complexes. Here we focus on California’s recently collapsed fall-run Chinook salmon (Oncorhynchus tshawytscha) and ask whether portfolio effect induced buffering is observed across the complexity hierarchy from individual populations to populations within a river basin (Sacramento, San Joaquin) to the entire Central Valley. Some buffering was observed when comparing the coefficient of variation in adult returns to a given river basin with its constituent populations but not when comparing returns to the entire Central Valley with its constituent basins because of disproportionately many fish returning to the Sacramento Basin. Moreover, we report that positive correlations in population dynamics between rivers were stronger in the last 25 years of the study compared with the first 25 years. Together, these results suggest evidence of only a weak portfolio effect that has deteriorated in recent years. Nonetheless, we also report that correlations between rivers decreased significantly with distance, suggesting that some biocomplexity remains. Our results suggest that the greatest potential for strengthening the portfolio effect would come through restoration of San Joaquin Basin populations, which at low abundance currently contribute little to the overall buffering capacity despite low cross-basin correlations.
Predation can affect both phenotypic variation and population productivity in the wild, but quantifying evolutionary and demographic effects of predation in natural environments is challenging. The aim of this study was to estimate selection differentials and coefficients associated with brown bear (Ursus arctos) predation in wild sockeye salmon (Oncorhynchus nerka) populations spawning in pristine habitat that is often subject to intense predation pressure. Using reconstructed genetic pedigrees, individual reproductive success (RS) was estimated in two sockeye salmon populations for two consecutive brood years with very different predation intensities across brood years. Phenotypic data on individual adult body length, body depth, stream entry timing and reproductive lifespan were used to calculate selection coefficients based on RS, and genetic variance components were estimated using animal models. Bears consistently killed larger and more recently arrived adults, although selection differentials were small. In both populations, mean RS was higher in the brood year experiencing lower predation intensity. Selection coefficients were similar across brood years with different levels of predation, often indicating stabilizing selection on reproductive lifespan as well as directional selection for longer reproductive lifespan. Despite these selection pressures, genetic covariation of morphology, phenology and lifespan appears to have maintained variation in spawner body size and stream entry timing in both populations. Our results therefore suggest considerable demographic but limited evolutionary effects of bear predation in the two study populations.Heredity advance online publication, 10 February 2016; doi:10.1038/hdy.2016.3.
This paper discusses the degree to which fishing causes evolution in fishes and how to detect and measure it. Fishing mortality is often very high and nonrandom with respect to several life-history traits that are at least partly heritable. Therefore, it seems likely that fishing causes evolution in fishes. Selective harvest of experimental populations has produced genetic changes in them, and natural selective agents, especially selective predation, have also caused genetic changes in populations of various species. However, the action of many other factors makes the detection and measurement of evolution difficult, so many observations that show changes in life-history traits of exploited fish populations are not sufficient by themselves to establish the occurrence of evolution. The difficulty of detecting and measuring evolution by observation alone should not be interpreted as evidence that evolution is not occurring; instead, it provides a opportunity for experimental research that has theoretical and practical importance. Some experimental approaches, which should be accompanied by simulations, are discussed.
The rate of evolution and the scope for phenotypic plasticity can be assessed by studying the adaptation of an introduced population to a new habitat and the response of established populations to progressive environmental change. Adult American shad (Alosa sapidissima), an introduced species, and sockeye salmon (Oncorhynchus nerka), a native species, migrate up the Columbia River (northwestern United States) in late spring and early summer to spawn. Based on records from Bonneville Dam, the river's spring warming has occurred progressively earlier since approximate to 1950, coinciding with a reduction in spring discharge. The date when 50% of the shad migrated past the dam is correlated with this shift in thermal and flow regimes; they now ascend the river approximate to 38 d earlier than they did in 1938. However, the mean temperature that they experience has actually decreased by 1.8 degrees C in 45 yr, indicating that the change in their migratory timing has outstripped the rate of environmental change. The upriver migration of sockeye salmon is also earlier than in past years, but their change in timing (approximate to 6 d since 1949) lags behind the rate of environmental change, and they are now experiencing approximate to 2.5 degrees C warmer temperatures than in past years. We hypothesize that the differences in response to changing environmental conditions between these species arise from differences in their migration patterns and early life histories. Shad spawn soon after they enter the river in its main stem where environmental conditions of the larvae will closely mirror those experienced by upstream-migrating adults. They may therefore have evolved a migratory pattern that allows greater behavioral response to environmental fluctuations than sockeye salmon, which spawn in distant locations many months after their upriver migration. Sockeye salmon migration may be more strongly controlled by innate responses to photoperiod, migrating at the time of year which is best on average because conditions in the lower river will not be indicative of those to be experienced by incubating embryos and juveniles.