... Fishery-independent surveys are designed to obtain samples that can serve as indices of stock status over time, whilst minimising bias (Hilborn and Walters, 1992;Fraser et al., 2007;Dennis et al., 2015). These indices are often used to estimate relative or absolute stock size (Hilborn and Walters, 1992;Walters and Pearse, 1996;Pennington and Strømme, 1998). ...
... Fishery-independent surveys are designed to obtain samples that can serve as indices of stock status over time, whilst minimising bias (Hilborn and Walters, 1992;Fraser et al., 2007;Dennis et al., 2015). These indices are often used to estimate relative or absolute stock size (Hilborn and Walters, 1992;Walters and Pearse, 1996;Pennington and Strømme, 1998). Estimating stock size is highly useful and can be a key piece of evidence for sustainable management advice (Pennington and Strømme, 1998;Fraser et al., 2007). ...
... Estimating stock size is highly useful and can be a key piece of evidence for sustainable management advice (Pennington and Strømme, 1998;Fraser et al., 2007). Such advice may be used to set a catch limit over a period or to control effort through various gear and vessel restrictions, to prevent overfishing and ensure long-term resource availability (Hilborn and Walters, 1992;Pennington and Strømme, 1998). ...
Article
Commercial fishing vessels can be a cost-effective alternative to research vessels for performing towed gear fishery-independent surveys, if catch rates are comparable among commercial vessels and with research vessels. A parallel fishing experiment was conducted off the coast of Wales, United Kingdom, to compare the king scallop (Pecten maximus) catch rates of three commercial vessels using commercial dredges and a research vessel using two types of scientifically modified dredges. The scientific dredges are currently used in the fishery-independent survey of local scallop populations. Size-structured scallop catch-per-unit-effort (CPUE) was compared among vessel-gear combinations. Two similarly sized commercial vessels had generally similar CPUEs, however there were some significant differences with scallop size. A smaller commercial vessel had significantly lower CPUEs for a broad range of scallop sizes. The research vessel dredges had significantly higher CPUE for smaller scallops than the commercial vessels. Vessel size is likely to be driving the differences among commercial vessels and belly ring size is likely to be driving differences among research and commercial dredges. These findings highlight commercial vessel CPUE should not be assumed the same, whilst also showing that vessel size may be the best indicator of catch rate similarity. These results also highlight that changing the fishery-independent vessel and gear to the commercial options trialled here would result in a considerable loss of information about the smaller scallops in the population. These findings will be of interest to fishery scientists or managers using multiple vessels, or considering a change of vessels, for fishery-independent surveys.
... Many data-rich stock assessments rely on some assumed spawning stock biomass (SSB)/recruitment (R) relationship (Ricker 1954;Cury et al. 2014). This relationship is both the most important and the most difficult in fisheries stock assessments (Hilborn & Walters 1992). ...
... The concept is simple: there must exist a connection between the breeding group of a population and the abundance of their offspring (Ricker 1954;Beverton & Holt 1957;Hilborn & Walters 1992;Cury et al. 2014). With an assumed connection, R should be estimable if the SSB is known. ...
... This may serve as a caution to using this calculator with species whose SSB/R relationships are environmentally driven: forecasts and subsequent management advice will be very dependent on the climate projections used. Hilborn and Walters (1992) and Chen and Irvine (2001) forewarn the use of environmental covariates in SSB/R relationships in general for this very reason-stating that these relationships have inherently low predictive capacity. However, this problem does not seem to be directly applicable to the dynamic BRP calculator, because its product is not, by definition, a forecast. ...
Article
Climate change is impacting many marine species distributions, life histories, and behaviors, as well as their associated fisheries and overall production. This is perhaps especially true for the Gulf of Maine (GOM). Here, warming rates are exceeding a vast majority of the world’s oceans. This highly dynamic system supports myriad species, but is both economically recognized and culturally known for its Atlantic sea scallop (Placopecten magellanicus) and American lobster (Homarus americanus) fisheries. This dissertation examines the influence of regional climate change on these species in an effort to predict how these stocks and their fisheries may change in the future. For scallops, this was accomplished by examining and aging shells collected throughout the GOM to determine if spatial and temporal differences in growth patterns could be explained by regional thermal habitats and salinities. For lobster, a five-step process was developed. Firstly, I conducted a simulation study to evaluate the stock assessment model performance under possible changes in lobster molting probability, lobster molt increment size, and size-at-maturity as a result of changes in thermal habitat. Secondly, using two temperature covariates important for early survival and development, a stock-wide, thermally-explicit Beverton-Holt stock-recruit relationship was estimated for the GOM. This relationship served as the basis of a framework to be used by management to test what levels of spawning biomass are necessary in the current year to achieve the desired levels of recruitment in the near future. Thirdly, a delta-generalized linear mixed model was used to predict lobster spatial density throughout the GOM. This spatial density informed a stock-wide abundance index which was used to replace the traditionally used design-based indices in the stock assessment model. Fourthly, a stock forecasting model was developed that could utilize the aforementioned stock-recruit relationship and consequences of ignoring this thermal influence on recruitment estimations were explored. Lastly, a bioclimate envelope model was used to determine relationships of multiple habitat covariates to lobster abundance from trawl survey data before using these relationships to map and forecast lobster habitat in the GOM.
... An active management framework could be used in the geoduck fishery, it is defined as the use of alternative models that are consistent with historical experience to identify a policy that offers a balance between probing for information versus caution about losses in short-term yield and long-term overfishing [38]. This process includes six main features, which are defined in Fig. 1. ...
... The Mexican Constitution establishes that the lands and waters included within the limits of the national territory correspond originally Table 1 Length-based indicators (LBIs) and reference points (RPs) taken from [72] and [27] for application in the fishing management of geoduck clam. [38]. ...
... The plan also should include how to manage the fishery when inadvertent situations arise, such as resource depletion or damage to stock due to environmental disturbance. These aspects demand a clear definition of the harvest strategy and biological RPs that determine how the catch will be extracted from the stock, how it will be adjusted from year to year depending upon the size of the stock, and what are the precautionary and warning levels for the fishery [38]. However, the fishery management plans for geoduck in Mexico are limited to a literature review, highlighting general information on the biology of the genus Panopea, historical aspects of the fishery, and the regulations applied to P. generosa on the coasts of the USA and Canada. ...
Article
Fishing management continues to be a challenge for the Mexican geoduck fishery, and it has shown several deficiencies to maintain the sustainability of populations. During the last two decades, the stock status and reference points have not been clearly defined; therefore, the legal framework to regulate the fishery has not been updated according to the stock status, the management objectives are contradictory and with clear overregulation in the fishery policy instruments, where the information contained is repetitive and inadequate for the biological characteristics of Mexican geoduck populations. Although there is a lot of scientific information on geoducks in Mexico, the lack of governance in the current top-down management has limited active cooperation among local and scientific groups, non-governmental organizations, and government agencies, which is essential for appropriate formulation of regulatory policy. In this way, changes in the fishing management of geoducks need to be implemented, which must include fishery data and updated knowledge to provide the best scientific advice, public participation, and regulatory policies that can be continuously evaluated to determine whether positive results are achieved through management objectives.
... There were a total of 116 814 size-at-age observations available after removing obvious errors, but these were subsampled because disproportionate sampling with size-selective gillnet meshes resulted in a non-representative sample (Hillborn and Walters 1992). Specifically, smaller mesh gillnets were used relatively rarely and thus too few observations of small individuals were available, resulting in unrealistic growth curves in preliminary modeling for many cohorts. ...
... This has not been done in the current study, and it may be best to borrow a term from the mark-recapture literature and refer to this as modeling 'apparent' growth (sensu 'apparent survival'; Schaub and Royle 2014). It is thus likely that the apparent growth model described here underestimates actual growth for many of the cohorts in this study, which is the case in most studies using size-at-age data to model growth (Hillborn and Walters 1992). Integrating growth and population models can help to account for size-selective harvest and other factors on sizeat-age data (Catalano andAllen 2010, van Poorten et al. 2018), while also enabling recruitment, survival and other processes to vary with environmental changes (Maunder and Punt 2013). ...
Article
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A combination of global changes such as species invasions, climate change and nutrient pollution have altered ecosystems, food webs and the bioenergetic processes that control growth. These changes are especially pronounced in freshwater ecosystems and often lead to rapid variation in fish growth and dependent ecosystems services such as fishery yield. Understanding the mechanisms driving growth responses to environmental change is important for interpreting past dynamics and sustainably managing ecosystems. This study uses integrated bioenergetics and growth modeling to understand how nutrient dynamics, species invasions and changing temperatures have altered growth of the keystone pelagic whitefish Coregonus wartmanni in Lake Constance, Germany from 1925 to 2020. Growth variation was modeled by allowing covariates to alter temperature-dependent consumption, while size-specific metabolism varied only with temperature. Consumption and growth increased strongly to a maximum with phosphorous, and this effect was stronger when intraspecific competition (measured as whitefish biomass) was low. Increasing whitefish biomass reduced growth under mesotrophic conditions, but had no effect under oligotrophic conditions. In contrast, increasing competition with invasive three-spined stickleback Gasteosteus aculeauts was predicted to reduce growth even under oligotrophic conditions. The invasion has effectively turned summer into winter for whitefish, with older fish ceasing to grow and younger fish losing up to 10% of their body weight during the normal growing season in subsequent years. Warming is predicted to further reduce whitefish growth due to competition with invasive stickleback, which would further alter zooplankton food availability and reduce already low fishery yields. These results demonstrate the importance of considering biotic interactions and synergistic effects in global change studies, as well as the value of mechanistic based models for understanding effects. Similar growth responses to ecosystem change are likely within and across ecosystems, and bioenergetic models can help understand effects to support informed ecosystem management.
... A fundamental question of harvested population models is related to characterizing the harvest rate that is both sustainable and economically viable. This is directly linked to the wellestablished maximum sustainable yield (MSY) calculations, that are, despite its limitations (Larkin, 1977;Caddy and Mahon, 1995), commonly used as sustainable benchmarks for harvested species in stock assessment reports, (see for example Winker et al., 2018;Haddon, 2001;Hilborn and Walters, 1992;Streipert et al., 2019;Government et al., 2019;PEW, 2019). Especially in the cases of limited available data, simple surplus models such as the Beverton-Holt model are critical for stock assessments (Dichmont et al., 2016;Punt et al., 2015), and metaanalysis of global fisheries (Winker et al., 2018;Froese et al., 2017;Rosenberg et al., 2018;Worm et al., 2009). ...
... Thus, simple population models are implemented specifically for species with limited data availability (Winker et al., 2018;Dichmont et al., 2016;Punt et al., 2015;Froese et al., 2017;Rosenberg et al., 2018;Worm et al., 2009). As mentioned in the Introduction, the maximum sustainable yield quantities are still used to determine sustainable harvest levels in fisheries, (see Haddon, 2001;Hilborn and Walters, 1992). NOAA's stock synthesis tool derives these quantities to discuss sustainable harvest levels for fish populations (Methot et al., 2013) and it is a fundamental piece for Australian's stock assessments (Government et al., 2019;PEW, 2019). ...
Article
We introduce the term net-proliferation rate for a class of harvested single species models, where harvest is assumed to reduce the survival probability of individuals. Following the classical maximum sustainable yield calculations, we establish relations between the proliferation and net-proliferation that are economically and sustainably favored. The resulting square root identities are analytically derived for species following the Beverton–Holt recurrence considering three levels of complexity. To discuss the generalization of the results, we compare the square root result to the optimal survival rate of the Pella–Tomlinson model. Furthermore, to test the practical relevance of the square root identities, we fit a stochastic Pella–Tomlinson model to observed Barramundi fishery data from the Southern Gulf of Carpentaria, Australia. The results show that for the estimated model parameters, the equilibrium biomass levels resulting from the MSY harvest and the square root harvest are similar, supporting the claim that the square root harvest can serve as a rule-of-thumb. This application, with its inherited model uncertainty, sparks a risk sensitivity analysis regarding the probability of populations falling below an unsustainable threshold. Characterization of such sensitivity helps in the understanding of both dangers of overfishing and potential remedies.
... The index capture per unit of effort (CPUE) was one of the first indicators of abundance (biomass) of a resource used in stock assessment [40], under the assumption that CPUE is linearly correlated with stock biomass and may therefore be used as its indicator. The most common phenomena affecting the proportionality between CPUE and biomass, that may invalidate its use as an indicator of biomass is hyperstability [41], which is likely to occur when fishing in areas of high concentration of the species, for example spawning aggregations [42]. This situation may be combined with searching strategies targeting different concentrations of the species [43], causing CPUE to stay stable even when the resources decline. ...
... One last important issue related to the use of global indicators of abundance such as CPUE or LPUE is the assumption that catches are a random sample of the total range of distribution of the species, meaning no selection of specific fishing grounds or areas with high density [41]. ...
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Landings by the multi-gear coastal fleet operating off the Portuguese continental coast include about 300 species, from which only a few are the object of management plans. In this study, daily landings (kg trip ⁻¹ ) are used, along with an effort indicator, vessel length overall (LoA), to obtain landings per unit of effort (LPUE) as a proxy for the species relative abundance, for a total of 48 species. LPUE indices were used as a response variable in linear models where year (2012–2016), season, region (north and south) and NAO index were explanatory variables. Seasonal and regional effects were found to significantly affect species abundance for a total of 41 and 40 species respectively, while year trends were found to be significant for 19 species, and the NAO index for 3 species. LPUE density maps are presented for several selected species and a subsample of trips, where VMS records were available. It is proposed that geographic and seasonal changes in LPUE can be used to understand trends in abundance and obtain information that can be used in support regional management plans.
... *** http://www.primer-e.com/index.htm **** Zar (1999) ***** Hilborn & Walters (1992) relative abundance, biomass or species richness were observed among 10 fisher catch monitoring locations that have been monitored between 2003 and 2010. However, relative fish biomass at many monitoring locations in the basin and reproductive success appears to have been relatively low since 2005-06 compared to earlier years. ...
... Exceptionally high rates of recruitment may have over-shadowed the effects of these management efforts to the extent that they were undetectable. Experimentation may be necessary to confirm the effects of gear confiscations, perhaps in the context of more adaptive management approaches (Hilborn and Walters, 1992). However, it is noted that the confiscation of more than 1,000 km of fine mesh fence in 2008 had no discernible benefits for recruitment or dai catch rates. ...
... Fisheries biology documents interactions among fish populations, the environment, and fishing communities to manage seafood resources. Traditionally, fishery-dependent data provided time series of effort and catch that informed the stock status of exploited species (Hilborn and Walters 1992). More recently, fishery vessel tracking systems collect highresolution spatial and temporal patterns of effort and catch that support geographic analyses (Gerritsen and Lordan 2011). ...
... These systems provide information for examining fishery interactions with target stocks and their habitats, assessing fishing behavior and vessel interactions, and evaluating fishing activity relative to area closures. In addition, fishery-independent surveys provide unbiased data on metapopulation-scale abundance or biomass indices and lifehistory information for target species (Hilborn and Walters 1992). Of the five disciplines involved in Fish Flow, fisheries biology is the most integrative, with many fisheries scientists now making use of oceanographic models, population genetics, ecology, and social sciences (Essington et al. 2017). ...
Article
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Novel methodologies now make it possible to track the complete geographical movements of seafood species from reproduction to human consumption. Doing so will better inform consumers and assist resource managers in matching fisheries and conservation policies with natural borders and pathways, including stock boundaries, networks of marine protected areas, and fisheries management areas. Such mapping necessitates an unprecedented synthesis of natural and social sciences, including knowledge of adult fish population abundance and movements, egg output, larval dispersal, and recruitment to juvenile and adult habitats, as well as fisheries stock assessment, capture, and distribution through human social networks. The challenge is to fully integrate oceanography, population genetics, ecology, and social sciences with fisheries biology to reveal the patterns and mechanisms of “Fish Flow” from spawning to supper. As practitioners representing all five of these disciplines, we believe that Fish Flow analyses will promote sustainable fisheries management and marine conservation efforts, and may foster public knowledge, wise seafood choices, and appreciation of social–ecological interconnections involving fisheries.
... Many world fishery resources lack the necessary information to carry out robust stock assessments in a timely manner before being exploited by humans. Fish stock assessments consider several sources of biological information, such as average individual growth, maturation, natural mortality rates, changes in length or age composition, and stock abundance estimates (Hilborn and Walters 1992;Quinn and Deriso 1999;Cooper 2006). Thus, the importance of research, such as the study presented here, that generates information dependent and independent of the fisheries, allows management decisions in situations of limited information of the target species of the fishery (Ricard et al. 2011). ...
Article
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Knowledge of biomass and demographic aspects is important in fish stock assessments. These aspects were analyzed on Micropogonias megalops in the Gulf of Cali-fornia, Mexico, using biological data from catches in 2010-12. Individual growth was estimated following a multi-model approach. Logistic models were used for first maturity and fishing selectivity, and natural mortality by means of empirical equations and biomass by the Pennington estimation. The results showed that the von Bertalanffy model best described growth for combined data (w i = 72.86 %), females (w i = 67.82 %) and males (w i = 69.42 %), but they showed sexual dimorphism on the species. First maturity was at 357.8 mm, fishing selectivity 323.35 and 366.35 mm for industrial and arti-sanal fleet, respectively, and average natural mortality of 0.51. Mean biomass was 14 412.9 tons contrasting the officially reported catch that represented only 8.7% of estimated biomass, showing evidence that M. megalops is still an underexploited resource.
... Ecosystem benefits include ecosystem health, a balanced biodiversity and stable biomass levels of the functional group in the system, whereas social and economic benefits include the employment through fishing and related processes, as well as fishing itself as a source of income (FAO 2020). The routine is a powerful tool to find a successful fishing policy, that should at best entail benefits for sustainability, society, equity of costs and benefits, and decrease of conflicts e.g., from competition between artisanal and semi-industrial fleets (FAO 2020;Hilborn and Walters, 2013). ...
Article
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The Gulf of Nicoya is a highly productive estuary located at the Pacific coast of Costa Rica. Previous studies have used trophic models to examine changes in the biomass of key species and in the food web in the last 25 years, revealing an overfished, degraded system with decreasing biomass of valuable target species. The ecosystem degradation was mainly driven by intensive fishing, while climate variations affected resource productivity additionally. This study tested the effectiveness of alternative scenarios including combinations of the current top-down fishing policy and the ban on shrimp trawling, together with a participatory management scenario developed in a previously performed stakeholder workshop. In parallel, the automated fishing policy search of the Ecopath with Ecosim (EwE) software was used to explore an optimized alternative management scenario. The analysis indicates that the ban on trawling is an important measure to allow for the recovery of certain target species, such as shrimps, demersal fish and their predators. However, this ban would not suffice to substantially rebuild the biomass of all key species in the system. Thus, two possible alternative management scenarios are proposed: in the first one, the economic losses are minimized, ecosystem health increases by 10% (by rebuilding target species biomass) and employment provided by fishing decreases (−15%). In the second scenario, higher economic losses are accepted (mainly for the semi-industrial fisheries sector) which allows for a higher increase in ecosystem health and biodiversity. Both scenarios call for additional reductions in fishing efforts, mainly by the semi-industrial purse-seine fleet and the artisanal longline fleet. This study exemplifies how holistic ecosystem models can be used for management advice, future policymaking and how stakeholders can be engaged in this process.
... Factors influencing recruitment are some of the most important biological questions for fisheries management and some of the most difficult to quantify because species-specific recruitment is often influenced by a complex of abiotic and biotic factors, spawning behaviors, and life histories (Hilborn and Walters 1992). Common abiotic factors that have been shown to influence recruitment include water temperature (and associated variability) (Hansen et al. 1998;Beard et al. 2003) and available spawning habitat . ...
Article
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Walleye Sander vitreus natural recruitment has declined in northern Wisconsin lakes over time. Several factors have been implicated to explain Walleye natural recruitment declines in Wisconsin including climate change, Largemouth Bass Micropterus salmoides interactions, less desirable fish communities, production overharvest, and depensatory effects on recruit survival. Previous research in other systems has suggested that White Crappie Pomoxis annularis negatively influence Walleye recruitment, but interactions between Walleye recruitment and Black Crappie P. nigromaculatus have not been examined. We evaluated trends between Black Crappie and age-0 Walleye relative abundance (CPE) collected in northern Wisconsin during 1991- 2017. Specifically, we tested for: 1) trends in age-0 Walleye and Black Crappie CPE over time; 2) a relationship between age-0 Walleye and Black Crappie CPE; and 3) the influence of several abiotic and biotic covariates (including Black Crappie CPE) on age-0 Walleye recruitment. Age-0 Walleye CPE declined, and Black Crappie CPE increased significantly during 1991-2017. Within lakes, the relationship between age-0 Walleye and Black Crappie CPE showed a threshold effect such that age-0 Walleye CPE was always low when Black Crappie CPE was high. Of the abiotic and biotic covariates tested to explain variability in the age-0 Walleye and Black Crappie CPE relationship, only Black Crappie CPE was significant. Our results suggest that Black Crappie may negatively influence Walleye natural recruitment; however, we caution that our findings only reveal pattern and not a mechanistic explanation for negative interactions between the species. Additional research is needed to test for mechanistic interactions between Walleye and Black Crappie and to inform co-management of these species.
... Concerning species diversity, all areas differed widely in terms of Shannon's Index. Spatial differences could reflect large-scale regional differences in the structure of the fish assemblages exploited by SSF, provided that the CPUE is proportional to the biomass of the resource [i.e., no occurrence of hyperdepletion-CPUE declining faster than biomass-or hyperstability-CPUE being insensitive to declines in biomass (Hilborn & Walters, 1992)], so that it can be used as a proxy for fish species abundance (but see Harley et al., 2001). Spatial variability can also respond to local environmental features, probably shaping the overall fish assemblages linked for instance to habitat and substrate geomorphological characteristics (García-Charton et al., 2004), seasonal variation or area-specific fishing behaviours. ...
Article
Achieving sound management of small‐scale fisheries (SSFs) is globally recognized a key priority for sustaining livelihoods, local economies, social wealth and cultural heritage in coastal areas. The paucity of information on SSFs often prevents the proper assessment of different socio‐ecological aspects, potentially leading to draw inappropriate conclusions and hampering the development and adoption of effective policies to foster SSF sustainability. To respond to the growing global call to assess these fisheries, we carried out a multi‐disciplinary and data‐rich assessment of SSFs at 11 areas in 6 Mediterranean EU countries, combining the analysis of 1292 SSF fishing operations and 149 semi‐structured surveys of fishers. Specifically, we aimed at assessing (1) landed species contribution to SSF catches and revenues and (2) the spatial variability in a set of fishery socio‐ecological descriptors. Results highlighted that, in spite of a high species diversity, Mediterranean SSFs actually rely economically upon a very limited number of species with catch and revenues per unit of effort mostly determined by less than 5 species, that can guarantee high and stable catches and revenues over time. Moreover, some fishing communities were found to rely on a restricted number of gears. These evidences suggest, that some SSFs' properties often assumed, but never broadly verified, should be carefully reconsidered, especially when viewed from a broader socio‐ecological perspective, as in the case of the diversified portfolio or of the polyvalence of fishing gears. Taking the local scale into proper account is likely to reduce the risk of implementing management strategies potentially generating socio‐ecological inequalities.
... In fisheries stock assessment, plastic body growth was generally thought to be less important for stock dynamics than environmentally driven recruitment variation, density dependence at early life stages and mortality (Hilborn & Walters 1992;Lorenzen 2016). Due to the accumulating evidence of time-varying and climate-driven changes in vital rates (surviva l, growth and reproduction), their relative importance for fisheries reference points and targets are now becoming acknowledged (Thorson et al. 2015;Lorenzen 2016). ...
Article
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Resolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size‐structure, and potential yields of marine fishes. Previous studies based on mechanistic size‐based food web models have found that bottom‐up processes are important drivers of size‐structure and fisheries yield in changing climates. However, we know less about the joint effects of ‘bottom‐up’ and physiological effects of temperature; how do temperature effects propagate from individual‐level physiology through food webs and alter the size‐structure of exploited species in a community? Here we assess how a species‐resolved size‐based food web is affected by warming through both these pathways, and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size‐structure, relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4‐NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature‐effects on physiology in addition to on basal productivity, projected size‐at‐age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size‐at‐age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in declines in the abundance of larger fish and hence spawning stock biomass. These results suggest that to understand how global warming affects the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for.
... However, given that the commercial fishery is primarily located on the west coast of Newfoundland, little information is available for the other stock Divisions, i.e., 4S and 4T (DFO 2015). It is also well known that fishery-dependent indices can often be disproportional to abundance, remaining high even when abundance is in decline (Hilborn and Walters 1992). ...
Article
In order to obtain a fishery-independent index covering a significant portion of the Gulf of St. Lawrence (GSL, NAFO Divisions 4RST) capelin (Mallotus spp.) stock area, the stomach contents of Atlantic cod (Gadus morhua) and Greenland halibut (Reinhardtius hippoglossoides) collected during the summer nGSL multispecies survey were examined. Using a bioenergetics approach, it was estimated that annual capelin consumption by the two predators continued to be higher than the commercial landings recorded for the GSL. These results support those obtained from previously published ecosystem models. All length classes combined, the percentage of capelin in the mean stomach contents of Atlantic cod shows greater interannual variation compared to the stomach contents of Greenland halibut. The use of capelin by Greenland halibut more closely reflected changes in the average number of capelin caught per tow in the nGSL multispecies surveys in years for which fish stomachs were available. However, several sources of uncertainty were raised regarding the stomach content data used and some of the assumptions in the methodology, and the need to collect samples at other times of the year was pointed out. Since capelin is one of the major forage species in the GSL, considering the population patterns of its predators and assessing their consumption of capelin would be additional aspects of interest to include in the assessment of this species.
... southern part of the study area) and a higher uncertainty where data are scarce. Use of fisheries dependent data could be criticised due to biases associated with the targeted nature of the dataset (Hilborn and Walters, 2015). Comparative studies have, however, shown that results from fisherydependent and fishery-independent data on species distribution and abundance analyses are consistent and complementary despite spatial and temporal differences in sampling (Pennino et al., 2016;Bourdaud et al., 2017;Elliott et al., 2020b). ...
Article
Little is still known about the biology and ecology of many elasmobranchs which often inhibits species specific management measures from being implemented. The primary aim of this study was to improve the knowledge on the distribution and habitat use of the threatened and data deficient shagreen ray, Leucoraja fullonica, using fisheries dependent data. To model its distribution, we used Bayesian hierarchical modelling, taking into consideration imperfect capture from the non-random nature of fishing gear type and spatial autocorrelation. Our second objective was to identify the potential functional role of the high occurrence area by analysing spatial length segregation using a generalised additive mixed model. From five environmental variables, depth, distance to coast, and seabed sediment type were used to model its habitat. L. fullonica was found to mainly inhabit an area of high concentration between the southern Celtic Seas and the northern Bay of Biscay. Within this area, smaller individuals were found in the deeper south-western part and larger individuals in shallower waters, closer to the coast, suggesting ontogenetic shift or spawning migration. L. fullonica were mainly caught by bottom trawl fishing gears. The isolated habitat occupancy of this species may increase its vulnerability, particularly since high fishing pressure has been observed in this area. These results highlight the importance of fisheries-dependent data for data-poor species and provide valuable new information on its ecology when considering management or conservation measures at a species level.
... Estas características de la comunidad no son estáticas, presentan una dinámica que cambia temporal y espacialmente. El conocimiento de la disponibilidad, diversidad y abundancia espacio-temporal de los recursos es de suma importancia para conocer el estado actual y potencial de las poblaciones en una determinada región, así como para diseñar planes de manejo y aprovechamiento sostenible del recurso (Hilborn y Walters, 2001;Achury et al., 2007). ...
Article
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The delta of Orinoco River constitutes a long estuarine extension of a great importance to fisheries at Venezuela, because, it is an indispensable area for reproduction, feeding and growing of several fish species, most of them with a commercial application. The purpose of this research was to identify and analyze the changes in fish diversity and the structural dynamic of the community at four zones of channel Manamo, during dry and rainy season. Samples were taken on March and May for dry period and July and August for rainy season. A total of 48 species were identified, grouped into 24 families and 42 genera. The diversity was higher in Bajo del Medio during the dry season (2.58 bits/ind), decreasing to 1.66 bits/ind in el Pajar (rains). The PERMANOVAS analyzes showed statistical differences in the composition of species with respect to the climate season (psed-F = 0.0365, p <0.05), but not between the sampling stations (psed-F 0.6668; p < 0.05). The results indicated that the fish fauna of the region is composed of elements characteristic of an estuary, being the climate seasons the most important factors for the evaluated group and this reflects the seasonal nature of this community.
... Although hyperstable catch rates have been known to exist in temperate marine commercial fisheries for decades (Creco and Overholtz, 1990;Hilborn and Walters, 1992;Harley et al., 2001), documentation of these patterns and the mechanisms underpinning hyperstability of catch rates in recreational fisheries has only emerged over the last twenty years (Hansen et al., 2005;Erisman et al., 2011;Ward et. al, 2013;Maggs et al., 2016;Mrnak et al., 2018;Dassow et al., 2020;Feiner et al., 2020). ...
Article
In commercial and recreational fisheries, catch rate is often assumed to be proportional to stock size and is used by managers and fishers as an indicator of fishery sustainability. If catch rate is proportional to stock size, it can signal a decline of stocks and managers can impose restrictive harvest policies or recreational anglers can move to a new system and allow the over-exploited system to rebound. A growing literature has documented catch rates remaining high even as fish stocks decline (i.e., hyperstability of catch rates) leading to delayed management intervention and overexploitation. Although recent evidence has indicated the presence of hyperstability of catch rates in recreational fisheries, whether hyperstability differs across species or system types remains unknown. To investigate whether catch rate hyperstability varies amongst species or systems, we first tested whether electrofishing catch per unit effort (efCPUE) was an appropriate proxy for true abundance. We then compared the relationship between angler catch rate and fish abundance for common freshwater sport fishes across gradients of habitat availability. We found significant differences in the strength of hyperstability amongst species. We did not identify a consistent influence of habitat on hyperstability of catch rates. Angler preferences and behavior may explain some of the variance in non-proportional catch rates. Future research investigating angler behavior, population size structure, and population dynamics in these systems may identify key interactions that create differences in vulnerability to population collapse.
... As described above, total effort increased and technology and gear deployment strategy changed. Linking the impacts of such changes quantitatively to fishing mortality rates is difficult (Hilborn & Walters 1992;Marchal et al. 2007) and is not possible for the 1800s Limfjord herring fishery: for example, details of fishing practices by the entire or even a large proportion of the fisher community are not documented nor were there independent research fisheries being conducted at the time using standardized fishing methods which could be used for population monitoring. However, given the increase in landings in the late 1810s-early 1820s, it is likely that fishing mortalities did increase, and were increasing the risk that the population would decline or even collapse. ...
Conference Paper
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Sustainable fish populations require both healthy ecosystems in which they can live and grow, and protection from overfishing. A rare historical example from the first half of the 19 th century allowed us to describe the chronology of how the vulnerability of a herring (Clupea harengus) population to ecosystem variability was increased by effects of fishing on the population and food web interactions within the ecosystem. Both the population and fishery collapsed when several years of increasing exploitation were followed by an extreme climatic-hydrographic perturbation in 1825 that affected herring survival and changed food web structure (jellyfish bloom). Estimated levels of fishing mortality in years leading up to the collapse of Limfjord herring were 3-5 fold higher than natural mortality rates and similar to those which later led to collapses of 3 major herring populations in the north Atlantic (North Sea Norwegian spring-spawning herring, Georges Bank). These high exploitation rates suggest that fishing was a key factor which increased the vulnerability of the Limfjord herring to collapse. Changes in trophic interactions in the Limfjord after 1825 were therefore facilitated by fishing, which had reduced the abundance of jellyfish food competitors (herring) to low levels, and consequently expanded a niche in the ecosystem for other zooplanktivores with oppportunistic lifehistories. Lowering the risks of future collapses of fish populations and of trophic re-organisations to less desirable configurations, including gelatinous dominance of foodwebs, requires low exploitation rates that buffer against environmental variability and measures to support well-functioning and structured ecosystems.
... Nonetheless, the living environments of organisms are complex systems, which contain multiple environmental factors, and thus many problems in the field of S-R relationship research of fishery resources remain unresolved. Studying the relationship between recruitment and environmental factors has become one of the most important and difficult tasks in current resource assessment (Hilborn and Walters, 1992). ...
Article
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Based on the data of Portunus trituberculatus and environmental factors in the northern East China Sea from 2001 to 2014, a Ricker-type model was used in investigating the effects of environmental factors on P. trituberculatus recruitment. The main environmental factors include the area of red tide, sea level height, sea surface salinity, and typhoon landing times with wind forces above 6 near the center. We assumed that the distributions of environmental data vary and selected AIC, BIC, and maximum likelihood as criteria for the selection of the best distribution of each environmental factor. Environmental factor data were simulated according to the distributions (repeated 10,000 times). The Ricker model with ln-linear environmental impact was used in predicting the recruitment of P. trituberculatus under different combinations of various environmental factors for a given spawning stock biomass. Results show that the predicted recruitment abundance most likely appears between 10 × 10 ³ and 15 × 10 ³ million individuals, and the probability is approximately 39.56%. The environmental condition in which the four environmental factors have the best and worst combinations was also simulated. Our results indicate that red tide and typhoon are the two dominant factors affecting the recruitment of P. trituberculatus . The results show that at the 5% significance level, if the recruitment is less than 6.394 × 10 ³ million individuals, then it is probably under a bad environment condition. Similarly, if recruitment is more than 28.305 × 10 ³ million individuals, then it is probably under a good environmental condition. This study provides a technical reference for the scientific prediction and management of P. trituberculatus and other fishery resources subjected to various environmental conditions.
... Although hyperstable catch rates have been known to exist in temperate marine commercial fisheries for decades (Creco and Overholtz, 1990;Hilborn and Walters, 1992;Harley et al., 2001), documentation of these patterns and the mechanisms underpinning hyperstability of catch rates in recreational fisheries has only emerged over the last twenty years (Hansen et al., 2005;Erisman et al., 2011;Ward et. al, 2013;Maggs et al., 2016;Mrnak et al., 2018;Dassow et al., 2020;Feiner et al., 2020). ...
Article
In commercial and recreational fisheries, catch rate is often assumed to be proportional to stock size and is used by managers and fishers as an indicator of fishery sustainability. If catch rate is proportional to stock size, it can signal a decline of stocks and managers can impose restrictive harvest policies or recreational anglers can move to a new system and allow the over-exploited system to rebound. A growing literature has documented catch rates remaining high even as fish stocks decline (i.e., hyperstability of catch rates) leading to delayed management intervention and overexploitation. Although recent evidence has indicated the presence of hyperstability of catch rates in recreational fisheries, whether hyperstability differs across species or system types remains unknown. To investigate whether catch rate hyperstability varies amongst species or systems, we first tested whether electrofishing catch per unit effort (efCPUE) was an appropriate proxy for true abundance. We then compared the relationship between angler catch rate and fish abundance for common freshwater sport fishes across gradients of habitat availability. We found significant differences in the strength of hyperstability amongst species. We did not identify a consistent influence of habitat on hyperstability of catch rates. Angler preferences and behavior may explain some of the variance in non-proportional catch rates. Future research investigating angler behavior, population size structure, and population dynamics in these systems may identify key interactions that create differences in vulnerability to population collapse.
... Effective fishery management benefits from rigorous and systematic fisheries independent surveys to provide fish abundance estimates (Hilborn and Walters, 1992). Fisheries independent surveys can take many forms, including hook and line, trawl, video, and acoustic sampling techniques. ...
Article
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Combining hydroacoustics and underwater video is an effective tool for generating fish population estimates. However, hydroacoustics cannot be used to differentiate fish from the seafloor within an area known as the acoustic dead zone. A common way to address this is to exclude data near the bottom. The effect of this exclusion zone on population estimates of nearshore semi-pelagic rockfish is unknown. This study explores the effect of a near bottom (0–1 m) exclusion zone by comparing ROV video data to data from a combined hydroacoustic and video method. Higher densities of semi-pelagic species (Black and Blue/Deacon Rockfish) were observed in the combined acoustic and video method, suggesting that most of the population resides above the exclusion zone. Demersal rockfish observed by the ROV did not contaminate acoustic data of semi-pelagic species, since they remained within the exclusion zone. Results demonstrate that extrapolation of school data into the exclusion zone provided a realistic correction to the acoustic data for Black Rockfish. Our work demonstrates that excluding the data within 1 m of the bottom does not negatively affect the ability of the combined video hydroacoustic method to sample semi-pelagic rockfish.
... Many stock assessment applications (Brodziak et al., 2011) and standard texts on the subject (e.g. Hilborn and Walters, 1992;Quinn and Deriso, 1999;Haddon, 2011) treat M in the recruited stock as constant. However, evidence for sizeand age-dependent M in juvenile and adult fishes has become all but insurmountable (Vetter, 1988;McGurk, 1986;Lorenzen et al., 2022). ...
Article
Natural mortality rates (M) in fish populations vary with body size and age, often by orders of magnitude over the life cycle. Traditionally, fisheries models and stock assessment methods have treated M as constant in the recruited stock, but that axiom has been challenged on empirical and theoretical grounds, and by practical assessment needs. Reviewing biological considerations, empirical generalizations, and theoretical models of size- and age-dependent natural mortality in fish populations, I show how multiple strands of evidence lead to a coherent new M paradigm best described as ‘generalized length-inverse mortality’ (GLIM). GLIM holds that mortality declines inversely with body length throughout much of the juvenile and adult phases of the fish lifecycle. Deviations from the length-inverse pattern may occur in older ages due to senescence and in early juveniles due to density-dependence. GLIM is strongly supported by empirical meta-analyses of mortality-size relationships and is also broadly consistent with multi-species and ecosystem models of predation mortality. Whether operationalized in closed functional form or through multi-species modeling of predation and residual mortality, GLIM provides a new ‘standard M′ for fish population modeling and stock assessment applications. Consequences of mis-specifying size- and age-dependent M in stock assessment applications vary from moderate in many cases to severe under certain conditions, but even moderate consequences can be quantitatively significant in stock assessment and management. Further research is indicated with regards to senescence and to the representation of residual or non-predation mortality (M1) in multi-species and ecosystem models.
... Due to the multi-gear, multi-species, and data-poor nature of smallscale fisheries in developing countries, particularly in tropics, applying conventional, data-intensive, and single-species model-based stock assessment methods is difficult (Costello et al., 2012;Dowling et al., 2015). Therefore, making management recommendations based on scientific studies for effective management policies is challenging (Hilborn & Walters, 1992;Dowling et al., 2008Dowling et al., , 2018. Given these situations, several approaches have been developed to evaluate the status of data-poor fish stocks (Cope & Punt, 2009;Froese et al., 2016;Honey et al., 2010;Martell & Froese, 2013;Prager, 1992;Reuter et al., 2010;Rosenberg et al., 2014;Winker et al., 2018), and these assessment methods are increasingly being used for management purposes. ...
Article
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Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh. But, due to a monotonic decline in catches over the last five years, it is essential to explore the current stock status concerning the removal rate to ensure the sustainability of this fishery. Therefore, given the reliability and minimal data requirements, this study employed an extended Bayesian State-Space Surplus Production Model, JABBA (Just Another Bayesian Biomass Assessment), to assess the stock rigorously. The results revealed that the stock biomass of the Pomfret fishery in the final year of the time series is significantly lower than B MSY , the biomass required to produce MSY. Consequently, this study recommends a yearly catch limit (TAC) of 10,000 metric tons to prevent further depletion of the stock biomass. Furthermore, to avoid growth overfishing by allowing all immature fishes to reproduce at least once before being caught, this study also calculated the optimum length (L opt) for catch for both species at which biologically maximum yield and revenue can be obtained. The estimated L opt is 25 cm for P. argenteus and 30 cm for P. chinensis, and not to capture fishes with lengths lower than these limits, this study further calculated the minimum mesh size limits for gill and set bag nets is 7.5 cm. Though the mesh size regulation was estimated using length-based reference points derived from an empirical equation, this regulation can be used as an associate reference point when TAC is applied to assure the sustainability of this fishery.
... Due to the multi-gear, multi-species, and data-poor nature of smallscale fisheries in developing countries, particularly in tropics, applying conventional, data-intensive, and single-species model-based stock assessment methods is difficult (Costello et al., 2012;Dowling et al., 2015). Therefore, making management recommendations based on scientific studies for effective management policies is challenging (Hilborn & Walters, 1992;Dowling et al., 2008Dowling et al., , 2018. Given these situations, several approaches have been developed to evaluate the status of data-poor fish stocks (Cope & Punt, 2009;Froese et al., 2016;Honey et al., 2010;Martell & Froese, 2013;Prager, 1992;Reuter et al., 2010;Rosenberg et al., 2014;Winker et al., 2018), and these assessment methods are increasingly being used for management purposes. ...
Article
Full-text available
Abstract Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh. But, due to a monotonic decline in catches over the last five years, it is essential to explore the current stock status concerning the removal rate to ensure the sustainability of this fishery. Therefore, given the reliability and minimal data requirements, this study employed an extended Bayesian State-Space Surplus Production Model, JABBA (Just Another Bayesian Biomass Assessment), to assess the stock rigorously. The results revealed that the stock biomass of the Pomfret fishery in the final year of the time series is significantly lower than BMSY, the biomass required to produce MSY. Consequently, this study recommends a yearly catch limit (TAC) of 10,000 metric tons to prevent further depletion of the stock biomass. Furthermore, to avoid growth overfishing by allowing all immature fishes to reproduce at least once before being caught, this study also calculated the optimum length (Lopt) for catch for both species at which biologically maximum yield and revenue can be obtained. The estimated Lopt is 25 cm for P. argenteus and 30 cm for P. chinensis, and not to capture fishes with lengths lower than these limits, this study further calculated the minimum mesh size limits for gill and set bag nets is 7.5 cm. Though the mesh size regulation was estimated using length-based reference points derived from an empirical equation, this regulation can be used as an associate reference point when TAC is applied to assure the sustainability of this fishery.
... The depletion method involves monitoring how catch-per-unit-effort (CPUE) -an index of fish abundance -declines in response to removals (catches) of fish to estimate the original population size. The population size corresponds to the predicted removals when the catch rate falls to zero (see Hilborn & Walters, 1992). It requires no sophisticated technology or expertise, but requires monitoring intensive fishing over a period of time when there is no significant immigration or emigration of fish to or from the pool (closed population). ...
... Age composition is a critical source of information for understanding fish population dynamics (Hilborn & Walters, 1992). Scale-based age estimation, preferred because of its simplicity and harmlessness to fish, is unsuitable for American eels because their scales first appear when they are several years old (Smith & Saunders, 1955). ...
Article
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A robust assessment of the American eel (Anguilla rostrata) stock, required to guide conservation efforts, is challenged by the species' vast range, high variability in demographic parameters and data inadequacies. Novel ideas and underutilised resources that may assist both analytic assessments and spatially oriented modelling include (1) species and environmental databases; (2) mining of data from scattered sources; (3) infilling of data gaps by spatial analysis; (4) age estimation from measurements of DNA methylation; evaluation of eel abundance by (5) larval, (6) glass-bottom boat, (7) net enclosure and (8) eDNA surveys; (9) accounting for dam-induced habitat increases in eel watercourse modelling; (10) spatially oriented modelling with and without temporal components; (11) geographically nested modelling of glass eel recruitment; (12) spawner per recruit modelling and (13) life cycle modelling to examine larval allocation effects. Eel biologists are too few to gather the required assessment data across all of the species’ range. Public posting of electrofishing and eDNA metabarcoding data sets and the use of machine learning techniques to comprehensively inventory small dams will help meet some data needs. These approaches address only a small proportion of the assessment challenges that face American eels. Worldwide collaboration amongst Anguilla scientists is a key enabler of progress towards stock assessment goals.
... Numerous reviews and evaluations of AM have been published on this topic (e.g. Holling, 1978;Walters, 1986;Hilborn and Walters, 1992;Lee, 1993;Gunderson et al., 1995;Lancia et al., 1996;Walters, 1997;Parma et al., 1998;Johnson, 1999;Grafton and Kompas, 2004;Schreiber et al., 2004;Walters and Martell, 2004;Crawford et al., 2005;Williams et al., 2009). ...
... Similarly, on average one might expect the sustainability status of these stocks to be preferable compared to stocks targeted by fleets lacking certification (hereafter, 'non-MSC stocks'). In fisheries, criteria for identifying 'sustainable' status are well established (e.g., Hilborn and Walters, 1992;Mace, 1994;Restrepo et al., 1998;Worm et al., 2009;Rice, 2014). Estimated abundance over time (typically expressed as biomass, B, or the total weight of a segment of a population) is benchmarked against a biological reference point, B BRP ; their ratio B/B BRP is referred to as 'relative biomass'. ...
Article
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Requirements for a fishery to achieve Marine Stewardship Council (MSC) certification include demonstrating that targeted populations ('MSC stocks') are fished at sustainable levels. The credibility of this claim can be evaluated by comparing estimated abundance of MSC stocks to benchmarks based on sustainability criteria. Additionally, to evaluate whether MSC certification provides a meaningful distinction, the sustainability status of MSC stocks can be compared with that of populations without a linked certificate ('non-MSC stocks'). It is expected that MSC stocks are more likely to be maintained at levels of high abundance relative to sustainability benchmarks compared to non-MSC stocks. Similarly, it is expected that MSC stocks are less likely to become overfished, and if they do become overfished, that fisheries are incentivised to aid in their rebuilding to avoid suspension of certification. We compare published biomass estimates relative to biological reference points between MSC stocks and non-MSC stocks of wild-caught marine fish and invertebrate species around the world. These are observational data, and though we control for the propensity of certification, certification is not independent of relative biomass and therefore we describe associations rather than causal influences. Individual stocks from both groups were highly variable in relative biomass trends over the past two decades, with substantial overlap in the distributions of MSC and non-MSC stocks. In recent years (2014-2018), MSC stocks had, on average, greater biomass relative to biomass at maximum sustainable yield (B MSY) than non-MSC stocks. MSC stocks were also less frequently overfished compared to non-MSC stocks, with estimated biomass below a limit reference point (B lim) for 9% of MSC stocks and for 26-33% of non-MSC stocks. Eight MSC stocks currently or previously certified and defined as overfished in 2017 or 2018 had previously entered the program based on scientific advice available at the time indicating they were fished within sustainable limits. Subsequently, when revised stock assessments estimated the biomass to be lower than Frontiers in Marine Science previously thought, fisheries for those stocks were suspended from certification. Together, these results suggest that eco-certification is associated with a credible claim on sustainable stock status and provides a useful distinction from other seafood. Further, our results show how the rare exceptions to this pattern may arise from retrospective changes in scientific advice.
... Fish communities are subject to a variety of influences and stressors, and the resulting population and stock dynamics may have far reaching implications for both ecosystems and fisheries (Collingsworth et al., 2017). The ability of researchers and fishery managers to track and understand these changes is however limited by the difficulty in achieving reliable assessments of fish populations with a meaningful resolution in time and space (Hilborn & Walters, 1992). Monitoring fish populations using invasive capture methods is problematic, especially in large, deep waters due to high time, labour and material costs, and the mortality of fishes (Bean et al., 1996;Murphy & Willis, 1996;Emmrich et al., 2012;EN 14757, 2015). ...
... During the mid-1980s the export of most of the resources was initiated, producing increases in captures, and once the accumulated biomass was used up, the resources remained at low and fluctuating levels ( Figure 22). In general, these fluctuations have been interpreted as the classical signs of a badly regulated fishery, as described by Hilborn & Walters (1992): discovery of a stock, development of its fishery and subsequent overexploitation and eventually collapse. ...
Article
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The Humboldt Current System (HCS) is one of the most productive marine ecosystems on earth. It extends along the west coast of South America from southern Chile (~42 ° S) up to Ecuador and the Galapagos Islands near the equator. The general oceanography of the HCS is characterised by a predominant northward flow of surface waters of subantarctic origin and by strong upwelling of cool nutrient-rich subsurface waters of equatorial origin. Along the coast of northern and central Chile, upwelling is localised and its occurrence changes from being mostly continuous (aseasonal) in northern Chile to a more seasonal pattern in southern-central Chile. Several important upwelling centres along the Chilean coast are interspersed with long stretches of coast without or with sporadic and less intense upwelling. Large-scale climatic phenomena (El Niño Southern Oscillation, ENSO) are superimposed onto this regional pattern, which results in a high spatiotemporal heterogeneity, complicating the prediction of ecological processes along the Chilean coast. This limited predictability becomes particularly critical in light of increasing human activities during the past decades, at present mainly in the form of exploitation of renewable resources (fish, invertebrates and macroalgae). This review examines current knowledge of ecological processes in the HCS of northern and central Chile, with a particular focus on oceanographic factors and the influence of human activities, and further suggests conservation strategies for this high-priority large marine ecosystem. Along the Chilean coast, the injection of nutrients into surface waters through upwelling events results in extremely high primary production. This fuels zoo-plankton and fish production over extensive areas, which also supports higher trophic levels, including large populations of seabirds and marine mammals. Pelagic fisheries, typically concentrated near main upwelling centres (20-22 ° S, 32-34 ° S, 36-38 ° S), take an important share of the fish production, thereby affecting trophic interactions in the HCS. Interestingly, El Niño (EN) events in northern Chile do not appear to cause a dramatic decline in primary or zooplankton production but rather a shift in species composition, which affects trophic efficiency of and interactions among higher-level consumers. The low oxygen concentrations in subsurface waters of the HCS (oxygen-minimum zone, OMZ) influence predator-prey interactions in the plankton by preventing some species from migrating to deeper waters. The OMZ also has a strong effect on the bathymetric distribution of sublittoral soft-bottom communities along the Chilean coast. The few long-term studies available from sublittoral soft-bottom communities in northern and central Chile suggest that temporal dynamics in abundance and community composition are driven by interannual phenomena (EN and the extent and intensity of the OMZ) rather than by intra-annual (seasonal) patterns. Macrobenthic communities within the OMZ are often dominated in biomass by sulphide-oxidising, mat-forming bacteria. Though the contribution of these microbial communities to the total primary production of the system and their function in structuring OMZ communities is still scarcely known, they presumably play a key role, also in sustaining large populations of economically valuable crustaceans. Sublittoral hard bottoms in shallow waters are dominated by macroalgae and suspension feeder reefs, which concentrate planktonic resources (nutrients and suspended matter) and channel them into benthic food webs. These communities persist for many years and local extinctions appear to be mainly driven by large-scale events such as EN, which causes direct mortality of benthic organisms due to lack of nutrients/food, high water temperatures, or burial under terrigenous sediments from river runoff. Historic extinctions in combination with local conditions (e.g., vicinity to upwelling centres or substratum availability) produce a heterogeneous distribution pattern of benthic communities, which is also reflected in the diffuse biogeographic limits along the coast of northern-central Chile. Studies of population connectivity suggest that species with highly mobile planktonic dispersal stages maintain relatively continuous populations throughout most of the HCS, while populations of species with limited planktonic dispersal appear to feature high genetic structure over small spatial scales. The population dynamics of most species in the HCS are further influenced by geographic variation in propagule production (apparently caused by local differences in primary production), by temporal variation in recruit supply (caused by upwelling THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILE 197 events, frontal systems and eddies), and topographically driven propagule retention (behind headlands , in bay systems and upwelling shadows). Adults as well as larval stages show a wide range of different physiological, ecological and reproductive adaptations. This diversity in life-history strategies in combination with the high variability in environmental conditions (currents, food availability, predation risk, environmental stress) causes strong fluctuations in stocks of both planktonic and benthic resources. At present, it remains difficult to predict many of these fluctuations , which poses particular challenges for the management of exploited resources and the conservation of biodiversity in the HCS. The high spatiotemporal variability in factors affecting ecological processes and the often-unpredictable outcome call for fine-scale monitoring of recruitment and stock dynamics. In order to translate this ecological information into sustainable use of resources, adaptive and co-participative management plans are recommended. Identification of areas with high biodiversity, source and sink regions for propagules and connectivity among local populations together with developing a systematic conservation planning, which incorporates decision support systems, are important tasks that need to be resolved in order to create an efficient network of Marine Protected Areas along the coast of northern-central Chile. Farther offshore, the continental shelf and the deep-sea trenches off the Chilean coast play an important role in bio-geochemical cycles, which may be highly sensitive to climatic change. Research in this area should be intensified, for which modern research vessels are required. Biodiversity inventories must be accompanied by efforts to foster taxonomic expertise and museum collections (which should integrate morphological and molecular information). Conservation goals set for the next decade can only be achieved with the incorporation of local stakeholders and the establishment of efficient administrative structures. The dynamic system of the HCS in northern-central Chile can only be understood and managed efficiently if a fluent communication between stakeholders, administrators, scientists and politicians is guaranteed.
... The age and growth studies of fishes within sexes (e.g. male and female) are consequently essential in assessing population characteristics that can impact the productivity of an ecosystem, food web structure of the water body and management of fisheries [1][2][3]. Accurate fish growth rates are important for growth analysis, age structure analysis and estimation of mortality rate [4][5][6]. The information of fish growth increment is also necessary to perceptive a species life history, reproductive biology, population dynamics, biomass and fisheries sustainability [7,8]. ...
Article
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Studies were undertaken during the period February 2019 to 2020 January from the lower stretch of the Tons River at Prayagraj, Uttar Pradesh, India. During the present work, 683 fish specimens of Nile Tilapia, Oreochromis niloticus (336 males and 347 females) were studied for estimation of age composition, age and growth increment. An overall representation of age, growth increment and age composition of O. niloticus has been obtained by the study of its key scales. The age composition of O. niloticus varied from 0+ to 7+ age groups. The maximum growth increment was recorded during first year of life cycle and showing a gradual decrease in growth as the fish got older. The minimum growth increment was recorded during the seven year of the life cycle. On the basis of pooled sampled specimen in the length ranges from 83 to 463 mm showed that the fish attained the mean length 159 mm in 1+, 237 mm in 2+, 309 mm in 3+, 357 mm in 4+, 394 mm in 5+, 429 mm in 6+ and 455 mm in 7+ age groups. The growth increments in O. niloticus was observed as 159 mm, 78 mm, 72 mm, 48 mm, 37 mm, 35 mm and 26 mm for 1+ to 7+ age groups, respectively. The slow growth increment observed after first year may be attributed to the maturity attained within first year of life. It is well known that the growth potential is used for the gonad development. The growth percentage varied from age to age in the male, female and pooled samples.
... The pollock assessment covers the period from 1970 to 2019 (50 years) and pollock ages 1-10 years, with age-10 defined as a "plus" group (i.e., all individuals age-10 and older). Population dynamics were modeled using standard formulations for mortality and fishery catch (e.g., Fournier and Archibald, 1982;Deriso et al., 1985;Hilborn and Walters, 1992). Year-and age-specific fishing mortality was modeled as a product of a year effect that represents the full-selection fishing mortality and an age effect representing the selectivity of that age group to the fishery. ...
Article
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Although highly variable in time and space, predation remains the greatest source of mortality for juvenile and lower trophic-level fishes. As such, predation can have substantial and long-term effects on the dynamics of these prey. Gulf of Alaska walleye pollock (Gadus chalcogrammus) has shown considerable variability in biomass over the past four decades. During this same time, the demersal fish community transitioned from being dominated by pollock to a system comprised primarily of upper trophic-level predators. We estimated time-varying predation mortality to better understand its effects on the population dynamics of pollock in this currently "top heavy" system. Our index of predation accounted for spatiotemporal variation in predator biomass, bioenergetics-based rations, and age-specific proportions of pollock consumed (1990-2019). To evaluate population-level impacts of predation, we included an index of removals as part of the stock assessment model. This formulation allowed for non-annual data inputs and included a proportionality constant with which to scale predation. Age-specific natural mortality was allowed to vary according to a penalized random walk. We found that natural mortality ranged from 37% higher to 17% lower than the long-term mean. Resulting estimates of total pollock biomass differed by as much as 37% relative to a model without time-varying natural mortality, though the maximum difference for exploitable biomass was only 14%. Using an empirically-derived predation index to modify constant natural mortality allows stock assessment scientists to evaluate impacts of time-varying predation on assessed species. This approach provides a relatively simple way of incorporating ecological information into single-species stock assessments and may reduce bias compared to conventional models that do not account for changes in predation mortality. Notably, including predation mortality in single-species assessments may help identify inconsistencies in biomass estimates that warrant further consideration.
... В модели JABBA также связь между U t и B t подразумевается прямопропорциональной, а улавливаемость q -стационарной по всем годам. Мы постараемся учесть эффект гиперстабильности или гиперчувствительности [Hilborn, Walters, 1992] ...
Article
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State of the greenland halibut stock in the Sea of Okhotsk fishing zone is evaluated as overfished with a high probability of 97.5 % by the index of fishable biomass, and the overfishing continued in 2021. This conclusion is based on results of double filtering the posterior parameter estimates in the state-space generalized surplus production model JABBA (Just Another Bayesian Biomass Assessment), with additional tuning of the new model taking into account these results. The overfishing was not caused by significant changes of environmental parameters (average SST and EOF modes of SST were examined), but its main reason was the overestimated target harvest rate established for the Far East of Russia as 10 % of the total biomass or a half of natural annual mortality (20 %). This incorrect value of the rate was based on incorrect determination of age structure and terminal age for the halibut by the fish scale method. The new approach of the stock status evaluation with JABBA model is independent on the age data. It includes the additional filtering of the JABBA model result, its refinement with stringent tuning using the algorithm of No-U-Turn sampler, and checking additional parameters on hyperstability or hypersensitivity. The new reference point of the target harvest rate is between 2.5 and 5.4 % (95 % credible interval) of the total biomass, with a median of about 3.75 %. This new value is slightly higher than that one used by ICES for greenland halibut in the northeastern Atlantic (3.5 % for fishable biomass, its reduction to 2.5 % is discussed), but these values cannot be compared because of different habitat conditions and probably different growth rate of greenland halibut in the Okhotsk Sea and the Atlantic. Researches on the optimal level of greenland halibut exploitation should be continued; anyway, the new reference point of the target harvest rate has to be implemented immediately and to be used at least until correction of the age-length key for greenland halibut in the Okhotsk Sea. The input data and Stan code of the new model are presented in the annexes.
... Statistical modelling aims to identify relationships between variables to identify patterns, make inferences and potentially predict focal variables (Ogle, 2018). In fisheries, linear regression, analysis of variance, multiple regressions, factor analysis, generalised linear models and non-parametric models are common methods to test how an independent variable or factor might be driving a dependent response variable (Hilborn & Walters, 1992 (Trifonova et al., 2017;Uusitalo et al., 2018), examine trophic dynamics in fisheries (Trifonova et al., 2015) or link social and ecological data directly to fisheries management (Naranjo-Madrigal et al., 2015;Parsons et al., 2021;Varkey et al., 2016). SEMs have been used to examine relationships between governance and ecological surprise in fisheries using the social-ecological systems framework (Filbee-Dexter et al., 2018), the factors underpinning livelihood resilience in small-scale fisheries (Amadu et al., 2021), the conditions leading to sustainability in small-scale fisheries (Robotham et al., 2019) and feedbacks in fisheries systems (Grilli et al., 2018). ...
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Estudio biológico y pesquero de Pseudopimelodus schultzi (Dahl, 1955) en la cuenca media y baja del río Atrato, Chocó Biological study and fishing Pseudopimelodus schultzi (Dahl, 1955) in the basin middle and lower Atrato river, Chocó Resumen Objetivo: Se estimaron algunos aspectos biológicos y pesqueros de Pseudopimelodus schultzi en la cuenca media y baja del río Atrato. Metodología: Se capturaron individuos provenientes de pesca arte-sanal, utilizando como arte de pesca la tola y el trasmallo; a los individuos se les registró la longitud total (LT) y la longitud estándar (LE) con un ictiómetro graduado en centímetros (cm) y el peso total (WT) al gramo más cercano con una balanza de precisión. Los ejemplares se evisceraron para determinar el sexo, estadíos de madurez sexual, extraer gónadas y estómagos. La información pesquera se registró a través de pescadores en las comunidades, con el fin de evidenciar el aporte en kg de P. schultzi. Resultados: Se capturaron 398 individuos, 228 fueron hembras y 170 machos. LT osciló entre 19,1 y 85,5 cm, mientras que LE estuvo en un rango entre 15,5 y 78 cm, WT entre 78 y 7.755 g. Esta especie presentó un crecimiento isométrico (b=2,9), proporción sexual de 1,3 (H): 1 (M) (p>0,05), dieta alimenticia carnívora de preferencia por los peces, y dos períodos reproductivos, de enero a abril y de agosto a septiembre. Conclusiones: P. schultzi es una especie que amerita especial atención, porque se encuentra en la categoría de casi amenazada y tiene gran importancia a nivel de comercialización y consumo; en los últimos años se ha registrado una disminución debido a la gran demanda y presión pesquera que se ejerce sobre este recurso. Abstract Objective: In this research some biological and fishing aspects of Pseudopimelodus schultzi in the Middle and Lower basin of the Atrato River were estimated. Methodology: Individuals from artisanal fishing were captured, using as fishing gear such as tola and trammel, the total length (LT) and standard length (LE) were recorded with an ichthyometer graduated in centimeters (cm), and the total weight (WT) to the nearest gram with a precision scale, the specimens were eviscerated to determine sex, stages of sexual maturity, extract gonads and stomachs. The fishing information was recorded through fishermen in the communities, in order to demonstrate the contribution in kg of P. schultzi. Results: 398 individuals were captured, 228 were female and 170 were male. LT ranged from 19.1 to 85.5 cm, while LE ranged from 15.5 to 78.0 cm, and WT ranged from 78 to 7.755 g. This species presented an isometric growth (b=2.9), a sexual ratio of 1.3 (H): 1 (M) (p>0.05), a carnivorous diet of preference for fish, and two reproductive periods, from January to April and from August to September. Conclusion: P. schultzi is a species that deserves special attention, since it is in the near threatened category and has great importance at the level of commercialization and consumption. In recent years there has been a decrease due to the great demand and fishing pressure exerted on this resource.
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Thesis
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Information on the biological parameters of exploited fish stocks facilitates the objective assessment and management of these living resources. The sardine (Sardina pilchardus) is considered as overexploited in northwest Africa. It is a key species of the Canaries current large marine ecosystem (CCLME) of the Atlantic Ocean due to its socioeconomic importance, as well as being a key intermediary species in marine food web. A massive decline in caught fish for Senegal over half a century is also reported (61,648 t in 1994 to 7486 t in 2017). Here, we analyzed the age and growth parameters of sardines in the Exclusive Economic Zone of northern Senegal. Maximum body size was 31 cm total length (TL). A growth performance index (φ′) and a growth rate coefficient (K) of 2.65 and 0.85, respectively, were determined, with this being the first record for this country. Sardines had higher asymptotic length (L∞, 30.5 cm TL) and age (6 years) in northern Senegal compared with Morocco (Atlantic Ocean) and the Mediterranean Sea. The asymptotic length found in Northern Senegal was also higher than in other part of the CCLME and Mediterranean Sea. This difference might be attributed to differences in the pelagic habitat, environmental factors, and/or fishing pressure. This study provides new insights towards establishing management measures, especially in data-poor fisheries and should act as an advocacy to increase sub-regional collaborations
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