Redd Superimposition and Egg Capacity of Pink Salmon Spawning Beds

Carmel River Steelhead Fisheries Report 2020

Technical Report

Full-text available

Jul 2020

LITERATURE REVIEW & MONITORING RECOMMENDATIONS FOR SALMONID SPAWNING HABITAT AVAILABILITY

Technical Report

Full-text available

May 1996

S 4 : A Spatially Continuous, Individual‐Based Model of Salmonid Redd Superimposition

Article

Full-text available

Feb 2019

Peter Dudley

Superimposition is one of the earliest risks faced by salmonids during their life cycle and can cause substantial egg mortality. Because habitat area is a determining factor in superimposition risk, agencies allocate large amounts of resources to spawning habitat restoration. Due to the superimposition mortality risk and the funding of spawning habitat restoration, freely available, user‐friendly models that accurately predict superimposition could be useful for strategic management. This paper presents an individual‐based model, the Salmonid Spawning Superimposition Simulator (S4), which is a spatially continuous spawning model with a daily temporal resolution and heterogeneous habitat. I used S4 to analyze the effects of spawning behavior, available habitat, habitat heterogeneity, and changing size and reproductive life span over the spawning season. Salmon may prefer to spawn on previously established redds, and this behavior increased superimposition risk at low spawning densities but had less of an effect as spawner density increased. Decreasing the density of spawners reduced the superimposition risk quickly down to a density threshold of 0.03 spawners/m2, below which there was less than a 5% change in the number of eggs killed. There were small effects from changing spawner length and reproductive life span over the spawning season. Finally, as the difference in habitat quality between patches increased, the effect of changing the percentage of superior‐quality habitat on the number of eggs killed became more peaked and asymmetric. This model and the associated findings can help managers to determine effective levels of spawning gravel additions, understand the causes of observed superimposition mortality, and assess the effects of restoration on superimposition risk.

Gerrard Rainbow Trout (Oncorhynchus mykiss) Spawner Migration and Residence Time as Estimated by Radio and Sonic Telemetry, 2004-2009

Technical Report

Full-text available

Apr 2010

EXECUTIVE SUMMARY The effects of ecological alterations in the Kootenay Lake watershed on abundance of the highly valuable Gerrard-origin rainbow trout have been monitored by a time series of daily spawner counts extending from 1961 to the present. Escapement estimates have been derived since 1978 by expanding the peak count at the spawning area at Gerrard by a factor of 3.08. Alternative analyses integrating all of the count data in a season, such as the area-under-the-curve (AUC) methodology or maximum likelihood-based run timing models, are attractive relative to the peak count methodology in that they account for variability in the shape and breadth of the spawner abundance curve, which can be substantial. In 2004 we initiated a telemetry study of Gerrard rainbow trout spawner movements, utilizing sonic and radio tags, with a particular focus on acquiring the spawner residence time estimates necessary for both the AUC and maximum likelihood analyses. Various fish capture methods were directed at the lower Duncan and Lardeau Rivers in 2004, with mixed success, but in 2005 and 2006 most tagged fish were captured using highly efficient tangle nets set in Kootenay Lake at the mouth of the lower Duncan River. A small number of captures using angling in the Lardeau River occurred during 2005-2007. We also monitored Gerrard rainbow trout tagged in Kootenay Lake as part of a separate study in 2008. Abundance of Gerrard rainbow trout milling at the mouth of the Duncan River, as indicated by capture rate in the tangle net during spring 2005 and spring 2006, appeared to be at its highest in late March and the beginning of April. Radio-tagged fish migrated past the Lardeau/Duncan confluence and into the Lardeau River over an extended period between the last week of March and the first week of May. Radio-tagged spawners that migrated as far as Gerrard took between 5 and 20 days to travel between the Lardeau/Duncan confluence and the outlet of Trout Lake. Several radio-tagged trout appeared to have spawned in locations other than Gerrard. Based on the total number of mature rainbow trout radio tagged at the mouth of the Duncan River in 2005 and 2006, and which went through the pattern of upstream migration followed by residence in a potential spawning stream and kelting past a fixed station (25 fish in total), 16% and 20% of radio-tagged trout spawned at other locations in the Lardeau River and at the Duncan Dam, respectively. Major, unexpected results of the study were the discovery of the population spawning below the tailrace of the Duncan Dam, and the discovery of potential methodologies for estimating their abundance including redd counts and nighttime boat surveys. Residence time at Gerrard did not differ greatly for tagged male and female rainbow trout spawners (6.18  1.33 days vs. 6.94  1.16 days, respectively), and the overall residence time estimate for the six years' pooled telemetry data (including 2008 Kootenay Lake-tagged fish without sex data) was 6.94 days (n = 33, SE = 0.852 days). Spawning timing for radio-and sonic-tagged females appeared to be representative of untagged fish. However, males from the early part of the run timing curve appeared to be under-represented in our telemetry sample. We recommend, therefore, that additional iii tagging and telemetry take place in future in order to increase representation of early-timed male rainbow trout spawners in the residence time estimate. Two population estimation methodologies, based on (1) trapezoidal AUC calculations and (2) a maximum likelihood run timing model, which incorporated the pooled residence time estimate, an estimate of the variability of observer efficiency based on replicate counts, and periodic count data from 1961-2009, showed relatively good agreement in their estimates and comparable confidence intervals. Expanded peak counts were in reasonable agreement with estimates generated using the trapezoidal AUC and maximum likelihood approaches, being on average 9.3% and 8.3% higher, respectively. Expanded peak counts were however highly variable relative to population estimates based on all the count data, ranging from 70% (1966) to 176% (2008) of the maximum likelihood estimates. The ability of the trapezoidal AUC and ML approaches to account for variability in the form of the spawner abundance curve, as well as provide estimates of uncertainty for the population estimates, suggest that these approaches are preferable for future monitoring and analyses of Gerrard rainbow trout spawner abundance.

Interactions between rainbow trout and bridgelip sucker spawning in a small Washington stream

Article

Full-text available

Mar 2005
NORTHWEST SCI

We investigated the interactions between two sympatric native fishes (rainbow trout and bridgelip sucker) spawning in Umtanum Creek, a tributary of the Yakima River in central Washington. We used redd surveys to determine spawn location and timing of rainbow trout and bridgelip sucker. We determined microhabitat characteristics of rainbow trout and bridgelip sucker spawning areas and measured the degree of disturbance of rainbow trout redds by spawning bridgelip sucker as well other rainbow trout. Emergence traps were used to compare the mean survival to emergence (STE) rate of experimentally protected rainbow trout redds to those left unprotected. The first behavioral observations of bridgelip sucker spawning are also reported here. Both temporal and spatial overlap in spawning of rainbow trout and bridgelip sucker were observed. No differences were found in the water depth and water velocity used by rainbow trout and bridgelip sucker for spawning. Spawning behavior of bridgelip sucker entailed extensive substrate modification (i.e., digging) prior to the release of gametes. During spawning surveys, bridgelip sucker were observed spawning in 3 of 21 rainbow trout redds in 1994 and 5 of 15 rainbow trout redds in 1995. Estimated mean STE of protected rainbow trout redds (11.2%) was significantly greater (P<0.02) than rainbow trout redds that were unprotected (2.6%). Of those unprotected rainbow trout redds, the mean STE of rainbow trout redds disturbed by bridgelip sucker and other rainbow trout was 0.4% and 2.8%, respectively. When spawning habitat is severely limited, emergence rates of earlier spawning rainbow trout may be reduced due to redd superimposition by bridgelip sucker. © 2005 by the Northwest Scientific Association. All rights reserved.

Interactions between rainbow trout and bridgelip suckers spawning in a small Washington stream

Article

Full-text available

Jul 2005
NORTHWEST SCI

Andrew R. Murdoch

We investigated the interactions between two sympatric native fishes (rainbow trout and bridgelip sucker) spawning in Umtanum Creek, a tributary of the Yakima River in central Washington. We used redd surveys to determine spawn location and timing of rainbow trout and bridgelip sucker. We determined microhabitat characteristics of rainbow trout and bridgelip sucker spawning areas and measured the degree of disturbance of rainbow trout redds by spawning bridgelip sucker as well other rainbow trout. Emergence traps were used to compare the mean survival to emergence (STE) rate of experimentally protected rainbow trout redds to those left unprotected. The first behavioral observations of bridgelip sucker spawning are also reported here. Both temporal and spatial overlap in spawning of rainbow trout and bridgelip sucker were observed. No differences were found in the water depth and water velocity used by rainbow trout and bridgelip sucker for spawning. Spawning behavior of bridgelip sucker entailed extensive substrate modification (i.e., digging) prior to the release of gametes. During spawning surveys, bridgelip sucker were observed spawning in 3 of 21 rainbow trout redds in 1994 and 5 of 15 rainbow trout redds in 1995. Estimated mean STE of protected rainbow trout redds (11.2%) was significantly greater (P<0.02) than rainbow trout redds that were unprotected (2.6%). Of those unprotected rainbow trout redds, the mean STE of rainbow trout redds disturbed by bridgelip sucker and other rainbow trout was 0.4% and 2.8%, respectively. When spawning habitat is severely limited, emergence rates of earlier spawning rainbow trout may be reduced due to redd superimposition by bridgelip sucker.

Factors affecting the duration of nest defense and reproductive lifespan of female sockeye salmon, Oncorhynchus nerka

Article

Dec 1998

Reproductive success of female animals is often affected by a combination of fecundity and parental care. In female salmonid fishes, acquisition of nest (redd) sites and prevention of their use by other females are critical to reproductive success. These factors are particularly important for stocks that spawn at high densities. Body size is positively correlated with fecundity and egg size, and has been hypothesized to control the outcome of intrasexual competition and longevity. We tested this hypothesis by evaluating the influences of body size, intrasexual aggression and arrival date on duration and success of redd guarding by female sockeye salmon, Oncorhynchus nerka, in a small Alaskan creek. Contrary to the hypothesis, larger females guarded their redds no longer than smaller females, and did not live as long in the stream. Aggression was not related to body size or overall longevity but was positively correlated with residence period on the redd. Females that entered the creek earlier lived longer, spent longer on their redds, and spent more time guarding their redds after spawning than females that entered the creek later. However, despite their longevity, early-arriving fish were more likely to have their redds reused by another female because they died before all the females had selected redd sites. The small average body size in this stock is consistent with weak selection for large size, and with our evidence that size provided little if any advantage in nest guarding.

A stock–recruitment model for highly fecund species based on temporal and spatial extent of spawning

Article

Sep 2013
FISH RES

A stock–recruitment model is described for highly fecund species based on the contraction of the spatial and temporal extent of spawning when a population is reduced in size: R = αK(1 − exp[−S/(mK)]), where S is the number of spawners, K is the carrying capacity in units of the number of habitat patches that can produce recruits, α is the average number of recruits per unit of habitat, and m is the number of spawners that group together to spawn. The model is based on three simplifying assumptions: (1) the environment is divided into K units; (2) the presence of one spawner provides sufficient eggs to fill the capacity of that unit, any additional spawners in that unit will not increase recruitment; and (3) groups of fish are randomly distributed over the environment. The model allows for a flat top curve, which is consistent with highly fecund species that are continuous spawners and do not aggregate to spawn. It also allows for a strong relationship between spawners and recruits, which is more consistent with species that aggregate in time and space to spawn. This stock–recruitment model can be approximated in terms of parameters commonly used in contemporary stock assessment models (virgin recruitment, R0, and steepness of the stock–recruitment relationship, h, virgin spawning biomass, S0): R = R0(1 − exp(5ln(1 − h)S/S0)). The functional form is compared with the Beverton–Holt stock–recruitment model.

Fine-scale temporal adaptation within a salmonid population: Mechanism and consequences

Article

Full-text available

Sep 2013
MOL ECOL

We demonstrate a clear example of local adaptation of seasonal timing of spawning and embryo development. The consequence is a population of pink salmon that is segmented into spawning groups that use the same limited habitat. We synthesize published observations with results of new analyses to demonstrate that genetic variation of these traits results in survival differentials related to that variation, and that density-dependent embryo mortality and seasonally variable juvenile mortality are a mechanism of selection. Most examples of local adaptation in natural systems depend on observed correlations between environments and fitness traits, but do not fully demonstrate local adaptation: that the trait is genetically determined, exhibits different fitness in common environments or across different environments, and its variation is mechanistically connected to fitness differences. The geographic or temporal scales of local adaptation often remain obscure. Here, we show that heritable, fine-scale differences of timing of reproductive migration in a pink salmon (Oncorhynchus gorbuscha) resulted in temporal structure that persisted several generations; the differences enable a density-dependent population to pack more spawners into limited spawning habitat, that is, enhance its fitness. A balanced trade-off of survivals results because embryos from early-migrating fish have a lower freshwater survival (harsh early physical conditions and disturbance by late spawners), but emigrant fry from late-migrating fish have lower marine survivals (timing of their vernal emergence into the estuarine environment). Such fine-scale local adaptations increase the genetic portfolio of the populations and may provide a buffer against the impacts of climate change.

Stream-bed scour, egg burial depths, and the influence of salmonid spawning on bed surface mobility and embryo survival

Article

May 1996

Bed scour, egg pocket depths, and alteration of stream-bed surfaces by spawning chum salmon (Onchorhynchus keta) were measured in two Pacific Northwest gravel-bedded streams. Close correspondence between egg burial depths and scour depths during the incubation period suggests an adaptation to typical depths of bed scour and indicates that even minor increases in the depth of scour could significantly reduce embryo survival. Where egg burial depths are known, expressing scour depth in terms of bed-load transport rate provides a means for predicting embryo mortality resulting from changes in watershed processes that alter shear stress or sediment supply. Stream-bed alteration caused by mass spawning also may influence embryo survival. Theoretical calculations indicate that spawning-related bed surface coarsening, sorting, and form drag reduce grain mobility and lessen the probability of stream-bed scour and excavation of buried salmon embryos. This potential feedback between salmon spawning and bed mobility implies that it could become increasingly difficult to reverse declines in mass-spawning populations because decreased spawning activity would increase the potential for bed scour, favoring higher embryo mortality. Further analysis of this effect is warranted, however, as the degree to which spawning-related bed loosening counteracts reduced grain mobility caused by surface coarsening, sorting, and redd form drag remains uncertain.

Genetic Variation of Return Date in a Population of Pink Salmon: A Consequence of Fluctuating Environment and Dispersive Selection?

Article

Full-text available

Nov 1997

A genetic basis for variation in the date that anadromous,salmon return to their natal or home stream was demonstrated by significant differences between return dates of pink salmon Oncorhynchus gorbuscha fami- lies. Of 120 families made by hierarchical matings of 60 males and 120 females, 118 families survived. The first half (60 families) and second half (60 families) were spawned,28 d apart. The 120 full-sibling families were incubated separately, released as fry with identifying coded microwire tags, and recovered entering the home stream as adults. Families in the first half returned on average 29 d before families in the second half ( P < 0.0001). Average return dates differed between families that were spawned on the same day by different fathers (P< 0.045 sons; P < 0.040 daughters). These differences indicate that additive genetic variance contributes to the natural variation of return date. Heritability of timing of anadromous migration in odd-year pink salmon spawned in Auke Creek, Alaska, was very high, perhaps near unity, over the entire population. For segments of the population spawning on the same date, heritability was about 0.2 (SE 0.2) in males and about 0.4 in females (SE 0.2). We suggest that such high genetic variability of a trait closely related to fitness is maintained by the fluctuating envi- ronment to which ,Auke Creek pink salmon must continually adapt or by dispersive selection caused by redd superimposition. In either case, generalizing to other salmon populations, rational management must preserve variability of return timing if the fitness of populations is to be conserved. Authors: WILLIAM W. SMOKER, ANTHONY J. GHARRETT, MICHAEL S. STEKOLL are professors with the University of Alaska Fairbanks,

Egg burial depth by sockeye salmon ( Oncorhynchus nerka ): implications for survival of embryos and natural selection on female body size

Article

Jan 1999
CAN J ZOOL

Insights into Chinook salmon movement ecology in the terminal reaches of the upper Yukon River during the spawning migration

Article

Jun 2022

Chinook salmon (Oncorhynchus tshawytscha, Walbaum 1792) from the upper Yukon River are highly unique, with some populations migrating nearly 3,000 km to spawning habitat near the northern range limit for the species. We conducted a 4-year study to understand the behaviour of Chinook salmon in the terminal reaches of their migration by tagging salmon with acoustic and radio transmitters in Whitehorse, Yukon, ~2800 rkm from the ocean. Various migration characteristics were quantified for Chinook salmon including en route mortality, diel behaviour, migration rates, and homing patterns, and associations with salmon origin (wild vs. hatchery), sex, size, and migration timing were explored. Salmon had high survival to spawning grounds (>98%) and migrated throughout all hours of the day, with higher proportions of nighttime movements in a smaller spawning tributary than in the Yukon River mainstem. Migration rates were faster for larger salmon as well as late-arriving salmon, which was likely necessary to ensure they had sufficient time and suitable conditions on spawning grounds to reproduce. Non-direct homing movements (e.g. tributary exploration) were more common in male salmon and considerably increased migration distance through the study area. Findings from this study may help to inform the complex international and inter-nation management of these increasingly threatened Chinook salmon populations.

Not All Rivers Are Created Equal: The Importance of Spring-Fed Rivers under a Changing Climate

Article

Full-text available

Jun 2021

In the Western United States, volcanic spring-fed rivers are anticipated to become increasingly more important for salmonids and other native fishes, as these rivers will retain coldwater habitats as the climate warms. Despite this, little is known about the hydro-biogeochemical interactions within these ecosystems. A review of existing literature on spring-fed rivers, coupled with a decade of research on volcanic spring-fed rivers of northern California, finds that these systems are exceptionally productive and exhibit stable environmental conditions. These unique conditions stem from hydrogeologic processes typical of young volcanic terrains. Aquatic macrophytes, common to some nutrient-rich spring-fed systems, play a disproportionate role in hydrologic and geomorphic processes by facilitating ecological interactions and velocity conditions that improve juvenile salmonid growth. We find that volcanic spring-fed rivers are also resilient to climate change, due not only to their ability to dampen water temperature changes through deep groundwater flow but also because of their nutrient-driven high ecosystem productivity, which may enable coldwater species to metabolically compensate for marginal increases in water temperature. Understanding the fundamental geomorphic and ecological differences between these rare ecosystems and their numerically dominant runoff rivers is essential for developing long-term conservation strategies for coldwater species under a rapidly changing climate.

Potential for ecological nonlinearities and thresholds to inform Pacific salmon management

Article

Full-text available

Dec 2020

Ecology is often governed by nonlinear dynamics. Nonlinear ecological relationships can include thresholds-incremental changes in drivers that provoke disproportionately large ecological responses. Among the species that experience nonlinear and threshold dynamics are Pacific salmon (Oncor-hynchus spp.). These culturally, ecologically, and economically significant fishes are in many places declining and management focal points. Often, managers can influence or react to ecological conditions that salmon experience, suggesting that nonlinearities, especially thresholds, may provide opportunities to inform decisions. However, nonlinear dynamics are not always invoked in management decisions involving salmon. Here, we review reported nonlinearities and thresholds in salmon ecology, describe potential applications that scientists and managers could develop to leverage nonlinear dynamics, and offer a path toward decisions that account for ecological nonlinearities and thresholds to improve salmon outcomes. It appears that nonlinear dynamics are not uncommon in salmon ecology and that many management arenas may potentially leverage them to enable more effective or efficient decisions. Indeed, decisions guided by nonlinearities and thresholds may be particularly desirable considering salmon management arenas are often characterized by limited resources and mounting ecological stressors, practical constraints, and conservation challenges. More broadly, many salmon systems are data-rich and there are an extensive range of ecological contexts in which salmon are sensitive to anthropogenic decisions. Approaches developed to leverage nonlinearities in salmon ecology may serve as examples that may inform analogous approaches in other systems and taxa.

Environmental influences on life history strategies in partial anadromous brown trout (Salmo trutta, Salmonidae)

Article

Full-text available

Aug 2019
FISH FISH

This paper reviews the life history of brown trout and factors influencing decisions to migrate. Decisions that maximize fitness appear dependent on size at age. In partly anadromous populations, individuals that attain maturity at the parr stage typically become freshwater resident. For individual fish, the life history is not genetically fixed and can be modified by the previous growth history and energetic state in early life. This phenotypic plasticity may be influenced by epigenetic modifications of the ge-nome. Thus, factors influencing survival and growth determine life-history decisions. These are intra-and interspecific competition, feeding and shelter opportunities in freshwater and salt water, temperature in alternative habitats and flow conditions in running water. Male trout exhibit alternative mating strategies and can spawn as a subordinate sneaker or a dominant competitor. Females do not exhibit alternative mating behaviour. The relationship between growth, size and reproductive success differs between sexes in that females exhibit a higher tendency to migrate than males. Southern populations are sensitive to global warming. In addition, fisheries, aquaculture with increased spreading of salmon lice, introduction of new species, weirs and river regulation, poor water quality and coastal developments all threaten trout populations. The paper summarizes life-history data from six populations across Europe and ends by presenting new research questions and directions for future research.

Modeling composite effects of marine and freshwater processes on migratory species

Article

Full-text available

Jul 2019

Life histories of migratory species such as anadromous fishes make them particularly susceptible to composite effects of processes experienced across distinct habitats and life stages. Therefore, their population dynamics are difficult to quantify and manage without tools such as life-cycle models. As a model species for which life-cycle modeling is particularly useful, we provide an analysis of influential processes affecting dynamics of the Central Valley fall-run Chinook salmon (CVFC) population (Oncorhynchus tshawytscha). This analysis demonstrates how, through identification of covariates that affect this population at each life stage and their relationship to one another, it is possible to identify actions that best promote sustainability for this anadromous species. We developed a life-cycle model for CVFC examining primary processes influencing variability in observed patterns of escapement from 1988 to 2016. CVFC are a valuable fishery along the US West Coast; however, their natural population is a fraction of its historic size, and recent low escapements have resulted in substantial restrictions on the fishery. Our model explains 68.3% of variability in historic escapement values. The most influential processes include temperatures experienced during egg incubation, freshwater flow during juvenile outmigration, and environmentally mediated predation during early marine residence. This work demonstrates the need, and methodology, for considering the interactions between freshwater and marine dynamics when evaluating the efficacy of managerial practices in freshwater and the ocean, especially in the context of increased environmental variability, climate change, and dynamic predator populations. The methodology developed in this study can be used toward improved conservation and management of other anadromous fishes and migratory species.

Modeling Spawning Habitat Potential for Chum (Oncorhynchus keta) and Pink Salmon (O. gorbuscha) in Relation to Landscape Characteristics in Coastal Southeast Alaska

Thesis

Full-text available

Jan 2018

Bernard Timothy Romey

In response to the increasing need for ecosystem services throughout the Southeast Alaska region, decision makers are tasked with balancing the need for natural resources with salmon conservation. However, accurate historical and current information on salmonid population abundance, freshwater distribution, and habitat quality are sparse with limited resolution for large portions of this remote and rugged landscape. Here, I created Intrinsic Potential (IP) models for chum and pink salmon to predict the potential for portions of coastal rivers to provide high-quality spawning habitat. I developed IP models for both species from field redd surveys and synthetic habitat variables derived from 1-m resolution digital elevation models. The surveys were performed at 49 study reaches in five coastal drainage basins on the north end of Chichagof Island, Southeast Alaska. I used a spatially balanced random sampling design that included field surveys for redds during two field seasons with contrasting precipitation patterns and disparate adult salmon escapements. The IP models predict probable spawning habitat for both species based on persistent landform characteristics and hydrologic processes that control the formation and distribution of spawning habitat across the landscape. Selection of persistent reach variables for both species IP models was informed by principal component analysis (PCA), resource selection ratios, random forest modeling, and regression models of field and synthetic variable comparisons. I observed primarily one spawning strategy by chum salmon associated with mainstem channels, and two distinct spawning strategies for pink salmon related to small moderate-gradient channels and tributaries, and lower drainage basin mainstem channels. The relationships suggest that chum and pink salmon primarily selected for unconstrained channel types in large-and small-size channels, with chum salmon being more selective toward the larger mainstem channels, and pink salmon selecting for smaller channels and tributaries. The prediction of chum salmon redd presence within a specific reach for both high and low streamflow regimes was explained by channel gradient, floodplain width, and mean annual flow in order of importance. In general, chum salmon redds were observed in larger unconstrained low-gradient floodplain reaches where accumulation of deposited gravels and adequate flow produce habitat heterogeneity suitable for spawning. Pink salmon redd presence for both survey years was explained by channel gradient, reach elevation, and mean annual flow, in order of importance. Specifically, when flows allowed upstream access, spawning pink salmon utilized smaller moderate-gradient channels where substrate size and flows were better suited to their smaller body size. Remotely sensed persistent fish habitat data is valuable information for helping understand fish population distributions across the landscape. These synthetic metrics enabled the identification and evaluation of persistent landscape features as probable predictors of IP. Validation of LiDAR-derived channel characteristics indicated channel lengths measured from the DEM were 12% longer than field measured channel length, primarily for channels wider than 10 meters. Thus, understanding the limitations of the data is important so that decision makers do not unintentionally set unrealistic objectives. This research highlights the utility of using IP models with high resolution remote sensing to expand known distributions and quality of spawning habitat for these two species in Southeast Alaska coastal streams.

Effects of density during freshwater and early marine rearing on juvenile sockeye salmon size, growth, and migration

Article

Full-text available

Sep 2017

We tested for density-dependent effects on the body size, ocean entry date, growth rate, and migration speed of juvenile sockeye salmon Oncorhynchus nerka in 2 yr with contrasting competitor densities during freshwater residence (intraspecific), as well as the first 2 mo of marine residence (intra- and interspecific). Juvenile sockeye salmon entering the marine environment during a year with high competitor densities (conspecifics and 9 other pelagic species groups) were, on average, 11% smaller and entered the ocean almost a week earlier. Differences between the high- and low-density years in entry size, but not entry date, were strongest in nursery lakes with high parental spawner abundance, consistent with density-dependent effects on freshwater growth. Mean daily growth rates of sockeye salmon during early marine residence did not vary between years after accounting for variation in ocean entry size and timing, even though the catch per unit effort of the most abundant juvenile salmon species increased more than 5-fold. However, juvenile sockeye salmon entering in the high-density year did migrate away from their ocean entry points significantly more rapidly (estimated ∼40% increase in body lengths per second). Our results suggest that juvenile sockeye salmon growth during early marine residence may not be strongly limited by competition and that shifts in migration speed or spatial distribution may buffer individuals from competitive interactions.

Monitoring Climate Impacts: Survival and Migration Timing of Summer Chum Salmon in Salmon Creek, Washington

Article

Sep 2017

In rivers of the Pacific Northwest, climate change is predicted to increase flow variability and water temperature, which may ultimately affect salmonid survival and the seasonal timing of key life history transitions. Summer Chum Salmon Oncorhynchus keta, native to tributaries flowing into Hood Canal and Strait of Juan de Fuca in Washington State, are particularly vulnerable to flow and temperature changes given their early spawn timing, yet relatively little is known regarding their juvenile life history. We investigated how flow and incubation temperatures influenced juvenile survival and timing of Chum Salmon in Salmon Creek between 2008 and 2016. Egg-to-migrant survival ranged from 0.9% to 46.3%, and was negatively related to the peak flow experienced during egg incubation from November 1 to January 31. Warm temperatures advanced emergence timing, as the number of days between the median spawning date and the median juvenile migration date was negatively related to average stream temperature during the same period. We used empirical data to estimate the range of accumulated temperature units (TUs) and survival that best explained the observed juvenile migration in the spring. The model indicated that incubating eggs experiencing warmer temperatures (2010, 2015, and 2016) accrued more TUs before emigration than did eggs incubating during colder years (2008, 2009, and 2014). Although the population exhibited some ability to compensate for warmer temperatures and stabilize emergence timing by increasing TU thresholds, our analysis, when combined with climate projections, suggests that warming temperature trends could significantly advance the timing of marine entry by weeks or more. Such a change could carry a corresponding impact on marine survival if emigration timing becomes desynchronized with spring zooplankton blooms in the marine environment, the primary source of nutrition for juvenile summer Chum Salmon. Received December 21, 2016; accepted April 16, 2017

Effects of introduced steelhead on resident brown trout population dynamics in a small low-gradient trout stream

Technical Report

Full-text available

Apr 2017

We used a before-after-control-impact study design to evaluate the effects of introducing migratory Rainbow Trout (steelhead) Oncorhynchus mykiss on the population dynamics of resident Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta from 1995–2008 in a small low-gradient Michigan trout stream. Data on resident trout population density, survival, and growth were collected from a treatment section of Hunt Creek, where adult steelhead were stocked each spring from 1998 through 2003, as well as from two reference stream reaches. We found no differences in population metrics of Brook Trout among treatment and reference sections during years with and without juvenile steelhead. The presence of steelhead had no apparent effect on the density of age-0 Brown Trout, but the mean density of all age-1 and older Brown Trout year classes that interacted with juvenile steelhead of the same age was 382 fish/ha compared to 702 fish/ha for age-1 and older year classes that did not interact with juvenile steelhead of the same age. By contrast, no differences in density of age-1 and older Brown Trout were detected in reference sections between the periods when steelhead were present or absent in the treatment section. Lower annual survival rates for year classes of age-0 Brown Trout that interacted with steelhead in the Hunt Creek treatment section were the primary reason that density of age-1 and older Brown Trout fell to approximately half the levels that existed before steelhead were introduced or after most steelhead had emigrated from the stream; overwinter survival of age-0 Brown Trout that interacted with steelhead was also significantly lower than survival of year classes that did not interact with steelhead. We found no significant differences in the mean length at age of any age class of Brown Trout among the treatment and reference sections that could be attributed to interactions with steelhead. Our examination of habitat use in the treatment section during spawning and rearing revealed that Brown Trout always exhibited a preference for deeper waters and stream segments with more large woody debris (LWD), but Brown Trout were more closely associated with LWD in the presence of steelhead. In 3 of 4 years that we monitored redd superimposition, less than 10% of Brown Trout redds were disturbed by subsequent steelhead spawning, which had no apparent adverse effect on the density of age-0 Brown Trout. Our case study showed that introducing steelhead into small low-gradient trout streams can result in lower densities of resident Brown Trout, largely due to reduced survival of Brown Trout from age 0 to age 1. However, we also showed that upstream passage of steelhead into high-quality trout streams offers tremendous potential to increase production of juvenile steelhead thereby reducing our reliance on hatchery reared fish to stock the Great Lakes.

Quantifying long-term population growth rates of threatened bull trout: Challenges, lessons learned, and opportunities

Article

Full-text available

Feb 2017

Temporal symmetry models (TSM) represent advances in the analytical application of mark-recapture data to status assessments. For a population of char, we employed 10 years of active and passive mark-recapture data to quantify population growth rates using different data sources and analytical approaches. Estimates of adult population growth rate were 1.01 (95% CI = 0.84-1.20) using a temporal symmetry model (λTSM), 0.96 (0.68-1.34) based on log-regressions of annual snorkel data (λA), and 0.92 (0.77-1.11) from redd counts (λR). Top performing TSMs included an increasing time trend in ‘recruitment’ (f) and changes in capture probability (p). There was only a 1% chance the population decreased ≥50%, and a 10% chance it decreased ≥ 30% (LMCMC). Size structure was stable; however, the adult population was dominated by small adults, and over the study period there was a decline in the contribution of large adults to total biomass. Juvenile condition decreased with increasing adult densities. Utilization of these different information sources provided a robust weight-of-evidence approach to identifying population status and potential mechanisms driving changes in population growth rates.

Adaptive variation in senescence: reproductive lifespan in a wild salmon population

Article

Full-text available

Jan 2003

Climate and conspecific density trigger pre-spawning mortality in sockeye salmon (Oncorhynchus nerka)

Article

Apr 2017
FISH RES

Pre-spawning mortality (PSM) has been occasionally observed in association with high densities of adult Pacific salmon (Oncorhynchus spp.), but because large escapements are rare, the phenomenon remains poorly understood. A large spawning escapement (∼12 times the 54 year median, and 3X the previous maximum) to a small stream in Alaska provided a unique opportunity to explore the factors that contribute to density-driven spawning ground mortality. After comparing patterns of mortality in 2014 with over 20 years of prior abundance and environmental data, we identified low dissolved oxygen (DO) as likely contributing to PSM. We then utilized a fish habitat-DO model to explore the roles of density-dependent and -independent factors in reducing DO. Stream flow and spawning density were identified as primary drivers of oxygen availability. Despite suboptimal oxygen levels the salmon did not die abruptly. Rather, on average they lived as long as in previous years (mean = 9.99 d), but many (55%) failed to complete spawning prior to death. Our results suggest that this mortality was ultimately a density-dependent process, exacerbated by low-flow conditions. Given projected effects of climate change on river flows and temperatures, similar events may occur more frequently in parts of the range of salmon where abundances remain high.

Semen quality of threatened native population of Mediterranean brown trout (Salmo cettii, Rafinesque 1810) in the Biferno river (Molise Region - South Italy)

Article

Full-text available

Mar 2016

This research aimed to provide a characterization of fresh semen in wild and threatened Mediterranean brown trout (Salmo cettii), inhabiting the Biferno River basin and to study the variance of sperm parameters in a reproductive system with high male competition. The evaluated sperm quality parameters were: volume, density, viability, motility and sperm movement duration. High variability in sperm traits were found probably in response to the heterogeneity of individual condition, social status, spawning activity and migration costs. Duration of motility was positively correlated (P<0.05) with age class of breeders and motility. Stronger positive correlations (P<0.001) were observed between motility and viability and between sperm counts and viable sperms. This study reported the first data about semen quality of an Italian wild population of native trout. These results are useful for planning efficient artificial fertilization protocols in restoration programs involving supportive breeding together with other innovative conservation strategies as gamete cryopreservation. © Published by Central Fisheries Research Institute (CFRI) Trabzon, Turkey.

Ecological and evolutionary patterns of freshwater maturation in Pacific and Atlantic salmonines

Article

Full-text available

Jan 2014
REV FISH BIOL FISHER

Matthew R. Sloat

Reproductive tactics and migratory strategies in Pacific and Atlantic salmonines are inextricably linked through the effects of migration (or lack thereof) on age and size at maturity. In this review, we focus on the ecological and evolutionary patterns of freshwater maturation in salmonines, a key process resulting in the diversification of their life histories. We demonstrate that the energetics of maturation and reproduction provides a unifying theme for understanding both the proximate and ultimate causes of variation in reproductive schedules among species, populations, and the sexes. We use probabilistic maturation reaction norms to illustrate how variation in individual condition, in terms of body size, growth rate, and lipid storage, influences the timing of maturation. This useful framework integrates both genetic and environmental contributions to conditional strategies for maturation and, in doing so, demonstrates how flexible life histories can be both heritable and subject to strong environmental influences. We also review evidence that the propensity for freshwater maturation in partially anadromous species is predictable across environmental gradients at geographic and local spatial scales. We note that growth is commonly associated with the propensity for freshwater maturation, but that life-history responses to changes in growth caused by temperature may be strikingly different than changes caused by differences in food availability. We conclude by exploring how contemporary management actions can constrain or promote the diversity of maturation phenotypes in Pacific and Atlantic salmonines and caution against underestimating the role of freshwater maturing forms in maintaining the resiliency of these iconic species.

Ecological and Evolutionary Significance of Freshwater Maturation in Pacific and Atlantic Salmonines

Conference Paper

Full-text available

Aug 2012

Populations of some Pacific and Atlantic salmon species contain a mixture of anadromous and non-anadromous individuals. Because of an increased interest in potential demographic and genetic advantages of populations exhibiting mixed migratory strategies, we provide a framework for investigating the ecological and evolutionary significance of freshwater maturation in salmonines. For convenience, we first independently consider hypotheses related to ultimate and proximate factors underlying freshwater maturation. We evaluate several evolutionary hypotheses to explain patterns of freshwater maturation among and within salmonines including phylogenetic history, irreversible evolutionary transitions within species (e.g., vicariance), geographic variation in selective pressures, and contemporary reductions in genetic variability in reactions norms (e.g., effects of domestication selection). Ecological hypotheses for proximate mechanisms underlying freshwater maturation include environmental constraints to freshwater maturation, interspecific interactions, and environmental stochasticity (e.g., dynamic vs. stable environments). We then consider the interaction of ecological and evolutionary processes underlying patterns of freshwater maturation and discuss how they influence demographic and genetic resilience of populations. Our goals are to elucidate patterns of freshwater maturation among and within species of salmonines, identify potential conservation actions that promote population recovery and resiliency by facilitating diversity in life history expression, and identify critical knowledge gaps.

Spawning Site Selection and the Influence of Incubation Environment on Larval Success in Interior Fraser Coho

Article

Crystal J. McRae

Density-dependent habitat selection of spawning Chinook salmon: Broad-scale evidence and implications

Article

Full-text available

Oct 2014
J ANIM ECOL

Matt Falcy

1.An extensive body of theory suggests that density-dependent habitat selection drives many fundamental ecological processes. The ideal free distribution and the ideal despotic distribution make contrasting predictions about the effect of total population size on relative abundances among habitats. Empirical assessment of these habitat selection models is uncommon because data must be collected over large temporal and spatial scales.2.I ask whether fluctuation in Chinook salmon (Oncorhynchus tshawytscha) spawner population size through time leads to different relative densities over space.3.Twenty six years of monitoring data on spawning Chinook salmon across the entire coast of Oregon, USA, were used to evaluate models that make contrasting statements about the interactions of a latent population abundance parameter with physical habitat characteristics.4.There is strong information-theoretic support for models that include terms that allow the spatial variation in density to change as population size changes through time. Analysis of the best model reveals nonlinear isodars, which suggests a “despotic” or “preemptive” distribution of individuals across habitats, indicating that dominant or early arriving individuals exclude others from breeding sites.5.This finding has implications for genetic dynamics, population dynamics, and conservation metrics of these highly valued fish. The novel application of modeling techniques used here to assess mechanisms of habitat selection from observational data can be used in the emerging field of eco-evolutionary dynamics.This article is protected by copyright. All rights reserved.

Optimal reproduction in salmon spawning substrates linked to grain size and fish length

Article

Full-text available

Feb 2014
WATER RESOUR RES

of dollars are spent annually on revitalizing salmon spawning in riverbeds where redd building by female salmon is inhibited by sediment that is too big for fish to move. Yet the conditions necessary for productive spawning remain unclear. There is no gauge for quantifying how grain size influences the reproductive potential of coarse-bedded rivers. Hence, managers lack a quantitative basis for optimizing spawning habitat restoration for reproductive value. To overcome this limitation, we studied spawning by Chinook, sockeye, and pink salmon (Oncorhynchus tshawytscha, O. nerka, and O. gorbuscha) in creeks and rivers of California and the Pacific Northwest. Our analysis shows that coarse substrates have been substantially undervalued as spawning habitat in previous work. We present a field-calibrated approach for estimating the number of redds and eggs a substrate can accommodate from measurements of grain size and fish length. Bigger fish can move larger sediment and thus use more riverbed area for spawning. They also tend to have higher fecundity, and so can deposit more eggs per redd. However, because redd area increases with fish length, the number of eggs a substrate can accommodate is maximized for moderate-sized fish. This previously unrecognized tradeoff raises the possibility that differences in grain size help regulate river-to-river differences in salmon size. Thus, population diversity and species resilience may be linked to lithologic, geomorphic, and climatic factors that determine grain size in rivers. Our approach provides a tool for managing grain-size distributions in support of optimal reproductive potential and species resilience.

Phenotypic variation and selective mortality as major drivers of recruitment variability in fishes

Article

Mar 2014
ECOL LETT

An individual's phenotype will usually influence its probability of survival. However, when evaluating the dynamics of populations, the role of selective mortality is not always clear. Not all mortality is selective, patterns of selective mortality may vary, and it is often unknown how selective mortality compares or interacts with other sources of mortality. As a result, there is seldom a clear expectation for how changes in the phenotypic composition of populations will translate into differences in average survival. We address these issues by evaluating how selective mortality affects recruitment of fish populations. First, we provide a quantitative review of selective mortality. Our results show that most of the mortality during early life is selective, and that variation in phenotypes can have large effects on survival. Next, we describe an analytical framework that accounts for variation in selection, while also describing the amount of selective mortality experienced by different cohorts recruiting to a single population. This framework is based on reconstructing fitness surfaces from phenotypic selection measurements, and can be employed for either single or multiple traits. Finally, we show how this framework can be integrated with models of density-dependent survival to improve our understanding of recruitment variability and population dynamics.

The influence of redd site selection, groundwater upwelling, and over-winter incubation temperature on survival of bull trout ( Salvelinus confluentus ) from egg to alevin

Article

Jan 1999
CAN J ZOOL

Survie embryonnaire du saumon Atlantique (Salmo salar) dans un cours d'eau du sud de son aire de répartition, La Nivelle

Article

Jan 2007

L’évaluation de la survie du saumon Atlantique entre la ponte et l’émergence des alevins hors des graviers est réalisée dans le bassin de la Nivelle dans les domaines accessible (trois tronçons) et non accessible (trois tronçons) aux géniteurs. Pour ce faire, des capsules d’incubation de 12 cm3, contenant des œufs fraîchement fécondés, sont insérées dans des frayères artificielles et naturelles. Le débit et la température de l’eau de surface, l’oxygène dissous des eaux de surface et interstitielle et les caractéristiques granulométriques du substrat des frayères sont contrôlés pendant toute la durée de l’expérience. La survie, de 28,6 % en moyenne dans l’ensemble des sites, est plus élevée dans les tronçons de l’amont (52,7 % dans la Très Haute Nivelle et son affluent, le Lapitxuri) que dans les autres sites, dont ceux actuellement colonisés par l’espèce (21,5 %). Il n’est pas observé de différence de survie entre les frayères artificielles et naturelles. Les mortalités interviennent essentiellement lors des épisodes de crues avant l’éclosion. Une corrélation positive forte existe entre la saturation en oxygène de l’eau interstitielle et la survie. Pour une saturation minimum en oxygène au-dessous de 62 %, la survie reste inférieure à 27 %. En revanche, la composition granulométrique du substrat ne semble pas agir directement sur la survie. Ce facteur n’étant pas corrélé avec l’oxygène dissous, ceci suggère que dans ce cours d’eau, le flux circulant dans les frayères ne provient pas uniquement de l’eau de surface, mais aussi de la nappe alluviale pauvre en oxygène dissous.

Redd superimposition mediates the accuracy, precision, and significance of redd counts for cutthroat trout

Article

Full-text available

Nov 2022

Redd counts are commonly applied to estimate spawning population size for salmonids and allow for broad spatial and temporal coverage in monitoring efforts. However, the utility of redd counts may be compromised by observation error, particularly with respect to superimposition, where later arriving spawners construct redds overlapping existing redds. Here, we provide a mechanistic evaluation of the effects of superimposition on the error structure and biological significance of redd count data for Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) spawning within tributaries to the Snake River, Wyoming. We used a Bayesian framework to parse observation error into distinct components and found low detection of redd clusters (i.e., areas of superimposition) was offset by overestimates of the number of redds per cluster, such that observed counts accurately reflected true redd abundance. However, a saturating relationship between redd counts and spawner abundance indicated that counts are best interpreted as effective reproductive effort rather than spawner abundance. Our results provide a mechanistic understanding of redd count data that can be used to assess their application and interpretation for monitoring.

High egg retention in Chinook Salmon Oncorhynchus tshawytscha carcasses sampled downstream of a migratory barrier

Article

Dec 2021

Barriers in rivers have the potential to severely decrease functional connectivity between habitats. Failure to pass barriers and reach natal spawning habitat may compromise individual reproductive success, particularly for semelparous, philopatric species that rely on free-flowing rivers to reach natal habitat during their once in a lifetime spawning migrations. To investigate the consequences of in-river barriers on fish spawning success, we quantified egg retention and spawning effort (caudal fin wear) in female Chinook Salmon Oncorhynchus tshawytscha carcasses collected downstream of the Whitehorse Hydro Plant on the upper Yukon River and at a nearby free-flowing tributary (Teslin River) from 2018-2020 (~2900 km migrations). Previous studies have demonstrated that a large proportion of fish attempting to reach spawning locations upstream of the hydro plant fail to pass the associated fishway. We estimated nearly all female salmon failing to pass the hydro plant attempted spawning in non-natal habitat downstream, but that these females retained ~34% of their total fecundity, compared to ~6% in females from the free-flowing river. Females downstream of the hydro plant also had lower wear on their caudal fin, a characteristic that was correlated with increased egg deposition. Egg retention did not vary across years with different run sizes, and we propose that egg retention downstream of the hydro plant was not driven by density-dependent mechanisms. Findings from this work indicate that female salmon can still deposit eggs following failed fish passage and failure to reach natal spawning sites, though egg retention rates are considerably higher and uncertainties remain about reproductive success. We encourage researchers to incorporate carcass surveys into fish passage evaluations for semelparous species to fully account for consequences of failed passage. This article is protected by copyright. All rights reserved.

A Review of Salmon Spawner-Recruitment Analysis: The Central Role of the Data and Its Impact on Management Strategy

Article

Sep 2021

Milo D. Adkison

Management of anadromous salmon stocks is usually based on an estimate of the spawner-recruitment relationship. A wide variety of estimation approaches have been developed, from simple to complex, and some worthwhile methodologies and auxiliary data are underutilized. The types and quality of the data available determine the most appropriate assessment methodology and the reliability of the assessment results. The management strategies available and the performance of these strategies are likewise highly dependent on the available data. This review gives an overview of the range of assessment methodologies, from the ad-hoc to hierarchical Bayesian state-space approaches. It emphasizes the central role of data; data types, data deficiencies, auxiliary information such as environmental indices, habitat characteristics, and similar stocks, and the effects of the data on the quality of guidance to managers.

Stability in reproductive timing and habitat usage of Chinook salmon across six years of varying environmental conditions and abundance

Article

Mar 2020

The spatial and temporal distribution of spawning activity by autumn‐run Chinook salmon Oncorhynchus tshawytscha (Walbaum) was examined across multiple years. The study period included two years of extreme drought conditions when water temperatures in the spawning reach of the Stanislaus River were considered sub‐optimal for spawning and egg incubation. Despite varying levels of superimposition, redd counts and densities remained stable and positively associated with river location, indicating that superimposition may be driven by habitat preference rather than the absence of suitable spawning locations. Spawning occurred slightly later during drought years (6–10 days later compared with wetter years). This delay was attributable to deferred migration instead of deferred spawning, and the majority of redds were constructed at water temperatures exceeding the optimal temperature range. As a consequence, estimates of juvenile production during 2014 and 2015 were among the lowest on record. These findings may be related in part to the high hatchery contribution to the population, above‐average temperatures during spawning and incubation, and superimposition rates. Management recommendations include adequate cold‐water storage in the upstream reservoir, refined spawning habitat restoration techniques in the light of superimposition rates and, on a broader system scale, actions that reduce the amount of stray hatchery Chinook salmon.

Spawning Habitat and Nest Depth of Female Dolly Varden Salvelinus malma of Different Body Size

Article

Jan 1995

Spawning habitat and nest depth in relation to female body size were studied in a small population of Dolly Varden Salvelinus malma. Females selected areas where gravel was prevalent and currents were slow for spawning. Neither substrate score, water depth, nor current velocity was significantly correlated with the female body size. Nest depth, however, was strongly correlated with female size. These results suggest that nests made by smaller females are more vulnerable to destruction both from flooding and from nest site reuse by later-spawning females.

Effects of variability in space and time on the production dynamcis of salmonid fishes

Article

Jan 1977

A. F. Tautz

Reproductive behavioral interactions between wild and captively reared coho salmon (Oncorhynchus kisutch)

Article

Dec 1997

Captive rearing is an evolving strategy for restoring depleted salmon populations; it involves capturing wild juvenile salmon from natural streams, rearing them in captivity to adulthood, and then releasing them as adults back into their natal streams to spawn naturally. The conservation benefit of captive rearing is that it bypasses the typically high smolt-to-adult mortality experienced by wild populations, but its success as a restoration strategy depends upon the ability of captively reared salmon to spawn and reproduce in natural streams. In an experimental channel, wild males dominated captively reared males of similar size in 86% of spawning events. Both wild and captively reared females attacked captively reared males more frequently than wild males, indicating a preference for wild over captively reared males, although the interplay between male dominance and female mate choice was unclear. Wild females established nesting territories earlier and constructed more nests per individual than captively reared females of similar size, suggesting a competitive advantage for wild females. Nevertheless, captively reared coho salmon demonstrated the full range of behaviors shown by wild coho salmon of both sexes and the ability to spawn naturally.

Taking Stock: Assessment of Salmon Runs on the North and Central Coasts of BC

Article

Misty MacDuffee sampling chinook and coho fry in a tributary of the Ecstall River. At 85,000 hectares, the Ecstall is the largest unlogged watershed on the North coast. It supports nine species of salmonids which spawn up to 96 km upstream and in more than one dozen of the watershed's tributaries and lakes. 36 The long term survival of salmon depends on maintaining genetic diversity, which in turn depends on adequate numbers of salmon returning to natal spawning grounds. DFO's ability to assess and manage for genetic diversity and nutrient returns were evaluated by posing 3 questions: • Is escapement adequately monitored? • Has DFO met its own target escapements? • Are these escapement targets adequate to sustain ecosystem and predator requirements? Answers to these questions will reveal DFO's successes or failure in managing for genetic diversity and nutrient returns. The most practical way to assess fishery managers' understanding of salmon diversity is to review DFO's own database on salmon presence and trends in river systems. Such information reflects the level of on-the-ground field knowledge of metapopulations and demes. We analyze and discuss the database that contains enumerations of salmon returning to their natal streams, namely DFO's salmon escapement database system (SEDS). Although there are limitations to the SEDS (discussed below), there are no alternative databases for the type of assessment attempted here. DFO attempts to enumerate salmon annually, an enormous undertaking given the size and geography of the north and central coasts, and the multiple species and river systems. Coho, for example, are elusive and can stay in a given river over a long period of time. The size and depth of larger systems and the turbid nature of glacially fed rivers makes observation of fish complicated. Methods used to count fish include permanent fences, observation/visual estimations (creek-walks), fish wheels, aerial counts and swims by divers.

Sensitivity of a salmon population model to alternative formulations and initial conditions

Article

Jul 1996
ECOL MODEL

John M. Bartholow

Salmon populations in many Pacific coast rivers are in serious decline and in danger of becoming threatened or endangered. A fish population model (salmod) that tracks fall chinook salmon has been developed for the Trinity River, California. The model considers the principal environmental factors influencing movement and mortality of young-of-the-year salmon from the time of spawning and egg deposition until they leave freshwater rivers as juveniles. Numbers of salmon produced by alternative managed flow regimes can be estimated using salmod. This paper explores the consequences of alternative model construction and formulation choices on model behavior, and the impact of the number of spawners returning from the ocean on development of a robust flow management decision. Results show that salmod is responsive to the user's choice of spawner nesting behavior (superimposition), but relatively insensitive to spatial scale describing fish rearing habitat quality. The choice of a suitable managed flow regime is sensitive to the number of adult fish returning to spawn and even more so to their distribution throughout the study area at time of spawning. It would be possible to tailor an adaptive annual flow regime based on monitoring of spawner numbers and their distribution.

The relationship between the snowmelt flood and the establishment of non‐native brown trout (Salmo trutta) in streams of the Chitose River, Hokkaido, northern Japan

Article

Oct 2013

Flow regime is one of the major determinants of establishment success for non-native aquatic organisms. Here, we examine the influence of flow variability associated with snowmelt flood on the establishment success of non-native brown trout in 10 streams in northern Japan. We regarded the presence of Age-0 brown trout as the index of the successful establishment. The emergence of Age-0 brown trout in our study region begins in May, a time that overlaps with the occurrence of snowmelt flood. The presence of Age-0 brown trout was negatively associated with flow variability, and it was also negatively associated with summer water temperature. Our results indicate that the non-native brown trout tends to establish in the streams with smaller snowmelt floods and lower summer water temperatures. Brown trout is an invasive, non-native species that is problematic all over the world, and effective management strategies for preventing their further expansion are urgently needed. This study suggests that river managers should recognise that stable streams such as spring-fed streams (i.e., low flow and summer water temperature) and flow-regulated streams, have a higher potential risk of brown trout invasion.

Salmon Life Cycle Considerations to Guide Stream Management: Examples from California's Central Valley

Article

Full-text available

Jun 2013

ABSTrACT A primary goal of the Central Valley Project Improvement Act is to at least double natural pro-duction of Chinook salmon (Oncorhynchus tshawy tscha), in California Central Valley (CV) streams on a sustainable basis. Achievement relies on restora-tion actions that involve both discharge (e.g., dam releases) and non-discharge (e.g., gravel augmenta-tion, screening) components. Annual adult and juve-nile abundance estimates for individual watersheds must be tracked to assess effectiveness of individual actions. However, to date, no substantial efforts have been taken to demonstrate success or deficiencies of their implementations. A major challenge in inter-preting time series of counts at any one life stage is that they reflect the cumulative effects of both fresh-water and marine factors over the full life cycle. To address this issue, we developed a conceptual frame-work based on ratios of the abundance of consecu-tive CV fall-run Chinook salmon life stages and how variation in these ratios tracks key independent vari-ables during the freshwater portion of the life cycle. Model validation with several case studies shows that estimates of previous stage class production cor-relate well with estimated individuals produced in the next class, indicating that transition rates tend to vary within a constrained range, and that monitoring programs generate abundance estimates whose errors are small enough not to swamp out the underlying signal. When selected environmental parameters were added to demonstration models, abundance esti-mates were more closely modeled and several tested relationships between environmental drivers and life-stage transition rates proved consistent across watersheds where data were available. Results from this generalized life-stage conceptual model sug-gest a potential framework for tracking the success of actions meant to improve survival for a given life stage within an individual stream and for determin-ing how successive stages respond to these changes. Though examples are provided for CV Chinook salm-on, these concepts can be applied wherever migratory salmonid populations and associated environmental data are being adequately monitored.

Reproduction du saumon atlantique (Salmo salar L.) en milieu semi-naturel contrôlé

Article

Jan 1983

Un ruisseau artificiel expérimental (chenal de fraie) a été réalisé sur un affluent de la Haute Nivelle au Pays Basque. Le dispositif est caractérisé par un environnement quasi naturel où certains paramètres (débit, profondeur d'eau et vitesse du courant, granulométrie) peuvent être manipulés ou contrôlés. En décembre 1981, 5 couples de Saumon atlantique (Salmo salar L.) introduits dans le chenal ont frayé naturellement. Le nombre de frayères et la surface moyenne occupée par femelle ont été précisés, ainsi que la durée de formation d'une frayère. Des observations ont été faites sur le comportement de reproduction, la répartition des frayères et le taux de surcreusement dans des conditions de densité faible. L'influence de la vitesse du courant et de la température sur le déroulement de la fraie est suggérée. L'estimation de la fécondité et du taux de rétention d'ovules a permis d'évaluer le succès de la reproduction. Les résultats relatifs à la survie pendant l'incubation et aux modalités de l'émergence et de la dévalaison des alevins seront présentés dans un prochain article.

Chinook salmon ( Oncorhynchus tshawytscha ) spawner characteristics in relation to redd physical features

Article

Jul 1983

We studied the spatial pattern and physical characteristics of chinook salmon (Oncorhynchus tshawytscha) redds with respect to length of redd occupancy and when redd construction began. Spawners arriving first deposited their eggs in larger redds constructed in deeper, slower moving water. Redds constructed by late arriving fish were smaller on average and were usually located in relatively shallow, fast-flowing water. Late arriving fish also had a shorter average redd residence time. We suggest that progeny of early arriving spawners may have a selective advantage over progeny of late arriving fish in the same run.

The relative influence of breeding competition and habitat quality on female reproductive success in lacustrine brook trout ( Salvelinus fontinalis )

Article

Dec 2005

Egg losses for female salmonines primarily occur through competition for egg incubation sites (i.e., redds) and the differences in quality among these sites. Through detailed observations and an experiment linking egg survival to groundwater flow, we estimated the relative influence of redd superimposition and habitat quality on female reproductive success for a population of lake-spawning brook trout (Salvelinus fontinalis). Three quarters of all spawning sites were reused by multiple females; however, brood loss was much less (28%-38%) because large females spawned earlier and constructed deeper nests. The relationship between groundwater flow rate and egg survival was not linear, with consistent egg survival occurring only at sites with flows over 20 mL·m-2·min-1. Varying scenarios of redd superimposition and habitat-related egg survival resulted in an estimated 4%-21% of deposited eggs surviving to emergence and greatly reduced the size-related advantages of larger females owing to fecundity. Limited numbers of high-quality spawning sites and overall low survival of eggs resulted in habitat being the dominant route of egg loss. In the absence of female competition, spawning habitat alone accounted for egg losses of 67%-91% and points to the importance of physical habitat features in the maintenance of brook trout populations.

A new method to evaluate egg-to-fry survival in salmonids, trials with Atlantic salmon

Article

Jan 2006

A new method to estimate the survival of salmonids from egg fertilization to fry emergence is described. Fine mesh screen cylindrical capsules, 12 cm3 in volume, filled with batches of 10 eggs of Atlantic salmon Salmo salar were implanted in the substratum using small removable guiding tubes inserted with a metal spike. The method was compared with two other commonly used techniques, capping redds with fry‐traps and fine mesh screen incubation‐emergence boxes buried into the gravel. Egg‐to‐fry survival was recorded for the three methods run in parallel in artificial redds created on three sites of the Nivelle River watershed (south‐west of France), two in the stream and one in an experimental spawning channel. In the channel, survival to the eyed stage and to hatching in capsules and incubation‐emergence boxes was also compared. The implant of capsules proved easier and faster to use than other methods, the structure of the surrounding substratum was less disturbed and the capsules were less vulnerable to spates. This technique provided survival values largely free of the bias induced by other methods and intermediate between that of incubators and of traps.

Spawning characteristics of the anadromous brown trout in a small Swedish stream

Article

Jan 2005

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length (LT) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ± s.d. number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ± s.d. 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ± s.d. 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.

Reproductive timing phenotypes in female salmon: True alternatives or extreme variants?

Article

Dec 2011

Kokanee salmon, Oncorhynchus nerka, can vary in their maturation status at arrival to spawning areas and in their subsequent behaviour. In Meadow Creek, British Columbia, typical 'red-arriving' females arrive with red nuptial coloration, spawn within a few days, and then defend their nests against digup by conspecifics. In contrast, atypical 'silver-arriving' females arrive with scales still present and delay maturation and spawning by 3-4 weeks. Our objective was to further describe the silver-and red-arriving phenotypes and to test the hypothesis that they are proxies for a dimorphism of life cycle variation. Colour was a good indicator of a female's stage of maturity and senescence because silver-arriving females had larger guts, larger and fattier livers, and smaller eggs containing less lean mass than red-arriving females. Colour, and therefore maturity status, covaried with life history traits: silver-arriving females were younger (in 2008 and 2009) and smaller (in 2008) than red-arriving females. The percentage of silver-arriving females was higher in 2009 (11.4%) than in 2008 (2.2%), possibly because of poor conditions for growth in 2009. We also observed some silver-arriving males, but they were much rarer (0.4% in 2008 and 1.5% in 2009). Scores on the first discriminant function based on colour information from digital photographs distinguished silver-arriving and red-arriving females. At the population level, these scores were bimodally distributed, but the dip between modes did not clearly separate silver-and red-arriving females. Although silver-and red-arriving phenotypes represent female reproductive tactics for delivering parental care, they are not distinct alternatives and instead represent the extremes of life cycle variation in this population.

Redd Superimposition and Egg Capacity of Pink Salmon Spawning Beds

Abstract

No full-text available

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