Chinook Salmon Spawning Research Articles

Connecting thiamine availability to the microbial community composition in Chinook salmon spawning habitats of the Sacramento River basin.

Thiamine deficiency complex (TDC) is a major emerging threat to global populations of culturally and economically important populations of salmonids. Salmonid eggs and embryos can assimilate exogenous thiamine, and evidence suggests that microbial communities in benthic environments can produce substantial amounts of thiamine. We therefore hypothesize that natural dissolved pools of thiamine exist in the surface water and hyporheic zones of riverine habitats where salmonids with TDC migrate, spawn, and begin their lives. To examine the relationship between dissolved thiamine-related compounds (dTRCs) and their microbial source, we determined the concentrations of these metabolites and the compositions of microbial communities in surface and hyporheic waters of the Sacramento River, California and its tributaries. Here we determine that all dTRCs are present in femto-picomolar concentrations in a range of critically important salmon spawning habitats. We observed that thiamine concentrations in the Sacramento River system are orders of magnitude lower than those of marine waters, indicating substantial differences in thiamine cycling between these two environments. Our data suggest that the hyporheic zone is likely the source of thiamine to the overlying surface water. Temporal variations in dTRC concentrations were observed where the highest concentrations existed when Chinook salmon were actively spawning. Significant correlations were seen between the richness of microbial taxa and dTRC concentrations, particularly in the hyporheic zone, which would influence the conditions where embryonic salmon incubate. Together, these results indicate a connection between microbial communities in freshwater habitats and the availability of thiamine to spawning TDC-impacted California Central Valley Chinook salmon.IMPORTANCEPacific salmon are keystone species with considerable economic importance and immeasurable cultural significance to Pacific Northwest indigenous peoples. Thiamine deficiency complex has recently been diagnosed as an emerging threat to the health and stability of multiple populations of salmonids ranging from California to Alaska. Microbial biosynthesis is the major source of thiamine in marine and aquatic environments. Despite this importance, the concentrations of thiamine and the identities of the microbial communities that cycle it are largely unknown. Here we investigate microbial communities and their relationship to thiamine in Chinook salmon spawning habitats in California's Sacramento River system to gain an understanding of how thiamine availability impacts salmonids suffering from thiamine deficiency complex.

Distribution and straying of minijack Chinook Salmon released from a captive broodstock hatchery program

AbstractObjectiveProduction of Chinook Salmon Oncorhynchus tshawytscha in hatcheries can unintentionally produce large numbers of age‐1 males, termed "minijacks," which pose ecological and genetic risks to target and nontarget populations. We evaluated the postrelease distribution of minijacks produced in a hatchery captive broodstock program targeting the White River in the Columbia River basin between 2010 and 2015.MethodsFish were passive integrated transponder (PIT)‐tagged in the hatchery (n = 218,555), and databases were searched to determine movement behavior and final detections on fixed PIT tag antenna arrays during the year in which they were released.ResultTwo main movement behaviors were detected: (1) residuals, which moved solely within the subbasin of release; and (2) migrants, which moved downstream into the Columbia River and then reascended the Columbia River in the year of release. Minijacks that reascended fish ladders in the Columbia River were most often detected at Rock Island and Bonneville dams, the nearest and furthest detection locations downstream of the Wenatchee River. Minijacks were last detected in all locations where spring Chinook Salmon spawn in the Wenatchee River subbasin (seven tributaries and one main‐stem area) and also in the Entiat River (an adjacent watershed); minijacks in eight of the nine locations were considered strays. Estimates of minijacks that strayed outside of the White River were between 61% and 100% annually and were influenced by release location. Minijacks were also more abundant than males of all older ages in some of the tributaries during some years. In addition, they were detected in these tributaries during periods when anadromous adults migrate into spawning areas and when spring Chinook Salmon spawn.ConclusionThe large amount of minijack production and the spatial and temporal overlap could pose genetic and ecological risks to both target and nontarget populations and particularly high straying poses risks to the maintenance of between‐population genetic variability.

Chinook Salmon habitat evolution following river restoration, drought, and flood

How rivers restored for aquatic biota such as Pacific Salmon (Oncorhynchus spp.) will evolve under shifting management and climate regimes is unknown. To inform this, we tracked the evolution of a highly impacted, regulated river reach following habitat restoration and subsequent drought and flood hydrology using a suite of data to better understand how created habitat evolves over time. Topographic change detection, riffle creation and persistence, substrate, and Chinook Salmon spawning and rearing habitat were evaluated for the three epochs. Sediment transport regimes and velocity outputs from the numerical flow model were used to interpret channel change associated with the flood season the site experienced. Salmon spawning observations and habitat suitability modeling demonstrated that habitat improved following restoration for both salmon spawning and rearing. Chinook Salmon spawning activity and the relative site utilization compared to escapement increased post Project. These benefits were largely maintained during drought and flood events, despite an absence of upstream coarse sediment supply. We hypothesize this was because the restoration design incorporated riffle-pool maintenance theories and the use of emergent islands that served as a local sediment source. Extrapolations of bioturbation by spawners suggest that if population targets for the river are met, topographic change due to spawning activity could exceed that caused by river flow under drought conditions and provide a modest contribution during flood years. Thus, this study demonstrates that river restoration can not only improve physical habitat, but also engage ecosystem engineers such as spawning salmonids to contribute to future habitat evolution.

Evaluating the Sensitivity of Multi‐Dimensional Model Predictions of Salmon Habitat to the Source of Remotely Sensed River Bathymetry

AbstractMulti‐dimensional numerical models are fundamental tools for investigating biophysical processes in aquatic ecosystems. Remote sensing techniques increase the feasibility of applying such models at riverscape scales, but tests of model performance on large rivers have been limited. We evaluated the potential to develop two‐dimensional (2D) and three‐dimensional (3D) hydrodynamic models for a 1.6‐km reach of a large gravel‐bed river using three sources of remotely sensed river bathymetry. We estimated depth from hyperspectral image data acquired from conventional and uncrewed aircraft and multispectral satellite imagery. Our results indicated that modeled water depth errors were similar between 2D and 3D models, with depth residuals that were comparable to the uncertainty associated with the bathymetry used as input. We found good agreement between measured and modeled depth‐averaged velocities generated by 2D and 3D models, while 3D models provided superior predictions of near‐bed velocities. We found that optimal model performance occurred for lower flow resistance values than previously reported in the literature, possibly as a consequence of the high‐resolution bathymetry used as model input. Model predictions of winter‐run Chinook salmon (Oncorhynchus tshawytscha) spawning and rearing habitat were not sensitive to the source of bathymetric information, but bioenergetic predictions related to adult holding costs were influenced by the input bathymetry. Our results suggest that hyperspectral imagery acquired from piloted and/or uncrewed aircraft can be used to map the bathymetry of clear‐flowing, relatively shallow large rivers with sufficient accuracy to support multi‐dimensional flow model development; models developed from multispectral satellite imagery had more limited predictive capability.

Chinook and Coho salmon hybrids linked to habitat and climatic changes on Vancouver Island, British Columbia.

Between 2013 and 2019, 63 presumed Chinook salmon Oncorhynchus tshawytscha sampled primarily in the Strait of Georgia (0.63% of total sample) were identified as potential Chinook–Coho (Oncorhynchus kisutch) hybrids by the presence of anomalous microsatellite genotypes. Their hybrid origin was confirmed by single nucleotide polymorphism amplification of two species‐specific amplicons. Mitochondrial DNA indicated that most of these fish resulted from the hybridization of Coho salmon females and Chinook salmon males. Although no diagnostic external features were identified, several individuals displayed an abnormal scale arrangement on the caudal peduncle. One hybrid juvenile examined for meristics exhibited a pyloric caeca count intermediate between published values for Chinook and Coho salmon. Most hybrids originated in the Cowichan River during the 2014 brood year. Their prevalence in the watershed is a naturally occurring event, likely exacerbated by prolonged low water levels which limit habitat and delay Chinook salmon spawning, in addition to the differential abundance of the parental species. This research is the first to document ongoing natural hybridization (Chinook–Coho salmon crosses) and link it to habitat and climatic changes, and includes the identification of eight F1 adults and two juvenile backcross or F2 hybrids. The potential negative impacts of hybridization, particularly in Coho salmon through potential introgression, warrant hybrid identification as an ecosystem monitoring tool within a survey program.

Effects of Two Activated Milt Residence Times on Landlocked Fall Chinook Salmon Egg Survival to the Eyed Stage of Development

AbstractDuring salmonid spawning, the amount of time required for activated milt to successfully fertilize eggs has not been well defined. This study examined the effects of two different activated milt residence times, 20 and 60 s, during production‐scale artificial spawning of 20 landlocked fall Chinook Salmon Oncorhynchus tshawytscha. Mean (SE) survival to the eyed stage of egg development was 29.2% (5.5) in the eggs that were subjected to the 20‐s milt residence time, which was not significantly different from the 32.3% (5.7) survival rate for eggs with the 60‐s residence time. There was considerable variation in egg survival among the individual female spawns, ranging from near 0% to 76.7%. These production‐scale results indicate that activated milt residence times as low as 20 s can be used during the landlocked fall Chinook Salmon spawning, with no significant effect on egg survival to the eyed stage of development.

Some (fish might) like it hot: Habitat quality and fish growth from past to future climates

Current expectation is that projected climate change may have adverse effects on fish habitats and survival. The analysis leading to these concerns is typically done at large scale with limited possibility to quantify the local biological response and compare with previous conditions. Our research investigated the effects of recorded climate conditions on Chinook salmon (Oncorhynchus tshawytscha) spawning and rearing habitats and growth responses to the local climate and compared those conditions to predicted responses to a climate change. The study site was a 7 km long reach of Bear Valley Creek, an important spawning stream for this US Endangered Species Act listed species, in the Pacific Northwest of United States. We used 2D numerical modeling supported by accurate, high-resolution survey data to calculate flow hydraulics at various discharges from base to bankfull flows. For past and future conditions, computed flow hydraulics were combined with habitat suitability indices (SI) to compute spawning and rearing habitat suitability. Information on habitat suitability along with fish density and stream water temperature informed a growth model to quantify the potential fish size, an index of survival rates and fitness. Our results indicate that yearly-averaged rearing habitat quality remains similar to historic, but the timing of high- and low-quality habitat periods shift within the calendar year. Future spawning habitat quality may be significantly reduced during the seasonal period to which Chinook have currently adapted their spawning behavior. The growth model indicates an increase in anticipated size of Chinook salmon for predicted future climate conditions due to water temperature increase. Consequently, future climate conditions may have a substantial negative impact on spawning and limited impact on rearing conditions due to flow reduction and thus quality and extent of available habitat. However, the expected warmer stream water temperatures may benefit rearing, because of increased fish size in these high elevation cold-water streams.

Estimates of Chinook Salmon Spawning Habitat in a Blocked Reach of the Columbia River Upstream of Grand Coulee Dam

Spawning habitat of Chinook salmon (Oncorhynchus tshawytscha) was estimated upstream of Grand Coulee Dam to support the feasibility evaluations of reintroducing anadromous salmon to this blocked reach of the Columbia River. A two-dimensional depth-averaged hydrodynamic model was developed for a 76-km reach between Kettle Falls, Washington, and the US-Canada international border and used to predict water velocities and depths at 10%, 50%, and 90% flow exceedance values. Hydrodynamic model outputs were combined with calculated bed slopes and empirical and modeled data on substrate availability to estimate salmon spawning habitat availability. A probabilistic spawning model was developed to estimate suitability for spawning salmon based on habitat characteristics at the exceedance flow levels and three substrate classifications. A majority of the highest probability salmon spawning habitat was located between Northport, Washington, and the international border. The model predicted 17.6 ha of spawning habitat at the 50% exceedance flow level for areas with pebble and cobble substrates; this equates to an approximate redd capacity of 2,893 to 4,091 non-overlapping redds, depending on mean redd size. Estimated capacity of spawning adults ranged from 5,786 (assuming two fish per redd and lowest number of redds) to 32,728 (assuming eight fish per redd at highest number of redds). We conclude that suitable Chinook salmon spawning habitat is available upstream of Grand Coulee Dam. The results of this study will be useful to fisheries managers considering salmon reintroduction and ecosystem function in various processes including the modernization of the Columbia River Treaty, the Northwest Power and Conservation Council's Fish and Wildlife Program, and tribal and other natural resource conservation initiatives.

Escapement of Broodstock Chinook Salmon From Whitlock Bay Spawning Station, Lake Oahe, South Dakota

Feral spawning fall Chinook salmon (Oncorhynchus tshawytscha) in Lake Oahe, South Dakota, are captured using a fish ladder and catch raceway at Whitlock Bay Spawning Station. The number of salmon that escaped the catch raceway and descended the fish ladder prior to spawning was unknown. During October 2017, all salmon that ascended the fish ladder at the spawning station were tagged. Tagged males remained in the catch raceway. Tagged females were moved to other secure raceways and used to estimate tag retention. Of the 383 tagged males, 159 (41.5%) were initially designated as escaped from the catch raceway. Tag loss in the females was 3.9%. Thus, the estimated male salmon escapement rate from the catch raceway was 37.6%. Male salmon remained in the catch raceway for one-to-three days before escaping. The escapement rate decreased over the month-long spawn, with nearly 60% of the males going back down the fish ladder in the first week of October, compared to less than 20% escapement by the final week. Such high rates of escapement from the spawning station may be negatively impacting the spawning efficiencies. Possible solutions include re-engineering of the fish ladder or daily removal of the salmon in the catch raceway to other more secure locations at the spawning station.

In a warming river, natural-origin Chinook salmon spawn later but hatchery-origin conspecifics do not

Median timing of reproduction in salmonid populations is generally consistent among years, reflecting long-term patterns of natural selection from characteristics of the local environment. However, altered selection from factors related to climate change or human intervention might shift timing over generations, with implications for the population’s persistence. To study these processes, we modeled median timing of redd (nest) counts as an index of spawning timing by natural-origin Chinook salmon (Oncorhynchus tshawytscha) in the Skagit River system in Washington State, USA. Over the last 2–6 decades, natural-origin salmon have been spawning later by 0.03–0.52 days·year–1, while a naturally spawning group that is influenced by strays from a hatchery has been spawning earlier by 0.19 days·year–1. Trends in the spawning timing of hatchery-origin strays may reflect opposing selection from the hatchery, where egg take for propagation has become earlier by 0.58 days·year–1. As mean August river temperatures have risen over the period of record, hatchery timing trends may be moving in the opposite direction from the plastic or adaptive patterns expressed by natural-origin fish.

Effect of Activated Milt Residence Time on Landlocked Fall Chinook Salmon Egg Survival

During artificial spawning of salmonids, activated sperm is allowed to remain in contact with eggs for variable durations. This study examined multiple residence times (20, 40, 60, 90, or 120 seconds) for activated sperm on landlocked fall Chinook salmon (Oncorhynchus tshawytscha) eggs during spawning. There was no significant difference in egg survival to the eyed-stage of development or to hatch among any of the treatments, with a mean (SE) percent survival to the eyed stage of 63.9 (5.8). These results indicate that only relatively short residence times of activated milt on eggs during landlocked fall Chinook salmon spawning are needed to ensure egg survival, resulting in potentially substantial reductions in production-level spawning times and associated labor costs.

Physical Controls on Salmon Redd Site Selection in Restored Reaches of a Regulated, Gravel‐Bed River

AbstractLarge‐scale river restoration programs have emerged recently as a tool for improving spawning habitat for native salmonids in highly altered river ecosystems. Few studies have quantified the extent to which restored habitat is utilized by salmonids, which habitat features influence redd site selection, or the persistence of restored habitat over time. We investigated fall‐run Chinook salmon spawning site utilization and measured and modeled corresponding habitat characteristics in two restored reaches: a reach of channel and floodplain enhancement completed in 2013 and a reconfigured channel and floodplain constructed in 2002. Redd surveys demonstrated that both restoration projects supported a high density of salmon redds, 3 and 14 years following restoration. Salmon redds were constructed in coarse gravel substrates located in areas of high sediment mobility, as determined by measurements of gravel friction angles and a grain entrainment model. Salmon redds were located near transitions between pool‐riffle bedforms in regions of high predicted hyporheic flows. Habitat quality (quantified as a function of stream hydraulics) and hyporheic flow were both strong predictors of redd occurrence, though the relative roles of these variables differed between sites. Our findings indicate that physical controls on redd site selection in restored channels were similar to those reported for natural channels elsewhere. Our results further highlight that in addition to traditional habitat criteria (e.g., water depth, velocity, and substrate size), quantifying sediment texture and mobility, as well as intragravel flow, provides a more complete understanding of the ecological benefits provided by river restoration projects.

Identification of Summer‐Run Chinook Salmon Spawning Areas in the Main‐Stem Columbia River Upstream of Wells Dam, Washington

AbstractSummer‐run Chinook Salmon Oncorhynchus tshawytscha historically spawned in the Columbia River as far upstream as British Columbia, Canada, but the upstream extent of main‐stem spawning in the contemporary Columbia River has been documented in the tailrace of Wells Dam, Washington. We utilized radiotelemetry and video monitoring equipment between 2011 and 2013 to track wild summer‐run Chinook Salmon upstream of Wells Dam and document any main‐stem spawning sites. Two small spawning areas totaling 3,389 m2 were identified within 1.76 km downstream of Chief Joseph Dam and were used by spawning salmon in each year of the study. Redd deposition totaled 70, 59, and 134 redds in 2011, 2012, and 2013, respectively. When considered with tributary redd counts upstream of Wells Dam from the Methow and Okanogan rivers, main‐stem spawning represented between 1.6% and 2.9% of the annual redd deposition upstream of Wells Dam within each spawning year. Redds were located in depths between 3.7 and 7 m, with spawning occurring between late October and mid‐November in each year. These novel results are the first to detail main‐stem spawning locations of summer‐run Chinook Salmon upstream of Wells Dam and should inform population monitoring metrics, such as annual escapement and prespawn mortality estimates.

Timing of Landlocked Fall Chinook Salmon Spawning and Egg Survival

Landlocked fall Chinook salmon (Oncorhynchus tshawytscha) in Lake Oahe, South Dakota, USA return to a remote spawning station either already having ovulated (ripe) or with the eggs still retained in the ovary (green).

Egg Viability and Egg‐to‐Fry Survival of Captive‐Reared Chinook Salmon Released to Spawn Naturally

AbstractConservation hatchery strategies for anadromous salmonids are designed to boost depressed wild populations while conserving genetic resources. Captive rearing is an approach in which eggs or juveniles are collected from wild fish, taken into a hatchery and reared to maturation, and then released to spawn. In this study, we quantified spawn timing and redd production for captive‐reared and wild Chinook Salmon Oncorhynchus tshawytscha and measured survival of eggs to the eyed stage of development (egg viability) and from egg to fry. The study objective was to determine whether there was a difference in egg viability and egg‐to‐fry survival between captive‐reared and wild Chinook Salmon that spawned in the wild. During 2007–2009, 90 redds were sampled in the East Fork Salmon River, Idaho; 45 of captive‐origin salmon and 45 of wild origin. Egg viability was significantly lower for captive‐reared fish (75.0%) than for their wild counterparts (95.6%). The overall mean egg‐to‐fry survival for captive‐reared fish was quite high (80.4%), and although it was significantly lower than that for wild fish (84.0%), biologically this survival difference was not large. While others have estimated the egg‐to‐fry survival of production hatchery Chinook Salmon in the wild, it had not previously been estimated for captive‐reared fish released to spawn. Through the use of novel techniques such as hydraulic pumping and egg capsules, we were able to successfully estimate egg viability and egg‐to‐fry survival of captive‐reared and wild Chinook Salmon spawning in the wild. Although egg viability and egg‐to‐fry survival of captive‐reared fish was lower than for their wild counterparts, both survival rates may be sufficient to provide a demographic benefit to the receiving wild population.

Catalog of Chinook Salmon Spawning Areas in Yukon River Basin in Canada and United States

Abstract Chinook Salmon Oncorhynchus tshawytscha return to the Yukon River in northwestern North America each summer, migrating to spawning destinations from the lower river to more than 3,000 km upstream. These returns support numerous fisheries throughout the basin. Despite a long history of fisheries research and management, there is no comprehensive account of Chinook Salmon spawning areas in the basin. To address this issue, we cataloged, summarized, and mapped the known spawning areas of Yukon River Chinook Salmon by using a variety of sources including published articles, gray literature, and information archived in agency databases. Most of our sources were published within the past 30 y, but some refer to observations that were recorded as long ago as the late 1800s. We classified spawning areas as major or minor producers with three indicators of abundance: 1) quantitative estimates of escapement (major producer if ≥500 fish, minor producer if <500 fish), 2) radiotelemetry-based proportions of annual production (major producer if ≥1% of the run, minor producer if <1% of the run), and 3) aerial survey index counts (major producer if ≥165 fish observed, minor producer if <165 fish observed). We documented 183 spawning areas in the Yukon River basin, 79 in the United States, and 104 in Canada. Most spawning areas were in tributary streams, but some were in main-stem reaches as well. We classified 32 spawning areas as major producers and 151 as minor producers. The Chinook Salmon spawning areas cataloged here provide a baseline that makes it possible to strategically direct abundance, biological sampling, and genetics projects for maximum effect and to assess both spatial and temporal changes within the basin.

Ovarian fluid impacts flagellar beating and biomechanical metrics of sperm between alternative reproductive tactics.

Alternative reproductive tactics (ARTs) are prevalent in nature, where smaller parasitic males typically have better sperm quality than larger territorial guard males. At present, it is unclear what is causing this phenomenon. Our objective was to gain insights into sperm form and function by examining flagellar beating patterns (beat frequency, wave amplitude, bend length, bend angle, wave velocity) and biomechanical sperm metrics (velocity, hydrodynamic power output, propulsive efficiency) of wild spawning Chinook salmon ARTs. Ovarian fluid and milt were collected to form a series of eight experimental blocks, each composed of ovarian fluid from a unique female and sperm from a unique pair of parasitic jack and guard hooknose males. Sperm from each ART were activated in river water and ovarian fluid. Flagellar parameters were evaluated from recordings using high-speed video microscopy and biomechanical metrics were quantified. We show that ART has an impact on flagellar beating, where jacks had a higher bend length and bend angle than hooknoses. Activation media also impacted the pattern of flagellar parameters, such that beat frequency, wave velocity and bend angle declined, while wave amplitude of flagella increased when ovarian fluid was incorporated into activation media. Furthermore, we found that sperm from jacks swam faster than those from hooknoses and required less hydrodynamic power output to propel themselves in river water and ovarian fluid. Jack sperm were also more efficient at swimming than hooknose sperm, and propulsive efficiency increased when cells were activated in ovarian fluid. The results demonstrate that sperm biomechanics may be driving divergence in competitive reproductive success between ARTs.

The role of density-dependent and -independent processes in spawning habitat selection by salmon in an Arctic riverscape.

Density-dependent (DD) and density-independent (DI) habitat selection is strongly linked to a species’ evolutionary history. Determining the relative importance of each is necessary because declining populations are not always the result of altered DI mechanisms but can often be the result of DD via a reduced carrying capacity. We developed spatially and temporally explicit models throughout the Chena River, Alaska to predict important DI mechanisms that influence Chinook salmon spawning success. We used resource-selection functions to predict suitable spawning habitat based on geomorphic characteristics, a semi-distributed water-and-energy balance hydrologic model to generate stream flow metrics, and modeled stream temperature as a function of climatic variables. Spawner counts were predicted throughout the core and periphery spawning sections of the Chena River from escapement estimates (DD) and DI variables. Additionally, we used isodar analysis to identify whether spawners actively defend spawning habitat or follow an ideal free distribution along the riverscape. Aerial counts were best explained by escapement and reference to the core or periphery, while no models with DI variables were supported in the candidate set. Furthermore, isodar plots indicated habitat selection was best explained by ideal free distributions, although there was strong evidence for active defense of core spawning habitat. Our results are surprising, given salmon commonly defend spawning resources, and are likely due to competition occurring at finer spatial scales than addressed in this study.

Habitat Use and Arrival Timing of Hatchery and Naturalized Chinook Salmon Spawning in a Great Lakes Tributary

AbstractLarge‐scale stocking programs have been used to introduce and maintain Chinook Salmon Oncorhynchus tshawytscha fisheries in the Laurentian Great Lakes since the late 1960s, with discoveries of naturalized populations in tributaries soon after the initial introduction. Characterizing ecological differences between hatchery and naturalized Chinook Salmon is becoming increasingly important for sustainable management of this species. We hypothesized that nonheritable traits (i.e., homing) and artificial selection might result in different habitat use and arrival timing between rearing origins occupying the same river, with the potential for reproductive isolation and divergence of naturalized and hatchery strains. In 2010 and 2011, using visual observations and PIT tags, we tracked individual hatchery and naturalized Chinook Salmon that spawned in the Sydenham River (Owen Sound, Ontario), one of the first tributaries in Lake Huron to be colonized by hatchery strays and establish a naturalized population. We estimated that 52–58% of the 3,200–3,300 fish returning to spawn in 3.5 km of accessible spawning habitat were hatchery fish. In females, the extent of prespawning movement increased with arrival date, decreased with fish length, and was lower for hatchery fish. Hatchery females also displayed a higher probability of direct homing to the stocking site than naturalized females. Prespawning movements by males were extensive but did not depend on rearing origin, arrival timing, or body size. We found no evidence of reproductive isolation, however. Spatial distributions of spawning locations were independent of rearing origin for both sexes, and arrival timing in the river was similar between rearing origins for both sexes. The lack of reproductive isolation is likely attributable to the small area of suitable habitat in this river. Our study represents the first comprehensive comparison of spawning habitat use and timing by hatchery and naturalized Chinook Salmon in the Great Lakes.Received October 26, 2016; accepted February 22, 2017 Published online April 24, 2017

Measuring the potential influence of cooking on the carbon and nitrogen isotopic composition of spawning Chinook salmon

This study considers the effect of heat treatment (cooking) on muscle tissue from modern spawning Alaskan Chinook salmon (Oncorhynchus tshawytscha) and implications for archaeological dietary reconstructions. Here, it is demonstrated that cooking, potentially through exposure to lighter volatiles present in wood smoke, significantly alters the stable carbon (δ13C) isotopic composition of muscle tissue, though the difference may be too slight (−0.50‰) to be incorporated into dietary mixing models. Cooking produces no significant change in nitrogen (δ15N) values. Additionally, this study identifies significant differences in stable nitrogen (δ15N) and carbon (δ13C) isotopic values between previous studies on coastal adult Chinook salmon and the spawning adult Chinook salmon from Central Alaska analyzed in this study, emphasizing the importance of employing isotopic data from local fauna in dietary reconstructions. The data presented here have implications not only for our understanding of general salmon ecology, but also for refining archaeological reconstructions of prehistoric diet in Central Alaska and other regions where smoke-preserved tissue was regularly consumed.