Andrew H. Dittman

Homing and Spawning Site Selection by Supplemented Hatchery- and Natural-Origin Yakima River Spring Chinook Salmon

Abstract It is well known that salmon home to their natal rivers for spawning, but the spatial scale of homing within a river basin is poorly understood and the interaction between natal site fidelity and habitat-based spawning site selection has not been elucidated. Understanding the complex trade-offs among homing to the natal site, spawning site selection, competition for sites, and mate choice is especially important in the context of hatchery supplementation efforts to reestablish self-sustaining natural spawning populations. To address these questions, we examined the homing patterns of supplemented Yakima River spring Chinook salmon Oncorhynchus tshawytscha released from satellite acclimation facilities after common initial rearing at a central facility. Final spawning location depended strongly on where fish were released as smolts within the upper Yakima River basin, but many fish also spawned in the vicinity of the central rearing hatchery, suggesting that some fish imprinted to this site. While...

Sensitization of Olfactory Guanylyl Cyclase to a Specific Imprinted Odorant in Coho Salmon

The role of cGMP in olfactory signaling is not fully understood, but it is believed to play a modulatory role in intracellular signaling in vertebrate olfactory receptor neurons (ORNs). Here, we present evidence that cGMP in ORNs may play an important role in recognition of biologically relevant odors and olfactory learning. Specifically, we investigated the cellular mechanisms underlying olfactory imprinting in salmon. Salmon learn odors associated with their natal site as juveniles and later use these odors to guide their homing migration. This imprinting is believed to involve sensitization of the peripheral olfactory system to specific homestream odorants. We imprinted juvenile salmon to the odorant beta-phenylethyl alcohol (PEA) and examined the sensitivity of olfactory adenylyl and guanylyl cyclases to PEA during development. Stimulation of guanylyl cyclase activity by PEA was significantly greater in olfactory cilia isolated from PEA-imprinted salmon compared with PEA-naive fish only at the time of the homing migration, 2 years after PEA exposure. These results suggest that sensitization of olfactory guanylyl cyclase may play an important role in olfactory imprinting by salmon.

Proximate Composition, Reproductive Development, and a Test for Trade-Offs in Captive Sockeye Salmon

Abstract Energy limitations during reproduction should lead to the evolution of adaptive patterns of energy use and should cause trade-offs in the expression of different traits. We addressed these issues by measuring secondary sexual development, gonad investment, and proximate composition for sockeye salmon Oncorhynchus nerka maturing in captivity. Each of the last 3 months before maturity was characterized by a different pattern of reproductive development and energy use. From June to July, gonad mass increased (1.1% to 5.2% of male body mass; from 1.3% to 2.7% of female body mass), muscle fat decreased (15.1% to 8.6% sex-specific values averaged), and viscera fat decreased (23.9% to 16.7%). From July to August, male gonad mass did not change appreciably, but female gonad mass nearly doubled (to 5.5% of body mass). Muscle fat and viscera fat continued to decrease (to 6.0% and 8.8%, respectively), but muscle protein remained relatively constant. From August to maturity (September–October), female gonad ...

Imprinting of Hatchery-Reared Salmon to Targeted Spawning Locations: A New Embryonic Imprinting Paradigm for Hatchery Programs

Straying by hatchery-reared salmon is a major concern for conservation and recovery of many salmon populations. Fisheries managers have attempted to minimize negative ecological and genetic interactions between hatchery and wild fish by using parr-smolt acclimation facilities to ensure successful olfactory imprinting and homing fidelity. However, the effectiveness of offsite acclimation for returning adults to targeted locations has been mixed. Since laboratory and field studies indicate that the period of hatching and emergence from the natal gravel is a sensitive period for olfactory imprinting, we propose an alternative imprinting approach wherein salmon are exposed as embryos to targeted waters transferred to their rearing hatchery. To test the feasibility of this approach, we conducted a series of electrophysiological and behavioral experiments to determine whether water can be successfully transferred, stored, and treated for pathogens without jeopardizing its chemical integrity. Stream water could ...

A Synthesis of Findings from an Integrated Hatchery Program after Three Generations of Spawning in the Natural Environment

AbstractThe Cle Elum Supplementation and Research Facility in the Yakima River basin, Washington, is an integrated spring Chinook Salmon Oncorhynchus tshawytscha hatchery program designed to test whether artificial propagation can increase natural production and harvest opportunities while keeping ecological and genetic impacts within acceptable limits. Only natural-origin (naturally spawned) fish are used for hatchery broodstock. Spawning, incubation, and early rearing occur at a central facility; presmolts are transferred for final rearing, acclimation, and volitional release at sites adjacent to natural spawning areas, where returning adults can spawn with natural-origin fish. The first wild broodstock were collected in 1997, and age-4 adults have returned to the Yakima River since 2001. An unsupplemented population in the adjacent Naches River watershed provides a reference for evaluating environmental influences. The program has been comprehensively monitored from its inception. A synthesis of findin...

Experimental Evaluation of Adult Spring Chinook Salmon Radio-Tagged during the Late Stages of Spawning Migration

Abstract We conducted an experiment to assess the effects of radio- tagging on adult spring Chinook salmon Oncorhynchus tshawytscha during the late stages of their spawning migration. Fish were captured at Roza Dam, Yakima River, Washington (river kilometer 208). Each fish had a radio tag inserted into the stomach via the esophagus and was then transported to a raceway and held for 50 d to assess survival. In the same raceway we also held a control group that was handled but not tagged and a group with externally attached transmitters. Survival of fish with gastrically implanted radio tags was low (10%), while 70% of controls and 90% of fish with externally mounted tags survived to the end of the experiment. Postmortem dissections revealed that after implantation, some radio tags had migrated from the stomach position to the posterior digestive tract and peritoneum. Fish from all treatments exhibited some level of tissue degeneration of the gastrointestinal tract. Gastric implantation should be used with ...

Combined Effects of Barge Transportation, River Environment, and Rearing Location on Straying and Migration of Adult Snake River Fall-Run Chinook Salmon

AbstractHoming and straying in salmon have been extensively studied, yet it has proven difficult to disentangle the biotic and abiotic factors that influence straying. In the Columbia River basin, some juvenile salmon are collected at dams and transported downstream to increase survival during seaward migration, and as returning adults they experience a range of environmental conditions as they ascend the river. We examined 8 years of PIT tag detection data for hatchery-reared, fall-run Chinook Salmon Oncorhynchus tshawytscha released in the Snake River to evaluate the combined effects of juvenile barging, rearing and release locations, and environmental conditions on adult migration speed and straying below and above the Columbia River–Snake River confluence. Straying to the upper Columbia River was 10–19 times more likely among adults that were barged as juveniles from Snake River dams than among adults that were in-river migrants or that were transported from McNary Dam (below the confluence) as juveni...

Experimental Evidence for Olfactory Imprinting by Sockeye Salmon at Embryonic and Smolt Stages

AbstractAnadromous salmonids have an extraordinary ability to migrate back to their natal streams to spawn as adults, but the mechanisms underlying this ability are not completely known. Many experiments indicate that salmon imprint on natal odors at the smolt stage prior to seaward migration, but the life history and population genetics of some species, notably Sockeye Salmon Oncorhynchus nerka, suggest that imprinting also occurs during the period between hatching and emergence from the gravel as fry. To test the hypothesis that Sockeye Salmon imprint during this period, we exposed juveniles to a mixture of odorants during either the alevin or smolt stage. The smolt exposure group was further divided into different exposure durations (6 weeks, 1 week, and 1 d) to evaluate the duration of odor exposure needed for imprinting during that stage. Imprinting was assessed by testing fish as mature adults in two-choice mazes containing unfamiliar water with and without the mixture of odorants. Fish exposed eith...

Evidence of Olfactory Imprinting at an Early Life Stage in Pink Salmon ( Oncorhynchus gorbuscha )

Pacific salmon (Oncorhynchus spp.) navigate towards spawning grounds using olfactory cues they imprinted on as juveniles. The timing at which imprinting occurs has been studied extensively, and there is strong evidence that salmon imprint on their natal water during the parr-smolt transformation (PST). Researchers have noted, however, that the life histories of some species of Pacific salmon could necessitate imprinting prior to the PST. Juvenile pink salmon (O. gorbuscha) spend less time in fresh water than any other species of Pacific salmon, and presumably must imprint on their natal water at a very young age. The time at which imprinting occurs in this species, however, has not been experimentally tested. We exposed juvenile pink salmon as alevins to phenethyl alcohol (PEA) or control water, reared these fish to adulthood, and then tested their behavioural responses to PEA to determine whether the fish successfully imprinted. We found that pink salmon exposed to PEA as alevins were attracted to the chemical as adults, suggesting that imprinting can occur during this stage. Our finding provides some of the first evidence to support the long-standing belief that imprinting can occur in pink salmon prior to the PST.

Spatial Variability of Chinook Salmon Spawning Distribution and Habitat Preferences

AbstractWe investigated physical habitat conditions associated with the spawning sites of Chinook Salmon Oncorhynchus tshawytscha and the interannual consistency of spawning distribution across multiple spatial scales using a combination of spatially continuous and discrete sampling methods. We conducted a census of aquatic habitat in 76 km of the upper main-stem Yakima River in Washington and evaluated spawning site distribution using redd survey data from 2004 to 2008. Interannual reoccupation of spawning areas was high, ranging from an average Pearson’s correlation of 0.62 to 0.98 in channel subunits and 10-km reaches, respectively. Annual variance in the interannual correlation of spawning distribution was highest in channel units and subunits, but it was low at reach scales. In 13 of 15 models developed for individual years (2004–2008) and reach lengths (800 m, 3 km, 6 km), stream power and depth were the primary predictors of redd abundance. Multiple channels and overhead cover were patchy but were ...