John E. Joyce

A comparison of genetic variation between an anadromous steelhead, Oncorhynchus mykiss, population and seven derived populations sequestered in freshwater for 70 years

In 1926 cannery workers from the Wakefield Fisheries Plant at Little Port Walter in Southeast Alaska captured small trout, Oncorhynchus mykiss, from a portion of Sashin Creek populated with a wild steelhead (anadromous O. mykiss) run. They planted them into Sashin Lake which had been fishless to that time and separated from the lower stream by two large waterfalls that prevented upstream migration of any fish. In 1996 we sampled adult steelhead from the lower creek and juvenile O. mykiss from an intermediate portion of the creek, Sashin Lake, and five lakes that had been stocked with fish from Sashin Lake in 1938. Tissue samples from these eight populations were compared for variation in: microsatellite DNA at 10 loci; D-loop sequences in mitochondrial DNA; and allozymes at 73 loci known to be variable in steelhead. Genetic variability was consistently less in the Sashin Lake population and all derived populations than in the source anadromous population. The cause of this reduction is unknown but it is likely that very few fish survived to reproduce from the initial transplant in 1926. Stockings of 50–85 fish into five other fishless lakes in 1938 from Sashin Lake did not result in a similar dramatic reduction in variability. We discuss potential explanations for the observed patterns of genetic diversity in relation to the maintenance of endangered anadromous O. mykiss populations in freshwater refugia.

Fine‐scale temporal adaptation within a salmonid population: mechanism and consequences

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.

Variation of Morphology among Juvenile Chinook Salmon of Hatchery, Hybrid, and Wild Origin

Abstract Body morphology differed significantly between juvenile hatchery Chinook salmon Oncorhynchus tshawytscha that have experienced five generations of hatchery culture and juveniles derived from the wild founding stock and cultured in the same environment. All lines tested were raised in a similar hatchery environment. Thin-plate spline analysis was used to characterize the morphometric variation among these lines of fish. Hatchery fish had a more compressed body, a narrower head, shorter maxillae, and a longer and narrower caudal peduncle than wild fish. Canonical discriminant analysis was able to correctly classify 88% of hatchery fish and 90% of wild fish. Second-generation hybrids of the two lines were morphologically intermediate to but significantly different from both the hatchery and wild lines, and they appeared to be more similar to the wild line. These results suggest that the differences observed between lines are largely genetic in origin and may be a result of the divergence of the hatc...

Small Vertical Raceways for Rearing Juvenile Salmon

Abstract We describe a micro-vertical raceway, a small floating container, for rearing small populations of fish. The container is a 170.6-L polyethylene drum fitted to a controlled water supply. An array of these containers was used to rear juvenile salmon simultaneously in 60 groups (200 fish each) to 6.0-g size. We compared growth rates of juvenile chinook salmon (Oncorhynchus tshawytscha) reared in these containers with those reared in large (70.8-m3) vertical raceways and conclude that micro-vertical raceways do not adversely affect fish growth.

The Effects of Stock and Prerelease Marine Net-Pen Culture on Survival to Adulthood, Age at Maturity, and Fisheries Contribution for Three Stocks of Chinook Salmon in Southeast Alaska

Abstract Three stocks of juvenile stream-type Chinook salmon Oncorhynchus tshawytscha were evaluated as part of an ocean ranching and broodstock development program at Little Port Walter, Southeast Alaska. Fish were either cultured in freshwater throughout the presmolt period or moved to marine net-pens with an artificial freshwater lens for five periods (2–210 d); all fish were released on the same day. The fish were tagged with coded wire tags to determine the effect, if any, of stock and duration of marine net-pen culture on precocity, fishery contribution, survival to adulthood, and size in the commercial fisheries relative to traditional freshwater culture. Recoveries of tagged fish in the fisheries and at the hatchery weir indicated significant overall effects of stock on marine survival; the Unuk stock survived better than the Chickamin and King Salmon stocks. Culture overwinter in marine net-pens produced higher survival to adulthood in all stocks but also resulted in higher mortality during cultu...

Successful Maturation and Spawning of Captive Chinook Salmon Brood Stock

Abstract Brood stock of chinook salmon (Oncorhynchus tshawytscha) cultured from egg to maturity had low prespawning mortality and highly viable offspring when fed a formulated brood diet and matured in a seawater net-pen with a surface freshwater lens. The brood fish were cultured in freshwater raceways as fry, reared in seawater net-pens from the juvenile (4.7 g) stage until 2 months before spawning, and then transferred into the seawater net-pen modified with a 1-m-thick freshwater lens. Diet was changed 12 months before spawning from a basic formulated commercial diet to a commercial brood-fish diet. The average egg viability to the eyed stage (72% for the progeny of nine females, each crossed with a single male) compared favorably with that of anadromous fish produced at the same facility. Although cultured fish matured younger and smaller, and thus produced smaller eggs and fry, than did wild or anadromous fish of the same stock, juvenile size did not differ after 6 months of freshwater rearing.

Growth and Survival of Alaska Stream-Type Chinook Salmon Cultured in Estuarine Net-Pens or Freshwater Raceways

Abstract The overwinter survival and growth and the subsequent marine survival of stream-type chinook salmon Oncorhynchus tshawytscha were compared between fish cultured in marine net-pens and their siblings cultured in freshwater. The net-pens were suspended in a stratified estuary with a low-salinity lens; the lens provided osmotic relief to the fish, and its depth and salinity varied seasonally. The median overwinter survival for chinook salmon from six brood years was 89.1% for the net-pen groups, significantly (P = 0.009) less than the median survival of 99.0% in freshwater. The median overwinter growth rate was 0.5% of body weight/d for the net-pen groups, significantly (P = 0.013) higher than the median growth rate of 0.2% for freshwater groups. The median marine survival of smolts from net-pen and freshwater groups was similar, 5.6% and 5.3%, respectively. These results demonstrate that juvenile stream-type chinook salmon can be cultured successfully over winter from the subyearling to smolt stage...