William R. Heard

Comment: A Review of the Hatchery Programs for Pink Salmon in Prince William Sound and Kodiak Island, Alaska

Recently, Hilborn and Eggers (2000) have asserted that hatcheries in Prince William Sound (PWS), Alaska, have caused a decline in the productivity of wild pink salmon Oncorhynchus gorbuscha in PWS and that hatchery fish to a large degree have replaced, not enhanced, pink salmon returns. Pink salmon catches in PWS are currently at historic highs, averaging 27 million fish per year over the past decade. Over 85% of the harvest is from a system of large hatcheries (Pinkerton 1994; McNair 2000). There is concern that hatchery production may have been deleterious to wild pink salmon in PWS, complicating management and the achievement of escapement goals and reducing productivity (e.g., Tarbox and Bendock 1996). Hilborn and Eggers estimate that more than 90% of the recent annual production would have been attained by wild stocks alone in the absence of hatchery production. We, however, find compelling evidence that hatchery fish have greatly increased the total pink salmon harvest in PWS and that Hilborn and Eggers’s estimates of wild stock productivity in the hypothetical absence of hatchery fish are not credible. While countervailing trends in the abundance of wild and hatchery pink salmon in PWS superficially appear to support Hilborn and Eggers’s arguments, careful consideration of the evidence indicates that the program has had substantial net benefits. We address three central points of the Hilborn and Eggers paper: (1) that retrospective analysis indicates that the proportional increases in pink salmon production in PWS have been similar to those in regions of Alaska without major hatcheries, on the basis of which Hilborn and Eggers conclude there is no evidence from between-region comparisons that the large increases in the catch in PWS were due to hatcheries; (2) that, because wild stock productivity is correlated negatively with the magnitude of fry releases from hatcheries, wild stock fish would have produced more than 90% of the current record runs in PWS in the absence of hatcheries; and (3) that wild stock escapements (i.e., the number of reproducing wild salmon) have declined due to deleterious interactions with salmon released from hatcheries. Proportionality Argument

Early male maturity in two stocks of chinook salmon (Oncorhynchus tshawytscha) transplanted to an experimental hatchery in southeastern Alaska

Progeny of 1976-brood chinook salmon (Oncorhynchus tshawytscha) from the Chickamin and Unuk rivers in southeastern Alaska were reared to the smolt stage in a hatchery 250 km northwest of their natal streams. As fingerlings, the fish were separated into eight groups to test the effect of stock, time of release, smolt size at release, and culture salinity on marine survival and rates of early male maturity (mature males returning earlier than the youngest mature females; i.e., ≤4 years in age). A total of 13 397 Chickamin River and 22 508 Unuk River smolts were tagged and released from the hatchery in 1978. From 1978 to 1982, 1373 fish from the Chickamin River and 1634 fish from the Unuk River stock were recovered in fisheries or as maturing fish returning to the release site. Age-5 chinook salmon of both sexes from the Chickamin River were larger than those from the Unuk River stock (P < 0.05), but age-6 fish of both stocks were similar in size, regardless of sex. Rates of early male maturity were 5.4–16.7% in the Chickamin River stock and 70.6–96.0% for the Unuk River stock, and stock was significant (P < 0.030) in determining early-male maturity. Smolt size at release, culture salinity, and time of release did not affect maturation age of males in either stock.

Relationship of size at return with environmental variation, hatchery production, and productivity of wild pink salmon in Prince William Sound, Alaska: does size matter?

Pink salmon (Oncorhynchus gorbuscha) returning to Prince William Sound (PWS), Alaska, have increased to historically high levels of abundance in recent years, but average body size at return has declined. We examined how body size at return of PWS pink salmon was related to 10 biophysical factors, including the scale of hatchery production. We also examined the effect of body size at return on productivity of wild pink salmon in PWS. For the 1975–1999 brood years, we found that an index of total abundance of pink salmon in the Gulf of Alaska and sea surface temperature during the year of return best explained the variation in pink salmon body size over time. Body size at return was significantly correlated with productivity of wild pink salmon. We used stepwise-regression to fit a generalized linear version of the Ricker spawner-recruit model to determine if body size would explain significant variation in wild-stock productivity in context with other environmental variation, including hatchery production. The results indicate that variability in wild-stock productivity is primarily driven by density-independent factors in the marine environment, but that body size of wild spawners also significantly affects productivity of wild PWS pink salmon. We conclude that the success of large-scale enhancement increasing the total run in PWS may have contributed to the decline in body size because of density-dependent growth in the Gulf of Alaska. We used a simulation model to estimate the impact of hatchery-induced changes in adult body size on wild-stock production in PWS. We estimated an annual wild-stock yield loss of 1.03 million pink salmon, less than 5% of the annual hatchery return of 24.2 million adult pink salmon for brood years 1990–1999.

Floating vertical raceway to culture salmon (Oncorhynchus spp.)

Abstract A floating vertical raceway was developed to culture salmon ( Oncorhynchus spp.), and tested for 12 years. The structure is composed of a durable, impervious liner suspended from a rigid flotation collar. Notable features of the raceway include low construction and maintenance costs, adaptability to sites that are remote or without suitable area for shore-based raceways, and high water quality in the rearing environment.

Culture of sockeye salmon (Oncorhynchus nerka) smolts in estuarine net pens and returns of adults from two smolt releases

Abstract In 1973, adult sockeye salmon, Oncorhynchus nerka , were transported from Nakvassin Creek, Baranof Island, southeastern Alaska, to a nearby research station and hatchery at Little Port Walter. Progeny from these fish were used for the study. The fry were initially cultured in freshwater, then transferred to an estuarine net pen as fingerlings (6.7 g) on 31 October 1974 for overwinter culture in seawater. Survival of the fingerlings from transfer until 21 April 1975 was 97%. Two groups of smolts were released from the net pen in 1975: an early group on 22 April and a late group on 7 June. The age, sex ratios, and size of returning adults from the two releases were similar. The proportion of the returning adults from each group, however, was significantly different ( P

Spawning Behavior of Pink Salmon on an Artificial Redd

Abstract The spawning behavior of pink salmon (Oncorhynchus gorbuscha) was observed and photographed through a glass viewing port in the bottom of an artificial redd in an observation tank. Females readily accepted the artificial redd and completed the normal prespawning behavior sequences, including redd defense, digging, and crouching, but did not complete the spawning act and extrude eggs. Males, however, frequently followed the courtship sequence through to milt ejections. In 14 incomplete spawning acts, milt was ejected by males but eggs were not released by females. Seven of these acts involved the same male, over a 9-day period. Failure of females to extrude eggs was attributed to some unknown limiting physical condition of the redd or tanks—possibly the smooth surface of the viewing port in the redd.

Comparison of muscle compositions between red-and white-fleshed chinook salmon (Oncorhynchus tshawytscha)

Abstract Sexually mature chinook salmon were classified as red- and white-fleshed, based on the carotenoid levels of muscle and integument. Chinook salmon with high levels of total carotenoids in either muscle or integument were regarded as red-fleshed, regardless of their muscle color. The salmon with low carotenoid levels of muscle and integument were considered white-fleshed. There were no significant differences in muscle compositions of moisture, protein, and lipid. The changes in “a” value, which expresses the red color of the muscle, were parallel with those of the carotenoid levels, as indicated by a coefficient of correlation of 0.95, while no close correlation ( r = 0.09) was found between lipid and carotenoid levels of red- and white-fleshed salmon. These results suggested that changes of muscle composition occurring during spawning migration of chinook salmon are related to their physiological state, but not their muscle color type.

The Use and Selectivity of Small-Meshed Gill Nets at Brooks Lake, Alaska

Abstract Fine-thread gill nets with meshes of 3/8-, 1/2-, 3/4-, 7/8-, and 1-inch (stretched measure) were used to sample lake-dwelling juvenile sockeye salmon (Oncorhynchus nerka) and associated small fishes in Brooks Lake, Alaska. Thirteen of 20 species known to occur in the lake were sampled with the small meshes. Sockeye salmon, Alaska blackfish (Dallia pectoralis), threespine stickleback (Gasterosteus aculeatus), ninespine stickleback (Pungitius pungitius) and sculpins (Cottus spp.) less than 50 millimeters in length were sampled. Different selectivity patterns were shown by different species in various mesh sizes. Meshes smaller than 1 inch had low catch efficiencies, although these meshes were useful for qualitative assessment of small fishes.

Simple Venturi Device for Mixing Freshwater and Seawater in an Estuarine Culture System

Abstract A venturi device made from standard sizes of polyvinyl chloride plumbing and rod-stock material was tested at Little Port Walter, an estuary in southeastern Alaska. When installed in a gravity-fed freshwater delivery system, the venturi injected seawater into the discharge water to produce a stable water flow of intermediate salinity. The use of interchangeable components with different-sized openings permits regulation of the salinity of the discharge water.