Katherine W. Myers

Anadromy and the marine migrations of Pacific salmon and trout: Rounsefell revisited

Anadromy is a defining trait in salmonid fishes but it is expressed to different extents among the species in the family, as reviewed in a classic paper by Rounsefell (1958). The present paper re-examines the subject, assessing the degree of anadromy within the genus Oncorhynchus, using Rounsefell’s six criteria: extent of migrations at sea, duration of stay at sea, state of maturity attained at sea, spawning habits and habitats, post-spawning mortality, and occurrence of freshwater forms of the species. The genus ranges from pink salmon (O. gorbuscha), the most fully anadromous species in the family, to entirely non-anadromous species closely related to rainbow trout (O. mykiss), including Mexican golden trout (O. chrysogaster), Gila and Apache trout (O. gilae), and sub-species of cutthroat trout (O. clarki). This paper provides updated information on anadromy and marine migration patterns, emphasizing the iteroparous species, cutthroat (O. clarki) and rainbow (O. mykiss) trout. These two species display widely ranging patterns of anadromy, including truly “landlocked” populations and residents with easy access to the sea. Anadromous rainbow trout (known as steelhead) populations also vary greatly in their distribution at sea, incidence of repeat spawning, and associated traits. We conclude, as did Rounsefell, that anadromy is not a single trait with two conditions (anadromous or non-anadromous). Rather, it reflects a suite of life history traits that are expressed as points along continua for each species and population. Further research is needed in the marine ecology of all species but especially trout, as they are less well known but apparently more variable in patterns of anadromy and life history than salmon species.

Evidence for Size-Selective Mortality after the First Summer of Ocean Growth by Pink Salmon

Abstract Pink salmon Onchorhynchus gorbuscha with identifiable thermal otolith marks from Prince William Sound hatchery release groups during 2001 were used to test the hypothesis that faster-growing fish during their first summer in the ocean had higher survival rates than slower-growing fish. Marked juvenile pink salmon were sampled monthly in Prince William Sound and the Gulf of Alaska, and adults that survived to maturity were recovered at hatchery release sites the following year. Surviving fish exhibited significantly wider circuli spacing on the region of the scale formed during early marine residence than did juveniles collected at sea during their first ocean summer, indicating that marine survival after the first growing season was related to increases in early marine growth. At the same circuli, a significantly larger average scale radius for returning adults than for juveniles from the same hatchery would suggest that larger, faster-growing juveniles had a higher survival rate and that signifi...

Magnitude and Trends in Abundance of Hatchery and Wild Pink Salmon, Chum Salmon, and Sockeye Salmon in the North Pacific Ocean

Abstract –Abundance estimates of wild and hatchery Pacific salmon Oncorhynchus spp. are important for evaluation of stock status and density-dependent interactions at sea. We assembled available salmon catch and spawning abundance data for both Asia and North America and reconstructed total abundances of pink salmon O. gorbuscha, chum salmon O. keta, and sockeye salmon O. nerka during 1952–2005. Abundance trends were evaluated with respect to species, regional stock groups, and climatic regimes. Wild adult pink salmon were the most numerous salmon species (average = 268 × 106 fish/year, or 70% of the total abundance of the three species), followed by sockeye salmon (63 × 106 fish/year, or 17%) and chum salmon (48 × 106 fish/year, or 13%). After the 1976–1977 ocean regime shift, abundances of wild pink salmon and sockeye salmon increased by more than 65% on average, whereas abundance of wild chum salmon was lower in recent decades. Although wild salmon abundances in most regions of North America increased in the late 1970s, abundances in Asia typically did not increase until the 1990s. Annual releases of juvenile salmon from hatcheries increased rapidly during the 1970s and 1980s and reached approximately 4.5 × 109 juveniles/year during the 1990s and early 2000s. During 1990–2005, annual production of hatchery-origin adult salmon averaged 78 × 106 chum salmon, 54 × 106 pink salmon, and 3.2 × 106 sockeye salmon, or approximately 62, 13, and 4%, respectively, of the combined total wild and hatchery salmon abundance. The combined abundance of adult wild and hatchery salmon during 1990–2005 averaged 634 × 106 salmon/year (498 × 106 wild salmon/year), or approximately twice as many as during 1952–1975. The large and increasing abundances of hatchery salmon have important management implications in terms of density-dependent processes and conservation of wild salmon populations; management agencies should improve estimates of hatchery salmon abundance in harvests and on the spawning grounds.

Summer-Fall Distribution of Stocks of Immature Sockeye Salmon in the Bering Sea as Revealed by Single-Nucleotide Polymorphisms

Abstract We report stock composition estimates for immature (ocean-age .1 and .2) sockeye salmon Oncorhynchus nerka distributed across the Bering Sea in late summer and fall. We establish a baseline data set composed of single-nucleotide polymorphism markers that can achieve very high accuracies in identifying sockeye salmon stocks from throughout their range in Asia and North America. We demonstrate the capabilities of this data set to address high-seas salmon issues by analyzing samples collected by researchers from Russia, Japan, and the United States during late summer and fall 2002–2004 as part of the Bering–Aleutian Salmon International Survey. According to our findings, (1) Gulf of Alaska (GOA) stocks formed a significant portion of the immature sockeye salmon migrating in the eastern and central Bering Sea in summer and fall, and western GOA stocks had a broader distribution in the Bering Sea than eastern GOA stocks; (2) Asian stocks migrated as far east as the western Aleutian Islands and the Don...

TEMPORAL USE OF AN OREGON ESTUARY BY HATCHERY AND WILD JUVENILE SALMON

Abstract Temporal use of Yaquina Bay, Oregon, (July 1977-December 1978) by accelerated-growth (age-0) hatchery coho (Oncorhynchus kisutch) and wild salmon (Oncorhynchus spp.) juveniles was determined by periodic sampling of nearshore and channel sites in the estuary. “Residency half-life” ranged from two to nine days for different release groups of hatchery coho juveniles, and was longer for fish released earlier in the year (June) than for groups released later (September-October). Wild populations of chum (O. keta) and coho were present at the sample sites for 2–3 mo (March-June), and wild chinook (O. tshawytscha) were present during 9 mo (January, April-November). Lack of overlap in peak abundances of wild chum (early April), coho (mid May), and chinook (mid July-early August), suggests interspecific temporal partitioning. Releasing age-0 hatchery coho after peak abundances of wild chinook should be considered as a means of decreasing overlap in temporal use of the estuary.

Early Marine Growth of Pink Salmon in Prince William Sound and the Coastal Gulf of Alaska During Years of Low and High Survival

Abstract Although early marine growth has repeatedly been correlated with overall survival in Pacific salmon Oncorhynchus spp., we currently lack a mechanistic understanding of smolt-to-adult survival. Smolt-to-adult survival of pink salmon O. gorbuscha returning to Prince William Sound was lower than average for juveniles that entered marine waters in 2001 and 2003 (3% in both years), and high for those that entered the ocean in 2002 (9%) and 2004 (8%). We used circulus patterns from scales to determine how the early marine growth of juvenile pink salmon differed (1) seasonally during May-October, the period hypothesized to be critical for survival; (2) between years of low and high survival; and (3) between hatchery and wild fish. Juvenile pink salmon exhibited larger average size, migrated onto the continental shelf and out of the sampling area more quickly, and survived better during 2002 and 2004 than during 2001 and 2003. Pink salmon were consistently larger throughout the summer and early fall duri...

Interannual Variability in Early Marine Growth, Size-Selective Mortality, and Marine Survival for Prince William Sound Pink Salmon

Abstract The main objective of this study was to use scale patterns to compare the early marine growth of the average pink salmon Oncorhynchus gorbuscha with that of fish from the same year-class that survived to adulthood to gain insight on critical periods for growth and survival. During 2001–2004, pink salmon that survived to adulthood were larger and grew faster than the average juvenile throughout the first growing season, indicating that larger, faster-growing juveniles experienced higher survival. Growth rate declined from mid–late June to early–mid-July for both juveniles at-large and fish that survived to adulthood. The adult survivors then grew at a faster rate than the average juvenile through September. Both the juvenile pink salmon population at-large and all cohorts that survived to adulthood grew at a faster rate during high-survival years than low-survival years from mid–late June to mid–late August. Greater variability in the growth trajectories of surviving adults was observed during high-survival years, potentially a result of diversified feeding or distribution strategies. This study supports findings that significant size-selective mortality of juvenile pink salmon occurs after the first growing season. Investigating the timing and magnitude of size-selective mortality on juvenile pink salmon during their first growing season is an initial step toward understanding the processes regulating growth and survival.

Genetic and Phenotypic Variation through the Migratory Season Provides Evidence for Multiple Populations of Wild Steelhead in the Dean River, British Columbia

Abstract We provide evidence for previously undetected population structure in a wild run of summer steelhead Oncorhynchus mykiss within a river that has considerable recreational importance (Dean River, British Columbia). Data were gathered from an existing catch-and-release fishery and examined for phenotypic and genetic variation through the migratory season. Specifically, we compared fish captured in different periods during the migration: early (July 2-30), middle (July 31-September 5), and late (September 6-30). Age (freshwater and saltwater), sex ratio, and body girth did not differ significantly among these groups for females or males. Body length increased through the migratory season for both sexes, perhaps because late-migrating fish had more time to feed in the ocean. Based on genotypes at 10 microsatellite loci, early and late groups showed highly significant genetic differences (P < 0.001). Assignment tests were able to classify individuals back to early or late groups with 84% accuracy (122...

Interannual and Spatial Feeding Patterns of Hatchery and Wild Juvenile Pink Salmon in the Gulf of Alaska in Years of Low and High Survival

Abstract To improve understanding of the mechanisms affecting growth and survival, we evaluated the summer diets and feeding patterns (prey composition, energy density, and stomach fullness) of hatchery and wild juvenile pink salmon Oncorhynchus gorbuscha in Prince William Sound (PWS) and the northern coastal Gulf of Alaska (CGOA). Our study (1999-2004) included 2 years of low (∼3%), mid (∼5%), and high (∼8-9%) survival of PWS hatchery pink salmon. Because variations in diet should affect growth and ultimately survival, we expected that the variations in diet, growth, and survival would be correlated. During August in the CGOA, pteropod-dominated diets and higher gut fullness corresponded to high survival (5-9%), and copepod-dominated diets and lower gut fullness corresponded to low survival (3%). Within years, no significant differences were found in diet composition or gut fullness between hatchery and wild fish or among the four PWS hatchery stocks. Diets varied by water mass (habitat) as juveniles mov...

Stock Origins of Chinook Salmon in Incidental Catches by Groundfish Fisheries in the Eastern Bering Sea

Abstract An estimated 386,946 chinook salmon Oncorhynchus tshawytscha were taken in incidental catches by foreign and joint-venture groundfish vessels operating in the Bering Sea portion of the U.S. exclusive economic zone, 1977–1986. Concern about the effect of incidental catches on the salmon fisheries of western Alaska provided the impetus for a study to determine the stock origins of chinook salmon in these catches. The proportions of regional (Asia, western Alaska, central Alaska, and southeast Alaska–British Columbia) and western Alaskan subregional (Yukon, Kuskokwim, and Bristol Bay) stocks of Chinook salmon in 1979, 1981, and 1982 samples collected by U.S. foreign fishery observers were estimated by scale pattern analysis. Estimated proportions ofthe regional stocks averaged 60% western Alaska, 17% central Alaska, 14% Asia, and 9% southeast Alaska-British Columbia. Western Alaska, which included Canadian Yukon fish, was the predominant regional stock in most age-group, time, and area strata. Stock...