R. M. Sweeting

Distribution and Migration of Juvenile Chinook Salmon Derived from Coded Wire Tag Recoveries along the Continental Shelf of Western North America

Abstract The effects of ocean conditions on highly migratory species such as salmon are difficult to assess owing to the diversity of environments they encounter during their marine life. In this study, we reconstructed the initial ocean migration routes of juvenile Chinook salmon Oncorhynchus tshawytscha originating from Oregon to Southeast Alaska using coded wire tag recovery data from Canadian Department of Fisheries and Oceans and National Marine Fisheries Service research surveys conducted between 1995 and 2006. Over this 12-year period, 1,862 coded-wire-tagged juvenile Chinook salmon were recovered along the coasts of Oregon, Washington, British Columbia, and Alaska from March to November. Except for those from the Columbia River, most juvenile Chinook salmon remained within 100–200 km of their natal rivers until their second year at sea, irrespective of their freshwater history and adult run timing. Northward migration of most coastal stocks was initiated during their second or possibly third year ...

Replacement of Wild Coho Salmon by Hatchery-Reared Coho Salmon in the Strait of Georgia over the past Three Decades

Abstract The percentage of hatchery-reared coho salmon Oncorhynchus kisutch in the Strait of Georgia, British Columbia, increased from nearly 0% in the early 1970s to more than 70% by 2001. These estimates were derived from fin clip and coded wire tag data collected from commercial and sport fisheries, research surveys conducted in the summer and fall of 1997 to 2000, and examination of the microstructure of otoliths extracted from juvenile coho salmon collected during our marine surveys. The increasing trend may be related to the proportions of hatchery and wild smolts entering saltwater, fishing rates, and changes in the ecological processes regulating coho salmon production in the ocean. The consequence for management is that the abundance of wild spawning salmon (escapement) depends on hatchery as well as wild production. The consequence for policy makers is that future enhancement activities need to have clear policies for assessing the effects of hatchery fish on the population dynamics of wild fish...

Ontogenetic Diet Shifts of Juvenile Chinook Salmon in Nearshore and Offshore Habitats of Puget Sound

Abstract Marine growth and survival of juvenile Chinook salmon Oncorhynchus tshawytscha depend in part on the quality and quantity of prey consumed during this potentially critical life stage; however, little is known about the early marine diet of these fish or factors that affect the diets variability. We examined the recent (2001–2007) dietary habits of Puget Sound, Washington, Chinook salmon (listed as threatened under the U.S. Endangered Species Act) during their first marine growing season (April–September). Juvenile Chinook salmon initially fed in nearshore marine habitats and then shifted to feed primarily offshore during July–September. Diet composition varied significantly among sampling regions (northern, central, and southern), habitats (nearshore, offshore), years, months, and fish size-classes. At nearshore sites, insects (all months) and gammarid amphipods (July) were dominant prey sources, whereas in offshore diets decapods (primarily crab larvae; July) and fish (September) were most impo...

Changes in the Population Ecology of Hatchery and Wild Coho Salmon in the Strait of Georgia

Abstract An analysis of the results of a 10-year study of the population ecology of juvenile hatchery and wild coho salmon Oncorhynchus kisutch in the Strait of Georgia produced new information about the interannual and interseasonal fluctuations in abundance and marine survival. A decline in the percentage of hatchery coho salmon was related to declines in hatchery fish abundance and marine survival; wild coho salmon abundance was more stable. The declining marine survival of hatchery coho salmon appeared to be related to a fixed average date of release from hatcheries and a possibility of earlier prey production. The relatively stable abundance of wild coho salmon may relate to a natural trend toward earlier ocean entry dates. Oscillations in hatchery coho salmon percentage and abundance were related to oscillations in abundance of juvenile pink salmon O. gorbuscha. The impact of oscillating density affected marine survival of hatchery coho salmon more than that of wild coho salmon. Marine survival and ...

The Synchronous Failure of Juvenile Pacific Salmon and Herring Production in the Strait of Georgia in 2007 and the Poor Return of Sockeye Salmon to the Fraser River in 2009

Abstract Trawl studies from 1998 to 2009 indicated that juvenile Pacific salmon Oncorhynchus spp. and Pacific herring Clupea pallasii represented 98 % of the fish in the surface waters of the Strait of Georgia during the day in the spring and early summer. Standardized catches of all juvenile Pacific salmon in the trawl surveys were lowest in 2007. Catches of young-of-the-year Pacific herring were also extremely low in 2007. Three years later, the 2007 year-class had the lowest recruitment to the fishery in recorded history. In 2007, juvenile coho salmon O. kisutch and Chinook salmon O. tshawytscha were small and had the lowest condition of the fish in all surveys as well as a high percentage of empty stomachs. The early marine survival of coho salmon in 2007 and the total survival in 2008 were exceptionally poor. Trawl catches of juvenile chum salmon O. keta in 2007 were the lowest of all surveys. Adult chum salmon from these juveniles that returned in 2010 had extremely poor survival. Juvenile sockeye salmon O. nerka that entered the Strait of Georgia in the spring of 2007 and returned to the Fraser River as adults in 2009 also had such exceptionally poor marine survival that a judicial inquiry was conducted to determine the causes. The synchronous poor growth, survival, or both of all of the major species in the surface waters of the Strait of Georgia in the spring of 2007 indicated that there was a common cause which we propose as poor food production. The causes of the high mortality likely represented a unique extreme in the variability of the factors that normally affect the survival of juvenile Pacific salmon and Pacific herring in the early marine period in the Strait of Georgia.

Early Marine Survival of Coho Salmon in the Strait of Georgia Declines to Very Low Levels

Abstract The marine survival of juvenile coho salmon Oncorhynchus kisutch from the time they enter the Strait of Georgia in mid-May to the time of our trawl survey in mid-September declined from an average of about 15% in 1998 to approximately 1% in 2007. Early marine survival rates for juvenile coho salmon have been consistently low (<5%) since 2002, and the rate of decline in early marine survival was greater for hatchery fish than for wild fish. This suggests that hatchery coho salmon are perhaps less able to survive than wild fish in the current marine ecosystem. The steady decline in total marine survival for coho salmon over the past four decades coincided with a warming of the Strait of Georgia, where both sea surface and sea bottom temperatures have increased by approximately 1°C since 1970. Another factor that appears to have contributed to the decline in early marine survival since the late 1990s is an increase in the number of days with an average sustained wind strength greater than 25 km/h. The linkage between wind strength and marine survival requires further study, but wind strength is known to affect the timing and level of primary productivity. The processes that caused the declining marine survival remain to be identified and may include factors associated with disease originating in both freshwater and salt water, metabolic stress, competition, and predation. The data suggest that coho salmon brood year strength is now mostly determined during the first 4 months spent in the Strait of Georgia. If the current low levels of marine survival continue, management initiatives to protect wild coho salmon will be urgently required, and it will be timely to critically evaluate the hatchery programs and policies.

The Influence of Climate on the Stock and Recruitment of Pink and Sockeye Salmon from the Fraser River, British Columbia, Canada

The relationships between the spawning stock and the subsequent recruitment of pink salmon Oncorhynchus gorbuscha and sockeye salmon O. nerka from the Fraser River improve significantly when the data are separated by climate and ocean regimes. Our analyses show changes in these relationships as regimes shift, indicating that the trend in marine survival of pink and sockeye salmon changes on a decadal scale. In general, the climate and ocean regime from 1977 to 1988 was productive for pink and sockeye salmon. However, the regime in the 1990s was characterized by reduced productivity for both species. The occurrence of a natural shift in the trend of pink and sockeye salmon production on a decadal scale should be incorporated into the management of Pacific salmon stocks to ensure that annual catches, escapements, and planned stock abundances are consistent with the productivity of a particular regime.

Wild chinook salmon survive better than hatchery salmon in a period of poor production

The population dynamics of chinook salmon (Oncorhynchus tshawytscha) from the Cowichan River on Vancouver Island, British Columbia, Canada are used by the Pacific Salmon Commission as an index of the general state of chinook salmon coast wide. In recent years the production declined to very low levels despite the use of a hatchery that was intended to increase production by improving the number of smolts entering the ocean. In 2008, we carried out an extensive study of the early marine survival of the hatchery and wild juvenile chinook salmon. We found that both rearing types mostly remained within the Gulf Islands study area during the period when most of the marine mortality occurred for the hatchery fish. By mid September, approximately 1.3% of all hatchery fish survived, compared to 7.8%–31.5% for wild fish. This six to 24 times difference in survival could negate an estimated increased egg-to-smolt survival of about 13% that is theorized to result through the use of a hatchery. Estimates of the early marine survival are approximate, but sufficient to show a dramatic difference in the response of the two rearing types to the marine nursery area. If the declining trend in production continues for both rearing types, modifications to the hatchery program are needed to improve survival or an emphasis on improving the abundances of wild stocks is necessary, or both. The discovery that the juvenile Cowichan River chinook salmon remain within a relatively confined area of the Gulf Islands within the Strait of Georgia offers an excellent opportunity to research the mechanisms that cause the early marine mortalities and hopefully contribute to a management that improves the production.

Improvement of juvenile Pacific salmon production in a regional ecosystem after the 1998 climatic regime shift

Abstract Beginning in 2000, juvenile Pacific salmon Oncorhynchus spp. in the Strait of Georgia, British Columbia, fed more frequently, contained greater volumes of prey in their stomachs compared with the previous 3 years, and increased in size. Abundances in July also increased in 2000 and 2001. Marine survival increased, as indicated by the early marine survival of coho salmon O. kisutch in 2000 and 2001, which improved to more than twice the annual survival estimates for 1997–1999. Other indicators of improved marine survival included exceptional returns of pink salmon O. gorbuscha to the Fraser River in 2001 and sockeye salmon O. nerka in 2002. The change to a more productive regime for juvenile Pacific salmon was a lagged response to an abrupt change in climate in 1998, as shown by regional, basin-scale, and planetary indices.

The Use of Acoustic Tags to Determine the Timing and Location of the Juvenile Coho Salmon Migration out of the Strait of Georgia, Canada

Abstract The migration of juvenile coho salmon Oncorhynchus kisutch out of the Strait of Georgia in 2006 was investigated by means of acoustic telemetry. During July and September, 173 juvenile coho salmon were caught in the strait with a purse seine, surgically implanted with acoustic tags, and released the same day. In 2006, approximately 19% of the fish tagged in July and 52% of those tagged in September left the Strait of Georgia. Most of these fish did so in October and November through Juan de Fuca Strait and not by a northward migration through Queen Charlotte Strait. This movement was several months later than that observed for coho salmon migrating out of Puget Sound. A small number of coho salmon that moved out of the Strait of Georgia migrated south to areas off the coast of Washington and Oregon. The documentation of a movement out of the Strait of Georgia late in the year was important, as it shows that population changes of the juvenile coho salmon that enter the strait during spring and sum...