AUKE BAY LABORATORY (ABL)

Marine Salmon Interactions Program

Southeast Alaska Coastal Monitoring: An Overview of Long-term Research on the Early Marine Ecology of Juvenile Salmon

The primary goal of the Southeast Coastal Monitoring Project (SECM) is to build and maintain a time series of biophysical oceanographic indices related to the seasonal growth, distribution, abundance, and habitat utilization of juvenile Pacific salmon (Oncorhynchus spp.) stocks. Since 1997, SECM researchers annually have measured seasonal biophysical parameters in conjunction with marine sampling of juvenile salmon. The research occurs monthly from May to August along a seaward migration corridor in neritic waters (3–65 km off shore) centered near Icy Strait in the northern region of southeastern Alaska. A series of 13 stations have been consistently sampled each year, and catches of juvenile salmon and ecologically related species were enumerated, measured, and processed after each haul.

Principal results from the research include information on marine habitat utilization patterns, stock-specific migration, hatchery and wild fish interactions, neritic carrying capacity, predation on juvenile salmon, and the use of juvenile salmon abundance indices to forecast adult salmon returns. Juvenile salmon occupied the epipelagic habitats transitionally; they were absent in May, occurred in high abundance in June or July, then abundance declined in August. Recovered marked stocks of juvenile salmon indicated stock-specific utilization of marine habitats, both for stream-type chinook salmon (O. tshawytscha) of Columbia River Basin origin and chum salmon (O. keta) of Southeast Alaska hatchery origin.

The composition of hatchery chum salmon from the two major enhancement facilities in the region in catches from Icy Strait generally amounted to more than 50% each year in June and July and less than 25% in August. Despite the high prevalence of hatchery chum salmon, results from a bioenergetics approach indicate that hatchery and wild chum salmon consumed only a small percentage of the available standing crop of zooplankton. Ecological interactions observed between juvenile salmon and their predators indicated that 7 of 21 predator species consumed juvenile salmon. Of these juvenile salmon predators, average interannual rates of predation ranged from less than 1% to about 30%.

Biophysical parameters and juvenile pink salmon (O. gorbuscha) indices were compared to the total commercial harvest of adult pink salmon in Southeast Alaska the following year. Juvenile pink salmon abundance proved to be highly correlated with adult pink salmon harvest and shows promise as a forecasting tool. This correlation of high juvenile pink salmon abundance in June and July to adult harvest may suggest that early marine conditions prior to these months govern survival. Longterm annual monitoring may help to better identify relationships between environmental change and salmon production, and improve our understanding of the coastal Alaska marine ecosystem.

By Joseph Orsi

Seasonal Variation in Whole Body Energy Content of Juvenile Coho Salmon in Marine Waters of Northern Southeast Alaska

Our study examined seasonal variation in whole body energy content (WBEC, cal/g dry weight) of juvenile coho salmon (O. kisutch) from neritic habitat in the marine waters of northern Southeast Alaska. This process study is one component of SECM, which for the last 8 years has monitored biophysical parameters that influence habitat use, marine growth, predation, stock interactions, year-class strength, and ocean carrying capacity of juvenile salmon. Juvenile coho salmon were sampled in 2001 during SECM rope trawl operations at stations in Icy Strait and Upper Chatham Strait (lat. 58°N, long. 135°W) from June to September. Mean WBEC was calculated from bomb calorimetry measurements of up to 10 specimens collected in each of four monthly intervals (n = 38).

Seasonal variation in WBECs occurred among juvenile coho salmon. The mean WBEC differed significantly by month (ANOVA, P = 0.000, df = 3) and were 4785.1, 4757.9, 4697.2, and 5245.7 cal/g dry weight for June, July, August, and September, respectively. Tukey’s pairwise comparisons identified significantly higher mean WBEC for September than for the three previous months. This result suggests that WBEC for juvenile coho salmon increases seasonally as the coho migrate to the open ocean, entering the Gulf of Alaska in the fall.

Such seasonal WBEC values should be incorporated into bioenergetics models that include a temporal aspect and be used when evaluating habitat quality of juvenile salmon. Furthermore, earlier samples of juvenile coho salmon (e.g., from May) should be examined to reflect condition immediately after saltwater entry and to provide a broader picture of the seasonal variation in WBEC of juvenile coho salmon.

By Emily Fergusson

Endangered Species Research at Little Port Walter

October 2004 marked the end of a successful season of intensive field investigations at the Little Port Walter Research Station. Activity at the station this year included research focused on inbreeding and outbreeding depression as related to the recovery of endangered stocks of steelhead trout (O. mykiss) and evaluating the possibility of using lakes as long-term refugia for endangered populations of steelhead.

In 2004, we conducted the sixth successive spawning of the 1996 captive brood and successfully propagated 80 families representing eight lines of steelhead and rainbow trout crosses. The 1996 brood was generated from captures of wild steelhead in Sashin Creek and wild resident rainbow trout in Sashin Lake that originated from a transplant of Sashin Creek steelhead in 1926.

We currently are evaluating differences between the two populations relating to important life history characters such as smolt production, early maturation, growth, and marine survival. Using the second generation progeny, we also are able to evaluate the effects of one generation of sibling mating (which has a high probability of occurrence in small, endangered populations) on survival potential in the wild for inbred progeny of both steelhead and rainbow lines.

Results from 2004 provide convincing evidence that even inbreeding levels as low as 0.25, which are not unusual in small captive populations, can have disastrous effects on the ability of the affected population to survive in the wild. These results have significant implications relating to the demographic risk of extinction faced by small populations and the use of captive broodstocks in restoration efforts.

By Frank Thrower

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AFSC Quarterly Research Reports Oct-Dec 2004