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Alaska Fishery Research Bulletin Issues, Vol.9 No. 2 - Winter 2002
Ecology of Herring and Other Forage Fish as Recorded by Resource Users of Prince William Sound and the Outer Kenai Peninsula, Alaska
Evelyn D. Brown, Jody Seitz, Brenda L. Norcross, and Henry P. Huntington - Vol. 9(2):75-101. 2002.
We documented qualitative ecological information about non-harvested fish age classes and species from resource users and area residents. Our primary objective was to compile local and traditional ecological knowledge about the distribution, abundance, ecology, and associated changes over time of Pacific herring Clupea pallasi and other forage fish species in Prince William Sound (PWS) and the Outer Kenai Peninsula (OK) in Southcentral Alaska. A secondary objective was to provide ecological information to aid in developing study or management plans concerning herring and other forage fish. Both objectives were met by developing an oral interview protocol, selecting and interviewing key informants in 5 Alaskan communities, and developing a geographic database. Researchers tape-recorded and mapped respondents' observations. Survey questions fell into 6 categories: 1) life history stage and species of the fish observed, 2) fish behavior and school characteristics, 3) presence and behavior of co-occurring predators, 4) seasonal spatial distributions observed, 5) decadal shifts observed, and 6) observation and method activity. Forty-eight interviews were conducted. The earliest observation was from 1934. Thirty-seven respondents were commercial fishermen and 17 were pilots. Respondents made most observations of juvenile herring schools from planes. Other observations came from net catches, visual sightings, and sonar output. Most observations were made during summer (June through August), probably due to both shallow distribution of schools and an increase in human activity during this season. In PWS the spring spatial distribution of herring was significantly different from summer and fall-winter, but the latter 2 were not significantly different. Spatial distributions of herring in the OK were significantly different from one another in all 3 seasons, and the differences were more highly significant than in PWS. Most observations concerned juvenile herring, but locations of herring spawning overlap with adult herring, Pacific sand lance Ammodytes hexapterus, capelin Mallotus villosus, capelin spawning, and eulachon Thaleichthys pacificus were also documented. Most respondents were able to distinguish herring from other species by their school shape, school color, behavior, and location within a bay. Some pilots believed sunny days were better than overcast days for distinguishing herring from forage fish schools because herring schools "flash silver" and forage fish (mainly sand lance), also called "feed fish" or "bait fish," look brown or gold. Pilots said that they did not see schools of salmon fry from the air. Juvenile herring were reported as broadly distributed, mainly in bays in PWS and the OK, and easily observed in the summer. Juvenile herring were found at the heads of bays during the winter. They were seen in winter with adult herring in a very limited number of sites. Decadal shifts were observed with an increase in juvenile herring from the 1970s to the 1980s and a much more restricted distribution in the 1990s. In PWS the 1970s distribution was not significantly different from the 1980s, but was highly significantly different from the 1990s. The 1980s and 1990s were also highly significantly different from one another. In the OK all 3 decades were significantly different from one another, and the level of significance was higher than for the PWS pairwise tests. Decadal shifts in the reported extent of juvenile herring distribution matched decadal trends in catches of the PWS adult herring population indicating that traditional ecological knowledge is a potentially valuable source of information for indicators of recruitment and population trends. Juvenile herring overlapped sand lance distribution to a large degree, and capelin and eulachon to a small degree. Herring spawning locations prior to the 1970s not previously reported by the Alaska Department of Fish and Game were documented. Our study preserves knowledge of the historical changes in distribution of Pacific herring in PWS and the OK that predates scientific data collection.
Full Article (PDF 961 kB)A Description of Escaped Farmed Atlantic Salmon Salmo salar Captures and Their Characteristics in One Pacific Salmon Fishery Area in British Columbia, Canada, in 2000
Alexandra Morton and John Volpe - Vol. 9(2):102-110. 2002.
Since 1995, the Canadian salmon farming industry as a whole has reported losing an average of 46,255 Atlantic salmon Salmo salar annually into the coastal waters of British Columbia. While the number of fish lost is arguably much higher, it is unarguable that the fate of these fish is largely unknown. This study was conducted on the fishing grounds of British Columbia by contacting commercial fishers frequently via VHF radio and boat visits. Atlantic salmon were collected directly from fishers, packers, and a processing plant. The goal of this project was to enumerate the number of Atlantic salmon caught by commercial fishers in Pacific Management Area 12, a region of intense salmon farm activity. Further, we wished to examine the condition of these escaped farm salmon to aid managers in determining their ability to survive in the wild. A total of 10,826 Atlantic salmon were caught in the 17 days of open fishing periods during this study, August 2, 2000 through September 22, 2000, by troll, seine, and gillnet gear. The mean fork length and weight of the sampled Atlantic salmon were 75.0 cm (±5.1 cm) and 4.8 kg (±1.3 kg), respectively. Autopsies on 775 whole or partial Atlantic salmon found identifiable stomach contents in 3.9% of the sample overall, and up to 24.4% at some sampling locations. Eighteen fish (2.3%) showed signs of sexual maturity. One group of escaped Atlantic salmon was sampled weekly over a fourteen-day interval, days 1, 8, 14, and an increase in foraging success was recorded. Gillnets were the most successful gear type in recovering escaped farm salmon. The present passive reporting system of Fisheries and Oceans Canada underestimates Atlantic salmon escapes. This study recorded 40.8% more Atlantic salmon caught in the 8 week study period in Pacific Management Area 12 by commercial fishers than the federal Fisheries and Oceans Canada's passive monitoring program.
Full Article (PDF 137 kB)A Bioenergetics Approach to Estimating Consumption of Zooplankton by Juvenile Pink Salmon in Prince William Sound, Alaska
Jennifer L. Boldt and Lewis J. Haldorson - Vol. 9(2):111-127. 2002.
Juvenile pink salmon Oncorhynchus gorbuscha were sampled through the summer and fall of 1998 in Prince William Sound, Alaska. Samples collected in the field and a bioenergetics model were used to estimate consumption of zooplankton by juvenile pink salmon during their first three months at sea. Based on an initial weight of 0.26 g and a growth rate of 4% body weight per day, a pink salmon would consume 27.9 g of wet weight in a 93 d residence time in Prince William Sound. A cohort of juvenile pink salmon would consume 5.53×109 g wet weight or 0.05 g Carbon/m2/year (g C/m2/year) in PWS. Sensitivity analyses indicate that residence time, mortality, and diet strongly influence consumption estimates. Assuming a primary production of 100 to 300 g C/m2/year, a transfer efficiency of 20%, and secondary production of 20 to 60 g C/m2/year, consumption by juvenile pink salmon was about 0.06-0.45% of annual secondary production. This estimate would be higher (up to 8.28%) if only nearshore areas of Prince William Sound are considered. The average daily consumption of large calanoid copepods was 2.2×10-4 g C/m2 or 1.5% of the large calanoid copepods available. If standing stocks were fixed over a 10-day period, pink salmon consumption would represent a large proportion of large calanoid copepods (15%) and amphipods (19%). Consumption by pink salmon and other planktivores needs to be considered along with geographic and interannual variability in zooplankton biomass and productivity when examining the carrying capacity of the Prince William Sound ecosystem.
Full Article (PDF 211 kB)A Simple Procedure to Evaluate Salmon Escapement Trends that Emphasizes Biological Meaning Over Statistical Significance
Harold J. Geiger and Xinxian Zhang - Vol. 9(2):128-134. 2002.
Statistical hypothesis testing for a "significant" decline is poorly suited for the analysis of salmon stock trends. Unfortunately, when statistical hypothesis-test machinery is applied to an escapement series, biologically unimportant, small downward fluctuations can be considered "significant," especially in long series. Alternatively, often very steep declines in escapement levels are found to be "not significant," especially in short series. The hypothesis test may tell more about the length of the series than the magnitude of the decline or the stock dynamics. We propose a simple and robust method of estimating the magnitude of stock decline (or increase), and propose a way to reference stock decline in terms of an underlying escapement level at the beginning of the series, so the decline can be judged in some kind of context. We regressed escapement on time using a resistant regression line. We propose using the back-cast estimate of what the escapement was in year zero of the series as a nonparametric escapement benchmark, and we call this benchmark the year-zero reference point. This back-cast estimate is just the estimated y-intercept of the regression line. In several 15-year series that we examined, we concluded that an escapement decline was biologically meaningful when the estimated underlying annual decline was more than 5% of the year-zero reference point, as that decline will result in the underlying escapement level dropping by half over a 10-year period.
Full Article (PDF 96 kB)