Session IX: Atlantic Salmon
Sharon A. MacLean
Infectious salmon anemia is a viral disease of Atlantic salmon, principally those in culture environments. The disease was first reported in Norway in 1984 and subsequently has been reported from Scotland, Faroe Islands, Canada, and the US. Genetic sequencing indicates two strains of virus: the Norwegian/Scottish strain and the North American strain. As indicated by its name, the disease is characterized by internal hemorrhaging resulting in severe anemia. Mortality rates typically are 50%. Currently more than 50% of the culture sites in Maine’s Cobscook Bay are diseased and fish health management plans are being implemented to limit the spread of the disease to other areas in Maine. There is concern for the potential impact of this virus on Atlantic salmon restoration efforts and on this endangered species. The presentation will discuss efforts to control this disease, vaccine development, bay-area management, coordinated US-Canada fish health management plans, research planned, and impacts on the Atlantic salmon restoration project.
Kocik1, Timothy F. Sheehan2, Kenneth F. Beland3,
and Jennifer FitzGerald2
US Atlantic salmon populations with a substantial naturally reproducing component are restricted to eight rivers in eastern Maine, listed as endangered. Adult assessments conducted since 1992 have indicated that abundance has declined and remains low. To identify causes for this decline, we initiated a program to quantify smolt production in the Narraguagus River and index production in the Pleasant and Sheepscot Rivers. In the Narraguagus and Pleasant Rivers, we conducted annual geographically-stratified basinwide estimates of large parr (>130 mm) abundance using electrofishing in late summer. From April until June, we monitored the emigration of Atlantic salmon smolts in all three rivers using rotary screw fish traps. In the Narraguagus River, parr estimates have ranged from 11,700 to 27,000 and corresponding emigrating smolt estimates ranged from 1,800 to 3,600. Even in years with substantial increases in large parr production (126%), smolt production has increased only modestly (3%) in the Narraguagus. In the Pleasant and Sheepscot Rivers, the smolt population has numbered less than 1,000. Our studies have also identified smolts in the Pleasant River that are of commercial aquaculture origin, confirming a fish-management concern. Total smolt production in these watersheds is well below the estimated production capacity of 300/ha and warrants continued study to determine mechanisms responsible for low production.
Keywords: salmon, endangered, smolt
Ruth E. Haas-Castro, John
F. Kocik, and Christopher M. Legault
Atlantic salmon in eight Maine rivers were listed in November 2000 as endangered under the Endangered Species Act. The Northeast Fisheries Science Center has monitored smolt production in Maine rivers from 1996 onwards. Atlantic salmon in the Pleasant River constitutes one of the eight remnant populations now protected under the Act. To monitor smolt production in this river, we deployed a rotary screw trap during early April-June in 1999, 2000, and 2001 at Columbia Falls. Scale samples were collected from 382 of 617 smolts captured in 1999 and 120 of 160 smolts caught in 2000. Tissue samples were also collected from a portion of the fish for genetic analysis. Although most smolts in both years were of wild origin, many of these fish exhibited fin deformities, coloration, and body form that suggested they were of hatchery origin. We therefore attempted to determine the feasibility of using scale characteristics to differentiate smolts into three categories: wild origin, early escaped hatchery origin, and hatchery origin. Our results will be important in determining the magnitude of hatchery origin and hatchery escaped fish in the Pleasant River, and in evaluating the efficacy of actions that have been taken to enhance the survival of wild fish.
F. Sheehan1, John F. Kocik2 and Ernest Atkinson3
We monitored stock-specific marine growth rates for two years from three Atlantic salmon populations in eastern Maine. Individuals were spawned at a federal hatchery and reared to smolt stage at commercial facilities. Approximately 1,000 individuals from each stock were transferred to two marine sites for two sea-winters of marine grow-out. We tagged each individual with an elastomer injection to allow for stock differentiation. Individuals at each site were reared in a single sea-cage and experienced similar environmental influences and growing conditions. Biological sampling occurred approximately every other month. Standardized photographs were taken of a random sample of individuals after two years of grow-out, and Truss Analysis (multivariate morphometrics) was conducted on the photographs. We tested for stock-specific differences in growth with univariate and multi-variate techniques. Significant differences in growth were evident at each site. Significant differences in growth, between populations reared within a common environment, indicate that these populations do harbor some genetic uniqueness. This information maybe useful in understanding the ecological implications of subtle genetic differences and may help managers better understand the dynamics of these stocks while developing conservation plans.
Craig A. Tinus and Russell
The fate of out migrating post-smolt Atlantic salmon is poorly understood because monitoring is extremely difficult once they have left the rivers and entered the marine environment. Over a two year period, the NEFSC Atlantic salmon task has developed a coordinated research program focused on hatchery and naturally reared Atlantic salmon smolts in the Penobscot watershed, which is the largest remaining population of wild Atlantic salmon in the United States. This coordinated program involves the marking and release of 170,000 –180,000 hatchery smolts, a rotary screw trap monitoring program at the head of tide, and an estuary and near shore marine trap survey program. In May, 2000 the NOAA- fisheries Atlantic salmon working group implemented a pair trawl sampling approach to the capture and live release of post-smolts based on technology originated by investigators in Norway and Canada. We pair trawled a modified mid-water trawl with an aluminum catch box at the cod end throughout Penobscot Bay and near shore waters of the Gulf of Maine. Our total catch was 1458 Atlantic salmon post-smolts with a handling mortality of 7.9%. Of those fish, 608 scale samples were taken and preliminary analysis suggests that 3.2% were naturally reared. Besides length, weight and condition we took 87 blood and 139 gill samples for analysis of smolt physiology. These data complete a physiology data series of marked hatchery reared pre-smolts that will yield a far better understanding of smolt physiology in a natural system. Ninety-nine stomachs were removed from mortalities and analyzed for contents. Those data suggest that post-smolts shift from feeding on riverine drift to being opportunistic piscivours soon after entering the marine system. Recovery of 355 elastomere marked fish will allow for evaluation of the relative contribution of different hatchery release groups to the post-smolt population. A rough understanding of migration routes was gained by catch data. A follow-up cruise in Spring 2002 will expand the spatial and temporal scale of sampling to further explore trends in near shore marine distribution. This sampling technique has demonstrated considerable potential for evaluating post-smolt biology at a critical life history stage.