Ecology of young-of-the-year Atlantic salmon: Evaluation of strain differences and over-winter survival

I investigated the survival and growth of four strains of Atlantic salmon during the first summer of stream residence. Summer conditions also were simulated in the laboratory and comparisons made between a land-locked and sea-run strain of Atlantic salmon. Winter survival and growth was evaluated through an in-situ caged experiment and a laboratory study. Laboratory estimates of growth, consumption, and respiration were used to calibrate a bioenergetics model. The temperature range for the model was 1°C to 25°C, encompassing fish from 0.25 to 20 g. Four genetic strains of Atlantic salmon were studied over four years, representing a sea-run and a land-locked strain in each year. During the first two summers (1998 and 1999), Grand Lake (land-locked) and Penobscot (sea-run) strains were studied, while during the last two summers (2000 and 2001) Lake Memphremagog (land-locked) and Merrimack River (sea-run) genetic strains were studied. The Lake Memphremagog strain had the highest growth rates. Laboratory investigations were conducted at six temperatures (12–25°C) to identify the optimum temperature for growth and food consumption. Maximum growth occurred at 18°C in both genetic strains. There was not a significant difference in growth rates between the two genetic strains for the range of temperatures evaluated. Winter studies were conducted on the Lake Memphremagog strain in the field and on the Lake Memphremagog and Merrimack River genetic strains in the laboratory. Fish survival over two winters studied in the field was 100%. The majority of the Atlantic salmon young-of-the-year lost weight over winter, with increases (less negative growth) observed later in the winter. Fish consumption and growth was observed in the laboratory at both 1°C and 4°C. Laboratory derived estimates of consumption, respiration, and growth were used to calibrate a bioenergetics model for Atlantic salmon. The calibrated model was then applied to growth rates observed in the field to estimate consumption and identify if food may be limiting in the study streams. Based on the model simulations, it did not appear that food was limiting growth during the first two months of the summer. The slight variations in model output among the stream sites appeared to be related to differences in stream temperatures at each site.