Effect of Summer Floods and Spatial-Temporal Scale on Growth and Feeding of Juvenile Atlantic Salmon in Two New Brunswick Streams

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Transactions of the American Fisheries Society, Vol: 131, Issue: 4

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Arndt, S KA; Cunjak, R A; Benfey, T J
anadromous species; ATLANTIC; Atlantic salmon; bioenergetics; BIOLOGY; body conditions; Canada; New Brunswick; Cohorts; Commercial species; control; DIFFERENCE; DISCHARGE; downstream; energetics; energy; energy budget; environmental effects; factors; feeding; feeding behavior; FEEDING RATE; feeding rates; Fish; Flooding; Floods; Food consumption; Freshwater fish; GROWING-SEASON; growth; Growth conditions; Growth rate; GROWTH-RATE; GROWTH-RATES; history; INDIVIDUAL FISH; juvenile; JUVENILE ATLANTIC SALMON; juvenile salmon; juveniles; length; LIFE; life history; LIFE-HISTORIES; life-history; parr; RATES; RATIO; Rivers; SALAR; Salmo; Salmo salar; salmon; SAMPLE; Samples; scale; season; seasons; spatial; stream; streams; summer; TIME; UNITS; upstream; VARIANCE
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The objectives of this study were (1) to determine how summer floods influenced the feeding, growth, and energy reserves of juvenile Atlantic salmon Salmo salar, and (2) to describe the short-term spatial and temporal variation in feeding and growth. Age-0 and age-1 Atlantic salmon were collected from two New Brunswick streams during the growing seasons of 1992 and 1993. Changes over time were monitored from samples collected at the beginning, middle, and end of 10-d periods. For each year-class, two control periods of relatively constant discharge were compared with two summer floods of a discharge magnitude that would occur once every 2-3 years on average. Feeding rates were measured by weighing the gut contents of sampled fish, and short-term changes in growth were assessed using the RNA:DNA ratio. The results showed that fine-scale spatial units (20 m in length) may be more important than large spatial differences (upstream versus downstream reaches) in explaining variation in feeding and growth. The amount of variance explained by day-to-day variation within the periods ranged from 0% to 19% for gut fullness and from 1% to 25% for the RNA:DNA ratio. A large percentage of variance in feeding and growth remained among individual fish after the temporal and spatial factors were accounted for. This percentage was higher in age-0 (60%) than in age-1 (40%) fish and tended to be greater during nonflood periods. Comparison of flood and control periods suggested that average feeding rates were not significantly reduced by floods. However, RNA:DNA ratios provided evidence that floods caused temporary reductions in growth rates (20-30%) of both year-classes, and after the flood peak the ratio of age-0 salmon recovered more quickly than that of age-1 parr. Juvenile salmon appear to be fairly resilient to floods of a magnitude that would occur as part of the normal life history of most cohorts