Atlantic Fisheries Research Document 1996/140

Indices of marine habitat for Atlantic salmon (Salmo salar) and trends in survival of hatchery-origin smolts

By C.J. Harvie; P.G. Amiro

Abstract

The variability of marine habitat indices for Atlantic salmon (Salmo salar) and correlation with annual return rates of hatchery-reared smolts is examined. Marine habitat indices for the months of January to April were used as independent variates in regression of annual survival rates of one-sea-winter grilse and two-sea-winter salmon for Saint John, LaHave, and Liscomb rivers. Covariate techniques were required to de-trend return rates and identify significant partitioning of data in pre- and post-1984 Salmon Management Plan which closed or reduced interception of salmon. "Plan" effect was not significant (p>0.05) in grilse or salmon returns to Saint John River and return rate had a significant negative trend for both grilse and salmon. Return rates for both grilse and salmon were significantly correlated with maximum habitat area of January to April in the grilse winter-at-sea, but did not account for as much of the variation as the temporal trend. "Plan" was not significant for Liscomb River grilse return rates and was marginally significant (p=0.049) for the salmon return rates. Negative trends in Liscomb return rates were marginally significant (p=0.051) for grilse and significant (p=0.005) for salmon in the post-plan years. January habitat index in the return year accounted for more of the variation in return rates that temporal trend for Liscomb data. "Plan" effect for LaHave River return rates was significant for grilse but not for salmon and January habitat accounted for about the same account of variation as marginally-significant negative temporal trends in return rates. The analysis indicated that even thought the plan reduced interception and caused a significant increase in marine survival in some stocks and ages, a decline in marine survival continued. Marine survival for these hatchery stocks was better associated with indices of marine habitat than simple negative linear trend. The possible causes of these associations are discussed as well as suggestions for improved forecast models of both hatchery and wild returns to rivers.

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