Research Document 1998/114

Spatial and temporal variation in Atlantic salmon abundance in the Newfoundland-Labrador region with emphasis on factors that may have contributed to low returns in 1997

By J.B. Dempson, D.G. Reddin, M.F. O'Connell, J. Helbig, C.E. Bourgeois, C. Mullins, T.R. Porter, G. Lilly, J. Carscadden, G.B. Stenson, and D. Kulka

Abstract

Salmon populations commonly experience fluctuations in abundance. At times, fluctuations can be quite severe and occur commonly over wide geographic areas and this, apparently, is what happened in Newfoundland in 1997. With few exceptions, total returns of small salmon to monitored Newfoundland rivers declined by 45% or more over 1996 in a number of areas (Exploits, Gander, Northeast Placentia, Humber, Torrent, and Western Arm Brook), while other stocks experienced declines of 20 to 40% (Terra Nova, Middle Brook, Campbellton, Northeast Trepassey, and Conne). For the most part, declines were not expected. Substantive increases in spawning escapements in northeast and northwest coast rivers beginning in 1992, high smolt production in 1996, increasing trends in smolt survival, improved ocean climate indices, and early smolt run timing were all suggestive of improved adult salmon returns for 1997. This report summarizes historic trends in Atlantic salmon abundance in Newfoundland and Labrador, along with an overview of the status of stocks in 1997. It also provides a review of various factors that may have contributed to the low returns in 1997. Factors examined that could possibly have contributed to low returns were legal and illegal fisheries, marine environmental conditions, predation, disease, parasites, and others such as delayed maturation. Most evidence points to increased mortality at sea, but no single factor was identified that could conclusively explain the cause of the low returns.

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