Research Document 1997/117

Trends in Atlantic salmon abundance illustrated using a scaled index of returns, and estimates of marine exploitation prior to the closure of the Newfoundland commercial fishery

By J.B. Dempson, D.G. Reddin, M.F. O'Connell, C.C. Mullins, and C.E. Bourgeois

Abstract

A simple index of salmon returns is used to illustrate the impact of the commercial Atlantic salmon fishery moratorium on Newfoundland stocks. The index is easy to calculate and understand, and is scaled to a common meaningful value for ease of comparisons among rivers. It can be used to examine the impact of the moratorium within an individual river (stock), or across rivers for specific zones (e.g. northeast, south and west coasts). The index is not related to conservation level requirements and the basic data used to derive the index can be used to infer past average levels of marine exploitation. Results indicate that salmon returns to rivers along the northeast and west coasts have increased substantially during the moratorium period (1992-1996) relative to pre-moratorium levels (1984-1991). This was not the case for returns to south coast rivers, some of which have decreased on average by as much as 50% or more. Many stocks reached their lowest or second lowest level of abundance in 1991. Several Newfoundland salmon stocks, for both small and large salmon components, were declining in abundance throughout the mid-to late 1980s and into 1991. Estimates of marine exploitation rates were 44.0% (± 9%) on small salmon and 74.9% (± 7.6%) on large fish. These estimates are considered minimum values. This is because there is evidence to suggest that overall natural survival, for some stocks, has been declining over time and was actually lower during the moratorium years than it was prior to the commercial salmon fishery moratorium.

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