Research Document - 2001/061

Gaspereau river alewife stock status report

By Gibson, A.J.F., R.A. Myers

Abstract

The Gaspereau River watershed in Nova Scotia supports a stock of anadromous alewives (Alosa pseudoharengus) of local economic and ecological importance. The stock is fished both recreationally and commercially as it ascends the river to spawn during May and June, with an average value for the commercial catch of $288,000 per year (range: $24,000 to $1,000,000) between 1974 and 1999. Estimated fishery exploitation rates for this stock in 1999 and 2000 were 88.4% and 89.4% respectively, two of the highest rates recorded for this stock. The stock exhibits the characteristics of a heavily impacted stock: the majority of fish belong to only 2 age classes and the percentage of repeat spawners in 2000 was less than 10%. We suggest that the spawning escapement that provides maximum sustainable yield can be used as a reference point for this stock, and estimate that MSY occurs when around 400,000 to 450,000 reach Gaspereau Lake to spawn. Recent spawner escapements to Gaspereau Lake are about 10% to 20% this target. Under current water management practices, alewives are diverted past 4 of the 5 generating stations in the watershed. Mortality of alewives at the White Rock station is unknown. Spawning biomass and the catch at MSY decline in proportion to the level of juvenile passage mortality. The fishery is sustainable even at high levels of adult passage mortality, because the fish have an opportunity to reproduce prior to passage. We suggest that the hierarchical and life history models used to calculate target escapements in this report have significant potential as management tools, but need further development. Given adequate spawner abundance, current water management practices to protect alewives could be re-evaluated to allow greater flexibility in water use for other purposes.

Complete document (PDF, 256 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.