Research Document - 2007/032

Gaspereau River alewife stock status report

By McIntyre, T.M., R.G. Bradford, T.D. Davies, and A.J.F. Gibson

Abstract

The anadromous alewife (Alosa pseudoharengus) population of the Black River – Gaspereau River system in Nova Scotia supports both recreational and commercial fisheries of local importance. Both fisheries target adult alewife as they migrate upstream through the river and estuary to spawn in lakes during May-June. The 2001 assessment found that the Gaspereau River alewife population exhibited the characteristics of a heavily exploited stock. Exploitation rates were high, nearly 80%, and the majority of fish in the spawning run belonged to only 2 age classes. A five-year fishery management plan came into effect for the start of the 2002 season with the goal of meeting the spawning escapement target of 400,000 adults through a reduction in fishing mortality. Exploitation rates have been lower in every year since the implementation of the management plan (average c. 55%; range c. 52% to c. 63.9%) than the average exploitation rate reported in the last assessment (c. 79.5%). Spawning escapement has doubled since the implementation of the management plan, but has yet to reach the target of 400,000 alewives with the exception of 2003. There are no indications that either alewife longevity or incidence of repeat spawning has increased in response to the decrease in exploitation and changes in fish passage that came into effect concurrently in 2002. Recruitment to the Gaspereau River adult population can occur as early as age three, most do not mature until ages four and five, with full recruitment to the adult population (and fishery) at age six. Therefore, 2006 was the earliest year that a measurable positive response, in terms of increased recruitment, to the reduction in exploitation, could be anticipated. Recruitment of age four spawners in the most recent year was low. There may be cause for concern with post-escapement and/or post-spawning survival should these characteristics not increase. Further monitoring of stock size and age structure is warranted to evaluate the response to changes made in 2002.

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