Research Document - 2012/066

Pre-COSEWIC review of variation in the abundance, distribution and productivity of white hake (Urophycis tenuis) in the southern Gulf of St. Lawrence, 1971-2010

By D.P. Swain, T.R. Hurlbut, and H.P. Benoît

Abstract

White hake (Urophycis tenuis) is a demersal gadoid fish found in the southern Gulf of St. Lawrence where it was historically the third or fourth most important groundfish resource in the region. The directed fishery for white hake in the southern Gulf (NAFO Div. 4T) was closed in 1995 and has remained under moratorium since then. COSEWIC (the Committee on the Status of Endangered Wildlife in Canada) will be conducting an assessment of the status of white hake in Canadian waters in terms of its risk of extinction. This paper compiles and presents information possessed by DFO on life history traits, trends in the abundance and distribution of this species, and threats to its persistence in the southern Gulf of St. Lawrence for the development of a status report for COSEWIC. The available data, including the results of a recent molecular genetic study, indicate that white hake in the southern Gulf of St. Lawrence approximate a designatable unit (DU). There was an 80-90% decline in the abundance of mature fish in this DU over the last three generations. Despite the moratorium on the directed fishery since 1995, and very low reported landings since then, there has been no recovery of this resource. Natural mortality increased to very high levels in the 1990s and 2000s; few white hake now live more than 5 years. The white hake population is being maintained by unusually high survival at early life stages. Fishing mortality is now negligible and high natural mortality is the main threat to population persistence. The high natural mortality is hypothesized to result from predation by grey seals.

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