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Research Document - 2007/089

Stock structure, life history, fishery and abundance indices for spiny dogfish (Squalus acanthias) in Atlantic Canada

By Campana, S.E., A.J.F. Gibson, L. Marks, W. Joyce, R. Rulifson and M. Dadswell

Abstract

In 2003, an intensive 5-year research program on Canadian dogfish was initiated by the Department of Fisheries & Oceans (DFO), conducted in cooperation with the dogfish fishing industry through a Joint Project Agreement (JPA). This report is an overview of all new and published work done to date to better understand the stock structure, migration patterns, abundance trends and current state of the Canadian portion of the Atlantic spiny dogfish population. The information and advice provided is expected to be used in the management of the fishery and to guide future discussions with the U.S.

Spiny dogfish have many characteristics of a metapopulation, whereby some dogfish aggregations colonize or depart Canadian waters en masse at periodic multi-year intervals, and then remain resident in those waters for many years at a time. For the most part, dogfish tagged in Canadian waters have remained in Canadian waters, and those tagged in U.S. waters have remained in U.S. waters. However, there is some movement (10-20%) between Canadian and U.S. waters, with the Gulf of Maine region being the primary mixing ground. The existence of a metapopulation would imply that managing northwest Atlantic dogfish as a single, well-mixed stock would be inappropriate.

In the absence of a viable population model, it was not possible to estimate the exploitation rate for spiny dogfish in Atlantic Canada. However, biological studies indicate that the Atlantic population of spiny dogfish is more productive than is the northwest Pacific population. However, the long gestation period (~ 2 years), late age of sexual maturation and slow growth rate for spiny dogfish means that the species is relatively unproductive compared to other fish species.

Spring minimum trawlable biomass estimates for spiny dogfish in Canadian and U.S. waters show similar trends, increasing from the early 1980s to the early 1990s, then declining somewhat to the present. Mean values for both indices were around 500,000 mt in the early 1990s, declining to about 300,000 mt in 2007 for the Canadian index. The Canadian spring index is considered to be a better indicator of total adult biomass than is the summer index.

It is not currently possible to estimate trends in mature female biomass for spiny dogfish in Atlantic Canada. However, mature female biomass in the U.S. spring RV survey has declined to much lower values in recent years, albeit with an upturn in the last two years. Without knowing the extent that Canadian spawners contribute to the health of northwest Atlantic dogfish metapopulation, it may not be wise to increase the exploitation rate on mature females.

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