Research Document - 2010/069

Assessment of Rock crab (Cancer irroratus) stock status in the coastal waters of Québec in 2009

By L. Gendron et G. Savard

Abstract

In Quebec, commercial fishing of rock crab began in 1988, but the fishery did not really begin to take off until 1995, first in the southern part of the Gaspé Peninsula and Magdalen Islands, then along the north shore of the Gaspé Peninsula and, since 2004, on the North Shore and Anticosti Island. It is common knowledge that rock crab is an important prey species for lobster. Thus, as soon as rock crab exploitation began, the fishery was managed by a conservation plan intended to protect the trophic relationships between these two species. The management measures currently in place are for protecting the reproductive potential by keeping exploitation rates low or moderate.

The present research document describes the data and analyses that served to determine stock status and provide recommendations for the 2010-2012 fishing seasons (MPO 2010). Stock assessment is based mainly on the review of abundance indicators (landings and catch rates) and demographic indicators (size of crabs landed), from the commercial fishery. The assessment was based on examination of historical trends highlighting the changes observed since the last stock assessment in 2006 (MPO 2007). Additionally, incidental catches of rock crab from a survey on lobster conducted since 1995 in the Magdalen Islands was used to estimate recruitment. A trap survey was also conducted in July 2008 along the north shore of the Gaspé Peninsula to follow the evolution of rock crab populations in exclusion (no-take) areas, in comparison with adjacent fishing areas.

The development of the rock crab fishery in the Gaspé Peninsula and Magdalen Islands in the past fifteen years has been done in a cautious manner. In 2009, in general, stock status indicators suggest that up to now, harvesting levels are not causing any major problems for populations. In a few cases, such as in the Magdalen Islands and on the North Shore, small reductions in quotas or fishing effort were recommended in order not to accentuate observed declines in CPUEs, or decreases in mean size or in the number of large-size crabs.

However, the management objectives of maintaining moderate harvesting levels are threatened by a lack of control of the by-catches by lobster vessels. In addition, the directed fishery effort currently deployed is significantly lower than that permitted by the existing management measures. The deployment of latent effort would increase the exploitation rate, with unknown consequences on the stability observed until now. Recommendations were given to eliminate this latent effort.

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