Research Document - 2012/088

Assessment of green sea urchin along the north shore of the Saint Lawrence Estuary in 2008

By B. Sainte-Marie, S. Brillon, and N. Paille

Abstract

The status of green sea urchin (Strongylocentrotus droebachiensis) populations along the North Shore of the St. Lawrence Estuary (fishing area 9) was assessed in 2008 from known catch and effort data from the commercial fishery, along with size measurements of urchins. Annual landings varied between 0.3 and 85.7 t from 1995 to 2002. Starting in 2003 landings increased sharply and reached a record of 689.3 t in 2007. Landings recorded as of August 2008, before the onset of the fall fishing season, were 231.9 t. The spatial distribution of fishing effort measured as boat-days (bd) was not similar over the years. The sector of area 9 to the west of the mouth of the Saguenay, and mostly portions of the coast around Saint-Siméon and on the north side of Île aux Lièvres, was targeted (i.e., a fishing effort of at least 20 bd) in 1996 and 1997 and again in 2003 and 2004. The sector east of the mouth of the Saguenay, and mostly the portions of the coast between Pointe à Boisvert and Pointe aux Outardes and close to Pointe des Monts, was targeted only in 2000. The mouth of the Saguenay, including the eastern part of Batture aux Alouettes, Baie Sainte-Catherine and Batture de la Pointe aux Vaches, was targeted starting in 2004. From 2005 to 2008, 98% of area 9 landings originated came from the mouth of the Saguenay, where most of the fishing effort was concentrated on a surface area of about 1.8 km².

The short history of the green sea urchin fishery, the inconstant spatio-temporal distribution and intensity of fishing effort, as well as the uneven quality of fishing data, hinder the analysis of the effects of exploitation. Around Saint-Siméon, catch per unit effort data (CPUE), measured as kilograms per bd (kg/bd) or per diver-hour (kg/dh), and verbal reports from fishermen suggest depletion of the resource after only two years of fishing (1996-1997). At the mouth of the Saguenay, from 2005 to 2007 the median diameter of landed urchins decreased from 61 to 60 mm and the median CPUE measured per dh declined by 18 %, while CPUE variability increased. During the spring fishing season of 2008, the mean diameter of landed urchin decreased even more, to 58 mm, and CPUE variability further increased. These changes are interpreted as signs of overfishing. A diver survey at the mouth of the Saguenay in June 2008 demonstrated the existence of still-important green sea urchin population around Batture aux Alouettes and allowed to characterize the abundance and size structure of urchins. However, the lack of information on the dynamics of this population prevents any conclusion regarding its productivity and resilience to exploitation. A greater control of fishing effort and capacity is recommended to ensure the fishery develops sustainably.

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