Science Advisory Report 2008/048

Assessment of green sea urchin of the North Shore of the St. Lawrence Estuary in 2008

Summary

• Green sea urchin landings in Area 9 (Upper North Shore) varied between 0 and 86 t annually from 1994 to 2002. Beginning in 2003, they rose sharply and reached 689 t in 2007. In 2008, preliminary recorded landings as of August totalled 232 t.
• Fishing effort, measured in boat-days, was not evenly distributed in Area 9 over the years. From 2005 to 2008, 98% of landings in Area 9 came from the mouth of the Saguenay. The fishery at the river mouth was concentrated over an area of less than 2 km² on the south-east side of Batture-aux-Alouettes. Around 25% of the landings occurred between early April and mid-May (spring) and 60% from early September to the end of November (fall).
• On Batture-aux-Alouettes, the mean catch per unit effort (CPUE) recorded in diver-hours decreased between 2005 and 2007, whereas the size of landed sea urchins remained the same in 2006, but dropped between spring and fall in 2007. Data from the spring fishery showed a steady increase in CPUE variability between 2006 and 2008, and the size of landed sea urchins in the spring of 2008 continued to drop compared to the fall of 2007. These changes can be interpreted as signs of overfishing.
• An underwater diving survey conducted at the mouth of the Saguenay in June 2008 confirmed the occurrence of a substantial sea urchin population around the Batture-aux-Alouettes and helped characterize the spatial distribution, density and size structure of sea urchins. An abundance of sea urchins of 15-25 mm in diameter suggests that recruitment was good in 2005 and 2006.
• Fishing effort and catches at the mouth of the Saguenay were five times higher in 2006 and 2007 compared to 2005. The 2008 fishing plan was aimed at considerably decreasing exploitation at the river mouth by reducing the fishing season to a month in the spring. Fishing effort and catches did in fact drop, but fishery statistics suggest that the two high-exploitation years have impacted the abundance and size of sea urchins. It is therefore recommended that the river mouth remained closed in the fall of 2008 and that the 2009 fishing effort be limited to a similar level as in the spring of 2008.

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