Research Document - 2009/030

An Assessment of the Eastern Scotian Shelf Shrimp Stock and Fishery in 2008 with an Outlook for 2009

By P. Koeller, M. Covey, and M. King

Abstract

The expected biomass decrease has begun and is progressing quickly as the 2001 year class passes through the population. Biomass decreased significantly (20%) since last year and 36% since the all-time high of 2004. It is now slightly below average for the 1995-2008, but above the low values of the 1980s survey series. However, the earlier series used a trawl which probably had a lower catchability factor for shrimp; consequently, the difference between the low biomasses of the 1980s and the high biomasses since 1994 may be exaggerated. Decreases were observed in all areas except the inshore, which remained about the same as 2007. The greatest decrease was observed in Shrimp Fishing Area (SFA) 14, which has been fished heavily during the last 3 years, and no longer shows the large biomass which had accumulated over the last 7 years. Effort in SFA 14 remained high in 2008 but due to the biomass decrease exploitation increased to 26%, the highest on record for this area. The spawning stock biomass (SSB) has decreased by 50% since the all time high of 2004 and is now slightly below average for the 1995-2008 series. It remains above the low values of the 1980s; however, the difference may also be exaggerated as described above. Female sizes have also decreased significantly since the mid 1990s; consequently, egg production per unit SSB is now lower. The population continues to be represented in fewer length (and year) classes than previously, which may decrease population stability and increase vulnerability to exploitation. Commercial counts since 2005 have been high due to the prominence of the 2001 year class and their relatively small size due to slower growth - growth overfishing continues to be a concern. Overall exploitation increased to 14.6%, above the average of 12.5%. Female exploitation increased sharply to 20%, near the observed maximum. The proportion of the catch taken during the ovigerous period also increased in 2008. The percentage of females in the catch continued to be low, presumably since many shrimp from the 2001 year have still not changed sex. Commercial catch rates remained high in 2008 and spatial indicators show that the area with the highest commercial catch rates remains large. However, the discrepancy between survey and catch per unit effort (CPUE) may be diagnostic of a large year class as it begins to decline and concentrate in dense shoals over smaller areas, as previously observed for the 1993-1995 year classes.

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