Science Advisory Report  2010/004

Assessment of Northern Shrimp on the Eastern Scotian Shelf (SFA 13-15)

Summary

• Total and spawning stock biomasses increased to the second highest on record.
• Total and female exploitation decreased to the second lowest on record.
• Changes in shrimp survey biomass since 2004 were probably due, in part, to survey catchability factors.
• Abundance appears to have remained high since 2004, and the decrease in TAC for 2009 appears to have been premature.
• The area of highest commercial catch rates remains large.
• Count estimates (numbers of shrimp per pound) in the fishery have decreased recently due to the growth of the 2001 year class, and fishers should have no difficulty in the immediate future in avoiding small shrimp.
• The long-term decreasing trend in length at sex change and maximum size has reversed somewhat due to delayed sex transition and an additional year(s) of growth of 2001 year class males.
• Belly-bag results in 2008 and 2009 indicated strong 2007 and 2008 year classes, which coincides with the maturation of the strong 2001 year class. This suggests that large year classes are associated with large spawning stock biomass.
• It is not clear if biomass will decrease before the next recruitment pulse due to uncertainty in the relative strength of succeeding year classes.
• It is likely that average catches higher than those taken during the modern fishery (approximately 4,000mt) are sustainable; however, it is important to accurately monitor the response of the population to increased exploitation.
• A generalized surplus production model suggests that a catch of 5,000mt would result in fishing mortalities that remain well below the fishing rate mortality at maximum sustainable yield (Fmsy) and biomasses well above biomass at maximum sustainable yield (Bmsy).
• An increase in the TAC for 2010 is supported by the current assessment, with cautious increases thereafter if biomass remains high and strong year classes continue to appear.

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