Research Document - 2008/052

An Assessment of the Eastern Scotian Shelf Shrimp Stock and Fishery in 2007 with an Outlook for 2008

By P. Koeller, M. Covey and M. King

Abstract

Stock biomass remains high - the 2007 DFO-industry survey index was the third highest of the 13 year series. Increases in Shrimp Fishing Areas (SFAs) 13, 15 and 17 offset a large decrease in SFA 14; however, the latter area continues to contain most of the biomass. The spawning stock biomass (females) remained high, as males from the large 2001 year class began to change sex. It is likely to remain high, as this year class continues to change sex during 2007- 2008. It should support the higher Total Allowable Catch (5000mt) effected in 2005 through 2008. The 2002-2007 year classes are weaker, consequently, a biomass decrease is expected following the passage of the 2001 year class through the population, but the timing and rate of decrease will depend on the rate of sex change, recruitment to the fishable biomass and natural mortality of females. The population is concentrated in fewer length (and year) classes than previously, which may decrease population stability and increase vulnerability to exploitation. Commercial counts in 2007 were the highest on record due to the prominence and relatively small size of the 2001 year-class, which constituted the majority of the catch by numbers during 2006-2007 and by weight in 2007. Effort in SFA 14 remained high as fishers continued to take advantage of good catch rates and accumulated biomass in this area. The proportion of the catch taken during the ovigerous period remained relatively low in 2007, with most of the effort occuring during the summer months. The percentage of females in the catch remained relatively low due to the large numbers of shrimp from the 2001 year class, which have delayed sex change, presumably due to their slower growth rate. Total and female exploitation remained below average; however, exploitation of the smallest shrimp (<19mm CL [carapace length]) increased substantially in 2007, apparently due to low recent recruitment and sustained effort. Exploitation of the largest >26mm shrimp also increased. Commercial catch rates remained high in 2007, and spatial indicators show that the area with the highest commercial catch rates remains large.

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