Research Document - 2006/001
An Assessment of the Eastern Scotian Shelf Shrimp Stock and Fishery in 2005 and Outlook for 2006
By Koeller, P., M. Covey and M. King
Abstract
The continued biomass increase projected last year did not materialise, due to the unforeseen density-induced slow growth and either inaccurate estimation or higher mortality of the strong 2001 year class. However, the 2005 DFO-industry survey total biomass index was still the second highest of the 11 year series, decreasing slightly from the record high of the previous year. The bulk of the biomass continues to concentrate in the offshore part of SFA 14 (i.e. survey stratum 14 or the Misaine Hole). The spawning stock biomass (females) also decreased from 2004 but was still the second highest on record. The 2001 year class in 2005 continues to be the largest on record at age 4 (~ 4 x average). Considering the exceptional continuing strength of this year class since its detection in 2002 belly bag samples, its slower growth is likely to continue, consequently not all of this year class is expected to become female for the 2006 fishery, or it may delay sex change entirely for a year. It should support the higher TAC effected in 2005 for several more years, however, concerns about growth overfishing continue and it is not advisable to increase the TAC above the 2005 level. The 2002-2004 year classes are weaker, consequently a biomass decrease is expected following the passage of the 2001 year class through the population. This is similar to what occurred during the last strong recruitment event (1994-1995), suggesting the establishment of a cyclical population dynamic often seen in established shrimp fisheries. Such a pattern may be indicative of decreased stability, re-enforcing the need for continued good monitoring information and a precautionary approach in managing this fishery.
Commercial counts in 2005 were the highest on record because of difficulty in avoiding the 2001 year-class. After shifting much of its effort and catch (60%) to the Louisbourg Hole (SFA 13) in 2004 where catch rates and counts were favourable, in 2005 the distribution of effort and catch was more evenly distributed between areas, including increased effort in SFA 14 and 15, while avoidance of the inshore area continued. There was also a temporal shift in effort that more fishing activity occurred during the fall months due to the increase in TAC, small\soft shrimp, and low prices, resulting in a larger percentage of ovigerous females in the catch. After a sustained increase of over a decade, commercial catch rates (standardized series) peaked in 2003. They have decreased slightly since but remain high. Spatial indicators suggest that the area with the highest commercial catch rates (<250 kg/hr-) is expanding. Despite concerns of growth overfishing, the TAC for 2005 was increased substantially to take advantage of a projected biomass increase, and past performance of fishers in avoiding small shrimp due to flexibility in choosing fishing areas (i.e. no area quotas). The 2005 TAC was not caught, for a number of reasons, including poor market conditions, bad weather, difficulties in finding large shrimp and widespread distribution of the 2001 year class. A requested season extension into early 2006 was not recommended due to the lower-than-projected biomass, the resulting higher than projected exploitation rates, and large numbers of small shrimp in the catch. The trap fishery did not take place in 2005 due to poor market conditions.
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