Research Document - 2005/001
An Assessment of the Eastern Scotian Shelf Shrimp Stock and Fishery in 2004 and Outlook for 2005
By Koeller, P., M. Covey, M. King, A. Thebeau
Abstract
The 2004 DFO-industry survey total biomass index was the highest of the 10 year series. While the bulk of the biomass (42%) continues to concentrate in the offshore part of SFA 14 (i.e. survey stratum 14 or the Misaine Hole), the biomass in the other areas has also increased substantially - all except the Canso Hole showed record estimates in 2004. The commercial fleet shifted much of its effort to the Louisbourg Hole (SFA 13), where both counts and biomass were favourable during most of the season. The spawning stock biomass (females) in 2004 was also by far the highest on record. This large increase in SSB was unexpected - in the 2003 survey the year class (~1999) recruiting to the 2004 female population only appeared about average. Biomass increases are expected to continue over the next several years as the exceptionally strong 2001 year class enters its last year as males in 2005 and recruits to the female population in 2006. In 2005 as much as 60% of this biomass could be comprised of this year class, consequently, it is expected that the difficulties predicted and experienced by fishers in avoiding small shrimp in 2004 will continue into the 2005 fishery. The 2001 year class, first characterised as strong from "belly bag" samples alone in the 2002 survey continues to appear exceptional in both belly bag and survey trawl catches in 2004. In belly bag samples the 2001 year class is about three times larger than the two succeeding year classes (i.e. 2002 and 2003). The 2003 year class appears stronger than the 2002 year class in belly bag samples, and the latter appears above average in the main survey trawl estimate, consequently, current recruitment appears to be good. It is possible that the 2001 year class will experience slower growth due to density dependence as was observed with the 1995 year class. Commercial catch rates (standardized series) appear to have levelled off at a high level in 2004. Spatial indicators suggest that the biomass is again beginning to expand in area, after a contraction associated with the concentration of the previous round of strong year classes (1993-1995) which allowed for continuing high commercial catch rates despite decreasing survey biomasses from 1999-2002. It should be noted that a new survey trawl was used for the 2004 survey which may account for some of the large biomass increase observed (increased trawl efficiency). However, the trawl was built to the same plans and specifications as the old trawl and NETMINDER mensuration showed that it performed in a similar manner. Traffic light indicators have improved during the last 3 years. A substantial increase is indicated in 2005 to take advantage of the accumulated and growing fishable biomass. There are two main concerns 1. although an increase in TAC appears warranted the large number of males from the 2001 year class may result in growth overfishing – the increase is based on the observation that in the past fishers have been able to avoid small shrimp due to the flexibility they have in fishing throughout the areas without major restrictions. 2. at the same time, this flexibility and the absence of area quotas tends to results in overexploitation in some areas and underexploitation in others.
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