Research Document - 2013/034
Scotian Shelf Shrimp 2012-2013
By D. Hardie, M. Covey, and M. King
Abstract
The Fisheries and Oceans Canada-industry survey stratified mean decreased for the third consecutive year, falling 8% from a total biomass estimate of 30,510 mt in 2011 to 28,028 +/- 4560 mt in 2012. Although spawning stock biomass also decreased by 12%, it remains in the Healthy Zone for this stock. A precautionary 9% reduction in the 2012 total allowable catch helped to ensure that female exploitation index (19%) did not exceed the removal reference point for this stock (20%). Overall, the survey and commercial catch per unit effort indices suggest that the stock is moderately abundant, which is consistent with the prediction that the 2007-2008 year classes would begin to recruit to the fishery in 2012. This is further corroborated by the commercial and survey length frequency distributions, as well as the modal analysis of survey data, which show that the fishable biomass is currently dominated by the 2007-2008 year classes, with very little indication of strong succeeding (>2009) year classes. The paucity of the succeeding year classes is consistent with recent trends in the survey belly-bag index, which has been low for 2010-2012 (2009-2011 year classes). Indices of stock dispersion suggest that the stock is currently composed of several year classes, and is relatively evenly distributed on the fishing grounds. Trends in shrimp size indices are consistent with expectations based on life history and growth rates of moderately abundant shrimp (i.e. no evidence of slower growth or delayed sex transition that have occurred in this more abundant cohorts/high density periods in this stock). The continuation of warmer temperatures on the shrimp grounds, coupled with continued low abundance of most sympatric cold water species, do not provide an optimistic expectation of strong juvenile recruitment deriving from the 2007-2008 year classes. Low predation indices suggest that natural mortality of shrimp due to predation is likely to remain low. Total and spawning stock biomass are expected to remain stable at moderately high levels for 2013 as the 2008 year class undergoes sex transition and contributes fully to the fishable stock. The stock may begin to decline in 2014 as the 2007 year class begins to reach the end of its life-expectancy and because succeeding year classes do not appear to be very abundant. In the medium-term, the expectation of several years of weak recruitment to the adult (fishable) biomass, coupled with the lack of evidence of a new recruitment pulse and continued trends of warm temperatures and low recruitment of sympatric cold water species suggest that that the stock is likely to decrease starting in 2014.
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