Research Document - 2015/062

Scotian Shelf Shrimp 2014-2015

By D. Hardie, M. Covey, K. Nickerson, and M. King

Abstract

The Fisheries and Oceans Canada-industry survey stratified mean remained approximately stable, decreasing just 1.5% from 39,381 (32,435-46,328) metric tonnes (mt) in 2013 to 38,791 (31,469-46,555) mt in 2014. Similarly, the spawning stock biomass (SSB) decreased by 1.5%, and remains in the Healthy Zone for this stock. The 18% increase in the TAC for 2014 (to 4500 from 3800 mt in 2013) to capitalise on the high fishable biomass of the abundant 2007/08 year classes was sufficiently precautionary to maintain female exploitation at 15%, below the 20% removal reference for this stock. Both commercial catch per unit effort indices declined by 30%, which is inconsistent with the stability of the total, and SSB, relative to 2013. Difficult springtime fishing conditions (wind and ice) were reported to have contributed to low catch rates by the Gulf fleet. Overall, commercial and survey sample length frequency distributions, modal analysis of survey data and the stabilisation of total and SSB indices at a relatively high values suggest that the stock is currently supported primarily by the moderately abundant 2007 and 2008 year classes, supplemented by the less abundant year classes from the subsequent years of low recruitment. The belly-bag index of age 1 abundance was the second highest on record, suggesting very high juvenile recruitment from the 2013 year class. If survival conditions are favourable, the 2013 year class may be evident in survey belly bag and main trawl samples in the 2015 survey, and to begin to recruit to the fishable biomass in 2016. 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 these more abundant cohorts/high density periods in this stock). Spring sea surface temperatures cooled for the fourth consecutive year, which is thought to be positive for shrimp, while bottom temperatures on the shrimp grounds remained warm, which is negative. Similarly, indices of predation provided somewhat equivocal results; cod recruitment was extremely low while the general index of abundance of shrimp predators was high. Low or decreasing indices of abundance of sympatric coldwater species suggest that the environment on the Scotian Shelf is becoming less favourable for coldwater species such as shrimp. The stock is expected to continue to gradually decline in 2015 as the 2008 year class begins to reach the end of its life-expectancy and because succeeding year classes do not appear to be very abundant.

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