Research Document - 2016/100

Information in Support of Recovery Potential Assessment for White Hake (Urophycis tenuis) from the Scotian Shelf (NAFO Divs. 4VWX5z)

By Guénette, S., and D. Clark

Abstract

The Northwest Atlantic Fisheries Organization (NAFO) Divs. 4VWX5Zc White Hake (Urophycis tenuis) population has significantly decreased in abundance since 1982 in spite of low fishing mortality. In NAFO Div. 4X5Zc, juveniles declined by 38% per decade since 1991 and adults by 46% per decade during 1982-2004 after which the abundance remained stable. Total instantaneous mortality is currently estimated at 1.03 for adults, while relative fishing mortality has declined since the 1970s and is currently estimated at 0.09 per year. The abundance is currently just above the proposed biomass recovery target while the proportion of older mature fish in the population is low (6% in 2013). At the current mortality rate, the Spawning Stock Biomass (SSB) has an 84% probability of remaining above the recovery target. Removing fishing mortality from the model does not result in any detectable changes in population trends.

In 4VW, juveniles declined at a rate of 33% per decade between 1982-2013 while adult abundance decreased more abruptly between 1982-1995 (73% per decade), after which the abundance remained stable. Total instantaneous mortality increased since the 1970s and is currently estimated at 1.6. Relative fishing mortality decreased during the same period. The population is currently below the proposed recovery target and with a low proportion of older mature fish (3%). At the current mortality rate and mean observed recruitment, SSB is predicted to increase above the recovery target; however, there is a 34% probability of being below the recovery target. If recruitment were to remain as low as the last three years and with the current mortality rate, there is a 63% probability that SSB would remain below the recovery target.

Both an increase in Grey Seal abundance and a decrease in Atlantic Herring may have contributed to higher mortality. For Divs. 4VW, adult abundance is below its recovery target; however, consequences of current fishing rates on population projections (relative to its recovery target) do not differ from conditions when F = 0.

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