Science Advisory Report  2016/035

Recovery Potential Assessment for White Hake (Urophycis tenuis): Population of the Atlantic and Northern Gulf of St. Lawrence

Summary

Biology, Abundance, Distribution and Life History Parameters

• White Hake in the Atlantic and northern Gulf of St. Lawrence (ANGSL) Designatable Unit (DU) was assessed as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in November 2013. Adult abundance was estimated to have declined by approximately 70% over the past three generations, with most of the decline occurring before the mid1990s.
• The ANGSL DU covers a very large geographic area of eastern Canada and several fisheries management units (Northwest Atlantic Fisheries Organization (NAFO) Divisions 3NO, Subdivisions 3Ps and 3Pn, Division 4RS, part of Division 4T, Divisions 4VWX and Canadian portions of Subarea 5), which have area-specific fisheries characteristics and management measures. The portion of the White Hake St. Lawrence ANGSL DU that extends into US waters of Divisions 5Y and 5Z and the portion in Division 4T that overlaps with the southern Gulf White Hake DU were not included in abundance and trends analyses for the ANGSL DU.
• Indices of abundance from DFO research surveys available for four management units within the DU were used to characterize trends in abundance, for population modelling of abundance, and to define recovery targets for each management unit.
• Biomass and abundance indices for Divs. 3NOPs White Hake have been stable at low levels since 2003. Trends in abundance are characterized by occasional large recruitment that is quickly removed by fisheries targeting this species in Canadian waters and in the NAFO Regulatory Area of Divs. 3NO.
• The abundance index for Divs. 4VW White Hake peaked in the 1980s, and has been low since the mid1990s. The juvenile abundance index declined by 33% each decade since 1982, while the adult index declined by 73% per decade in 1982 to 1995 and remained stable afterwards.
• The abundance index for Divs. 4X5Zc White Hake peaked in the 1980s and 1990s, and has been variable at low levels in the 2000s. The juvenile abundance index declined by 31% each decade since 1991, while the adult index declined by 46% per decade during 1982 to 2004, and remained stable afterwards.
• The abundance index for Divs. 4RST* White Hake was higher in 1985 to 1990, declined to a minimum in 1994, then remained low. Total population abundance decreased by 80% over 1985 to 2014, while declines in abundance of mature and immature components were 64% and 69% (respectively) over 1987 to 2014.
• Although area occupied decreased over a short time period (1985 to 1992) in Divs. 4RST*, at a coarse geographic scale, there has not been any change in general distribution of White Hake in this DU.
• Recruitment of juveniles remains high in Divs. 4X5Zc, while the last three years showed low recruitment in Div. 4VW.
• In the past two decades, a primary source of mortality for White Hake in Divs. 4RST*, Divs. 4VW, and Divs. 4X5Zc was natural mortality (M), as indicated by high total mortality estimates (Z), correspondingly low relative fishing mortality values (F), and an ongoing decline or lack of increase (Divs. 4RST*) in adult indices. For Divs. 3NOPs, highly variable recruitment followed by directed fishing for White Hake (in Canadian waters and the NRA) appear to determine subsequent changes in adult biomass.

Threats and Limiting Factors to the Survival and Recovery of White Hake

• The only quantified threat to recovery of White Hake over the entire ANGSL DU is ongoing fishing mortality, which occurs in Canadian directed fisheries in Divs. 3NOPs and Subdiv. 3Pn, in the NRA by NAFO-member countries, and as bycatch in other commercial groundfish fisheries. However, fishing mortality presently appears not to be a limiting factor to White Hake survival and recovery.
• Habitat does not appear to be, nor is likely to become, a limiting factor to White Hake survival and recovery. There are no known anthropogenic threats that have reduced habitat quantity or quality for White Hake in the ANGSL DU.
• The causes of high natural mortality (M) of White Hake are largely unexplained in all units of the ANGSL DU. Seal predation is proposed as an important source of increased natural mortality of White Hake in the sGSL DU but available evidence is not conclusive for White Hake of the ANGSL DU.

Recovery Targets

• The proposed recovery target for the White Hake ANGSL DU is for indicators of abundance in the four management units to be sustained at levels above the proposed management unit-specific recovery targets. These recovery targets may include a distribution component.
• Abundance targets were defined for four management units in this DU, and correspond to an increase to sustained abundance at or above 40% of B_MSY (biomass at maximum sustainable yield).
• The proposed distribution target for White Hake recovery is to maintain current distribution and, specifically for Divs. 4RST*, to return to a distribution similar to the area covered during its most recent productive period (1987 to 1990).

Projections

• For Divs. 3NOPs, there is a 97% probability of remaining above the recovery target over the next fifteen years, under current conditions, and at a fishing rate of F_MSY.
• For Divs. 4VW, there is a 66% probability of reaching its recovery target under current conditions and at average recruitment, however, at recent low levels of recruitment, there is a 63% probability of the biomass being below the recovery target. Trajectories and probabilities of achieving this recovery target do not differ from conditions when F = 0 (no fishing related mortality).
• For Divs. 4X5Zc, there is an 84% probability of maintaining spawning stock biomass above the recovery target under current conditions. Trajectories and probabilities of remaining above the recovery target do not differ from conditions when F = 0.
• No projections are possible for the Divs. 4RST* management unit. Under current conditions, the adult abundance index has varied without trend since 1995.

Scenarios for Mitigation of Threats and Alternatives to Activities

• Possible mitigation measures to decrease fishing mortality in Canadian waters include: closing White Hake directed fisheries, closing bycatch (groundfish) fisheries, implementing White Hake bycatch protocols, increasing at-sea fisheries observer coverage to record otherwise unreported discards, and limiting fishing gear type, size, and amounts by fishery, season, and location.

Allowable Harm Assessment

• White Hake mortality due to fishing continues in all management units. Consequences of current fishing rates on adult abundance trends and population projections do not differ from conditions when F = 0 (no fishing related mortality).
• For Divs. 3NOPs, abundance is above its recovery target under current conditions and fishing rates, and current levels of fishing mortality are not jeopardizing survival or recovery.
• For Divs. 4VW, adult abundance is below its recovery target. However, consequences of current fishing rates on adult abundance trends and population projections (relative to its recovery target) do not differ from conditions when F = 0.
• For Divs. 4X5Zc, adult abundance is above its recovery target under current conditions and fishing rates, and current levels of fishing mortality are not jeopardizing survival or recovery. White Hake biomass is expected to increase at recent levels of fishing mortality.
• For Divs. 4RST*, abundance indices of recent years are below the abundance recovery target. Consequences of the current relative fishing rate of F = 0.007 are considered to have a negligible impact on White Hake recovery potential.

This Science Advisory Report is from the January 14 to 16, 2015 meeting on the Recovery Potential Assessment – White Hake (Urophycis tenuis), population of the southern Gulf of St. Lawrence and population of the Atlantic and northern Gulf of St. Lawrence. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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