Terms of Reference

Recovery Potential Assessment – Winter Skate (Leucoraja ocellata), Gulf of St. Lawrence population and Eastern Scotian Shelf – Newfoundland population

Zonal Peer Review Meeting – Gulf, Maritimes, Newfoundland and Labrador, Quebec regions

January 19-21, 2016
Moncton, New Brunswick

Chairperson: Gérald Chaput

Context

After the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses an aquatic species as Threatened, Endangered or Extirpated, Fisheries and Oceans Canada (DFO) undertakes a number of actions required to support implementation of the Species at Risk Act (SARA). Many of these actions require scientific information on the current status of the wildlife species, threats to its survival and recovery, and the feasibility of recovery. Formulation of this scientific advice has typically been developed through a Recovery Potential Assessment (RPA) that is conducted shortly after the COSEWIC assessment. This timing allows for consideration of peer-reviewed scientific analyses into SARA processes including recovery planning.

In the first assessment of Winter Skate (Leucoraja ocellata Mitchill 1815) in Canadian waters from May 2005, COSEWIC assessed the species as four populations or Designatable Units: the southern Gulf of St. Lawrence population (endangered), the northern Gulf of St. Lawrence and Newfoundland population (data-deficient), Eastern Scotian Shelf population (threatened), and the Western Scotian Shelf population (special concern). Recovery Potential Assessments were completed for the southern Gulf of St. Lawrence population and the Eastern Scotian Shelf population (DFO 2005a, 2005b).

In the re-assessment of the species in eastern Canada of April 2015, COSEWIC revised the population structure down to three populations and revised the status of these populations. The three populations identified by COSEWIC are:

• The Gulf of St. Lawrence population: comprised of the previous southern Gulf of St. Lawrence and the northern Gulf portion of the previously identified Northern Gulf and Newfoundland population. It is designated endangered by COSEWIC. Abundance of mature individuals is estimated to have declined 99% since the early 1980s, and is now at a historically low level. There has also been a severe reduction in range size, which is also at a historical low. If current trends continue, this population is in danger of imminent extinction. There is no commercial fishery for this population, though declines in the 1970s and 1980s may have been due to an unsustainable rate of mortality from bycatch in fisheries targeting other groundfish species. Currently, no bycatch of winter skate can be retained. The species has a slow rate of population growth, and the main threat appears to be unsustainably high non-fishing mortality, possibly due to predation by Grey Seals.
• The Eastern Scotian Shelf – Newfoundland population: comprised of the previous Eastern Scotian Shelf population and the Newfoundland portion of the previously identified Northern Gulf and Newfoundland population. It is designated endangered by COSEWIC. Abundance of mature individuals is estimated to have declined 98% since the early 1970s, and is now at a historically low level. This population’s range size has varied over this time, having increased until the mid-1980s, with a decrease since then. Overfishing in the 1980s and 1990s, including from directed skate fisheries, may have contributed to declining abundance over that period. The main threats since then have been unsustainably high non-fishing mortality, possibly due to predation by Grey Seals, as well as fishing mortality due to bycatch in fisheries targeting other species.
• The Western Scotian Shelf population: has remained unchanged in structure from the 2005 COSEWIC assessment. It is designated as not at risk by COSEWIC and is not subject to a recovery potential assessment.

In support of listing recommendations for Winter Skate by the Minister, DFO Science has been asked to undertake an RPA, based on the national RPA Guidance. The advice in the RPA may be used to inform both scientific and socio-economic aspects of the listing decision, development of a recovery strategy and action plan, and to support decision making with regards to the issuance of permits or agreements, and the formulation of exemptions and related conditions, as per sections 73, 74, 75, 77, 78 and 83(4) of SARA. The advice in the RPA may also be used to prepare for the reporting requirements of SARA s.55. The advice generated via this process will update and/or consolidate any existing advice regarding Winter Skate.

Objectives

• For the Gulf of St. Lawrence Winter Skate population and the Eastern Scotian Shelf – Newfoundland Winter Skate population, to provide up-to-date information, and associated uncertainties, to address the following elements:

Biology, Abundance, Distribution and Life History Parameters

Element 1: Summarize the biology of the respective populations of Winter Skate (Leucoraja ocellata).

Element 2: Evaluate the recent species trajectory for abundance, distribution and number of populations.

Element 3: Estimate the current or recent life-history parameters for Winter Skate.

Habitat and Residence Requirements

Element 4: Describe the habitat properties that Winter Skate needs for successful completion of all life-history stages. Describe the function(s), feature(s), and attribute(s) of the habitat, and quantify by how much the biological function(s) that specific habitat feature(s) provides varies with the state or amount of habitat, including carrying capacity limits, if any.

Element 5: Provide information on the spatial extent of the areas of the distribution of Winter Skate that are likely to have these habitat properties.

Element 6: Quantify the presence and extent of spatial configuration constraints, if any, such as connectivity, barriers to access, etc.

Element 7: Evaluate to what extent the concept of residence applies to the species, and if so, describe the species’ residence.

Threats and Limiting Factors to the Survival and Recovery of Winter Skate

Element 8: Assess and prioritize the threats to the survival and recovery of the Winter Skate .

Element 9: Identify the activities most likely to threaten (i.e., damage or destroy) the habitat properties identified in elements 4-5 and provide information on the extent and consequences of these activities.

Element 10: Assess any natural factors that will limit the survival and recovery of the Winter Skate .

Element 11: Discuss the potential ecological impacts of the threats identified in element 8 to the target species and other co-occurring species. List the possible benefits and disadvantages to the target species and other co-occurring species that may occur if the threats are abated. Identify existing monitoring efforts for the target species and other co-occurring species associated with each of the threats, and identify any knowledge gaps.

Recovery Targets

Element 12: Propose candidate abundance and distribution target(s) for recovery.

Element 13: Project expected population trajectories over a scientifically reasonable time frame (minimum of 10 years), and trajectories over time to the potential recovery target(s), given current Winter Skate population dynamics parameters.

Element 14: Provide advice on the degree to which supply of suitable habitat meets the demands of the species both at present and when the species reaches the potential recovery target(s) identified in element 12.

Element 15: Assess the probability that the potential recovery target(s) can be achieved under current rates of population dynamics parameters, and how that probability would vary with different mortality (especially lower) and productivity (especially higher) parameters.

Scenarios for Mitigation of Threats and Alternatives to Activities

Element 16: Develop an inventory of feasible mitigation measures and reasonable alternatives to the activities that are threats to the species and its habitat (as identified in elements 8 and 10).

Element 17: Develop an inventory of activities that could increase the productivity or survivorship parameters (as identified in elements 3 and 15).

Element 18: If current habitat supply may be insufficient to achieve recovery targets (see element 14), provide advice on the feasibility of restoring the habitat to higher values. Advice must be provided in the context of all available options for achieving abundance and distribution targets.

Element 19: Estimate the reduction in mortality rate expected by each of the mitigation measures or alternatives in element 16 and the increase in productivity or survivorship associated with each measure in element 17.

Element 20: Project expected population trajectory (and uncertainties) over a scientifically reasonable time frame and to the time of reaching recovery targets, given mortality rates and productivities associated with the specific measures identified for exploration in element 19. Include those that provide as high a probability of survivorship and recovery as possible for biologically realistic parameter values.

Element 21: Recommend parameter values for population productivity and starting mortality rates and, where necessary, specialized features of population models that would be required to allow exploration of additional scenarios as part of the assessment of economic, social, and cultural impacts in support of the listing process.

Allowable Harm Assessment

Element 22: Evaluate maximum human-induced mortality and habitat destruction that the species can sustain without jeopardizing its survival or recovery.

Expected Publications

• CSAS Science Advisory Reports: one for Gulf of St. Lawrence Winter Skate population, one for Eastern Scotian Shelf – Newfoundland Winter Skate population
• CSAS Research Document(s)
• CSAS Proceedings

Participants

• Fisheries and Oceans Canada (Ecosystems and Oceans Science, Ecosystems and Fisheries Management sectors)
• Other invited experts

References

Benoît, H.P. 2006. Estimating the discards of winter skate (Leucoraja ocellata) in the southern Gulf of St. Lawrence, 1971-2004, under multiple sources of uncertainty. DFO Can. Sci. Advis. Sec. Res. Doc. 2006/002.

Benoît, H.P., Swain, D.P., Hammill, M.O. 2011. A risk analysis of the potential effects of selective and non-selective reductions in grey seal abundance on the population status of two species at risk of extirpation, white hake and winter skate in the southern Gulf of St. Lawrence. DFO Can. Sci. Advis. Sec. Res. Doc. 2011/033. iv + 30 p.

DFO. 2005a. Recovery Potential Assessment for Winter Skate on the Eastern Scotian Shelf (NAFO Division 4VW). DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2005/062.

DFO, 2005b. Recovery Potential Assessment for Winter Skate in the southern Gulf of St. Lawrence (NAFO Division 4T). DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2005/063.

DFO. 2010. Estimated bycatch mortality of winter skate (Leucoraja ocellata) in the southern Gulf of St. Lawrence scallop fishery (2006 to 2008). DFO Can. Sci. Advis. Sec. Sci. Resp. 2010/009.

Swain, D.P., J.E. Simon, L.E. Harris, and H.P. Benoît. 2005. Recovery potential assessment of 4T and 4VW winter skate (Leucoraja ocellata): biology, current status and threats. DFO Can. Sci. Advis. Sec. Res. Doc. 2006/003.

Swain, D.P., I. Jonsen, and R.A. Myers. 2005. Recovery potential assessment of 4T and 4VW winter skate (Leucoraja ocellata): Population models. DFO Can. Sci. Advis. Sec. Res. Doc. 2006/004.

Swain, D.P., Jonsen, I.D., Simon, J.E., and Myers, R.A. 2009. Assessing threats to species at risk using stage-structured state–space models: mortality trends in skate populations. Ecol. Applic. 19: 1347-1364.