Science Advisory Report 2014/027
Big skate (Raja binoculata) and Longnose skate (R. rhina) stock assessments for British Columbia
Summary
- Big Skate (Raja binoculata) is an important component of both the trawl and the hook and line commercial groundfish fisheries off British Columbia, Canada. Currently, the largest fishery in British Columbia that encounters skate is the groundfish trawl fishery. Big Skate are predominately captured by bottom trawl in Hecate Strait (5CDE). The majority of Longnose Skate catch (R. Rhina) is made off the west coast of Vancouver Island (3CD). Hook and line catches of Longnose Skate are currently larger than trawl catches in Queen Charlotte Sound (5AB) and in Hecate Strait.
- Based on tagging results and fishery spatial patterns, science advice was provided by four Skate Management Areas (Figure 1): 3CD (including minor areas 19 and 20 of 4B); 5AB (including minor area 12 of 4B); 5CDE; 4B (minor areas 13 - 18, 28, 29 only). Based on feedback from the commercial sector, coastwide harvest advice was provided for Longnose Skate, in addition to the four proposed Skate Management Areas.
- Several methods (including Bayesian surplus production modeling and data-limited approaches) were explored to provide detailed stock assessments for these data-limited species. None were able to provide reliable estimates of biomass, preventing evaluation of current and future stock status relative to reference points.
- It was recommended that harvest yields should be selected based on mean historic catch, with consideration given to results of trend analyses of research survey indices and to the ranges of maximum sustainable yield (MSY) estimates identified by the new Catch-MSY approach. The Catch-MSY results were extremely sensitive to assumptions and so could not be used as the sole basis of advice to managers.
- For area 4B, insufficient data existed for Catch-MSY or survey trend approaches. The recent average catch is only 9 t for both species combined, and information on mean historic catches and spatial distribution was provided.
- For Big Skate, there were no significant trends in abundance indices from surveys. For all Skate Management Areas, average historical catches were below the maximum MSY estimate from the Catch-MSY results.
- For Longnose Skate, trawl survey data indicated statistically significant declines in abundance; no significant trends were detected for the longline survey data. For all Skate Management Areas (and the coastwide aggregate), average historical catches exceeded the maximum MSY estimate from the Catch-MSY results.
This Science Advisory Report is from the May 16th, 2013 Regional Peer Review Meeting on the “Review of Assessment of Longnose Skate and Big Skate stocks in areas 4B, 3CD, 5AB and 5CDE in British Columbia”. Additional publications from this process will be posted as they become available on the Fisheries and Oceans Canada Science Advisory Schedule.
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