2019 STAR Panel: Trawlable area in cowcod conservation area

[chantelwetzel-noaa]

As the WCGBTS is highly informative in the model, maintaining full coastwide survey effort is essential. However, currently the survey does not include a large fraction of the habitat south of 36°N, the cowcod conservation areas. Despite a lack of data in this large area, catch is allocated north and south of 36°N based on the estimated fraction of sablefish in these areas, and this fraction, in turn, is based on an extrapolation of survey catch rates outside the CCAs to those inside. As fish within the CCAs are only subject to fishing pressure if and when they move, and movement rates are variable, this concentration of effort outside of the CCAs could potentially lead to localized depletion, which in turn could bias the signal in fishery (and potentially survey) age and length composition from the fished areas. It would be beneficial to have survey data from within the CCAs to inform the survey, and to allow for some evaluation of whether and how population structure may vary inside and outside of the CCAs. There could be some potential for local depletion elsewhere as well, given the concentration of trawl effort off of Oregon and Washington and the decline in fishing effort and catches of both trawl and fished gear in California north of 36°N.

Work with @Curt-Whitmire-NOAA to see if we can determine estimates of trawlable area that are within the CCA.

[Curt-Whitmire-NOAA]

@chantelwetzel-noaa I think we can come up with a reasonable estimate of trawlable area within the CCA. We have decent bathymetric information in the CCA, from which we can derive various terrain metrics (slope, rugosity, curvature, etc.) and analyze in the context of historical survey tow tracks in similar habitats south of 34°N and outside the CCA. Eventually, I'd like to develop a similar analysis coastwide, but using the SoCal Bight as a test case might be more practical and help inform a more geographically extensive analysis.

I'd be happy to meet soon to brainstorm some ideas.

[chantelwetzel-noaa]

Thanks @Curt-Whitmire-NOAA. The way we calculate our indices extrapolates across missing areas, so the estimated biomass should account for this to some extent, assuming that the distributions in the closed areas are comparable to the nearby sampled areas for a mobile species like sablefish. However, it may be useful to quantify the proportion of unsampled areas to address this point from the last STAR panel.