Benchmark Workshop for selected elasmobranch stocks (WKELASMO)

  

A Benchmark Workshop for selected elasmobranch stocks (WKELASMO) was convened to evaluate the appropriateness of data and methods to assess and provide short-term forecast of four stocks: Porbeagle in the Northeast Atlantic (por.27.nea), thornback ray in the Bay of Biscay (rjc.27.8), undulate ray in the Channel (rju.27.7de), and cuckoo ray in western waters (rjn.27.678abd).

For porbeagle in the Northeast Atlantic, the workshop (and the reviewers from the stock identity working group (SIMWG)) considered that there is not enough evidence to split the stock despite genetic analysis and mark-recapture data indicating a possibility of two components. A SPiCT assessment using reported landings since 1926, three commercial indices and one reconstructed survey, was accepted and the forecast settings agreed, leading the stock into category 2. The stock is estimated to be harvested largely below FMSY (F/FMSY = 0.02), and the biomass, while increasing, remains below MSY-Btrigger (B/BMSY = 0.43). The 35th percentile of the catches at Ftarget is 324 tonnes.
Members of WKELASMO from the International Commission for the Conservation of Atlantic Tunas (ICCAT) provided additional assessments using JABBA and SPicT, both using a Fox model. Results were very similar and gave the same perception as the final accepted SPiCT assessment.

For thornback ray in the Bay of Biscay, a synthesis of work on stock boundaries within Subarea 8 was presented, indicating that this species in this area may be considered to comprise of two stocks: 8.abd and 8.c. The workshop (and the review from SIMWG) agreed to follow this conclusion.

· Thornback ray in divisions 8.abd: a Bayesian state-space biomass production model including Close kin mark-recapture (CKMR) results was accepted as the basis of the assessment and forecast, leading the stock into category 2. The stock is estimated to be exploited close to FMSY, and Biomass close to BMSY. The forecast at FMSY provides catches (35th percentile) 34% lower than the previous advice.

· Thornback ray in Division 8.c: sensitivity analyses using SPiCT do not allow to overcome the very high uncertainty around the F estimate. Therefore, the workshop recommends that this stock remains in category 3 with empirical methods to be used as the basis of the advice. 

For undulate ray in the English Channel, a SPiCT assessment using removals since 2005 and two survey indices (FR-CGFS, since 1990, and Q1SWECOS, since 2006) was accepted. The workshop also agreed on the settings for the short-term forecast, leading the stock into category 2. This stock, formerly considered depleted, is now estimated to be harvested well below FMSY with a biomass above BMSY. Given the change of perception of the state of the stock and the use of a forecast and reference points, the workshop considered that the large increase of the forecasted removals (3.6 times higher than the previous advice) is sensible.

For cuckoo ray in the western waters, investigations on stock identity did not provide enough evidence to split the stock, which may be a metapopulation. A SPiCT assessment using a combined index of stock abundance (from six surveys) and the landings since 2005 was accepted. The workshop also agreed on the settings for the short-term forecast, leading the stock into category 2. The stock is estimated to be harvested below FMSY with a biomass above BMSY, which is considered to be the consequence of the cuckoo ray being a non-target species with a rather high intrinsic growth rate (r~0.5). The 35th percentile of the landings at FMSY is largely higher (~3 times) than the previous advice.