Report of the Benchmark Workshop on Pelagic Stocks (WKPELA 2012)

Benchmark Workshop on Pelagic Stocks (WKPELA) 2012 was convened between 25 October 2011 and 17 February 2012. It met three times (once by WebEx) and worked intersessionally by correspondence. Its remit was to determine and review the appropriate stock assessment methods for five pelagic stocks: herring in Division VIIa (Irish Sea), sardine in Division VIIIc–IXa, blue whiting combined stock (Subareas I–IX, XII and XIV); herring in Subdivision 30 (Bothnian Sea), herring in IV, VIId (North Sea autumn spawners). 43 people participated from over 16 countries. The participants included stakeholders with interest in four of the stocks. Four independent scientists from outside the ICES community took part in the process and reviewed with the findings of the workshop. See the participants list in Annex 1.
The main outcomes of the workshop were:
Irish Sea herring. WKPELA 2012 accepted a SAM framework for the assessment of the stock. The workshop provided a useful forum to explore and increase our under-standing of the properties of the catch and survey data. Proposals were made for future integration of an index of juvenile mixing (with Celtic Sea) into the assessment. The values of M where changed to reflect similar estimates to that recently reported for other herring stocks. Fmsy reference points were proposed.
Sardine in Division VIIIc–IXa. WKPELA 2012 accepted that SS3 was an appropriate model for the stock assessment. The workshop explored the impact of assumptions about selectivity. It also revised M estimates and investigated the sensitivity of the survey weightings. The group proposed Fmsy reference points.
Blue whiting (combined stock). WKPELA 2012 agreed that there was only one stock which spawned together and was predominantly fished together. The workshop also agreed that the SAM framework was the appropriate assessment method for the stock. None of the recruitment indices were included in the assessment. Methods will be explored to bring those indices into the projections with metrics of an environ-mental signal. The Fpa reference points were dropped.
Bothnian Sea herring. The workshop rejected the use of XSA to assess this stock due the impact of convergence (resulting SSB could be determined by the choice of the number of iterations). The workshop also rejected the use of a production model due to a lack of stability in carrying capacity over time and worries expressed about representativeness of the trapnet cpue. The workshop recommended that currently the acoustic survey (only five years) be used as an index of trends in abundance. A Bayesian assessment method has been under development but was not ready to be used as the assessment model for this stock.
North Sea herring. The workshop recommended that the SAM framework was appropriate for this stock. It replaced time invariate estimates of M with time variable estimates of M coming from the North Sea SMS model. The workshop reevaluated reference points. The time-series of the assessment was extended to 1947.
The outputs of the workshop are this report and the new stock annexes to be used for the assessment of the stocks in the ICES advisory process.