Report of the Benchmark Workshop on Sandeel (WKSAN)
A Benchmark Workshop on Sandeel in Subarea IV excluding the Shetland (WKSAN) met at ICES Headquarters in Copenhagen, Denmark on September 6–10, 2010. Dr. Jim Berkson (US) served as the Workshop’s Chair, Dr. Ewen Bell (UK) served as the ICES Coordinator, and Dr. Robert Furness (UK) served as an external expert.
WKSAN has adopted the recomendataions of previous ICES Workshops on Sandeel in terms of moving from a single area assessment to assessing separate stock compo-nents based on stock structure identified using published information on larval distribution, connectivity, and growth differences. There are now seven separate stock components identified, although analytical assessments are only possible in four areas. In addition to this fundamental change in the treatment of North Sea sandeels, the assessment model structure has evolved to now utilize a statistical catch-at-age model as opposed to a deterministic VPA approach as used in the past. The inclusion of the dredge survey has eliminated historic retrospective patterns in Areas 1–3, a problematic artifact of previous assessments. New analyses demonstrate that the dredge survey in Area 1 allows for greater confidence in short-term forecasts. All of these developments represent significant improvements in assessment and forecast methodology.
Four alternative sandeel management scenarios were presented to WKSAN: the cur-rent ICES management plan, the plan being implemented by the Norwegian govern-ment in the Norwegian EEZ, a proposal by the Danish Fisherman’s Association, and a proposal by the Norwegian Fishermen’s Association. All four management plans could be implemented in Areas 1, 2, and 3 using existing data sources with agreed-upon assessment and forecasting methods. Both the Norwegian government’s and the Norwegian Fisherman’s Association’s proposed management scenarios could be implemented in Area 5. Data is insufficient to evaluate whether the management scenarios could be implemented in Areas 4 and 6.
Intensive in-season catch sampling and data processing has been required to provide TAC advice in the past in areas 1–3. The WKSAN determined that pre-season dredge survey information is sufficient to provide TAC advice in Areas 1 and 2 in most years, without requiring the more intensive in-season catch sampling and data proc-essing. Increasing the time-series length and coverage in Areas 3, 5 and 6 may lead to a similar reduction or elimination of the need for more intensive in-year data collec-tion and processing. However, the dredge survey in area 4 cannot be used to produce a stock assessment without additional within season sampling, preferably from fish-eries catches.
Improving the assessment will require its further spatial stratification, including pro-viding natural mortality rate estimates by area. Current natural mortality rate estimates were derived from predator stomachs collected 20 years ago region-wide. A new stomach collection study is required to provide updated, area-specific mortality estimates. Additional research priorities include studies of the relationship between sandeel biomass and predator condition, growth or recruitment success to provide better knowledge for setting reference points which takes account of effects on preda-tor populations. A more detailed list of research needs is provided within the document.
Industry representatives from both Denmark and Norway attended the entire WKSAN. Although they were invited to attend as observers, their expertise and opinions were sought throughout. As a result, they provided useful information throughout the workshop. In particular, they provided critical information on the timing and causes of changes in catchability, which were then incorporated into the assessment model. Industry representatives also provided details on marine spatial planning issues having the potential to impact the sandeel fishery in the future (e.g. windfarms, Natura2000). Their participation was not only welcome, but also necessary.
Published under the auspices of the following ICES Steering Group or Committee