Report from the Benchmark Workshop on Icelandic Stocks (WKICE)
WKICE was set up to provide standards for assessing Greenland cod, Icelandic cod and Icelandic capelin.
Results from genetic investigations and tagging experiments suggest that the Atlantic cod (Gadus morhua) in Greenland waters is comprised primarily of three spawning stocks (Storr-Poulsen et al., 2003; Therkildsen et al., 2013):
1 ) West Greenland inshore;
2 ) West Greenland offshore; and
3 ) East Greenland offshore.
Until 2011, ICES advice was provided for all three stock components combined. Since 2012 separate advice has been given for the inshore stock component. WKICE evaluated the case for separating the two offshore components based on the tagging and genetic studies as well as advice from ICES SIMWG and concluded that they should be assessed separately.
For the inshore Greenland cod stock, none of the proposed analytical assessment approaches provided convincing results and were not considered appropriate to generating advice. However, the currently used approach (DLS on the survey) was also rejected and an alternative regression approach was approved by WKICE as the best available alternative to generate advice. It is based on a simple linear regression between survey indices and subsequent catches, but incorporates age-specific survey trends. Although it rests on some key assumptions, it provides a pragmatic way of generating advice incorporating precautionary considerations and a Utrigger proxy.
The regression approach should however be considered an interim solution until an approach that utilizes the data to a fuller extent (i.e. a credible full stock assessment) is developed. Whatever approach is developed, it should consider the mixed-stock fishery and preferably incorporate new information on the degree of offshore input to the catches; both survey and commercial. WKICE also recommended that that alternative assessment models, other than those already tested, should be investigated to determine whether they perform better.
For the West Greenland offshore cod stock, all information from the fishery and surveys indicates that stock biomass continues to be low. The fishery has been closed for more than two decades and survey indices have been low. However, recent surveys have shown an increasing abundance of cod which is mainly composed of the 2009 year class. The presence of a single year class is not considered sufficient for advising an opening of the fishery.
No stock assessment can be undertaken for this stock, due to the lack of significant rebuilding since the stock collapsed in the late 1960s. The advisory process should consider this rebuilding process when generating advice in the near future. WKICE agreed that there was little further work that this benchmark meeting could usefully undertake at this time, but recommended that it continue to be monitored using the current German and Greenland surveys.
For the East Greenland offshore cod stock, several assessment models were presented, but none were approved as a basis for advice. Among the models presented, a separable model showed the most promise. However, it was not possible within the time frame of WKICE to explore the model fully, nor to develop alternative models.
In general, all models in combination with the survey results support an increasing trend in stock size.
As no analytical assessment was agreed for the East Greenland offshore cod, the DLS Method 3.2 approach incorporating survey indices was adopted. WKICE concluded that it is appropriate to apply the DLS approach, and that this should be done in a manner that takes observation error into account. However, WKICE believed that the DLS approach should only be considered an interim solution, pending development of an alternative analytical assessment approach. WKICE believes that the available data should be adequate for a full analytical stock assessment approach to be developed, and that assessment models incorporating a range of recommendations should be actively pursued. If a suitable model can be developed, an interim benchmark is recommended.
WKICE accepted the current Icelandic stock assessment, as described in the stock annex in this report, as a benchmark assessment. The assessment methodology and outputs have been relatively consistent since at least 2009, and the workshop judged the current assessment to be reliable and robust. The 2009 assessment produced projections to 2015 that are compatible with the results of the current assessment, although rebuilding is estimated to have occurred at a faster rate than that indicated by the 2009 projections.
The stock appears to have rebuilt from relatively low levels in the last 2–3 decades of the 20th century to levels corresponding to the 20% harvest control rule in recent years.
However, more work is needed on stock structure and migration patterns for the Icelandic cod and Greenland cod stocks, particularly if the distribution of the stocks alters as a result of climate change. Tagging studies, genetics studies and, to a lesser extent, morphology studies should be augmented to more fully address stock structure and catch composition issues.
For Icelandic capelin, WKICE agreed that for the final TAC advice a stochastic projection of the stock should be conducted starting from acoustic measurements, aiming at a TAC that is associated with p(SSB WKICE accepted the assessment methodology for Icelandic capelin, as described in the stock annex in this report, as a benchmark assessment. While it appears that the stock is currently lower than historical levels, it is estimated to be well above Blim.
WKICE participated in a joint session with WKARCTIC where work presented for the Barents Sea capelin stressed the importance of capelin as a keystone species in the ecosystem. This is likely to also be true for Icelandic capelin. WKICE therefore recommended that studies of optimal harvesting of IGJM capelin should be conducted and presented to the NWWG. The NWWG should also initiate a review of the role of capelin in the Icelandic Sea ecosystem, and in particular whether the population size and growth of capelin predators shows a response to changes in capelin abundance.
Finally, further work on the new framework for setting the advice is needed, including detailed examination of the series of historical bootstrap estimates and additional tests of the predation model for cod, haddock and saithe, based on the groundfish survey in March (IGFS) data.
Published under the auspices of the following ICES Steering Group or Committee