Stock assessment

Assessment of the stock size of demersal fishes, and invertebrates is done at various times of the year and the results are the basis for the annual TAC recommendations. Acoustic methods are used to assess the herring, capelin and oceanic redfish stocks for the same purpose.

Cod assessment - in brief

Stock assessment and prognosis is based on a well defined long-term process. Taking cod as an example, the scientific data is collected mainly in three ways.

• Systematically from the landed catch all around Iceland,
• by the MRI research vessels,
• in the groundfish survey.

The groundfish survey was started over 20 years ago and for this some four trawlers are hired in spring and autumn for a systematic survey of the fishing grounds. Their main targets are cod and haddock. A total of approx. 15,000 cod are analyzed each year for length, weight and age distribution of the catch.

For an estimate of stock size it is important to have a continuous series of population analysis to build on. The most accurate analysis of each year class is done just at the end of its life, when almost all the fish from that year class have been caught or died from natural causes, perhaps by the age of 12 for cod. In the Icelandic cod stock it is estimated that the natural death rate is about 20% annually.

The groundfish surveys, computer technology and scientific teamwork all add to the accuracy in cod stock assessment but much is still to be learnt from research on the effects of other stocks that constitute important feed for cod. This is currently the subject of extensive research.

Redfish assessment - in brief

The redfish stocks are difficult to assess for several reasons. There are no proven methods for determining the age of the catch and hence it is not possible to assess the size of individual year classes comprising the fishable stock. Redfish is also found in a very wide area in Icelandic waters and beyond the EEZ. Furthermore, there are at least two separate species of commercial importance (Sebastes marinus and S. mentella) and there are at least two separate S. mentella stock components that vary in distribution and abundance.

Catch per unit effort (CPUE) has been recorded systematically in the groundfish surveys since 1985 and by fishing trawlers since 1986. Catch and mean length of the catch is now recorded separately for each species. Trends in average fish size and CPUE serve as indicators of stock condition and abundance.

Northern shrimp assessment - in brief

Inshore and offshore shrimp are assessed and managed separately. Local stocks of inshore shrimp differ in abundance over time and from one area to another. Each fishing area is therefore also a management unit and TACs are allocated in accordance with scientific recommendations for each area.

Shrimp stock assessment is based on CPUE and shrimp abundance in surveys but also on shrimp size distribution in the catch, shrimp growth, stock recruitment and male/female ratio in relation to shrimp size. Abundance of young cod is also a factor in TAC recommendations for offshore shrimp since shrimp is important as feed for cod.

Capelin assessment- in brief

Assessment of the capelin stock takes place in late autumn and winter. Capelin is short lived, liable to change its distribution pattern and varies considerably from one season to the next in size and maturity at age. The stock is assessed by acoustic methods and analysis of catch composition.

The English summary of the report of the Marine Research Institute headed: State of Marine Stocks in Icelandic Waters 2007/2008 and prospects for the Quota Year 2008/2009 details assessment results and recommendations for most commercial stocks.

Editor