WP 2: Case study – Icelandic capelin

Lead: Marine Research Institute, Iceland

Capelin (Mallotus villosus) spawn off the south and southwest coasts of Iceland in February-March but the nursery and feeding grounds are on the shelves off the northwest, north and northeast coasts. Feeding migrations of adults to the deep Sub-Arctic and Arctic waters of the Iceland Sea occur during June-September. Upon returning to the northern shelf, and until spawning off the southwest coast, capelin is preyed upon in large quantities.

The recruitment of the capelin stock is believed to depend on environmental conditions on the spawning grounds while later growth of the capelin is believed to depend mainly on the environmental conditions in the Iceland Sea and the nearby waters but there are also certain indications that a small spawning stock will lead to a poor recruitment. Furthermore, predation by whales, fish and the fisheries exploitation are considered important factors in determining the development of the spawning stock.

Since 1998, the distribution and main fishing area of capelin in the Iceland Sea has changed and this has led to difficulties in assessing the size of the stock. Short-term fishery advice is derived mainly from direct survey estimates of abundances of recruits and spawners. Since 2003 reduced stock size and changes in the capelin stock has made it difficult to assess abundances of the 1 year old fish and therefore only in three years since then has it been possible to announce an initial quota one year in advance. Icelandic authorities strictly follow this working methodology and base advice on this methodology, both for deciding about the size of the preliminary quota and then for setting the final quota each year.

Since the early 2000s, young capelin (immature at age 1 and 2) has been found to be more westerly and northerly distributed than before, i.e. outside of the Icelandic continental shelf. This shift in distribution coincides with the onset of greatly reduced recruitment to the capelin stock and has been attributed to warmer climate in recent years. The 2009 year-class has been the only strong year-class since 2003. It has been postulated that the failure in recruitment is related to the combined effect of environmental factors affecting the larval stage and the change in distribution. This, however, needs a much further investigation similar to which is to be attempted in the present project.

Analyses involving Icelandic capelin will therefore involve processes affecting recruitment, and also the migration and distribution of the stock, which affects the success and effectiveness of fishing operations. Both of these life-history events (recruitment, migration) are hypothesized to be linked to zooplankton abundances and will be the foci of analyses in this workpackage.