WP 1: Case study - North Sea sandeel

Lead: National Institute of Aquatic Resources, Denmark

Sandeel (Ammodytes marinus) in the North Sea feeds mostly on copepods; consequently its growth, maturation, reproductive success and survival will be closely influenced by variations in primary and secondary producers. For example, during the years 1983-2006, the recruitment of sandeel in the North Sea was significantly correlated to indices ofCalanus finmarchicus abundance and spawner biomass; sandeel growth is also influenced by abundance of this species.

The short-term projections and catch advice for North Sea sandeel are uncertain mainly due to (a) the inability to deliver an early preliminary prognosis 6 to 12 months prior to the fishing season, and (b) large unpredictable fluctuations in mean-weight-at-age, making the projections rather uncertain. Short-term projections are made annually in February to allow the announcement of a TAC in March. The fishing season starts April 1st and lasts for three months, leaving almost no time for the fishery and fish meal industry to adjust their capacity based on most recent advice. During the remainder of the year, i.e., between July 1st and April 1st of the following year, most age-1+ sandeel aestivate buried in the sand and are therefore not vulnerable to the fishery. This short-time period between advice provision and fishing operations is a major problem because the sandeel TAC occasionally changes by a factor of ten from one year to the next.

A further source of projection uncertainty originates from the assumption of constant or stable growth and weight-at-age. Mean-weight-at-age in the sandeel stock is highly variable and spans, for age-1 sandeel in the 1st half year, from 3.5 g (2003) to 8.1 g (1991), and the prediction of the mean-weight-at-age in the projection year is currently based on a simple three year average (the previous three years).

These considerations indicate that zooplankton has key roles on the growth and recruitment of North Sea sandeel. We will expand these analyses by considering whether links between climate oceanographic variables and zooplankton and fish responses show lagged responses which could increase forecast horizons and lead times, and we will implement the existing and updated zooplankton-fish relationships in short-term forecast procedures.