The Barents Sea capelin stock 1972-1997. A synthesis of results from acoustic surveys

Abstract

The abundance of the Barents Sea capelin stock has been monitored using acoustic methods since 1972. Today, 25 years later, it is one of the few stocks within the ICES area for which an annual acoustic stock size estimate serves as the only basis for stock assessment and management. The methods have changed and a large development has taken place in the technical equipment since the early 1970s. The time series of acoustic estimates from the annual autumn surveys, as well as the development of methods in the period 1972-1984 were reviewed in previous reports. Since then, another 13 years have been added to the time series and the development of methods has continued. Some amendments and corrections have been made to the software used for calculation of stock abundance, and in the present review all stock size estimates have been recalculated. Therefore, the estimates presented here may deviate somewhat from those presented earlier. An assessment of the goodness of the acoustic stock size estimates is attempted, but the lack of independent estimates makes this difficult. The accomplishment of a fishery regulation based on these stock size estimates in the past, where recruitment overfishing has been avoided, is put forward as an argument that no large, systematic, overestimation is probably taking place. On the other hand, when a small stock size has been estimated by acoustic methods, the situation has been confirmed by low availability of capelin to the fishing fleet, indicating that a gross underestimation is probably not taking place either. Results from studies on cod consumption confirms that the availability of capelin has varied in time with the acoustic estimates. However, the absolute consumption estimates on capelin by cod seem to be high compared to the acoustic estimates, and indicates that the acoustic method is underestimating the stock size to a certain degree.