Research Document - 2001/074

Incorporating uncertainty into estimates of Atlantic cod, capelin and Arctic cod consumption by harp seals in NAFO Divisions 2J3KL

By Stenson, G. B., Perry, E.

Abstract

Consumption of prey by harp seals in NAFO divisions 2J3KL was estimated by synthesizing and integrating information on individual energy requirements, population size, distribution, and diet composition. Diets were estimated using reconstructed stomach contents collected between 1982 and 1998, inclusive. Uncertainty in the estimates of numbers at age, diets, residency in 2J3KL and the proportion of seals in nearshore areas, was incorporated into the consumption estimates. Based on their average diet, harp seals consumed an estimated 893,000 (95% CI: 682,000-1,100,000) tonnes of capelin, 186,000 (95% CI: 58,000-457,000) tonnes of Arctic cod and 37,000 (95% CI: 14,000-62,000) tonnes of Atlantic cod in 2000. The proportion of cod in nearshore diets varied among years and seasons with a significant increase in cod present in the winter 1998 diet. Generally low levels of cod were present in offshore winter diets while no cod were present in the Summer. Examination of the proportion of nearshore seal stomachs containing cod (prevalence), mean weights of Atlantic cod, Arctic cod and capelin in the stomach, and mean lengths of cod consumed indicated that during the winter of 1998, the prevalence of Atlantic cod in harp seals was higher than average but not the highest documented. However, the mean weight of cod in stomachs and the length of cod consumed were greater than previously seen. Improvements in estimates of consumption can be achieved by further diet sampling in offshore areas and increased information on residency of seals of all ages in the area. However, estimates will likely remain highly variable owing to the strong temporal and spatial variation observed in diet composition.

Complete document (PDF, 542 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.