Prey consumtion by Barents sea harp seals in the period 1990-2005

Abstract

The Barents Sea ecosystem has experienced major fluctuations in species abundance in the past 20-30 years. The mechanisms behind these fluctuations are complex and arise from numerous interactions between species and the environment. Previous and present attempts to assess multi-species interactions in the Barents sea ecosystem has resulted in increased focus on the foraging ecology of the most conspicuous high trophic-level predators in the ecosystem. The Barents Sea stock of harp seals Pagophilus groenlandicus is, along with Arctic cod Gadus morhua, considered as the most conspicuous high trophic-level predator in the Barents Sea ecosystem. The abundance and feeding ecology of the Barents Sea stock of harp seals has been monitored the past 15 years. Previous prey consumption estimates suggests that harp seals consume range between 3.3 and 5 million tonnes of prey annually, depending on the choice of input parameters in the bioenergetic model. There were a considerable amounnt of uncertainty attached to the input data in the consumption model, in particular the important harp seal diets during summer (May-August). Also, uncertainty estimates of the prey consumption were not given in the previous study. An important objective of this study was to estimate the uncertainty of the prey consumption estimates by using a standard Monte-Carlo framework; random draws from probability distributions of diet and abundance were performed. Additionally, new diet data from May-July has become available and is included in the analysis. The summer consumption was to a large extent dominated by krill, whereas polar cod also contributed importantly. All sampling were performed in a period with low capelin abundance – this may have influenced the results.