The Baltic grey seal

The Baltic Grey seal population is increasing in numbers, with a current estimated population size of 45 000 animals. This species regularly interacts with fisheries, and as a consequence, demands for higher hunting quotas are common. At the same time, strong signs of potential density dependence, and the negative impact of other stressors such as climate change are beginning to be observed, with lowered body condition and population growth rate. The main goal of this project is to develop a Population Viability Analysis models (PVA) to investigate the effect from important stressors; population density, sea ice extent and hunting and to provide a user friendly model for stake holders concerned with management. In order to link population density and body condition to population level effects we will also develop a new bioenergetic model to better predict how body condition and population growth depend on food avalability and other stressors. The relative impact of various stressors will be systematically investigated in terms of the increased risk of population decline that they impose. The project will organize meetings twice a year with a Reference Group representing different stakeholders, such as the hunters organisation, the Environmental Protection Agency, C ounty C ouncils and Environmental organisations for constructive two-way exchange of information. Also international stakeholders such as HELC OM Seal expert group will be involved. The overall aim is to build a user friendly model interface where the impact of various hunting scenarios can be investigated and designed to be as sustainable as possible. The model will be useful to the Environmental Protection Agency both for setting hunting quotas and to stimulate constructive discussions about the seal-fishery conflicts and possibilities.

Karin Hårding, Gothenburg University

840 000 SEK

This is an application for the second year in an ongoing project, it is revised after feedback from referees. Marine mammals contribute critically to the resilience of marine ecosystems and provide ecosystem services through top-down food-web interactions. Understanding the dynamics of seal-fish interactions is a major global task when formulating conservation and management actions for marine ecosystems. The grey seal populations in the Baltic Sea are far from historical abundances, and at the same time a recent decline has been documented in body condition, likely due to declining nutritive value of their fish prey. The current understanding of the functioning of the Baltic food web is insufficient to establish cause-effect relationships. Here, I propose to further develop a new so called ''dynamic bioenergetic model'' for grey seals to quantify the link between fish populations and grey seal populations in the Baltic. The model uses energy as a common currency and relates fat content of fish to energetic expenditure of seals and estimate how variation in food is reflected in body growth, fertility and survival. The outcome of the project will contribute to the Baltic Sea Action Plan and to the work for a Good Environmental Status within the HELC OM and IC ES frameworks. Furthermore, this new bioenergetic model will reveal how seal populations affect fish stocks and will help to untangle the current challenge to model complexity of species interactions in the food web by contributing a powerful modelling tool box.

Karin Hårding, Gothenburg University

2 059 000 SEK