Swedish
Variations in seal foraging behavior - Important knowledge for developing ecosystem-based management
Following successful conservation efforts, harbor seals in the Skagerrak have recovered from record low levels in the 1970s. This research project will analyze over 2000 diet samples from the past two decades to understand the seals' ecological role and develop sustainable management strategies.
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Financing
The Swedish Environmental Protection Agency’s environmental research grant finances the initiative in collaboration with Formas.
Project background and challenge
Historical recovery
The harbor seal population in Skagerrak has recovered from approximately 2000 individuals in the 1970s thanks to successful conservation efforts after overexploitation and environmental toxin impact.
Increasing conflicts
As the number of seals increased, conflicts with fishing intensified, leading to the reintroduction of hunting as a management measure from 2009 with regional quotas of up to 900 seals annually.
Knowledge gaps
Fundamental knowledge about what harbor seals eat, how their diet varies throughout the year and between different life stages, is lacking for developing evidence-based management strategies..
Research Questions and Goals
01
Spatial and temporal variation
How does the diet of harbor seals vary between different regions, seasons, and years in the Skagerrak?
02
Prey availability and diet choice
How is the seals' diet affected by local availability and distribution of prey species?
03
Age and sex effects
How do age and sex affect the seals' diet preferences and feeding habits?
04
Consumption calculations
How do the seals' total prey consumption and resource needs vary seasonally and over time?
The project will answer critical questions about the ecological role of seals by analyzing unique long-term data and advanced statistical models.
Malin Karlsson examines prey remains under the microscope during seal diet analysis. Photo: Monica Mion
Unique data material and methodology
Extensive dataset
Over 2000 diet samples from harbor seals collected along the Swedish Skagerrak coast over the past 25 years (1999-2024), including both fecal samples and digestive organs from hunting.
Advanced analysis
Morphological identification of prey remains combined with machine learning models to distinguish difficult-to-identify species such as codfish.
Spatial modeling
Generalized linear mixed models with Gaussian random fields to understand spatial and temporal variation in seal foraging behavior.
Three working packages for comprehensive analysis
WP1: Sample processing and diet analysis
Processing of approximately 2000 diet samples with morphological identification of prey remains. Otoliths and other skeletal parts are analyzed to determine species identity, number of individuals, and size of consumed fish.
WP2: Prey selectivity and spatio-temporal analysis
Spatio-temporal generalized linear mixed models to understand how the seals' diet varies across space and time, as well as in relation to local prey availability from coastal fish monitoring data.
WP3: Consumption modeling
Bioenergetic models to estimate the seals' total consumption of different prey species, with uncertainty analysis for population size, diet composition, and bioenergetic parameters.
Research team
Monica Mion - Project Manager
PhD in Ecology from SLU with expertise in diet analysis and fish ecology, focusing on the biology and growth of Baltic cod. Leads project coordination and all three work packages.
Contact:
Karl Lundström - Researcher
Researcher at SLU with long-standing expertise in marine mammal ecology. Responsible for stakeholder interactions and supports analysis in all work packages.
Max Lindmark - Researcher
Researcher at SLU specializing in temperature and body size effects on fish populations. Contributes to statistical analysis and modeling in WP2-3.
Karin Hårding - Professor
Professor at the University of Gothenburg with expertise in population dynamics and bioenergetic modeling of marine mammals. Supports analysis in WP2-3.
+46 0761105154
Budget and timeline
3.1M
Total Budget
sek
34
Project Duration
months from March 2025 to December 2027
Resource allocation per work package
Expected results and impact
Understanding diet patterns
The analysis will determine whether harbor seals have consistent dietary patterns or if their prey preferences have changed over time due to shifts in prey availability, using spatio-temporal models.
Quantification of consumption
By applying bioenergetic models, we will estimate energy requirements and prey choice based on the energy content of various fish species, answering "How much fish does the seal population need?"
Support for ecosystem-based management
The results will clarify the harbor seals' role in the marine food web and inform policies that balance seal conservation with sustainable fishing practices.
Towards a sustainable future for seals and fisheries
This project will provide the scientific basis needed for ecosystem-based management and support the sustainable coexistence between harbor seals, fish, and human activities. By offering detailed insights into the seals' foraging ecology and its ecological consequences, the research will inform decision-making and promote balanced management strategies.
The project will reduce conflicts between different stakeholders by providing knowledge about the seals' eating habits and their importance in the ecosystem, contributing to the development of ecosystem-based management and more informed decisions for the conservation of seals, fish, and fisheries.
Photo by Karl Lundström