Identifying foraging habitats of Baltic ringed seals using movement data.

Sari M Oksanen,Marja Niemi,Markus P Ahola,Mervi Kunnasranta

doi:10.1186/s40462-015-0058-1

Sari M Oksanen, Marja Niemi + Show 2 more

Open Access

https://doi.org/10.1186/s40462-015-0058-1

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Abstract

BackgroundIdentification of key foraging habitats of aquatic top predators is essential for designing effective management and conservation strategies. The Baltic ringed seal (Phoca hispida botnica) interacts with anthropogenic activities and knowledge of its spatial ecology is needed for planning population management and mitigating interactions with coastal fisheries. We investigated habitat use and foraging habitats of ringed seals (n = 26) with satellite telemetry in the northern Baltic Sea during autumn, which is important time for foraging for ringed seals. We used first passage time (FPT) approach to identify the areas of high residency corresponding to foraging areas.ResultsTracked seals showed considerable movement; mean (±SD) home ranges (95 % adaptive local nearest-neighbour convex hull, a-LoCoH) were 8030 ± 4796 km2. Two seals moved randomly and foraging areas could not be identified for them. The majority (24/26) of the studied seals occupied 1–6 main foraging areas, where they spent 47 ± 22 % of their total time. Typically the foraging areas of individuals had a mean distance of 254 ± 194 km. Most of the seals (n = 17) were “long-range foragers” which occupied several spatially remote foraging areas (mean distance 328 ± 180 km) or, in the case of two individuals, did not concentrate foraging to any particular area. The other seals (n = 9) were “local foragers” having only one foraging area or the mean distance between several areas was shorter (67 ± 26 km). Foraging areas of all seals were characterised by shallow bathymetry (median ± SD: 13 ± 49 m) and proximity to the mainland (10 ± 14 km), partly overlapping with protected areas and coastal fisheries.ConclusionsOur results indicate that in general the ringed seals range over large areas and concentrate feeding to different—often remote—areas during the open water season. Therefore, removal of individuals near the fishing gear may not be a locally effective method to mitigate seal depredation. Overlap of foraging areas with protected areas indicate that management of key foraging and resting habitats could to some extent be implemented within the existing network of marine protected areas.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-015-0058-1) contains supplementary material, which is available to authorized users.

Highlights

Identification of key foraging habitats of aquatic top predators is essential for designing effective management and conservation strategies
Identifying areas that are important in fulfilling different life history priorities, such as breeding and foraging habitats, is often an initial step in understanding habitat use of mobile aquatic predators, and thereby in designing effective management and conservation strategies [1, 2]
Two tags only functioned < 20 days and these data sets were excluded from the home range analyses

Summary

Introduction

Identification of key foraging habitats of aquatic top predators is essential for designing effective management and conservation strategies. The Baltic ringed seal (Phoca hispida botnica) interacts with anthropogenic activities and knowledge of its spatial ecology is needed for planning population management and mitigating interactions with coastal fisheries. Identifying areas that are important in fulfilling different life history priorities, such as breeding and foraging habitats, is often an initial step in understanding habitat use of mobile aquatic predators, and thereby in designing effective management and conservation strategies [1, 2]. Many seal species interact with fisheries while feeding [3,4,5], studying foraging habitats may help to Arctic ringed seal (Phoca hispida) in general inhabits remote locations and interacts relatively little with humans, the Baltic subspecies The Baltic ringed seal are suggested to be sedentary [25], but detailed studies on its spatial ecology are lacking

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