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Habitat-mediated dive behavior in free-ranging grey seals.

Jessopp M, Cronin M, Hart T - PLoS ONE (2013)

Bottom Line: Pelagic dives were more common at night than during the day.Seals performed more pelagic dives over fine sediments (mud/sand), and more benthic dives when foraging over more three-dimensionally complex rock substrates.A low probability of repeat pelagic dives suggests that pelagic prey were encountered en route to the seabed.

View Article: PubMed Central - PubMed

Affiliation: Coastal & Marine Research Centre, Environmental Research Institute, University College Cork, Cork, Ireland. mjessopp@gmail.com

ABSTRACT
Understanding the links between foraging behaviour and habitat use of key species is essential to addressing fundamental questions about trophic interactions and ecosystem functioning. Eight female grey seals (Halichoerus grypus) were equipped with time-depth recorders linked to Fastloc GPS tags following the annual moult in southwest Ireland. Individual dives were coupled with environmental correlates to investigate the habitat use and dive behaviour of free-ranging seals. Dives were characterised as either pelagic, benthic, or shallow (where errors in location and charted water depth made differentiating between pelagic and benthic dives unreliable). Sixty-nine percent of dives occurring in water >50 m were benthic. Pelagic dives were more common at night than during the day. Seals performed more pelagic dives over fine sediments (mud/sand), and more benthic dives when foraging over more three-dimensionally complex rock substrates. We used Markov chain analysis to determine the probability of transiting between dive states. A low probability of repeat pelagic dives suggests that pelagic prey were encountered en route to the seabed. This approach could be applied to make more accurate predictions of habitat use in data-poor areas, and investigate contentious issues such as resource overlap and competition between top predators and fisheries, essential for the effective conservation of these key marine species.

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Related in: MedlinePlus

Location of tagging site in Southwest Ireland, with seal tracks and seabed sediment type.Seals (n = 8) were tagged with a Fastloc GPS/GSM tag, and foraged over a range of different sediment types, from fine mud and sand through to more three-dimensionally complex rock substrates.
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pone-0063720-g001: Location of tagging site in Southwest Ireland, with seal tracks and seabed sediment type.Seals (n = 8) were tagged with a Fastloc GPS/GSM tag, and foraged over a range of different sediment types, from fine mud and sand through to more three-dimensionally complex rock substrates.

Mentions: We used Spatial Analyst to extract values for bathymetry and sediment type to each dive in ArcMap 10 (ESRI). The GEBCO_08 global 30 arc-second grid altimeter dataset for ocean bathymetry, freely available through the British Oceanographic Data Centre (BODC), was used to determine water depth. Sediment type follows the EUNIS 2007–11 classification system and is based on the predictive EUNIS seabed habitat map for the North Sea and Celtic Sea, created using pre-processed input datasets for substrate, biological zone and energy using raster input layers with a cell size of 0.003 decimal degrees (∼167×333 m). These data were downloaded from the EUSeaMap web portal administered through the JNCC (http://jncc.defra.gov.uk/page-5040). Sediment types were pooled to create three broad habitat classes for the analysis: fine (mud/sand), coarse (gravel/mixed ground), and rocky (rock/till) sediments. Some areas over which seals foraged have not been surveyed, and were therefore classed as ‘unclassified’ (Fig. 1). Day and night determinations were made based on the timing of local sunrise and sunset at each given dive date, time and location (latitude/longitude).


Habitat-mediated dive behavior in free-ranging grey seals.

Jessopp M, Cronin M, Hart T - PLoS ONE (2013)

Location of tagging site in Southwest Ireland, with seal tracks and seabed sediment type.Seals (n = 8) were tagged with a Fastloc GPS/GSM tag, and foraged over a range of different sediment types, from fine mud and sand through to more three-dimensionally complex rock substrates.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3646810&req=5

pone-0063720-g001: Location of tagging site in Southwest Ireland, with seal tracks and seabed sediment type.Seals (n = 8) were tagged with a Fastloc GPS/GSM tag, and foraged over a range of different sediment types, from fine mud and sand through to more three-dimensionally complex rock substrates.
Mentions: We used Spatial Analyst to extract values for bathymetry and sediment type to each dive in ArcMap 10 (ESRI). The GEBCO_08 global 30 arc-second grid altimeter dataset for ocean bathymetry, freely available through the British Oceanographic Data Centre (BODC), was used to determine water depth. Sediment type follows the EUNIS 2007–11 classification system and is based on the predictive EUNIS seabed habitat map for the North Sea and Celtic Sea, created using pre-processed input datasets for substrate, biological zone and energy using raster input layers with a cell size of 0.003 decimal degrees (∼167×333 m). These data were downloaded from the EUSeaMap web portal administered through the JNCC (http://jncc.defra.gov.uk/page-5040). Sediment types were pooled to create three broad habitat classes for the analysis: fine (mud/sand), coarse (gravel/mixed ground), and rocky (rock/till) sediments. Some areas over which seals foraged have not been surveyed, and were therefore classed as ‘unclassified’ (Fig. 1). Day and night determinations were made based on the timing of local sunrise and sunset at each given dive date, time and location (latitude/longitude).

Bottom Line: Pelagic dives were more common at night than during the day.Seals performed more pelagic dives over fine sediments (mud/sand), and more benthic dives when foraging over more three-dimensionally complex rock substrates.A low probability of repeat pelagic dives suggests that pelagic prey were encountered en route to the seabed.

View Article: PubMed Central - PubMed

Affiliation: Coastal & Marine Research Centre, Environmental Research Institute, University College Cork, Cork, Ireland. mjessopp@gmail.com

ABSTRACT
Understanding the links between foraging behaviour and habitat use of key species is essential to addressing fundamental questions about trophic interactions and ecosystem functioning. Eight female grey seals (Halichoerus grypus) were equipped with time-depth recorders linked to Fastloc GPS tags following the annual moult in southwest Ireland. Individual dives were coupled with environmental correlates to investigate the habitat use and dive behaviour of free-ranging seals. Dives were characterised as either pelagic, benthic, or shallow (where errors in location and charted water depth made differentiating between pelagic and benthic dives unreliable). Sixty-nine percent of dives occurring in water >50 m were benthic. Pelagic dives were more common at night than during the day. Seals performed more pelagic dives over fine sediments (mud/sand), and more benthic dives when foraging over more three-dimensionally complex rock substrates. We used Markov chain analysis to determine the probability of transiting between dive states. A low probability of repeat pelagic dives suggests that pelagic prey were encountered en route to the seabed. This approach could be applied to make more accurate predictions of habitat use in data-poor areas, and investigate contentious issues such as resource overlap and competition between top predators and fisheries, essential for the effective conservation of these key marine species.

Show MeSH
Related in: MedlinePlus