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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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Schematic of dive classification.Dives were identified as ‘shallow’, ‘benthic’, and ‘pelagic’. All dives in water depth of less than 50 m were classified as ‘shallow’. Remaining dives were further divided into ‘benthic’ and ‘pelagic’ dives based on proximity of dive to the seabed.
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pone-0063720-g002: Schematic of dive classification.Dives were identified as ‘shallow’, ‘benthic’, and ‘pelagic’. All dives in water depth of less than 50 m were classified as ‘shallow’. Remaining dives were further divided into ‘benthic’ and ‘pelagic’ dives based on proximity of dive to the seabed.

Mentions: Dive types were assigned using conditional statements (Fig. 2). Disproportionately high errors in the ratio of water depth to dive depth in water less than 50 m resulted in low confidence in describing dives as pelagic or benthic. These dives were therefore classified as shallow. Dives in water deeper than 50 m were classified according to their proximity to the benthos. Two thresholds were identified based on the distribution of data (see Fig. S1). Proximity to the sea floor was calculated as a ratio of dive depth divided by bathymetric depth, with ratios <0.95 classified pelagic dives and >0.95 benthic dives.


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

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

Schematic of dive classification.Dives were identified as ‘shallow’, ‘benthic’, and ‘pelagic’. All dives in water depth of less than 50 m were classified as ‘shallow’. Remaining dives were further divided into ‘benthic’ and ‘pelagic’ dives based on proximity of dive to the seabed.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0063720-g002: Schematic of dive classification.Dives were identified as ‘shallow’, ‘benthic’, and ‘pelagic’. All dives in water depth of less than 50 m were classified as ‘shallow’. Remaining dives were further divided into ‘benthic’ and ‘pelagic’ dives based on proximity of dive to the seabed.
Mentions: Dive types were assigned using conditional statements (Fig. 2). Disproportionately high errors in the ratio of water depth to dive depth in water less than 50 m resulted in low confidence in describing dives as pelagic or benthic. These dives were therefore classified as shallow. Dives in water deeper than 50 m were classified according to their proximity to the benthos. Two thresholds were identified based on the distribution of data (see Fig. S1). Proximity to the sea floor was calculated as a ratio of dive depth divided by bathymetric depth, with ratios <0.95 classified pelagic dives and >0.95 benthic dives.

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