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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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Frequency of pelagic dives occurring over fine, coarse, and rock substrates during day and night.Data represent frequency of pelagic dives out of all dives occurring over areas with available substrate data (n = 43,737), calculated for each seal, and averaged across all (n = 8) seals. For example, over fine sediment, approximately 30% of dives were pelagic during the day, while approximately 50% of dives were pelagic during the night. Error bars represent standard errors. Graph also illustrates how with increasing sediment size/habitat complexity, there is a corresponding decrease in the frequency of pelagic dives.
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pone-0063720-g004: Frequency of pelagic dives occurring over fine, coarse, and rock substrates during day and night.Data represent frequency of pelagic dives out of all dives occurring over areas with available substrate data (n = 43,737), calculated for each seal, and averaged across all (n = 8) seals. For example, over fine sediment, approximately 30% of dives were pelagic during the day, while approximately 50% of dives were pelagic during the night. Error bars represent standard errors. Graph also illustrates how with increasing sediment size/habitat complexity, there is a corresponding decrease in the frequency of pelagic dives.

Mentions: A linear model was used to investigate the effect of sediment type (where this was known) and time of day on the proportion of pelagic dives. Individual was included to account for non-independence of values from the same seal. The model explained 63% of the total variation (R2 = 0.63), and showed that the frequency of pelagic dives varied by sediment type (F2,34 = 3.55, P = 0.04), with the frequency of pelagic dives over fine sediment being significantly higher than over both coarse and rock sediments. Overall, pelagic dives were more frequent at night (44%±24%) than day (28%±17%, F7,34 = 11.41, P = 0.002), and the frequency of pelagic dives was highly significant between individuals (F2,34 = 5.53, P<0.001). The interaction between sediment type and time of day was not significant (F2,34 = 0.35, P = 0.710). The frequency of pelagic dives decreased with habitat complexity. Over fine sediment, 36% (±18%) of dives were pelagic during the day, while 52% (±32%) were pelagic during the night, while this was 28% (±17%) by day and 39% (±22%) by night for coarse sediments, and 20% (±16%) by day and 39% (±17%) by night for rock substrates (Fig. 4).


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

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

Frequency of pelagic dives occurring over fine, coarse, and rock substrates during day and night.Data represent frequency of pelagic dives out of all dives occurring over areas with available substrate data (n = 43,737), calculated for each seal, and averaged across all (n = 8) seals. For example, over fine sediment, approximately 30% of dives were pelagic during the day, while approximately 50% of dives were pelagic during the night. Error bars represent standard errors. Graph also illustrates how with increasing sediment size/habitat complexity, there is a corresponding decrease in the frequency of pelagic dives.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0063720-g004: Frequency of pelagic dives occurring over fine, coarse, and rock substrates during day and night.Data represent frequency of pelagic dives out of all dives occurring over areas with available substrate data (n = 43,737), calculated for each seal, and averaged across all (n = 8) seals. For example, over fine sediment, approximately 30% of dives were pelagic during the day, while approximately 50% of dives were pelagic during the night. Error bars represent standard errors. Graph also illustrates how with increasing sediment size/habitat complexity, there is a corresponding decrease in the frequency of pelagic dives.
Mentions: A linear model was used to investigate the effect of sediment type (where this was known) and time of day on the proportion of pelagic dives. Individual was included to account for non-independence of values from the same seal. The model explained 63% of the total variation (R2 = 0.63), and showed that the frequency of pelagic dives varied by sediment type (F2,34 = 3.55, P = 0.04), with the frequency of pelagic dives over fine sediment being significantly higher than over both coarse and rock sediments. Overall, pelagic dives were more frequent at night (44%±24%) than day (28%±17%, F7,34 = 11.41, P = 0.002), and the frequency of pelagic dives was highly significant between individuals (F2,34 = 5.53, P<0.001). The interaction between sediment type and time of day was not significant (F2,34 = 0.35, P = 0.710). The frequency of pelagic dives decreased with habitat complexity. Over fine sediment, 36% (±18%) of dives were pelagic during the day, while 52% (±32%) were pelagic during the night, while this was 28% (±17%) by day and 39% (±22%) by night for coarse sediments, and 20% (±16%) by day and 39% (±17%) by night for rock substrates (Fig. 4).

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