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Migration pathways, behavioural thermoregulation and overwintering grounds of blue sharks in the Northwest Atlantic.

Campana SE, Dorey A, Fowler M, Joyce W, Wang Z, Wright D, Yashayaev I - PLoS ONE (2011)

Bottom Line: Although functionally blind at depth, calculations suggest that there would be a ~2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth.Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks.However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway.

View Article: PubMed Central - PubMed

Affiliation: Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, Nova Scotia, Canada. steven.campana@dfo-mpo.gc.ca

ABSTRACT
The blue shark Prionace glauca is the most abundant large pelagic shark in the Atlantic Ocean. Although recaptures of tagged sharks have shown that the species is highly migratory, migration pathways towards the overwintering grounds remain poorly understood. We used archival satellite pop-up tags to track 23 blue sharks over a mean period of 88 days as they departed the coastal waters of North America in the autumn. Within 1-2 days of entering the Gulf Stream (median date of 21 Oct), all sharks initiated a striking diel vertical migration, taking them from a mean nighttime depth of 74 m to a mean depth of 412 m during the day as they appeared to pursue vertically migrating squid and fish prey. Although functionally blind at depth, calculations suggest that there would be a ~2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth. Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks. However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway. The relative abundance of deep-diving sharks, swordfish, and sperm whales in the Gulf Stream and adjacent waters suggests that it may serve as a key winter feeding ground for large pelagic predators in the North Atlantic.

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Examples of blue shark dive profiles overlaid on the temperature field.Time-weighted depths of individual blue sharks (solid black lines) from 2006 (left panels) and 2007 (right panels) at 6-hr intervals, overlaid on the colour-coded water temperature field as recorded by the PAT. Note the initiation of daily deep diving behaviour shortly after encountering the warm surface waters of the Gulf Stream.
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pone-0016854-g007: Examples of blue shark dive profiles overlaid on the temperature field.Time-weighted depths of individual blue sharks (solid black lines) from 2006 (left panels) and 2007 (right panels) at 6-hr intervals, overlaid on the colour-coded water temperature field as recorded by the PAT. Note the initiation of daily deep diving behaviour shortly after encountering the warm surface waters of the Gulf Stream.

Mentions: Diel vertical migration was apparent in blue sharks at all times of the year, but was greatly amplified after entry into the Gulf Stream (Fig. 5). Outside of the Gulf Stream, there was a small but significant increase in mean depth during the daytime, from 26 m at 0000 hr to 39 m at 1200 hr, with a very small decline in ambient temperature (Fig. 6). Within the Gulf Stream however, the vertical migration was of large amplitude and exactly daily in its timing, taking the shark from a mean of 74 m at midnight, to a mean of 412 m at noon. Although there were variations in daily dive depths among and within sharks, there were few exceptions to the daily deep diving behaviour, either across days or across years (Fig. 7). Since water temperature declined with depth, the daily deep diving behaviour took sharks from surface water temperatures with a mean of 18.6°C in the nighttime, to a mean temperature of 15°C at depth (Fig. 6). Interestingly, the coolest temperatures experienced during the deep dives east of the Gulf Stream were similar to the typical temperatures experienced by the sharks west of the Gulf Stream.


Migration pathways, behavioural thermoregulation and overwintering grounds of blue sharks in the Northwest Atlantic.

Campana SE, Dorey A, Fowler M, Joyce W, Wang Z, Wright D, Yashayaev I - PLoS ONE (2011)

Examples of blue shark dive profiles overlaid on the temperature field.Time-weighted depths of individual blue sharks (solid black lines) from 2006 (left panels) and 2007 (right panels) at 6-hr intervals, overlaid on the colour-coded water temperature field as recorded by the PAT. Note the initiation of daily deep diving behaviour shortly after encountering the warm surface waters of the Gulf Stream.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3044145&req=5

pone-0016854-g007: Examples of blue shark dive profiles overlaid on the temperature field.Time-weighted depths of individual blue sharks (solid black lines) from 2006 (left panels) and 2007 (right panels) at 6-hr intervals, overlaid on the colour-coded water temperature field as recorded by the PAT. Note the initiation of daily deep diving behaviour shortly after encountering the warm surface waters of the Gulf Stream.
Mentions: Diel vertical migration was apparent in blue sharks at all times of the year, but was greatly amplified after entry into the Gulf Stream (Fig. 5). Outside of the Gulf Stream, there was a small but significant increase in mean depth during the daytime, from 26 m at 0000 hr to 39 m at 1200 hr, with a very small decline in ambient temperature (Fig. 6). Within the Gulf Stream however, the vertical migration was of large amplitude and exactly daily in its timing, taking the shark from a mean of 74 m at midnight, to a mean of 412 m at noon. Although there were variations in daily dive depths among and within sharks, there were few exceptions to the daily deep diving behaviour, either across days or across years (Fig. 7). Since water temperature declined with depth, the daily deep diving behaviour took sharks from surface water temperatures with a mean of 18.6°C in the nighttime, to a mean temperature of 15°C at depth (Fig. 6). Interestingly, the coolest temperatures experienced during the deep dives east of the Gulf Stream were similar to the typical temperatures experienced by the sharks west of the Gulf Stream.

Bottom Line: Although functionally blind at depth, calculations suggest that there would be a ~2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth.Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks.However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway.

View Article: PubMed Central - PubMed

Affiliation: Bedford Institute of Oceanography, Fisheries and Oceans Canada, Dartmouth, Nova Scotia, Canada. steven.campana@dfo-mpo.gc.ca

ABSTRACT
The blue shark Prionace glauca is the most abundant large pelagic shark in the Atlantic Ocean. Although recaptures of tagged sharks have shown that the species is highly migratory, migration pathways towards the overwintering grounds remain poorly understood. We used archival satellite pop-up tags to track 23 blue sharks over a mean period of 88 days as they departed the coastal waters of North America in the autumn. Within 1-2 days of entering the Gulf Stream (median date of 21 Oct), all sharks initiated a striking diel vertical migration, taking them from a mean nighttime depth of 74 m to a mean depth of 412 m during the day as they appeared to pursue vertically migrating squid and fish prey. Although functionally blind at depth, calculations suggest that there would be a ~2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth. Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks. However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway. The relative abundance of deep-diving sharks, swordfish, and sperm whales in the Gulf Stream and adjacent waters suggests that it may serve as a key winter feeding ground for large pelagic predators in the North Atlantic.

Show MeSH
Related in: MedlinePlus