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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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Maximum daily depth of blue sharks across months.Maximum depths varied with the month, but were much greater after entry into warm Gulf Stream waters (red) than prior to entry (green). Symbols show mean ± 1 SE.
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pone-0016854-g003: Maximum daily depth of blue sharks across months.Maximum depths varied with the month, but were much greater after entry into warm Gulf Stream waters (red) than prior to entry (green). Symbols show mean ± 1 SE.

Mentions: Blue shark entry into the Gulf Stream was always accompanied by the initiation of a striking deep-diving behaviour which persisted throughout their residence in the Gulf Stream and Sargasso Sea (Fig. 3). Prior to entry into the Gulf Stream, daily maximum dive depths averaged 86±4 m (mean ± SE; n = 773), and dives exceeding 200 m were rare. However in all sharks, daily dives of more than 200 m began an average of only 1.4±1.9 days after first encountering the Gulf Stream. The initiation of deep diving behaviour was so characteristic of recent entry into the Gulf Stream that it could be used as an entry diagnostic by itself. Daily maximum dive depths while in the Gulf Stream averaged ±8 m (n = 883) with a maximum of 1008 m, and varied across months. Temperature exposure also changed after entry into the Gulf Stream, but less markedly than depth. Prior to entry into the Gulf Stream, blue sharks were exposed to a mean temperature of 15.0±0.8°C. Mean temperature increased significantly (p < 0.05) to 17.1±0.1°C after entry into 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)

Maximum daily depth of blue sharks across months.Maximum depths varied with the month, but were much greater after entry into warm Gulf Stream waters (red) than prior to entry (green). Symbols show mean ± 1 SE.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0016854-g003: Maximum daily depth of blue sharks across months.Maximum depths varied with the month, but were much greater after entry into warm Gulf Stream waters (red) than prior to entry (green). Symbols show mean ± 1 SE.
Mentions: Blue shark entry into the Gulf Stream was always accompanied by the initiation of a striking deep-diving behaviour which persisted throughout their residence in the Gulf Stream and Sargasso Sea (Fig. 3). Prior to entry into the Gulf Stream, daily maximum dive depths averaged 86±4 m (mean ± SE; n = 773), and dives exceeding 200 m were rare. However in all sharks, daily dives of more than 200 m began an average of only 1.4±1.9 days after first encountering the Gulf Stream. The initiation of deep diving behaviour was so characteristic of recent entry into the Gulf Stream that it could be used as an entry diagnostic by itself. Daily maximum dive depths while in the Gulf Stream averaged ±8 m (n = 883) with a maximum of 1008 m, and varied across months. Temperature exposure also changed after entry into the Gulf Stream, but less markedly than depth. Prior to entry into the Gulf Stream, blue sharks were exposed to a mean temperature of 15.0±0.8°C. Mean temperature increased significantly (p < 0.05) to 17.1±0.1°C after entry into 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