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A comparison of the seasonal movements of tiger sharks and green turtles provides insight into their predator-prey relationship.

Fitzpatrick R, Thums M, Bell I, Meekan MG, Stevens JD, Barnett A - PLoS ONE (2012)

Bottom Line: We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship.In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds.On average, tiger sharks were concentrated around Raine Island throughout the year.

View Article: PubMed Central - PubMed

Affiliation: School of Marine and Tropical Biology, James Cook University, Cairns, Queensland, Australia.

ABSTRACT
During the reproductive season, sea turtles use a restricted area in the vicinity of their nesting beaches, making them vulnerable to predation. At Raine Island (Australia), the highest density green turtle Chelonia mydas rookery in the world, tiger sharks Galeocerdo cuvier have been observed to feed on green turtles, and it has been suggested that they may specialise on such air-breathing prey. However there is little information with which to examine this hypothesis. We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship. Specifically, we tested the hypothesis that tiger shark movements are more concentrated at Raine Island during the green turtle nesting season than outside the turtle nesting season when turtles are not concentrated at Raine Island. Turtles showed area-restricted search behaviour around Raine Island for ∼3-4 months during the nesting period (November-February). This was followed by direct movement (transit) to putative foraging grounds mostly in the Torres Straight where they switched to area-restricted search mode again, and remained resident for the remainder of the deployment (53-304 days). In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds. On average, tiger sharks were concentrated around Raine Island throughout the year. While information on diet is required to determine whether tiger sharks are turtle specialists our results support the hypothesis that they target this predictable and plentiful prey during turtle nesting season, but they might not focus on this less predictable food source outside the nesting season.

Show MeSH
Mean distance from Raine Island for tiger sharks and green turtles. Mean and standard error distance from Raine Island for each month for all tiger sharks and green turtles (a). Mean and standard error distance from Raine Island for tiger sharks during the green turtle nesting season (nesting) and outside the nesting season (not nesting) (b).
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pone-0051927-g003: Mean distance from Raine Island for tiger sharks and green turtles. Mean and standard error distance from Raine Island for each month for all tiger sharks and green turtles (a). Mean and standard error distance from Raine Island for tiger sharks during the green turtle nesting season (nesting) and outside the nesting season (not nesting) (b).

Mentions: Tiger sharks largely remained in the vicinity of Raine Island (Fig. 3a). During the green turtle nesting phase (Nov – Feb) the sharks were 68.89±71.58 km from Raine Island and outside of the nesting phase they were 115.82±131.08 km from Raine (Fig. 3b). We found no evidence to suggest that shark distance from Raine Island was different in the nesting season compared to outside the nesting season with the intercept only model ( model) having much higher support (wAICc  = 0.78) than the slope model (wAICc  = 0.22) (Figs. 3 and 4). However, some sharks did travel further afield. Sharks 79974 and 62849 moved into the Coral Sea, to the south-east of Papua New Guinea (Figs. 2 and 5). These sharks also had two of the three longest data records (209 and 356 days) (Table 1). Interestingly, these transits were of short duration and didn’t result in area-restricted search behaviour in the Coral Sea and both sharks returned to Raine Island outside of the green turtle nesting season (Fig. 5). In contrast, shark 79972 which had location data for 231 days stayed relatively close to Raine Island, never leaving the northern Great Barrier Reef region and never showing transit movement (Figs. 2 and 5). While there were no differences in proximity to Raine Island overall between nesting and non-nesting season, half of the shark deployments conformed with the prediction of being closer to Raine Island in the green turtle nesting season. For the tiger sharks with long enough deployments (62849, 79972 and 79974), two of these fit the prediction (Fig. 5). During the 2010/11 summer expeditions to Raine Island two satellite tagged tiger sharks were also observed feeding on a dead turtle, but neither animal was recaptured.


A comparison of the seasonal movements of tiger sharks and green turtles provides insight into their predator-prey relationship.

Fitzpatrick R, Thums M, Bell I, Meekan MG, Stevens JD, Barnett A - PLoS ONE (2012)

Mean distance from Raine Island for tiger sharks and green turtles. Mean and standard error distance from Raine Island for each month for all tiger sharks and green turtles (a). Mean and standard error distance from Raine Island for tiger sharks during the green turtle nesting season (nesting) and outside the nesting season (not nesting) (b).
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Related In: Results  -  Collection

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pone-0051927-g003: Mean distance from Raine Island for tiger sharks and green turtles. Mean and standard error distance from Raine Island for each month for all tiger sharks and green turtles (a). Mean and standard error distance from Raine Island for tiger sharks during the green turtle nesting season (nesting) and outside the nesting season (not nesting) (b).
Mentions: Tiger sharks largely remained in the vicinity of Raine Island (Fig. 3a). During the green turtle nesting phase (Nov – Feb) the sharks were 68.89±71.58 km from Raine Island and outside of the nesting phase they were 115.82±131.08 km from Raine (Fig. 3b). We found no evidence to suggest that shark distance from Raine Island was different in the nesting season compared to outside the nesting season with the intercept only model ( model) having much higher support (wAICc  = 0.78) than the slope model (wAICc  = 0.22) (Figs. 3 and 4). However, some sharks did travel further afield. Sharks 79974 and 62849 moved into the Coral Sea, to the south-east of Papua New Guinea (Figs. 2 and 5). These sharks also had two of the three longest data records (209 and 356 days) (Table 1). Interestingly, these transits were of short duration and didn’t result in area-restricted search behaviour in the Coral Sea and both sharks returned to Raine Island outside of the green turtle nesting season (Fig. 5). In contrast, shark 79972 which had location data for 231 days stayed relatively close to Raine Island, never leaving the northern Great Barrier Reef region and never showing transit movement (Figs. 2 and 5). While there were no differences in proximity to Raine Island overall between nesting and non-nesting season, half of the shark deployments conformed with the prediction of being closer to Raine Island in the green turtle nesting season. For the tiger sharks with long enough deployments (62849, 79972 and 79974), two of these fit the prediction (Fig. 5). During the 2010/11 summer expeditions to Raine Island two satellite tagged tiger sharks were also observed feeding on a dead turtle, but neither animal was recaptured.

Bottom Line: We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship.In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds.On average, tiger sharks were concentrated around Raine Island throughout the year.

View Article: PubMed Central - PubMed

Affiliation: School of Marine and Tropical Biology, James Cook University, Cairns, Queensland, Australia.

ABSTRACT
During the reproductive season, sea turtles use a restricted area in the vicinity of their nesting beaches, making them vulnerable to predation. At Raine Island (Australia), the highest density green turtle Chelonia mydas rookery in the world, tiger sharks Galeocerdo cuvier have been observed to feed on green turtles, and it has been suggested that they may specialise on such air-breathing prey. However there is little information with which to examine this hypothesis. We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship. Specifically, we tested the hypothesis that tiger shark movements are more concentrated at Raine Island during the green turtle nesting season than outside the turtle nesting season when turtles are not concentrated at Raine Island. Turtles showed area-restricted search behaviour around Raine Island for ∼3-4 months during the nesting period (November-February). This was followed by direct movement (transit) to putative foraging grounds mostly in the Torres Straight where they switched to area-restricted search mode again, and remained resident for the remainder of the deployment (53-304 days). In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds. On average, tiger sharks were concentrated around Raine Island throughout the year. While information on diet is required to determine whether tiger sharks are turtle specialists our results support the hypothesis that they target this predictable and plentiful prey during turtle nesting season, but they might not focus on this less predictable food source outside the nesting season.

Show MeSH