Evaluating the landscape of fear between apex predatory sharks and mobile sea turtles across a large dynamic seascape

Abstract

Abstract. The ''landscape of fear'' model has been proposed as a unifying concept in ecology, describing, in part, how animals behave and move about in their environment. The basic model predicts that as an animal's landscape changes from low to high risk of predation, prey species will alter their behavior to risk avoidance. However, studies investigating and evaluating the landscape of fear model across large spatial scales (tens to hundreds of thousands of square kilometers) in dynamic, open, aquatic systems involving apex predators and highly mobile prey are lacking. To address this knowledge gap, we investigated predatorprey relationships between tiger sharks (Galeocerdo cuvier) and loggerhead turtles (Caretta caretta) in the North Atlantic Ocean. This included the use of satellite tracking to examine shark and turtle distributions as well as their surfacing behaviors under varying levels of home range overlap. Our findings revealed patterns that deviated from our a priori predictions based on the landscape of fear model. Specifically, turtles did not alter their surfacing behaviors to risk avoidance when overlap in shark-turtle core home range was high. However, in areas of high overlap with turtles, sharks exhibited modified surfacing behaviors that may enhance predation opportunity. We suggest that turtles may be an important factor in determining shark distribution, whereas for turtles, other life history trade-offs may play a larger role in defining their habitat use. We propose that these findings are a result of both biotic and physically driven factors that independently or synergistically affect predator-prey interactions in this system. These results have implications for evolutionary biology, community ecology, and wildlife conservation. Further, given the difficulty in studying highly migratory marine species, our approach and conclusions may be applied to the study of other predatorprey systems.

A dawn peak in the occurrence of ‘knifing behaviour’ in blue sharks

“…Similarly, a new study evaluated predator-prey interactions between tiger sharks (Galeocerdo cuvier) and loggerhead turtles (Caretta caretta) by testing for differences in their surfacing behaviour (derived from the frequency of Argos messages received from satellite tags, as in our study) in and out of home range overlap areas [26]. The wider implications of our study are that blue sharks may be more vulnerable to bycatch from surface longlines during the twilight periods.…”

Use of marine protected areas and exclusive economic zones in the subtropical western North Atlantic Ocean by large highly mobile sharks

“…As such, we cannot conclude that our data is representative of the entire population within the region. For tiger sharks, individuals tagged in the Florida and Bahamas study sites generally showed similar residency and home range patterns (Hammerschlag et al ., , ). However, it would be valuable to include data from tagging efforts across various sites of the tropical and subtropical Atlantic.…”

Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry

“…Movements of turtles can be linked with predation (Heithaus et al 2008, Hammerschlag et al 2015, environmental change (Pike 2008, Schofield et al 2009), or anthropogenic pressure, to distinguish what factors affect turtle foraging, migration, and development (Taquet et al 2006, Heithaus 2013. While our study has provided valuable data regarding the movements of juvenile hawksbill turtles around an offshore developmental habitat, other methods of long-term monitoring, such as satellite telemetry and stable isotope analysis, would permit insights even if tracked individuals were to leave the atoll (Shimada et al 2014).…”