AES Behavior, Movements & Habitat Use I2021-07-22 09:15 - 10:15 |
| Moderator: Brooke Anderson |
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1. 09:15 IN-PERSON A day in the life: Accelerometry and acoustic telemetry reveal multiple drivers of activity and behaviour of coastal shark species. Rob Bullock*, Bimini Biological Field Station; Simon Dedman, Stanford University; Ian Cowx, University of Hull; Mike Elliott, University of Hull; Tristan Guttridge, Bimini Biological Field Station simondedman@gmail.com
Twenty-three nursery-bound juvenile and subadult lemon sharks (TL 78-187 cm) were tagged and tracked for over 115 active tracking days with combined accelerometer and acoustic transmitter tag packages. A further seven sharks (TL 97 – 122 cm) were tagged and observed in semi-captive pens to catalogue behaviours and validate wild shark accelerometer data. Overall dynamic body acceleration (ODBA) and three distinct behavioural modes (resting, swimming and bursting) were used to resolve activity and behaviour in wild animals in space and time. Tidal phase had a strong influence on habitat use, activity and resting behaviour. Generally, sharks used nearshore areas over the high tide, were less active overall, and exhibited a marked increase in resting behaviour. At low tides sharks used open lagoon areas further from shore, were more active overall, and rested less often. Diel phase had the strongest effect on expression of bursting behaviour, deemed to represent foraging activity, with peaks over the dusk periods. Larger sharks used nearshore areas far less and were less active overall, displaying less resting behaviour. No size-related changes in bursting behaviour were recorded. Findings here reveal multiple, co-occurring drivers of activity and behaviour in young nursery-bound sharks and highlight the significant effects of ontogeny, even across relatively restricted size and age classes. |
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2. 09:30 VIRTUAL Swimming Kinematics of Predatory Great Hammerhead Sharks and their Blacktip Shark Prey. Braden Ruddy*, Florida Atlantic University; Delanie Kirwan, Florida Atlantic University; Stephen Kajiura, Florida Atlantic University; Marianne Porter, Florida Atlantic University bruddy2018@fau.edu
Schooling, or polarized collective movement, is hypothesized to provide increased predator awareness to individual fish. Prey swimming kinematics are influenced by distances among neighbors in the school and the predator. As the school gets closer to the predator, tailbeat frequency of the prey fish increases to initiate an escape response. We examined predator-prey interactions between great hammerhead (Sphyrna mokarran;predator) and blacktip sharks (Carcharhinus limbatus;prey) in the wild to quantify distances among animals, excitation wave initiation, and swimming kinematics . We predicted that the individual blacktip sharks nearest to the predator would initiate escape responses that would propagate throughout the group, and would exhibit the most dramatic kinematic variables. We captured video of interactions (N=17) with an aerial drone flown nearshore in Palm Beach County, FL (USA). We examined 11 individual hammerheads, and 185 blacktip sharks, which averaged 14 animals per group. Using motion tracking software, we calculated kinematic variables (body curvature, tailbeat frequency, tail beat amplitude, and velocity) and quantified nearest-neighbor and predator-prey distances. Blacktips within three body lengths of the hammerhead, exhibited increased body curvature, velocity, and tailbeat frequency compared to individuals farther from the predator. None of these interactions resulted in successful predation, and hammerhead kinematics did not change over the three tailbeats quantified. These data show that changes in swimming kinematics vary with distance from potential predators and propagate within a school which can be manifest as a Trafalgar effect. |
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4. 10:00 IN-PERSON Multi-decadal high-resolution data reveal the cryptic vertical movement patterns of a large marine predator along the Californian coast. Samantha Andrzejaczek*, Hopkins Marine Station, Stanford University; Taylor Chapple, Coastal Oregon Marine Station, Oregon State University; Salvador Jorgensen, Monterey Bay Aquarium; Scot Anderson, Monterey Bay Aquarium; Michael Castleton, Hopkins Marine Station, Stanford University; Paul Kanive, Montana State University; Timothy White, Hopkins Marine Station, Stanford University; Barbara Block, Hopkins Marine Station, Stanford University sammyaz@stanford.edu
Over the past two decades, satellite tags deployed on white sharks Carcharodon carcharias on the coast of central California have revealed a predictable migratory cycle. Foraging white sharks aggregate on the coast near pinniped rookeries from late summer (August in the northern hemisphere) and undergo long-distance migrations (> 2000 km) to offshore pelagic habitats in winter. Our current understanding of the vertical movement patterns exhibited by white sharks during these coastal and offshore phases, however, remains limited. Here, we used recovered datasets from 31 archival satellite tags to quantify the cryptic vertical movement patterns of white sharks during the coastal foraging phase of their migration. Tags were deployed on sub-adult and adult individuals between 2000 and 2018 and recorded depth and temperature data at 1-120 second intervals before being recovered up to a year after deployment. Additionally, four individuals were concurrently tagged with acoustic tags, providing horizontal position data that allowed us to explore how reported vertical movements vary spatially. While on the coast, white sharks moved at a mean depth ± SD of 14.3 ± 4.0 m, and occupied significantly deeper depths during the day than the night. High individual, temporal and spatial variation was evident in vertical movements, and consistent diel and lunar effects were assumed to be associated with hunting behaviours. Future use of higher-resolution biologging techniques are required to validate the processes driving the fine-scale vertical movement behaviours observed here, and to examining the specific foraging events that could not be isolated in the present study. |