Abstract
Assessing sea turtle behavior at the foraging grounds has been primarily limited to the interpretation of remotely-sensed data. As a result, there is a general lack of detailed understanding regarding the habitat use of sea turtles during a phase that accounts for a majority of their lives. Thus, this study aimed to fill these data gaps by providing detailed information about the feeding habits, prey availability, buoyancy control and water column usage by 73 loggerhead turtles across 45.7 hours of video footage obtained from a remotely operated vehicle (ROV) from 2008 – 2014. We developed an ethogram to account for 27 potential environmental and behavioral parameters. Turtles were filmed through the entire water column and we quantified the frequency of behaviors such as flipper beats, breaths, defecations, feedings and reactions to the ROV. We used the ROV’s depth sensor and visible cues (i.e. water surface or benthic zone in view) to distinguish depth zones and assess the turtles’ use of the water column. We also quantified interactions with sympatric biota, including potential gelatinous and non-gelatinous prey species, fish (including sharks), marine mammals and other sea turtles. We discovered that turtles tended to remain within the near surface and surface zones of the water column through the majority of the footage. During benthic dives, turtles consistently exhibited negative buoyancy and some turtles exhibited a dichotomous foraging behavior, first foraging within the water column, then diving to the benthic environment. Videography allowed us to combine behavioral observations and habitat features that cannot be captured by traditional telemetry methods, resulting in a broader understanding of loggerheads’ ecological role in the U.S. Mid-Atlantic.
Highlights
Among sea turtles, loggerheads (Caretta caretta) are considered one of the most generalized species in terms of feeding and foraging behavior (Bolton, 2003)
With the combined advances in in-water videography and the corresponding development of integrative behavior-coding software, this study presents the first ethogram for foraging loggerheads in the seasonally important region of the MidAtlantic Bight
Telemetry devices, due to their inability to accurately gauge the near surface zone below ∼1 m of resolution or due to a low sampling rate to conserve battery, group depths such that any dive appearing to be above a specified threshold (e.g., ∼5 m) is considered “surface” time associated with breathing (Fedak et al, 2002; Polovina et al, 2003; Hazel et al, 2009; Hagihara et al, 2011)
Summary
Loggerheads (Caretta caretta) are considered one of the most generalized species in terms of feeding and foraging behavior (Bolton, 2003) Throughout their lives, their diet is composed of a broad array of prey items, including macro algae, plants, and animals, ranging from surface dwelling species to obligate benthic organisms (Witherington, 2002; Seney and Musick, 2007; Casale et al, 2008). For loggerheads foraging in the Northwest Atlantic Ocean, several studies have been conducted to track their movements and behaviors through satellite telemetry with over 350 tag deployments (Hawkes et al, 2007; McClellan and Read, 2007; Mansfield et al, 2009; Turtle Expert Working Group, 2009; Arendt et al, 2012a,b). Satellite telemetry research has provided valuable data in establishing the importance of the Mid-Atlantic as an important foraging ground for loggerhead turtles, as tracked juveniles, nesting females, and males all have maintained seasonal residency within the region
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