Diving behavior and thermal habitats of gravid hawksbill turtles at St. Croix, USA

Abstract

29.06 ± SD 0.43 °C). Two turtles attained the deepest recorded dives for gravid hawksbills (95.1 and 84.4 m) and sometimes remained at depths greater than 60 m for up to 30 min. Although we recorded instances of relatively deep diving for the species, the overall pattern of seafloor resting and infrequent diving was consistent with hawksbills in other ocean basins with different offshore habitats. We propose that benthic resting is common behavior for gravid hawksbills globally, and protection of benthic habitats near the nesting beach should be a management priority.

COVID‐19 disruption reveals mass‐tourism pressure on nearshore sea turtle distributions and access to optimal breeding habitat

“…Consequently, when visitor pressure is high, turtles might prematurely shift to deeper waters to evade humans. Because the window of opportunity for nesting on Zakynthos is highly constrained at the start of the nesting season (late May to late June) by suboptimal thermal conditions (Schofield et al, 2013, 2015), the onset of nesting and the duration of the internesting period (Hays et al, 2002; Hill et al, 2017; Mazaris et al, 2008) are strongly influenced by sea temperature. Furthermore, extending nesting later risks clutches failing to hatch when sand temperatures drop below the threshold for embryo development in September (Katselidis et al, 2012).…”

“…Consequently, when visitor pressure is high, turtles might prematurely shift to deeper waters to evade humans. Because the window of opportunity for nesting on Zakynthos is highly constrained at the start of the nesting season (late May to late June) by suboptimal thermal conditions (Schofield et al, 2013(Schofield et al, , 2015, the onset of nesting and the duration of the internesting period (Hays et al, 2002;Hill et al, 2017;Mazaris et al, 2008) are strongly influenced by sea temperature. Furthermore, extending nesting later risks clutches failing to hatch when sand temperatures drop below the threshold for embryo development We assumed 325 turtles were present, with nesting periods of 30, 44 and 68 days (shaded areas, minimum-maximum; line, mean) for two internesting scenarios: (1) 13-day intervals inside the zone and 17-day intervals (mean) outside the zone (orange shading), and (2) 13-day intervals inside the zone and 22-day intervals (maximum recorded) outside the zone.…”

“…Sea temperature regulates the number of days that turtles need to mature eggs before laying them, with >20 days required at 20°C, 12 days at 27–29°C (Hamel et al, 2008; Hays et al, 2002; Hill et al, 2017; Storch et al, 2005), and with upper limits of 30–32°C (Hill et al, 2017; Storch et al, 2005), above which metabolic rate (and hence energetic expenditure) and organ functioning are impacted (Fossette et al, 2012; Gangloff & Telemeco, 2018; Shine et al, 2005). Thus, turtles accessing optimal sea temperatures could lay more clutches than those in thermally suboptimal areas, assuming sufficient energetic reserves are accumulated during the foraging period (Broderick et al, 2001; Matsinos et al, 2008; Tucker, 2010).…”

“…Studies using various tracking and logging devices at sea turtle breeding areas (Rees et al, 2016) have repeatedly confirmed the fundamental importance of sea temperature (optimal sea surface temperature: typically 26-29°C; range 22-32°C) in regulating the onset of nesting activity (Almpanidou et al, 2016;Mazaris et al, 2008;Weishampel et al, 2010) and the interval between successive nesting events (e.g. Hamel et al, 2008;Hays et al, 2002;Hill et al, 2017;Weber et al, 2011), including associated energetic implications (Fossette et al, 2012). Loggerhead sea turtles (Caretta caretta) have the most temperate breeding distributions of all sea turtle species (Casale et al, 2018;Dodd, 1988); consequently, thermal selection is very important at sites on the limits of this range, such as the Greek island of Zakynthos (Mediterranean Sea).…”

Novel Bio-Logging Tool for Studying Fine-Scale Behaviors of Marine Turtles in Response to Sound

“…For example, satellite tags have been used to document the broad-scale movements of marine turtles, as well as to infer their home range, migratory corridors, suitable habitats, and exposure to threats (e.g., reviewed by Godley et al, 2008). In addition, passive and active acoustic telemetry tags (e.g., Taquet et al, 2006;Lamont et al, 2015), time-depth recorders (TDRs; e.g., Eckert et al, 1989;Hill et al, 2016), and animal-borne video tags (e.g., Seminoff et al, 2006;Arthur et al, 2007) have been used to infer fine-scale movements and behaviors of animals, particularly in relation to foraging ecology and diving behavior. Bio-logging tools that combine acoustic and fine-scale movement measurements (e.g., digital acoustic recording tags, Dtags, Johnson and Tyack, 2003;Acousonde, Burgess, 2009) are a particularly useful tool for quantifying behaviors of marine organisms in response to sound; however, to our knowledge have not yet been applied with marine turtles.…”