Complex movement patterns by foraging loggerhead sea turtles outside the breeding season identified using Argos‐linked Fastloc‐Global Positioning System

Abstract

We used Argos‐linked Fastloc‐Global Positioning System (Argos‐linked Fastloc‐GPS) satellite tags to investigate how loggerhead sea turtles use neritic foraging habitats at multiple scales. Out of 24 turtles, six individuals used more than one foraging site, with all sites being separated by >25 km. These six individuals used up to four sites, remaining at each site for a mean of 150 days and returning to the same site a minimum of 52 days later. The other 18 turtles remained in a single site. The area within sites was not used uniformly, with 15 out of 24 turtles exhibiting complex movement patterns within and amongst up to five focal patches, which were typically 0.1–5.0 km apart within a single site. Movements between sites and patches might sometimes have reflected overwintering behaviour; however, similar movement patterns occurred at multiple times of the year, suggesting other factors were also involved. Use of multiple sites and patches might be driven by differences in resource availability, such as food and/or night‐time refuges, competition, or exploratory movement to investigate or locate alternative patches. We confirmed competition via direct visual observations of aggressive interactions between individuals at one foraging patch. Our results illustrate the importance of standardizing data to the same number of locations per day and night to accurately delineate key areas used by turtles or for evidence‐based marine protected area planning.

Social media reveals consistently disproportionate tourism pressure on a threatened marine vertebrate

“…Thus, even when migrant breeders are present in the bay in large numbers, operators preferentially target areas used by residents rather than randomly searching for turtles. Previous telemetry studies (Dujon et al, 2018) and long-term direct in-water observations confirm high utilization of this part of the bay by residents (Papafitsoros and Schofield, 2016). Fidelity to foraging sites has been widely recorded in sea turtle species (Limpus et al, 1992;Broderick et al, 2007;Rees et al, 2013;Shimada et al, 2020).…”

“…Without question, preventing human-induced mortality of male turtles should be a management focus, particularly in light of the known lower survival rates of males in this population (Schofield et al, 2020), the lower relative numbers of adult males present in the breeding population (1 male to four females; Schofield et al, 2017) and the fact that offspring production is strongly female biased globally, with that bias possibly persisting in the adult populations (Hays et al, 2014). Wildlife watching vessels have been shown to primarily use a restricted area of the bay (Schofield et al, 2015), which overlaps with the area frequented by resident male and immature turtles for foraging (based on Fastloc GPS tracking data; Dujon et al, 2018), particularly the key six individuals (Kostas Papafitsoros-personal observations).…”

“…An important management intervention could include the compulsory use of propeller guards on all viewing and private vessels used within Laganas Bay, which combined with a strong enforcement of the current 6 knot limit in maritime zones B and C, could significantly reduce propeller strikes in this focal area. Due to the strong overlap in operator area use with resident turtle area use (Schofield et al, 2013, Schofield et al, 2015, Dujon et al, 2018, another possible solution could be to restrict the use of this part of the bay (currently the least restricted maritime zone C or key foraging spots; Figure 1), with a temporary (time of day or day of month) no-entry "refuge" zone for residents (Williams et al, 2009). The restriction of unregulated recreational craft has been shown to have a positive impact on killer whales and dolphins (Jelinski et al, 2002;Duprey et al, 2008).…”

“…Here, we aimed to address this knowledge gap at an important breeding site for loggerhead sea turtles in the Mediterranean by combining data derived from social media and photo-identification techniques to evaluate whether wildlife viewing activities disproportionately target certain individuals at a site used by both resident and migrant individuals. Laganas Bay on Zakynthos, Greece, supports a seasonal breeding aggregation of over 200 loggerhead sea turtles (Caretta caretta) (from April to early August of each year), but also a small population of resident male and immature turtles (Schofield et al, 2015;Dujon et al, 2018). This site was ideal for our study because it is also a popular summer tourist destination in the Mediterranean attracting over 850,000 visitors between late-April and late-October, and it supports wildlife-watching activities.…”

Spatial ecology of loggerhead turtles: Insights from stable isotope markers and satellite telemetry

“…Marine turtles often migrate across ocean basins between foraging and nesting grounds (e.g., Shillinger et al, 2008), and several geographically distinct foraging areas are typically used by individual nesting populations (e.g., Dujon, Schofield, Lester, Papafitsoros, & Hays, 2018;Hays, Hobson, Metcalfe, Righton, & Sims, 2006;Seminoff et al, 2008;Stokes et al, 2015). Traditionally, conservation, and conservation-driven research, of marine turtles has been focused on easily accessible nesting grounds (Bjorndal, 1999;Hamann et al, 2010), protecting nesting females and their eggs, thus potentially only protecting a small proportion of the life cycle of the species.…”