310 N. Wildermann et al.
FIG. 2 Home ranges (95% utilization distribution) and core area (50% utilization distribution) (upper panels), and changes in behaviour (lower panels) of four turtles tracked with satellite telemetry. Black horizontal midline, mean persistence velocity; grey hoizontal outer lines, variability (standard deviation) of persistence velocity; τ, tortuosity (cooler colours indicate relative straighter movements, whereas warmer colours indicate more relative tortuous movements); vertical purple lines, significant change points (indicative of significant changes in turtle behaviour); grey shaded area, scallop harvest season. AP, Aquatic Preserve; NWR, National Wildlife Refuge.
core areas appear to be on average smaller during the scallop harvest season, but the small sample size impeded statistical assessment of these observations. The spatial distribution of home ranges before and during the scallop season varied among individuals, with no consistent pattern: Cm_1 used multiple areas near- and further offshore, Cm_2 and Lk_1 remained in near-shore waters, and Cc_1 remained relatively nearshore during both periods.
Changes in individual marine turtle behaviour
In general, a significant change point was identified on the day (Fig. 2a, c) or close to the beginning of the scallop har- vest season (Fig. 2b, d). In all cases, there was an increase in the persistence velocity after the significant change point (Fig. 2; Table 2). The travel speed and variability in the per- sistence velocity of three of four turtles increased after the change point, whereas tortuosity varied among individuals (Fig. 2; Table 2).
Discussion
Our study indicates that scallop recreational fisheries can potentially influence the temporary distribution of marine turtles and drive changes in their movement ecology. It is likely that the observed changes (e.g. turtles shifting further
nearshore, faster and more frequent movements during the scallop harvest season) are a behavioural response to the seasonal increase in the presence of boats (moving and sta- tionary) and people (snorkelling) within the turtles’ habitat. Based on interviews carried out in a larger study of the per- ceptions and motivation of boaters in Crystal River,,90% of respondents indicated they use the area for scalloping and fishing (MMPBF, pers. obs.). Practices employed to harvest scallops recreationally include travelling and anchoring boats, and snorkelling at depths of 1–3 m to manually re- move the scallops from the seagrass beds (FWC, 2017). These harvest practices are unlikely to pose an imminent risk to marine turtles, compared to entanglement and po- tential mortality in fishing nets and lines used in other coastal fisheries (Sasso & Epperly, 2006; Gilman et al., 2010). However, marine turtles are probably startled by the presence of high numbers of boats and swimmers (Hodgson & Marsh, 2007; Powell & Wells, 2011), which can lead to changes in their behaviour and could potentially have repercussions for their fitness. Boating and fishing activities in nearshore areas can af-
fect ecosystems at different levels, from individual fitness and population dynamics to changes in the physical struc- ture of the habitat, community structure and ecosystem pro- cesses (Auster & Langton, 1999). At the individual level, higher exposure to vessels increases the risk of boat-strikes (Hazel et al., 2007) and noise pollution (Samuel et al., 2005),
Oryx, 2020, 54(3), 307–314 © 2018 Fauna & Flora International. This is a work of the U.S. Government and is not subject to copyright protection in the United States. doi:10.1017/S0030605318000182
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