308 N. Wildermann et al.
FIG. 1 Spatial distribution of relative turtle abundance (95% represents total area and 50% represents hotspots) based on sightings (a) before and during the scallop harvest season, and (b) in relation to vessel density (cell size = 500 × 500 m) during the scallop harvest season.
Currently, the scallop fishery is open access, with regula- tions set only on individual bag limits and no monitoring of the number of users or the spatial extent of the fishery (Geiger et al., 2015). The fishery attracts thousands of users each year to centralized, easily accessible locations with high scallop densities (Greenawalt-Boswell et al., 2007). This has the potential to affect turtle distributions, in- crease mortality from vessel strikes, and damage sensitive seagrass habitat (NMFS & USFWS, 1991; NMFS et al., 2011). Despite the overlap between marine turtles and the scallop fishery, the potential impact on marine turtles in the region is unknown. To investigate the potential impacts of recreational fish-
eries on marine turtles we first explored the distribution of marine turtles before and during the scallop harvest season, and assessed the overlap between recreational harvesters and turtles. We then evaluated if home ranges of individual turtles changed before and during the scallop harvest season and whether associated boating activities from the recre- ational scallop fishery affected marine turtle behaviour.
Study area
This study was conducted in the coastal waters of the upper Eastern Gulf of Mexico in the vicinity of Crystal River in Citrus County (Fig. 1). The study area contains three management areas designed to promote the conservation and restoration of aquatic resources: St. Martins Marsh Aquatic Preserve, Chassahowitzka National Wildlife Refuge, and a Manatee Protection Zone (Supplementary Fig. 1). The region has been identified as important marine habitat for green, loggerhead, and Kemp’s ridley marine turtles (Schmid, 1998; Barichivich, 2006; Eaton et al., 2008) and is also a popular area for recreational harvest of the bay scallop, a species of ecological and economic im- portance in the region (Geiger et al., 2015). Some species
of turtles, loggerhead and Kemp’s ridley turtles in particular, have been reported to feed on scallops and other bivalves (Burke et al., 1994; Makowski et al., 2006; Warden, 2011). The harvest area spans 430 km of coast (Supplementary Fig. 1), and is particularly popular in Steinhatchee, Port St Joe, and Crystal River/Homosassa Springs. The 2016 scallop harvest season was 25 June–24 September.
Methods
Vessel and turtle sighting distribution Vessel locations were obtained by randomly selecting the northern or southern boundary of the study area and then systematically recording the location of each vessel from north to south or south to north, dependent on start loca- tion, using a laser rangefinder with a global positioning sys- tem (GPS). One continuous transect was performed during each survey day, for a total of 7 transects before the scallop harvest season, and 10 transects during the season (Supplementary Table 1). Turtle sightingswere recorded op- portunistically when observed during vessel surveys. Vessel and turtle sightings were standardized based on the number of survey days in each season. Survey days were randomly selected within each month, between 22 May and 24 September 2016. A separate 10-day trip was conducted to capture and tag
turtles. Turtles were captured using the rodeo technique (Limpus &Walter, 1980; Fuentes et al., 2006) and by dipnet, and brought to the boat to be processed. Standard straight carapace length (± 0.1 cm; SCL) wasmeasured from the an- terior point at midline (nuchal scute) to the posterior tip of the supracaudals (Balazs, 1999). Each individual turtle was marked with two Inconel flipper tags (Style 681, National Band and Tag Company, Newport, USA) and a passive integrated transponder (PIT tag, Biomark, GPT12; Balazs,
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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