Effects of a power plant closure on home ranges of green turtles in an urban foraging area

T Eguchi,S Graham,B Saunders,J Bredvik,R Leroux,Ja Seminoff

doi:10.3354/esr01027

Abstract

A natural experiment was conducted to determine effects of a fossil-fueled power plant on home ranges of east Pacific green turtles Chelonia mydas in an urban foraging ground. The power plant, located in south San Diego Bay, California, USA, co-existed with a resident foraging aggregation of ~60 green turtles for ~50 yr. It was decommissioned during a long-term green turtle monitoring study, thus providing a rare opportunity to evaluate how the cessation of warm-water effluent affected turtle movements and habitat use in the area. During pre- and post-decommissioning of the power plant, 7 and 23 green turtles, respectively, were equipped with GPS-enabled satellite transmitters. Useful data were obtained from 17 turtles (4 for pre- and 13 for post-decommissioning). Core use areas (50% utilization distribution [UD]) increased from 0.71 to 1.37 km2 after the power plant decommissioning. Increase in post-power plant 50% UD was greater during nighttime (0.52 to 1.44 km2) than daytime (1.32 to 1.43 km2). Furthermore, UDs moved from the effluent channel to an area closer to seagrass pastures, a presumed foraging habitat of the turtles. The observed expansion of green turtle home ranges may increase turtle-human interactions, such as boat strikes, within the foraging ground; this underscores how seemingly innocuous human actions contribute to inadvertent consequences to wildlife. Possible management and conservation actions include increasing awareness of the public regarding turtle presence in the area through signage and education as well as legislating for a reduction in boat speeds in select areas of the bay.

Highlights

Humans have inhabited coastal areas because they provide accessibility to sustenance from coastal and nearshore areas, provide opportunities for trade and transportation, and have a moderate climate compared to inland areas
The northern-most foraging areas of east Pacific green turtles can be found along the West Coast of the USA, where at least 2 long-term foraging grounds have been identified: San Diego Bay (SDB) and areas near Long Beach, California
We investigated the effects of human activity, namely a power plant closure, on green turtle home ranges using GPS-based telemetry

Summary

Introduction

Humans have inhabited coastal areas because they provide accessibility to sustenance from coastal and nearshore areas, provide opportunities for trade and transportation, and have a moderate climate compared to inland areas. To reduce the number of ship strikes on the endangered North Atlantic right whale Eubalaena glacialis, the shipping lanes along the eastern seaboard of the USA have been modified and ship speed decreased (Vanderlaan & Taggart 2007, Silber et al 2012) For another example, to reduce the negative effects of light on nesting turtles and emerged hatchlings, street lights have been modified in parts of Florida, USA, while providing sufficient lighting for human activities (Salmon 2006). To reduce the negative effects of light on nesting turtles and emerged hatchlings, street lights have been modified in parts of Florida, USA, while providing sufficient lighting for human activities (Salmon 2006) To make these mitigation efforts successful, the development of effective conservation and protective measures requires knowledge of an organism’s habitat use and behavior as well as spatial and temporal distribution of anthropogenic threats (Ross et al 2011)

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