No place to nest or bask: Effects of human disturbance on the nesting and basking habits of yellow-blotched map turtles (Graptemys flavimaculata)

Abstract

Considerable recent attention has focused on how human disturbance alters the behaviour of imperiled taxa. Data on such impacts are common for waterfowl, marine mammals, and some large game animals. However, little is known about how human disturbances affect reptiles, perhaps because most reptiles are secretive and are not commonly seen by the public. We studied the impact of human disturbances on the nesting and basking behaviour of the yellow-blotched map turtle (Graptemys flavimaculata) on the Pascagoula River in southeastern Mississippi, USA. We found that both nesting and basking behaviour of map turtles were altered by human recreational activities. Turtles attempting to nest commonly abandoned their attempts upon the approach of a boat and, prior to nesting, numerous individuals waited several hours near the beach without emerging. Basking turtles frequently dove into the water upon the approach of a boat and some did not return to bask. Anglers in small boats that remained in the vicinity of basking sites caused the most disturbances, whereas personal water crafts (jet skis) caused fewer disturbances. Our data suggest that interruption of nesting activities may have an especially severe impact on the viability of this population through changes in numbers of clutches females are able to lay and altering the microhabitat females select for their nests.

Introduction

Although habitat destruction or modification and the introduction of invasive species are generally considered to be among the most important threats to biodiversity (Foin et al., 1998), considerable attention recently has focused on the ways in which human disturbance alters the behaviour of imperiled taxa (see review in Frid and Dill, 2002) and whether such alteration leads to reduced population sizes (Gill et al., 1996, Beale and Monaghan, 2004). Studies on organisms as diverse as waterfowl (Gill et al., 1996, Rodgers and Schwikert, 2002), marine mammals (Constantine et al., 2004, King and Heinen, 2004), and large terrestrial game species (Stockwell et al., 1991) indicated that human disturbance can significantly alter feeding schedules, habitat use, and time spent nursing young. Even though the population consequences of such disturbances often are not known, changes in behaviour and habitat use concern conservation biologists and wildlife managers.

Despite the wealth of information available for birds and mammals, comparatively little is known about how human disturbances affect reptiles, perhaps because most reptiles are secretive and are not commonly seen by the public (but see Johnson et al., 1996, Hecnar and M.’Closkey, 1988, Parent and Weatherhead, 2000). However, in many aquatic habitats, freshwater turtles are frequently seen basking and nesting, especially in river systems where human recreational activities are common. Direct harassment of basking turtles by recreational shooters (“plinking turtles”) is a well-known activity in much of North America (Ernst et al., 1994) and has obvious negative impacts. The ways by which less overt disturbances affect aquatic turtles is poorly known, but given the rapid decline seen in many turtle species throughout the world (Gibbons et al., 2000), data on such impacts clearly are needed.

From 1993 to 1997, we studied the behavioural and reproductive ecology of the yellow-blotched map turtle (Graptemys flavimaculata) on the Pascagoula River in southeastern Mississippi, USA. This turtle underwent a severe decline in the 1980s and is currently listed as Threatened under the US Endangered Species Act of 1973, as amended. One of the major factors contributing to this decline is human disturbance, especially on sandbars where this species nests (U.S. Fish and Wildlife Service, 1991). Here, we report information on nesting and basking behaviour in this species, specifically on the impacts resulting from human disturbance. Further, we make recommendations to area managers as to how these impacts could be minimized.