Marine Debris and Human Impacts on Sea Turtles in Southern Brazil

doi:10.1016/S0025-326X(01)00147-3

Marine Pollution Bulletin

Volume 42, Issue 12, December 2001, Pages 1330-1334

https://doi.org/10.1016/S0025-326X(01)00147-3 Get rights and content

Abstract

Dead stranded sea turtles were recovered and examined to determine the impact of anthropogenic debris and fishery activities on sea turtles on the coast of Rio Grande do Sul State, Brazil. Esophagus/stomach contents of 38 juvenile green Chelonia mydas, 10 adults and sub-adults loggerhead Caretta caretta, and two leatherback Dermochelys coriacea turtles (adult or sub-adult) included plastic bags as the main debris ingested, predominated by white and colorless pieces. The ingestion of anthropogenic debris accounted for the death of 13.2% of the green turtles examined. Signs of damage over the body and carapace indicated that fishing activities caused the death of 13.6% (3/22) of loggerheads and 1.5% (1/56) of green turtles. Therefore, it appears that direct and indirect effects of fishing activities may pose a threat to these species in Brazilian waters. Other sources of plastic debris should be investigated as well as the direct impact of fisheries, especially bottom trawl and gill nets, in order to establish effective conservation action.

Introduction

The green turtle Chelonia mydas, loggerhead turtle Caretta caretta and leatherback turtle Dermochelys coriacea are endangered species (IUCN, 1996). Wyneken et al. (1988) mentioned that the overall reduction of sea turtle populations has been directly or indirectly attributed to the destruction of habitats, to anthropic action on the nesting beaches, and also the strong evidence of predation of the young, theft of eggs and adults, predatory fishing, and pollution. Among the main obstacles to sea turtle survival is marine pollution by oils and persistent plastics, which could directly affect the turtles, their food supplies, or their habitats (Bourne, 1985). Sea turtles of all species are particularly prone to eating pieces of plastic and other floating debris (Carr, 1987). The five sea turtle species which nest in Brazil, North of 23° latitude (Marcovaldi and Marcovaldi, 1999), also occur in southern Brazilian waters: C. caretta, C. mydas, D. coriacea, Lepidochelys olivacea and Eretmochelys imbricata (Lema, 1994; Pinedo et al., 1996). The three former species are frequently found stranded on the beaches of the State of Rio Grande do Sul. Throughout four years, from 1992 to 1995, 91 C. caretta, 58 D. coriacea and 24 C. mydas were found in Rio Grande do Sul (Pinedo et al., 1996). Despite the relatively high number of stranded sea turtles on southern Brazilian beaches, there is no comprehensive study on the anthropogenic debris ingestion, and the studies on fishery interactions in the area are scarce. In this study we present data on debris intake by green, loggerhead, and leatherback turtles, and fishery interactions that may have an effect on the conservation of these species in southern Brazil.

Section snippets

Materials and Methods

From August 1997 to July 1998, stranded sea turtles were collected on 11 occasions, along 150 km of beach between Pinhal (30°15^′S; 50°15^′W) and Lagoa do Peixe (31°20^′S; 51°05^′W) in the Brazilian southernmost State of Rio Grande do Sul. One field trip was performed on a larger area, along the entire coast of Rio Grande do Sul State, approximately 620 km long, between Torres (29°20^′S; 49°44^′W) and Arroio Chuı́ (33°45^′S; 53°22^′W) (Fig. 1). We surveyed the beach monthly by car, at a speed of around

Results and Discussion

A total of 92 stranded sea turtles were found, of which 56 green, 16 loggerhead, and 2 leatherback turtles were measured, and 38, 10 and 2 gut contents collected, respectively. The CCL of green turtles found dead on the beaches of Rio Grande do Sul ranged from 28 to 50 cm $(x ̄ =37.7±3.1 cm,n=56)$ . These individuals were all determined to be juveniles based on carapace length. Loggerheads ranged from 63 to 97 cm $(x ̄ =73.4±10.2 cm,n=16)$ and were classified as adults (n=6; 77–97 cm) and sub-adults (n

Acknowledgements

We would like to thank PIBIC-UFRGS/CNPq for the Scientific Initiation scholarship, granted to the first author, UNESCO for financial support to the main project `Monitoring birds, mammals and reptiles in South Brazil' (under the responsibility of the third author for account of the Universidade do Vale do Rio dos Sinos, which also provided logistic support and facilities), and the Department of Zoology at UFRGS for the possibility of performing this work.

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