Differences in pesticide levels in two species of dolphins (Tursiops truncatus and Stenella attenuata) in Golfo Dulce, Costa Rica are related to foraging strategies.
Priscilla Cubero¹, Paul Forestell², Luisa Crespo¹, and Victor Montenegro¹
¹Centro de Proyeccion del Ambiente Marino, PO Box 11709-1000, San Jose, Costa Rica
²Southampton College of Long Island University, Southampton, NY, 11968, USA
Bottlenose (Tursiops truncatus) and spotted (Stenella attenuata) dolphins are found in Golfo Dulce, a fjord-like 750km² embayment in southwestern Costa Rica. A 60-m deep sill at the mouth slows exchange with the open ocean. Inside the sill, depth increases to 210 meters. Anoxic conditions below 40m prevent organic matter degradation throughout the center of the Gulf. DDT from plantations along rivers flowing into the Gulf has created toxic deposits near river mouths. Preliminary studies indicate resident bottlenose dolphins feed near river mouths. Spotted dolphins occasionally visit Golfo Dulce, but remain over deep water in the center. We hypothesized that bottlenose dolphins should show higher fat deposits of DDT-related metabolites than spotted dolphins, reflecting different foraging strategies, and greater susceptibility to toxins present near rivers. Fifteen attempts to obtain biopsy samples from both species resulted in 8 "hits". Two darts were not recovered; two of the six recovered had insufficient material for analysis. Of four usable samples, two were from spotted dolphins, and two were from bottlenose. Fat samples from both species indicated presence of DDE-para para-pesticide, a degraded metabolic derivative of DDT. However, bottlenose concentration was much higher than spotted. DNA testing showed one male and one female was sampled from each species; no differences were found between the sexes. Our results suggest a need for continued study to determine overall concentrations of toxins, whether DDT is still used in this area, and the extent of threat that exists for marine mammals in Golfo Dulce.
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