At-sea density and abundance estimates of the olive ridley turtle Lepidochelys olivacea in the eastern tropical Pacific

Abstract

The first at-sea estimates of density and abundance of the olive ridley turtle Lepidochelys olivacea in the eastern tropical Pacific (ETP) were produced from shipboard line-transect data. Multi-ship surveys were conducted in 1992, 1998, 1999, 2000, 2003, and 2006 in the area defined by 5N, 120W, and 25N and the coastline of Mexico and Central America. Sighting data of olive ridleys were stratified by survey effort and sighting conditions, thereby reducing potential biases from heterogeneous observation conditions. Dive data from satellite telemetry studies were used to correct for the proportion of turtles that were submerged and unavailable for detection during the surveys. A weighted average of the 5 by-year estimates (1998 to 2006) was 1.39 million (coefficient of variation, CV = 19.7%; approximate 95% CI: 1.15 to 1.62 million). Our findings are consistent with the dramatic increases of olive ridley nesting populations that have been reported over the past decade for beaches in the ETP.