Long-term decline of the western Pacific leatherback, Dermochelys coriacea: a globally important sea turtle population

Abstract

The leatherbacks nesting at Bird’s Head Peninsula, Papua Barat, Indonesia, account for 75% of the total leatherback nesting in the western Pacific and represent the last sizeable nesting population in the entire Pacific. Sporadic nest counts at Jamursba Medi Beach at Bird’s Head have indicated a declining trend from the 1980s through 2004, although a relatively high amount of nesting has recently been documented at Wermon Beach, located 30 km east of Jamursba Medi. We used expanded year-round nesting surveys from 2005 to 2011 at these two primary nesting beaches to obtain more robust estimates of the nesting population size and to evaluate long-term nesting trends. We found a 29% decline in nesting at Jamursba Medi and a 52% decline at Wermon from 2005 through 2011. We found that the estimated annual number of nests at Jamursba Medi has declined 78.3% over the past 27 years (5.5% annual rate of decline) from 14,522 in 1984 to 1,596 in 2011. Nesting at Wermon has been monitored since 2002 and has declined 62.8% (11.6% annual rate of decline) from 2,994 nests in 2002 to 1,096 in 2011. Collectively, our findings indicate a continual and significant long term nesting decline of 5.9% per year at these primary western Pacific beaches since 1984. Mark-recapture with PIT tags, initiated in 2003, resulted in the tagging of 1,371 individual nesting females as of March 2012. Observed clutch frequencies ranged from 3-10 per season with a mean of 5.5 6 1.6 and, based on nest counts, provide an estimate of approximately 489 females nesting in 2011. The persistent and long term decline we report for the Bird’s Head leatherback population follows other dramatic declines and extinctions of leatherback populations throughout the Pacific over the last 30 years. These findings highlight the urgent need for continued and enhanced conservation and management efforts to prevent the collapse of what might be the last remaining stronghold for leatherbacks in the Pacific.