Noemi Duran Royo

Sea turtle hatchlings from Honduran beaches along the Pacific coast must swim more than 30 km through the shallow, presumably predator-rich waters of the Gulf of Fonseca before reaching the open ocean. Olive ridley hatchlings from Punta Ratón, Honduras, were tracked during the first 2 h of their offshore migration to assess aquatic predation rates. No predation events were observed. The absence of rocky bottom areas and reef structures where predators can refuge, and a decline in the number of predators due to overfishing are two possible reasons for this unexpected result. Additionally, diurnal and nocturnal swimming patterns of recently emerged olive ridley hatchlings were compared with regard to their position in the water column while swimming. At night hatchlings swam near the surface 97.5% of the time, with only sporadic brief dives. During daytime, however, hatchlings spent 78% of the time swimming at depth, going back to the surface for brief periods to breathe. Due to the high turbidity of the Gulf of Fonseca waters, this daytime behavior may serve to keep hatchlings out of sight of predatory sea birds. This newly described differential swimming behavior may have adaptive significance in avoiding aerial predation in the specific conditions of the Gulf of Fonseca.

In this dissertation, I investigated the reproductive ecology and hatchling behavior of the olive ridley (Lepidochelys olivacea) sea turtle population nesting in Pacific Honduras. I begin by reviewing olive ridley reproduction, human use of this species, and past and present conservation on nesting beaches. I also propose a conservation strategy to improve nesting beach conservation programs in developing countries. In the first of four empirical studies, I used microsatellite markers to assess multiple paternity levels of the Honduran population, and found evidence for multiple paternity in 75% of the nests examined. This rate, higher than expected for a population of solitary nesters, suggests that some females may be coming from Nicaraguan mass nesting beaches. The second study compared thermal profiles, hatching success, and hatchling characteristics of nests left in situ on the beach with nests from a local hatchery. I also assessed the effects of retaining hatchlings for 24 hours after emergence. Incubation temperatures were higher, and hatching success was lower, in the hatchery compared to the beach. Mean nest temperature during the second third of incubation was a good predictor of hatching success. Retention for 24 hours reduced hatchling weight, running speed, and active swimming time. In the third study, I compare diurnal and nocturnal hatchling swimming patterns, finding that hatchlings at night swam near the surface 98% of the time, yet during the day they spent 78% of the time swimming at depth. This diurnal pattern of deep swimming may be used by hatchlings to avoid avian predation. In the fourth study, I investigated the effects of tidal currents on hatchling movements during offshore migration. Hatchlings moved away from the coast during outgoing tides, but were pulled back to the shore during incoming tides. I found that a change in the timing of hatchling releases helped counter backward movements and increased effective distances covered by the hatchlings. This dissertation represents the first comprehensive study on the reproductive ecology of the Honduran olive ridley population. My findings provide useful information for improving ongoing conservation efforts for this species.