Estimates of survival probabilities for oceanic-stage loggerhead sea turtles (Caretta caretta) in the North Atlantic

Estimates of instantaneous mortality rates (Z) and annual appar­ ent survival probabilities (Φ) were generated from catch-curve analyses for oceanic-stage juvenile loggerheads (Caretta caretta) in the waters of the Azores. Two age distributions were analyzed: the “total sample” of 1600 log­ gerheads primarily captured by sight­ ing and dipnetting from a variety of vessels in the Azores between 1984 and 1995 and the “tuna sample” of 733 log­ gerheads (a subset of the total sample) captured by sighting and dipnetting from vessels in the commercial tuna fleet in the Azores between 1990 and 1992. Because loggerhead sea turtles begin to emigrate from oceanic to neritic habitats at age 7, the best estimates of instantaneous mortality rate (0.094) and annual survival probability (0.911) not confounded with permanent emi­ gration were generated for age classes 2 through 6. These estimates must be interpreted with caution because of the assumptions upon which catch-curve analyses are based. However, these are the first directly derived estimates of mortality and survival probabilities for oceanic-stage sea turtles. Estimation of survival probabilities was identified as “an immediate and critical require­ ment” in 2000 by the Turtle Expert Working Group of the U.S. National Marine Fisheries Service. Manuscript approved for publication 21 April 2003 by Scientific Editor. Manuscript received 26 June 2003 at NMFS Scientific Publications Office. Fish. Bull. 101:732–736 (2003). Estimates of survival probabilities for oceanic-stage loggerhead sea turtles (Caretta caretta) in the North Atlantic