Seasonal abundance and adult survival of bottlenose dolphins (Tursiops truncatus) in a community that cooperatively forages with fishermen in southern Brazil

A subgroup of a population of Tursiops truncatus in southern Brazil is known for a cooperative behavior with artisanal fishermen whereby the dolphins shoal fish towards net-casting fishermen. Combining photo-identification data collected between September 2007 and 2009 with mark-recapture and Pollock's robust design models, we assessed abundance within seasons and survival and temporary emigration rates of dolphins between seasons. We also reanalyzed a previous data set collected during 19891991, and Cormack-Jolly-Seber models were applied to estimate survival rates for each of the study periods. The abundance of marked cooperative dolphins varied between seasons from 18 (CI: 1724) to 21 (CI: 2024). The total abundance varied from 59 in the winter of 2008 (CI: 4972) to 50 in the autumn of 2009 (CI: 4062). The annual adult survival was estimated to be 0.917 (CI: 0.8760.961), close to that estimated from data collected in the 1990s (0.941; CI: 0.8880.998). The emigration probability was low (0.031; CI: 0.0110.084) and different capture probabilities between the cooperative and noncooperative dolphins indicated a degree of behavioral segregation. The precision of our estimates is likely to provide sufficient power to detect population change, but we recommend a precautionary management approach to protect this vulnerable dolphin community and its unique cooperative feeding tradition.