Abstract: Information on the abundance and distribution of cetaceans is essential to management and conservation and necessary to assess mortality trends and anthropogenic impacts for stock assessment. Line-transect aerial surveys (n = 45) were conducted to assess bottlenose dolphin (Tursiops truncatus) abundance, distribution, and group composition in the Indian River Lagoon (IRL) estuary system, Florida, from 2002 to 2004. Calves composed 9.41% of all known age class animals sighted. Multiple covariate distance sampling was used to estimate abundance. Abundance estimates varied seasonally, ranging between 362 (95% CI = 192 to 622; summer 2003) and 1,316 dolphins (95% CI = 795 to 2,061; winter 2002-2003), with a mean abundance of 662 dolphins (95% CI = 544 to 842). Abundance estimates for the Mosquito Lagoon sub-basin exhibited the greatest seasonal variability. Seasonal differences in abundance within strata suggest seasonal movement patterns. This study provides the first abundance estimate for IRL dolphins in over 30 y. Further studies that investigate evidence of influx/efflux are needed to better under-stand the population biology of IRL dolphins.

Key Words: abundance, aerial survey, bottlenose dolphin, Tursiops truncatus, distance sampling, distribution, Indian River Lagoon, line transect

Document Type: Research article

DOI: 10.1578/AM.37.2.2011.175

Page Numbers: 175-186