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Monitoring Seasonal Abundance of Indian River Lagoon Bottlenose Dolphins (Tursiops truncatus) Using Aerial Surveys
Abstract: Systematic long-term monitoring of abundance and distribution is essential to management and conservation and necessary to assess mortality trends and anthropogenic impacts for cetacean stock assessment. Line-transect aerial surveys (n = 42) were conducted to assess bottlenose dolphin (Tursiops truncatus) abundance, distribution, and group composition in the Indian River Lagoon (IRL) estuary system, Florida, from 2005 to 2011. Multiple covariate distance sampling was used to estimate abundance, and experimental trials were utilized to estimate dolphin availability. Abundance estimates varied seasonally, ranging between 483 (95% CI = 345 to 672; summer 2008) and 1,947 dolphins (95% CI = 1,198 to 2,590; winter 2009-2010), with a mean abundance of 1,032 dolphins (95% CI = 809 to 1,255). The largest abundance estimates for IRL dolphins occurred during extremely cold winter events, suggesting seasonal changes may influence dolphin movements. Mean visibility depth (125.14 ± 38.29 cm) suggested the availability bias did not largely influence estimates of dolphins in this shallow estuary when surveys are conducted under optimal sighting conditions. However, there was some evidence of seasonal changes in availability that may influence abundance estimation, and this should be further investigated. Seasonal trends and corresponding genetic and movement data suggest Mosquito Lagoon may be a disjunct community from the IRL proper. This study provides abundance data to assess the IRL bottlenose dolphin stock prior to the largest Unusual Mortality Event on record for this population, which occurred in 2013.
Key Words: abundance, aerial survey, availability bias, bottlenose dolphin, Tursiops truncatus, multiple covariate distance sampling, distribution, Indian River Lagoon, line transect, trend analyses
Document Type: Research Article
Page Numbers: 90-112