Environmental predictors of bottlenose dolphins distribution and core feeding densities in Galveston Bay, Texas

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Title: Environmental predictors of bottlenose dolphins distribution and core feeding densities in Galveston Bay, Texas
Author: Moreno, Maria Paula Teixeira
Abstract: Coastal dolphins are often exposed to habitat degradation and direct interactions with humans . Major factors that influence dolphin distribution , critical for conservation concerns , are still poorly understood even for the bottlenose dolphin , the best -studied cetacean . To establish the environmental conditions that best predict occurrence of bottlenose dolphins and high feeding densities in Galveston Bay , I conducted a total of 367 boat surveys in five locations of the estuary , totaling 3 ,814 .77 km of search effort . I counted groups of dolphins and measured surface water temperature , salinity , turbidity , total number of boats , shrimp vessels , and number of seabirds . Using geospatial tools , these data - - along with location , distance to the Gulf of Mexico and water depth - - were analyzed on a 500 - m resolution grid . Temporal factors at daily and seasonal scales were also examined . Occurrence was modeled using a Generalized Additive Model and core feeding densities (i .e . , feeding densities above 2 SD of the mean ) were modeled with a Generalized Linear Model . A total of 1 ,802 dolphins in 262 groups were detected , 56 .87 % of which were feeding . I found that all factors except warm /cold seasons and turbidity were useful to predict dolphin distribution , which was related non -linearly to most predictors . Fewer variables were relevant in predicting core feeding densities . These were , in decreasing order of relevance , distance to the Gulf of Mexico , surface water temperature , depth , number of boats , and warm /cold seasons . Feeding was highly clustered and the main core areas , less than approximately 3 km2 wide , were stable across time of day and season . The majority of the occurrences (86 .2 % ) and feeding groups (94 % ) were situated in two bay locations - Galveston Ship Channel (GSC ) and Bolivar Roads (BRD ) - that amounted to only one - fifth of the surveyed area . Compared to conditions in GSC and BRD when no dolphins were sighted , feeding cores weredeeper and more seabirds were observed . This fine -scale study of bottlenose dolphin distribution may contribute to a better understanding of habitat requirements for coastal dolphins . It also may provide information needed to minimize potential negative impacts to this population caused by human activities .
URI: http : / /hdl .handle .net /1969 .1 /3803
Date: 2006-08-16

Citation

Environmental predictors of bottlenose dolphins distribution and core feeding densities in Galveston Bay, Texas. Available electronically from http : / /hdl .handle .net /1969 .1 /3803 .

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