A Small Resident Community of Bottlenose Dolphins, Tursiops truncatus, in Texas: Monitoring Recommendations

A small community of bottlenose dolphins (Tursiops truncatus) in western Galveston Bay, Texas, was first studied in 1990 with subsequent study from 1995 through 2001. These animals showed strong site fidelity with seasonal variation in habitat use, From 1997 to 2001, three methods of assessing dolphin occurrence and abundance in this location were compared for efficiency and accuracy: photoidentification (photo-ID) for occurrence patterns and counts of individual animals; capture-recapture analyses from photo-ID data for abundance estimates; and line transect surveys for dolphin density estimates. Our line transect data were thought to be positively biased and that method is not recommended for this location. Counts of animals with site fidelity were consistent with abundance estimates of all dolphins using the bay from capture-recapture analysis. Resident animal counts ranged from 28 to 34 in different survey years. Abundance estimates for all dolphins using the bay, including nonresident animals, ranged from 28 to 38. Specific recommendations are made for long-term low-level monitoring of dolphins in this study area. These guidelines may be useful to researchers studying similar small coastal dolphin communities when appropriately modified and applied to their research sites

Patterns of Social Affiliation and Group Composition for Bottlenose Dolphins (Tursiops truncatus) in San Luis Pass, Texas

Group sizes, group composition, and association patterns of bottlenose dolphins (Tursiops truncatus) were investigated in the San Luis Pass area (Sep. 1995- Aug. 1996) of the Galveston Bay Estuary to examine differences in community structure of individuals inhabiting different portions of the estuary. Group sizes (n = 83) ranged from 1 to 29 (x̄ = 10.6) and were seasonally variable, with the largest groups occurring in spring (x̄ = 16.3) and the smallest groups during the fall (x̄ = 6.3). Seventy-one individuals were identified using photoidentification, and the sex of six dolphins (three males, three females) was determined. At least 31 (48.4%) groups were of mixed sex. Twenty-nine dolphins that were identified five or more times were used to calculate half-weight coefficients of association (COAs), which ranged from 0.00 to 0.83 (x̄ = 0.46). Coefficients of association for male pairs were higher than COAs for female and mixed-sex pairs. Permutation tests were performed to test for nonrandom associations and presence of preferred or avoided companions. The null hypothesis of random association was rejected, indicating that dolphins preferentially associated with some individuals and avoided others. In all replicates, three known-male pairs had significantly large COAs. These preliminary results suggested that, excluding mother-calf pairs that were not examined, male pairs formed the most stable social bonds

Summer Movement Patterns of Bottlenose Dolphins in a Texas Bay

Radiotracking of 10 bottlenose dolphins (Tursiops truncatus), from 9 July 1992 to 13 Sep. 1992, was conducted in Matagorda Bay, Texas. The mean range size was 140 km2 (SD = 90.7). Males and females had similar range sizes, though males visited the extremities of their ranges more frequently. Several generalities were observed: (1) dolphins were capable of traversing their range in several hours; (2) dolphins traveled widely on some days, whereas on other days, movement was very confined, within 1-2 km2; (3) dolphins tended to spend about 1-4 d in a particular portion of their range; (4) movement tended to be more confined at night than during daytime; and (5) dolphins tended to visit the extremes of their ranges only in the daytime. Individually, dolphins showed preferences for geographic regions within the bay; ranges overlapped strongly for some dolphins, yet only at range boundaries for others. Photoidentification surveys between May 1992 and June 1993 indicate that some individuals probably reside in Matagorda Bay for one or more years, whereas other individuals do not and can be found in other Texas bays. Limited ranging within the bay system and a lack of movement offshore may indicate that some of the dolphins are susceptible to localized anthropogenic and naturally occurring toxins. Examples of movement between bays, though few in the present data set, indicate that on the Texas coast, within-bay dolphin populations are probably not truly isolated

Behavior Patterns of Bottlenose Dolphins in San Luis Pass, Texas

Common bottlenose dolphins (Tursiops truncatus) are behaviorally flexible cetaceans that have adapted to a wide variety of habitats. In the San Luis Pass area near Galveston, Texas, there are two populations of bottlenose dolphins, distinguished through long-term photo-identification studies, which use adjacent habitat in different ways. A small resident population makes use of the shallow bay system, while the larger, more transient population remains outside the bay along the Gulf of Mexico coastline. A 13-mo study was conducted to examine the behavior of these populations and to explore the hypothesis that although they overlap geographically, each population utilizes the area differently. The behavior of focal groups was assessed by instantaneous sampling, and a time budget of each behavior per unit effort was calculated. When these populations mix in Gulf of Mexico waters, social activity and travel were the primary behaviors observed. Resident dolphins foraged predominantly in the bays and pass, and displayed group foraging behavior. In contrast, Gulf dolphins were only observed foraging in coastal waters, and did so individually. These behavioral differences may reflect strategies based on habitat variation, but may also be indicative of distinct social structures between resident and Gulf populations. There was a seasonal component to behavior and group size, with larger mixed groups and more social behavior occurring in summer. Finally, resident dolphin behavior varied by time of day, with a peak in foraging in the morning and socializing in the afternoon. The results of this study suggest that these adjacent groups are distinct populations that have partitioned their habitat into separate niches, and thus should be treated separately in management decisions

Social Structure of Sperm Whales in the Northern Gulf of Mexico

Sperm whales exhibit highly structured social behavior that depends on sex, age, and possibly local ecological characteristics. We analyzed sighting data collected between 1994 and 2005 to determine the social structure of sperm whale groups in the northern Gulf of Mexico (714 good-quality photographs of 285 individual whales). Average typical group size was approximately eight when estimated with mark-recapture techniques and using data from 2003 to 2005. Lagged association rate analyses including data from 1994 to 2004 indicated average group sizes of 11.41. Therefore, groups in the Gulf are considerably smaller than groups in the Pacific Ocean, but similar to those from the Caribbean Sea. Similarly, groups in the Gulf of Mexico remained stable for longer periods (62.5 d, SE = 47.62) than Pacific groups, but were comparable to groups from the Gulf of California. Such differences and similarities between populations could be due to adaptations to local conditions, indicating that Gulf of Mexico sperm whales may live in ecological conditions more similar to those of the Caribbean and the Sea of Cortez than to the Pacific

Multi-locus phylogeography of the dusky dolphin (Lagenorhynchus obscurus): passive dispersal via the west-wind drift or response to prey species and climate change?

<p>Abstract</p> <p>Background</p> <p>The dusky dolphin (<it>Lagenorhynchus obscurus</it>) is distributed along temperate, coastal regions of New Zealand, South Africa, Argentina, and Peru where it feeds on schooling anchovy, sardines, and other small fishes and squid tightly associated with temperate ocean sea surface temperatures. Previous studies have suggested that the dusky dolphin dispersed in the Southern Hemisphere eastward from Peru via a linear, temperate dispersal corridor provided by the circumpolar west-wind drift. With new mitochondrial and nuclear DNA sequence data, we propose an alternative phylogeographic history for the dusky dolphin that was structured by paleoceanographic conditions that repeatedly altered the distribution of its temperate prey species during the Plio-Pleistocene.</p> <p>Results</p> <p>In contrast to the west-wind drift hypothesis, phylogenetic analyses support a Pacific/Indian Ocean origin, with a relatively early and continued isolation of Peru from other regions. Dispersal of the dusky dolphin into the Atlantic is correlated with the history of anchovy populations, including multiple migrations from New Zealand to South Africa. Additionally, the cooling of the Eastern Equatorial Pacific led to the divergence of anchovy populations, which in turn explains the north-south equatorial transgression of <it>L. obliquidens </it>and the subsequent divergence of <it>L. obscurus </it>in the Southern Hemisphere.</p> <p>Conclusion</p> <p>Overall, our study fails to support the west-wind drift hypothesis. Instead, our data indicate that changes in primary productivity and related abundance of prey played a key role in shaping the phylogeography of the dusky dolphin, with periods of ocean change coincident with important events in the history of this temperate dolphin species. Moderate, short-term changes in sea surface temperatures and current systems have a powerful effect on anchovy populations; thus, it is not infeasible that repeated fluctuations in anchovy populations continue to play an important role in the history of coastal dolphin populations.</p

Observations on the Behavioral Responses of Bowhead Whales (Balaena mysticetus) to Active Geophysical Vessels in the Alaskan Beaufort Sea

The responses of bowhead whales to controlled approaches by geophysical vessels producing airgun blasts were observed during the course of four field experiments conducted in the Alaskan Beaufort Sea in September 1984. Behavioral responses included shorter surfacing and dive times, fewer blows per surfacing, longer blow intervals and subtle to overt changes in surface behaviors. Subtle behavioral responses occurred at 3.5 and 8.2 km with received airgun noise levels of 142 and 157 dB respectively (all levels in dB re 1 micro Pa). Partial avoidance (i.e., some whales leaving the observation area while others remained) occurred at ranges of 3.5 and 7.6 km, with sound levels of 142 and 158 dB respectively. Total avoidance (i.e., all whales leaving the observation area) occurred at 1.3, 7.2, 3.5 and 2.9 km, with corresponding sound levels of 152, 165, 178 and 165 dB. The similarities among experiments reported here support the conclusion that short-term behavioral changes occur when bowhead whales are exposed to airgum blasts from approaching geophysical vessels at ranges &lt;10 km. These disturbance efforts wane within one hour after a disturbance; long-term effects on social, behavioral or physiologic parameters are not known at this time.Key words: bowhead whale, Balaena mysticerus, geophysical vessel, bioacoustics, airgunsMots cl&eacute;s: baleine franche, Balaena mysticetus, navire de prospection g&eacute;ophysique, bioacoustique, canons &agrave; ai

Cetaceans, Sea Turtles and Seabirds in the Northern Gulf of Mexico: Distribution, Abundance and Habitat Associations, Volume 1: Executive Summary

This report covers three years of research on the distribution and number of whales, dolphins, sea turtles, and sea birds in the Gulf of Mexico