Recent Abstracts ----------------------------------------------------------------------

List of Titles:

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Barre, L. M., and R. H. Defran. 1995. Sequential aspects of behavior in Pacific coast
bottlenose dolphins. Paper presented at the Eleventh Biennial Conference on
the Biology of Marine Mammals, Orlando, FL, USA.

Abstract

A 533 hour behavioral database collected on Pacific coast bottlenose dolphins was analyzed for the presence of sequential relationships between behavior states of travel, feed, social, play and rest. Transition matrix and chi square analyses showed that travel both preceded and followed all other behavior states more often than expected. Similarly, feed followed social and social followed feed more often than expected. Surprisingly, feeding, which is an energetically costly behavior, was followed by rest less often than expected. Behavior sequences containing rest or play with either social or feed occurred less often than expected. All of these sequential relationships were consistent across all three years of the study and across all but a few combinations of day period and tidal current. The strong predictive relationships documented between feed and travel as well as between feed and social suggests that conventional behavior sampling strategies frequently used to study a variety of cetacean species probably underestimate feeding time by labeling movements within a feeding bout as travel. In turn, such behavior labeling strategies probably lead to an overestimation of social behavior and an underestimation of feeding during episodes of cooperative foraging. Similarly, feeding/foraging associated movements labeled as travel may account for the absence of an expected predictive relationship between feed and rest.


Bilgre, B. A., and R. H. Defran. 1996. Photographic assessment of Tursiops
occurrence and home range in Turneffe Atoll, Belize. Paper presented
at the XXI International Meeting for the Study of Marine Mammals,
Chetumal, Quintana Roo, Mexico, April 8-12.

Abstract

A three-year photographic database was used to assess the occurrence and home range of bottlenose dolphins (Tursiops truncatus) in Turneffe Atoll, a shallow-water platform composed of seagrass beds, mangrove islands and coral reefs located 32-km east of mainland Belize. We carried out 425 photographic surveys, which were concentrated in the southern portion of Turneffe, and photographically identified 79 individual dolphins. Surveys were conducted between March - April 1992 (n = 22), July - December 1992 (n = 95), March - December 1993 (n = 145) and March - December 1994 (n = 163). New dolphins continued to be discovered throughout the three-year study period: in 1992 60% (n = 48) of the study population was identified, in 1993 24% (n = 19) was identified, and in 1994 15% (n = 12) was identified. The continued influx of new dolphins into the study population suggests that the population was larger than the one we sampled. The declining percent of new dolphins over the three study years, however, suggests that a finite population uses some part of the atoll. Sighting frequencies ranged between 1 and 57 with 58% (n = 46) sighted 5 times or less and 11% (n = 9) sighted 31 times or more. Forty-two percent (n = 33) of the identified dolphins were photographed only during a single year, but another 42% were photographed during all three years. Site fidelity varied greatly among individuals. This study provides important baseline information on bottlenose dolphins in a previously unstudied habitat type and in a region of limited human impact.


Bilgre, B. A., C. Graham, and R. H. Defran. 1995. Photoidentification analysis of
bottlenose dolphins (Tursiops truncatus) in Turneffe Atoll, Belize. Paper
presented at the Eleventh Biennial Conference on the Biology of Marine Mammals,
Orlando, FL, USA.

Abstract

We carried out 243 photographic surveys and identified 62 individual bottlenose dolphins within the Turneffe Atoll reef, 32-km east of mainland Belize. Surveys were conducted between July--December 1992 and March--December 1993. The rate of discovery for newly identified individuals increased throughout the study, suggesting the existence of a larger population than we sampled. Sighting frequencies ranged between 1 and 38 with 24% (n=15) of the population sighted only once, 23% (n=14) sighted 15 or more times, and 6% (n=4) sighted 20 or more times. When the study was divided into four successive time blocks, 31% (n=19) of the dolphins were photographed during all four blocks and 50% (n=31) were photographed during three or more blocks. The high overall encounter rate across the study indicates a high degree of residentiality for a subset of the population. Turneffe Atoll is a shallow, diversified and productive platform surrounded by a deep water channel. This research is providing needed data on the population dynamics of bottlenose dolphins within this previously unstudied habitat type and in this low human impact location.


Day, J. R., and R. H. Defran. 1995. Nocturnal activity of Pacific coast bottlenose
dolphins (Tursiops truncatus) in California. Paper presented at the Eleventh
Biennial Conference on the Biology of Marine Mammals, Orlando, FL, USA.

Abstract

Prior to this research nothing was known about the nocturnal activity budget of Pacific coast bottlenose dolphins. We studied both the nocturnal and diurnal activity of bottlenose dolphins between May 1994 and July 1995. During 60 boat-based behavioral surveys along a 32-km stretch of the north San Diego County coastline we accumulated 134 hours of direct observation on dolphin behavior. Nocturnal observations were made with light-enhancing night vision goggles. Results of our behavior proportion analysis showed that dolphins rested 2.1 times less during nocturnal periods (3.7%) than during diurnal periods (7.9%). Conversely, dolphins fed 1.7 times more at night (15.8%) than during the day (9.2%). Finally, we found 1.8 times more social behavior at night (15.8%) than during the day (8.8%) and less travel at night (64.2%) than during diurnal periods (71.9%). Behavior sequence analyses carried out by Barre and Defran (1995, this conference) suggested that some behaviors labeled social behavior may actually have been cooperative feeding. In the aggregate, our data show that bottlenose dolphins in San Diego probably utilize nighttime periods for enhanced feeding opportunities. The diminished rest and travel we observed at night are complimentary to this hypothesis.


Tepper, E. M., and R. H. Defran. 1995. Feeding duration in Pacific coast bottlenose
dolphins. Paper presented at the Eleventh Biennial Conference on the Biology
of Marine Mammals, Orlando, FL, USA.

Abstract

A total of 712 hours of land-based behavioral observations on Pacific coast bottlenose dolphins were carried out in San Diego between 1988--1995 and were analyzed to evaluate the impact of a number of ecological variables on feeding duration. Feeding bouts were significantly longer during crepuscular than midday time periods and during flood than ebb tidal states. Feeding duration was also significantly longer during periods when dolphins exhibited a back-and-forth movement pattern within a 2-km core area (localized movement) than when dolphins engaged in uniformly directional coastal movement of at least 5-km (directional movement).

Research by Hanson and Defran (1993) as well as by others in our laboratory has documented greater occurrence of feeding during high tidal current (ebb and flood), crepuscular day periods and during localized movement and suggested that such circumstances are associated with greater prey species abundance. This current analysis of feeding duration shows that our dolphins appear to lengthen their feeding bouts as a mechanism to exploit these circumstances of greater prey species availability. Longer feeding bouts may, therefore, be an optimizing (more energetically efficient) strategy which permits these dolphins to reduce the time spent searching, cooperatively foraging and capturing prey items.


Campbell, G. S., B. A. Bilgre, and R. H. Defran, Residence and social
affiliation patterns of bottlenose dolphins (Tursiops truncatus) in Turneffe Atoll, Belize.
Poster presented at the 1997 American Cetacean Society Meeting, San Pedro, CA, USA

Abstract

The residence and social affiliation patterns of bottlenose dolphins were assessed within Turneffe Atoll, a shallow-water platform composed of mangrove islands, seagrass beds and coral reefs located 32-km east of mainland Belize, C.A. A total of 544 photographic surveys were conducted from March 1992 to March 1996. School sizes ranged from 1 to 27 ( = 3.7) for the 815 groups encountered, and 100 individuals were photographically identified. Sighting frequencies ranged between 1 and 68 with 51% (n = 51) of the photographed population sighted 4 times or less and 18% (n = 18) sighted 25 times or more. New dolphins continued to be sighted throughout the study period which suggests that the actual population was larger than the one sampled. Analyses of social affiliation patterns were conducted on the 49 dolphins sighted five or more times. Results showed that 85% (n = 1009) of the CoA were low level (0.00 - 0.09) while only 0.4% (n = 5) were above 0.50, indicating a fluid social system. Population dynamics and residence patterns of Turneffe dolphins had similarities to both the Southern California Bight and the Sarasota populations. The majority of the Turneffe dolphins exhibited low site fidelity patterns and very low CoA similar to coastal dolphins in Southern California. Like the Sarasota community, school sizes in Turneffe were small, but relatively few individuals showed the persistent site fidelity characteristic of many Sarasota dolphins.


Campbell G. S. 1998. Occurrence, Site Fidelity, and Group Characteristics of Bottlenose Dolphins
(Tursiops truncatus) in the Drowned Cayes Region of Belize. Scientific report to the Oceanic Society.
 

Abstract

The occurrence, site fidelity, and group characteristics of bottlenose dolphins (Tursiops truncatus) in the Drowned Cayes region of Belize were assessed during a five-month boat-based photoidentification study. A total of 84 surveys were conducted between February 10, 1997 and July 02, 1997. School sizes ranged from 1-8 (mean = 2.3, SD=1.35) for the 119 groups encountered and 43 individuals were photographically identified. Sighting frequencies ranged between 1 and 15 (mean = 2.8, SD=3.1) with 21% (n = 9) of the photographed population sighted 4 times or more and 51% (n = 22) sighted only once. New dolphins continued to be sighted throughout the study period, suggesting that the population was larger than the one sampled. Individual distribution patterns were variable with some dolphins preferring particular regions within the study area. The 43 dolphins identified in the Drowned Cayes study area were compared with the 100 individuals identified in Turneffe Atoll and no matches were found despite the fact that the two study areas are only 16 km apart. The patterns of site fidelity identified for this dolphin community appear similar to those observed in Turneffe Atoll and thus it appears likely that the analogous habitat and prey species found in the two locations are strong selective pressures in determining dolphin population dynamics in this region.


Howarth, E.S., and R. H. Defran. 1997. A Sonobuoy Array for Two-Dimensional Location of
Dolphin Vocalizations.  Poster presented at the 134th Meeting of the Acoustical Society of
America, San Diego, CA, USA.

Abstract

In southern California coastal waters, two-dimensional locations of underwater biological sound sources were accomplished by arrival-time-difference measurements on a four sonobouy array. The array was deployed in the waters of southern California and the sonobouys separated by a range of 367 to 1585 meters. Accuracy of the locations depended on relative location of the source to the nearest sonobouys. The sensitivity of the system was inversely related to the intensity of noise propagating from both environmental and equipment sources. Global Positioning Satellite and theodolite locations are compared to predicted acoustic arrival-time-differences of several calibration sounds. Sources located by the array included bottlenose dolphins (Tursiops truncatus), passing boats and others of unknown origin. Other bioacoustic signals that were identified are snapping shrimp and fish. In the coastal waters of summertime, the sound levels varied on identical hydrophones. Effects from shallow water propagation, equipment age, signal transmission distance and natural diurnal fluctuations were suspected as the causes of the variation in the sound levels. Single hydrophone variations in signal intensity over time of the fish and shrimp were audible on multiple hydrophones simultaneously. It is suspected that these variations are of natural origin.

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