Tag Archives: Cetacea

Summer movement patterns of bottlenose dolphins in a Texas bay

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Radio-tracking of 10 bottlenose dolphins (Tursiops truncatus), from 9 July 1992 to 13 September 1992, was conducted in Matagorda Bay, Texas. Mean range size was 140 km^2 (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, while on other days movement was very confined, within 1-2 km^2; (3) dolphins tended to spend about 1-4 days 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. Photo-identification surveys between May 1992 and June 1993 indicate that some individuals probably reside in Matagorda Bay for one or more years, while 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.

Lynn, S.K., and B. Würsig. 2002. Summer movement patterns of bottlenose dolphins in a Texas bay. Gulf of Mexico Science 20(1):25-37.

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Mother-infant spatial relations in captive bottlenose dolphins, Tursiops truncatus

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The prolonged nursing period and strong, extended mother-infant bond observed among bottlenose dolphins may reflect social and physical ontogeny critical for infant survival. This study was conducted to quantify ontogentic changes in mother-infant contact time and the amount of time infants spent in specific spatial states with their mothers from birth to age 12 mo. These behaviors were studied through a systematic, longitudinal study of six mother-infant pairs of captive bottlenose dolphins from three different social groups. There was a significant decrease in the time infants spent with their mothers (logistic regression, P< 0.001), following the general mammalian pattern of increasing independence with age. When with their mothers, the probability that infants would be found in “echelon” position, flanking the mother, decreased as the calf aged (logistic regression, P< 0.001), possibly due to anatomical and hydrodynamic factors. The probability that infants would be found in “infant” position, underneath the mother, increased with calf age (logistic regression, P< 0.001). Results obtained in this study are consistent with similar studies of wild bottlenose dolphin mother-infant pairs, indicating a suite of ontogenetically comparable behaviors between wild and captive bottlenose dolphins.

Gubbins, C., B. McCowan, S.K. Lynn, S. Hooper, and D. Reiss. 1999. Mother-infant spatial relations in captive bottlenose dolphins, Tursiops truncatus. Marine Mammal Science 15(3):751-765.

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Behavior of cetaceans in the northern Gulf of Mexico relative to survey ships and aircraft

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Data on behavior may help address relative differences in sightability and identifiability among species. As part of the 1992–1994 GulfCet program of shipboard and aerial cetacean surveys in the north-central and western Gulf of Mexico, we assessed cetacean responses to survey ships and aircraft. Pygmy and dwarf sperm whales and beaked whales showed the most avoidance reactions towards the ships (73%, 11 of 15 sightings), with large delphinids (e.g., blackfish) at 15% (7/48), small delphinids (e.g., Stenella spp.) at 6% (15/247), and Atlantic spotted and bottlenose dolphins at 0% each (26 and 88 sightings, respectively). Striped dolphins moved to avoid the ships in 33% (9/27) of sightings. Species which responded to the ships (either approaching or avoiding) also changed behavior in response to the survey airplane. Pygmy/dwarf sperm whales changed their behavior in response to the airplane during 40% (12/30) of sightings, and beaked whales during 89% (8/9). Several of the smaller delphinids also showed sensitivity to disturbance by the airplane. “Diving” and “other” were the most common responses to the airplane. Over all cetacean species, the behavioral states “milling” and “resting” appeared to be sensitive to disturbance; over 39% of initial observations of these behaviors were followed by a new behavior. Cryptic species, such as pygmy and dwarf sperm whales and beaked whales, which were seen resting on most occasions, responded to the airplane a high proportion of the time. Less cryptic species, such as the small delphinids, may have responded as often, but their response did not necessarily make them harder to identify. These data indicate that the sightability and identification of cetaceans may change with the variable behavior of species, and should be taken into account when extrapolating from sightings to population status. These behavioral differences may have effects on resulting density estimates. Density estimates for long-diving cetaceans, such as sperm whales, and species which often react negatively to the survey vessel, such as striped dolphins, may tend to be biased downwards, while the reverse may be true for species which tend to approach the ship, unless data can be collected to estimate the value of the detection function.

Würsig, B., S. K. Lynn, T. A. Jefferson, and K. D. Mullin. 1998. Behavior of cetaceans in the northern Gulf of Mexico relative to survey ships and aircraft. Aquatic Mammals 24(1):41-50.

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Behavioral and wound healing responses of bottlenose dolphins to biopsy sampling

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Information on reactions of delphinids to biopsy sampling and healing of associated biopsy wounds is limited. Results presented here report on the behavioral responses of free-ranging bottlenose dolphins (Tursiops truncatus) to remote biopsy sampling procedures, and provide information on stages of surgical biopsy wound repair. Biopsy samples of free-ranging dolphins were collected between February–May 1992 in Galveston Bay, Texas, using a sterilized corer-tipped bolt, launched from a crossbow. A total of 8 direct ‘hits’ were documented, 4 hits (50%) in which a tissue sample was obtained, 2 hits (25%) from which no sample was retrieved, and 2 hits (25%) in which the bolt struck the water (within approximately 30–60 cm) prior to striking the animal (no samples). Behav- ioral reactions were similar for all eight dolphins directly struck by a bolt, and were best character- ized as startle responses. As part of a NMFS sponsored capture effort to assess a 1992 bottlenose dolphin die-off in Matagorda Bay, Texas, surgical biopsy samples were taken from 35 dolphins (Sweeney, 1992). Biopsies roughly 3–5 cm in diam- eter and 1 cm deep, were surgically removed. While surgical biopsy wounds were not identical to remote biopsy wounds, they were comparable. Sixteen of the 35 surgically biopsied individuals were photographically resighted between July 1992 and December 1993. Photographs of biopsies immedi- ately after completion of surgical procedures and up to 476 days post-biopsy were classified into four stages of healing. Epidermis appeared to have cov- ered wounds by 40–42 days post-biopsy, but in some cases possibly as early as 15–26 days. Repig- mentation of epidermal tissue varied between indi- vidual dolphins, but in no cases occurred prior to 61 days post-biopsy. No indication of infection or related pathologies were detected from any of the biopsy wounds monitored during this study. Find- ings reported here suggest that when adequate care and caution are used, biopsy sampling of bottlenose dolphins is not likely to produce long-term behavioral alterations or result in physiological complications during wound healing.

Weller, D. W., V. G. Cockcroft, B. Würsig, S. K. Lynn, and D. Fertl. 1997. Behavioral and wound healing responses of bottlenose dolphins to biopsy sampling. Aquatic Mammals 23(1): 49-58.

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Movements, site fidelity, and respiration patterns of bottlenose dolphins on the central Texas coast

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Radio-tracking of 10 bottlenose dolphins (Tursiops truncatus), from 9 July 1992 to 13 September 1992, and photographic surveys of 35 freeze-branded dolphins, from May 1992 to June 1993, were conducted in the Matagorda Bay area of Texas, in response to a mass mortality event which occurred between Matagorda and Aransas Bays, Texas, during spring 1992. The primary goals of the study were to assess range size and site fidelity, as well as to initiate a long-term ecological study by collecting data on social and behavioral patterns.

The Matagorda Bay dolphin population was found to be numerically robust, occupying all regions of the bay surveyed. Mean range size, based on radio telemetry, was 140 km2 (SD = 90.7, n = 10 dolphins). Males and females had similar range sizes though males visited the extremities of their ranges more frequently or for longer periods. Several generalities were observed: (1) Dolphins were capable of, and often did, traverse their range in several hours. (2) Dolphins traveled widely on some days, perhaps crossing their own ranges, while on other days movement was very confined, within 1–2 km2. This did not appear to have a temporal or geographic pattern. (3) Dolphins tended to spend about 1–4 days in a particular portion of their range. (4) Movement tended to be more confined at night than during daytime. (5) Dolphins tended to visit the extremes of their ranges only in the daytime. The assertions of (4) and (5) may be biased as a result of less sampling effort at night, with fewer triangulations than during daytime and no visual sightings.

Most, if not all, of the 35 freeze-branded dolphins appeared to be resident to the Matagorda–Espiritu Santo Bay area with much fluidity of group membership. Overall mark/recapture population size estimates from photo-identification suggested that 218 ± 71.4 (95% CI) dolphins utilized an area of 312 km2 in Matagorda and Espiritu Santo Bays, similar to an estimate made in 1981. Dolphins spent longer times at the surface and dove less often at night, indicating lower activity levels at night. Observations of long-distance movement between Texas bays, and an autumn increase in dolphin numbers in the study area, suggested that the study animals were not an isolated population.

Wursig, B. and S. K. Lynn. 1996. Movements, site fidelity, and respiration patterns of bottlenose dolphins on the central Texas coast. NOAA Tech. Mem. NMFS-SEFSC-383, 111 pp.

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Observations of an interaction between sperm whales and short-finned pilot whales in the Gulf of Mexico

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On 24 August 1994 an unusual interaction between short-finned pilot whales (Globicephala macrorhynchus) and sperm whales (Physeter macrocephalus) was observed during a study of acoustic and surface behavior of sperm whales in the north central Gulf of Mexico (28°43.20’N, 88°44.13’W). We report here the defense reaction of sperm whales to the presence of pilot whales and give an indication of the generality and rate of interactions such as this from studies of tracked sperm whales in the South Pacific…

Weller, D. W., B. Würsig, H. Whitehead, J. Norris, S. K. Lynn, R. Davis, N. Clauss, and P. Brown. 1996. Observations of an interaction between sperm whales and short-finned pilot whales in the Gulf of Mexico. Marine Mammal Science 12(4):588-593.

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Movements, Site Fidelity, and Surfacing Patterns of Bottlenose Dolphins on the Central Texas Coast

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Radio-tracking of 10 bottlenose dolphins (Tursiops truncatus), from 9 July 1992 to 13 September 1992, and photographic surveys of 35 freeze-branded dolphins, from May 1992 to June 1993, were conducted in the Matagorda Bay area of Texas, in response to a mass mortality event which occurred between Matagorda and Aransas Bays, Texas, during spring 1992. The primary goals of the study were to assess range size and site fidelity, as well as to initiate a long-term ecological study by collecting data on social and behavioral patterns.

The Matagorda Bay dolphin population was found to be numerically robust, occupying all regions of the bay surveyed. Mean range size, based on radio telemetry, was 140 km2 (SD = 90.7, n = 10 dolphins). Males and females had similar range sizes though males visited the extremities of their ranges more frequently or for longer periods. Most, if not all 35 freeze-branded dolphins, appeared to be resident to the Matagorda-Espiritu Santo Bay area with much fluidity of group membership. Overall mark/recapture population size estimates from photo-identification suggested that 218 ± 71.4 (95% CI) dolphins utilized an area of 312 km2 in Matagorda and Espiritu Santo Bays, similar to an estimate made in 1981. Dolphins spent longer times at the surface and dove less often at night, indicating lower activity levels at night. Observations of long-distance movement between Texas bays, and an autumn increase in dolphin numbers in the study area, suggested that the study animals were not an isolated population.

Lynn, S.K. 1995. Movements, Site Fidelity, and Surfacing Patterns of Bottlenose Dolphins on the Central Texas Coast. M.S. thesis, Texas A&M Univeristy.

Marine mammal sightings in the Caribbean Sea and Gulf of Mexico, Summer 1991

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In the summer of 1991, we conducted marine mammal surveys in the Gulf of Mexico, Caribbean Sea, and a small portion of the southwestern North Atlantic. A total of 193 hours of survey effort was conducted, and there were 60 marine mammal sightings. Species identified (number of sightings in parentheses) were: sperm whale Physeter catodon L. (6), Cuvier’s beaked whaleZiphius cavirostris G. Cuvier (1), short-finned pilot whale Globicephala macrorhynchus Gray (1), rough-toothed dolphin Steno bredanensis (Lesson) (1), bottlenose dolphin Tursiops truncatus (Montagu) (6), Atlantic spotted dolphin Stenella frontalis (G. Cuvier) (2), pantropical spotted dolphin S. aftenuata (Gray) (10), spinner dolphin S. longirostris (Gray) (1), and striped dolphin S. coeruleoalba (Meyen) (3). Distribution of sightings was largely related to sighting conditions, but there were concentrations of sightings in areas with high sea floor relief – in the Straits of Florida, the area west of Martinique, and along the Mexican Ridge.

Jefferson, T., and S. K. Lynn. 1994. Marine mammal sightings in the Caribbean Sea and Gulf of Mexico, Summer 1991. Caribbean Journal of Science 30(1–2):83–89.

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