Schistosoma bovis: Variability of cercarial production as related to the snail hosts: Bulinus truncatus, B. wrighti and Planorbarius metidjensis

Development of Schistosoma bovis from Spain in different species or genus of intermediate hosts (Bulinus truncatus, B. wrighti and Planorbarius metidjensis) modifies cercarial productivity and its dynamics. From B. truncatus to B. wrighti and to P. metidjensis, cercarial productivity decreases while the length of the production period is increased. Variations in the dynamics are less obvious between the two species of Bulinus than between Bulinus spp. and P. metidjensis. In the latter the emission pattern is characterized by a 45–48-day production rhythm. These differences are explained in terms of larval demographic strategies and biotic capacities of the hosts. The validity of employing cercarial production as an indicator of host-parasite compatibility is discussed.     

Action competitive d'Helisoma duryi,wetherby (Planorbidae: Helisomatinae) a l'egard de divers mollusques vecteurs de trematodoses humaines et animales. II. Biomphalaria pfeifferi,krauss, Bulinus truncatus sericinus,jickeli et limnea natalensis,krauss

The authors studied biological competition between some african snails (Biomphalaria pfeifferi, Bulinus truncatus sericinus, Limnea natalensis) and Helisoma duryi in the laboratory.The results are irregular and less successful than with the closely related species, Biomphalaria glabrata.

avec la collaboration technique de R. THOMASSET     

RESIDENCE PATTERNS OF BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) IN THE STONO RIVER ESTUARY, CHARLESTON COUNTY, SOUTH CAROLINA, U.S.A.

Residence patterns of inshore bottlenose dolphins ( Tursiops truncatus ) in the Stono River estuary, Charleston County, South Carolina were investigated as part of a larger effort to better understand stock structure of these dolphins along the east coast of the United States. Eighty-seven small-boat surveys for bottlenose dolphins were conducted from October 1994 through January 1996. Dolphins were sighted during all surveys. Approximately 304 h were spent surveying the study area; 64% ( n = 196 h) of this time was spent observing and videotaping dolphins. A catalog, containing 112 individually identified dolphins was compiled. Thirty-two percent ( n = 36) of identified dolphins were sighted once, while 28% ( n = 31) were sighted five or more times. Nineteen percent ( n = 21) of identified dolphins were determined to be year-round residents; eight percent ( n = 9) seasonal residents. The majority (64%, n = 72) of identified dolphins were sighted in the study area during a single season or in two consecutive seasons and were classified as transients. This study documents the northernmost known site of a resident bottlenose dolphin community on the east coast of the United States, suggesting a complex bottlenose dolphin stock structure.     

EXPERIMENTAL RETURN TO THE WILD OF TWO BOTTLENOSE DOLPHINS

In the first scientific experiment of its kind, two young male bottlenose dolphins ( Tursiops truncatus ) were captured in Tampa Bay, Florida, and then returned to the wild at the same locale in October 1990, after two years in captivity. The dolphins' age/sex class and the capture and release site were selected prior to their collection. The ranging and social association patterns of the host community were examined prior to, and, including the two animals, after release. The dolphins remained together for the first month, then began interacting more with other dolphins and less with each other. Within the first year, one dolphin returned to the waters near his capture site and has remained there at least through September 1993. The other dolphin has remained in his original home range at least through June 1996. Observations of each dolphin have shown them to be fully integrated into the local dolphin societies. They displayed typical behavioral, ranging, and social association patterns. Their body condition has been excellent at each observation. They have not been observed interacting with humans. The apparent success of this experiment cannot necessarily be generalized to all potential candidates for return to the wild, but the results can be used to guide future experiments.     

ABUNDANCE OF SOUTHERN CALIFORNIA COASTAL BOTTLENOSE DOLPHINS ESTIMATED FROM TANDEM AERIAL SURVEYS

We describe a tandem aerial survey method for bottlenose dolphins ( Tursiops truncatus ) that uses two aircraft and independent observer teams to conduct consecutive surveys of the same coastal strip one hour apart. Alternatively, one aircraft with one observer team surveys the same coastal strip twice over several hours. Using mark-recapture analysis, we corrected survey counts for visibility bias resulting from missing dolphin groups at the surface and submerged groups. Dolphin groups were considered "recaptured" when we determined that both observer teams had detected the same group. This tandem method is highly useful for estimating abundance (and visibility bias) for species where population closure may be assumed between flights. We assumed population closure between flights and matched groups using geographic location, group size, and expected travel rates. We derive a new variance estimator of population size which incorporates group-size variability commonly encounteted in cetacean surveys. From six tandem surveys conducted from 1991 to 1994, we estimated the abundance of southern California coastal bottlenose dolphins to be between 78 (95% CI 60-102) and 271 (240-306) animals, with an average of 140 (128-154). Variability in abundance estimates is likely due to seasonal and interannual movement of animals along the California and Baja California coast. Abundance estimates from tandem surveys averaged 53% higher than dolphin counts obtained from individual survey flights, demonstrating the importance of correcting for visibility bias.     

EFFECTS OF WATERCRAFT NOISE ON THE ACOUSTIC BEHAVIOR OF BOTTLENOSE DOLPHINS, TURSIOPS TRUNCATUS, IN SARASOTA BAY, FLORIDA

Watercraft may provide the greatest source of anthropogenic noise for bottlenose dolphins living in coastal waters. A resident community of about 140 individuals near Sarasota, Florida, are exposed to a vessel passing within 100 m approximately every six minutes during daylight hours. I investigated the circumstances under which watercraft traffic may impact the acoustic behavior of this community, specifically looking for short-term changes in whistle frequency range, duration, and rate of production. To analyze whistles and received watercraft noise levels, acoustic recordings were made using two hydrophones towed from an observation vessel during focal animal follows of 14 individual dolphins. The duration and frequency range of signature whistles did not change significantly relative to vessel approaches. However, dolphins whistled significantly more often at the onset of approaches compared to during and after vessel approaches. Whistle rate was also significantly greater at the onset of a vessel approach than when no vessels were present. Increased whistle repetition as watercraft approach may simply reflect heightened arousal, an increased motivation for animals to come closer together, with whistles functioning to promote reunions. It may also be an effective way to compensate for signal masking, maintaining communication in a noisy environment.     

Tight spatial coupling of a marine predator with soniferous fishes: Using joint modelling to aid in ecosystem approaches to management

Aim

Understanding the distribution of marine organisms is essential for effective management of highly mobile marine predators that face a variety of anthropogenic threats. Recent work has largely focused on modelling the distribution and abundance of marine mammals in relation to a suite of environmental variables. However, biotic interactions can largely drive distributions of these predators. We aim to identify how biotic and abiotic variables influence the distribution and abundance of a particular marine predator, the bottlenose dolphin (Tursiops truncatus), using multiple modelling approaches and conducting an extensive literature review.

Location

Western North Atlantic continental shelf.

Methods

We combined widespread marine mammal and fish and invertebrate surveys in an ensemble modelling approach to assess the relative importance and capacity of the environment and other marine species to predict the distribution of both coastal and offshore bottlenose dolphin ecotypes. We corroborate the modelled results with a systematic literature review on the prey of dolphins throughout the region to help explain patterns driven by prey availability, as well as reveal new ones that may not necessarily be a predator–prey relationship.

Results

We find that coastal bottlenose dolphin distributions are associated with one family of fishes, the Sciaenidae, or drum family, and predictions slightly improve when using only fish versus only environmental variables. The literature review suggests that this tight coupling is likely a predator–prey relationship. Comparatively, offshore dolphin distributions are more strongly related to environmental variables, and predictions are better for environmental-only models. As revealed by the literature review, this may be due to a mismatch between the animals caught in the fish and invertebrate surveys and the predominant prey of offshore dolphins, notably squid.

Main Conclusions

Incorporating prey species into distribution models, especially for coastal bottlenose dolphins, can help inform ecological relationships and predict marine predator distributions.     

东海水域瓶鼻海豚种群数量和分布的初步研究

运用截线抽样法调查了北纬２５°～３０°,东经１２５°以西的东海水域中瓶鼻海豚在夏季７～９月间的种群密度和数量,得出的最小估计值分别为０．１４００头／ｋｍ２和９９４０头。瓶鼻海豚在该水域的分布特点为：随纬度增加（由南向北）密度逐渐减少,而在经度方向上则没有明显的密度变化规律。     

BOTTLENOSE DOLPHINS CAN GENERALIZE RULES and DEVELOP ABSTRACT CONCEPTS

Abstract: Generalization of a rule is demonstrated if the rule governs a class of problem, and the subject, after successful experience with a limited number of problems, can apply the governing rule to new problems within that class. We show that the bottlenose dolphin ( Tursiops truncatus ) is capable of such generalization for classes of problems requiting the matching of one of two alternative stimuli to a "sample" stimulus to which the animal had been previously exposed, regardless of the sensory domain used: vision, passive listening, or active echolocation. We also show this generalization capability in a related class of problem requiring a judgment of whether a single "probe" stimulus is the same as, or different from, a stimulus or stimuli previously presented. Further, one dolphin was shown capable of developing a true abstract concept of same/different through its ability to categorize pairs of simultaneously presented objects as identical or not. The suggestion that such generalization ability of dolphins may be in question because of so-called exclusion effects is shown to be not tenable when the whole body of available data is considered.