Bottlenose Dolphin Sightings Research Articles

Northern Range Expansion of California Coastal Bottlenose Dolphins (Tursiops truncatus)

The California coastal stock of bottlenose dolphins (Tursiops truncatus) expanded its range north from the Southern California Bight, its historical range, into Central California coincident with the 1982-1983 El Niño event. Since the late 1980s, bottlenose dolphin sightings north of Central California have been increasingly reported. To determine the present-day northern range limit for these dolphins, photo-identification efforts were carried out from 2007 to 2018 in San Francisco Bay and nearby coastal waters during which 84 individuals were identified. The results demonstrate a significant range expansion along the Northern California coast at least as far as Sonoma County (38.7º N). Comparisons with photo-identification catalogs compiled south of San Francisco from 1981 to 2015 revealed that 92% of the 84 dolphins were matched to Monterey Bay (n = 77), Santa Barbara (n = 27), Santa Monica Bay (n = 29), Orange County (n = 9), Corona Del Mar (n = 2), San Diego (n = 31), and Ensenada, Mexico (n = 1). Many of the 84 dolphins (54%) showed long-range movements across the stock’s range between the Southern California Bight and the San Francisco Bay Area. The greatest movement distance recorded was by two individuals first observed in San Diego, California, in the 1980s and subsequently in Puget Sound, Washington (47º N), in 2017, setting a coastal bottlenose dolphin long-distance movement record of at least 2,500 km.

Occurrence, site fidelity, and abundance of bottlenose dolphins (Tursiops truncatus) in the Western Ligurian Sea

This study represents the first complete assessment of the population dynamics and residency of common bottlenose dolphins in the Western Ligurian Sea, an area where bottlenose dolphin sightings have been rare in the past. Despite being greatly affected by human pressure, information about this population is poor and sporadic. The study took place from April 2018 to December 2020. One hundred and seventy‐one dedicated boat surveys were performed year‐round resulting in 95 sightings, and 123 individuals were identified through mark‐recapture photo‐identification techniques. Dolphins were found to be present year‐round. Most of the animals (79) used the area sporadically and only 19.5% of the dolphins (24) were seen regularly. Bottlenose dolphin abundance was estimated at 248 using open POPAN population models (CI 95% = 217–284). These results help fill a knowledge gap by highlighting the regular presence of bottlenose dolphins in the study area. Moreover, they represent a baseline for future studies investigating abundance trends and the conservation status of this population

Distribution, abundance and sighting patterns of multiple stocks of bottlenose dolphins (Tursiops truncatus) in coastal Virginia waters

Three stocks of bottlenose dolphins (Tursiops truncatus) are currently known to co‐occur in the coastal waters off Virginia. A combination of visual line‐transect survey and photo‐identification (photo‐ID) methods was used to gather information on the occurrence, distribution and density of bottlenose dolphins in the coastal areas of Norfolk and Virginia Beach. Sixty‐one line‐transect surveys were completed in two zones (inshore and offshore) between August 2012 and August 2015, with on‐effort coverage of 6,550 kilometres (km) of trackline over 349.6 hours. Conventional line‐transect analysis of bottlenose dolphin sightings showed both spatial and temporal variation in density (D) and abundance (N), with highest density in the inshore zone during warm‐water months (June–November). Inshore densities were calculated as 3.51 individuals per square kilometre (km2) (N = 1,090) in the warm‐water season and 0.73 individuals/km2 (N = 225) in cool‐water months (December–May). Densities in the offshore zone were 1.24 individuals/km2 (N = 741) in the warm‐water season and 0.61 individuals/km2 (N = 366) in the cool‐water season. Warm‐water density peaks support previous research; however, this study documents a cold‐season presence of dolphins in both zones not previously reported. Twenty‐seven photo‐ID surveys were completed and a photo‐ID catalogue was created using photos taken during both dedicated photo‐ID and line‐transect surveys, containing 1,335 unique individuals. Re‐sighting numbers were low, with less than 17% of individuals documented on more than one occasion, and only 4% sighted on three or more occasions, with a maximum of 4 re‐sightings. Days between re‐sightings ranged from 5 to 970, though distance between re‐sightings spanning greater time was minimal (less than 25km). Sighting locations of photo‐IDed dolphins were broken into three regions to investigate seasonal and spatial patterns of individual distribution; dolphins sighted only in the Cape Henry (CH) or Inner Bay (IB) region were observed mostly during summer and fall seasons (93% CH, 100% IB) with none occurring during winter. For the Outer Coastline (OC) region, the majority of sightings (88%) occurred during fall and winter. Additionally, there were two individuals sighted during winter months also sighted during summer more than 130km to the north inside Chesapeake Bay (matched to a different catalogue). These sightings support the possibility that the current stock structure does not account for all dolphins in the region. Stock structure as currently understood is complicated, with overlapping spatial distribution of three stocks that separate seasonally. Our study provides information that may be useful for management, but also additional findings that could impact future stock designations

Mapping the Exposure of Pantropical Spotted Dolphins and Common Bottlenose Dolphins to Different Categories of Vessel Traffic in Maui Nui, Hawai‘i

The increase and diversification of vessel traffic worldwide has resulted in a variety of known disturbances to dolphins. As a remote island chain, the Hawaiian Islands rely heavily on the marine environment for transportation, recreation, and fishing that aggregates into significant levels of vessel traffic. Given the known presence of dolphins in this region, there is a gap in knowledge regarding the relative exposure risk that vessel traffic poses to island-associated dolphin populations in Hawai‘i. This research identified the spatial distribution of pantropical spotted dolphins (Stenella attenuata) and common bottlenose dolphins (Tursiops truncatus) and determined the extent of their overlap with various categories of vessel traffic in Maui Nui, Hawai‘i. Species distribution was determined using kernel density estimates based on sighting data from 50 spotted dolphin sightings and 75 bottlenose dolphin sightings collected from 2013 to 2018. A combination of vessel GPS and Automatic Identification Systems (AIS) vessel tracks were used to quantify vessel traffic within the study area, resulting in 22,464 vessel tracks that were subsequently compiled into categories for analysis from 2014 to 2017. Risk of vessel exposure between vessels and dolphins, or co-occurrence, was determined by calculating the product of predicted dolphin density and predicted vessel density. Both species were exposed to vessel traffic risk over 100% of their distribution, but their highest exposure risk varied spatially, with high risk defined as > 0.25 on a normalized scale of low (0) to high (1) risk. The highest vessel exposure risk for spotted dolphins occurred in deeper, offshore waters, while the highest risk for bottlenose dolphins was in shallow, coastal waters. The vessel categories with the largest area of high risk to spotted dolphins were tour vessel and commercial fishing vessel traffic, while commercial transportation traffic had the highest exposure risk for bottlenose dolphins. This article provides baseline information for understanding the vulnerability of two island-associated dolphin populations to the threat of vessel traffic and highlights the differences in relative exposure risk based on species and vessel categories.

Patrones de comportamiento diurnos y estacionales de Tursiops truncatus y Stenella attenuata (Mammalia: Delphinidae) en el Golfo Dulce, Costa Rica

From July 1996 to June 1997, 123 sightings of bottlenose dolphins and 17 sightings of spotted dolphins were made in Golfo Dulce. south Pacific of Costa Rica. Behavioral patterns of both bottlenose and spotted dolphins were analyzed. classifying behavior in five categories such as travelling. feeding. passive socializing. active socializing and milling. Instantaneous data recording was used, and only sightings equal or longer than 15 minutes were considered. Correspondence Analysis revealed differences in diurnal patterns between the two species while seasonal patterns showed important similarities. Diurnal differences were explained in terms of external aspects (i.e. prey) instead of internal requirements due to time proportions for each activity were similar. Coincidence of time proportion spent on feeding activities during dry season (January-April) as well as coincidence of time proportion invested on active social activities during late wet season (September-December) in the two species were explained on a survival basis.

Reports of strandings and sightings of bottlenose dolphins (Tursiops truncatus) in northeastern Brazil and Brazilian oceanic islands

This study revises and updates information on bottlenose dolphin Tursiops truncatusstrandings and sightings in northeastern Brazil. A total of 72 strandings were recorded from 1992 to 2010, and 51 sightings were recorded from 1988 to 2010 along the states from Ceará to Bahia, including Fernando de Noronha and São Pedro and São Paulo archipelagos, Rocas Atoll and Abrolhos Bank. Most strandings were recorded in the states of Pernambuco, Bahia and Rio Grande do Norte. The number of reports was higher during summer, but no statistically significant difference was found between summer and other seasons. The majority of the stranded animals were adults (70.6%). Stranded calves were not observed. Total body length ranged from 138 to 321cm: 138 to 310cm for males; and 168 to 288cm for females. The average adult body length was 281cm (SD = 0.22). For stranding events where sex was determined (n = 29), a highly statistically significant difference was found between the number of males (n = 21) and females (n = 8). A total of six animals (8.3%) showed evidence of fisheries interactions such as net marks or removal of meat, blubber and eyes. Twenty-two sightings were recorded in the northeastern region, mostly in small islands and Rocas Atoll. This finding shows that the bottlenose dolphin is mainly an oceanic species in the region. More efforts are needed to improve our understanding of the populations and conservation status of bottlenose dolphins in this region.

The Indo-Pacific bottlenose dolphin (Tursiops aduncus) in Tañon Strait, central Philippines

Previous sightings of bottlenose dolphins in Tanon Strait, central Philippines, in the late 1980’s to early 1990’s were limited to the southern section of the strait, in waters <500 m deep, and the species was formerly identified as Tursiops truncatus. Photo-identification surveys (n = 117) conducted in 2014 and 2015 in Tanon Strait resulted in 50 encounters of Indo-Pacific bottlenose dolphins Tursiops aduncus. No common bottlenose dolphin T. truncatus was seen. The Indo-Pacific bottlenose dolphin has only recently been confirmed to occur in coastal waters in the Philippines and thus very little is known of its local distribution and ecology. In Tanon Strait, the species was seen across a wide range of water depth (4–668 m, x = 309 m) in groups ranging from 1 to ~60 individuals. We provide a photographic verification of this species and first evidence of a seemingly small population in a tropical protected seascape in the Philippines.

Occurrence of Atlantic humpback (Sousa teuszii) and bottlenose (Tursiops truncatus) dolphins in the coastal waters of Guinea-Bissau, with an updated cetacean species checklist

There is a paucity of information on the cetacean fauna of Guinea-Bissau in West Africa. We compiled records published in the literature and novel unpublished sighting data (2008–2014) to examine the occurrence and distribution of cetacean species. At least 10 species were verified to occur in Guinea-Bissau waters, of which eight were documented from a small number of sightings, whaling captures or skeletal remains. By far the most frequently recorded species were the common bottlenose dolphin (Tursiops truncatus) (N = 146) and the Atlantic humpback dolphin (Sousa teuszii) (N = 110). These two species were sympatric in distribution, both being found throughout coastal waters from the northern regions of Canal de Jeta and Rio Mansôa south to the Rio Cacine and around the Arquipélago dos Bijagós. However, differences were apparent in their finer-scale distribution and in the distance of sightings from shore, with bottlenose dolphin sightings generally occurring further from shore (and especially in the region of the Canal do Gêba) than Atlantic humpback dolphins. Sightings indicate that both species likely inhabit Guinea-Bissau waters throughout the year. Dedicated systematic cetacean survey work is urgently needed in coastal Bissau-Guinean waters in order to ascertain the abundance, spatio-temporal distribution, population structure and causes of mortality of bottlenose and Atlantic humpback dolphins, particularly given the Vulnerable conservation status of the latter species. Clarification of the status of cetaceans in offshore waters requires survey effort throughout the Guinea-Bissau EEZ.

Sex Difference in Bottlenose Dolphin Sightings during a Long-term Bridge Construction Project

Almost nothing is known about the effect of long-term bridge construction on free-ranging bottlenose dolphins (Tursiops truncatus). The species' natural history predicts that there should be sex differences in reaction to construction because bottlenose dolphins show sex differences in most of their behaviors. A 5-year bridge construction project over a narrow but important dolphin corridor at John's Pass tidal inlet, St. Petersburg FL, brought chronic environmental changes. The purpose of this 8-year study was to determine if bridge construction was associated with changes in dolphin sightings. The sex difference hypothesis was tested with a comparison of sighting probabilities before, during and after bridge construction. Sighting probabilities were generated for 68 adults seen n = 6504 times during N = 951 small-boat surveys of the 6.5-mile estuarine study area, documented with photo identification June 2005-December 2012. The sex difference hypothesis was supported with a significant interaction between construction and gender. Female sightings showed a significant linear decline across construction. Male sightings did not change across construction. The main conclusion is that adult males and females may react differently to habitat changes associated with anthropogenic activities. Sex differences in environmental monitoring and vigilance associated with maternal behavior may have played a role. This is the first report on John's Pass dolphins that evaluates changes in their behavior during a major construction project across a narrow but important dolphin corridor.

Abundance and distribution of Tursiops truncatus in the Western Mediterranean Sea: An assessment towards the Marine Strategy Framework Directive requirements

The Mediterranean Sea common bottlenose dolphin population has been assessed as Vulnerable according to the IUCN Red List Criteria. The species is also included in several International Agreements, European Union Regulations and Directives. Amongst them, a strict protection and identification of special conservation areas are requested by the EU Habitats Directive. Despite direct takes, by-catch, chemical and acoustic pollution, and prey depletion, general habitat degradation and fragmentation have been indicated as detrimental for the species, the degree to which these threats pose population risk is still largely unknown. At present it is thus not possible to depict the actual status of the population and to assess prospective trends. To address this gap in the current knowledge, line transect distance sampling aerial surveys were conducted in a wide portion of the Western Mediterranean Sea between the summer of 2010 and winter 2011. A total of 165 parallel transects equally spaced at 15 km were designed providing homogeneous coverage probability. Overall, 21,090 km were flown on effort and 16 bottlenose dolphin sightings were recorded and used for the analysis. The surface abundance and density estimates resulted in 1676 animals (CV = 38.25; 95% CI = 804–3492) with a density of 0.005 (CV = 38.25%). These results represent the first ever estimates for the common bottlenose dolphin over a wide portion of the Western Mediterranean Sea Subregion, with the potential to be useful baseline data to inform conservation. Specifically, they could be used as indicators under the Marine Strategy Framework Directive requirements, in conjunction with other study methods.

Where's That Dolphin?

Scientific research is interdisciplinary and often incorporates math, technology, and geography. Mapmaking and the use of global positioning system (GPS) technology, for example, are vital parts of many research endeavors that allow us to visualize patterns that might otherwise go unnoticed. Researchers frequently use these technologies to plot the locations of organisms or events. This helps them learn about habitat preferences and behaviors of certain animals. Our own research in Savannah, Georgia, uses handheld GPS devices to record the sightings of bottlenose dolphins. We then compile this information on a map, which provides us with clues about environmental or human factors affecting the dolphins' behavior or habitat. This article describes an activity in which students examine spatial data from five pairs of dolphins in our study and then form hypotheses about the spatial patterns they observe. In the process, they learn not only about the ecology of bottlenose dolphins but also that scientific research is interdisciplinary and can involve subjects such as math and geography. The activity is geared toward high school biology or environmental science classes but can be modified for other grade levels. It addresses numerous science education standards (see Figure 1, p. 26). FIGURE 1 Relevant Next Generation of Science Standards (NGSS). HS-LS2 Ecosystems: Interactions, Energy, and Dynamics Performance Expectation Students who demonstrate understanding can: HS-LS2-2: Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales. Common Core State Standards Connections: ELA/Literacy: WHST.9-12.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes. (HS-LS2-2) Mathematics: MP.2 Reason abstractly and quantitatively. (HS-LS2-2) MP.4 Model with mathematics. (HS-LS2-2) HSN-Q.A.1 Choose and interpret the scale and the origin in graphs and data displays. (HS-LS2-2) HSN-Q.A.2 Define appropriate quantities for the purpose of descriptive modeling. (HS-LS2-2) ADAPTED FROM NGSS P. 92 (NGSS LEAD STATES 2013) About bottlenose dolphins Bottlenose dolphins, or Tursiops truncatus, live in ocean waters as well as tidal rivers and creeks and exhibit different feeding strategies depending on their location. In Georgia, for example, some dolphins rush up a mud bank and push fish onto the shore to eat, a process known as strand feeding (Hoese 1971). This is seen in small creeks during low tide, when mud banks are exposed (Bowen 2011). Many dolphins in the area also eat fish stirred up by fishing nets or discarded from shrimp trawlers (Kovacs 2012). Several beg for food from humans in boats (Perrtree 2011). We identify individual dolphins in our study by patterns of nicks and notches in their dorsal fins. We assign each dolphin a numerical code and sometimes a name so we can keep track of which dolphins engage in which foraging techniques. The area where the dolphins are found is the utilization area. We determine utilization area by creating a minimum convex polygon (MCP)--the smallest possible polygon that encloses all points where we have sighted dolphins, without any internal or concave angles (Figure 2, p. 27). The activity Materials To conduct this activity, students need the following: * metric rulers, * calculators, * pencils, and * colored pencils or thin markers. Methods To begin, we introduce the class to basic information about bottlenose dolphins, geographic coordinate systems, and utilization areas using a PowerPoint presentation that is available online (see On the web). …

Records of bottlenose dolphins, Tursiops spp., in New Caledonian waters

Observations of bottlenose dolphins, Tursiops spp. were made opportunistically between 1993 and 2009 in New Caledonian waters (eastern Coral Sea, south-western Pacific). Two morphotypes, defined from pigmentation patterns, were observed: morphotype-B individuals possessed a distinctive, extensive pale-grey blaze that indents the darker-grey dorsal cape towards the basis of the dorsal fin while morphotype-A individuals lacked it. Morphotype-A bottlenose dolphins occurred in pods of 2–10 individuals whereas pods of morphotype-B bottlenose dolphins comprised up to ~30 individuals. All morphotype-A bottlenose dolphin sightings were made in inshore waters, and all morphotype-B bottlenose dolphin sightings were made offshore. Wounds inflicted by large sharks, including the tiger shark, were documented for morphotype-A bottlenose dolphins. Leisure-boat traffic is likely to be the cause of additional injuries to bottlenose dolphins in the New Caledonian lagoon. Pigmentation patterns and correlated habitat preferences of morphotype-A and -B bottlenose dolphins were consistent with those of, respectively, T. aduncus and T. truncatus in the western Coral Sea and elsewhere in the Pacific Ocean.

Integrating multiple data sources to assess the distribution and abundance of bottlenose dolphins Tursiops truncatus in Scottish waters

Abstract The distribution, movements and abundance of highly mobile marine species such as bottlenose dolphins Tursiops truncatus are best studied at large spatial scales, but previous research effort has generally been focused on relatively small areas, occupied by populations with high site fidelity. We aimed to characterize the distribution, movements and abundance of bottlenose dolphins around the coasts of Scotland, exploring how data from multiple sources could be integrated to build a broader‐scale picture of their ecology. We reviewed existing historical data, integrated data from ongoing studies and developed new collaborative studies to describe distribution patterns. We adopted a Bayesian multi‐site mark‐recapture model to estimate abundance of bottlenose dolphins throughout Scottish coastal waters and quantified movements of individuals between study areas. The majority of sightings of bottlenose dolphins around the Scottish coastline are concentrated on the east and west coasts, but records are rare before the 1990s. Dedicated photo‐identification studies in 2006 and 2007 were used to estimate the size of two resident populations: one on the east coast from the Moray Firth to Fife, population estimate 195 [95% highest posterior density intervals (HPDI): 162–253] and the second in the Hebrides, population estimate 45 (95% HPDI: 33–66). Interaction parameters demonstrated that the dolphins off the east coast of Scotland are highly mobile, whereas those off the west coast form two discrete communities. We provide the first comprehensive assessment of the abundance of bottlenose dolphins in the inshore waters of Scotland. The combination of dedicated photo‐identification studies and opportunistic sightings suggest that a relatively small number of bottlenose dolphins (200–300 individuals) occur regularly in Scottish coastal waters. On both east and west coasts, re‐sightings of identifiable individuals indicate that the animals have been using these coastal areas since studies began.

Movement patterns of coastal bottlenose dolphins in the presence of a fast-flowing, prevailing current: shore-based observations at Cape Vidal, South Africa

The presence and movement of Indo-Pacific bottlenose dolphins Tursiops aduncus were investigated using shore-based observations made during a humpback whale Megaptera novaeangliae migration survey at Cape Vidal, South Africa, undertaken between June and October 1988–1991. Occurrence was analysed as counts of dolphin sightings per hour within a generalised estimating equation framework. Bottlenose dolphin sightings decreased throughout the daily survey period, and there was a small seasonal peak in sightings during August. Data on movement trajectory were collected using a theodolite for 60% of the groups of dolphins sighted. Most groups were observed travelling in a northerly direction, with few groups recorded moving south. A generalised linear model indicated that northward-travelling dolphins were located closer to shore, travelled at higher speeds, and occurred in bigger groups under low-tide conditions, than those seen moving in a southerly direction. The southward-flowing Agulhas Current is close to shore at Cape Vidal, where the continental shelf is particularly narrow. We suggest that bottlenose dolphins in this area have adopted a specific movement regime to cope with the consistent fast-flowing currents that dominate their environment at Cape Vidal.

Cetacean sightings and strandings: evidence for spatial and temporal trends?

Cetacean species and their habitats are under threat and effective marine management mitigation strategies require knowledge and understanding of cetacean ecology. This requires data that are challenging and expensive to obtain; incidental sightings/strandings data are potential underused resources. In this study, incidental cetacean sightings (N = 6631) and strandings (N = 1856) in coastal waters of Cornwall, south-west Britain (1991 to 2008) were analysed for evidence of spatial and temporal patterns or trends. Eighteen species were recorded sighted and/or stranded; key species were identified as bottlenose dolphin (Tursiops truncatus), harbour porpoise (Phocoena phocoena), common dolphin (Delphinus delphis), Risso's dolphin (Grampus griseus) and minke whale (Balaenoptera acutorostrata). There were significant decreases in bottlenose dolphin sightings and pod size but an increase in harbour porpoise and minke whale sightings. Cetacean strandings showed a recent decrease over time although there was a significant positive trend in harbour porpoise strandings that correlated with sightings. Incidence of sightings and strandings were both greater on the south coast than the north coast. When Marine Tour Operator data were analysed, distinct species-specific inshore and offshore habitat use was evident. With rigorous interrogation and editing, significant patterns and trends were gained from incidentally collected data, highlighting the importance of public engagement with such recording schemes and the potential of these underused resources.

Southernmost records of bottlenose dolphins, Tursiops truncatus

Bottlenose dolphins (Tursiops spp.) are cosmopolitan animals widely distributed in waters of both hemispheres. The taxonomy of Tursiops has long been controversial, with over 20 specific names being published, and subspecies and inshore/offshore forms being proposed. In the southwestern South Atlantic, subspecies T. truncatus truncatus and T. truncatus gephyreus were proposed for specimens along the coasts of Brazil, Uruguay, and Argentina. Sightings of bottlenose dolphins are common along the coast of Argentina as far south as the Province of Chubut (ca. 46°S). Here, we summarize and discuss the southernmost records of bottlenose dolphins. We cannot make inferences about the species or subspecies to which these animals belong given the small number of specimens. Future studies of external measurements, pigmentation, DNA, and isotopes from both sides of the continent should help clarify the situation off southern South America. Furthermore, research is needed to explore a possible link between an effect of general global warming and the Tursiops specimens found this far south. The sighting and specimens described here, at 53°S–nearly 55°S, are the southernmost records for the genus and extend the range of the species in the southern South Atlantic.

Residency Patterns, Abundance, and Social Composition of Bottlenose Dolphins (&lt;I&gt;Tursiops truncatus&lt;/I&gt;) in Bahía San Antonio, Patagonia, Argentina

Residency patterns, abundance, and social composition of bottlenose dolphins (Tursiops truncatus) were assessed from 2006 to 2008 in Bahia San Antonio (BSA), Patagonia, Argentina. A total of 714 survey hours resulted in 132 contact hours with 224 bottlenose dolphin groups. Results indicated that dolphins can be seen year-round on average every 4 h, with sighting periods lasting an average of 45 min. A total of 57 bottlenose dolphins were positively identified in the bay, of which 56% showed a degree of residency, including almost all mother and calf pairs. Using the closed time heterogeneity model (Mth), and accounting for the proportion of unidentifiable individuals, calculations resulted in a corrected abundance estimate of 83 individuals for the study area. Further analysis revealed that individual dolphins associated at random and that the entire community exhibits rapid disassociations and two levels of casual acquaintances. Data suggest that the shallow waters of BSA support a relatively resident community of bottlenose dolphins, living in a fission-fusion society in which companionships frequently change. The relative constant presence of calves in more than 50% of the dolphin groups and the observed presence of neonates might furthermore indicate that dolphins specifically use this area, among others, to give birth and nurse their young. In addition, a reported decline in bottlenose dolphin sightings in the larger area of the Argentinean coast might indicate that BSA is one of the last remaining refuges of the species in the country. Further research seems vital for their conservation.

Ecology of marine tucuxi, Sotalia guianensis, and bottlenose dolphin, Tursiops truncatus, in Baía Norte, Santa Catarina state, southern Brazil

The marine tucuxi (Sotalia guianensis) occurs in coastal waters of western Central and South America sympatric to the bottlenose dolphin (Tursiops truncatus) throughout its range. This paper presents information on ecology based on 228 marine tucuxi and 36 bottlenose dolphin sightings collected during 226 boat-based surveys conducted from 1993 to 2002 in Baía Norte (27°30'S and 48°31'W), Santa Catarina state, southern Brazil. Both species were found year round although seasonal occurrence, sighting indices, sightings per unit of effort as well as group size and composition were strongly different. These features were different for marine tucuxis but similar to bottlenose dolphins when compared to other areas. Marine tucuxis were only found in the western part of the bay while bottlenose dolphins occurred mostly in the eastern section. Distances between species' sightings on the same days averaged 6.9km. Observations were made of both dolphin species feeding on the same fish species, of tucuxis being displaced by bottlenose dolphins and of an adult tucuxi bearing tooth rakes likely to have been caused by bottlenose dolphin attacks. Spatial segregation was not clearly explained by the environmental variables analyzed, suggesting that biological features such as aggression or competition may be influencing tucuxi distribution and social structure in Baía Norte.

Bottlenose Dolphin (&lt;I&gt;Tursiops truncatus&lt;/I&gt;) Predation on a Marine Fin Fish Farm: Some Underwater Observations

This paper reports on the results of underwater observations of bottlenose dolphin feeding behaviour in a marine fin fish farm on the Sardinian coast in Italy from 2000 to 2005. During the study period, 178 underwater encounters were noted during 79 sightings of bottlenose dolphins at a fish farm. Total time spent underwater in the presence of dolphins was 284 min, with a mean encounter duration of 1.6 ± 1.3 min. Bottlenose dolphins were primarily observed hunting both schooling and solitary prey around the fish farm cages, using seven cooperative and individual feeding strategies throughout the water column. The underwater observations suggest that the use of different feeding strategies is consistent with the hypothesis that bottlenose dolphins apply common decision rules in relation to prey availability, resulting in the use of different foraging techniques. The observed frequency of the feeding strategies employed by dolphins preying directly on farmed fish could be worrisome for aquaculture.

CALIFORNIA SEA LIONS USE DOLPHINS TO LOCATE FOOD

Abstract Aggregations by 3 species of dolphins (the bottlenose dolphin [Tursiops truncatus], the short-beaked common dolphin [Delphinus delphis], and the long-beaked common dolphin [Delphinus capensis]) and California sea lions (Zalophus californianus) were investigated in Santa Monica Bay, California. Groups were followed and observed during 201 boat-based surveys conducted in 1997–2001 documenting that sea lions were aggregated in 18.6% of the sightings with bottlenose dolphins (150 bottlenose dolphin sightings) and in 45.9% of the sightings with 1 of the 2 species of common dolphins (98 common dolphin sightings). Aggregations of bottlenose dolphins and sea lions were observed in inshore ( 500 m) waters, whereas common dolphins and sea lions were observed only in offshore waters. These aggregations were often recorded feeding near escarpments and submarine canyons, showing a striking preference for these bathymetric features. The results show that sea lions spend a signi...