Abundance Of Bottlenose Dolphins Research Articles

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

Occurrence, site-fidelity and abundance of bottlenose dolphins (Tursiops truncatus) in Broadhaven bay, northwest Ireland during long-term construction of a gas pipeline

During the construction of a pipeline from an offshore gas field in northwest Ireland, shore-based watches and opportunistic boat-based photo-identification surveys for bottlenose dolphins Tursiops truncatus were undertaken. Seven years of data were used to investigate the influence of Construction-Related Activity (CRA) on the occurrence of dolphins in the bay where the pipeline made landfall. CRA varied substantially over the seven years and included dredging, pipe-laying, and rock armouring as well as seismic surveys. While individual activities could not be examined in isolation, there was no evidence of aggregated CRA or season influencing occurrence, despite a greater number of CRA days during summer months. There was weak support for the influence of year, but lower occurrence rates did not correspond to years with more CRA days, or vice versa. The uncorrected (marked animals, only) and corrected (accounting for unmarked individuals) annual abundance estimates with the lowest coefficient of variation were 67 (95% CI = 62–84; CV = 0.08) and 140 (95% CI = 106–174; CV = 0.12) in 2010, which was comparable to estimates from a neighbouring region on the west coast of Ireland. Of the well-marked individuals approximately 50% were re-sighted in two or more years and re-sightings within years were as high as 70%. Overall, there was little evidence to suggest that the extended period of CRA resulted in a short- or long-term reduction in the occurrence of dolphins within the bay. However, given the relatively coarse spatial and temporal scale of the CRA data it was not possible to assess fine-scale movements, such as redistribution within the bay in response to CRA within the immediate area. To better inform management and mitigation practices, greater emphasis should be placed on designing robust monitoring programmes that focus beyond fine-scale displacement as the sole indicator of an impact.

Abundance estimates and habitat preferences of bottlenose dolphins reveal the importance of two gulfs in South Australia

Informed conservation management of marine mammals requires an understanding of population size and habitat preferences. In Australia, such data are needed for the assessment and mitigation of anthropogenic impacts, including fisheries interactions, coastal zone developments, oil and gas exploration and mining activities. Here, we present large-scale estimates of abundance, density and habitat preferences of southern Australian bottlenose dolphins (Tursiops sp.) over an area of 42,438km2 within two gulfs of South Australia. Using double-observer platform aerial surveys over four strata and mark-recapture distance sampling analyses, we estimated 3,493 (CV = 0.21; 95%CI = 2,327-5,244) dolphins in summer/autumn, and 3,213 (CV = 0.20; 95%CI = 2,151-4,801) in winter/spring of 2011. Bottlenose dolphin abundance and density was higher in gulf waters across both seasons (0.09-0.24 dolphins/km2) compared to adjacent shelf waters (0.004–0.04 dolphins/km2). The high densities of bottlenose dolphins in the two gulfs highlight the importance of these gulfs as a habitat for the species. Habitat modelling associated bottlenose dolphins with shallow waters, flat seafloor topography, and higher sea surface temperatures (SSTs) in summer/autumn and lower SSTs in winter/spring. Spatial predictions showed high dolphin densities in northern and coastal gulf sections. Distributional data should inform management strategies, marine park planning and environmental assessments of potential anthropogenic threats to this protected species.

Site fidelity, residency, and abundance of bottlenose dolphins (Tursiops sp.) in Adelaide's coastal waters, South Australia

AbstractLittle is known about the ecology and behavior of southern Australian bottlenose dolphins (Tursiops sp.). This hinders assessment of their conservation status and informed decision‐making concerning their management. We used boat‐based surveys and photo‐identification data to investigate site fidelity, residency patterns, and the abundance of southern Australian bottlenose dolphins in Adelaide's coastal waters. Sighting rates and site fidelity varied amongst individuals, and agglomerative hierarchical cluster analysis led to the categorization of individuals into one of three groups: occasional visitors, seasonal residents, or year‐round residents. Lagged identification rates indicated that these dolphins used the study area regularly from year to year following a model of emigration and reimmigration. Abundance estimates obtained from multisample closed capture‐recapture models ranged from 95 individuals (SE ± 45.20) in winter 2013 to 239 (SE ± 54.91) in summer 2014. The varying levels of site fidelity and residency, and the relatively high number of dolphins found throughout the study area highlights the Adelaide metropolitan coast as an important habitat for bottlenose dolphins. As these dolphins also appear to spend considerable time outside the study area, future research, conservation, and management efforts on this population must take into account anthropogenic activities within Adelaide's coastal waters and their adjacencies.

Photo-identification of bottlenose dolphins in the far south of New Zealand indicates a ‘new’, previously unstudied population

Declines in the abundance of bottlenose dolphins in the Bay of Islands and in Doubtful Sound have contributed to the species being classified as Nationally Endangered in New Zealand waters. Updated information on distribution and abundance nationwide is therefore a high priority. This study presents data from the first photo-identification surveys of Paterson Inlet, Stewart Island, conducted to document bottlenose dolphin presence, abundance and residency. Open-population mark-recapture models indicate that 18 (95%CI = 15–20) dolphins regularly use Paterson Inlet. Photo-identification of dolphins from unknown populations during two chance encounters in Otago Harbour and Dusky Sound included 11 individuals previously identified at Stewart Island. These results indicate that dolphins found regularly at Stewart Island are part of a larger, wide ranging southern population with a minimum population abundance of 92 (95%CI = 80–111) individuals.

Structure and abundance of bottlenose dolphins (Tursiops truncatus) in coastal Setúbal Bay, Portugal

The environmental plasticity of bottlenose dolphins leads to a range of inter-specific variations in ecological parameters that make worldwide generalizations difficult. Thus, regional studies about bottlenose dolphins are important to the overall conservation of this species. The aim of this study was to characterize for the first time bottlenose dolphins that occur in the coastal regions of Setúbal (Portugal) using two temporally distinct datasets: dataset 1 (1998–2001) and those in dataset 2 (2007–2011). Bottlenose dolphins identified in dataset 1 were considered a closed and a more cohesive group than dataset 2, with stable associations and an abundance of 106 (95% CI = 69–192) individuals. Dataset 2 seemed to be composed of an open group of 108 (95% CI = 83–177) animals, with a migration rate of 19% (SE = 0.1) individuals per year, and with low association values. The proportion of ‘regulars’ (dataset 1, 22%; dataset 2, 12%), ‘frequent’ (dataset 1, 10%; dataset 2, 14%) and ‘occasional’ (dataset 1, 68%; dataset 2, 73%) animals was relatively similar between datasets. In addition, there was no matching of individuals between datasets which could be related to large-scale movements of the individuals and/or the carrying capacity of the study area.

Sighting frequency and relative abundance of bottlenose dolphins (<i>Tursiops truncatus</i>) along the northeast coast of Margarita Island and Los Frailes Archipelago, Venezuela

The study of local cetaceans in Venezuela has a very recent history, and few efforts have been made in the assessment of coastal populations based on field research. The occurrence of whales and dolphins along the northeast coast of Venezuela has been documented through sightings and stranding records. Given the underwater topographical features and the influence of upwelling processes, this area is considered a very productive coastal ecosystem. Our objective was to establish the sighting frequency and relative abundance of bottlenose dolphins in the area. Sighting records were gathered on bottlenose dolphins and other cetacean species occurring along the northeast coast of Margarita Island and Los Frailes Archipelago through direct observation during land-based (6 surveys, 48 hours of observation) and boat-based surveys (24 surveys, 121 hours of observation, 1295 km covered). A sighting frequency was calculated using two methodologies and then compared, considering: 1) a mean effective observation time (4.27 hours), and 2) distance covered with cetacean sightings (1108 kin). A third method is proposed relating a mean effective distance covered with cetacean sightings and expressed as a percentage. The abundance index was calculated using the mean effective observation time. The sighting frequency of Tursiops truncattus in the study area was 3 - 4 sightings per day of 4.27 observation hours, or by 185 kilometers covered. The relative abundance was calculated as 35 dolphins in the study area, so a total population of less than 60 dolphins could inhabit the proposed range. Tursiops truncatus is the dominant species in the northeast coast of Margarita Island and Los Frailes Archipelago with 70% of all the sightings, so this locality could be termed as the distribution range of a possible local population of bottlenose dolphins.

Abundance of Bottlenose Dolphins (Tursiops truncatus) in Estuarine and Near-Shore Waters of North Carolina, USA

Abstract A capture-recapture survey of bottlenose dolphins (Tursiops truncatus) was conducted in the sounds, estuaries and near-shore waters of North Carolina during July 2006, using photographic identification techniques; 291 dolphins were identified from distinctive nicks and notches on their dorsal fins. The results of our photographic analyses were applied to several capture-recapture models. The best estimate of the number of bottlenose dolphins present in estuarine waters of North Carolina during July 2006 was 813 with a 95% Confidence Interval of 483–1,142. Previously in July 2000, 1,033 (95% CI: 860-1,266) dolphins were estimated to be present in the estuaries of North Carolina. When the analysis from the 2006 surveys was expanded to include adjacent coastal waters, then the estimate of abundance increased to 1,138. Therefore, the abundance of dolphins in this area remained relatively stable between the two studies. Most dolphins were found in the northern part of the study area and there was very little exchange between the northern and southern areas of the state. The recapture data was also used to identify a spatial boundary between two putative management units that may be useful for future stock delineations. Additionally, an unexpected potential bias was introduced with the transition from slide film to digital media in the evaluation of the distinctiveness scoring.

Distribution and abundance estimates of bottlenose dolphins (Tursiops truncatus) around Lampedusa Island (Sicily Channel, Italy): implications for their management

This paper represents the first quantitative assessment of the distribution and abundance of bottlenose dolphins (Tursiops truncatus) inhabiting the waters around Lampedusa Island, Italy. Eleven years of photo-identification data, collected from 1996 to 2006 by three different research groups, were brought together, reviewed and analysed to fulfil the following objectives: (i) to obtain baseline information on the abundance and residency of the local bottlenose dolphin putative population; (ii) to review the current Marine Protected Area (MPA) boundaries, especially those referred to waters around Lampedusa Island, with a view to establish a new Special Area of Conservation (SAC); and (iii) to explore the potential and limits of analysing heterogeneous datasets to improve future data collection methods. The most resident dolphins were regularly observed in six specific areas around Lampedusa Island. From a total of 148 photo-identified bottlenose dolphins, 102 were classified as well-marked. The capture histories and the distribution of sightings clearly show a number of dolphins regularly use the study area. Best estimates for the first period within the ‘core study area’ were obtained for 1998 data. The 2005 estimate was significantly larger than the 1998 estimates (z = 2.160;P< 0.05) compared to that of 1998. Implications of our results for the current MPA, for transboundary conservation initiative involving Italy, Malta and Tunisia and for directing future research within and outside the MPA are fully discussed.

Abundance of bottlenose dolphins, Tursiops truncatus (Cetacea: Delphinidae), inhabiting the Patos Lagoon estuary, southern Brazil: implications for conservation

A new mark-recapture abundance estimate and a photographic census were carried out to investigate the possible decline in the abundance of the bottlenose dolphins, Tursiops truncatus (Montagu, 1821), in the Patos Lagoon estuary due to the high levels of bycatch mortality which occurred between 2002 and 2006 in oceanic coastal areas close to the estuary. Fourteen systematic boat surveys were conducted between August and early December 2005 to photo-identify the bottlenose dolphins. The estimated number of animals, with long-lasting marks, in the population obtained from Chapman's and Mth models were 51 (95% CI = 49-53) and 52 (95% CI = 51-60), respectively. Taking into account the proportion of dolphins with long-lasting marks in the population, the total estimated population size ranged between 84 (95% CI = 76-93) and 86 (95% CI = 78-95) individuals, respectively, which was very similar to the 84 individuals revealed by the population census. Our results did not differ from the abundance estimate carried out in 1998, prior to the high fishing-related mortality event, suggesting that the population is stable. Plausible argument to explain the stability of the population is that some carcasses found on the oceanic coastal beaches near Patos Lagoon estuary come from animals that do not belong to the estuary community. Future studies should investigate fine-scale habitat partition between estuarine and adjacent coastal dolphins. If the existence of different communities living in close proximity (estuarine and coastal areas near to the estuary) is confirmed, a new abundance estimate is needed to access the conservation status of bottlenose dolphins in this region.

The abundance and distribution of bottlenosed dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand

Photographic identification and standardized zigzag surveys were used to study the distribution and abundance of bottlenose dolphins in Doubtful Sound, New Zealand. Forty individuals were identified from nicks and markings on their dorsal fins. Chapman's and Bailey's modifications to the Lincoln–Petersen estimate and the computer program CAPTURE were used to estimate the number of marked individuals in the population, which ranged from 30 to 40 animals for three survey periods (two summers and a winter). The proportion of identifiable individuals in the population was assessed empirically as 65.5%. These data resulted in a total population estimate of approximately 58 individuals. The majority of the dolphins in the catalogue were found in each survey period, indicating their residency in the fiord. Movements of dolphins around the sound were not predictable, but there were areas in which dolphins were more likely to be found and other areas in which dolphins were never seen. However, there were no obvious seasonal or daily movement patterns.

Abundance of Bottlenose Dolphins, Tursiops truncatus, in the Coastal Gulf of Mexico

The abundance of bottlenose dolphins (Tursiops truncatus) for many coastal areas of the United States Gulf of Mexico is poorly known. During spring and fall 1987, we used aircraft and strip transects to estimate bottlenose dolphin abundance within 37 km of the U.S. Gulf shore. Greatest estimated dolphin densities were in the north-central Gulf (spring), northern Florida (fall) and Louisiana study areas (fall) (about 0.30 dolphins / km2). We estimated the coastal U.S. Gulf population of bottlenose dolphins to be 16,892 ± 3,628 (95% Cl) and 16,089 ± 3,338 in spring and fall, respectively. Bottlenose dolphins were found throughout the U.S. Gulf waters searched, but herds offshore of Texas were concentrated near passes and Louisiana herds were more common in and near eastern bays. Our estimates are one of the first assessments of the abundance and density of bottlenose dolphins throughout the coastal U.S. Gulf and may provide useful baseline estimates.