Capitoline Dolphins: Residency Patterns and Abundance Estimate of Tursiops truncatus at the Tiber River Estuary (Mediterranean Sea)

Periodic assessments of population status and trends to detect natural influences and human effects on coastal dolphin are often limited by lack of baseline information. Here, we investigated for the first time the site-fidelity patterns and estimated the population size of bottlenose dolphins (Tursiops truncatus) at the Tiber River estuary (central Mediterranean, Tyrrhenian Sea, Rome, Italy) between 2017 and 2020. We used photo-identification data and site-fidelity metrics to study the tendency of dolphins to remain in, or return to, the study area, and capture–recapture models to estimate the population abundance. In all, 347 unique individuals were identified. The hierarchical cluster analysis highlighted 3 clusters, labeled resident (individuals encountered at least five times, in three different months, over three distinct years; n = 42), part-time (individuals encountered at least on two occasions in a month, in at least two different years; n = 73), and transient (individuals encountered on more than one occasion, in more than 1 month, none of them in more than 1 year; n = 232), each characterized by site-fidelity metrics. Open POPAN modeling estimated a population size of 529 individuals (95% CI: 456–614), showing that the Capitoline (Roman) coastal area and nearby regions surrounding the Tiber River estuary represent an important, suitable habitat for bottlenose dolphins, despite their proximity to one of the major urban centers in the world (the city of Rome). Given the high number of individuals in the area and the presence of resident individuals with strong site fidelity, we suggest that conservation plans should not be focused only close to the Tiber River mouths but extended to cover a broader scale of area.

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Ecology and comparison of coastal and offshore bottlenose dolphins (Tursiops truncatus) in California

Marine and Freshwater Research ◽

10.1071/mf08279 ◽

2009 ◽

Vol 60 (6) ◽

pp. 584 ◽

Cited By ~ 18

Author(s):

Maddalena Bearzi ◽

Charles A. Saylan ◽

Alice Hwang

Keyword(s):

Tursiops Truncatus ◽

Site Fidelity ◽

Bottlenose Dolphins ◽

Photo Identification ◽

Santa Monica Bay ◽

Santa Monica ◽

Inshore Waters

Populations of coastal and offshore bottlenose dolphins (Tursiops truncatus) are considered to differ ecologically, with implications for their protection and management. We assessed occurrence, distribution and behaviour of coastal and offshore populations of dolphins during a photo-identification study in Santa Monica Bay and nearby areas (1997–2007). Bottlenose dolphins occurred year-round and were encountered on 44.2% of all surveys (n = 425). We photo-identified 647 individuals; of these, 375 (58.0%) were coastal (<1 km from shore), 241 (37.2%) offshore (1–65 km from shore) and 31 were both (4.8%). Dolphins mostly travel (69.0%) and travel-dive (61.5%), with offshore dolphins socialising more (22.6%) than coastal. There were low re-sighting rates for both coastal and offshore dolphins. Low re-sighting rates of coastal individuals provide little evidence of year-round site fidelity, suggesting their range is greater than the study area. Several individuals were re-sighted between and over 1-year periods, often foraging. This suggests that coastal dolphins: (1) are highly mobile within inshore waters, but spend time foraging in the study area, and (2) range >1 km from shore, contrary to what has been previously reported.

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Salinity and Water Temperature as Predictors of Bottlenose Dolphin (Tursiops truncatus) Encounter Rates in Upper Galveston Bay, Texas

Frontiers in Marine Science ◽

10.3389/fmars.2021.754686 ◽

2021 ◽

Vol 8 ◽

Author(s):

Vanessa J. Mintzer ◽

Kristi L. Fazioli

Keyword(s):

Water Temperature ◽

Tursiops Truncatus ◽

Prey Availability ◽

Bottlenose Dolphins ◽

Predictor Variable ◽

Suitable Habitat ◽

Galveston Bay ◽

Linear Regression Models ◽

Encounter Rates ◽

Photo Identification

Bottlenose dolphins (Tursiops truncatus) that inhabit urban estuaries like Galveston Bay, Texas, are exposed to cumulative stressors including pollution, fisheries, shipping, freshwater inflows, and construction operations. With continuing development, it is imperative to understand the key environmental variables that make the Galveston Bay estuary suitable habitat for this protected species. The Galveston Bay Dolphin Research Program conducted monthly photo identification surveys of bottlenose dolphins in a previously understudied 186 km2 area in upper Galveston Bay (UGB). To understand occurrence patterns in this region, we calculated monthly encounter rates of dolphins (dolphins/km) for four consecutive years (2016–2019). Using multiple linear regression models, we investigated the relationship between encounter rates, and water temperature and salinity. Monthly encounter rates ranged from 0.00 to 1.23 dolphins/km with an average of 0.34 dolphins/km (SE = 0.05). Over 80% of the variance was explained by the predictor variables water temperature and salinity (R2 = 0.820). Water temperature had a positive linear effect on encounter rates at over 23.37°C (SE = 1.42). Accordingly, higher encounter rates occurred during months with warm temperatures (May–September) compared to cooler months (November–April), indicating a predictable yearly movement pattern. Moreover, salinity was a highly significant predictor variable, with encounter rates dropping linearly with decreases in salinity. Higher numbers of dolphins are found in UGB during summer, but an exodus of dolphins occurs with low salinity levels, regardless of the time of year and water temperature. These findings should be considered during infrastructure projects (i.e., flood gate system) that may alter dolphin habitat and prey availability.

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Long-term site fidelity and residency patterns of bottlenose dolphins (Tursiops truncatus) in the Tramandaí Estuary, southern Brazil

Latin American Journal of Aquatic Mammals ◽

10.5597/00224 ◽

2017 ◽

Vol 11 (1-2) ◽

pp. 155-161 ◽

Cited By ~ 7

Author(s):

Amanda Baron Di Giacomo ◽

Paulo Henrique Ott

Keyword(s):

Tursiops Truncatus ◽

Site Fidelity ◽

Bottlenose Dolphins ◽

Southern Brazil ◽

Local Conservation ◽

Entire Study ◽

Photo Identification ◽

Average Observation ◽

Number Of Individuals

The occurrence of common bottlenose dolphins (Tursiops truncatus) in Tramandaí Estuary, southern Brazil, is described based on a photo-identification study conducted between January 2009 and February 2010. A total of 128 survey days were conducted with an average observation effort of 2.6 hours per day (SD = 0.6). Approximately 2050 photographs were taken from a shore land location at the mouth of the estuary. A total of nine dolphins were identified, including three calves. The dolphins were observed during all seasons, with a greater frequency during fall (79.3% of the days) and winter (60.7% of the days). The summer presented the lowest occurrence (2.4% of the days) of dolphins. During the entire study period, the maximum number of individuals sighted in any given day ranged from one to seven (average = 2.8 dolphins; SD = 1.35; n = 51). The residence indices, based on the resighting frequency of dolphins during the study period, ranged from 0.02 to 0.24 (average = 0.13; SD = 0.08; n = 9). However, most of the animals (67%) were resighted in over five months during a year and could be classified as residents. Longterm site fidelity was detected by resightings of four dolphins for over 18 years. These data combined reinforce the importance of the Tramandaí Estuary for the common bottlenose dolphins in the region and highlight the need for local conservation efforts to guarantee the long-term persistence of these coastal populations.

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Seasonal Abundance and Site Fidelity of Bottlenose Dolphins (Tursiops truncatus) in Mississippi Sound

Aquatic Mammals ◽

10.1578/am.30.2.2004.299 ◽

2004 ◽

Vol 30 (2) ◽

pp. 299-310 ◽

Cited By ~ 24

Author(s):

Carrie W. Hubard ◽

Kathy Maze-Foley ◽

Keith D. Mullin ◽

William W. Schroeder

Keyword(s):

Tursiops Truncatus ◽

Site Fidelity ◽

Bottlenose Dolphins ◽

Seasonal Abundance ◽

Mississippi Sound

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Occurrence of bottlenose dolphins (Tursiops truncatus) in the Río Negro Estuary, Argentina, and their mid-distance movements along the northeastern Patagonian coast

Latin American Journal of Aquatic Mammals ◽

10.5597/00226 ◽

2017 ◽

Vol 11 (1-2) ◽

pp. 170-177

Author(s):

Mauricio Failla ◽

Verónica A. Seijas ◽

Els Vermeulen

Keyword(s):

Tursiops Truncatus ◽

Feeding Activity ◽

Bottlenose Dolphins ◽

Activity Patterns ◽

Long Distance ◽

Identification Rate ◽

Photo Identification ◽

Rio Negro ◽

Patagonian Coast ◽

Main Activity

A systematic study was carried out on bottlenose dolphins (Tursiops truncatus) in the Río Negro Estuary (RNE), Patagonia, Argentina, to analyze their occurrence and activity patterns in this region. The photo-identification data of this study was further compared to data from an adjacent region to gain information on the animals' movements along the northeastern Patagonian coast. Information was gathered through land-based observations between the months of March and July of 2008 up to 2011. Data on dolphin activity patterns were collected via an ad libitum focal-group sampling mode. At the same time, dorsal fin images were obtained from as many dolphins as possible for identification and subsequent re-identification of individuals. Total effort equaled 188h, resulting in 58h of observation of 124 dolphin groups [sightings per unit effort (SPUE) = 0.66 group/h]. Most of the groups observed contained between one and five individuals, and two main activity states could be determined, namely traveling (65%) and foraging (26%). The photo-identification effort, which started opportunistically in 2006, resulted in a catalogue of 17 individual dolphins, with a total mean re-identification rate of nine days (max. = 24 days). When comparing these pictures to the existing catalogue of Bahía San Antonio (BSA; approximately 200km west from the study area) dorsal fins of 15 individuals could be matched and most (n = 12) could be subsequently re-identified in both areas, indicating their long distance movements along the northeastern Patagonian coast during the austral autumn months. This season coincides with the lowest dolphin abundance and feeding activity in BSA. This study indicates that bottlenose dolphins enter the RNE to forage at least during autumn. It further suggests that the search for food resources is the main trigger for their movement patterns along the northeastern Patagonian coast during this season, at least for certain individuals. More research is needed to accurately confirm these hypotheses.

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A time-based method for defining associations using photo-identification

Behaviour ◽

10.1163/1568539x-00003455 ◽

2017 ◽

Vol 154 (9-10) ◽

pp. 1029-1050 ◽

Cited By ~ 4

Author(s):

D.R. Johnston ◽

W. Rayment ◽

E. Slooten ◽

S.M. Dawson

Keyword(s):

New Zealand ◽

Tursiops Truncatus ◽

Group Membership ◽

Bottlenose Dolphins ◽

Digital Photography ◽

Social Structures ◽

Data Set ◽

Association Analyses ◽

Photo Identification

Photo-identification is an invaluable method for documenting associations. Based on the assumption that individuals photographed close together in time are physically close in space, the metadata associated with digital photography offers an opportunity to base association analyses on time between images. This was tested via analysis of associations within a population of bottlenose dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand. We compared the widely used group-membership method and an alternative time-based method. Overall social structures between methods were similar; high degrees of association among all individuals and little support for sub-groups. Results also indicated an increase in the precision of pairwise indices for the time-based method. This study validated the approach of using time as a basis for analyses of associations. Importantly, this method can be retrospectively applied to any photo-ID data set in which images of uniquely identifiable individuals are time-stamped by the camera.

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Abundance estimate and seasonal patterns of grey seal (Halichoerus grypus) occurrence in Brittany, France, as assessed by photo-identification and capture–mark–recapture

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315407054586 ◽

2007 ◽

Vol 87 (1) ◽

pp. 365-372 ◽

Cited By ~ 13

Author(s):

Maureen Gerondeau ◽

Christophe Barbraud ◽

Vincent Ridoux ◽

Cécile Vincent

Keyword(s):

Breeding Season ◽

Site Fidelity ◽

Seasonal Abundance ◽

Breeding Period ◽

Home Ranges ◽

Grey Seal ◽

British Isles ◽

Mark Recapture ◽

Abundance Estimate ◽

Photo Identification

It has been suggested that the large grey seal colonies around the British Isles form local populations within a metapopulation, and that seal movements outside the breeding season lead to considerable overlap between individual home ranges. Individual behaviour and population dynamics of small peripheral colonies may also play a role in the metapopulation. We studied the French grey seal colony of the Molène archipelago, at the southern-most limit of the species' range. We analysed photo-identification data with capture–mark–recapture techniques in order to estimate the total seasonal abundance of grey seals in the archipelago and to quantify the seasonal rates of occurrence or movements of male and female seals. We found that between 58 (95% confidence interval: 48–71) and 98 (95% CI: 75–175) individuals hauled out in the archipelago during the summers of 1999 and 2000. The use of multistate models allowed the assessment of seasonal site fidelity and indicated that it varied between key periods of the annual cycle, particularly for females. Males showed a constant fidelity rate of 56% from one season to another. Hence, even though they showed high inter-annual site fidelity, they did not seem to have a preferred season for using the archipelago. On the contrary, female grey seals showed the highest site fidelity between moult and summer (around 80%), and the lowest fidelity between summer and the breeding period (34–43%). Thus, females seem to use the Molène archipelago preferentially in summer and leave the site before the breeding season, which explains the very low local pup production. Philopatry may explain this pre-breeding emigration, and we suggest that most grey seals observed in the Molène archipelago were born and breed in other local breeding populations, probably the south-western British Isles.

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Individual movements between local coastal populations of bottlenose dolphins (Tursiops truncatus) in the northern and eastern Black Sea

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315416001296 ◽

2016 ◽

Vol 98 (2) ◽

pp. 223-229 ◽

Cited By ~ 3

Author(s):

Elena Gladilina ◽

Olga Shpak ◽

Valentin Serbin ◽

Anna Kryukova ◽

Dmitry Glazov ◽

...

Keyword(s):

Black Sea ◽

Bottlenose Dolphin ◽

Tursiops Truncatus ◽

Site Fidelity ◽

Bottlenose Dolphins ◽

The Black Sea ◽

Small Range ◽

Short Term ◽

High Population Growth ◽

Physical Barriers

The Black Sea subspecies of the bottlenose dolphin (Tursiops truncatus ponticus) is threatened and has a small range. Its population structure is little known: it possibly includes a few local coastal populations. We assessed connectivity between coastal groupings in six localities along 800 km of the coastline based on records of photo-identified animals between 2004 and 2014. Abundance of these groupings, as estimated, ranged between 76 and 174 individually distinctive dolphins. In total, there were 350 identified individuals, of which 91 (26%) were resighted within the same areas. However, only three cases of individual movements between local coastal populations were recorded at the distances between 135 and 325 km. Therefore, despite the absence of physical barriers, the coastal Black Sea population is fragmented into numerous resident or locally migrating groupings with site fidelity. These local populations are loosely connected to each other with rare movements between them. This fragmentation can be a factor contributing to short-term fluctuations in abundance of Black Sea bottlenose dolphins and their decline in some localities, despite the potentially high population growth rate.

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Inshore and offshore bottlenose dolphin (Tursiops truncatus) communities distinguished by association patterns near Grand Bahama Island, Bahamas

Canadian Journal of Zoology ◽

10.1139/z99-018 ◽

1999 ◽

Vol 77 (4) ◽

pp. 581-592 ◽

Cited By ~ 17

Author(s):

Kelly A Rossbach ◽

Denise L Herzing

Keyword(s):

Bottlenose Dolphin ◽

Tursiops Truncatus ◽

Site Fidelity ◽

Bottlenose Dolphins ◽

Social Groups ◽

Foraging Strategies ◽

Association Patterns ◽

Simple Ratio ◽

Water Depths

Little is known about the behavior of offshore dolphin populations. Our purpose was to distinguish and describe stable social groups of bottlenose dolphins (Tursiops truncatus) between inshore and offshore West End, Grand Bahama Island (26°42'N, 79°00'W). Photoidentification was conducted from May to September, 1994 to 1996. A simple ratio index described association patterns between dolphins. Multidimensional scaling of association indices (n = 1711 dolphin pairs) distinguished two dolphin communities consisting of 28 dolphins (19 of known sex) found inshore and 15 dolphins (12 of known sex) found greater than or equal to 27 km offshore. Eight of the 15 offshore dolphins were opportunistically photographed in the same region between 1986 and 1990. The two communities were found at different water depths (Mann-Whitney U test, p < 0.01), over distinct bottom types (Kruskal-Wallis test, p < 0.01), and used different bottom-foraging strategies. Long-term site fidelity of up to 10 years and repeated dolphin associations of up to 8 years occurred greater than or equal to 27 km from shore. Dolphins sighted greater than or equal to 15 times averaged 48 associates (SD = 11, n = 28). A dolphin's closest associate was of the same gender 74% of the time. This study is the first to report long-term site fidelity and association patterns of bottlenose dolphins found far from shore.

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