scholarly journals Interactions between Mediterranean bottlenose dolphins (Tursiops truncatus) and gillnets off Sardinia, Italy

2006 ◽  
Vol 63 (5) ◽  
pp. 946-951 ◽  
Author(s):  
Bruno Díaz López
Keyword(s):  
Group Size ◽  
Tursiops Truncatus ◽  
Bottlenose Dolphins ◽  
Size Analysis ◽  
Encounter Rate ◽  
New Approach ◽  
Annual Loss ◽  
Direct Observations ◽  
Annual Estimate ◽  
Northeastern Coast

Abstract A first attempt at analysing interactions between bottlenose dolphins and gillnets along the northeastern coast of Sardinia (Italy) was conducted between October 1999 and December 2004. A new approach was used: combining interviews with fishers with boat-based direct observations and behavioural and group size analysis. Fishers on monitored boats noted 2556 days on which gillnet damage was caused by bottlenose dolphins, 68.7% of the total fishing days, with no difference between seasons. An annual estimate of the number of bottlenose dolphins caught in the gillnets was 1.47 (0.98 immatures and 0.49 adults). In all, 317 days were spent making observations at sea, of which 330.6 h were spent directly observing the dolphins. There were no changes in the distribution of daily encounter rate among seasons, group size, or number of immatures, in the presence or the absence of gillnets. However, bottlenose dolphins spent more time both in the study area and feeding when gillnets were present. The extent of the estimated bycatch is worrisome in terms of the ability of bottlenose dolphins off Sardinia to sustain such an annual loss.

scholarly journals Intertidal habitat use of bottlenose dolphins (Tursiops truncatus) in Bahía San Antonio, Argentina

2017 ◽  
Vol 98 (5) ◽  
pp. 1109-1118
Author(s):  
Els Vermeulen
Keyword(s):  
Habitat Use ◽  
Intertidal Zone ◽  
Tursiops Truncatus ◽  
San Antonio ◽  
Bottlenose Dolphins ◽  
High Tide ◽  
Marine Conservation ◽  
Shallow Waters ◽  
Encounter Rate ◽  
Western Atlantic

Very little information is available on bottlenose dolphin (Tursiops truncatus) habitat use in the South-western Atlantic. It is, however, essential in understanding their ecology and to improve conservation management. In this study, habitat use of bottlenose dolphins was examined in Bahía San Antonio, an area frequented by the species. Given the large tidal amplitude and extended intertidal zone in this bay, special focus was given to the intertidal vs subtidal habitat use patterns. Bottlenose dolphins were observed in only half of the surveyed area, with on average 1 dolphin group encountered per 100 km surveyed. All dolphin groups were seen in shallow waters <10 m deep. GLM analyses showed that especially during high tide, depth had an important effect on the dolphin encounter rate, with most dolphin groups encountered in the intertidal zone. While in the intertidal zone, most dolphin groups were observed to be engaged in surface feeding activities. The presented data indicate dolphins remained in shallow waters, and moved to the intertidal zone during high tide where they appear to find feeding opportunities. This information is believed to be of high value in understanding this population's ecological needs, and essential when aiming to improve marine conservation efforts at times of increased anthropogenic pressures in the area.

Influence of artisanal fisheries on the behaviour and social structure of Tursiops truncatus in the South-western Gulf of Mexico

2019 ◽  
Vol 99 (8) ◽  
pp. 1841-1849
Author(s):  
Nataly Morales-Rincon ◽  
Eduardo Morteo ◽  
Christian Alejandro Delfín-Alfonso
Keyword(s):  
Gulf Of Mexico ◽  
Group Size ◽  
Age Structure ◽  
Human Activities ◽  
Tursiops Truncatus ◽  
Bottlenose Dolphins ◽  
Vantage Point ◽  
Competitive Interactions ◽  
Artisanal Fisheries ◽  
Behavioural Plasticity

AbstractBehavioural plasticity in animals is tested whenever competitive interactions for space and/or food resources occur between wildlife and human activities. This study uses the concepts of operational and non-operational interactions between bottlenose dolphins (Tursiops truncatus) and artisanal fisheries in Alvarado, to search for differences in behaviour, age structure and group size. We conducted 20 surveys between 2015 and 2016, and recorded 64 groups by means of scan sampling from either a research boat or a fixed vantage point. Average dolphin group size was small (${\bar{\rm x}}$ = 3.2, SD = 2.2 individuals) and fewer individuals were commonly present when interaction with fisheries occurred. Operational interactions were defined within the first 30 m and occurred mainly with lone individuals (54% recorded from the lighthouse and 82% during surveys); this benchmark also accounted for higher frequencies in locomotion and feeding (χ2 = 83.10; df = 7; P < 0.001). We found a higher rate of new behavioural events for dolphin groups furthest from human activities, as well as a decrease in behaviours that imply greater body exposure as dolphins approach the fishing spots. Age structure and dolphin group size were not different during and in the absence of interaction with fisheries, but most interactions involved male dolphins. Behavioural variations in the dolphins' repertoire are likely a strategy to reduce the risk of injuries or death when interacting with human activities; these dolphins seem to have habituated to or at least tolerate fishing activities within the study area, possibly constituting a sex-biased pressure.

scholarly journals Distribución espacial, estructura social y amenazas de conservación de una pequeña comunidad de delfines nariz de botella, Tursiops trunca (Odontoceti: Delphinidae) en Ecuador

2019 ◽  
Vol 67 (4) ◽  
Author(s):  
Fernando Félix ◽  
Melanie Zavala ◽  
Ruby Centeno
Keyword(s):  
Group Size ◽  
Tursiops Truncatus ◽  
Marine Protected Area ◽  
Bottlenose Dolphins ◽  
Northwestern Part ◽  
Small Community ◽  
Population Unit ◽  
Fishing Boat ◽  
Boat Traffic ◽  
Santa Elena

Socio-ecological and conservation aspects of a small community of bottlenose dolphins Tursiops truncatus (Odontoceti: Delphinidae) in Santa Elena, Ecuador. A resident community of bottlenose dolphins (Tursiops truncatus) has been studied irregularly between 2005 and 2018 around the tip of the Santa Elena Peninsula, Ecuador (2°11'S, 81°0.7'W). Opportunistic sightings and systematic surveys from the beach and at sea from a boat were carried out along 40 km of coast, accounting for 917.2 km of tracking by car from land and 707.4 km of boat tracking by sea. Average group size was 5.31 dolphins/group (SD= 1.97, range 1-10), with no significant changes throughout the study period. From land, however, the group size was underestimated 32% on the average. This small dolphin community currently has only nine individuals, including six adults, one immature and two calves. The relative abundance ranged between 0.03 dolphins/km in the northwestern part and 0.32 dolphins/km in the south, where dolphins concentrate their activities, possibly because human activities are less intense. Dolphins were generally distributed in the first 200 m from the shore, reaching up to 1,200 in the northern shallower part and where port and tourist activities concentrate. The dolphins’ speed was significantly higher when they were followed from a boat at close range (5.87 km/h) than when they were monitored from the beach (2.9 km/h) (P < 0.01), which suggests that boat tracking had an effect on dolphin´s movements. Pairwise cluster analysis showed that animals from this community show high rates of association among each other (average 0.67, range 0.01-1.0), indicating this is highly cohesive population unit. Dolphins also showed high level of residence (average occurrence index = 0.62). During the study, two main threats were identified, a gillnet fishery in the southwestern part and an intense fishing boat traffic in the northwestern. This coastal bottlenose dolphin community is the smallest of this species ever reported in the Gulf of Guayaquil, probably is a remnant of a larger population that would be in process of extinction. Most of the study area is currently part of a coastal-marine protected area created in 2008, which offers an opportunity for the recovery and conservation of this dolphin community. Given the fragility of this population unit, we recommend to environment authorities addressing potential threats by eliminating gillnets, implementing an exclusion zone for fishing gear and fishing boat traffic of 1 km width from the shore and limit the speed of any type of vessel to 10 knots within the reserve.

scholarly journals Distribution and abundance of bottlenose dolphin (Tursiops truncatus) over the French Mediterranean continental shelf

2019 ◽  
Author(s):  
Hélène Labach ◽  
Caroline Azzinari ◽  
Maxime Barbier ◽  
Cathy Cesarini ◽  
Boris Daniel ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Bottlenose Dolphin ◽  
Tursiops Truncatus ◽  
Bottlenose Dolphins ◽  
Encounter Rate ◽  
Habitat Directive ◽  
Photo Identification ◽  
Gulf Of Lion ◽  
Capture Recapture ◽  
First Time

AbstractThe Mediterranean bottlenose dolphin (Tursiops truncatus) sub-population is listed as vulnerable by the International Union for Conservation of Nature. This species is strictly protected in France and the designation of Special Areas of Conservation (SAC) is required under the European Habitat Directive. However, little information is available about the structure, dynamic and distribution of the population in the French Mediterranean waters. We collected photo-identification data over the whole French Mediterranean continental shelf all year round between 2013 and 2015. We sighted 151 groups of bottlenose dolphins allowing the individually photo-identification of 1,060 animals. The encounter rate distribution showed the presence of bottlenose dolphins over the whole continental shelf all year round. Using capture-recapture methods, we estimated for the first time the size of the bottlenose dolphin resident population at 557 individuals (95% confidence interval: 216-872) along the French Mediterranean continental coast. Our results were used in support of the designation of a new dedicated SAC in the Gulf of Lion and provide a reference state for the bottlenose dolphin monitoring in the French Mediterranean waters in the context of the Marine Strategy Framework Directive.

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

2004 ◽  
Vol 30 (2) ◽  
pp. 299-310 ◽  
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

Whale Poaching Detection Based on Microscopic Characteristics of Bottlenose Dolphins’ (Tursiops truncatus) Bone Fragments

2018 ◽  
Vol 43 (5) ◽  
pp. 519-528
Author(s):  
Manuela Zadravec ◽  
Zvonimir Kozarić ◽  
Snježana Kužir ◽  
Mario Mitak ◽  
Tomislav Gomerčić ◽  
...  
Keyword(s):  
Tursiops Truncatus ◽  
Bottlenose Dolphins ◽  
Bone Fragments
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