Modelling dolphin distribution within an Important Marine Mammal Area in Greece to support spatial management planning

1. Understanding marine mammal distributions is essential for conservation, as it can help identify critical habitat where management action can be taken. The semi‐enclosed Gulf of Corinth, Greece, has been identified as an Important Marine Mammal Area by the International Union for Conservation of Nature (IUCN) Marine Mammal Protected Areas Task Force, based on the regular occurrence of odontocete populations. A 7‐year (2011–17) dataset of boat‐based surveys was used to model and predict the distribution of striped dolphins, Stenella coeruleoalba, common dolphins, Delphinus delphis, and common bottlenose dolphins, Tursiops truncatus, in the entire Gulf (2400 km²).
2. Multiple geographic, bathymetric, oceanographic, and anthropogenic variables were incorporated in a combined generalized additive model and generalized estimation equation (GAM‐GEE) framework to describe dolphin occurrence and produce distribution maps.
3. Modelling indicated that striped and common dolphins prefer deep waters (>300 m) in the central and southern part of the Gulf, whereas bottlenose dolphins prefer shallow waters (<300 m) and areas close to fish farms along the northern–central shore.
4. Model‐based maps of the predicted distribution identified a preferred habitat encompassing most of the Gulf, also revealing: (i) hot spots of dolphin distribution covering about 40% of the Gulf's surface; (ii) an almost complete overlap of striped and common dolphin distribution, consistent with the hypothesis that common dolphins modified their habitat preferences to live in mixed species groups with striped dolphins; (iii) a clear partitioning of striped/common and bottlenose dolphin habitat; and (iv) the important role played by fish farms for bottlenose dolphins, consistent with studies conducted elsewhere in Greece.
5. Evidence provided by this study calls for area‐specific and species‐specific management measures to mitigate anthropogenic impacts.

     

Bottlenose dolphins share fish farm areas while maintaining sexual segregation: Investigating group memberships through spatially and temporally explicit parameters

1. Group membership is a key attribute of animal societies and central to the study of social structure in several taxa. However, social structure analyses are sensitive to the way data are collected and associations defined.
2. In this study, a time–space method was used to investigate the social structure of common bottlenose dolphins Tursiops truncatus observed and photographed across 7 years in the semi-enclosed Gulf of Corinth, Greece. Instead of adopting traditional group definitions, individuals were considered as being members of the same group if photographed within a specific time and space window. This approach can be applied post hoc across studies and can offer advantages under challenging sampling conditions (e.g. when dealing with groups spread over vast areas or when group membership is otherwise hard to assess).
3. Dolphins were mostly found around coastal cage aquaculture facilities farming European sea bass Dicentrarchus labrax and gilthead seabream Sparus aurata.
4. Dolphins formed clusters largely or entirely composed of individuals of the same sex, suggestive of sex-based homophily. Habitat partitioning was not detected: there was substantial spatial overlap among dolphin clusters, with all individuals using a relatively small area in the northern portion of the Gulf, where most of the productive fish farms were located. Associations between females were stronger than those between males, and daughters tended to stay in the group of their mothers.
5. Sex-based social clustering may allow females and calves to limit interactions with potentially aggressive males, while individuals of both sexes benefit from prey concentrated around fish farms.
6. Adaptation to foraging around farms can result in trade-offs between the costs and benefits of nourishment and social interaction. This may have both positive or negative effects on the animals that should be considered in the context of ensuring their favourable conservation status.

     

Natural and anthropogenic drivers of foraging behaviour in bottlenose dolphins: Influence of shellfish aquaculture

1. In the coastal environment, marine mammals are exposed to one of the fastest growing food production sectors; namely, the shellfish farming industry. Identification of critical habitats, such as foraging grounds in highly human‐impacted areas, is essential to species conservation. Therefore, understanding the variables that influence a species' foraging behaviour is important for their conservation, especially for long‐lived mammals such as cetaceans.
2. The aims of this study were (a) to identify and quantify the environmental and anthropogenic drivers of wild bottlenose dolphin (Tursiops truncatus) foraging behaviour, and (b) to investigate whether the shellfish farming industry influences the behaviour of this species.
3. Behavioural observations were conducted along the north‐western coast of Spain, an area affected by intensive human activities, particularly the shellfish aquaculture industry.
4. A multi‐modelling approach highlighted the importance of shellfish farm areas as a foraging ground for bottlenose dolphins. Dolphins were predicted to be more likely found foraging inside shellfish farm areas than outside (57% vs. 43%).
5. Variability in bottlenose dolphin behaviour is likely a result of the interactions of environmental and anthropogenic drivers with prey availability and the physiological needs of the dolphins. Although shellfish farm areas provide high prey density for dolphins, they can also pose threats in a number of ways (i.e. collisions with vessels, entanglement with ropes, habitat loss, noise and water pollution).
6. From a conservation perspective, aquaculture management should consider the presence of dolphins foraging and minimize the associated risks that this industry may pose to these coastal cetaceans.

     

Artisanal fishing,dolphins, and interactive pinger: A study from a passive acoustic perspective

1. Dolphins interact with many types of fishing gear, causing damage to fishing activities and in some cases facing harm and becoming entangled as bycatch.
2. In this study, the behaviour of bottlenose dolphins during their interaction with set nets, equipped with and without interactive pingers, was investigated. Acoustic monitoring of the nets was conducted for a total of 56 hauls and 814.9 hr of recordings, from the 16 October to 13 November 2015, along the coast of Lampedusa island (Sicilian Channel, Italy, Mediterranean Sea).
3. The level of interaction between dolphins and the nets was evaluated considering the number of dolphin clicks grouped over time (single acoustic incursion on each net), the duration of every acoustic incursion, and the number of dolphin clicks per incursion. Moreover, the catch rate was measured as the number of fish per hour for each net.
4. Based on the recording time of dolphin clicks, the spatio-temporal development of the interaction with the nets located in different bays of the island was assessed.
5. The duration of the interaction between dolphins and nets significantly increased over the study period, with a concomitant reduction in catch rate. The interactive pinger showed efficacy in protecting the nets from dolphin depredation during the first period of 36 hauls and 11 fishing days (higher catch rates and lower incursion durations), whereas no differences were found in any interaction parameters between pinger and control nets in the second period (20 hauls and six fishing days).
6. Interactive pingers may be an effective, short-term (2–3 weeks) tool in deterring depredation by bottlenose dolphins in small-scale artisanal fisheries. Other mitigation approaches, such as gear modification, lessons learned through outreach, and passive acoustic monitoring of the nets, could improve the management of the interactions between fisheries and bottlenose dolphins.

     

Abundance,distribution and diet of the common dolphin,Delphinus delphis,in the northern Aegean Sea (Greece)

1. The abundance, distribution and diet of the short-beaked common dolphin were investigated as part of the first detailed study on cetacean populations in the North Aegean Sea. Since 2004, the area has been proposed by national and international entities as a marine protected area for common dolphins and other cetacean species owing to its high biodiversity.
2. Abundance and distribution were investigated between 2005 and 2013 through dedicated scientific marine transect surveys, covering 14,701 km, in sea conditions of Beaufort sea state 3 and below. The line-transect sampling method was used to estimate relative abundance, using Distance 6.0 software. Encounter rate for this species in the study area was estimated to be 0.24 groups/100 km (1.5 dolphins/100 km), with a mean group size of 6.88 (SE = 1.90).
3. Common dolphin sightings were analysed for correlations with eight environmental variables (distance from the coast, depth, slope, median salinity, gradient of salinity, median temperature, gradient of temperature and mean current) using generalized additive modelling. Common dolphin sightings were significantly correlated to depth, temperature and salinity.
4. Stomach-content analyses were performed on eight suitable samples from common dolphins stranded in the study area. The trophic level of the species was calculated, indicating that this species is a top predator.
5. This research provides the first estimates for abundance and distribution and the first diet analysis for this Mediterranean Endangered dolphin species in the study area based on a year-round long-term study.

     

Common bottlenose dolphin (Tursiops truncatus) abundance and distribution patterns in St Andrew Bay,Florida, USA

1. Common bottlenose dolphins (Tursiops truncatus) are found in temperate and tropical waters of the world across a wide range of habitats. Along Florida's north‐western coast, this species resides in the bays, sounds, and estuaries (BSE) and coastal (CST) waters of the northern Gulf of Mexico. The National Marine Fisheries Service has identified one CST (Northern Coastal Stock) and seven adjacent BSE dolphin stocks, including the St Andrew Bay BSE Stock.
2. Baseline data are critical to assess the impacts of ongoing and future anthropogenic stressors on these stocks. Currently, there is no comprehensive abundance estimate for the St Andrew Bay BSE Stock, and there are limited data on distribution patterns and site fidelity for this stock. In addition, little is known about the Northern Coastal Stock hypothesized to range from the Big Bend of Florida to the Mississippi River Delta, inclusive of the CST waters adjacent to St Andrew Bay.
3. The goals of this study were to conduct photographic‐identification surveys during 2015 and 2016 to determine abundance, distribution, and site fidelity of common bottlenose dolphins in the St Andrew Bay BSE Stock over four primary periods (July and October 2015, and April and October 2016).
4. St Andrew Bay BSE dolphin abundance was lowest in April 2016 (199, 95% confidence interval [CI] 173–246), followed by July 2015 (249, 95% CI 199–338), and highest in October 2015 (299, 95% CI 259–361) and October 2016 (315, 95% CI 274–378). Few individuals were sighted in both BSE and CST waters (N = 25/353; 7%), and this fact, taken in tandem with limited connections between the BSE and CST environments, suggests that there may be minimal overlap between the St Andrew Bay BSE and Northern Coastal Stocks.

     

Assessing common bottlenose dolphin (Tursiops truncatus) population structure in Mississippi Sound and coastal waters of the north central Gulf of Mexico

1. Population structure of highly mobile marine organisms can be complex and difficult to study, but it is important to understand how populations partition themselves within their environment for accurate assessment of both natural and anthropogenic impacts and successful management. The 2010 Deepwater Horizon oil spill negatively impacted common bottlenose dolphins (Tursiops truncatus) within Mississippi Sound and the surrounding north central Gulf of Mexico (GOMx); however, little was known about their underlying population structure in these waters. Thus, it was unclear how many demographically independent populations were affected by the spill.
2. Common bottlenose dolphin samples were collected throughout inshore waters of Mississippi Sound and coastal waters of the north-central GOMx. Mitochondrial DNA control region sequence data and 19 nuclear microsatellite loci were analysed to determine how many populations are present and characterize their range throughout these waters.
3. Bayesian clustering and migration analyses identified two genetically distinct and demographically independent populations: one predominantly inhabiting Mississippi Sound and adjacent coastal waters, and a second population extending generally from offshore of Mobile Bay, Alabama, east along the Florida Panhandle. Neither of these populations align with the currently delineated management stocks previously used to estimate impacts from the oil spill on common bottlenose dolphins in this portion of the GOMx.
4. These results suggest that revisions may be necessary so that management stocks accurately represent the demographically independent populations present in these waters. Furthermore, better comprehension of underlying population structure will enhance impact assessments on common bottlenose dolphins and provide more appropriate baseline data to support future restoration and conservation objectives.

     

Abundance estimates of three cetacean species in the coastal waters of Matang,Perak, Peninsular Malaysia

1. The paucity of baseline data on coastal cetaceans due to a lack of research in developing countries frequently precludes assessment of their status and informed management actions for conservation.
2. This study provides the first abundance estimates of Indo-Pacific humpback dolphins, Irrawaddy dolphins, and Indo-Pacific finless porpoises in the coastal waters of Matang, Peninsular Malaysia.
3. Boat-based surveys covering 1,152 km² of coastal waters with 4,108 km of survey effort were conducted between 2013 and 2016 to collect data for line transect analysis of Irrawaddy dolphins and finless porpoises. Photo-identification data of humpback dolphins were concurrently collected for mark–recapture analysis.
4. Estimates of abundance from four sampling strata totalled 763 Irrawaddy dolphins (CV = 13%, 95% confidence interval (CI) [588, 990]) and 600 Indo-Pacific finless porpoises (CV = 27%, 95% CI [354, 1,016]).
5. The annual abundance estimates of humpback dolphins ranged between 171 (95% CI [148, 208]) in 2014–2015 and 81 (95% CI [67, 98]) in 2015–2016, likely due to the presence of offshore individuals that moved in and out of the study area. The estuarine strata were inhabited by 68 (95% CI [63, 73]) inshore humpback dolphins in 2013–2014 to 87 (95% CI [78, 97]) dolphins in 2014–2015.
6. As an International Union for Conservation of Nature important marine mammal area, the productive coastal waters of Matang are shown to support a high density of small coastal cetaceans, and the results serve as an important baseline for future studies to identify population trends for conservation management plans.

     

Common dolphins,common in neritic waters off southern Israel,demonstrate uncommon dietary habits

1. During the last decade, the common dolphin (Delphinus delphis) has become the second most sighted species in Israeli coastal waters, after the common bottlenose dolphin. Documentation mostly relies on opportunistic, photo and/or video-backed second-party reports, delimited within a 10 km near-shore strip.
2. Sightings occur year round, are confined to the southern part of the Israeli coast and typically comprise relatively large groups (mean ± SD: 21.5 ± 13.3), often with young calves.
3. Strandings are relatively scarce, typically one per year, and have so far yielded five upper digestive tract contents for diet analysis.
4. Cephalopods comprised 1.2% of the estimated number of prey items in the combined content. Surprisingly, by far the most abundant and prevalent prey item found (57% of pooled prey items; present and dominant in four out of five tracts) was the Balearic eel (Ariosoma balearicum), a sand burrower which is also a major dietary component of the common bottlenose dolphins.
5. Bottlenose dolphins in Israel are known to forage in association with bottom trawlers, leading to the notion that common dolphins also make use of this foraging mode. Indeed, in addition to their association with purse seiners, they have been documented accompanying bottom trawlers, by both day and night. The slender Balearic eels are frequently found protruding from the net's eyes, presumably making easy prey for both dolphin species.
6. Information gaps on common dolphins include range extension to the south/south-west, abundance estimation and genetic flow/isolation. Even so, its unusual diet and the fact that the closest known populations to the north/north-west are from the Aegean Sea, were major considerations in the recent designation of the ‘Coastal Shelf Waters of the South-east Levantine Sea’ as a Mediterranean Important Marine Mammal Area.

     

Site‐fidelity and movement patterns of bottlenose dolphins (Tursiops truncatus) in central Argentina: essential information for effective conservation

1. The effectiveness of conservation measures such as marine protected areas (MPAs) for the conservation of cetaceans is determined by how well their home range or critical habitat is covered. The present study seeks to provide information on the site‐fidelity and movement patterns of individual bottlenose dolphins (Tursiops truncatus) in central Argentina.
2. Between 2007 and 2013, photo‐identification data of bottlenose dolphins were collected in four study sites some 90–200 km apart from each other along the central Argentinean coast.
3. Results show long‐term site‐fidelity (over 5 years) in one of the study areas. Re‐sighting rates further suggest the existence of different sub‐populations of bottlenose dolphins, but also confirm some connectivity (with movements over 200–290 km) and thus potential for gene flow within the region.
4. Considering the population declines of bottlenose dolphins in Argentina, information on site‐fidelity and movement patterns will be of value to improve the effectiveness of existing MPAs for the conservation of the species as well as prioritizing areas for increased research.

Copyright © 2016 John Wiley & Sons, Ltd.     

Decreasing population trend in coastal bottlenose dolphin (Tursiops truncatus) from the Gulf of Guayaquil,Ecuador

1. The population status of the coastal bottlenose dolphin (Tursiops truncatus) inhabiting the inner estuary of the Gulf of Guayaquil, Ecuador (3°S, 81°W) was assessed. Evaluated aspects included social organization, abundance and spatial distribution.
2. Surveys focused on the western part of the estuary (Posorja and Estero Salado) but other areas in the central and eastern inner estuary were also surveyed.
3. Effort included 68 trips, 5001 km of survey and 288.8 h at sea. Between 735 and 793 dolphins in 92 groups were recorded during the study.
4. Dolphins are not evenly distributed but concentrated their activities in the mouths of large channels.
5. A cluster analyses indicated that dolphins organize in partially discrete subunits referred to as communities.
6. Abundance estimations were obtained using mark–recapture modelling for two communities: Posorja and Estero Salado (43 dolphins, 95% CI 37–49 and 65 dolphins, 95% CI 52–82 respectively).
7. Four demographic parameters: average size of communities, average group size, average encounter rate and average density were compared with information obtained during the 1990s. In all cases the current values were between 39 and 54% lower; in the last three cases the difference was statistically significant.
8. Possible causes of this apparent decline include bycatch, ship strikes, pollution and habitat degradation; however, none of these have been assessed in depth. Most probably, different stressors are affecting dolphin communities to different extents.
9. A comprehensive assessment of the whole population inside the gulf is needed. Identifying major threats is a priority to define concrete actions to prevent further population decline.

     

Occurrence of common dolphins (Delphinus delphis) in the Gulf of Trieste and the northern Adriatic Sea

1. The Mediterranean common dolphin (Delphinus delphis), considered to have been very common in the past, had undergone a dramatic decline across most of the basin by the end of 1970s. In the northern Adriatic Sea, one of the regions with most available historical information, the common dolphin is thought to have been the most common and abundant cetacean throughout most of the 20th century. However, by the end of 1970s, it had virtually disappeared from the region and is now considered generally absent from the entire Adriatic Sea.
2. This contribution summarizes the occurrence of common dolphins in the Gulf of Trieste and provides a brief review of published records in other parts of the Adriatic Sea.
3. Systematic boat surveys in the wider area of the Gulf of Trieste between 2002 and 2019 confirmed that the common bottlenose dolphin (Tursiops truncatus) is the only regularly occurring cetacean species in this area. Despite this, several records of common dolphins were documented in the Gulf of Trieste between 2009 and 2012, through sightings of live animals or recovery of dead stranded animals.
4. Dorsal fin markings allowed the photo-identification of some of these, suggesting that at least four different live individuals (three adults and one calf) occurred here in recent times. Most cases involved single adult individuals, but one included a mother-calf pair that was temporarily resident in a port for several months, a behaviour atypical for this species. Photo-identification showed that the presumed mother had previously been sighted in the Ionian Sea in Greece, over 1,000 km from the Gulf of Trieste, making this the longest documented movement for this species worldwide.
5. At present, the common dolphin continues to be rare in the region.

     

Occurrence and present status of coastal dolphins (Delphinus delphis and Tursiops truncatus) in the eastern Ionian Sea

• 1. Boat surveys aimed at studying short‐beaked common dolphins and common bottlenose dolphins in eastern Ionian Sea coastal waters were conducted between 1993 and 2003. During 835 survey days, 24 771 km of total effort was distributed within an area of 480 km², resulting in 428 common dolphin and 235 bottlenose dolphin sightings.
• 2. Individual photo‐identification was performed extensively throughout this study, making it possible to monitor the number of animals seen in the study area each year and their long‐term residency patterns.
• 3. Common dolphins declined across the study period, from 2.18 encounters/100 km in 1997 to 0.40 encounters/100 km in 2003. In contrast, there was a relatively stable presence of bottlenose dolphins, some individuals showing high levels of site fidelity and others using the area only occasionally.
• 4. The local decline of common dolphins and the low density of bottlenose dolphins appeared to reflect the general status of these cetacean species in the wider Mediterranean region, where common dolphins were classified as endangered in the IUCN Red List in 2003.
• 5. Based on the available evidence, we infer that the present unfavourable status of common dolphins in eastern Ionian Sea coastal waters is largely a consequence of prey depletion.

Copyright © 2005 John Wiley & Sons, Ltd.     

Dolphins in a bottle: abundance,residency patterns and conservation of bottlenose dolphins Tursiops truncatus in the semi‐closed eutrophic Amvrakikos Gulf,Greece

• 1. Boat surveys were conducted between 2002 and 2005 to study bottlenose dolphins living in the 400 km² Amvrakikos Gulf, western Greece. During 116 survey days, 4705 km of total effort resulted in the individual photo‐identification of 106 animals, through long‐term natural markings on their dorsal fins.
• 2. Mark–recapture analyses based on the M_th model provided estimates of 82 marked individuals in 2003 (95% CI=80–91), 92 in 2004 (95% CI=86–108) and 98 in 2005 (95% CI=94–110). To include the unmarked portion of the population, the proportion of unmarked individuals was computed based on the number of photographs of marked and unmarked dorsal fins. The mean proportion of unmarked animals in the population was 0.338 (95% CI=0.288–0.389). By adding this to the estimate for marked animals in 2005, considered as the most robust, a total population estimate of 148 individuals (95% CI=132–180) was obtained.
• 3. Dolphin encounter rates in 2003–2005 did not show significant variations, and averaged 7.2 groups per 100 km or 72.5 individuals per 100 km. Encounter rates within the Gulf were about one order of magnitude greater than those found for bottlenose dolphins in nearby eastern Ionian Sea coastal waters.
• 4. Mean dolphin density in the Gulf was 0.37 animals km^?2. This relatively high density, together with high levels of site fidelity shown by most individuals, was thought to be related primarily to prey availability, particularly of epipelagic schooling fish.
• 5. The importance of the semi‐closed Amvrakikos Gulf for bottlenose dolphins and other threatened species encourages the adoption of measures aimed to conserve its valuable ecosystems and raise the naturalistic profile of the area, while promoting environment‐conscious development. Meaningful action includes restoring natural hydrology (e.g. freshwater input from rivers), curtailing pollution from various sources, responsible fisheries and aquaculture management, and control of illegal fishing. Interactions between dolphins and fisheries also deserve careful quantitative investigation.

Copyright © 2007 John Wiley & Sons, Ltd.     

Demography of southern Australian bottlenose dolphins living in a protected inverse estuary

1. Assessments of demographic parameters are essential to understand the dynamics of wild populations, and for their efficient conservation and management. Here, sex‐specific abundance, apparent survival and temporary emigration of southern Australian bottlenose dolphins (Tursiops cf. australis ) in Coffin Bay (CB), South Australia, is investigated.
2. Results are based on capture–recapture modelling of photo‐identification data and molecular analyses of biopsy samples collected during boat‐based surveys between September 2013 and October 2015 in the inner and outer areas of CB.
3. The total super‐population of dolphins (including calves) using the entire study area (263 km²) was estimated with POPAN models at 306 (95% CI: 291–323), which included 71 (68–73) marked females and 57 (55–60) marked males.
4. Seasonal estimates of abundance for the inner area of CB (123 km²) obtained with Pollock's Closed Robust Design models remained relatively constant over the two years (marked females: 52–60, marked males: 46–52, and total: 193–209).
5. The high density of dolphins inhabiting the inner area (seasonal range: 1.57–1.70 individuals km^?2), high apparent survival rates estimated for both sexes (females: 0.99; 95% CI: 0.96–1.0; males: 0.95; 0.82–0.99), and low temporary emigration rates (0.02; 95% CI: 0.01–0.11) indicate that the inner area of CB offers highly favourable habitat for these dolphins.
6. High biological productivity and low predation risk may promote these demographic patterns in the inner area of CB.
7. This study provides a robust baseline of sex‐specific population demographics of southern Australian bottlenose dolphins with important implications for future research and their management and conservation in South Australia.

     

Responses of bottlenose dolphins (Tursiops spp.) to small drones

1. Recent advances in aerial drones offer new insights into the biology, ecology and behaviour of marine wildlife found on or near the ocean’s surface. While opening up new opportunities for enhanced wildlife monitoring, the impacts of drone sampling and how it might influence interpretations of animal behaviour are only just beginning to be understood.
2. The capacity of drones to record bottlenose dolphin (Tursiops spp.) behaviour was investigated, along with how the presence of a small drone at varying altitudes influences dolphin behaviour. Over 3 years and eight locations, 361 drone flights were completed between altitudes of 5 and 60 m above the ocean.
3. Analyses showed that dolphins were increasingly likely to change behaviour with decreasing drone altitude. A positive correlation was also found between time spent hovering above a group of dolphins and the probability of recording a behavioural response. Dolphin group size also influenced the frequency of an observed behavioural change, displaying a positive correlation between behaviour change and group size.
4. Overall, although drones have the potential to impact coastal dolphins when flown at low altitudes, they represent a useful tool for collecting ecological information on coastal dolphins owing to their convenience, low cost and capacity to observe behaviours underwater. To maximize benefits and minimize impacts, this study suggests that drones should be flown 30 m above coastal bottlenose dolphins.

     

Fine‐scale population structure and connectivity of bottlenose dolphins,Tursiops truncatus,in European waters and implications for conservation

1. Protecting species often involves the designation of protected areas, wherein suitable management strategies are applied either at the taxon or ecosystem level. Special Areas of Conservation (SACs) have been created in European waters under the Habitats Directive to protect bottlenose dolphins, Tursiops truncatus, which forms two ecotypes, pelagic and coastal.
2. The SACs have been designated in coastal waters based on photo‐identification studies that have indicated that bottlenose dolphins have relatively high site fidelity. However, individuals can carry out long‐distance movements, which suggests potential for demographic connectivity between the SACs as well as with other areas.
3. Connectivity can be studied using genetic markers. Previous studies on the species in this area used different sets of genetic markers and therefore inference on the fine‐scale population structure and demographic connectivity has not yet been made at a large scale. A common set of microsatellite markers was used in this study to provide the first comprehensive estimate of genetic structure of bottlenose dolphins in European Atlantic waters.
4. As in previous studies, a high level of genetic differentiation was found between coastal and pelagic populations. Genetic structure was defined at an unprecedented fine‐scale level for coastal dolphins, leading to identification of five distinct coastal populations inhabiting the following areas: Shannon estuary, west coast of Ireland, English Channel, coastal Galicia, east coast of Scotland and Wales/west Scotland. Demographic connectivity was very low among most populations with <10% migration rate, suggesting no demographic coupling among them. Each local population should therefore be monitored separately.
5. The results of this study have the potential to be used to identify management units for bottlenose dolphins in this region and thus offer a significant contribution to the conservation of the species in European Atlantic waters. Future studies should prioritize obtaining biopsies from free‐living dolphins from areas where only samples from stranded animals were available, i.e. Wales, west Scotland and Galicia, in order to reduce uncertainty caused by sample origin doubt, as well as from areas not included in this study (e.g. Iroise Sea, France). Furthermore, future management strategies should include monitoring local population dynamics and could also consider other options, such as population viability analysis or the incorporation of genetic data with ecological data (e.g. stable isotope analysis) in the designation of management units.

     

Dolphin population specialized in foraging with artisanal fishers requires zero-bycatch management to persist

1. The small population paradigm assumes that populations with low numbers of individuals intrinsically have a high probability of extinction. The small population of Lahille’s bottlenose dolphins Tursiops truncatus gephyreus that specializes in foraging with artisanal fishers in Laguna, southern Brazil, faces human pressures including bycatch in fishing gear. The viability of this population was modelled over 30 and 100 years under different levels of bycatch, including the current scenario of two bycatches every year, two scenarios with higher incidence of bycatches and three management scenarios. The sensitivity of predicted growth rates to fixed-proportion and observed-variation changes in life history parameters was explored.
2. The current scenario predicted a declining population (r = −0.014; λ = 0.986) with a high probability of extinction in the long term (PE = 0.71). A small increase in bycatches would result in a marked increase in the probability of extinction. Management scenarios seem promising, but only the zero-bycatch management scenario would make the difference between a declining and an increasing population.
3. As expected for slow-growing species, population growth rate was most sensitive to proportional changes in adult female and juvenile survival. However, considering observed variation in vital rates, population dynamics were most influenced by variation in reproductive rates.
4. To determine the highest priority for management action, another simulation was made of how additional threat scenarios of recognized human activities (i.e. bycatch influencing adult survival and increased underwater noise or pollution influencing calf survival) would affect population dynamics. Population growth rate was very sensitive to changes in adult bycatch (especially females), as expected, and only subtly sensitive to a reduction in calf survival.
5. The current level of bycatch is unsustainable. Bycatch needs to be eliminated to maximize the probability of long-term persistence of this dolphin population. However, this population’s persistence could be threatened by natural variation in reproductive rates.