Ketos Ecology

Kingsbridge, United Kingdom

Ketos Ecology

Kingsbridge, United Kingdom
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Jefferson T.A.,Clymene Enterprises | Weir C.R.,Ketos Ecology | Anderson R.C.,Manta Marine Pvt Ltd | Ballance L.T.,Southwest Fisheries Science Center | And 2 more authors.
Mammal Review | Year: 2014

The global range of Risso's dolphin Grampus griseus is not well known, and there has been confusion in the literature as to whether the species has a broad, circumglobal range or only occurs along continental margins. To clarify the species' distribution and habitat preferences, we compiled and reviewed all available (published and unpublished) records of sightings and captures of this species for the past 62 years (1950-2012, n=8068 records). Stranding records were not included. The results showed that the species has a range that extends across ocean basins and spans between at least 64°N and 46°S, and is apparently absent from high-latitude polar waters. Although Risso's dolphins occur in all habitats from coastal to oceanic, they show a strong range-wide preference for mid-temperate waters of the continental shelf and slope between 30° and 45° latitude. Although a number of misconceptions about the distributional ecology of Risso's dolphin have existed, this analysis showed that it is a widespread species. It strongly favours temperate waters and prefers continental shelf and slope waters to oceanic depths. These habitat preferences appear to hold throughout much or all of the species' range. © 2013 The Mammal Society and John Wiley & Sons Ltd.

Nelms S.E.,University of Exeter | Piniak W.E.D.,Gettysburg College | Weir C.R.,Ketos Ecology | Godley B.J.,University of Exeter
Biological Conservation | Year: 2016

Seismic surveys are widely used in marine geophysical oil and gas exploration, employing airguns to produce sound-waves capable of penetrating the sea floor. In recent years, concerns have been raised over the biological impacts of this activity, particularly for marine mammals. While exploration occurs in the waters of at least fifty countries where marine turtles are present, the degree of threat posed by seismic surveys is almost entirely unknown. To investigate this issue, a mixed-methods approach involving a systematic review, policy comparison and stakeholder analysis was employed and recommendations for future research were identified. This study found that turtles have been largely neglected both in terms of research and their inclusion in mitigation policies. Few studies have investigated the potential for seismic surveys to cause behavioural changes or physical damage, indicating a crucial knowledge gap. Possible ramifications for turtles include exclusion from critical habitats, damage to hearing and entanglement in seismic survey equipment. Despite this, the policy comparison revealed that only three countries worldwide currently include turtles in their seismic mitigation guidelines and very few of the measures they specify are based on scientific evidence or proven effectiveness. Opinions obtained from stakeholder groups further highlight the urgent need for directed, in-depth empirical research to better inform and develop appropriate mitigation strategies. As seismic surveying is becoming increasingly widespread and frequent, it is important and timely that we evaluate the extent to which marine turtles, a taxon of global conservation concern, may be affected. © 2015 The Authors. Published by Elsevier Ltd.

Zwart S.J.,Africa Rice Center | Weir C.R.,Ketos Ecology | Weir C.R.,University of Aberdeen
Marine Biodiversity Records | Year: 2014

A sighting of four Atlantic humpback dolphins (Sousa teuszii) was recorded and photographed close to the Benin coast on 3 November 2013. This is the first record of the species for Benin, and also represents the first verified record within a 3,065Â km stretch of coast extending from Sierra Leone to Nigeria (encompassing the entire northern coast of the Gulf of Guinea). The sighting supports the possibility that some other potential range states may have remained unconfirmed to date due to a paucity of field research in suitable nearshore habitat rather than an absence of the species. Copyright © Marine Biological Association of the United Kingdom 2014.

Weir C.R.,Ketos Ecology | Weir C.R.,University of Aberdeen
Mammal Review | Year: 2010

The cetacean fauna of the west coast of Africa is poorly described. Therefore, literature on the occurrence of cetacean species in the waters of 13 potential West African range states from the Gulf of Guinea to Angola was reviewed, including sighting, stranding, capture, bycatch and whaling records. At least 28 species of cetacean were documented in the study region, comprising seven baleen whale species and 21 species of toothed whale (including at least 17 delphinid species). Cetaceans could be broadly split into seven ecological categories, based on their distribution. A warm temperate/tropical deep-water cetacean community dominated the study area. Cooler water from the Benguela Current influenced southern Angola (≤16°S latitude) and at least three cetacean species occurred predominantly in this region. Only three or fewer species were confirmed in the waters of Togo, Nigeria, Cameroon and the Democratic Republic of Congo. Seventeen or more species were documented in Ghana, Gabon and Angola, where dedicated cetacean research projects have been initiated in recent years. Angola had the most diverse documented cetacean community: 28 confirmed species. The humpback whale Megaptera novaeangliae was the most widely recorded species, and was documented in 11 (85%) countries. Sperm whales Physeter macrocephalus, Bryde's whales Balaenoptera cf. brydei, bottlenose dolphins Tursiops truncatus and Atlantic spotted dolphins Stenella frontalis were recorded in over half of the countries. © 2010 The Author. Journal compilation © 2010 Mammal Society.

Weir C.R.,Ketos Ecology | Weir C.R.,University of Aberdeen
Bioacoustics | Year: 2010

The Atlantic humpback dolphin Sousa teuszii is endemic to the west coast of Africa and is poorly studied. During January 2008, 2.7 hr of acoustic recordings were made during 11 S. teuszii encounters in the Namibe province of Angola. Echolocation click trains were audible in most recordings. A total of 298 individual dolphin whistles were recorded, of which 86 were of sufficient signal to noise ratio for the measurement of 10 fundamental frequency variables. Sousa teuszii whistles occurred in the 2.5 to 23.4 kHz fundamental frequency range and were relatively simple in structure, with 85% having a single inflection point. The fundamental frequency was relatively low, with mean minimum and maximum frequencies of 4.8 and 8.2 kHz respectively. Harmonics occurred in 92% of whistles, sometimes extending beyond the 44 kHz recording range. The most frequently recorded contour categories were convex and concave, and very few whistles exhibited complex modulation. The whistles produced by S. teuszii are broadly comparable with those published for the Indo-Pacific humpback dolphin S. chinensis. Future studies should consider context-specific use of whistle types, and should include comparisons with S. teuszii groups in other geographic locations to ensure the full species' whistle repertoire is adequately characterised. © 2010 AB Academic Publishers.

Weir C.R.,Ketos Ecology | Weir C.R.,University of Aberdeen
African Journal of Marine Science | Year: 2011

The species richness, spatial distribution, seasonality and interspecific associations of cetaceans in tropical oceanic waters between the Gulf of Guinea and Angola were examined using 5 905.3 h of dedicated survey effort collected from 13 platforms of opportunity (geophysical vessels) between 2004 and 2009, and from incidental records. Most effort (87.8%) was recorded in waters >1 000 m deep. A total of 1 814 on-effort and 1 496 incidental sightings were recorded, comprising 22 species. Physeter macrocephalus and Megaptera novaeangliae were the most frequently sighted cetacean species, with Globicephala macrorhynchus and Stenella frontalis the most frequently sighted delphinids. Five species occurred in both neritic and oceanic waters, while the remainder had exclusively oceanic distributions. The occurrence of P. macrocephalus and M. novaeangliae differed significantly according to depth category. Most species occurred year-round; however, M. novaeangliae exhibited a strong, significant winter and spring occurrence. There were 65 interspecific groups recorded, involving at least 12 species. Mixed schools of G. macrorhynchus and Tursiops truncatus accounted for 55.4% of recorded associations. This extensive year-round dataset adds considerably to the understanding of cetacean distribution in the eastern tropical Atlantic and provides baseline information on which to base cetacean conservation and management in this poorly studied region. © NISC (Pty) Ltd.

Weir C.R.,Ketos Ecology | Weir C.R.,University of Aberdeen
African Journal of Marine Science | Year: 2015

Ecological data for the Atlantic humpback dolphin Sousa teuszii are scant. Six on-effort Sousa teuszii sightings were recorded during 817.6 km of boat-based effort in the Río Nuñez region of Guinea during October and November 2013. Two incidental sightings were also reported. Groups comprised 1–25 animals. Photo-identification produced a minimum population estimate of 47 animals. Most sightings (n = 5) were located close (<1 km) to shore along a 5.7 km stretch of coast on the west side of Île de Taïdi, primarily over shallow, sand–mud habitat. Two very distinctive individuals were present in all four Taïdi photo-identification encounters, suggesting high site fidelity and stable associations. Two sightings occurred in the outer Río Nuñez Estuary much farther from the coast (5–12 km) but in relatively shallow water (≤15 m) over sand–mud sediment. Focal follows (n = 5: 0.2–3.8 h duration) produced 9.02 h of behavioural data. Travel (51%), foraging (39%) and feeding (9.2%) dominated, with Taïdi dolphins spending more time foraging and feeding than the outer estuary groups. Three individuals had linear-severed dorsal fins consistent with injuries from fishing line. Some management implications of variation in habitat, site fidelity and movements of Sousa teuszii groups are discussed. © 2015 NISC (Pty) Ltd.

Weir C.R.,Ketos Ecology | Collins T.,Wildlife Conservation Society | Carvalho I.,University of Algarve | Rosenbaum H.C.,Wildlife Conservation Society
Journal of the Marine Biological Association of the United Kingdom | Year: 2010

Killer whales Orcinus orca are considered to be relatively uncommon in tropical waters. Few sightings have been reported from the west coast of Africa due to a paucity of survey coverage. We present data on 32 killer sightings from tropical waters off Angola (N = 18), Gabon (N = 7), São Tomé (N = 6) and Cameroon (N = 1), comprising a combination of dedicated survey sightings (N = 21) and reliable anecdotal records (n = 11). Killer whales were reported from coastal waters, the shelf edge and deep, oceanic areas. Sightings indicate a probable year-round occurrence of killer whales within the region. Mean group size was 5.6 animals. There was no difference in group size between sightings in waters >200 m deep and those on the continental shelf. No photo-identification matches were found between Angola, Gabon and São Tomé. Re-sightings of two individuals occurred annually in São Tomé during 2002-2004. Killer whales had external appearance consistent with the Type A nominate species form. Antagonistic encounters were recorded between killer whales and humpback whales Megaptera novaeangliae off Angola, Gabon and Cameroon, and with sperm whales Physeter macrocephalus off Angola. Predation on ocean sunfish Mola mola was recorded in São Tomé, and possible predation on sharks was recorded twice in Gabon.

Weir C.R.,Ketos Ecology | Collins T.,Wildlife Conservation Society
Advances in Marine Biology | Year: 2015

Understanding of the distributional ecology of the Atlantic humpback dolphin (Sousa teuszii) has been hampered by a lack of systematic and consistent sampling effort. The only comprehensive species distribution review was published in 2004; since then a considerable amount of novel information has emerged. We compiled 853 sighting, capture and specimen records of the species, and produced global and regional distribution maps. Of the 830 records where year was available, 63.1% dated from ≥. 2005 and confirm a contemporary occurrence in six marine ecoregions and 11 countries: Western Sahara, Mauritania, Senegal, Gambia, Guinea-Bissau, Guinea, Benin, Cameroon, Gabon, Congo Republic and Angola. Additionally, Togo is a recently confirmed range state. Group sizes ranged from 1 to 45 animals, with small groups of 1 to 10 animals comprising 65% of the sightings. Similarities were noted in the regions inhabited by Atlantic humpback dolphins across their range, particularly an occurrence in relatively shallow (predominantly ≤ 20 m) depths, in warm waters (average SSTs of 15.8-31.8 °C) and in dynamic habitat strongly influenced by tidal patterns. These conditions occur in various habitats occupied by the species, including estuarine systems, open coasts, archipelagos, tidal mud-flats and sheltered bays. Sightings were recorded at distances of 13. m to 12.8. km (mean of 573 m) from land, indicating that the species occurs several kilometres from shore when suitable shallow habitat is present. The Atlantic humpback dolphin may be a 'nearshore' species based on oceanographic definitions incorporating water depth, wave action and sedimentation rather than on spatial distance from the coast. © 2015 Elsevier Ltd.

During October and November 2015, the first systematic survey of Sousa teuszii was carried out in the Saloum Delta (Senegal, West Africa), comprising 1 617.5 km of boat-based survey coverage. Thirty sightings were recorded in the Saloum and Diomboss rivers, and along the southern coastline. Dolphins were also observed entering the Bandiala and Djinack channels, and travelling across the border into Gambia. The initial sighting locations were 0.043–1.192 km from shore, and tracked dolphins did not move more than 2.082 km from shore. Groups comprised 1–29 animals (mean 9.3 animals), and at least three neonate calves were observed during November. The overall relative abundance was 0.018 sight. km−1 and 0.175 ind. km−1. Sightings were concentrated in the Diomboss where relative abundance reached 0.037 sight. km−1 and 0.331 ind. km−1. Non-intensive photo-identification produced a minimum population size of 103 animals, the highest recorded for S. teuszii anywhere in its range. Photo-identification also confirmed a movement of individuals between different parts of the Saloum Delta. Combined travel–forage dominated the behaviour. Dolphins were photographed capturing mullet (Mugil sp.) on three occasions. The distribution, population size and movements of S. teuszii are discussed in relation to management. © 2016 NISC (Pty) Ltd.

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