Risso's Dolphin Grampus Griseus Research Articles

First record of Risso's dolphin Grampus griseus (Cuvier, 1812) in Icelandic waters.

In July 2022, two Risso's dolphins were reported stranded in Hrútafjörður (N65° 09,503; W21° 05,529), a fjord in northern Iceland. These events represent the first confirmed observations and strandings of Risso's dolphins in Icelandic waters. Given the uniqueness of these events, a decision was made to conduct full necropsies on these individuals. This study reports findings from viral and parasitological investigations, morphological and fitness measurements, as well as stomach and intestine content analysis for each of the Risso's dolphin specimens. The results of the necropsies do not suggest any other cause of death than lack of food and exhaustion. A large plastic fragment in one individual's stomach supports these suggestions. The presence of those specimens in the middle of the subarctic ocean illustrates ongoing changes in spatial distribution expanding northward, impacting not only Risso's dolphins but more generally marine life and biodiversity.

ARIANNA: A novel deep learning-based system for fin contours analysis in individual recognition of dolphins

Starting from a digital image that represents the dolphin's body, distinctive features are extracted and used to find the identity of the unknown dolphin in a set of known individuals. This process is called photo identification, used by experts to monitor dolphins, providing relevant data to preserve the environment and its biodiversity. In this work, we show how semantic segmentation can be used to automatically extract a dolphin's fin contour starting from a cropped photo of the fin, and how this contour can be used for individual identification. A novel contour-based system, called ARIANNA, for the automated cetacean photo identification was designed, developed and tested. The novelty of this system is the adoption of two original modules. The first one, which takes as input a new cropped fin image of unknown dolphin, is devoted to the extraction of a mask that depicts the outline of the unknown fin; the core of this module is a trained neural network, specialized in semantic segmentation of images. The second module is designed to compare the outline of the unknown fin with the outlines of all known dolphins, collected in a referring catalogue, returning a ranked list of the best matches where to search the dolphin identity. The experiments were conducted on images collected between 2013 and 2020 in the Northern Ionian Sea (Central-eastern Mediterranean Sea), which presented cropped fins of Risso's dolphin Grampus griseus, one of the least-known cetacean species on a global and Mediterranean scale. The results suggest that ARIANNA provides advances over the state-of-the-art methods, can efficiently assist researchers in the photo identification of dolphins and can be a starting point for further studies on the photo identification of different species based on semantic segmentation.

A Comparative Study of Mini-FLOTAC With Traditional Coprological Techniques in the Analysis of Cetacean Fecal Samples.

Free-ranging cetaceans are considered sentinels for the marine ecosystem's health. New and non-invasive methods have been set up for the collection of fecal samples from free-ranging big whales at sea, permitting to gain an excellent epidemiological picture of parasitic infections in wild populations. To select the best protocol to be used for copromicroscopic examination in cetaceans stool samples, we evaluated the sensitivity of two commonly used techniques, i.e., a sedimentation-floatation method and the Mini-FLOTAC through validation by helminth isolation from the digestive tract. For this aim, gastrointestinal content and fecal samples were collected during necropsy from 44 cetaceans, including bottlenose dolphins (Tursiops truncatus), striped dolphins (Stenella coeruleoalba), sperm whales (Physeter macrocephalus), Risso's dolphins (Grampus griseus), Cuvier's beaked whales (Ziphius cavirostris), pilot whale (Globicephala melas), and fin whales (Balaenoptera physalus). Helminths were recovered through washing and filtering of the gastrointestinal contents and morphologically identified. Copromicroscopic examinations were performed on formalin-preserved fecal samples, using a sodium nitrate, sodium thiosulphate, and sucrose solution (s.g. = 1.450) for both methods. Helminths belonging to 9 taxa (i.e., the trematodes Synthesium tursionis, Synthesium delamurei, Campula palliata, Braunina cordiformis, Pholeter gastrophilus, the nematode Anisakis sp., cestodes of the family Tetrabothriidae and the acanthocephalan Bolbosoma sp.) were isolated. Eggs referable to the same taxa, with the exception of cestodes, were found in copromicroscopic analyses. Sensitivity of the Mini-FLOTAC method appeared higher or equal for all taxa, proving superior to the sedimentation-flotation method for the detection of all except Anisakis sp. The concordance of the two tests indeed revealed a moderate to perfect agreement (kappa values 0.42–1). Not excluding the limitations inherent to the techniques themselves, explanations for false-negative results at copromicroscopy could be linked to parasite-related factors, including prepatent infections, low parasitic burdens, or intermittent egg shedding. Notwithstanding these limitations, this study evidenced that the Mini-FLOTAC protocol approximates more accurately the composition of the gastrointestinal helminthic community of cetaceans from copromicroscopic examination, providing at the same time a quantitative estimation.

Multiple‐model stock assessment frameworks for precautionary management and conservation on fishery‐targeted coastal dolphin populations off Japan

Abstract Stock assessment approaches are often oversimplified due to lack of biological knowledge and insufficient data. In spite of world‐wide attention, fishery‐targeted coastal dolphin species in Japan have lacked in‐depth quantitative stock assessments because of limited time series of population size and an absence of associated biological information. We consequently developed integrated population models that analysed multiple sources of data simultaneously with published biological information within a Bayesian framework. We estimate population status and trends for three main species targeted by fisheries, bottlenose dolphins Tursiops truncatus, Risso's dolphins Grampus griseu, and short‐finned pilot whales Globicephala macrorhynchus, using single‐species age‐aggregated and age‐structured population dynamics models. Models were fit to absolute abundance estimates from systematic line‐transect surveys, four series of abundance indices calculated from fisher's logbooks, and historical catch records. Published biological information was used to develop prior distributions for the biological parameters. We assessed the possible effects of ecological disturbance and competition using state‐space and multispecies models. The multispecies model was selected by the model selection both for the age‐aggregated and the age‐structured approaches. Single‐species assessments found that population size declined 4.2% (Risso's dolphin) to 8.0% (bottlenose dolphin) for three species since the late 1800s based on median posterior values, while the state‐space and multispecies models found that environmental disturbance and an interaction among species could have reduced population size more substantially. Policy implications. Simple single‐species models are often used to provide conservation and management advice for wild animals but, in this case, results from such models are overly optimistic because they overlook important ecological process. In contrast, current population status could be less favorable if environmental disturbance and interspecific competition actually control population dynamics. Even if that is not the case, considering ecological process in the model will provide more precautionary ways. Our approach of combining multiple modelling frameworks is applicable to many other management systems, and offers increased confidence in estimated status and trends over assessments that consider only a single model.

Ingestion of macroplastics by odontocetes of the Greek Seas, Eastern Mediterranean: Often deadly!

Plastic pollution is an omnipresent problem that threatens marine animals through ingestion and entanglement. Marine mammals are no exception to this rule but their interaction with plastic remains understudied in the Mediterranean Sea. Here we highlight this problem by analyzing the stomach contents of 34 individuals from seven odontocete species stranded in Greece. Macroplastic (>5 mm) was found in the stomachs of nine individuals from four species (harbour porpoise Phocoena phocoena, Risso's dolphin Grampus griseus, Cuvier's beaked whale Ziphius cavirostris and sperm whale Physeter macrocephalus) with the highest frequency of occurrence in sperm whales (60%). Gastric blockage from plastic was presumably lethal in three cases, with plastic bags being the most common finding (46%). Plastic ingestion is of particular conservation concern for the endangered Mediterranean sperm whales. A regular examination of stranded cetaceans with a standardised protocol is critical for allowing spatiotemporal comparisons within and across species.

Ecological and Biological Characteristics for the Risso's Dolphins (Grampus griseus) Off Taiwan, with Conservation Evaluations on Potential Anthropogenic Threats

Risso's dolphin (Grampus griseus) is one of the cetacean species commonly encountered off the eastern coast of Taiwan. The species appears to occur in Taiwanese waters year-round. Many biological and ecological characteristics, including group size, habitat preference, and ages at weaning and sexual maturity, are by-and-large in accord with earlier reports for populations in other geographic regions. Morphological assessments, dietary analyses, and genetic data altogether suggest the dolphins found in Taiwanese and Japanese waters are from the same population, which exhibits high genetic diversity and a sign of recent demographic expansion. The dolphin species is endorsed a “Rare and Valuable Species (Class II)” status and is protected by the Wildlife Conservation Act in Taiwan. However, it is still vulnerable to human activities, in terms of whale-watching tourism and coastal gill-net fisheries, with a growing concern on the level of heavy metal residues found in dolphin tissues. Current knowledge for the species is mostly derived from relatively limited information. Assessments on key biological and ecological features, e.g., population size, residency, social structure, and group composition, shall be prioritised for conservation initiatives.

Morbillivirus infection in Risso's dolphin Grampus griseus: a phylogenetic and pathological study of cases from the Canary Islands.

The earliest evidence of cetacean morbillivirus (CeMV) infection dates from 1982, when the dolphin morbillivirus strain (DMV) was identified in bottlenose dolphins Tursiops truncatus stranded in the mid-Atlantic region. Since then, CeMV has been detected globally in at least 26 species of mysticetes and odontocetes, causing widespread mortality and a wide range of pathological effects. In the Canary Islands, DMV and pilot whale morbillivirus have been detected in cetacean species, including short-finned pilot whales Globicephala macrorhynchus and bottlenose dolphins. Risso's dolphins Grampus griseus have been reported year-round in waters of the Canary Islands and are considered a resident species. No information is currently available on CeMV prevalence in this species in this ocean region. We searched for evidence of CeMV infection in 12 Risso's dolphins stranded in the Canary Islands from 2003 to 2015 by means of histopathology, PCR and immunohistochemistry. PCR revealed 2 CeMV-positive animals (16.6%). Phylogenetic analysis showed that the strains from the 2 positive specimens were phylogenetically quite distant, proving that more than 1 strain infects the Risso's dolphin population in this region. We also determined that the strain detected in one of the specimens mainly circulated in the northeastern Atlantic Ocean from 2007 to 2013.

Three Cases of Anomalously White Risso's DolphinsGrampus griseusin Japan

Three male anomalously white Risso's dolphins Grampus griseus were observed in the waters off Taiji, Wakayama, Japan. One (GG-1) was captured alive in 2007, and the other two (GG-2 and GG-3) were captured in 2014. The color pattern of GG-1 is approximately divided into two parts; the middle of the trunk and the lower part of the dorsal fin are white, whereas the anterior and caudal portions have dark pigmentations. GG-2 has an almost white body with some dark pigmentation in the head region, and GG-3 has a completely white body with some sparse dark flecks around the throat. All three dolphins have dark eyes similar to a normally pigmented Risso's dolphin; however, the oral mucosa of GG-2 and GG-3 and the mucosa in the blowhole of GG-3 are white to pinkish in color without any dark pigmentation. Furthermore, the mucosa in the blowhole of GG-2 is a mixture of white patches and dark pigmentation. These three dolphins are the first anomalously white Risso's dolphins to be kept in captivity; therefore they are valuable for understanding the cause of body color variations and the anomalous coloration effects in animals.

Cetacean stranding and diet analyses in the North Aegean Sea (Greece)

Cetacean stranding reports in the North Aegean Sea were recorded since 1998 from Strimonikos Gulf in Chalkidiki up to Alexandroupoli on the Turkish border and in a few northern Aegean islands. On site, the specimens were examined to identify species, gender, approximate age and, when possible, cause for stranding. A total of 26 filled stomachs of five cetacean species collected since 2002 were analysed: bottlenose dolphinsTursiops truncatus(N = 8), common dolphinsDelphinus delphis(N = 8), harbour porpoisesPhocoena phocoena(N = 5), striped dolphinsStenella coeruleoalba(N = 4) and Risso's dolphinsGrampus griseus(N = 1). From the analysed stomachs it was found that the bottlenose dolphins fed mainly on snake blennyOphidion barbatum(34%), bogueBoops boops(22%) and round sardinellaSardinella aurita(13%); common dolphins on round sardinella (17%), picarelsSpicaraspp. (10%) and Cocco's lantern fishLobianchia gemellaris(9%); harbour porpoises on Gobidae (four-spotted gobyDeltentosteus quadrimaculatus41% and black gobyGobius niger37%) and round sardinella (7%); striped dolphins on Myctophydae (Madeira lantern fishCeratoscopelus maderensis51%), and on Pfeffer's enople squidAbraliopsis morisii(10%) and bogue (8%); and Risso's dolphin exclusively on Teuthidae (31%), the umbrella squidHistioteuthis bonellii(30%) and the reverse jewel squidH. reversa(14%). The present work represents the first attempt to investigate the diet up to species level for several cetaceans in Greek waters and for harbour porpoises stranded in the Mediterranean Sea.

Fluorescent microbead-based immunoassay for anti-Erysipelothrix rhusiopathiae antibody detection in cetaceans.

A fluorescent microbead-based immunoassay (FMIA) for detection of anti-Erysipelothrix rhusiopathiae antibodies in pigs was adapted for use in cetaceans. The FMIA was validated and adjusted using serum samples from 10 vaccinated captive bottlenose dolphins Tursiops truncatus collected between 1 and 13 mo after immunization. The technique was then used to analyze specimens from 15 free-ranging cetaceans stranded alive on the Valencian Mediterranean coast between 2006 and 2014: 11 striped dolphins Stenella coeruleoalba, 3 Risso's dolphins Grampus griseus and 1 bottlenose dolphin Tursiops truncatus. One of these wild animals was confirmed to have died from E. rhusiopathiae septicemia, but no anti-E. rhusiopathiae antibodies were detected in its serum, pericardial fluid or milk samples. Another free-ranging individual, which lacked any signs or lesions that might be indicative of E. rhusiopathiae infection, showed high fluorescence intensity similar to that measured in captive dolphins at 6-13 mo after vaccination. These results suggest that this animal underwent an E. rhusiopathiae infection several months before stranding. The findings in the present study suggest that FMIA can be useful for detecting anti-E. rhusiopathiae antibodies in cetaceans, and its application to free-ranging animals is particularly interesting because of the great value of these specimens. Furthermore, the FMIA can be multiplexed to allow the determination of up to 100 analytes per sample in a single well, thereby reducing the cost, time and sample volume needed.

The Influence of Topographic and Dynamic Cyclic Variables on the Distribution of Small Cetaceans in a Shallow Coastal System

The influence of topographic and temporal variables on cetacean distribution at a fine-scale is still poorly understood. To study the spatial and temporal distribution of harbour porpoise Phocoena phocoena and the poorly known Risso’s dolphin Grampus griseus we carried out land-based observations from Bardsey Island (Wales, UK) in summer (2001–2007). Using Kernel analysis and Generalized Additive Models it was shown that porpoises and Risso’s appeared to be linked to topographic and dynamic cyclic variables with both species using different core areas (dolphins to the West and porpoises to the East off Bardsey). Depth, slope and aspect and a low variation in current speed (for Risso’s) were important in explaining the patchy distributions for both species. The prime temporal conditions in these shallow coastal systems were related to the tidal cycle (Low Water Slack and the flood phase), lunar cycle (a few days following the neap tidal phase), diel cycle (afternoons) and seasonal cycle (peaking in August) but differed between species on a temporary but predictable basis. The measure of tidal stratification was shown to be important. Coastal waters generally show a stronger stratification particularly during neap tides upon which the phytoplankton biomass at the surface rises reaching its maximum about 2–3 days after neap tide. It appeared that porpoises occurred in those areas where stratification is maximised and Risso’s preferred more mixed waters. This fine-scale study provided a temporal insight into spatial distribution of two species that single studies conducted over broader scales (tens or hundreds of kilometers) do not achieve. Understanding which topographic and cyclic variables drive the patchy distribution of porpoises and Risso’s in a Headland/Island system may form the initial basis for identifying potentially critical habitats for these species.

The cetaceans of Aruba, southern Caribbean

Aruba is one of the most densely populated islands in the Caribbean. However, very little is known about its cetaceans. In 2010 and 2011, a total of 19721 km (1686 h) boat-based surveys over nearshore transects resulted in 117 positively-identified sightings comprising eight species. New records are also added for one of three previously-documented species. Five additional species were documented from strandings or reports by others. This brings the total number of cetacean species identified in Aruban waters to 16, of which nine are authenticated here for the first time. Atlantic spotted dolphin (Stenella frontalis(N = 59) and bottlenose dolphin (Tursiops truncatus) (N = 33) were the most frequently observed species, with sightings of both year-round, followed by spinner dolphin (S. longirostris) and false killer whale (Pseudorca crassidens). Additional species recorded are pantropical spotted dolphin (S. attenuata), striped dolphin (S. coeruleoalba), common dolphin (Delphinus capensis), rough-toothed dolphin (Steno bredanensis), short-finned pilot whale (Globicephala macrorhynchus), killer whale (Orcinus orca), Risso's dolphin (Grampus griseus), humpback whale (Megaptera novaeangliae), Bryde's/Eden's whale (Balaenoptera brydei/edeni), sperm whale (Physeter macrocephalus) and an unidentified beaked whale (Mesoplodonsp.). All cetaceans were sighted within 22 km of the coast in relatively shallow waters. Sighting rate was low (0.69 cetacean sightings per 100 km). Sightings of calves and neonates indicate that Aruba may be a nursing or breeding area for some species. The presence of several species of cetaceans in Aruba's coastal waters year-round indicates that status and threat assessments are needed to protect them.

Insight into niche separation of Risso's dolphin (Grampus griseus) in the southwestern South Atlantic via δ13C and δ15N values

Fil: Riccialdelli, Luciana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

Marine megavertebrates of Cornwall and the Isles of Scilly: relative abundance and distribution

We document patterns of distribution and relative abundance of marine megavertebrate fauna around Cornwall and the Isles of Scilly from a combination of aerial and boat-based surveying. Between January 2006 and November 2007, 20 aerial surveys were undertaken, comprising over 40 hours of on-effort flying time. In April to October of these years, 27 effort-corrected ferry surveys were also conducted from a passenger ferry travelling between Cornwall and the Isles of Scilly. Opportunistic sightings were also logged by the crew members of the ferry and another vessel travelling regularly along the same route on 155 days. Ten megavertebrate species were sighted: basking sharksCetorhinus maximus, sunfishMola mola, common dolphinsDelphinus delphis, harbour porpoisePhocoena phocoena, grey sealsHalichoerus grypus, Risso's dolphinsGrampus griseus, bottlenose dolphinsTursiops truncatus, minke whalesBalaenoptera acutorostrata, long-finned pilot whalesGlobicephala melasand killer whaleOrcinus orca. During aerial surveys, 206 sighting events of seven species were made, compared with 145 sighting events of eight species during ferry surveys and 293 sighting events of 10 species from opportunistic ship-board data collection efforts. Seasonal and spatial patterns in species occurrence were evident. Basking sharks were the most commonly-sighted species in the region and were relatively abundant throughout the estimated 5 km-wide strip of coastal waters covered by the aerial surveys, during spring and summer. Ferry surveys and opportunistic vessel-based sightings data confirmed that the distribution of surface-feeding aggregations of this species was largely around the coasts. Despite the limited scope of this study, it has provided valuable baseline data, and possible insights into the marine biodiversity of the region.

Pulmonary fungal infection caused byNeoscytalidium dimidiatumin a Risso's dolphin (Grampus griseus)

Neoscytalidium dimidiatum was isolated from two 12-18 cm abscesses in the lung and the mediastinal lymph nodes of a stranded Risso's dolphin (Grampus griseus). Histopathologic examination of samples of these organs revealed the presence of hyphae and sclerotic body-like fungal elements. Photobacterium damselae subsp. damselae was recovered from the dolphin's organs which also were found to contain numerous Monorygma grimaldii cysts. No histopathological signs of morbillivirus infection were seen. To the best of our knowledge, this is the first report of N. dimidiatum infection in a sea mammal.

Risso’s and Pacific white-sided dolphin habitat modeling from passive acoustic monitoring

Habitat characterization allows prediction of dolphin distributions in response to oceanographic processes and can be used to understand and predict effects of anthropogenic disturbances. Many habitat models focus on contemporary dolphin occurrence and environmental predictor data, but time-lagged oceanographic data may increase a model's predictive power due to ecological successional processes. Using hourly occurrence of Risso's dolphin Grampus griseus clicks and 2 types of Pacific white-sided dolphin Lagenorhynchus obliquidens clicks in autonomous passive acoustic recordings, we investigate the importance of time-lagged predictor variables with general- ized additive models. These models relate dolphin acoustic activity from recordings at 6 sites in the Southern California Bight between August 2005 and December 2007 to oceanographic variables including sea surface temperature (SST), SST coefficient of variation (CV), sea surface chlorophyll concentration (chl), chl CV, upwelling indices, and solar and lunar temporal indices. The most consis- tently selected variables among the trial models evaluated during cross-validation were SST (100% of models) and SST CV (80%) for Risso's dolphin clicks; solar indices (100%) and SST and SST CV (60% each) for Pacific white-sided type A (PWS A) clicks; and SST CV (100%), solar indices (100%) and SST (80%) for Pacific white-sided type B (PWS B) clicks. Best predictive models for Risso's dolphins and PWS A clicks included time-lagged variables, suggesting the importance of ecological succession between abiotic variables and dolphin occurrence, while best models of PWS B clicks were for current conditions, suggesting association with prey-aggregating features such as fronts and eddies.

First mass stranding of Risso's dolphins ( Grampus griseus) in Peru and its destiny as food and bait

The first mass stranding of Risso's dolphins Grampus griseus on the Peruvian coast occurred on Pozo de Lizas Beach (17°42′30.3″S 71°18′48.7″W), port of Ilo, Department of Moquegua, southern Peru, between 7 and 8 June 2007. At least 14 Risso's dolphins were stranded along 1.5 km of beach. Just 7 of them could be sized and 8 sexed; this group was composed of 7 males and a single female plus a juvenile of undetermined sex. Mean standard body length of the males was 299.67 cm (SD: 9.91 cm, range: 292–317 cm) and the female measured 289 cm. The entire group, including four individuals found alive, was illegally butchered by the local people to use the meat as food, while other remains were used as bait in the pelagic long-line fishery. This record fills a distributional gap of about 1000 km in the known distribution of the species between central Peru and northern Chile. Additional education is required for improved conservation strategies in future cetacean strandings.

Partitioning of the Pelagos Sanctuary (north-western Mediterranean Sea) into hotspots and coldspots of cetacean distributions

This study used Monte Carlo methods to generate simulations that considered the effort distribution to determine the locations of significant aggregations of cetacean sightings inside the northern Pelagos Sanctuary (north-western Mediterranean Sea). For three years, monitoring has been conducted from five motor vessels covering about 30,050 km. The most frequently encountered species were the striped dolphinStenella coeruleoalbarepresenting 64.7% of all sightings, the fin whaleBalaenoptera physalus(17.0%), Cuvier's beaked whaleZiphius cavirostris(9.9%), Risso's dolphinGrampus griseus(4.3%) and the sperm whalePhyseter catodon(2.2%). Sightings' positions and effort coverage were distributed over a grid of 5′ longitude and 5′ latitude. Spatial concentrations of sightings were analysed according to the distribution of effort to identify ‘hotspots’ (locations where the species occurred at a significantly greater frequency than expected), and ‘coldspots’ (locations with a significantly lower frequency than expected). Most fin whale hotspots (14) were located on the bathyal plain between 2000 and 2500 m, four hotspots were around the 1000 m isobaths, and one is located close to the seamount off Genoa. Fin whale coldspots were mainly along the coast. Striped dolphin hotspots were widely distributed over two main areas, in waters with depths between 2000 and 2500 m and at the continental slope; coldspots for this species were also mainly along the coast in the northern part of the study area. Many hotspots were found in the Genoa Canyon, and hotspots of striped dolphins, Cuvier's beaked whales, sperm whales and Risso's dolphins overlapped in this region. Some of the hotspots of Cuvier's beaked whales were identified at the seamount in the study area, where no other species was sighted frequently. Risso's dolphin hotspots were mainly near the 1000 m isobath. For sperm whales, several hotspots were identified: three associated with steep slope features (such as canyons or the continental slope), and one was in the centre of the flat area of Pelagos where the depth is 2500 m. This study highlights the ecological importance of particular locations inside the Pelagos Sanctuary—locations that should be protected from anthropogenic degradations for marine mammal conservation.

Cuvier's beaked whale distribution in the Mediterranean Sea: results from small boat surveys 1996–2007

A total of 17,651 km of sailboat survey effort obtained with very good sighting conditions was pooled over the period 1995 to 2007 to provide an insight into Cuvier's beaked whales' (Ziphius cavirostris) distribution in the western and central Mediterranean Sea. Although only six confirmed sightings were obtained under such conditions, complementary sightings made a total of eleven confirmed records. Their distribution showed that only slope habitat, and its close proximity, was favourable to the species. In contrast to regions pointed out in the recent literature, such as the Alboran, Ligurian and Ionian Seas, it appeared that the Tyrrhenian Sea was likely to be an important area for Cuvier's beaked whales in the Mediterranean. Sighting rates of 0.1–0.25 sighting/100 km and sighting rates for individuals of 0.2–0.5 individual/100 km were obtained in favourable regions. When compared to sighting rates obtained on Risso's dolphinsGrampus griseusduring the same surveys, the Cuvier's beaked whale appeared to be quite a frequent species in its favoured habitats. The present study contributes a better knowledge of this poorly-known species, in the context of increasing and threatening anthropogenic noises.

SUMMER DISTRIBUTION AND RELATIVE ABUNDANCE OF CETACEANS OFF THE WEST COAST OF IRELAND

From May to September 2004 a survey of cetacean distribution and relative abundance was conducted on board a 'ship of opportunity'—a vessel used as a survey platform but not chartered for this purpose—off the west coast of Ireland. In total, 508 hours of survey effort were completed, with 304.2 hours in Beaufort sea-state 3 or less. Two hundred and thirty one sightings of eight species—common dolphin Delphinus delphis (L.), Atlantic white-sided dolphin Lagenorhynchus acutus (Gray), bottlenose dolphin Tursiops truncatus (Montagu), harbour porpoise Phocoena phocoena (L.), Risso's dolphin Grampus griseus (Cuvier), pilot whale Globicephala melas (Traill), minke whale Balaenoptera acutorostrata (Lacepede) and fin whale Balaenoptera physalus (L.)—were recorded, totalling 2,933 individuals. The greatest diversity and relative abundance were recorded on the Rockall Bank where Atlantic white-sided dolphin was the most abundant species. The common dolphin was the most abundant species recorded on the continental shelf to the south-west of Ireland, while the relative abundance of cetaceans off the north coast was very low. The data suggest that cetacean species composition and relative abundance can vary greatly between adjacent marine habitat types and over relatively small geographical distances.