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Kongens Lyngby, Denmark

Christensen-Dalsgaard S.N.,Norwegian Institute for Nature Research | Christensen-Dalsgaard S.N.,University of Tromso | Aars J.,Norwegian Polar Institute | Andersen M.,Norwegian Polar Institute | And 2 more authors.
Polar Biology | Year: 2010

Validation of age estimation from tooth cementum growth layers was conducted for 32 polar bears (Ursus maritimus) of known age, by two readers. Both readers correctly estimated age for 24% of the bears, and 50-53% were within the year of correct age. The age of young animals (age 1-8) was overestimated, while ages for bears over 8 years were underestimated. Comparison between the readings of the two readers indicated that the precision was low. Further, one of the readers reread tooth slides earlier prepared and read by another age estimation laboratory. There was a large discrepancy between these readings indicating a bias in the ages estimated. We conclude that age estimation of polar bears can be difficult, particularly in populations where individuals may forage throughout the year. As tooth growth layers may deposit differently for bears from different areas, and as different laboratories may read the same slides according to different criteria, an evaluation of the methods should be conducted for all populations, based on a significant number of tooth slides, with a broad age range, from animals of known age. © 2009 Springer-Verlag. Source

Fernandez-Contreras M.M.,University of Barcelona | Cardona L.,University of Barcelona | Lockyer C.H.,Age Dynamics | Aguilar A.,University of Barcelona
ICES Journal of Marine Science | Year: 2010

The numbers of short-beaked common dolphins captured annually by pairtrawlers operating off Galicia (northwestern Spain) and the operational factors influencing the bycatch were evaluated using on-board observations. Hauling time, fishing depth, and season of the year were identified as the key factors involved in the incidental capture. The dolphins were most vulnerable to trawls at night from May to September, around the continental shelf break. Most of the dolphins in the bycatch were males, and the average age was 13.4 ± 4.4 years for males and 11.5 ± 4.8 years for females. The sex ratio was male-biased owing to a few capture events involving several males each, supporting the notion that bachelor groups exist in the area. The annual bycatch in 2001 and 2002 was an estimated 394 dolphins [95 confidence interval (CI) 230-632], most taken from May to September (mean 348 dolphins, 95 CI 200-590) and just a few from October to April (mean 46 dolphins, 95 CI 0-132). This level of bycatch could be reduced significantly if trawlers were restricted to operating in water deeper than 250 m and likely avoided entirely if they were restricted to water deeper than 300 m. © 2010 International Council for the Exploration of the Sea. Source

Wiemann A.,University of Potsdam | Andersen L.W.,National Environmental Research Institute of Denmark | Berggren P.,University of Stockholm | Siebert U.,University of Kiel | And 10 more authors.
Conservation Genetics | Year: 2010

The population status of the harbour porpoise (Phocoena phocoena) in the Baltic area has been a continuous matter of debate. Here we present the by far most comprehensive genetic population structure assessment to date for this region, both with regard to geographic coverage and sample size: 497 porpoise samples from North Sea, Skagerrak, Kattegat, Belt Sea, and Inner Baltic Sea were sequenced at the mitochondrial Control Region and 305 of these specimens were typed at 15 polymorphic microsatellite loci. Samples were stratified according to sample type (stranding vs. by-caught), sex, and season (breeding vs. non-breeding season). Our data provide ample evidence for a population split between the Skagerrak and the Belt Sea, with a transition zone in the Kattegat area. Among other measures, this was particularly visible in significant frequency shifts of the most abundant mitochondrial haplotypes. A particular haplotype almost absent in the North Sea was the most abundant in Belt Sea and Inner Baltic Sea. Microsatellites yielded a similar pattern (i.e., turnover in occurrence of clusters identified by STRUCTURE). Moreover, a highly significant association between microsatellite assignment and unlinked mitochondrial haplotypes further indicates a split between North Sea and Baltic porpoises. For the Inner Baltic Sea, we consistently recovered a small, but significant separation from the Belt Sea population. Despite recent arguments that separation should exceed a predefined threshold before populations shall be managed separately, we argue in favour of precautionary acknowledging the Inner Baltic porpoises as a separate management unit, which should receive particular attention, as it is threatened by various factors, in particular local fishery measures. © Springer Science+Business Media B.V. 2009. Source

Bloch D.,Faroese Museum of Natural History | Desportes G.,Faroese Museum of Natural History | Harvey P.,The Shetland Amenity Trust | Lockyer C.,Age Dynamics | Mikkelsen B.,Faroese Museum of Natural History
Aquatic Mammals | Year: 2012

Risso's dolphins (Grampus griseus) were taken for the first time by the opportunistic drive fishery in the Faroe Islands in two separate incidents: three in September 2009 and 21 in April 2010, with in total 16 females and eight males. Their sizes ranged from 193 to 308 cm in length and 60 to 395 kg in weight for females, and 186 to 323 cm in length and 70 to 505 kg in weight for males; the maximum weights are heavier than previously documented for this species. The smallest mature female was 277 cm long, while the youngest and also lightest mature female was 8 y old and weighed 280 kg. Sperm competition and a pro-miscuous mating system were suggested for the species based on large testicular masses. The diet was composed of cephalopods from both the water column (Todarodes and Loligo) and the ocean floor (Eledona and Todaropsis). Although both schools landed showed a mixed diet, the September school diet centred on a pelagic squid (Todarodes sagittatus), while the April school diet centred upon a benthic octopod (Eledona cirrhosa). Since August 2009, Risso's dolphins have been observed on five occasions in waters around the Faroese north of 61° 34' N, the northernmost observation situated at a latitude of 62° 23' N. Sightings of the species off Shetland occur mostly between April and September, with a peak in August and September, the observations in Faroese waters (2 in April, 1 in August, and 2 in September) falling within this period. While the species had not previously been observed in this area north of the Shetland-Faroe Channel, these observations in Faroese territorial waters indicate a likely northward extension of the known range of the species. Source

Galatius A.,University of Aarhus | Bossi R.,University of Aarhus | Sonne C.,University of Aarhus | Riget F.F.,University of Aarhus | And 4 more authors.
Environmental Science and Pollution Research | Year: 2013

Profiles of seven compounds of perfluoro-alkyl substances (PFASs) were compared among three species of top predators from the Danish North Sea: the white-beaked dolphin (Lagenorhynchus albirostris), the harbor porpoise (Phocoena phocoena), and the harbor seal (Phoca vitulina). The seals had higher total burdens (757.8 ng g-1 ww) than the dolphins (439.9 ng g-1 ww) and the porpoises (355.8 ng g-1 ww), probably a reflection of feeding closer to the shore and thus contamination sources. The most striking difference among the species was the relative contribution of perfluorooctanesulfonamide (PFOSA) to the profiles; the seals (0.1 %) had much lower levels than porpoises (8.3 %) and dolphins (26.0 %). In combination with the values obtained from the literature, this result indicates that Carnivora species including Pinnipedia have a much higher capacity of transforming PFOSA to perfluorooctane sulfonic acid (PFOS) than cetacean species. Another notable difference among the species was that the two smaller species (seals and porpoises) with supposedly higher metabolic rates had lower concentrations of the perfluorinated carboxylic acids, which are generally more easily excreted than perfluorinated sulfonamides. Species-specific characteristics should be recognized when PFAS contamination in marine mammals is investigated, for example, several previous studies of PFASs in cetaceans have not quantified PFOSA. © 2013 Springer-Verlag Berlin Heidelberg. Source

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