No abstract

Stomach contents of 17 sperm whales Physeter rnacrocephalus stranded in Scotland and Denmark during 1990-96 were analysed. All were sub-adult or adult males and stranded between November and March. They had presumably entered the North Sea during their southward migration from feeding grounds in Arctic waters. Other studies indicate that the majority of the whales were apparently healthy. The diet of these whales was found to consist almost entirely of cephalopods, principally squid of the genus Gonatus (hereafter 'Gonatus', but probably G. fabncii, an oceanic species characteristic of Arctic waters). The other prey species identified were also mostly oceanic cephalopods: the squids Hjstioterlthis bonnellii, Teuthowenia megalops and Todarodes sagjttatus and the octopus Hahphron atlanticus. Although these results are consistent with other recent studies in the area based on single stranded whales, they chffer from results of work on whales caught during commercial w h a h g operations in Icelandic waters (1960s to 1980s) in that little evidence of predation on fish was found in the present study. Remains of single indviduals of the veined squid LoLigo forbesi, the northern octopus Eledone cirrhosa and the saithe PoUachius virens provided the only possible evidence of feeding in the North Sea. We infer that sperm whales do not enter the North Sea to feed. The timing, and large and uniform sizes of the Gonatus species eaten (most had mantle lengths in the range 195 to 245 mm), as estimated from measurements of the lower beaks, and the seasonality of the strandings is consistent with the whales having fed on mature squid, possibly spawning concentrations-as has recently been reported for bottlenose whales. Assuming that the diet recorded in this study was repre sentative of sperm whales during the feeding season, as much as 500000 t of Gonatus could be removed by sperm whales in Norwegian waters each year and up to 3 times that figure from the eastern North Atlantic as a whole. Evidence from other studies indicates that Gonatus is an important food resource for a wide range of marine predators in Arctic waters.

The onset and timing of epiphyseal ankylosis in the vertebral column and flippers and ankylosis of the hyoid and sternal bones were studied in 350 skeletons of the harbour porpoise (Phocoena phocoena) originating from the Baltic and North Sea and held in the collections of the Zoological Museum (University of Copenhagen), the Museum of Natural History (Gothenburg), the National Museum of Natural History (Stockholm), and the German Oceanographic Museum (Stralsund). Epiphyseal ankylosis in the vertebral column started in the anterior cervical region and then initiated around the 23rd to 26th caudal vertebrae from where it proceeded in both directions. The progression of vertebral epiphyseal ankylosis eventually terminated in the thoracic and lumbar regions. Epiphyseal ankylosis in the flippers began at the distal end of the humerus and the proximal ends of the radius and ulna. The timing of ankylosis in the flippers was more consistent across the specimens than the timing of vertebral ankylosis. Males and females had similar timing of ankylosis in the vertebral column and the flippers. Complete fusion of the hyoid and sternal bones occurred within the first year of life in most specimens. The early development of the hyoid apparatus may be linked to use of suction in feeding.

Fish and marine mammal populations in the Baltic Sea and Skagerrak have undergone major fluctuations over the past five centuries. We summarize how these fluctuations may have depended on various forms of predation (e.g., cannibalism, fishing, hunting) and environmental processes. The best-documented long-term fisheries in this region are the herring (Clupea harengus) fisheries near Bohuslän, western Sweden, and in the Øresund. These fisheries have been important since at least the 1200s and appear to be partly climatically driven. However, in the rest of the Baltic, information about fisheries for herring and other fish species is rare until after 1900. During the 20th century, while the Baltic underwent eutrophication, the biomass and landings of three fish species (cod (Gadus morhua), herring, and sprat (Sprattus sprattus)) all increased, whereas the biomass of marine mammals (grey seals (Halichoerus grypus), ringed seals (Phoca hispida), harbour porpoises (Phocoena phocoena)) decreased. The relative roles of exploitation, marine mammal predation, and environmental variability (e.g., eutrophication, major inflows of saline water, climate change) on the long-term dynamics of key fish species is not clear and requires increased collaboration among historians, fisheries and marine mammal ecologists, oceanographers, and climatologists.

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.