A PREHISTORIC BREEDING POPULATION OF HARP SEALS (PHOCA GROENLANDICA) IN THE BALTIC SEA

The pelagic and gregarious, low Arctic harp seal ( Phoca groenlandica ) is the most common seal species in most refuse faunas from coastal hunter-gatherer sites dating from the late Atlantic to the early Subboreal period ( ca. 4000-2000 cal B. C.) in the Baltic Sea. Our main objective was to examine the migration contra breeding population hypotheses regarding the Baltic harp seals. Analyses of epiphyseal fusion data and osteometry of archeological harp seal remains from 25 dwelling-sites suggest that a local breeding population established itself in the early Subboreal period. In the Middle Neolithic the rookery possibly was situated in the Baltic proper, south of Aland and west of Gotland. The mean adult size of the Baltic harp seals decreased, suggesting minimal genetic exchange with the north Atlantic Ocean population. Genetic drift, interspecific competition, and over-hunting by humans are all factors likely to have contributed to the eventual extinction of harp seals in the Baltic Sea.     

THERMAL FUNCTION OF PHOCID SEAL FUR

In phocid seals, blubber serves as the main thermal insulation instead of fur. The thermal function of fur, at least in adult phocid seals, has therefore been questioned. We measured the relative contribution of fur to the combined thermal resistance (insulation) offered by blubber, skin, and fur in newborn and adult harp ( Pagophilus groenlandicus ) and hooded ( Cystophora cristata ) seals, in air and water, to elucidate the role of fur as insulation in phocid seals. In air the fur contributed 90% of the combined thermal resistance of blubber, skin, and fur in newborn harp seal pups and 29% in adulrs, whereas in hooded seals the fur contributed 73% in newborn pups and 34% in adults. When submerged the thermal resistance of the fur was reduced by 84%-92%, and contributed 65% to the total insulation in newborn harp seal pups and 3% in adults, and 26% in newborn hooded seal pups and 5% in adults. We conclude that in air the fur of phocid seals makes an important contribution to the insulation of pups, and also contributes considerably to the insulation of adult animals. In water, even though the thermal resistance of the fur is dramatically reduced, the fur still contributes substantially to the insulation of pups, but its contribution in adults is negligible.     

DIGESTIBILITY OF CRUSTACEANS and CAPELIN IN HARP SEALS (PHOCA GROENLANDICA)

Gross energy intake (GEI), apparent digestible efficiency (%DE), and body-mass change were studied both in recently weaned and in subadult harp seals fed capelin ( Mallotus villosus ) and crustaceans ( Parathemisto libellula and Thysanoessa sp.) ad lib. The median %DE of Parathemisto libellula (with a wet-weight energy density (ED) of 3.9 kJ/g) and Thysanoessa sp. (ED: 2.3 kJ/g) was 81% and 83%, respectively, while the median %DE of capelin (ED: 8.6 kJ/g) was 94% and 93% for subadult harp seals and one harp seal pup, respectively. No correlation between age and %DE was obtained (P > 0.05). Despite ad lib. access to the food, the harp seal pups were unable to maintain body mass while on a crustacean diet, and it is therefore suggested that harp seal pups most likely must supplement their crustacean diets with fish to maintain growth.     

TRACE METALS AND METHYL MERCURY: ASSOCIATIONS AND TRANSFER IN HARP SEAL (PHOCA GROENLANDICA) MOTHERS AND THEIR PUPS

Milk samples from the stomachs of harp seal pups were analysed for Cu, Zn, Se, Cd and Hg, as were liver, kidney, and muscle from mother-pup pairs. Tissues were also analysed for MeHg. Milk contained, in addition to essential trace metals, Cd and Hg (57 ng/g and 6.5 ng/g respectively).
Pups had mercury in all three tissues. The percent methyl mercury in liver of pups was higher than in liver of mothers. Mercury in muscle was mostly methyl mercury in both mothers and pups. Total mercury in liver of mothers but not pups was correlated positively with selenium. Estimates of ingested mercury by pups indicated they had acquired most of their mercury during gestation.
Although mothers had cadmium in liver and kidney, it was not detected in tissues of pups. Cadmium did not transfer across the placenta, while mercury did. Tissue concentrations of Cu and Zn were higher in pups than mothers. The presence of metallothionein in pup tissues was postulated.
A strong positive correlation of copper and selenium between mothers and pups indicated transfer of these elements from mother to pup in direct proportion to their concentrations in maternal liver and kidney.     

SEASONAL CHANGES IN FOOD INTAKE OF HARP SEALS (PHOCA GROENLANDICA) AT 69°N

Food intake (PI), body mass ( BM ), and compartmental growth were recorded for 12 mo in four captive 2–4-yr-old male harp seals ( Phoca groenlandica ), exposed to an artificial light regime that closely resembled natural day length at 69°. In early May before molting, both FZ and BM decreased in all four animals. Total body fat ( TBF ) declined from 51% of BM in March (n = 4) to 30% in August (n = 2), while total body water ( TBW ) concomitantly increased from 37% to 51% and total body protein ( TBP ) from 11% to 17%. In July FI started to increase, while BM started to increase in August. TBF increased while TBW and TBP decreased from August, all three parameters reaching a stable level in October at 47%, 39%, and 12%, respectively. Thereafter, body composition was maintained rather constant until May. Between October and March/April FI fluctuated for all animals, while BM showed a fairly steady increase. Average daily amount of capelin consumed was 2.67 kg·d⁻¹, equivalent to 25,600 kJ·d⁻¹, or 343 kJ·kg⁻¹·d⁻¹.     

PHOCINE DISTEMPER VIRUS INFECTION IN HARP SEALS (PHOCA GROENLANDICA)

Antibodies against phocine distemper virus were found in liver and serum specimens of harp seals from the Barents Sea and north of Jan Mayen (West Ice) in 1987 and 1989. By immunoperoxidase testing, antibodies against phocine distemper virus could be demonstrated in 34 of 74 liver specimens (46%) from 1987 and in 44 of 126 liver specimens (35%) from 1989. The prevalence of neutralizing serum antibodies against phocine distemper virus was found to be 98% in 1989. Both findings clearly demonstrate the presence of a widespread infection with phocine distemper virus or a closely related virus in harp seals. The significance of these findings to the recent outbreak of phocine distemper virus infection in harbor seals in Northwestern Europe is discussed and it is concluded that there may be an epizootiological link between this outbreak and the large migration of harp seals in 1987.     

Paternity exclusion by DNA fingerprinting,and mate guarding in the hooded seal Cystophora cristata

Hooded seal Cystophora cristata trios consist of an adult female, her pup, and an attending adult male. Using DNA fingerprinting, we excluded the possibility that the attending males within hooded seal trios were the fathers of the pups, proving that these hooded seals did not remain paired from one breeding season to the next. Behavioural observations of the trios after capture and release revealed that male hooded seals displace one another in attending nursing females. Mate guarding appears to be the preferred mating strategy available to male hooded seals given intense competition for females, a very brief nursing period, and oestrus occuring soon after weaning, but its effectiveness remains unclear.     

THE TROPHIC ROLE OF MARINE MAMMALS IN THE NORTHERN GULF OF ST. LAWRENCE

The trophic role of apex predators was evaluated in the northern Gulf of St. Lawrence ecosystem. An Ecopath model was developed for the period 1985–1987 prior to the collapse of commercially exploited demersal fish stocks in this area. Marine mammal trophic levels were estimated by the model at 4.1 for cetaceans, 4.4 for harp seals (Pagophilus groenlandicus), 4.7 for hooded seals (Cystophora cristata), 4.5 for gray seals (Halichoerus grypus), and 4.3 for harbor seals (Phoca vitulina). Harp seals were the third most important predator on vertebrate prey following large Atlantic cod (Gadus morhua) and redfish (Sebastes spp.). Different seal species preyed on different levels of the food chain. Harp seals preyed on most trophic groups, whereas larger seals, such as gray seals and hooded seals, mainly consumed higher trophic levels. The model suggested that apex predators had a negative effect on their dominant prey, the higher trophic level fish, but an indirect positive feedback on the prey of their preferred prey, mainly American plaice (Hippoglossoides platessoides), flounders, skates, and benthic invertebrates. Our results suggest that both marine mammals and fisheries had an impact on the trophic structure.     

GENETIC SUBSTRUCTURE OF THE PACIFIC HARBOR SEAL (PHOCA VITULINA RICHARDSI) OFF WASHINGTON, OREGON, AND CALIFORNIA

Genetic substructure among groups of Pacific harbor seals, Phoca vitulina richardsi , along the western coast of the United States was investigated using mitochondrial DNA sequences. Blood and tissue samples were removed from 86 seals inhabiting Puget Sound and the Pacific coasts of Washington, Oregon, and California. A 320 base-pair segment of the control region was amplified using the polymerase chain reaction and directly sequenced. These data indicated a high level of diversity. Thirty variable sites were found that define 47 mitochondrial haplotypes. Among groups of P. v. richardsi sampled, 5 haplotypes were shared, but most (42) were unique to a locality. Haplotypic frequency and an Analysis of Molecular Variance (A mova ) revealed significant differences ( P = 0.001) among regions. Phylogenetic analysis indicated Puget Sound seals possess unique divergent lineages not found in seals from the coasts of Washington, Oregon, and California. These lineages may represent haplotypes from north of Washington, which is consistent with late reproductive timing of harbor seals from Puget Sound.     

SPATIO‐TEMPORAL CHANGES IN THE STRUCTURE OF AN AUSTRALIAN FROG HYBRID ZONE: A 40‐YEAR PERSPECTIVE

Spatio‐temporal studies of hybrid zones provide an opportunity to test evolutionary hypotheses of hybrid zone maintenance and movement. We conducted a landscape genetics study on a classic hybrid zone of the south‐eastern Australian frogs, Litoria ewingii and Litoria paraewingi. This hybrid zone has been comprehensively studied since the 1960s, providing the unique opportunity to directly assess changes in hybrid zone structure across time. We compared both mtDNA and male advertisement call data from two time periods (present and 1960s). Clinal analysis of the coincidence (same center) and concordance (same width) of these traits indicated that the center of the hybrid zone has shifted 1 km south over the last 40 years, although the width of the zone and the rate of introgression remained unchanged. The low frequency of hybrids, the strong concordance of clines within a time period, and the small but significant movement across the study period despite significant anthropogenic changes through the region, suggest the hybrid zone is a tension zone located within a low‐density trough. Hybrid zone movement has not been considered common in the past but our findings highlight that it should be considered a crucial component to our understanding of evolution.