Sheila S. Anderson

Grey seal males: energetic and behavioural links between size and sexual success

Abstract The costs of breeding in male grey seals (Halichoerus grypus) have been estimated by repeated weighings of animals on the breeding grounds. Individual variations in male size and rate of weight loss were positively correlated with measures of sexual behaviour. Grey seal males did not form a linear dominance hierarchy, nor were they of equal status, but large males lost few encounters. Finite resources set a limit on the time that can be spent ashore being sexually active. These limits can be predicted using the collected data on size and energy use, and the results emphasize the significance of large size in relation to breeding success in grey seal males. The largest males may on average sire 10 times as many offspring as the smallest breeding males.

Time budgets and topography: how energy reserves and terrain determine the breeding behaviour of grey seals

Abstract Grey seals (Halichoerus grypus) fast during the pupping and mating season; they are polygynous and throughout their breeding range they occupy a variety of habitats. Time allocation patterns are consistent with the fact that grey seal energy reserves are limited during the breeding season. Variations in the activity budgets of seals in different types of habitat appear to be determined by the nature of the terrain occupied. This behavioural flexibility may well have been an important feature in the evolution of the species.

Male mating success and paternity in the grey seal, Halichoerus grypus: a study using DNA fingerprinting

Grey seals breed colonially on remote coastal sites. Within the colony, males compete aggressively for access to the females. We compare field observations of breeding behaviour with paternity, as determined by DNA fingerprinting, in the breeding colony on the island of North Rona. In 89% of cases where paternity was assigned, the father was observed near the mother during her perioestrous period, although in some cases this was discovered retrospectively. However, the most likely candidate male, judged on the basis of behavioural criteria, was shown not to be the father in 36% of cases. Overall, DNA typed males were more dominant, maintained positions amongst the females for longer, and accounted for disproportionately more paternities than untyped males. However, the reproductive success of the typed males is not as great as their behavioural domination of copulatory opportunities would suggest. Possible contributory factors which could explain this include: (i) imprecision in the estimates of copulatory opportunity due to mobility of males or topographical influences on individual behaviour; and (ii) opportunities for subordinate males to copulate with receptive females, either sneakily within the colony or in the water.

Evidence for Mate Fidelity in the Gray Seal

Colonially breeding gray seals are polygynous. Males are larger than females, compete with each other for position among aggregated females, and contribute no parental care. Genetic analysis of pups born on the island of North Rona, Scotland, reveals large numbers of full siblings, although dominant males father disproportionately few of these. This result cannot be explained by mating patterns based solely on male dominance and the spatio-temporal organization of the breeding colony. Instead, many full siblings must result from choices favoring previous parental combinations. Thus, polygyny and partner fidelity appear to operate simultaneously in this breeding colony.

Radionuclides in grey seals

Milk from live female grey seals (Halichoerus grypus) and tissues from dead individuals were analysed for caesium isotopes and for plutonium and americium. The samples were collected at two sites, one in the North Sea and one in the north-east Atlantic. Levels of Cs137 in milk were low (mean value 2.9 Bq I−1) and were only slightly higher in tissues (range 6.4–27.5 Bq kg−1). Plutonium and americium levels were at or below detection limits in most samples. There were no differences between the results from the two locations. Radionuclide levels were similar to those in fish species commonly consumed by grey seals.

The pathology of the grey seal (Haliochoerus grypus). I. Pups.

SUMMARY This paper reports the pathological and bacterial findings in 68 Grey Seal pups. A wide variety of disease processes were found. The predominant finding was that the animals were nearly all grossly under-weight, either due to failure of the mother-pup bond or due to the effects of disease. The single commonest disease process was infection of the umbilicus with spread of infection to the peritoneum and other sites. Death was frequently due to septicaemia, drowning and trauma.