Female Grey Seals Halichoerus Grypus Research Articles

Integrating heterogeneity of detection and mark loss to estimate survival and transience in UK grey seal colonies

Summary 1. We present new developments in statistical methodology allowing in‐depth analysis of realistic, complex biological models for longitudinal data sets. Important biological details such as mark‐loss and recapture heterogeneity can be identified. 2. We use a Bayesian hidden process framework for a comparative analysis of long‐term (1978–2006) capture–recapture data with various combinations of marking methods for adult female grey seals Halichoerus grypus at two UK colonies. 3. Seals were identified using three different methods: flipper tags, brands, or natural pelage markings. Animals identified by brands or natural markings were re‐sighted more effectively than those with tags. 4. Flipper tag‐loss rates differed between colonies, and there was evidence for non‐independent tag‐loss in double‐tagged animals. There was also evidence at one colony for the presence of transient animals, which attend the colony for 1 year only. Apparent survival was higher and more consistent at one site, and the differences in survival between the two colonies were able to explain contrasting pup production trends at these sites. 5. Synthesis and applications. Longitudinal studies allow for the estimation of demographic parameters which have important implications for our understanding of population dynamics and for the conservation and management of populations. Using new statistical developments to allow for the analysis of missing/incomplete data and partial observations, we show how survival can be estimated from complex mark–recapture data, allowing for the effects of mark loss. The re‐sightability of different marks is estimated, indicating that photo‐ID based on natural pelage markings is a very effective method for identifying grey seals. There are notable contrasts in survival estimates between breeding colonies which can explain contrasts in population trends at these sites, confirming the importance of adult survival in driving population dynamics in this long‐lived species.

Acoustic Structure and Individual Variation of Grey Seal (Halichoerus Grypus) Pup Calls

Throughout lactation, pups of pinnipeds regularly vocalize, including during interactions with their mother. In all studied species of otariids and in some phocids, these calls exhibit sufficient acoustic variation for individual recognition. As female grey sealsHalichoerus grypus(Pinnipedia: Phocidae) often pup in dense colonies, and regularly leave their offspring alone to go to sea, the selective pressure for mutual vocal recognition between mothers and pups could be high. To investigate call variation in pups of this species, 170 calls of ten individual pups were analysed. Out of seven acoustic features studied, location of maximum signal strength, the number of harmonics and the frequency and strength of the fundamental show the highest individuality. However, the apparent infrequent use of pup calls during mother-pup reunions suggests that vocal signals may not play the major role in pup discrimination by female grey seals, as observed in other phocids which females do not vocalize to their pup.

Functions of female aggression during the pupping and mating season of grey seals, Halichoerus grypus (Fabricius)

Aggression of female grey seals Halichoerus grypus toward conspecifics was studied during the pupping and mating season on Sable Island, N.S. The responses of 65 individually identified females with pups toward known males and females were recorded throughout each female's stage of lactation. Female aggression varied both quantitatively and qualitatively as a function of the sex of an approaching animal. Males were threatened more often than females even though females outnumbered males. The likelihood of females threatening other females was affected by the location of the threatening female's pup, but aggression towards males was not affected by the pup's position. Females responded aggressively less often in the second half of lactation, when both weaning of the pup and oestrus occur, than in the first half. They were also more likely to threaten transient males than tenured males. However, a male approaching or mounting a female, whatever his status, was more likely to be challenged by another male if the female threatened him than if she did not. These challenges generally interrupted a male's approach or mount and hence a potential copulation. The results are consistent with the hypothesis that female aggression during the lactation period helps to protect the pup and increases the likelihood that a female mates with a dominant male. This latter function may be viewed as a form of mate choice.