A descriptive and quantitative comparison of the communication of grey seals, Halichoerus grypus, at three sites in the North Atlantic Ocean

Lawson, John W. (1993) A descriptive and quantitative comparison of the communication of grey seals, Halichoerus grypus, at three sites in the North Atlantic Ocean. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Detailed, comparative studies of pinnipeds are rare, particularly between breeding and non-breeding groups of phocids. During 1988 and 1989 I observed two breeding colonies of the land-breeding grey seal, Halichoerus grypus, at North Rona, Scotland (59° 08’ N; 5° 49' W), and Sable Island, Nova Scotia (43° 55' N; 59° 48' W). I also observed a non-breeding aggregation during the summers of 1986 to 1988 on the island of Miquelon (45° 45’ N; 56° 14’ W). At these sites, from distances as little as one metre, I videotaped sequences of behavioural interaction that occurred between seals of all age classes and both sexes. During frame-by-frame analyses of the video records I quantified 34 measures (one of which included 33 behavioural acts in an ethogram) for each behavioural act within the sequences. -- Although behaviour types in the ethogram were robust, and clearly discernible by a naive observer, grey seal behaviour was individually variable. Except for the male Open Mouth Display, coefficients of variation for a number of measures (e.g., duration and inter-seal distance) were large, and behavioural acts were often used in a variety of contexts. Most behaviour types were of short duration (< 5 sec) and were performed in close proximity to other interactants (< 1 m). Except during play, copulation or unusually aggressive interactions, grey seals avoided physical contact and normally oriented their bodies and heads in a parallel or head-on configuration to emphasise the mouth, eyes and enlarged snout. -- While sex, age and reproductive stage affected patterns of communication, topographic and meteorological features of the local habitats had little effect. Though many aspects of interactive behaviour were similar at all three locales, significant differences included: 1) differences in the form, frequency and inter-seal distance of behaviour categories among the colonies (which may be explained by the differing social structure of seals on Miquelon and Sable Island), 2) male-male interactions were briefer than male-female or female-female, 3) play occurred almost exclusively in the non- breeding group and had many behaviour types in common with aggressive interactions and 4) a male behaviour common at breeding sites, Open Mouth Display, was not seen at Miquelon. -- Markov analyses established that grey seal communication was structurally variable, but that succeeding acts (intra-individual) or responses (inter-individual) were predictable on the basis of immediately antecedent acts (first-order), but primarily during interactions between males at all sites (and male-female bouts at North Rona). -- These data establish significant behavioural differences between breeding and non- breeding grey seals, and support a prediction of game theory that suggests animals engaged in agonistic interactions minimise the quantity of information they transmit about their intentions, and react less predictably to the signals of cohorts. Differences in communication between breeding and non-breeding grey seals were greater than those between the breeding sites on opposite sides of the Atlantic Ocean. These dissimilarities were small relative to the marked individual variability in behaviour at all sites.

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