Hankering back to ancestral pasts : constraints on two pinnipeds, Phoca vitulina & Leptonychotes weddellii foraging from a central place

• Main Author: Liebsch, Nikolai S.
• Format: Thesis
• Language: English
• Published: 2006
• Subjects: Weddell; harbour seal; Phoca vitulina; Weddell Seal; Weddell Seals
• Online Access: https://oceanrep.geomar.de/id/eprint/59642/; https://oceanrep.geomar.de/id/eprint/59642/1/d1860.pdf

Pinnipeds show huge inter-specific variability in the lengths of time that they spend on land and at sea over the year and consequently in the range over which they forage. The reasons for the inter- and intra-specific variability are not immediately obvious although each species-specific strategy presumably represents an idealized solution which integrates maximized energy acquisition at sea with optimized time spent at the haul-out site. Foraging behaviour, divided into transit time spent commuting between the haul-out site and foraging zone, as well as the transit between the water surface and the hunting depths once the animals are in the foraging zone, is liable to play a key role in this. This thesis examines the foraging behaviour of two pinniped species, the harbour seal Phoca vitulina and the Weddell seal Leptonychotes weddellii in order to tease out the precise factors that modulate the length and duration of foraging trips compared to haul-out periods. Methodological advances in technology are developed and tested to achieve this. Dead-reckoning principles contained within an archival tag were used to examine the fine-scale movement of animals underwater and, via consideration of the logged parameters, to determine how animals divided their time into various activities and how these were related to locality. The location of feeding behaviour was determined by using the dead-reckoner in conjunction with an inter-mandibular angle sensor (IMASEN). Consideration of time allocated to various phases of the dives conducted, together with the data on animal speed, pitch and roll indicated that harbour seals have specific travelling dives, prospecting dives, prey-searching dives and sleeping dives. Apart from the sleeping dives, these are also mirrored by Weddell seals. Track tortuosity, which is believed to correlate with prey searching behaviour, was highest in water deeper than 10 m and starting at distances of 15 km from the haul-out site for harbour seals. This concurred with seal density and allowed ...