Antarctic Pack-Ice Seals (APIS) Project

Background to developmental and broad-scale survey work in 1995/96, 1996/97, 1997/98 and 1998/99

Dr Colin Southwell, Australian Antarctic Division
For more information, email: seals@antdiv.gov.au

Aim of APIS

Pack-ice seals are among the dominant top predators of the Antarctic marine ecosystem. The Crabeater seal is the most abundant of the pack-ice seals, and is thought to be the largest single consumer of krill. Better knowledge of the distribution and abundance of pack-ice seals, particularly the Crabeater seal, is essential for understanding predator-prey interactions in the Antarctic marine ecosystem, and is required for developing predator-prey models which will enable prediction of the effects of krill fishing on species dependent on krill.

The Antarctic Pack-Ice Seals program (APIS) is a multi-national project aimed at quantifying the role of pack-ice seals in the Antarctic marine ecosystem. The major element of the APIS project is a synoptic, circumpolar survey of pack-ice seal abundance and distribution in 1998/99.

International co-ordination

Previous attempts to estimate pack-ice seal populations have been undertaken by individual nations. The success of these attempts has been hindered by the enormous extent of pack-ice (4 million square kilometres in late summer, 20 million square kilometres in early spring) and the logistical problems in obtaining a representative sample over the pack-ice. A critical element of the APIS program is participation and co-ordination at an international level. The success of the circumpolar survey is dependent on the co-ordination of several participating nations in time and space. The Australian Antarctic Division will be a major participant in the circumpolar surveys.

Australia's contribution to APIS

Australia's contribution to APIS will be to survey abundance and distribution in a 60° sector of the Australian Antarctic waters. Surveys will be undertaken from ships and long-range helicopters along north-south transect routes running from the edge of the sea-ice to the coast.

Behavioural and survey work

There are two basic elements to the survey work:

Studies of haul-out behaviour on a representative sample of seals in the survey sector. From these studies we will estimate the proportion of time seals spend on top of the ice during the daylight hours when surveys are undertaken.
Ship and helicopter-based surveys over a representative sample of the survey sector. From these surveys we will estimate the number of seals hauled out on the ice during the daylight hours.

An estimate of the total number of seals in the survey sector (ie on the ice and in the water) is obtained by combining these two estimates (for example, if we estimated that seals spent only half their time on the ice during the day, we would have to double our estimate of seals counted on the ice the arrive at an estimate of all seals).

Behavioural studies involve attachment of satellite-linked dive recorders (SLDR) to a sample of seals in the survey area. Satellite-linked instruments are necessary because it is extremely difficult to recapture pack-ice seals due to the remoteness and inaccessibility of their pack-ice habitat. Seals are caught and anaesthetised, and the SLDR is attached to the seal by glueing it to the fur on the seal's back. Data on haul-out behaviour are transmitted to a satellite then relayed to the Division's computers in Hobart, hence it is not necessary to recapture the seal to retrieve the data.

Ship and helicopter surveys involve recording the number of seals seen within an area approximately 500 metres to either side of the ship or helicopter as it travels along a transect route. We also record the perpendicular distance to each seal, which enables us to determine whether any seals away from the line were missed, and if so to correct for these missed animals.

Surveys need to be timed to occur when haul-out on the ice is maximised. Pack-ice seals haul-out on the ice to breed in spring (October) and to moult in summer (January-February), and show a pattern of maximum haul-out during the middle of the day. With respect to seasonal timing, spring surveys have biological advantages over summer surveys in that a known component of the population (the breeding population) is hauled-out. The disadvantage of spring surveys is the large extent of ice which must be surveyed. Summer surveys have the logistical advantage of reduced ice extent, but the biological disadvantage that the component of the population that is hauled-out is not as well understood as in spring.

This document is http://www.antdiv.gov.au/aad/sci/bio/pack_seals/pack_seals.html.