The Satellite-Linked Data Acquisition and Photogrammetry System (SLiDAP): Assessment of seasonal and individual Steller sea lion body condition and population trends.

Summary | Background | Concept | Objectives | Hypotheses | Update | Literature

The polar regions cover areas of intense biological interest. The southern circumpolar seas have been fairly untouched by commercial enterprises and remain one of the few ecosystems subjected to comparatively little impact from human activities. Conversely, arctic regions around and including the Bering Sea comprise delicate ecosystems threatened by profound regime shifts. The Bering Sea region represents one of the biologically and economically most important ecosystems in the United States, providing over 5% of fish and shellfish catches in a multi-billion dollar industry. In a troubling development, most apex predators in this ecosystem have exhibited dramatic population declines over the past three decades. Steller sea lions, as one such species have declined to less than 15% of peak population levels and are currently listed as endangered in the western portion of their range (along the Aleutian Islands and in the Bering Sea). Northern fur seals, harbor seals and several seabird species have exhibited less dramatic but nonetheless severe declines. Extensive removal of fish biomass through commercial trawling has been hypothesized as one possible factor involved in the decline of Aleutian and Bering Sea pinnipeds. Despite years of intense research efforts by many agencies and institutions, no conclusive data exists to shed light on the hypothesized link between commercial fisheries, nutritional stress and reduced reproductive output of pinnipeds, or to allow for analysis of proximate mechanisms linking hypothesized cause and effect. Significant fisheries management decisions are being made under scarcity of adequate data. This lack of vital data on polar pinnipeds and seabirds encompasses some of the most basic life-history information:

• Year-round population census figures of sufficient spatial and temporal resolution, including details on the age structures of populations.
• Body mass and body condition estimates, both in form of longitudinal data from individual animals and cross-sectional data for meta populations.
• Year-round detailed foraging behavior data of sufficient temporal and spatial resolution to accurately assess fisheries interactions.

Several reasons can be listed for this lack of conclusive data. The species of interest reside in very remote and inaccessible locations in predominantly extreme environments. They include some of the most difficult marine mammal and seabird species to work with, partly on account of their extreme shyness and sensitivity to disturbances. Rookeries and haulouts are difficult to approach, let alone land on, frequently impossible on a repeated basis. Most observations have been limited to the reproductive season during local summer.

Present State of Technology

Traditionally, two types of telemetry approaches have been used on polar pinniped and seabird species. Aerial photography has been used in arctic regions for most pinniped stock assessments and population monitoring. In remote island areas with frequent dense cloud covers, such an approach is extremely costly and dangerous while delivering data of limited accuracy. The reduced accuracy is a result of the two most common problems in aerial or remote imaging census operations: redundant animal counting from overlapping images, and animals being obscured from given perspectives. Frequently only one or two assessments can be done per year.

To address these shortcomings, we have pursued several innovations in telemetry of seals and sea lions.  In our Life History Transmitter project we have developed new transmitters to allow remote monitoring of individual animals over their entire life.  In the SLiDAP technical development project, we pursued technology to remotely monitor seals and sea lions at their rookeries and haul-outs.  The combination of these approaches will allow us to collect a majority of the vital data described above.