SLiDAP: The Satellite-Linked Data Acquisition and Photogrammetry System.
Background Information:
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 (Schumacher 2000). The Bering Sea region represents one of the biologically and economically most important ecosystems in the United States, providing over fifty percent of fish and shellfish catches in a multi-billion dollar industry (Fritz et al. 1995, Fritz & Ferrero 1998). In a troubling development, most apex predators in this ecosystem have exhibited dramatic population declines over the past three decades (Loughlin 1998). Steller sea lions, as one such species have declined to about ten percent 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 (Loughlin 1998, Fritz & Ferrero 1998). 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 (Merrick & Loughlin 1997, Calkins et al. 1998). 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 dearth of adequate data.
This lack of vital data on polar pinnipeds and seabirds encompasses some of the most basic life-history information:
The importance of this type of data has been highlighted by recent plans including the Bering Sea Ecological Research Plan draft (BSERP 1999), several workshops organized by the Steller sea lion recovery team reviewing Steller-related research efforts (Williams et al. 1999, Springer et al. 1999) and a workshop on otariid reproductive biology (Horning & Davis 1996). Specific research recommendations include: detailed population monitoring including age structure assessments in rookeries and specifically the enhancement of photo-based census operations, as well as obtaining higher-resolution, long-term foraging behavior data. A similar lack of data applies to many south polar pinnipeds and seabirds. However, the absence of intense economic interests in the area has prevented the attraction of widespread attention to this knowledge deficit to date.
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.
Animal-borne data recording tags have been used on many marine mammal and seabird species to obtain detailed foraging behavior and movement pattern data. These tags have to be recovered to obtain access to the previously stored data. Such repeat captures are highly challenging or even impossible to perform. Recently, animal-borne tags have been used with the capability of uplinking condensed data via the ARGOS/NOAA satellite system. Due to ARGOS bandwidth constraints, recovery of high density behavioral data remains elusive. In addition, externally attached devices rarely permit observations beyond a few months, mostly due to regular molt of the study animals. In a recent workshop on implantable telemetry devices, the use of implantable archival tags was listed as the most likely successful approach to long-term monitoring of pinnipeds in the near future (Horning et al. 1999). However, data recovery from implanted devices is even more challenging than from external animal-borne loggers. To address this challenge, the same workshop recommended the development of automated data downloading and relay stations, capable of linking with implantable devices via bi-directional radio data links.
© M. Horning 1999, 2000.
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