HARBOR SEAL TRACKING AND TELEMETRY BY SATELLITE

TLDR

Satellite telemetry for pinnipeds is limited by the current 1 per 45‑minute transmission rate, hindering detailed foraging and at‑sea movement studies. The study aimed to evaluate the usefulness of a satellite Platform Transmitter Terminal for tracking harbor seal behavior and movements at sea. Researchers tested a PTT on a laboratory float, captive seals, and a free‑ranging harbor seal, and used time‑depth recorder data to interpret PTT location and dive records. The PTT achieved daily uplinks for 70–82% of passes, confirmed 20 of 62 Argos locations at sea, revealed a maximum 48‑km range but most within 5 km, and showed ±15‑km sea‑location accuracy versus ±1.5 km ashore, with fewer detections during dives and PTT‑.

Abstract

A bstract We tested a satellite Platform Transmitter Terminal (PTT) in the laboratory (on a float and on captive seals) and on a free‐ranging harbor seal in the Southern California Bight to investigate the utility of satellite telemetry in documenting seals’at‐sea behavior and movements. We used records from a microprocessor‐based time‐depth recorder (TDR) to interpret location and diving records from the PTT. For the free‐ranging harbor seal, we obtained at least one uplink during 70% (while the seal was at sea) to 82% (while she was ashore) of satellite passes and at least one location each day. Of 62 locations determined by Service Argos for the free‐ranging seal, 20 were verified from TDR records to have been at sea; these indicated that the seal may have ranged up to 48 km from the haul‐out site, although most locations were within 5 km. The accuracies of locations calculated when the seal was at sea (±15 km) were substantially less than when it was ashore (±1.5 km), thus limiting at‐sea tracking of seals by satellite to rather gross movements. Fewer transmissions were detected and locations calculated when the seal was actively diving than when it was swimming near the surface as it departed from or returned to the haul‐out site. Consequently, average dive durations indicated by the PTT were substantially shorter than those calculated from TDR records. Documentation of foraging areas and detailed at‐sea movements using satellite technology may not be possible for pinnipeds unless PTT‐transmission rates are increased substantially from the 1 per 45 set maximum rate now permitted by Service Argos.