Techniques for real-time, active tracking of sea lions

Abstract

The movements of otariids at sea are generally studied by satellite telemetry. At fine scales (1-20 km), however, the level of precision provided by this technique (± mean 1.5-19 km) may be insufficient to accurately reconstruct the track of an individual and/or integrate such movement data with habitat and environmental features. An alternative technique is the boat-based active tracking of individuals by very high frequency (VHF) or acoustic telemetry. By following an individual equipped with transmitters, detailed observations of habitat use, predator occurrence, social context, behavioral state, and prey availability may be integrated to provide a real-time context in which to place the animals' movements. For species such as the Steller sea lion (Eumetopias jubatus), which are difficult to recapture, such techniques enable the collection of much needed contextual information. Here we describe the methods we applied to actively track Steller sea lions. Twenty-one juveniles were captured in Southeast Alaska during October 2003 and February 2004. They were fitted with a variety of VHF, satellite, and/or acoustic tags and were tracked through the winter and spring of [2003][2004]. The use of ship-based VHF telemetry in conjunction with real time navigation plotting software was highly successful and provided 37 fine-scale tracks of coastal and pelagic 1 Current

Jellyfish Support High Energy Intake of Leatherback Sea Turtles (Dermochelys coriacea): Video Evidence from Animal-Borne Cameras

“…Despite this overlap, the marine environment is dynamic, with prey often distributed heterogeneously within the landscape over space and time. The location of these prey are likely predictable at a large oceanographic scale, given the long-distance migrations of leatherback turtles and inter-annual fidelity to foraging areas [24] , [25] . However, locating prey patches of jellyfish at meso-scales may be more difficult, as they vary spatially and temporally with influences from the movement of surface water and associated nutrients caused by wind [26] and tidal cycles.…”

“…However, locating prey patches of jellyfish at meso-scales may be more difficult, as they vary spatially and temporally with influences from the movement of surface water and associated nutrients caused by wind [26] and tidal cycles. Because of this heterogeneity in prey presence with space and time, collecting simultaneous information about a predator's prey field and their movements [24] , [25] , [27] is necessary to try to understand an animal's foraging behavior. However, such sampling is expensive and logistically difficult.…”

Diet composition of Steller sea lions (Eumetopias jubatus) in Frederick Sound, southeast Alaska: a comparison of quantification methods using scats to describe temporal and spatial variabilities

“…The haul-out sites around Frederick Sound in SEAK are used yearround and form an important metapopulation cluster (Raum-Suryan et al 2004), representing >10% of the regional population following the breeding season (Womble et al 2005) as animals return from the coastal rookery complexes (Raum-Suryan et al 2004;Marcotte 2006). Consequently, this key area has been the focus of extensive research, including regular aerial counts (Womble et al 2005), telemetry and behavioural studies (e.g., Raum-Suryan et al 2004;Pitcher et al 2005;Lea and Wilson 2006), and prey availability and quality assessments (Vollenweider 2004;Thedinga et al 2006;Sigler et al 2009). However, basic diet descriptions for the Frederick Sound metapopulation (as well as most other Steller sea lion diet studies) have been limited to reporting prey occurrence (e.g., Trites et al 2007a).…”