The deployment of electronic data storage tags that are surgically implanted or satellite-linked provides marine researchers with new ways to examine the movements, environmental preferences, and physiology of pelagic vertebrates. We report the results obtained from tagging of Atlantic bluefin tuna with implantable archival and pop-up satellite archival tags. The electronic tagging data provide insights into the seasonal movements and environmental preferences of this species. Bluefin tuna dive to depths of >1000 meters and maintain a warm body temperature. Western-tagged bluefin tuna make trans-Atlantic migrations and they frequent spawning grounds in the Gulf of Mexico and eastern Mediterranean. These data are critical for the future management and conservation of bluefin tuna in the Atlantic.

Sexual segregation in foraging is predicted from the great size disparity of male and female northern elephant seals, Mirounga angustirostris. Our aim was to test this prediction by measuring diving and foraging behavior, foraging locations, and distribution of the sexes during biannual migrations in the northeastern Pacific Ocean. Daily movements of 27 adult males and 20 adult females, during 56 migrations from Añ o Nuevo, California, USA, were determined by Argos satellite telemetry via head-mounted platform transmitter terminals. Diving records were obtained with archival time-depth-speed recorders attached to the backs of seals that were recovered when the seals returned to the rookery. Pronounced sex differences were found in foraging location and foraging pattern, as reflected by horizontal transit speed and diving behavior. Males moved directly north or northwest at a mean speed of 90 Ϯ 27 km/d to focal foraging areas along the continental margin ranging from coastal Oregon (534 km away) to the western Aleutian Islands (4775 km away). Males remained in these areas (mean size ϭ 7892 km 2 ) for 21-84% of their 4-mo stays at sea. The predominance of flat-bottom dives in these areas suggests concentrated feeding on benthic prey. Migration distance and estimated mass gain were positively correlated with male size, and individual males returned to the same area to forage on subsequent migrations. In contrast, females ranged across a wider area of the northeastern Pacific, from 38Њ to 60Њ N and from the coast to 172.5Њ E. Focal foraging areas, indicated by a reduction in swim speed to Ͻ0.4 m/s, were distributed over deep water along the migratory path, with females remaining on them a mean of 3.5 d before moving to another one. Jagged-bottom dives that tracked the deep scattering layer prevailed in these areas, suggesting that females were feeding on pelagic prey in the water column. Females took roughly similar initial paths in subsequent migrations, but large deviations from the previous route were observed. We conclude that there is habitat segregation between the sexes. Females range widely over deep water, apparently foraging on patchily distributed, vertically migrating, pelagic prey, whereas males forage along the continental margin at the distal end of their migration in a manner consistent with feeding on benthic prey.

Electronic tags have enhanced our understanding of the movements and behavior of pelagic animals by providing position information from the Argos system satellites or by geolocation estimates using light levels and/or sea surface temperatures (SSTs). The ability to geolocate animals that remain submerged is of great value to fisheries management, but the accuracy of these geolocation estimates has to be validated on free-swimming animals. In this paper, we report double-tagging experiments on free-swimming salmon sharks Lamna ditropis and blue sharks Prionace glauca, tagged with satellite telemetry and pop-up satellite tags, which provide a direct comparison between Argos positions and geolocation estimates derived from light levels and SSTs. In addition, the Argosbased pop-up satellite tag endpoints and GPS-based recapture locations of Atlantic bluefin tunas Thunnus thynnus were compared with the last geolocation estimates from pop-up satellite and archival tags. In the double-tagging experiments, the root mean square errors of the light level longitude estimates were 0.89 and 0.55°; while for SST latitude estimates, the root mean square errors were 1.47 and 1.16°for salmon sharks and blue sharks respectively. Geolocation estimates of Atlantic bluefin tuna, using archival data from surgically implanted archival tags or recovered pop-up satellite tags, had root mean square errors of 0.78 and 0.90°for light level longitude and SST latitude estimates, respectively. Using data transmitted by pop-up satellite tags deployed on Atlantic bluefin tunas, the light level longitude and SST latitude estimates had root mean square errors of 1.30 and 1.89°, respectively. In addition, a series of computer simulations were performed to examine which variables were most likely to influence the accuracy of SST latitude estimates. The simulations indicated that the difference between the SST measured by the electronic tag and the remotely sensed SST at a given location was the predominant influence on the accuracy of SST latitude estimates. These results demonstrate that tag-measured SSTs can be used in conjunction with light level data to significantly improve the geolocation estimates from electronic tags.

Until recent declines in Arctic sea ice levels, narwhals () have lived in relative isolation from human perturbation and sustained predation pressures. The resulting naïvety has made this cryptic, deep-diving cetacean highly susceptible to disturbance, although quantifiable effects have been lacking. We deployed a submersible, animal-borne electrocardiograph-accelerometer-depth recorder to monitor physiological and behavioral responses of East Greenland narwhals after release from net entanglement and stranding. Escaping narwhals displayed a paradoxical cardiovascular down-regulation (extreme bradycardia with heart rate ≤4 beats per minute) superimposed on exercise up-regulation (stroke frequency >25 strokes per minute and energetic costs three to six times the resting rate of energy expenditure) that rapidly depleted onboard oxygen stores. We attribute this unusual reaction to opposing cardiovascular signals-from diving, exercise, and neurocognitive fear responses-that challenge physiological homeostasis.