Turtles on the edge: movement of loggerhead turtles (Caretta caretta) along oceanic fronts, spanning longline fishing grounds in the central North Pacific, 1997–1998

Abstract

Nine juvenile loggerhead sea turtles tracked during 1997 and 1998 in the central North Pacific by satellite telemetry all travelled westward, against prevailing currents, along two convergent fronts identified by satellite remotely sensed data on sea surface temperature (SST), chlorophyll and geostrophic currents. These fronts are characterized by gradients in sea surface height that produce an eastward geostrophic current, with gradients in surface chlorophyll and SST. Six of the turtles were associated with a front characterized by 17°C SST, surface chlorophyll of about 0.2 mg m–3, and eastward geostrophic current of about 4 cm s–1, while the other three turtles were associated with a front with 20°C SST, surface chlorophyll of about 0.1 mg m–3, and eastward geostrophic flow of about 7 cm s–1. These results appear to explain why incidental catch rates of loggerheads in the Hawaii longline fishery are highest when gear is set at 17°C and 20°C, SST. Further, from the seasonal distribution of longline effort relative to these fronts, it appears that the surface longline fishing ground lies largely between these two fronts during the first quarter and well to the south of the 17°C front, but including the 20°C front, in the second quarter. These findings suggest seasonal or area closures of the longline fishery that could be tested to reduce incidental catches of loggerheads. Finally, these results illustrate the insights which can be achieved by combining data on movement of pelagic animals with concurrent remotely sensed environmental data.

Movements and habitat use of reef manta rays off eastern Australia: offshore excursions, deep diving and eddy affinity revealed by satellite telemetry

“…Previous tracking studies have highlighted the importance of productive regions or features, such as oceanographic fronts and mesoscale eddies, in providing foraging opportunities (Polovina et al 2000, Bailleul et al 2010) for marine species, including plankton-feeding sharks (Sims & Quayle 1998, Sims et al 2003. Planktivorous elasmobranchs must acquire sufficient energy from minute and diffuse prey.…”

Inferring vertical and horizontal movements of juvenile marine turtles from time-depth recorders

“…While the horizontal and vertical movements of large marine vertebrates are being increasingly described (Priede 1984, Duron-Dufrenne 1987, Polovina et al 2000, Block et al 2005, Bonfil et al 2005, remote recording of accurate spatial movements made by smaller species or early life stages has been slower, due to the challenges of miniaturising power sources, development of attachment techniques and hydrodynamic packaging of equipment (Watson & Granger 1998, Wilson & McMahon 2006, Pavlov et al 2007, Godley et al 2008). …”

Oceanic survival and movements of wild and captive-reared immature green turtles (Chelonia mydas) in the Indian Ocean

“…Between 3 and 5 years of age, they move to coastal habitats, becoming omnivorous and then herbivorous (Bjorndal, 1985). The spatial distribution and migration patterns of immature sea turtles are thought to depend upon environmental factors like oceanic fronts and gyres (Carr, 1987;Polovina et al, 2000). However, movements of immature turtles are poorly understood, as they can only be observed when they depart their place of birth, or when they are incidentally caught by offshore fisheries (Polovina et al, 2000).…”

“…The spatial distribution and migration patterns of immature sea turtles are thought to depend upon environmental factors like oceanic fronts and gyres (Carr, 1987;Polovina et al, 2000). However, movements of immature turtles are poorly understood, as they can only be observed when they depart their place of birth, or when they are incidentally caught by offshore fisheries (Polovina et al, 2000). Mark-recapture experiments traditionally used for adult turtles (Le Gall and Hughes, 1987;Limpus et al, 1992;Miller et al, 1998) require that animals bear tags for long periods, and that the probability of recapture is large enough to get a significant number of observations.…”

“…This methodology was also used for studying movements and diving behaviour on foraging areas or nesting areas (Godley et al, 2002;Hays et al, 1991Hays et al, , 1999Hays et al, , 2000Hays et al, , 2001Renaud and Carpenter, 1994;Stoneburner, 1982) and seasonal migrations (Bentivegna, 2002). As for young turtles in the pelagic environment, the only reported satellite tracking experiment concerned wild loggerhead turtles (Caretta caretta) in the Pacific (Polovina et al, 2000). In the neritic environment, movements of juvenile turtles have been tracked from radio or sonic transmitters for loggerheads (Gitschlag, 1996;Timko and Deblanc, 1983) and for green turtles (Brill et al, 1995).…”