Living between widely separated areas: Long-term monitoring of Mediterranean loggerhead turtles sheds light on cryptic aspects of females spatial ecology (original) (raw)
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Marine Biology, 2005
An aerial survey was conducted in early spring 2002 over the continental shelf of the Balearic Archipelago to study the distribution of neritic loggerhead turtles. Furthermore, five juvenile loggerhead turtles [straight carapace length (SCL) range 37.1-48.7 cm], were instrumented with transmitters and monitored during 2003 by satellite tracking to study habitat use over a broader geographical range. The distribution of the turtles over the continental shelf matched habitat availability, as defined by depth. However, those tracked by satellite spent most of the time in the oceanic waters of the Algerian basin and generally avoided continental shelf areas. In these turtles, average speed of travel and mean cosine of turning angle did not significantly differ between habitats, indicating that avoidance of shelf areas is not due to active habitat selection. On average, tracked turtles spent 35.1±19.7% of the time at the surface, although surface time was much greater in the turtle with the shortest carapace length, suggesting that this individual had limited swimming capacity. We conclude that the transition between passive drifting and active habitat selection occurs at an SCL of about 40 cm. The turtles followed tracks that matched prevailing currents, but on some occasions they also swam upstream. Hence, the distribution of late juvenile log-gerhead turtles in the southern and central western Mediterranean may reflect a combination of passive drifting and active habitat selection.
2008
Sea turtle populations worldwide suVer from reduced survival of immatures and adults due to Wshery bycatch. Unfortunately, information about the whereabouts of turtles outside the breeding habitat is scarce in most areas, hampering the development of spatially explicit conservation plans. In the Mediterranean, recoveries of adult females Xipper-tagged on nesting beaches suggest that the Adriatic Sea and Gulf of Gabès are important foraging areas for adults, but such information could be heavily biased (observing and reporting bias). In order to obtain unbiased data, we satellite-tracked seven loggerhead sea turtles after they completed nesting in the largest known Mediterranean rookery (Bay of Laganas, Zakynthos, Greece). Three females settled in the north Adriatic Sea, one in the south Adriatic Sea and two in the Gulf of Gabès area at the completion of their post-nesting migrations (one individual did not occupy a distinct foraging area). The concordance of tracking results with information from recoveries of Xipper-tagged turtles suggests that the north Adriatic Sea and the Gulf of Gabès represent key areas for female adult Mediterranean loggerhead sea turtles.
Aquatic Conservation: Marine and Freshwater Ecosystems, 2012
1. Identifying highly frequented areas is a priority for sea turtle conservation. Although juveniles represent the bulk of the population, a minority of studies have investigated their movement patterns. 2. Six large juvenile loggerhead turtles that were found and released in an important foraging ground in the Mediterranean, the Tunisian continental shelf were tracked. Tracking data were obtained via satellite for periods ranging from 120 to 225 days and allowed the identification of high use areas. 3. All turtles generally performed apparently non-directed, wandering movements in waters with a wide range of seafloor depths. They showed clear residential behaviour to the region with no evident seasonal pattern. Core areas of residence were in the neritic zone or on the edge of the continental shelf, largely overlapping among individuals, and were much smaller than residential oceanic areas reported elsewhere. 4. When integrated into current knowledge, these results suggest an ecological-behavioural model of a gradual shift from a pelagic-vagile to a benthic-sedentary life style with progressive reduction of home ranges. 5. They also highlight an area of the continental shelf and offshore waters as potential core foraging ground for large juvenile loggerhead turtles in the Mediterranean informing future spatial management for loggerhead turtles.
Mediterranean Marine Science
The Adriatic Sea is one of the main foraging areas for marine turtles of the Mediterranean Sea, but the specific high-use sites are poorly known, due to the scarceness of satellite tracking data available for juvenile turtles frequenting the area. In the present study, we tracked 8 juvenile and adult loggerhead turtles (Caretta caretta) that were released along the north-western Adriatic coast after a rehabilitation period having been equipped with Argos-linked satellite transmitters. Tracked turtles displayed quite variable movement patterns, but mostly remained in the north-western Adriatic, especially during the summer months. A marked preference for specific coastal sites was revealed in many turtles, that actively moved towards these specific locations when released south of it or having spent the winter away. Pooling these data with those obtained in previous studies on a further 10 turtles, we highlighted the presence of two main high-use areas, north and south of the Po Rive...
Marine Biology, 2007
Sea turtle tagging carried out in Italy in the period 1981-2006 resulted in 125 re-encounters of loggerhead turtles (Caretta caretta) after a mean of 2.5 years, from diVerent marine areas in the Mediterranean. At Wrst Wnding, turtles ranged 25-83 cm of curved carapace length. Data were analyzed according to size, area, habitat type, season, in order to provide indication of movement patterns. When integrated with other information, results indicate that: (1) a part of turtles in the oceanic stage show a nomad behavior with movements among diVerent oceanic areas; (2) another part show Wdelity to an oceanic area; (3) turtles in the neritic stage show Wdelity to neritic areas, and once settled to one area, change to other neritic areas is unlikely; (4) nomad oceanic turtles are signiWcantly larger than sedentary ones, and also larger than turtles found in neritic areas; it is hypothesized that these could be Atlantic turtles that eventually leave the Mediterranean; (5) ecological transition from oceanic to neritic habitats occurs at a wide range of sizes, and some turtles may have a very brief oceanic stage; (6) turtles in the oceanic stage are more likely to recruit to neritic areas close to their oceanic areas than to distant ones; (7) part of turtles from some Mediterranean nesting beaches might frequent a relatively limited area range, including both oceanic and neritic areas; (8) in most of the Mediterranean, latitudinal seasonal migrations are unlikely. A general model of movement patterns of loggerhead turtles in the Mediterranean is proposed. Communicated by R. Cattaneo-Vietti.
Long-Term Tracking of Adult Loggerhead Turtles (Caretta caretta)in the Mediterranean Sea
Journal of Herpetology, 2013
Three adult-sized Loggerhead Turtles (Caretta caretta), captured incidentally by bottom trawlers, were tracked by satellite in the Mediterranean Sea for a substantial part of their annual cycle, including the period preceding nesting. The three turtles performed longdistance movements that were variable between individuals but shared common features such as seasonal migration. Very prolonged dives (up to over 300 min) were associated with temperature drops to below 188C , likely an overwintering strategy. Our findings integrate recent tracking data on the postnesting migrations of Mediterranean Loggerhead Turtles, documenting the movement patterns made during the poorly known nonreproductive phase.
Marine Biology, 2012
Knowledge about migratory routes and highly frequented areas is a priority for sea turtle conservation, but the movement patterns of juveniles frequenting the Adriatic have not been investigated yet, although juveniles represent the bulk of populations. We tracked by satellite six juvenile and one adult female loggerhead from the north Adriatic. The results indicated that loggerhead juveniles (1) can either show a residential behaviour remaining in the Adriatic throughout the year or perform seasonal migrations to other areas, (2) can remain even in the coldest, northernmost area during winter, (3) can frequent relatively small foraging areas, (4) mostly frequent the eastern part of the Adriatic, and (5) follow preferred migratory routes along the western and eastern Adriatic coasts. The movements of the adult turtle also revealed (6) a behavioural polymor-phism in Mediterranean adults, which included a lack of area Wdelity and connection between distant neritic foraging grounds.
Modeling Loggerhead Turtle Movement in the Mediterranean: Importance of Body Size and Oceanography
Ecological Applications, 2008
Adapting state-space models (SSMs) to telemetry data has been helpful for dealing with location error and for modeling animal movements. We used a combination of two hierarchical Bayesian SSMs to estimate movement pathways from Argos satellite-tag data for 15 juvenile loggerhead turtles (Caretta caretta) in the western Mediterranean Sea, and to probabilistically assign locations to one of two behavioral movement types and relate those behaviors to environmental features. A Monte Carlo procedure helped propagate location uncertainty from the first SSM into the estimation of behavioral states and environmentbehavior relationships in the second SSM. Turtles using oceanic habitats of the Balearic Sea (n ¼ 9 turtles) within the western Mediterranean were more likely to exhibit ''intensive search'' behavior as might occur during foraging, but only larger turtles responded to variations in seasurface height. This suggests that they were better able than smaller turtles to cue on environmental features that concentrate prey resources or were more dependent on highquality feeding areas. These findings stress the importance of individual heterogeneity in the analysis of movement behavior and, taken in concert with descriptive studies of Pacific loggerheads, suggest that directed movements toward patchy ephemeral resources may be a general property of larger juvenile loggerheads in different populations. We discovered sizebased variation in loggerhead distribution and documented use of the western Mediterranean Sea by turtles larger than previously thought to occur there. With one exception, only individuals .57 cm curved carapace length used the most westerly basin in the Mediterranean (western Albora´n Sea). These observations shed new light on loggerhead migration phenology.
MOVEMENTS OF THREE LOGGERHEAD SEA TuRTLES IN TuSCANy WATERS
The coastal waters along Tuscany (Central Italy) are thought to represent a good foraging ground for loggerhead turtles (Caretta caretta), especially, but not only, during the juvenile phase. We describe the movements of three juvenile loggerheads released along the Tuscany coast after having been accidentally caught by fishermen and rehabilitated by recovery centres of the region. The turtles were tracked by satellite for 20-125 days, displaying two main movement patterns. Two turtles remained in neritic coastal waters for the whole duration of tracking, while the third one moved north soon after release, reaching the northern Ligurian Sea with an open-sea route. These findings show that loggerheads can use Tuscany waters both as a profitable long-term foraging site and as a transit area during their movements towards other destinations.