1,720,985 research outputs found
Tag loss is a minor limiting factor in sea turtle tagging programs relying on distant tag returns: the case of Mediterranean loggerhead sea turtles
No full textAs in many other species, tagging has been routinely conducted for decades in over a hundred sea turtle capture-mark-recapture (CMR) programs worldwide. Tag loss is a key limiting factor because it violates the main assumption in CMR models; however, very few estimates of tag loss exist, and we provide here a review. No published estimations of tag loss are available for the Mediterranean, in spite of intensive tagging since the 1980s. This study aims to provide an estimation of tag loss in loggerhead turtles tagged in the Mediterranean. We modeled 64 tag returns out of ca. 2200 loggerhead turtles tagged at Mediterranean foraging grounds, with mark-recapture intervals up to 11.5 years, in order to estimate a daily tag loss probability of the most used tag applied to the most common turtle species in the region. Five models were evaluated through maximum likelihood estimation. The model with the best fit described a tag loss initially high and then decreasing to a lower asymptote, which is probably due to some defective tag applications. The resulting tag loss (0.15 in the first year and 0.31 after 5 years) was comparable or even lower than those from other areas and/or species and predictions indicate that double tagging can make a turtle identifiable for a long period. Hence, in our tagging program and probably in similar ones as well, tag loss appears to be the less important of the factors affecting tag returns, and efforts in other directions are more likely to improve CMR results
Mortality induced by drifting longline hooks and branchlines in loggerhead sea turtles, estimated through observation in captivity
No full text1. Drifting longlines are considered a major threat to endangered sea turtle populations worldwide. However, for a number of reasons, the mortality rate of captured turtles is not known with any certainty. 2. Information on 409 loggerhead turtles (Caretta caretta), collected during the day-to-day activities of a turtle rescue centre in Lampedusa island, central Mediterranean, in the period 2001-2005 has been analysed. 3. Observations indicate that: (i) drifting longlines are a major cause of mortality for sea turtles in the area; (ii) in addition to the hook, the piece of line attached to it (branchline) can easily cause death if it is long enough and well-anchored; (iii) hooks and branchlines cause death in the short and long term, respectively; (iv) a turtle with a hook in the lower oesophagus/stomach has a very low chance of surviving the combined effect of hook and branchline; (v) the mortality of turtles with a hook in the mouth or higher oesophagus is probably important, though less than that of turtles with a hook in the lower oesophagus/stomach; (vi) in the study fishery, the average mortality of a turtle caught by a drifting longline is probably much higher than 30%. 4. Without specific investigations on the mortality of turtles with hooks in the mouth or higher oeasophagus, which are usually removed, the mortality induced by drifting longlines will remain unknown, preventing a full understanding of the effect on population growth and the real effectiveness of conservation measures such as use of different hooks and fishing depths, and proposals for adequate fishery management measures. 5. The number of turtles captured by drifting longlines should be drastically reduced, and because of the above uncertainty and the socio-economic importance of the fishery sector, an ecosystem-based management scheme should be promoted that is not limited to addressing only the turtle issue. Copyright © 2007 John Wiley & Sons, Ltd
Histological validation of gonad gross morphology to sex juvenile loggerhead sea turtles (Caretta caretta)
No full textSea turtles exhibit sexual dimorphism only as adults, hence diagnosing the sex of hatchlings and juveniles requires the employment of different techniques that vary in their level of accuracy and costs. In order to validate the observation of external gross morphology of gonads as a sexing method for juveniles, we compared results obtained in this way with those obtained through histology in 99 loggerhead turtles with curved carapace length (CCL) ranging from 24.0 to 69.0 cm, found in the Adriatic Sea and in the central Mediterranean. Sex was correctly diagnosed in 92.9% of the 99 cases. The highest error rate due to wrong or uncertain sexing was found in turtles with a CCL less than 30.0 cm (33.3%). In turtles with a CCL of 30.0-40.0 cm and 40.0-50.0 cm, the error rates were low (5.3% and 6.7%, respectively), while no errors occurred in larger individuals (CCL greater than 50.0 cm). The results show that gonadal morphology is a reliable sexing method for large juveniles, but for those of less than 30 cm CCL we recommend verification by histology
Biases and best approaches for assessing debris ingestion in sea turtles, with a case study in the Mediterranean
No full textIn a sample of 567 loggerhead turtles (Caretta caretta) from the central Mediterranean, debris occurrence varied
according to methods and turtle source, and was up to 80% in pelagic turtles. Frequencies of plastic types, size and
color are also reported. These results and a critical review of 49 studies worldwide indicate that: (i) the detected
occurrence of plastic (% turtles) is affected by several factors (e.g., necropsy/feces, ecological zone, type and date
of finding, captivity period for feces collection), (ii) mixed dataset and opportunistic approaches provide results
which are biased , not comparable, and ultimately of questionable value, (iii) only turtles assumed to have had a
normal feeding behaviour at the time of capture or death should be considered, (iv) turtle foraging ecology and
possible selectivity may undermine the use of turtles as indicator species for monitoring marine litter, as recently
proposed for the Mediterranean
Interaction of the static net fishery with loggerhead sea turtles in the Mediterranean: Insights from mark-recapture data
No full textComparison of mark-recapture data collected using different fishing methods suggests that in the Mediterranean the interaction of sea turtles with the static net fishery is very important and comparable to other fisheries. Given the high mortality rate observed in this and other studies, static nets are likely to represent a serious threat to Mediterranean sea turtle populations
Epibiotic barnacles and crabs as indicators of Caretta caretta distribution and movements in the Mediterranean Sea
No full textThe occurrence of barnacles and crabs on Caretta caretta specimens found in the waters around Italy was analysed. In the seas surrounding Italy balanomorph barnacles occur mainly on turtles frequenting shallow waters and crabs display a strong west-east gradient. Patterns of turtle distribution and movements are proposed. The abundance of turtle-specific barnacles may be dependent on, and so an indicator of, turtle density
Incidental catch of marine turtles by Italian trawlers and longliners in the central Mediterranean
No full text1. The fishing effort and turtle catch of vessels harbouring at Lampedusa island and fishing in the wider central Mediterranean area was monitored using a voluntary logbook programme. Two large trawlers were monitored between 2003 and 2005 and six small vessels using trawl nets, pelagic longline or bottom longline were monitored in the summer 2005. 2. The observed turtle catch rates of pelagic longline and bottom trawl were among the highest recorded in the basin, and high catch rates by bottom longline were observed too. This suggests that the area contains major oceanic and neritic habitats for the loggerhead turtle Caretta caretta in the Mediterranean Sea. 3. When fishing effort is considered, these results suggest a very high number of captures by Italian trawlers and longliners in the area, as well as by fleets from other countries. This is reason of concern for the conservation of the loggerhead turtle within the Mediterranean Sea. 4. Different fishing gear have different technical/operational characteristics affecting turtle catch and mortality and the present knowledge about associated parameters of these gear varies too. 5. All this considered, specific actions are recommended: (i) an awareness campaign to fishermen to reduce post-release mortality, (ii) technical modifications to pelagic longline gear to reduce turtle catch, (iii) further investigation into turtle bycatch in all fishing gear, with priority given to bottom longline fishing and quantification of mortality caused by trawlers, (iv) assessment of the turtle populations affected by fishing activity in the area, and (v) international cooperation in undertaking threat assessments, and implementing regulations, management measures and monitoring. Copyright © 2007 John Wiley & Sons, Ltd
A model of area fidelity, nomadism, and distribution patterns of loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea
No full textSea 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 different marine areas in the Mediterranean. At first finding, 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 different oceanic areas; (2) another part show fidelity to an oceanic area; (3) turtles in the neritic stage show fidelity to neritic areas, and once settled to one area, change to other neritic areas is unlikely; (4) nomad oceanic turtles are significantly 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. © 2007 Springer-Verlag
Adult sex ratios of loggerhead sea turtles (Caretta caretta) in two Mediterranean foraging grounds
Full text linkSea turtles show temperature-dependent sex determination (TSD) and information on sex ratios at different life stages is necessary both for population dynamics models for conservation and to shed light on the possible adaptive value of TSD. Adults represent the less abundant class of sea turtle populations and adult sex ratios at foraging grounds are very difficult to obtain. We first analysed biometric data of 460 juvenile and adult loggerhead sea turtles ranging from 60 to 97.5 cm curved carapace length (CCL), in which a clear bimodal distribution of tail length (the main secondary sexual character of adult males) was observed in the size class >75 cm CCL. We then sexed 142 adult turtles in this size class collected from the Tunisian shelf and from the southeastern Tyrrhenian Sea, observing a proportion of females of 51.5% (95% CI: 41.2-61.8%; n=97) and 40.0% (95% CI: 25.7-55.7%; n=45) respectively. Our results complement previous studies and support their findings of similar and more balanced sex ratios in adult and juvenile loggerhead turtles in the Mediterranean, in contrast with highly female-biased sex ratios of hatchlings. © 2014 CSIC
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