1,721,145 research outputs found
Sea turtle by-catch in the Mediterranean
No full textSea turtle by-catch data in the Mediterranean were reviewed and analysed with fishing effort. The results indicate over 132000 captures per year, with probably over 44000 incidental deaths per year, while many others are killed intentionally. Small vessels using set net, demersal longline or pelagic longline represent most of the Mediterranean fleet and likely cause more incidental or intentional deaths than large vessels typically using bottom trawl or pelagic longline. When interactions, mortality, intentional killing, size (a proxy for reproductive value) and turtle populations are considered, results indicate that Mediterranean green (Chelonia mydas) and loggerhead turtles (Caretta caretta) are more affected (i) by fishing gears such as bottom trawlers, demersal longlines and set nets, (ii) by small-scale fisheries, and (iii) by fishing in the eastern basin. Although small-scale fisheries should be the priority target, available measures are easier to implement on the fewer large vessels. Moreover, these measures are few, and they are not implemented yet, while others should still be tested for the Mediterranean fisheries. Thus, measures for reducing captures or mortality through changing gear-specific characteristics may help, but probably a more holistic conservation strategy aimed to an ecosystem-based fishery management for a sustainable fishing would be the only solution for the long-term survival of Mediterranean Sea turtle populations and their habitats. Small-scale fisheries should manage marine resources, including turtles, in a responsible and sustainable way. Turtles may not only benefit from but can also help this process if their non-consumptive value is fully recognized. © 2010 Blackwell Publishing Ltd
Movement patterns of marine turtles in the Mediterranean Sea: a review
Full text linkUnderstanding the at-sea spatial behaviour of sea turtles is a priority for their conservation. In the present paper, the current information on the distribution and movement patterns of the two species breeding in the Mediterranean, the loggerhead and the green turtle, is reviewed, focusing mainly on the 195 published routes of satellite-tracked turtles. A satisfactory level of knowledge about adults’ migrations and other movements is reached only for loggerheads breeding at Zakynthos Island, Greece, and for green and loggerhead females nesting in Cyprus, while studies at foraging grounds are limited to loggerheads in the western and central parts of the basin. Adult males and females mostly show quite uniform post-breeding migratory patterns, typically moving towards individually specific neritic foraging grounds. A much higher variability is shown by loggerhead juveniles, which is probably associated with differences in their spatial behaviour while in oceanic or neritic waters. Evidence of seasonal migrations driven by lower temperatures in winter is available only for adult and juvenile loggerheads frequenting the two northernmost parts of the basin, i.e. the Ligurian and the northern Adriatic Sea. Current knowledge gaps and priorities for further research in the Mediterranean are discussed
The first "lost year" of Mediterranean sea turtles: dispersal patterns indicate subregional management units for conservation
No full textHow much sea turtle bycatch is too much? A stationary age distribution model for simulating population abundance and potential biological removal in the Mediterranean
Full text linkMediterranean populations of loggerhead Caretta caretta and green sea turtles Chelonia mydas are subject to several anthropogenic threats, with documented mortality from incidental capture in fishing gear. However, how such mortalities actually affect the populations is uncertain without an estimate of population size. We derived a theoretical demographic structure for each species in the Mediterranean, assuming a stationary age distribution in a stable population with constant proportions of turtles in each life stage, using distributions of age-specific vital rates. We incorporated uncertainty into the main vital rate parameters to identify a likely order of magnitude of turtle abundance in different life stages. Through this approach, we aim to (1) provide a rough estimate of all population stage classes, particularly the juvenile classes that are most subject to fisheries interactions, (2) provide an estimate of reproductive life span, (3) identify and review the key demographic parameters, and (4) identify the priority gaps in our information in need of further investigation. The range of population abundance estimates from the models constructed with uncertainty (95% CI) was 0.81-3.38 million loggerheads and 0.26-2.21 million green turtles, Mediterranean-wide. When we calculated the potential biological removal for the segment of the population at risk of fisheries capture, our estimates were comparable to or lower than the estimated bycatch levels in fisheries. Although the model assumes a stable population and provides only a rough estimate of abundance, these results suggest that the current bycatch level should be regarded as unsustainable for Mediterranean turtle populations
Age at size and growth rates of early juvenile loggerhead sea turtles (Caretta caretta) in the Mediterranean based on length frequency analysis
No full textGrowth rate is a fundamental parameter in understanding sea turtle population dynamics and is also important for the conservation of these threatened species. It can be influenced by both environmental and genetic factors, and thus it can vary according to the area. Growth rates and age at size of loggerhead turtles (Caretta caretta) are estimated for the first time in the Mediterranean sea and in particular for the elusive first period of life, through length frequency data from 88 turtles ranging from 6.4 to 30 cm curved carapace length found in Italian waters. A visual examination of the length distribution of small turtles found in pelagic habitats suggests a preliminary growth curve for early juveniles in the Mediterranean. Results indicate that this size range includes turtles in the first four years of life. Growth rates ranged from 11.8 cm/yr in the first six months of life to 3.6 cm/yr at the age of 2.5-3.5 years and are similar to those estimated from the Atlantic. Results also suggest a secondary increase in growth rates in larger turtles recruiting to neritic habitats, supporting a polyphasic growth pattern proposed for other populations and other sea turtle species
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
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