Untitled - CNR

Marine research at CNRranean coasts. Over 30,000 captures peryear are estimated mainly in coastal areasof Tunisia, Libya, Greece, Turkey, Cyprus,Croatia, Italy, Morocco, Egypt, France[13], Figure 2. Juveniles are frequentlycaught nearby nesting areas in Greece,Turkey and Cyprus. [28] reported thatin Mediterranean French coast loggerheadsea turtles are mainly captured with trammelnets and bottom trawl.Very little information is available forpelagic pair trawl, even if in the NorthAdriatic an annual estimate reports thatabout 1,550 turtles per year are caught accidentally[29] with all turtles released alive.The purse seines seem to represent a minorproblem.3 Technical parametersaffecting turtle bycatchandLoggerhead sea turtle bycatch strongly dependson different parameters. The mostimportant factor is the fishing effort: numberof vessels, engine power, Gross Tonnage,time at sea, dimension of the gears(length, high etc). The mortality ratelargely depends on gear type, practices onboard before and after the catch and on capabilityof surviving to forced apnoea.In the longline technical details of hookscan be defined by: shape, dimensions, material(steel, inox), point (with barb or not),shape of eye flat or twisted (Figure 3).In the hooking process, the most importantparameters are: the overall hook width,which can be correlated with turtle mouthdimension, its gap, which ensures deeperpenetration of the point and better holdingpower of the fish, its shape which can influencethe hooking position.The direct mortality induced by longlinesappears to be low (Table 1) but the delayedmortality, widely unknown, is suspected tobe very high. The low direct mortalitycan be justified by the fact that the hookedturtles maintain enough power to raise thelines to the surface and to breathe. Thepost-release mortality strongly depends onthe hooks position in the digestive tract. Inparticular, if the hook is swallowed in thelower oesophagus or in the stomach the turtlehas a very low chance of surviving. Onthe contrary the mortality of turtles with ahook in the mouth or higher oesophagusseems to be less important, even if a hookin the mouth could compromise the feedingperformance [22]. Studies made by rescuecentres showed a high post-release mortality,both in the short- and in the long-term.The parameters barb size and hook lengthcan affect the capacity of the turtle to disengage:some studies showed that the useof barbless hooks implied a small reductionin unhooking time, leading to an improvementof survival rate.In addition to the hook, the branchlines,which is the piece of line attached to thehook, can easily cause turtle death aftermany days, especially if it is long enoughto be affected by intestinal peristalsis [30].Unfortunately fishermen are used to cut thebranchline from the deck, while the turtle isstill in the water, leaving lethal branchlineslonger than 1 m. Albacore and bluefin tunalonglines generally produce higher directmortality than swordfish longlines. This isprobably because of the gear structure andhook size but it could be also due to thefishing depth or to the distance from thecoast. Turtle mortality could be stronglyaffected by the depth of the main line setting.Loggerhead sea turtles spend most oftheir time at less than 40 m and they do notdive deeper than 100 m. Thus the main1843