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An introduction to Mediterranean deep-sea biology* - page 25 / 32

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Management, perspectives and final comments

There is no specific regulation for deep-water fisheries in the central Mediterranean. For the trawl fishery, other technical measures, such as the cod- end mesh size (40 mm stretched, Ragonese and Bianchini, 1996; Bianchinni et al., 1998; Ragonese et al., 2001), are also in force and other effort restrictions are adopted in the various countries, such as the 45-day closed period in Italy and the four-month closed season (from June to September) in Greece.

No precautionary reference points have been defined until now for the deep-water shrimps A. foli- acea and A. antennatus. An increase in the size at first capture and a closed season during spring-summer are recommended in order to reduce fishing pressure on juveniles. The introduction of a larger mesh size than the present one (40 mm stretched) would appear to be feasible as part of the regulation of an almost mono-specific fishery targeting deep-water shrimps on the slope. Systematic studies on this demersal resource are mostly carried out as part of national research programs, such as GRUND for the Italian waters (Relini, 1998), and the international trawl sur- veys MEDITS (Bertrand et al., 2002) and COCTEL or DESEAS (Sardà et al., 2001, 2003).

We agree with the comments made by Merrett and Haedrich (1997) regarding the questions of whether the system would be capable of supporting the fishery as a top predator, how the system responds to the new predator pressure and whether this already highly adapted system has the capacity to adapt further.

The main authors of this book also agree that the deep-sea megafauna follow the K ecological strate- gy in the more abundant and possible commercial species. Moreover, the main species studied concen- trate the ovigerous females in the deepest grounds of their distribution range. The low fecundity and the low metabolic rates in a more stable environment represent a high vulnerability of these populations. According with Kostlow et al. (2000), most deep- water stocks are today overfished or even depleted. Depletion of species from deep-sea environments that dominate mid- to upper trophic levels may have long-term ecological implications, but the risk of reducing stock size and age structure to population viability, the potential for species replacement, and the impacts on prey and predator populations are not generally known. However, trawl fisheries have been shown to have potentially severe impacts on

the benthic fauna of seamounts where these fish aggregate. The deep-sea fauna, with a high level of endemism, suggests limited reproductive dispersal. The ability of the benthic community to recover fol- lowing its removal by trawling is not known.

Thus, considering these ecological characteris- tics, the failure of management of shallower fish- eries and the Precautionary Principle with regard to the lack of knowledge of these deep ecosystems, we recommend no commercial exploitation of depths below 1000 m.

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