Extended abstract

The fishery approach

Most living marine resources are exploited on the continental shelves at depths of less than 400 m, but in recent years deep-sea fisheries have been developed all over the world. Traditional trawl and long-line fisheries capable of reaching depths down to nearly 1 000 m have been operating in the Mediterranean Sea for many years. These fisheries target both shrimps as well as hake and sharks. In this situation, we might ask ourselves the significance of the development of a deep-water fishery in terms of sustainability. It is clear to me personally that this has to be regarded as a failure on two fronts: 1) management and control of fisheries on the continental shelf and 2) application of the precautionary approach to the exploitation of all resources.
If coastal resources were not overexploited, economic yields high, and fishing effort properly distributed, then there would surely be no need to seek out deeper fishing grounds. The two concepts of sustainability and economic development are diametrically opposed, and it is hard to achieve a balance between the two. There is much talk about sustainability, but this concept and the precautionary approach are never actually implemented, indeed quite the contrary. Are deep-sea resources really exploitable in the Mediterranean? How does fisheries exploitation affect deep-sea systems? What do we really know about deep-sea resources and their connections to the coastal zone? Are management policies for the Mediterranean actually in place and/or are they the right ones? To what extent should fisheries management policies impede the development of a given industrial sector? The answers to these questions may well be more political than biological, but the scientist's role is to expand our understanding in the hope that it will be put to use for the good of the resources.

Deep-sea resources

Based on our general knowledge of deep-sea species, the following populational features may or may not be universal: the sea bed is inhabited by generally slow-growing species that are less dependent on the production blooms that occur closer to the surface; these species tend to be more specialized feeders, in part because of their morphological and functional adaptations to great depth, low light levels, and low food availability; populations have lower densities and communities less diversity. These environments can be said to be more stable than the coastal environment, which means that they are less able to recover from anthropogenic disturbances. Such a situation makes these environments and populations especially vulnerable to exploitation and recovery more difficult. On the other hand, they have the advantage of covering broad expanses, which will help offset initial exploitation for a time. Still, there are major exceptions, both local and with respect to depth. The most important deep-sea species in the Mediterranean are, for crustaceans, the shrimps and crabs Aristeus antennatus, Aristaeomorpha foliacea, Plesionika sp., Acanthephira sp., Geryon sp, and Paromola cuvieri; for fishes, mainly Alepocephalus rostratus and Trachyrynchus trachyrynchus along with certain species of sharks. These species may attain high biomass levels, which could mean that some will constitute resources attractive to fishermen, and indeed some already are. In point of fact, construction of trawlers capable of working depths below 1 000 m is now starting to get under way.

Aristeus antennatus: an example

A specific example will be helpful in demonstrating the importance of these resources and their role in the system, a good example being the deep-water red shrimp Aristeus antennatus. Certain aspects attaching to this species can be extrapolated to other species. The red shrimp is a highly eurybathic decapod crustacean species inhabiting a depth range running from 80 m to 3 300 m in the Mediterranean. This is in itself a highly singular characteristic, though many deep-water species are also quite eurybathic. According to the current state of knowledge, in the western Mediterranean the densest shoals of this shrimp can be found at depths between 400 and 900 m on the middle and lower slope. There is evidence of extensive spatio-temporal migrations by this species at these depths, connected with bottom geomorphology (submarine canyons). At this time the precise role of submarine canyons in the dynamics of marine species as a result of their geomorphology and their ability to concentrate certain energy phenomena, matter flows, and hydrographic flows has yet to be explained. Information is available for only a small part of this species' distribution range. What happens below 900 m? The resource decreases down to around 1 500 m, where there are indications of a sharp rise in biomass. Below that depth it becomes increasingly scarce and ceases to be found at depths below 3 300 m. If a resource's distribution and abundance are taken to depend on the energy available in its habitat to enable it to complete its life cycle successfully, a eurybathic species' adaptation to each of the systems it colonizes should give rise to different population structures. This effect has been demonstrated in Plesionika in the correlation of the distribution of juveniles and mature females with the presence of nepheloid layers at certain depths. There is also reliable evidence that the population structure (size range, density, and sex ratio) of Aristeus antennatus also varies in time and in space as well as with depth.

Perspectives for study

Thus, the deep sea zone in the Mediterranean exhibits certain special structural features, e.g.: submarine canyons that form an important link between the coastal zone and the deep sea zone; the existence of bathyal basins (western, central, and eastern Mediterranean and Black Sea) relatively isolated from each other; and depth zonation affecting community diversity. The upshot of this is that a) many resources may be distributed over the bottoms of the basins, thereby linking different populations more or less subject to coastal influences (metapopulations), and b) currents play a role in larval drift and recruitment, which at the same time are also linked to the swimming ability of the resources (gene flow). This means that from a global perspective deep-sea resources may be looked upon as being shared to a much greater extent than coastal resources, not just because they can be exploited outside the territorial jurisdictions of the different countries but also because they make up a continuous biomass between coastal zones connected by the bottom. Furthermore, weather phenomena and sedimentary events have been shown to exert a relatively fast influence on deep-sea populations, which suggests that deep-sea systems are by no means unaffected by climate change, despite their deep-water distributions.
Still, by way of a general observation, the individual deep-sea basins and the fauna they contain are nonetheless relatively isolated in terms of their energy characteristics (e.g., oligotrophic differences with longitude). For one thing, there are both biogeographical differences and differences in fauna among them, and these differences are obviously much more pronounced as compared to the Atlantic and the Red Sea. These differentiating aspects, when combined with the higher level of ecological stability in the deep sea zones and the fact that their more or less isolated populations are less able to replenish themselves, make clear the greater vulnerability of these zones in the Mediterranean as areas receiving high inputs of both terrestrial and air pollution.

Some reflections

"If we talk about sustainability, it is because the equilibrium has already been disrupted. If we talk about the deep-sea zone in the Mediterranean, it is because exploitation of that zone has already begun."

"Are we truly interested in acting in accordance with the precautionary approach? If so, we should not waste time discussing how curbing the exploitation of marine resources slows development and costs jobs. We should first address the scientific and moral issues, then we can work on the economy (modified and rewritten from Tiziano Terzani: Letters against the war)

"Is a multidisciplinary approach truly as beneficial to resource management as it is to scientific knowledge? Ultimately, who really ends up giving way in resource management agreements?"

BIBLIOGRAPHY

Childress, J.J.-1995. Are there physiological and biochemical adaptations of metabolism in deep-sea animals?. Tree, 10(1):30-35.

Féral, J.-P., J.-G. Ferrand and A. Guille. - 1991. Macrobenthic physiological responses to environmental fluctuations: the reproductive cycle and enzymatic polymorphism of a eurybathic sea-urchin on the northwestern Mediterranean continental shelf and slope. In Particle fluxes and ecosystems response on a continental margin (Monaco, A., P.E. Biscaye and P. Pocklington, Guest editors). Cont. Shelf Res. 10 (9-11): 1147-1155.

Gage, J.D. and PA Tyler.-1991. Deep-sea Biology. Cambridge University Press. 504 pp.

Merrett, N.R. and R.L. Haedrich.-1997. Deep-sea Demersal Fish and Fisheries. Chapman and Hall. N.Y., 282 pp.

Sardà, F., J.B. Company and F. Maynou.-2002. Deep-sea shrimp Aristeus antennatus Risso 1816 in the catalan sea, a review and perspectives. NAFO Journal of Northwest Atlantic Fishery Science, 31:1-10.

Tselepides A., and T. Polychronañi.- 2000. Pelagic-benthic coupling in the oligotrophic Cretan sea. Prog. in Oceanogr. 46 (2-4): 480 pp.