X hits on this document

PDF document

An introduction to Mediterranean deep-sea biology* - page 22 / 32





22 / 32

trip is 1-5 days. The fishery is carried out through- out the year. The catch consists of large specimens (100-200 k each one). The daily catch could be 1000 k. By-catch species are mainly Conger conger and Squalus spp. (Stergiou et al., 1996, 1997). However, these species have a negligible importance com- pared to those caught by deep-water bottom trawl- ing. Longliners are mainly distributed in the south- ern Adriatic fishing hake as target species between 200 and 400 m (De Zio et al., 1998).

The trawl fishing activities in the Greek Ionian Sea do not generally exceed 400-500 m in depth. The most commercially important species within this depth range are Merluccius merluccius, Mullus






Micromesistius poutassou, Parapenaeus lon- girostris and Illex coindetii. In deeper waters, fish- ing activities are limited and related mainly to the fishery of hake and wreck fish (Polyprion ameri- canus) with longlines, fishery of hake in summer with nets and fishery of bluefin tuna and swordfish with surface lines (Papaconstantinou and Stergiou, 1995; Stergiou et al., 1997). The fishery in deeper waters is limited (1) because of the inexperience of the fishers with working at these depths, (2) because the fishers do not know that there are important commercial stocks at these depths, and (3) because the price of the deep-water resources in the market is until now very low. Thus, the fishery in the Greek Ionian Sea is limited to the continental shelf, the sur- face of which is very narrow. Some Italian bottom trawlers are working in the international waters close to the Greek coasts of the Ionian Sea, espe- cially during summer when the weather is better and when the Greek trawlers are not working. Target species at depths of 400 to 800 m are A. antennatus, A. foliacea, N. norvegicus, M. merluccius, M. poutassou, T. lyra, H. dactylopterus and Scorpaena spp. The contribution of the two red shrimps in the total catch during sampling in the deep water project at depths of 300-500 m was 6% and at depths of 500-750 m 30%. A common conclusion of the research project that has been carried out so far is that A. foliacea is more abundant than A. antennatus (Mytilineou and Politou, 1997; Politou et al., 2003; Papaconstantinou and Kapiris, 2003). The discovery of new fishing resources in the deep waters of the Greek Ionian Sea is very important. As a result, the area in which the fishing effort is exercised will be extended and the production will increase. The already known biological resources could be less exploited and new socio-economic perspectives for

28 F. SARDÀ et al.

the inhabitants will arise (Papaconstantinou and Kapiris, 2001, 2003).

The Deep-sea biocenosis

Among the habitats affected by the deep-water fisheries in the Mediterranean, the biocenosis of the bathyal mud is the most widespread and two facies can be distinguished: a) that of the viscous mud with a very fluid superficial layer characterised by the big sea pen Funiculina quadrangularis and the crus- taceans Parapenaeus longirostris and Nephrops norvegicus; b) that of firm and compact muds char- acterised by the cnidarian species Isidella elongata and Actinauge richardi, the crustaceans Aristeus antennatus, Aristaeomorpha foliacea, Plesionika edwardsi, Plesionika martia, Munida intermedia, and the cephalopods Sepietta oweniana, Neorossia caroli and Pteroctopus tetracirrus. Within these two facies the strictly benthic species Funiculina quad- rangularis and Isidella elongata have almost com- pletely disappeared from the trawlable bottoms of the most Mediterranean areas, except in a few limit- ed zones (e.g. Malta bottoms).

The western Mediterranean is characterised by a narrow and sinuous shelf grooved by deep subma- rine canyons and channels between islands frequent- ly reaching more than 1500 m depth. The muddy substratum is affected by frequent slide processes near the margins of canyons. These structures sup- port different species of fish and invertebrates with life cycles adapted to space-temporal processes linked to these geomorphological structures. Due to the frequent trawling in these regions, no specific biocenosis can be defined. However, when experi- mental hauls are performed in virgin grounds, Issidella elongata appears in high quantities. The same species named in the previous paragraphs are also found at this depth.

On the bathyal ground of the northern Ionian Sea a broad biocenosis of white-corals has been identified at depths between 450 and 1100 m (Mastrototaro et al., 2002; Tursi et al., 2004). Living colonies of the branched species Madrepora oculata and Lophelia pertusa with the solitary species Desmophyllum cristagalli were found. The calcareous clumps are made up of white and living branches at the top and dead darkened corals at the base. The epibiotic fauna is dominated by sponges, bivalves and poly- chaete worms. This biocenosis, which provides refuges for marine fauna, is vulnerable to the

Document info
Document views74
Page views74
Page last viewedThu Dec 08 00:34:30 UTC 2016