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Recent changes of Adriatic ichthyofauna:threat or benefit to local fishery

During the last ten years, there are frequent records of new fish species in the Adriatic Sea, as well as spreading and changes of distribution of species previously described only in southeastern Adriatic. Most of the new species are termophilic and has tropical origin. Dulčić et al. (1999) published list of 30 new termophilic species recorded in Adriatic during the last 25 years. Few species are of interest for local fishery, and among them; groupers of Epinephelus genus are of highest market value. The presence of new species in native Adriatic coastal fish communities will initiate changes, which could be either threat or benefit to local coastal fishery. The colonisation of groupers exhibits similar patterns, as with other termophilic species. Firstly, we observed a migration of adult specimens of dusky and golden grouper, events often reported by divers. After adaptation to conditions of new habitats, reproduction and recruitment of fingerlings started. However, reproduction and recruitment was unstable and different from year to year, as observed with E. marginatus and E.caninus in the water around Dubrovnik area (Glamuzina et al., 1999a). However, new intruders in Adriatic surely induce changes in autochthonous communities, especially coastal fish assemblages. Furthermore, their presence could potentially present a new fishing resource. This presentation will focus on present status of groupers of genus Epinephelus in Adriatic, changes of their distribution and abundance, and estimations of their influence on local fishery. Groupers are top carnivorous fish in food chains as well as among the biggest fish of coastal marine waters. They have a high market value and are object of intensive fishing efforts. Up to the nineteen's groupers were relatively rear in Adriatic, mostly distributed in southern part. During the last ten years, we observed many unusual events in their populations. Good recruitment of dusky grouper, Epinephelus marginatus, golden grouper, Epinephelus costae, and doogtooth grouper, Epinephelus caninus fingerling were recorded in some years, but also lack totally in other years. In the waters around Dubrovnik, we catch fingerlings of white grouper, Epinephelus aeneus, and this was the species first record in Adriatic waters (Glamuzina et al., 1999b). Changes in grouper distribution, abundance and colonisation of new areas would have a significant influence on autochthonous communities. Grouper juveniles inhabit shallow coastal rocky habitats representing competitors in food chain to many other important fish species. Adult specimens represent the biggest predators in coastal waters. New populations of different grouper species represent a new fishery resource and they rise values of coastal fishery. However, taking into account only few biological characteristics of groupers, such as growth, distribution, abundance, survival, feeding, predator-prey relationship and territoriality, we could estimate possible damage and benefit of these species on ecosystems and fishery. The growth of groupers in Adriatic is lower if compared to tropical populations of same or similar species. This means also that feeding frequency and quantity of consumed food is lower. I estimate, based on literature data and results of our aquaculture experiments (Glamuzina, 1998), that grouper of 3-kg weight consumed during its life around 30 kg of prey. The value of 3-kg grouper is approximately 30 US $. Secondly, we have to estimate value of consumed prey. According to literature the main grouper preys are octopus, fish and crustaceans, but the percent of each prey varies with habitats (Jardas, 1996). So, if octopus as a prey dominates in grouper diet, calculated value of prey is around (3 US $ per kg of octopus) 60 US $, which is fairly higher than grouper value itself. However, if the diet consists of fish, mostly of no economical value and interest (species from Gobidae, Blennidae or Serranidae families), than the value of grouper is higher and represents new benefit to local fishery. It is clear that these calculations don’t integrate many factors, which influence growth and survival of groupers and their prey, as well as properties of different coastal ecosystems. New investigations has to be initiated on ecology of new species in new habitats, to give a more precise and definitive answer about their status and benefit to local fishery.

groupers; changes in distribution

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