Changing habits and foreign immigrants

Ichthyologists have mapped the most important spawning grounds for fish on the shores of the Thracian Sea, especially east of Lake Vistonida. The Kavala Gulf is regarded as an important breeding ground for red mullet, while juvenile anchovies swarm in the shallows of the Thermaic Gulf. None of these breeding areas, researchers noted, lie near river mouths that are considered polluted. Instead, they are found on the edges of such areas, where the effects of pollution are lessened and the water is rich in nutrients. In such areas, biologists say, the sea pulsates with life. These areas lie off the Pieria coastline and in the eastern part of the Gulf, near Poseidi, Halkidiki. Changes in fish habits, such as those of the swordfish, because of rising temperatures, have predictably changed catches. Professional fishermen in the Toronaic Gulf have seen more variety in their nets. Among the species that have invaded Greek waters through the straits of Gibraltar and Suez – probably due to rising water temperatures – is one fish, dubbed lagos by local fishermen, that has come right from the tropics. A small, non-commercial fish, it has been found in small numbers by MEDITS teams in the northern Aegean. «We might not have direct measurements of the degree of changes in water temperature, but through the species we catch, we can see that species distribution is changing,» Kallianiotis said. Inevitably, species that are vulnerable to temperature increases such as sardines (one of the most nutritious fishes for human beings), Atlantic and chub mackerel are adversely affected. The changes observed have made specialists revise previous views that overfishing is responsible for a sharp decrease in some species, an attitude which had laid all the burden on the shoulders of fishermen. «In managing fish stocks, the environmental aspect must be factored in, although we need more studies before we have a complete picture,» Kallianiotis concluded.