CROATIAN FAUNA 2007 - CRABS - LOBSTER

Lobster (Palinurus elephas Fabricius) Lobsters belong to the family Palinuridae or spiny lobsters (from the genus Palinurus – long-tailed or spiny lobsters). They are distributed from Norway on the north, along the western coast of Ireland, the western and southern coast of the British Isles (to the north up to the Orkney Islands and Shetland Islands), to the south to the Azores, in the western Mediterranean and the Adriatic Sea and the Aegean Sea. They can be found in the open deep-sea rocky bottom in the circa-littoral and infra-littoral zone (below the sub-littoral zone of the tide) at the depths of 5 to 70 metres, but they could be found at greater depths, up to even 160 metres. It is known that they actively migrate in the course of the year into greater depths of the Atlantic to return to the shallower parts of the -coastal area. It has been recorded that they start for the deeper regions at the end of the year and return in spring, so it can be assumed that the migrations are linked to the temperature change of the sea. In females the migration is linked to the developmental cycle of the maturing of their eggs – the females return in spring to the shallow waters before the eggs start hatching. The fecundity of females depends on their size – larger females produce more eggs. The recorded values for the researched populations in the western Mediterranean range from 23,000 to 202,000 eggs. The spawning takes place from late summer to winter, depending on the geographical position of the population. Four weeks before the spawning a special molting takes place. When the female is ready for the spawning, it produces or sends special sounds called stridulation that attract the males. The male deposits spermatophores, small capsules of spermatozoa, below the sperm duct on the female. Ten days later the female casts out her eggs,”tearing” with the “pincers” of the fifth pair of her walking legs the spermatophore and thus facilitates impregnation. The incubation of eggs in the Atlantic population lasts about nine months, while in the Mediterranean it lasts only five months owing to the higher temperatures of the water. From the eggs larvae are hatched that live on plankton for 5 to 6 months. The larvae go through a metamorphosis in the course of which they molt, grow, change and slowly develop into adult lobsters. The body of adult lobsters is covered with a thick shell, an exoskeleton. The adult samples have the total length of between 40 to 50 cm, (maximal length up to 60 cm), and weigh between 6 to 8 kilos. The males are usually larger than the females. They do not grow continuously but through molting, which means when they lose their rigid shell and while their body is soft they grow in length and then their shell gets rigid again. The increase in length per molting comes up to between 2 to 14% of the lobster’s length. In older lobsters that have come close to their maximal length, the increase in length in the course of molting is slowing down. The increase also depends on the climate, i.e. the water temperature, so that specimens in warmer waters grow faster. Spiny lobsters are similar to the European lobster, (Homarus gammarus), but in contrast to them do not have claws, and their back antennae are very long, longer than their bodies. The shell is usually orange above, with darker long and strong thorns -rostella directed forward, while underneath it is light-coloured (white), but there are red-purple and brown specimens recorded as well. They walk along the sea bottom but can also swim. They are omnivorous though their diet is mainly based on brown bullhead, mollusks (snails and shells), shrimp larvae, invertebrate, Pentapora fascialis and seaweed. They are social animals, gathering in groups, but their mutual social contacts have so far not been sufficiently researched. They can often have Marifugia cavatica (featherhead), shells, Pentapora fascialis and Rayed Mediterranea limpet fastened onto them. The numerosity of the population has been significantly decreasing which becomes obvious from the data about the decreased fishing results and the average smaller length of the caught lobsters. The reasons for this are numerous, from excessive uncontrolled fishing out to the changes of the ecological conditions in their habitats.