| Abstract [eng] |
Abudance, biology and ecology characteristic of Twaite shad (Alosa fallax (Lacèpéde)) in ecosystem of Curonian Lagoon Toma Žemgulytė Vilnius university SUMMARY The abundance of twaite shad in the Curonian Lagoon has been steadily increasing since 1994. According to investigations made by net set with different mesh sizes (Neuman et al., 1997), the total amount of twaite shad migrating to the Curonian Lagoon reached 250–400 thousands individuals every year in 2003–2007. The most intensive migration was observed in May–June. The spawning was most intensive in the depths 1.5–2.5 m. Like other, by way of feeding twaite shad is attributed to zoophages with eyesight dominated. Whereas mature fish during pre-spawning migrations and accumulations majority almost do not feed. Twaite shad was feeding mainly on zooplankton (54.7 %) and chironomids (39.6 %). Fish, mainly roach, made only 5.7 % of food composition. The body length of twaite shad females varied from 34.5 to 51 cm, the most common body length ranging from 41–47 cm (L). The body length of males varied from 29 to 49.2 cm, males in the body length range 35–45 cm prevailing. In experimental catches females reliably differed from males in greater mean length, weight and age. These differences became apparent as males most often reach maturity a year earlier than females. The dynamics of age structure of twaite shad in different years indicates the stability of twaite shad population. Recomendation - To ensure further growth in twaite shad abundance, it is recommendable to enhance their protection on their main spawning grounds and migratory routes as well as reduce the pollution of the lower reaches of the Nemunas river and in both (Lithuanian and Russian) parts of the Curonian Lagoon. |
