Stocking results of spray-marked one-summer old anadromous European whitefish in the Gulf of Bothnia

• Published in: Annales zoologici fennici 2004, Vol.41 (1), p.171-179
• Main Authors: Leskelä, Ari, Jokikokko, Erkki, Huhmarniemi, Alpo, Siira, Antti, Savolainen, Heikki
• Format: Article
• Language: English
• Subjects: Age groups; Anadromous fishes; Animal age determination; Aquaculture and stocking; Colors; Fingerlings; Fisheries; Freshwater fishes; Gill nets; Marine; Quarks; Whitefish
• ISSN: 0003-455X; 1797-2450

About 6 million one-summer-old, fluorescent pigment marked whitefish were released in the northern and central parts of the Gulf of Bothnia in 1995—1998. Growth and dispersal of the stocked fish were followed by detecting and recording marked whitefish in samples from the professional fisheries catch during 1999—2002. The yield produced by stocked fish was estimated by assuming that the proportion of the marked fish in the total catch was the same as in the samples. The total yield from the stockings in 1995 was estimated to be 55—90 kg/1000 released fingerlings. A better result from the stockings could be achieved by increasing the recruitment size in the fishery. Even for the 1995 stockings, a few of the released fish were probably still migrating in the sea at the end of the study period, although the main part had already been caught. For fish released in 1996 or later, no exact estimates of total yield can be given, as a considerable part of the catch was still to come. The estimates from the preliminary re-catches, however, suggest that the stockings in northern parts produce lower catches than stockings in central parts of the Gulf of Bothnia.