Pilkųjų ruonių apsilankymų dažnio Lietuvos pakrantėje ir poveikio žvejybos efektyvumui nustatymas remiantis žvejybos žurnalų duomenimis /

• Main Author: Jarmontovičiūtė, Gabrielė
• Format: Bachelor Thesis
• Language: Lithuanian; English
• Published: Institutional Repository of Vilnius University 2020
• Subjects: North Atlantic
• Online Access: https://repository.vu.lt/VU:ELABAETD193302208&prefLang=en_US

Grey seals (Halichoerus grypus) are large marine mammals, prevailing on the North Atlantic coast. There are no seal houl-out sites in Lithuania, however they migrate to the Lithuanian coast to following the fish. This is the main cause of a major conflict between seals and fishermen. The aim of this study was to determine the frequency of the Grey seal visits on Lithuanian coast and their impact on fishing efficiency based on fishing logbook data. The data of fish catches, fishing effort and seal observations during 2016-2019 was gathered from daily fishermen logbooks of 5 different coastal fisheries companies. The length (p < 0,01), the effort (p < 0,001) and the productivity (nets: p < 0,001; traps: p < 0,05) of the fishing gear were higher in those companies that fish in the north part of Lithuanian coast than companies fishing in the south. The efficiency of nets of the northern fishing companies was lower (p < 0,001), however there was no significant difference of efficiency in traps. Higher frequencies of seal visits have also been recorded in northern fishing companies, which used nets (p < 0,05). There was no significant difference in seal visits next to fish traps either. Seals were visible when there were 21% longer nets (p < 0,001), 19% higher effort (p < 0,001), 40% of lower efficiency (p < 0,001) and 22% of lower catches, although this indicator did not differ significantly. There was no relationship between frequency of seal visits and the fishing effort or wall length of fish traps per month, nor did seals have any significant impact on the fish trap productivity and efficiency. The frequency of gear use and seal visits were highest during the south-east wind direction (32 % of nets, 29,76 % of traps and 35 % of seal visits). The monthly frequency of seal visits was not affected by precipitation, air temperature or wind speed.