Maritime activity includes fishing, mariculture, fish processing and fishery products. In poor countries, this activity is vital to feed the population, while developed countries encourage the consumption of seafood for the purpose of a healthy nutrition. The research part of this paper was conducted by the method of surveying fishermen on the island of Ugljan to obtain data on fish species and marine organisms caught, their quantity and fishing gear in the period since 1980, and to collect data on qualitative and quantitative changes in this sector of maritime activity. The aim was to gather as much information as possible about the qualitative and quantitative changes in fisheries and other marine organisms on the island of Ugljan. The data collected indicate that nets were used in all time periods and were the main tool used by fishermen. Respondents also pointed out the change in the size of target species that were larger in the past than today and the reduction in the presence of certain fish species in by-catches. The last twenty years have been mostly good catches of common two-banded seabreams (Diplodus vulgaris), mullets (Liza aurata), gilthead sea bream (Sparus aurata), common pandoras (Pagellus erythrinus) and bogues (Boops boops). None of the surveyed fishermen used accessories such as GPS, sonar, or radar to modify their fishing gear. The only changes that have been made are changes in the size and number of hooks. Research conducted on this topic tells us how to better manage and establish sustainable management of mariculture in the Republic of Croatia. An answer will also be given to the question of how important it is for the island of Ugljan itself to acquire and spread local ecological knowledge about the maritime fishing industry. Existing knowledge in the field of fisheries contributes to better management and establishment of sustainable fisheries management in the Republic of Croatia and this research will further highlight the importance of acquiring and disseminating local ecological knowledge about fisheries in the island of Ugljan to understand long-term changes in the ecosystem.