Kvalitativ og kvantitativ inventering av fiskesamfunnet i Ytre Oslofjord : En beskrivelse av diversitet og generelle trekk ved fiskesamfunnet i Færder- og Ytre Hvaler nasjonalparker for perioden 2017-2019.
MetadataShow full item record
Original versionSkjæveland, S. B. (2020) Kvalitativ og kvantitativ inventering av fiskesamfunnet i Ytre Oslofjord : En beskrivelse av diversitet og generelle trekk ved fiskesamfunnet i Færder- og Ytre Hvaler nasjonalparker for perioden 2017-2019. (Master's thesis). University of Agder, Kristiansand.
A three-year study was performed annually from 2017 to 2019 in Færder- and Ytre Hvaler national parks located in outer Oslofjord. Data collection was conducted in shallow- and deep water habitats using catch-based methodologies in 2017 - 2019 (eel fyke net and trap) and visual methodology (stereo-video)in 2019. In the period of study, a total of 9733 individual fish were recorded among 37 species from 19 families. Shallow water fish assemblage (1 - 10 m) sampled by fyke net was dominated by a selection of wrasses (goldsinny wrasse and corkwing wrasse) and small, stationary species of non-commercial importance. Sampled by trap at deeper habitats (10 - 30 m), flounders dominated the total catch by 87 %. As well as the goldsinny wrasse, high numbers of commercially important mobile predatory fish (cod, saithe and whiting)were recorded by stereo-video. Goldsinny wrasse and corkwing wrasse by fyke net were species with highest relative abundance and consistently high density. At deeper habitats, common dab (trap), goldsinnny wrasse and cod (stereo-video) were species with high relative abundance and density. Temporal differences in composition of the fish assemblage were not documented. Density of fish was significantly higher in 2018, with high input by wrasses. A negative 91.3 % difference in percent occurrence was evident for cod in the study period. Positive differences in percent occurrence were observable in some mesopredators (five-bearded rockling, black goby and shorthorn sculpin). Stereo-video was considered a useful alternative to catch-based methods as the methodology recorded highest species richness, diversity and density of fish. With the exception of density, where density was significantly higher in Færder national park by trap and stereo-video, no further significant geographical differences between the national parks were detected. An increased diversity with increasing depth was documented for stereo-video and trap. A variety of cod-sizes was recorded by stereo-video, while catch-based methodology mainly sampled larger individuals. Variable catchability by extractive methodologies, size-selectivity and seasonal variation were considered essential factors for the study's results.
Master's thesis in Coastal ecology (BIO501)