| Summary: | Marine based salmon aquaculture inputs large amount of organic material into the surrounding environment. This organic material is mainly composed of uneaten salmon feed and faeces. This material often accumulates in the environment under the cages. In Iceland there is no data on organic output coming from aquaculture nets and sparse data on the impacts of accumulation of this organic material. This study will be the first in Iceland to look at the amount of organic material that accumulates under salmon cages and areas of greatest accumulation. Six sediment traps were used to sample sediment underneath two salmon cages in Fossfjördur Iceland Three were placed 20 m from the cages and three were placed 0 m from the cages. The trap contents were then dried, weighed, and placed into a sodium hypochlorite solution in order to dissolve organic material. After organic material was dissolved samples were dried and weighed to determine how much of the original dry weight was organic. Traps that were closest to the nets (0 m) had greater organic content when compared to traps that were father from nets (20 m). Traps that were down current also collected greater amounts of organic material when compared to traps up stream. This spatial trend was linked to deposition rates of feed pellets settling in a closer proximity to cages whereas faeces dispersed farther. Throughout the study period the overall trap organic material increased. This temporal trend was linked to the increase use of feed pellets as the fish grew throughout study. This study was the first study of its kind in Iceland and aims to provide baseline data into organic output and accumulation occurring underneath salmon cages. The methods used in the study can also be utilized as a tool for management and the development of a monitoring program. This data shows that there is an opportunity for further research into mitigation and management of this issue in order to try and reduce the impact of organic accumulation.
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