The impacts of an oil spill on fisheries and mariculture activities can be categorised as direct or indirect. Direct impacts can include contamination of the boats and gear used in catching or cultivating marine species. Damage to stocks as a result of toxic or smothering effects of the oil would also be considered a direct impact. In a few cases, the physical interaction of species with oil can result in mortalities.
Indirect impacts can be observed through the interruption of fishing activities due to the presence of oil or clean-up operations.
In some cases, in order to preserve market confidence and to protect fishing gears, fishing or harvesting bans may be imposed or voluntarily implemented. In other cases, although less commonly, fishing and harvest bans are imposed as contamination in seafood exceeds acceptable limits.
When a fishery has reportedly suffered losses following a spill, in order to facilitate the compensation process, all damages will need to be documented and where possible supported by evidence. This will often require rigorous scientific sampling and analysis. Nevertheless, even where scientific approaches are taken, it is often difficult to separate the effects of an oil spill from other factors, eg over-fishing and industrial pollution. Therefore, in order to make the best assessment of damages caused by a spill, it is necessary to make comparisons of the post-spill recovery with the pre-spill status of the fishery.