Studies of long-term effects on the marine environment have not been carried out, including damage to non-targeted species. Results of the devices are mixed, and they have proved ineffective in some circumstances, especially over the long term, while design improvements such as electric fences to keep seals from climbing into enclosures, gear modification to exclude certain species, and keeping aquaculture plants clean of dead fish have often been effective at solving the problem of keeping predatory species away.[1][5][3] Reports indicate that in contrast to the harassment devices, the deterrent devices have been very effective in dealing with cetacean bycatch.