Search The Database

Documented entanglement cases for sea turtles and cetaceans in mussel aquaculture gear worldwide were collected. Online surveys and semi-structured interviews with mussel operators were used in Iceland. A total of seven entanglement reports were collected, four baleen whales, one harbour porpoise (Phocoena phocoena) and two leatherback sea turtles (Dermochelys coriacea). Mussel spat collecting ropes were involved in the majority of cases. Out of the seven reports, two occurred in Iceland. The proximity between cetacean distributions and mussel farming sites is likely a factor in these interactions. In addition, in Icelandic summer spat collection occurs when the largest concentrations of cetaceans are found in its waters. Iceland should consider some sort of mandatory reporting system for these interactions.

Field testing was conducted in the lower Bay of Fundy, Canada, during 1996 and 1997 to determine the effectiveness of acoustic alarms (Netmark 1000) in reducing bycatch rates of harbor porpoises (Phocoena phocoena) in gillnets. Alarms were spaced 100 m apart along the gillnet float-line. There was a 77% reduction in bycatch of harbor porpoises in nets equipped with alarms compared to those with no alarms. There were no significant differences in catch rates of target species, Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus) and pollock (Pollachius virens). 

Four commercially available pingers (AIRMAR, Aquamark 100, Fumunda, Save Wave Saver) were tested on vessels operating in Cornwall targeting hake (Merluccius merluccius) with gillnets. Pingers were tested for their effectiveness at reducing incidental interactions between the gillnets and porpoises (Phocoena phocoena). Only one of the four tested pingers, AIRMAR, performed 'satisfactorily' (i.e. suited for offshore gillnet fishery). 

The impact of Medina panels attached to tuna purse seine nets operating in the US fishery was investigating for their effect on porpoise mortality. Medina panels are reduced mesh size netting hung from 2-inch mesh webbing on the purse seine. The authors took measurements of penetration of porpoise snouts and flippers through mesh openings of 2, 1 7/8, 1 1/2 and 1 inch to determine the potential reduction in porpoise entanglements. Even the smallest-sized porpoise could not fit its snout through the 1 inch panel, even with its mouth closed. Recent tests of porpoise 'aprons' and 'chutes' could be promising in making these small mesh panels compatible with tuna purse seine performance.

The experiment evaluated the effectiveness of two types of pingers (Aquamark 100 and Aquamark 200) to reduce the bycatch rate of harbor porpoise (Phocoena phocoena) in a set gillnet fishery in the Black Sea. The study also evaluated the effects of the pingers on catch of target and non-target fish species. There was no significant difference in catch of target and non-target fish species in trials with pingers versus control sets. There was also no significant difference between number of harbor porpoises caught in nets using pingers and when no pingers were used, although a low overall number of porpoises were caught (eight harbor porpoises were caught during the experiment – three in control nets, three in nets using the Aquamark 100, and one in nets using the Aquamark 200). 

Pearl Nets, a passive acoustic deterrent, were tested in commercial gillnet fisheries in the Western Baltic Sea. Compared to a control, the Peal Nets reduced harbor porpoise bycatch and maintained target catch rate for Atlantic cod.

This study investigated harbor porpoise (Phocoena phocoena)  bycatch in bottom gillnets and trammel nets targeting turbot (Scophthalmus spp.) in the Black Sea between 2019-2021 via independent observers, questionnaires and stranding data. Cetaceans were caught on 55% of trips, and most were harbor porpoises. The study confirmed that bycatch is the most serious and immediate threat to the Black Sea harbor porpoises, with as many as 16,200 individuals caught annually. 

The authors evaluated factors influencing marine mammal bycatch in static net fishing operations in the UK between 1996 and 2023. Since 2014, harbour porpoise (Phocoena phocoena)  bycatch has been decreasing while common dolphin (Delphinus delphis) bycatch has been increasing; grey seal (Halichoerus grypus) and harbour seal  (Phoca vitulina) bycatch has been increasing gradually across the time period. Influential factors included seasonal patterns, water depth, and level of fishing effort. 

An analysis of records of static net bycatch sampling in the United Kingdom from 1996-2023 found that use of acoustic deterrent devices (ADDs) reduced harbor porpoise (Phocoena phocoena) bycatch per haul (BpH) to 0.23 of the background rate. BpH increased for harbor seals and grey seals (Phoca vitulina and Halichoerus gryphus) when ADDs were used. Current efforts to reduce harbor porpoise bycatch may be increasing seal mortality in the same fisheries. 

Three types of acoustic deterrent devices were tested in the Icelandic cod gillnet fishery:  Fishtek Banana pingers, Porpoise ALert devices (PAL), and wideband PAL (wPAL) with a modified pinger signal (PAL device emitting a wideband pinger signal with a frequency range of 20 – 160 kHz and signal duration of 0.3 s (every 4–30 s) with the same source level at 145 db and maximum depth (320 m)). Banana pingers and PALs did not demonstrate any reduction of bycatch of marine mammals, while the wPAL-equipped nets had no bycatch during the trial. Fish catch and overall commercial value was significantly reduced in gillnets equipped with banana pingers and PALs.