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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.  

Between 2019 and 2022, trials using three different pinger models (Future Oceans 10 kHz, Future Oceans 70 kHz, and PAL Wideband) were conducted in Bulgaria during standard turbot (Scophthalmus maeoticus) fishing operations. Marine mammal bycatch was observed in  61% of all hauls. No significant difference in bycatch rates between active and control nets was observed in trials involving Future Oceans 10 kHz (17 trials) and 70 kHz (6 trials) pingers. However, a significant reduction (74%) in cetacean bycatch was recorded during the trials conducted with PAL Wideband pingers. 

Small cetaceans are by-caught in salmon gillnet fisheries in British Columbia (BC) waters. In Canada, there is currently no generic calculation to identify when management action is necessary to reduce cetacean bycatch below sustainable limits. The researchers estimated potential anthropogenic mortality limits for harbour (Phocoena phocoena) and Dall’s (Phocoenoides dalli) porpoises and Pacific white-sided dolphins (Lagenorhynchus obliquidens) using quantitative objectives from two well-established frameworks for conservation and management (the United States’ Marine Mammal Protection Act and the Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas), which are similar to some management objectives developed for marine mammal stocks elsewhere in Canada. Limits were calculated as functions of (i) a minimum abundance estimate (2004–2005); (ii) maximum rate of population increase; and (iii) uncertainty factors to account for bias in abundance estimates and uncertainty in mortality estimates. Best estimates of bycatch mortality in 2004 and 2005 exceeded only the most precautionary limits and only for porpoise species. Future research priority should be given to determining small cetacean stock structure in BC and refining species-specific entanglement rates in these and other fisheries. The approach offers a quantitative framework for Canada to meet its stated objectives to maintain favorable conservation status of cetacean populations.

Harbour porpoise (Phocoena phocoena) bycatch was significantly lower (p<0.01) in high-density Iron Oxide (IO) gill nets compared to control nets. There was no significant difference in the acoustic target strength of the IO and control nets, and both nets behaved similarly in flume tank tests. The authors conclude the reduction of harbour porpoise bycatch in the IO nets was a result of the mechanical properties of the nets.

The study tested the vocalization response of harbor porpoises (Phocoena phocoena) to two different acoustic pingers, the AQUAmark 100 (20-160 kHz) and the AQUAmark 300 (10 kHz). Trials in Scotland and Denmark found that the AQUAmark 100 resulted in a significant reduction of porpoise vocalizations at 0,200, and 400 meters distance from the pingers. The vocalization behavior reveal no signs of habituation. Studies of the AQUAmark 300 resulted in a significant reduction of vocalizations at 0m and no significant reduction at 300m. Additionally, at one station, habituation effects were found.

The study evaluated the reactions of a six-year old harbor porpoise (Phocoena phocoena) to a banana pinger (Fishtek Marine Ltd.) in a controlled experiment at the SEAMARCO Research Institute in the Netherlands. The banana pinger sounds were comprised of signal blocks (duration ~0.5 s), each containing four frequency components (8–125 kHz; peak 70 kHz). Sounds were played back at mean received levels of 83, 89, 95, 101, and 107 dB re 1 μPa. Behavioral responses, including increased respiration rate, jumping, and swimming faster and farther away from the source, occurred from 95 dB re 1 μPa. At sea, distances at which harbor porpoises are deterred by pingers will depend on environmental parameters influencing sound propagation. 

Threatened common bycatch species in the Baltic Sea and North Sea include harbor porpoise (Phocoena phocoena), common eider (Somateria mollissima) and velvet scoter (Melanitta fusca), as well as the non-threatened grey seal (Halichoerus gryphus) and harbor seal (Phoca vitulina). Interactions primarily occur in static net gear, such as gillnets and trammel nets, mainly used by coastal small-scale fisheries. Although technical bycatch mitigation methods are available for most fishing gears interacting with cetaceans and seals, measures focused on mitigating seabird interactions with gillnets are limited.

A monofilament gill net (267 mm stretched mesh, 10.5 meshes high, 10 mm braided float line with a foam core, twine diameter of 0.65 mm and a length of six nets at 120 m per net) was deployed in November 2019 at a depth of approximately 25 m off the coast of Cornwall (UK) during normal fishing operations. A single male bycaught porpoise (Phocoena phocoena) was recovered upon hauling the net. A multi-hydrophone passive acoustic monitoring system tracked the three-dimensional movements and acoustic behavior of the harbor porpoise, as well as a second animal that was in close proximity but did not interact with the net. The results indicated that the porpoises were foraging around the net prior to the bycatch event, that the bycaught animal lifted the net by approximately 7 m while entangled and that the two animals were potentially a social unit, with the surviving porpoise exhibiting unusual communication behavior for several hours after the bycatch occurred. Understanding behaviors prior to and during a bycatch event could significantly improve bycatch mitigation strategies in static net fisheries. 

Harbor porpoise (Phocoena phocoena) avoided an area around a non-lethal, experimental gillnet equipped with a pinger in British Columbia, Canada. In a separate experiment with gillnets in the Baltic Sea, pingers did not affect the catch of targeted herring (Clupea harengus).

This study investigated spatiotemporal patterns in harbor porpoise (Phocoena phocoena) bycatch rates in the Swedish gillnet fishery, including a first assessment of harbor porpoise bycatch along the Swedish south coast. Bycatch rates were higher along the southern than the western coast. Further, porpoise bycatch in the south likely is from the endangered Belt Sea subpopulation, rather than the critically endangered Baltic Sea subpopulation. The estimates also indicate a declining trend in the number of bycaught individuals, likely reflecting reduced gillnet fishing effort over time.