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Monkfish (Lophius sp.) in the US mid-Atlantic and northeast are targeted through sink gillnets that also capture Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). Large-mesh gillnets are required to fish seasonally using tie-downs as part of the Harbor Porpoise Take Reduction Plan. This study looked at the effects of tie-downs (control: 12 meshes x 30.5 cm stretch mesh with four mesh tie-downs, experimental: same, no tie-downs) on Atlantic sturgeon and marine mammal bycatch. Atlantic sturgeon bycatch (CPUE) did not differ between gillnet configurations. The experimental gillnets without tie-downs significantly decreased monkfish landings and resulted in common dolphin (Delphinus delphis) mortalities.       

This study characterizes bycatch of marine mammals in fisheries that export fish to the United States of America from Ecuador, and identifies opportunities for collaboration on bycatch mitigation. The marine mammal species reported most frequently as bycatch were the humpback whale (Megaptera novaeangliae), bottlenose dolphin (Tursiops truncatus) and common dolphin (Delphinus delphis). Most interviewees indicated that the mammal bycatch rate has remained unchanged or increased over the last five years.

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 the effect of acoustic pingers on the behavior of Burmeister's porpoise (Phocoena spinipinnis) in the vicinity of the Peruvian small-scale driftnet fleet. Over a 4-yr period (2009-2012), 116 control (without pingers) and 94 experimental (with pingers) fishing sets were observed, and porpoise acoustic activity around nets was recorded using passive acoustic loggers (C-PODs). In regions of preferred habitat associated with cooler (17-18 C), shallow waters (within the 100 m. isobath), the use of pingers lead to an 86% reduction in porpoise activity around nets. The results suggest that pingers are likely to be effective at deterring Burmeister's porpoises from fishing nets, and given the vast capacity of this and other fleets in the region, may substantially reduce mortality.

Researchers used data from long-term cetacean and fisheries monitoring programs in the Santos Basin of Brazil to assess the spatial overlap between cetaceans and gillnet fisheries, identify areas of high potential bycatch exposure, and determine the relative susceptibility of cetacean species to these interactions. Gillnet fisheries concentrate primarily along the continental shelf, overlapping the most with Guiana dolphin (Sotalia guianensis), Franciscana (Pontoporia blainvillei), and bottlenose dolphin (Tursiops truncatus). The Guiana dolphin and the Franciscana appear particularly vulnerable due to their conservation status and habitat use. Researchers also identified priority areas for bycatch risk assessment and management, including a region of high cetacean diversity. 

A cumulative impact analysis framework integrating species habitat suitability and fishing effort data, stratified by gear type, was used to assess bycatch risk for threatened and protected species in China's seas and adjacent waters. Across all taxonomic groups examined, including seabirds, sea turtles, marine mammals, elasmobranchs, bony fishes, and benthic invertebrates, the highest bycatch risk was concentrated between 23°N and 25°N. For marine mammals and sea turtles, elevated risk was concentrated along China's southeastern coast, extending through inshore waters from the Yangtze River Estuary south to 20°N, with trawls and gillnets contributing most significantly to risk. Seabird bycatch hotspots were primarily located around islands, bays, and estuaries north of 20°N, where gillnets posed the greatest threat. Elasmobranchs experienced high bycatch risk from the Taiwan Strait to the Yangtze River Estuary and around Jeju Island, and were the most vulnerable taxa group overall. Bycatch risk for benthic invertebrates was largely restricted to narrow nearshore areas and was associated primarily with dredging activities. The study also found that marine protected areas generally exhibited lower bycatch risk than surrounding waters.

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.