Search The Database

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 retrospective analysis evaluated how mitigation measures in Hawaii (U.S)'s shallow-and deep-set longline fisheries influenced the probability of interaction and disposition (alive v. dead) of Laysan (Phoebastria immutabilis) and black-footed (P. nigripes) albatrosses. Most mitigation measures efficiently reduced seabird bycatch, however, few influenced whether interactions were fatal. In the shallow-set fishery, side-setting and stern-setting proved equally effective. Night-setting is highly effective at reducing interactions, though interaction and mortality rates were much higher during the full moon, when most shallow-set effort occurs. The use of blue-dyed bait and strategic offal/bait discharge were associated with increased interactions. 

Average annual seabird bycatch in Alaska (U.S.) has declined by 73% in the last 5 years (2002-2006) compared to bycatch from the late 1990s. Despite the recent reductions resulting from mandatory mitigation requirements, seabirds continue to be caught at higher rates than would be expected, given results of controlled studies that demonstrated bycatch reductions of nearly 100% with paired streamer lines. The results of this study demonstrate that a few individual vessels continue to be responsible for the majority of seabird bycatch.

Tests were conducted aboard pelagic longline vessels fishing off the coast of Uruguay, to determine the effect of hook type (circle hook vs J-hook) on the catch and length composition of target and non-target species.  Both American and Spanish style longlines were used during these experiments.  American style longlines consist of a 3.6 mm polyamide monofilament mainline with polyamide or polyester buoys lines 9-36 m long.  Spanish style longlines consist of 5-mm polyethlene multifilament mainline with buoy lines (similar in thickness and material to mainline) 12-18 m long.  On the American style longlines, albacore tuna (Thunnus alalunga) and shortfin mako shark (Isurus oxyrinchus) catches were significantly higher on circle vs J-hooks. Catches of other tunas and sharks (blue (Prionace glauca) and porbeagle (Lamna nasus) were also higher on circle hooks, but were not significantly higher.  There was no significant difference in the catches of seabirds or sea turtles between the two types of hooks on the American style longlines.  On the Spanish style longlines, albacore tuna catches were also significantly higher on circle compared to J-hooks, and there was a significant decrease in pelagic stingray (Pteroplatytrygon violacea) catches on circle hooks.  No significant difference in the catch rates of seabirds or sea turtles was seen between the two types of hooks on this type of longline.  There was no significant difference in the length distribution for any species between the two hook types on either type of longline.  There were also no significant differences between hook types for any hooking location of incidentally caught sea turtles.

Penguins are one of the most threatened groups of seabirds, with 10 of the world’s 18 species listed as Vulnerable or Endangered on the IUCN Red List. At-sea threats, such as the bycatch of penguins in fishing gear has been the subject of few directed studies and has not been fully assessed. In this literature review, researchers assess which species and fishing gear are largest contributors to penguins globally. Authors suggest the accuracy of fully assessing penguin bycatch may be deceptive and quantitative estimates prove difficult as a lack of overall research, publishing bias, and random sampling in areas of perceived conflict or resource availability should be taken into consideration. 

Findings of this review identified 14 of the 18 total penguin species were recorded in bycatch events. Gillnets, and to a lesser extent trawls, were shown to pose the greatest threat to penguins. Of the 14 species, yellow-eyed Megadyptes antipodes (Endangered), Humboldt Spheniscus humboldti (Vulnerable) and Magellanic Spheniscus magellanicus penguins (Near Threatened) were the species of most concern in these bycatch events. Penguins face many threats; reducing bycatch mortality in fishing gear will greatly enhance the resilience of penguin populations to threats from habitat loss and climate change that are more difficult to address in the short term.

The use of blue-dyed squid bait on pelagic longlines was tested to determine its ability to reduce both surface and subsurface interactions with seabirds.  In addition, blue-dyed fish bait was tested for its ability to reduce seabird strikes at the surface. Blue-dyed squid bait reduced seabird interactions by 68% compared to non-dyed squid bait when the longline was submerged, and only 3-8% of the blue-dyed squid bait were struck at the surface, compared to 75-98% of non-dyed squid bait.  Around 48% of blue-dyed fish bait was struck at the surface during the first two days of the trial, and 90% were struck over the last three days of the trial.

This paper focuses on mitigation measures specified by the International Commission for the Conservation of Atlantic Tunas (ICCAT) related to threatened seabirds foraging in the south Atlantic Ocean. The authors developed an ecological risk assessment for various combinations of mitigation measures to protect five threatened albatross and petrel populations, comparing those specified by ICCAT to those recommend by the Seabird Bycatch Working Group of the Agreement on the Conservation of Albatrosses and Petrels (ACAP). They conclude that updating existing mitigation measure specifications for pelagic longlining in the South Atlantic to reflect current best practice guidelines would potentially reduce seabird mortality by 41–86 %, and predict that simultaneous application of all three ACAP recommended mitigation measures recommended (includingnight setting, branch line weighting, bird-scaring lines, and hook shielding devices) could reduce seabird mortality by 72–93 % and therefore should be considered by ICCAT.

This study analyzed seabird bycatch data across gear types in the Greenland halibut (Reinhardtius hippoglossoides) fishery spanning 2019-2019. Northern fulmars (Fulmarus glacialis) were the most frequently reported seabird bycatch species, with August, September and October having the highest levels caught. Seabird bycatch overall was highly variable between years, but did not seem to be related to the level of total allowable catch.

A meta-analysis of 15 papers examined the general impact of seabird bycatch reduction device (BRD) technology on commercial longline fishing operations. Since there were relatively few papers with data suitable for meta-analysis, the researchers pooled studies with BRD-and fishery-related metrics included as covariates. The analysis found a small (9%) increase in target catch with BRD use in longline fisheries, while seabird bycatch was reduced by 89%. This pattern does not change with respect to geographic location or BRD type, indicating that efforts to reduce seabird bycatch are generally effective under different conditions. 

Cory's shearwater, Calonectris diomedea, is the main seabird species incidentally caught by the Spanish longline fleet in the western Mediterranean Sea. The authors used onboard observer data to model the longline bycatch of Cory's shearwaters as a function of time of the year, technical characteristics of the fishing operation, and geographical location. The most explanatory factor for bycatch was the geographical location and then the technical characteristics (number of hooks and fishing during non-working days). Seabirds are more likely to approach longline vessels when trawlers are not allowed to operate (non-working days), so the authors conclude that activity of longliners should be limited to working days.