How does longline fishing impact seabirds?
The longline method of fishing involves a mainline that can extend up to 80km in length, gangions (short lines attached to a trawl) and thousands of baited, barbed hooks at regular intervals, set behind a fishing vessel and suspended to the desired depth within the water column, depending on the species targeted for capture.
Most seabirds are captured during the setting of the longlines (Zhou et al. 2019), during an attempt to grab bait off the hooks, but others will dive down into the water and try to capture the hooked target species, impaling themselves on the barbs, by their bills, bodies or wings.
If seabirds caught during the setting process cannot free themselves, they are dragged beneath the surface when the longline is lowered into the water and drown. Seabirds may be released by fishermen and discarded overboard, dead or alive (see Bycatch & Incidental Capture of Cetaceans under Impacts).
There have been reports of fishermen cutting off the beaks of live seabirds to release them from longline hooks and throwing them into the ocean. Seabirds that can free themselves sustain potentially life-threatening or debilitating injuries with impacts to their health and long-term survival.
The pelagic seabird species most often caught in longlines are shearwaters, albatrosses and petrel, with at least 160,000 and potentially more than 320,000 seabirds killed every year, at mortality levels unsustainable for species and populations (Anderson et al. 2011).
Fisheries compete with seabirds
Seabirds are the most threatened group of bird species, with a study of the population trend of 19% of global monitored seabirds between 1950 and 2010 indicating a 69.7% community-level population decline (Paleczny et al. 2015).
A report compared the amount and type of fish consumption by a billion seabirds (276 seabird species in 1,482 populations) with industrial fisheries intake data from 273 countries. Results indicated that between 1970 and 2010, annual seabird fish consumption decreased from 70 to 57 million tonnes, while catches from industrial fisheries increased from 59 to 65 million tonnes (Grémillet et al. 2018).
The researchers are concerned that seabirds could be extinct within the next 50 years unless the fishing industry adopts more sustainable practices and suggest no-take marine protected areas (see Marine Protected Areas & IMMAs under Solutions) and enforcement of fishing quotas (see Responsible Fishing & Sustainability under Solutions) are viable solutions to ensure the long-term protection of seabirds.
Seabird conservation efforts
Strategies to reduce seabird bycatch in pelagic longline fisheries include setting of lines after dark (night setting), use of heavily weighted hooks that sink quickly (line weighting) and bird-scaring lines (a tori or streamer) (see Bycatch Reduction & Exclusion Strategies under Solutions).
The Albatross Task Force (ATF) in Namibia have been working for over ten years with industry and fisheries management and their efforts have resulted in a 98% reduction in seabird deaths in demersal longline fisheries (Da Rocha et al. 2021). Improved fishing practices in South African longline tuna fisheries have significantly reduced annual seabird bycatch.
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Anderson ORJ, Small CJ, Croxall JP, Dunn EK, Sullivan BJ, Yates O, Black A (2011) Global seabird bycatch in longline fisheries. Endang Species Res 14:91-106. https://doi.org/10.3354/esr00347
Nina Da Rocha, Steffen Oppel, Stephanie Prince, Samantha Matjila, Titus M. Shaanika, Clemens Naomab, Oliver Yates, John R.B. Paterson, Kaspar Shimooshili, Ernest Frans, Suama Kashava, Rory Crawford, Reduction in seabird mortality in Namibian fisheries following the introduction of bycatch regulation, Biological Conservation, Volume 253, 2021, 108915, ISSN 0006-3207, https://doi.org/10.1016/j.biocon.2020.108915
Grémillet, D., Ponchon, A., Paleczny, M., Palomares, M., Karpouzi, V.S., & Pauly, D. (2018). Persisting Worldwide Seabird-Fishery Competition Despite Seabird Community Decline. Current Biology, 28, 4009-4013.e2. https://doi.org/10.1016/j.cub.2018.10.051
Paleczny M, Hammill E, Karpouzi V, Pauly D (2015) Population Trend of the World’s Monitored Seabirds, 1950-2010. PLOS ONE 10(6): e0129342. https://doi.org/10.1371/journal.pone.0129342
Zhou C, Jiao Y, Browder J (2019) How much do we know about seabird bycatch in pelagic longline fisheries? A simulation study on the potential bias caused by the usually unobserved portion of seabird bycatch. PLOS ONE 14(8): e0220797. https://doi.org/10.1371/journal.pone.0220797