Fishing for balance
Fishing is a vital industry: providing over 3.3 billion people with at least 20% of their animal protein, and employing around 38 million people, globally. Different gear types, such as gillnet, longline, purse seine, and trawl, are used depending on the target catch. Trawl fishing, where boats tow a cone-shaped net using trawl cables (or warps), accounts for around 35% of all wild-caught seafood annually. The sustainable management of fisheries is of paramount importance for global food security and livelihoods, but must also ensure environmental conservation.
Fishing boats, including trawlers, which target commercial fish often have wider impacts on the ecosystem. The gear they use can damage sensitive habitats, become lost and contribute to pollution, and catch other marine species that were not the targets of the fishery – known as incidental mortality or “bycatch”.
Bycatch has the highest at-sea impact on seabirds, killing hundreds of thousands, potentially over 1 million, seabirds annually and affecting 30% of the world’s 359 recognised species. Seabirds are the most threatened bird group, with about half experiencing population declines and 31% globally threatened – making this a critical global conservation issue. Addressing bycatch by understanding the overlap between seabird distributions and fishing effort is a key goal of the Seabird Tracking Database.
Albatrosses and giant petrels feeding around a trawl vessel in Argentina (© Nahuel Chavez – ATF Argentina / Aves Argentinas)
Why does bycatch happen? Seabirds spend most of their lives at sea and are attracted to fishing boats due to their incredible ability to detect food from large distances – up to 30 km away! This behaviour has been shown by satellite tracking studies for many species. They seek bait, catch and discarded fish waste around boats as an ‘easy’ meal. In trawl fisheries, seabirds such as albatrosses that feed on the surface of the water are drawn to discards and can either collide with trawl warps or get entangled in nets.
What is the scale of the problem? Research has provided estimates of global bycatch in gillnet and longline fisheries: 400,000 and 160,000 seabirds per year, respectively. These numbers help raise awareness and understanding about the problem, identify which species and areas are most at-risk, and highlight where more data is needed. Importantly, this research supports the creation and enforcement of legislation, providing decision-makers with evidence that emphasises the need for mandatory seabird conservation measures and monitoring in their fisheries.
Despite this, research has not provided a global estimate of seabird bycatch in trawl fisheries
– until now!
Fishing for facts
A new study conducted by the British Antarctic Survey (BAS), the University of Edinburgh, and the BirdLife International Marine Programme with input from many other collaborators, presents the first global review of seabird bycatch in trawl fisheries. This research reviewed available bycatch data from 27 monitored trawl fisheries, with four aims:
- estimate a global total of seabird bycatch in trawl fisheries,
- identify data gaps,
- identify the most susceptible seabird species to trawl bycatch,
- compare bycatch before and after implementing solutions.
Global bycatch estimate & data gaps
Starting with the headline: an estimated 44,000 seabirds per year are killed in monitored trawl fisheries globally. However, the researchers concluded this is actually a conservative estimate.
This is firstly because it only accounts for monitored fisheries: those for which there is sufficient, reliable and publicly available bycatch data, which here only amounts to 27 fisheries. The researchers identified 16 fisheries in which seabird bycatch likely occurs, but for which there are limited or non-existent publicly available data.
Secondly, cryptic mortality affects this estimate. These are seabird deaths resulting from fishing gear interactions that are unobserved and/or unrecorded, such as when a bird is injured or dies due to lost or abandoned gear, or when bycaught birds are released alive but die later (e.g., from injuries). In this study, only two of the 27 monitored fisheries had bycatch totals that accounted for cryptic mortality.
The scale of these data gaps and unrecorded fatalities leads to significant underestimations of true bycatch rates. Considering this, the researchers concluded that at least 50,000 seabirds may die annually in global trawl fisheries.
Availability of data on estimated total seabird bycatch in different trawl fisheries in FAO Major Fishing Areas (Phillips et al., 2024, Fig. 1).
Susceptible species
Across all 27 monitored fisheries, more than 50 seabird species were reported as bycatch. The most frequently caught were Northern Gannets in the Northern Hemisphere, and albatrosses and large petrels in the Southern Hemisphere. The global distributions of many of these species are well known from tracking studies.
A considerably higher proportion of bycaught species in the Southern than in the Northern Hemisphere are globally threatened – listed as Vulnerable (VU), Endangered (EN) or Critically Endangered (CR) on the IUCN Red List. In the former, this comprised 14 of the 37 reported species – including the Grey-headed Albatross (EN), compared to three of the 21 species in the latter – including the Balearic Shearwater (CR).
Balearic Shearwater (Puffinus mauretanicus) (© Cabrera Natura – IUCN Red List). This species is listed as Critically Endangered globally on the IUCN Red List – its small population of 19,000 mature individuals is declining due to a number of threats – including bycatch in longline, purse seine and trawl fisheries
Bycatch before and after mitigation
This study showcases several trawl fisheries that have made a crucial difference in combating seabird bycatch, achieving incredible bycatch reductions following the implementation of mitigation measures – particularly managing discards and using bird-scaring lines (BSL). Among others, this includes fisheries with which our Albatross Task Force (ATF) teams have worked. For example:
- The BirdLife-South Africa team have been working with the South African wet fish and freezer fleets since 2006 – this fishery has achieved an incredible bycatch reduction from 9,300 to 990 birds per year (2004-2010) due to voluntary use of BSLs and a reduction in fishing effort.
- In the Namibian hake demersal trawl, with which the ATF team in Namibia has been working since 2008, bycatch reduced from 7,030 to 1,452 birds per year (2009-2017) thanks to the required use of BSLs under legislation as well as bycatch mitigation training.
These successes underscore the critical role of ongoing international collaboration, research and robust legislation in seabird conservation.
A bird-scaring line being used on a South African trawl vessel (© RSPB (rspb-images.com)). Bird-scaring lines are a seabird bycatch mitigation measure used in both longline and trawl fisheries – the brightly coloured, shiny streamers act like a scarecrow, deterring birds from coming too close.
Fishing for the future
This important review shows us that, whilst seabird bycatch in trawl fisheries has been reduced in some fisheries, it remains a significant global threat to seabirds – including a number of globally threatened species.
A key ongoing challenge identified by the researchers is under-reporting and insufficient monitoring; replicating the above successes on a global scale requires more effective and representative bycatch monitoring across fleets, and research that accounts for things like cryptic mortality. Future efforts must focus on improving and enforcing legislation, placing more observers on fishing boats, and using Electronic Monitoring systems, such as cameras, to monitor bycatch. Managing the discards from trawl vessels is a key way to reduce seabird bycatch, which may require innovative boat design and construction.
Such efforts are crucial for understanding the true scale of the issue, informing effective conservation policies, and ensuring sustainable fishing practices that safeguard our fishing industry, the oceans and their magnificent inhabitants.