Fishing gear night setting is the best strategy to prevent accidental seabird bycatches

Between 160,000 and 300,000 seabirds die each year around the world due accidental bycatch in longliners. Night setting, tori lines to scare birds and putting weight on the baits are effective strategies that reduced by more than 90 % the accidental catch of marine birds in fishing areas worldwide (Southern Ocean, Alaska, South Africa, Namibia, New Zealand, Australia, etc.). Mitigation strategies have been applied in the Southern Hemisphere for decades to protect the populations of different species of albatrosses and petrels. Tori lines to scare birds are used in Antarctic and Subantarctic areas of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR).

Longliners and seabirds: an open conflict in the Mediterranean

There isnʼt any measure in the Mediterranean yet to mitigate the impact of fishing activities on seabirds, which is the main cause of the decline of the three endemic species: Scopoliʼs shearwater (Calonectris diomedea), the Mediterranean shearwater (Puffinus yelkouan) and the Balearic shearwater (Puffinus mauretanicus), listed as endangered species by the International Union for Conservation of Nature (IUCN).

“We are two decades late in the Mediterranean if we want to tackle and solve this problem. If we do not stop accidental bycatch by longliners, the most threatened shearwater species could disappear from our seas in a few decades, specially the Balearic shearwater”, warns the lecturer Jacob González-Solís, from the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB and IRBio.

Night setting to prevent seabirds from dying

Within the framework of this research, from 2013 to 2014 the UB-IRBio team analysed the efficiency of several strategies to mitigate accidental fishing in longliners that captured hake (Merluccius merluccius) in western Mediterranean waters. The experts tested four mitigation measures: adding weight to speed up the baits going underwater; using tori lines to scare birds from attacking the baits; using artificial baits which are less attractive to birds (such as sardines), and night setting, when birds do not display a lot of activity.

Night setting reduced the amount of birds that tried to steal the baits. Moreover, this strategy does not affect hake (or other non-target species) catching. However, night setting being mandatory could reduce the allowable fishing time, especially in Summer, when nights are shorter.

“Evidence points out that the decline of the populations of the three endemic shearwater species in the Mediterranean is a direct consequence of longline fishing and therefore, the solution needs a brave, immediate and determining intervention by the national, State and European Administration. Our study shows that, at this moment, night setting is by far the most effective method to reduce accidental seabird bycatches in demersal longliners in the Spanish coast and the Mediterranean. Unless we find more efficient options -and following an essential principle of prevention- it would be necessary to implement night setting urgently in those longliners in the Spanish coast and the Mediterranean, at least on those that use the most dangerous techniques for birds and during the risky months for birth accidental bycatches”, adds González-Solís.

“On the other hand -he continues- research will be still necessary regarding the effective alternatives, which can adopt the different fishing methods in the peninsular coast”.

Are weighted baits and tori lines effective?

Adding weight to the baits caused some operational problems in some occasions. Also, the speed increase was relatively short and therefore, the difficulty to access the baits was minimal. Moreover, the use of artificial baits reduced substantially the volume of captures of their target fish (hake), and its generalization could create a big economic impact in the fishing sector.

Regarding the bird scaring lines, “this strategy could reduce the risk of accidental capture because it takes away the attacks to those baits that are away from the boat stern”, says Vero Cortés, UB-IRBio researcher and first author of the article.

“However, on calm days -continued Vero Cortés- those lines did not move and birds came near the boat. If there was a windy day the lines got stuck to the longine sometimes”. The new study in PLOS ONE states this strategy is not effective enough by itself in order to reduce accidental bycatches, and its effectiveness should be boosted if combined with other measures (night setting, higher sinking speed, etc.).

Mediterranean: a marine habitat with less active birds at night

At a global scale, several studies note that night setting is one of the most effective measures to reduce bird bycatch in demersal longiners. However, the efficacy of each measure depends on each marine area. “Therefore, it is essential to test the different measures of the fleet of each area since the results may be different”, say Jacob González-Solís and Vero Cortés, authors of Manual de buenas prácticas en la pesca de palangre de fondo. 

Regarding the Mediterranean, most species are diurnal or crepuscular -there are a few that are active by night- and therefore night setting is especially efficient. Also, the rate of accidental bird bycatch is higher in particular months of the year, especially from March to June. “Limiting the activity of longliners that work during the months of higher risk is another measure to protect populations of the most threatened seabirds in the Mediterranean coasts”, conclude the authors.