Abstract
Bottom-contact fisheries are unquestionably one of the main threats to the ecological integrity and functioning of deep-sea and circalittoral ecosystems, notably cold-water corals (CWC) and coral gardens. Lessons from the destructive impact of bottom trawling highlight the urgent need to understand how fisheries affect these vulnerable marine ecosystems. At the same time, the impact of other fishing gear and small-scale fisheries remains sparsely known despite anecdotal evidence suggesting their impact may be significant. This study aims to provide baseline information on coral bycatch by bottom-set gillnets used by artisanal fisheries in Sagres (Algarve, southwestern Portugal), thereby contributing to understand the impact of the activity but also the diversity and abundance of corals in this region. Coral bycatch frequency and species composition were quantified over two fishing seasons (summer-autumn and spring) for 42 days. The relationship with fishing effort was characterized according to metiers (n = 6). The results showed that 85% of the gillnet deployments caught corals. The maximum number of coral specimens per net was observed in a deployment targeting Lophius budegassa (n = 144). In total, 4,326 coral fragments and colonies of 22 different species were captured (fishing depth range of 57-510 m, mean 139 ± 8 m). The most affected species were Eunicella verrucosa (32%), Paramuricea grayi (29%), Dendrophyllia cornigera (12%), and Dendrophyllia ramea (6%). The variables found to significantly influence the amount of corals caught were the target species, net length, depth, and mesh size. The 22 species of corals caught as bycatch belong to Orders Alcyonacea (80%), Scleractinia (18%), Zoantharia (1%), and Antipatharia (1%), corresponding to around 13% of the coral species known for the Portuguese mainland coast. These results show that the impact of artisanal fisheries on circalittoral coral gardens and CWC is potentially greater than previously appreciated, which underscores the need for new conservation measures and alternative fishing practices. Measures
Highlights
The impact of human activities on marine life is a global crisis that has left virtually no area of the ocean unaffected, with benthic habitats like coral-dominated ecosystems among those most strongly impacted (Halpern et al, 2008)
The coral removal rates reported here, while far lower than those reported for bottom trawling (Clark et al, 2016; Victorero et al, 2018), are substantially higher than what has been described for other fishing gears such as longlines and traps (Mytilineou et al, 2014; Pham et al, 2015)
Similar to previous studies conducted in other regions, bottomset gillnets had a substantial impact on coral gardens and cold-water corals (CWC) reefs in Sagres with high levels of coral removal (Shester and Micheli, 2011)
Summary
The impact of human activities on marine life is a global crisis that has left virtually no area of the ocean unaffected, with benthic habitats like coral-dominated ecosystems among those most strongly impacted (Halpern et al, 2008). The direct impact of fisheries using bottom-contact gear remains the primary cause of habitat destruction and biomass removal (Hall–Spencer et al, 2002; Glover and Smith, 2003; Hourigan, 2009) This is of special concern for circalittoral and deep coral communities (i.e., those below 50 m depth, referred to as “deep”) such as coral gardens and cold-water corals (CWC), which have lifehistory traits (e.g., slow growth rates and late age at maturity) that make recovery from physical damage especially difficult, if even possible. The tridimensional complex species that build these habitats, known as engineers, create high structural complexity that provides shelter, feeding, and nursery grounds for many organisms, including many species of commercial value (Buhl-Mortensen et al, 2010; Ashford et al, 2019), supporting levels of biodiversity comparable to those found in tropical coral reefs and terrestrial forests (Rossi, 2013; Rossi et al, 2017). As a result of several resolutions of the UNGA, Regional Fisheries Management Organizations (RFMO) and local governments adopted several measures to protect VMEs (UNGA, 2019), including the reduction of the frequency of significant adverse impacts by bottom-contact fisheries like trawling (e.g., encounter or “move-on” rule triggered by a bycatch threshold) (Parker et al, 2009; Aguilar et al, 2017; Davies et al, 2017) and the creation of Marine
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