Abalones at risk: A global Red List assessment of Haliotis in a changing climate

Discussion Our analysis clearly shows that abalone species exposed to fishing have a reduced resilience and a significantly greater chance of extinction compared to those that are unexploited. The few unexploited species assessed as threatened are generally characterised by occurring within a highly restricted range where MHWs and loss of habitat could drive an extinction event. Although overfishing for abalones can be observed through an historical lens, the impact is felt to this day in fisheries around the world where widespread stock declines have left remaining populations more vulnerable to a suite of stressors [53]. Most fisheries nowadays are subject to management controls ranging from total closure to enforcement of quotas, mandatory data loggers and the banning of SCUBA. Management measures that restrict catch provide greater protection of minimum abalone densities necessary for successful fertilization. These include bag and size limits, permanent MPAs to protect identifiable populations, and prohibition of SCUBA for deep stock conservation, rather than seasonal closures which simply shift catch effort to later seasons. Monitoring stocks using fishery independent surveys provides baselines estimates for comparisons following major environmental events [95]. Ideally, this should include kelp and algal cover, as well as competitors such as sea urchins, and also predators that can, when out of balance, severely impact abalones. Pre-impact data can also inform managers of the causes of any subsequent population declines, including identification of harmful algal

blooms [96] that also devastate farmed abalones [97]. Although wild abalone fisheries have declined in most regions globally, with estimated 1970s landings of 20 000 tonnes reduced to 4500 tonnes by 2020/21 [54], the commercial loss has been more than replaced by an upscaling in aquaculture, where total global production in 2010 of 65 344 tonnes had, by 2020/21, reached 243 506 tonnes. Aquaculture production is dominated by China with 89% of the total, followed by Korea with 8%, South Africa at 1% and ten other countries each below one percent [54]. Regrettably, this explosive development has not seemingly reduced the pressure on wild populations which continue to be fished, often to unsustainable levels. Nevertheless, aquaculture offers a bonus in sourcing seed for augmenting depleted wild fisheries, enabling ocean ranching and encouraging population recovery [98], although reintroduction programmes demand complex and costly stock management and record-keeping to safeguard the genetic diversity of wild populations. Heasman et al. (2007) suggest a minimum number of parents at 30 to 40 of each sex, with a large number of mating pairs over each successive generation to avoid inbreeding problems [98]. Fig 8. H. rufescens (CR). At 313 mm, the world’s largest abalone Reprinted under a CC BY license with permission from Buzz Owen, original copyright. https://doi.org/10.1371/journal.pone.0309384.g008 PLOS ONE Abalones at risk: A global Red List assessment of Haliotis PLOS ONE | https://doi.org/10.1371/journal.pone.0309384 December 23, 2024 18 / 25