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

There are few data on its ecology. H. drogini (VU), endemic to Cocos Island, although also suffering a paucity of data owing to its highly restricted range, is vulnerable to catastrophic events such as MHWs. Of the remaining Eastern Pacific abalone, all but one are listed as CR, including the white abalone (H. sorenseni) (CR) which is on the U.S. Endangered Spe- cies List and on the verge of extinction in the wild [5]. This species now has a well-estab- lished recovery programme including a captive breeding component which has been in the making for nearly 20 years when the first wild white abalone were captured for conservation aquaculture. Today, thousands of juveniles have been produced and a robust partnership has been developed with federal, state, universities and private partners [65], leading to an annual restocking programme begun in 2019, but with abundant predators in the region and a loss of kelp through MHWs, reseeding has been challenging and remnant populations continue to decline. Black abalone (H. cracherodii) (CR) was also overfished and then suf- fered mass mortalities owing to Withering Syndrome, a disease triggered when abalone test- ing positive to the causative bacteria are exposed to warm water events. Today, there are some hopeful signs of recruitment in some areas being reported, but other areas, including Mud Creek in central California, have been hit by landslides occurring when heavy winter rains fall in fire-scarred areas of the central California coastline. Pink abalone (H. corrugata)

(CR) continues to be at low densities in California [90] compared to the 1970s when it was a dominant species in the fisheries. Subsequent to the southern California fisheries closure in 1997 there has been persistent recruitment failure resulting from the Allee Effect. Green abalone (H. fulgens) (CR) is still uncommon in most locations after more than 24 years of fishery closure, but is making a comeback in very few locations in southern California such as Santa Catalina Island [91] although their spatially restricted rebound is a concern for their vulnerability. Flat abalone (H. walallensis) (CR) is also close to extinction in the wild. In the past, this species was always low in abundance with a very narrow distribution [10]. Today it has disappeared from the Monterey area and recent surveys (2022) in northern California, a former stronghold of the species, resulted in no flat abalone sightings (Rogers- Bennett pers. observ.). Northern or pinto abalone (H. kamtschatkana) (EN) in contrast has a wide geographical distribution and, in some regions, such as British Columbia, are numer- ous with signs of recruitment with juveniles greater than 20 mm [92]. This species has two morphologies with H. kamtschatkana kamtschatkana or pinto abalone (aka northern aba- lone) in the north and H. kamtschatkana assimilis or threaded abalone in the south of its range. In southern regions, it is less abundant, and populations continue to decline. In Washington State, there is an active restoration programme and juveniles produced in

hatcheries are stocked in the wild, where they are showing good signs of growth and sur- vival, particularly at some restoration sites [93]. Red abalone (H. rufescens) (CR) (Fig 8), once the foundation of the commercial abalone fishery, was extirpated in central California owing to a combination of fishing and sea otter predation but remained for a time abundant in southern California until their decline due to overfishing, forcing the closure of all aba- lone fisheries in the south in 1997 [13]. There had been a robust free diving (only) recrea- tional fishery in northern California worth an estimated $44 M with more than 31 000 participants per year [94]. The fishery had many sustainability management measures in place including size limits, seasonal closures, daily and annual bag limits as well as gear restrictions including no SCUBA. From 2014–2016 a massive MHW decimated the bull kelp (Nereocystis luetkeana) forests and sea urchin populations increased, dominating the system leading to mass abalone mortalities. Rapid declines by more than 80% of the red aba- lone [21, 52] led to the closure of this, the last open abalone fishery in the United States in 2018 (with the exception of small-scale subsistence fisheries for pinto abalone in SE Alaska). 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 17 / 25