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

taxonomic integrity. This enforces consistency in application and facilitates the evaluation pro- cess. It allows the user to enter biological, population, range, and habitat information about each species. Comments, references, detailed data, and edit history are also captured to provide transparency and facilitate evaluation. Central to the SIS software is a data “calculator” that by applying the logical process described in the section above, determines the appropriate Red List categories and criteria from the species’ data entered, in particular reductions in popula- tions, distribution, and other variables against defined parameters that influence survival. It can also calculate a range of possible categories based on uncertain or incomplete information. The user can, however, overrule any categories and criteria that have been automatically deter- mined if so required. IUCN standards follow a defined methodology whereby each species must be assessed within six key areas: distribution, population, habitats & ecology, use & trade, threats and con- servation. The research into these six areas provides the data for determining the criteria to which one of the nine categories may be assigned: Distribution and location. There are two measures of the spatial spread relevant to the assessments together with an indicator of event occurrences (location) that could result in extinction: a) Extent of Occurrence (EOO) is a minimum convex polygon drawn around the species’ range that may include unsuitable habitat such as land, as well as deep water across which lar-

vae may disperse but unsuited for settlement, and b) Area of Occupancy (AOO) which is the sum of the areas of habitat in which the species is known to occur. For shallow water species, including the majority of haliotids, the AOO may be calculated from the length of coastline in which the species occurs extended by the width of habitat along its bathymetric range, or, for these mostly linear habitats, standard 4 km2 (2 km by 2 km) cells as suggested in IUCN standards [55]. Location. Species that occur within a restricted EOO or AOO are at greater risk from cat- astrophic events. The ‘location’ count indicates the number of areas in which a single cata- strophic event, for example a MHW or oil spill from adjacent refinery, could affect all individuals of the taxon present and cumulatively drive a species into extinction. Distribu- tion and location are both key factors in determining extinction risk to species of restricted range. Population. Measurements of population size may indicate temporal variations in abun- dance and the probability of species decline leading to extinction. For cryptic species and those in inaccessible habitats such as deep water, this may be difficult to determine. For the majority of abalone species, predominantly those of no commercial interest, the literature is silent on population sizes, however, for species that are commercially fished, data are frequently avail- able from the regulating authorities for establishing baseline abundance / density or to deter-

mine a total allowable catch (TAC) for stock management. These normally include separate quotas for recreational and/or Indigenous fishers. These source data, including variations in tonnage landed and, more rarely, catch per unit effort (CPUE) can act as proxies for determin- ing the rate of change in a population [56]. One caveat: with highly aggregated species such as abalone, CPUE may be hyperstable and a poor predictor of declining trends up until the popu- lation crashes [57, 58]. Fishery data however, by their nature, are unable to accurately quantify illegal, unreported and unregulated (IUU) fishing that continues to blight many abalone fish- eries worldwide [54, 59]. Habitats and ecology. Abalone larvae require crustose coralline algae (CCA) on which to settle and for early development, before migrating onto algal beds to sustain them in their adult lives [48]. Natural and manmade threats including seaweed harvesting, pollution, MHWs, and herbivorous intruders, can modify the natural ecology and result in semi-sessile 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 7 / 25