Ecological vulnerability of the chondrichthyan fauna of southern Australia to the stressors of climate change, fishing and other anthropogenic hazards

Abstract

We develop a potentially widely applicable framework for analysing the vulnerability, resilience risk and exposure of chondrichthyan species to all types of anthropogenic stressors in the marine environment. The approach combines the three components of widely applied vulnerability analysis (exposure, sensitivity and adaptability) (ESA) with three components (exposure, susceptibility and productivity) (ESP) of our adaptation of productivity–susceptibility analysis (PSA). We apply our 12‐step ESA‒ESP analysis to evaluate the vulnerability (risk of a marked reduction of the population) of each of 132 chondrichthyan species in the Exclusive Economic Zone of southern Australia. The vulnerability relates to a species’ resilience to a spatial (or suitability) reduction of its habitats from exposure to up to eight climate change stressors. Vulnerability also relates to anthropogenic mortality added to natural mortality from exposure to the stressors of five types of fishing and seven other types of anthropogenic hazards. We use biological attributes as risk factors to evaluate risk related to resilience at the species or higher taxonomic level. We evaluate each species’ exposure to anthropogenic stressors by assigning it to one of six ecological groups based on its lifestyle (demersal versus pelagic) and habitat, defined by bathymetric range and substrates. We evaluate vulnerability for 11 scenarios: 2000–2006 when fishing effort peaked; 2018 following a decade of fisheries management reforms; low, medium and high standard future carbon dioxide equivalent emissions scenarios; and their six possible climate–fishing combinations. Our results demonstrate the value of refugia from fishing and how climate change exacerbates the risks from fishing.

Gillnet selectivity for non‐targeted shark species in temperate Australia

“…Sharks are captured in multispecies fisheries worldwide and are highly vulnerable to overexploitation due to their low biological productivity (Stevens et al, 2000). Currently, a third of the world's sharks and rays are classed as threatened according to IUCN (International Union for Conservation of Nature) extinction risk categories due to overfishing (Dulvy et al, 2021), but sustainable exploitation is possible for target shark fisheries (Walker, 1998) and other retained and discarded chondrichthyans (Walker et al, 2021). The use of size‐selective fishing gear such as demersal gillnets has been a key for successfully managing shark populations in Australia (Prince, 2005; Walker, 1998).…”

“…Understanding gear selectivity (the relative capture probability of an individual of a given size encountering the gear) allows an accurate interpretation of catch composition and is important for modern stock assessment modelling (e.g., Methot & Wetzel, 2013) and ecological risk assessment from the effects of fishing (e.g., Walker et al, 2021). Despite its importance as a management tool and as an input to stock assessments, gear selectivity has been estimated for only a small fraction of shark species (Baremore et al, 2012; Carlson & Cortés, 2003; Ceyhan et al, 2010; McLoughlin & Stevens, 1994; Ramírez‐Amaro & Galván‐Magaña, 2019; Thorpe & Frierson, 2009).…”

M-Risk: A framework for assessing global fisheries management efficacy of sharks, rays, and chimaeras

“…However, if information about the fishing grounds and depths of species becomes easier to acquire, there is potential to include exposure in future M-Risk work. Additionally, this framework does not consider cumulative impacts due to multiple fisheries or threats, including climate change, environmental modifications and other anthropogenic hazards, that may significantly increase overall risk to some species (Walker et al, 2021). However, this framework could be readily adapted to incorporate vulnerability to climate change through the addition of Equation 3, section 2.2.12 of Walker et al (2021).…”

“…Additionally, this framework does not consider cumulative impacts due to multiple fisheries or threats, including climate change, environmental modifications and other anthropogenic hazards, that may significantly increase overall risk to some species (Walker et al, 2021). However, this framework could be readily adapted to incorporate vulnerability to climate change through the addition of Equation 3, section 2.2.12 of Walker et al (2021). We have not explored the implications of multiple assessments through time, however, anticipate this could provide valuable indications of management improvement or decline, given the assessments are completed against the same criteria in the same manner.…”

“…For example, fishers in Kenya increased their Adaptive Capacity to climate change by increasing community infrastructure and access to credit (Cinner et al, 2015). Ecological risk assessments can take several different forms, however, all measure similar aspects of risk such that a species’ vulnerability ( V ) is a function of their intrinsic life history sensitivity (Intrinsic Sensitivity), Exposure to fishing pressure, say as inferred from the spatial and depth overlap with the species’ distribution, and the species’ catchability in the fishing gears (Hobday et al, 2011; Walker et al, 2021). All this Potential Impact can be offset by Adaptive Capacity: This generic risk assessment framework has been pruned down to focus only on the Potential Impact, specifically the interplay of sensitivity and exposure.…”