4.2 | Implications for fisheries management
Re-emergence of AVG remains a significant threat to the economic viability of H. rubra fisheries in south-eastern Australia (Lafferty et al. 2015; Corbeil 2020). Therefore characterising the spatial distribution and prevalence of disease resistant genotypes will help managers identify stocks expected to be either resilient or vulnerable to AVG re-emergence. Previous population genomic research has indicated a lack of biological stock structure in these fisheries (Miller et al. 2016), suggesting that gene flow could contribute to the spread of adaptive genotypes and resilience of naïve fishing stocks. However, gene flow from unaffected parts of the fishery could eventually reduce the frequency of adaptive genotypes over time in the absence of ongoing selection. Whether selection for resistance will be a recurring process is still unclear. However, for the first time in a decade AVG was recorded in 2021, leading to abalone mortalities at a few proximal fishing locations heavily impacted by AVG in the early 2000s (Agriculture Victoria 2021). Unlike the first outbreak, animal mortality and disease spread has been minimal. While environmental and epidemiological factors may be contributing to the suppression of the disease (Bai et al. 2019a; Corbeil 2020), it is possible that the presence of adaptive phenotypes has already reduced the number of susceptible animals and overall viral load within affected fishing stocks.
Evidence of panmixia in H. rubra (Miller et al. 2016) suggests that standing genetic variation is likely to persist within disease naïve populations allowing for in situ adaptation to HaHV-1. However, strategic stock augmentation activities, involving the translocations of animals with AVG resistant genotypes, could potentially assist the spread of genotypes to reduce risks of vulnerability across wild fisheries. Also, there may be future opportunities to biosecure farm fisheries through the establishment of AVG resistant breeding programs, similar to disease related breeding programs in other farmed mollusc, crustacean and finfish fisheries around the world (Ragone Calvo et al. 2003; Kjøglum et al.2008; Moss et al. 2012; Potts et al. 2021). Overall, these results add to those of Miller et al. (2019) demonstrating patterns of genetic adaptation across environmental gradients and the adaptability of H. rubra populations to new environmental conditions. This is pertinent in south-eastern Australia where rapid changes in the physical marine climate are threatening commercial fisheries through shifts in species distributions (Ling 2008; Johnsonet al. 2011), changes in habitat and trophic interactions (Holland et al. 2021), and risks of infectious diseases (Oliveret al. 2017).