Spatial abundance patterns and recruitment of a virus‐affected commercial mollusc fishery

Abstract

Infectious pathogens figure prominently among those factors threatening marine wildlife. Mass mortality events caused by pathogens can fundamentally alter the structure of wild fish stocks and depress recruitment rates and yield. In the most severe instances, this can precipitate stock collapses resulting in dramatic economic losses to once valuable commercial fisheries. An outbreak of a herpes‐like virus among commercially fished abalone populations in the south‐west fishery of Victoria, Australia, during 2006–2007, has been associated with high mortality rates among all cohorts. Long‐term records from fishery‐independent surveys of blacklip abalone Haliotis rubra (Leach) enabled abundance from pre‐ and post‐viral periods to be analysed to estimate stock density and biomass. The spatial distribution of abundance in relation to physical habitat variables derived from high‐resolution bathymetric LiDAR data was investigated. Significant differences were observed in both measures between pre‐ and post‐viral periods. Although there was some limited evidence of gradual stock improvement in recent years, disease‐affected reefs have remained below productivity rates prior to the disease outbreak suggesting a reduction in larval availability or settlement success. This was corroborated by trends in sublegal sized blacklip abalone abundance that has yet to show substantial recovery post‐disease. Abundance data were modelled as a function of habitat variables using a generalised additive model (GAM) and indicated that high abundance was associated with complex reef structures of coastal waters (<15 m). This study highlights the importance of long‐term surveys to understand abalone recovery following mass mortality and the links between stock abundance and seafloor variability.

What are the drivers of the occurrence of illegal fishing and conservation barriers of sturgeons in the Caspian Sea?

“…The excessive exploitation of natural fisheries has, however, led to drastic declines in the abundance of key fish species across the globe, such as several sturgeon species (Bronzi & Rosenthal, ), and by 2011 over 60% of world commercial fishery stocks were fully harvested (Pitcher & Cheung, ; Worm & Branch, ). Anthropogenic forces, including habitat degradation, disease prevalence, instability in fishing, and non‐compliance with relevant regulations and standards regarding the optimal utilization of natural resources, have raised many concerns in recent times (Gavin, Solomon, & Blank, ; Jagers, Berlin, & Jentoft, ; Jalali, Ierodiaconou, Gorfine, Christiansen, & Young, ; Pitcher, Kalikoski, Pramod, & Short, ). In addition, global warming exacerbates these concerns by impacting species distribution and range shifts, and by creating inconsistent fishery productivity, especially in the tropical seas where people's lives depend largely on marine resources (Cheung et al, ; Cheung, Watson, & Pauly, ; Jones, Dye, Pinnegar, Warren, & Cheung, ; Sumaila et al, ).…”