Diving into archival data: The hidden decline of the giant grouper (Epinephelus lanceolatus) in Queensland, Australia

Abstract

The giant grouper (Epinephelus lanceolatus) is the largest reef fish in the Indo-Pacific (~2.5 m TL, >400 kg), and it is highly susceptible to overfishing. Despite regional protections and documented population declines, the species is listed by IUCN as Data Deficient due to minimal long-term population data and a paucity of life history information. This study used historical fishing records derived from newspaper articles, fishing magazines, grey literature and naturalists' descriptions to collate life history information and reconstruct giant grouper population trends from 1854 to 1958 in Queensland, Australia. Historical recreational catch trends of four biologically distinct grouper size classes demonstrated that over 92 years, fishing disproportionately affected two size classes: immature (fish below reproductive size) and mature individuals. Changes in the probability of capturing a grouper within a recreational fishery were examined as a proxy of relative abundance. The probability of catching a giant grouper within a popular recreational fishery significantly declined from 81% in 1860 to 2% in 1958. Further analysis based on a non-probabilistic method of giant grouper sighting records showed fluctuations in the giant grouper population trajectory, from a steady decline during the early 20th century to an increase during WWII (1939–1945) followed by a reduction in the last half of the 20th century. This study highlights the importance of archival sources to uncover population trends of rare species by combining quantitative assessments and biological inferences to determine the timing and occurrence of population declines and recoveries and inform how vulnerable fish species respond to the cumulative effects of fishing over time.