Impacts of trophy collection and commercial fisheries on sawfishes in Queensland, Australia

Abstract

Globally, populations of sawfishes (Batoidea: Pristidae) have declined due to directed fishing and bycatch. Before international trade protection, sawfish rostra were often collected as trophies, and sawfish fins could fetch some of the highest prices in the shark fin trade. Australia is now considered a global stronghold for 4 out of 5 species. The present study analyses data of 723 sawfish rostra from all 4 Australian species that were caught in Queensland over the last 100 years. The majority of rostra (92.2%) originated from gillnet captures. Morphometric data from rostra were used to calculate sawfish total lengths and ages at mortality using published ratios. Rostra were split into the mass retention subgroup (n = 569), which originated from ≤5 active commercial inshore gillnet fishers with known large geographic origin regions and decades of origin, and the small-scale retention subgroup (n = 154), for which individual years and locations are known. Across all regions of Queensland, species composition changed significantly before and after the year 2000. After 2000, Anoxypristis cuspidata became the dominant species on the east coast. Large adult Pristis zijsron were present across Queensland before 2000 and numbers declined after this. The commercial gillnet industry likely impacts all life history stages of sawfishes. Since 2002, it has become compulsory for Queensland’s commercial fishers to report interactions with sawfishes in SOCI (Species of Conservation Interest) logbooks. Comparison of rostra from gillnet captures with logbook data indicates that underreporting is higher than previously assumed.