Gillnets and stomach content metabarcoding - sharks and rays

Gillnets are the world’s most common net-based fishing gear, comprising
walls of light mesh designed to entangle fish. Gillnets are often
retrieved with holes in the netting, which means some animals escape or
are depredated unseen, but with some mortality. To effectively manage
fisheries around the world, information is required on not only the
harvested and discarded mortalities, but also problematic interactions and
mortalities caused by the fishing gear and especially those involving
protected species. This study sought to assess a novel method for
determining such interactions by sampling five adjacent pieces of netting
around each of ten holes in two bather protection polyethylene gillnets
for environmental DNA or ‘eDNA’. Here we show that eDNA correctly
identified all previously entangled-and-landed species. Also, eDNA from
three uncaptured taxa were recorded: bull shark, Carcharhinus leucas,
white shark, Carcharodon carcharias and dolphins (Delphindae),
illustrating the potential to reveal previously cryptic gillnet
interactions. We propose that as scientific methods evolve and autonomous
real-time DNA surveillance becomes routine, eDNA testing of fishing gears
and vessels could provide a novel, complementary fishery-monitoring tool.