DNA metabarcoding as a marine conservation and management tool: a circumpolar examination of fishery discards in the diet of threatened albatrosses
Résumé
Almost all of the world’s fisheries overlap spatially and temporally with foraging seabirds,
with impacts that range from food supplementation (through scavenging behind vessels),
to resource competition and incidental mortality. The nature and extent of interactions
between seabirds and fisheries vary, as does the level and efficacy of management and
mitigation. Seabird dietary studies provide information on prey diversity and often identify
species that are also caught in fisheries, providing evidence of linkages which can be used
to improve ecosystem based management of fisheries. However, species identification
of fish can be difficult with conventional dietary techniques. The black-browed albatross
(Thalassarche melanophris) has a circumpolar distribution and has suffered major
population declines due primarily to incidental mortality in fisheries. We use DNA
metabarcoding of black-browed albatross scats to investigate their fish prey during
the breeding season at six sites across their range, over two seasons. We identify the
spatial and temporal diversity of fish in their diets and overlaps with fisheries operating
in adjacent waters. Across all sites, 51 fish species from 33 families were identified,
with 23 species contributing >10% of the proportion of samples or sequences at any
site. There was extensive geographic variation but little inter-annual variability in fish
species consumed. Several fish species that are not easily accessible to albatross, but
are commercially harvested or by-caught, were detected in the albatross diet during the
breeding season. This was particularly evident at the Falkland Islands and Iles Kerguelen
where higher fishery catch amounts (or discard amounts where known) corresponded
to higher occurrence of these species in diet samples. This study indicates ongoing interactions with fisheries through consumption of fishery discards, increasing the risk
of seabird mortality. Breeding success was higher at sites where fisheries discards were
detected in the diet, highlighting the need to minimize discarding to reduce impacts on
the ecosystem. DNA metabarcoding provides a valuable non-invasive tool for assessing
the fish prey of seabirds across broad geographic ranges. This provides an avenue for
fishery resource managers to assess compliance of fisheries with discard policies and
the level of interaction with scavenging seabirds.