Journal
PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
Volume 286, Issue 1903, Pages -Publisher
ROYAL SOC
DOI: 10.1098/rspb.2019.0353
Keywords
ecosystem; myctophid; mesopelagic fish; acoustics; biomass; Southern Ocean
Categories
Funding
- Ecosystems Programme at the British Antarctic Survey, Natural Environment Research Council, UK Research and Innovation
- NERC GW4+ Doctoral Training Partnership from the Natural Environment Research Council [NE/L002434/1]
- European H2020 International Cooperation project MESOPP (Mesopelagic Southern Ocean Prey and Predators)
- NERC [bas0100035] Funding Source: UKRI
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Within the twilight of the oceanic mesopelagic realm, 200-1000 m below sea level, are potentially vast resources of fish. Collectively, these mesopelagic fishes are the most abundant vertebrates on Earth, and this global fish community plays a vital role in the function of oceanic ecosystems. The biomass of these fishes has recently been estimated using acoustic survey methods, which rely on echosounder-generated signals being reflected from gas-filled swimbladders and detected by transducers on vessels. Here, we use X-ray computed tomography scans to demonstrate that several of the most abundant species of mesopelagic fish in the Southern Ocean lack gas-filled swimbladders. We also show using catch data from survey trawls that the fish community switches from fish possessing gas-filled swimbladders to those lacking swimbladders as latitude increases towards the Antarctic continent. Thus, the acoustic surveys that repeatedly show a decrease in mesopelagic fish biomass towards polar environments systematically overlook a large proportion of fish species that dominate polar seas. Importantly, this includes lanternfish species that are key prey items for top predators in the region, including king penguins and elephant seals. This latitudinal community switch, from gas to non-gas dominance, has considerable implications for acoustic biomass estimation, ecosystem modelling and long-term monitoring of species at risk from climate change and potential exploitation.
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