Swimbladder morphology masks Southern Ocean mesopelagic fish biomass

Tracey Dornan*, Sophie Fielding, Ryan A. Saunders, Martin J. Genner

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

25 Citations (Scopus)
194 Downloads (Pure)


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.

Original languageEnglish
Article number20190353
Number of pages8
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1903
Publication statusPublished - 29 May 2019


  • Acoustics
  • Biomass
  • Ecosystem
  • Mesopelagic fish
  • Myctophid
  • Southern Ocean


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