Near equal compressibility of liver oil and seawater minimises buoyancy changes in deep-sea sharks and chimaeras

Imants G. Priede, Rhoderick W. Burgass, Manolis Mandalakis, Apostolos Spyros, Petros Gikas, Finlay Burns, Jim Drewery

Research output: Contribution to journalArticle

Abstract

Whereas upper ocean pelagic sharks are negatively buoyant and must swim continuously to generate lift from their fins, deep-sea sharks float or swim slowly buoyed up by large volumes of low-density oils in their livers. Investigation of the Pressure, Volume, Temperature (PVT) relationships for liver oils of 10 species of deep-sea Chondrichthyes shows that the density difference between oil and seawater, Δρ remains almost constant with pressure down to full ocean depth (11 km, 1100 bar); theoretically providing buoyancy far beyond the maximum depth of occurrence (3700 m) of sharks. However, Δρ, does change significantly with temperature and we show that the combined effects of pressure and temperature can decrease buoyancy of oil by up to 10% between the surface and 3500 m depth across interfaces between warm southern and cold polar waters in the Rockall Trough in the NE Atlantic. This increases drag more than 10 fold compared with neutral buoyancy during horizontal slow swimming (0.1 m s-1) but the effect becomes negligible at high speeds. Chondrichthyes generally experience positive buoyancy change during ascent and negative buoyancy change during descent but contrary effects can occur at interfaces between waters of different densities. During normal vertical migrations buoyancy changes are small, increasing slow-speed drag by no more than 2-3 fold. Equations and tables of density, pressure and temperature are provided for squalene and liver oils of Chimaeriformes (Harriotta raleighana, Chimaera monstrosa, Chimaera monstrosa), Squaliformes (Centrophorus squamosus, Deania calcea, Centroscymnus coelolepis, Centroscyllium fabricii, Etmopterus spinax) and Carcharhiniformes (Apristurus laurussonii, Galeus murinus).

Original languageEnglish
Article numberjeb222943
JournalJournal of Experimental Biology
Volume223
Issue number9
Early online date14 Apr 2020
DOIs
Publication statusPublished - 11 May 2020

Keywords

  • Buoyancy
  • Chimaeras
  • Deep-sea
  • Liver oil
  • Sharks
  • Squalene

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science

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