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weight of water in a large shark. Liver oil provides, in sea water, about 5-6 times the buoyancy of an equal weight of solute-free water and varies from an almost negligible fraction of total weight in some juveniles up to about 25% of the weight of certain adults. In larger individuals within a species, liver oil is accumulated in a nearly constant weight ratio to liver tissue. Regression analyses lead to rectilinear correlations which are sufficiently strong to be of value in studies concerned with quantitative liver oil relationships. Indications with large sharks are that buoyancy control holds priority over lipid reserve as a function of liver oil. Primarily as a result of liver buoyancy, the loading of hydrodynamic lifting surfaces in mature sharks is maintained within narrow limits over the range of sizes found for that species. That wide variations in ratios of underwater weights and pectoral fin areas were not encountered with adult sharks of the same species suggests that major excursions from an optimum relationship are not tolerated for long periods of time. Deterioration of hydrostatic and/or hydrodynamic equibilibrium with the environment would be expected to adversely affect a shark's ability to capture food and might be a factor in leading the animal to seek out relatively helpless prey, including swimmers at beaches and victims of air and sea disasters.

Observed variations in specific gravities of sharks of the same species were shown to be caused primarily by differences in buoyancy provided by the animal's livers. Shark livers vary greatly in content of low density oil with species, size, and physical condition of the shark. Procedures were developed for determining average densities (conventional specific gravities) and sinking factors (specific gravities referred to sea water at ambient temperature) of large sharks, either dead or anesthesized. Consideration of liver buoyancy permitted calculation of average values for densities and sinking factors of liver-free bodies from 13 species of sharks common to the eastern Gulf of Mexico.