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Postwar retrospection in consort with discouraging results of numerous additional carefully controlled tests cast such doubt on the efficacy of Shark Chaser that it was ultimately phased out of the military procurement schedule. With wartime pressures and priorities relaxed, shark research was put in proper perspective, and competed for available limited funding with studies on numerous other hazards of biological origin that threaten the well-being of naval personnel. The Navy created a special division, the Human Ecology Branch, within the Office of Naval Research to study personnel operations and survival under extreme environmental stresses, e.g., arctic, desert, and tropic environments. Essentially, shark research, atom bombs, television, and modern rocketry are all siblings, born of the urgencies of World War II. The United States Navy's concern with sharks remains very practical and basic: keep them from interfering with naval operations and from harassing naval personnel.

Accurate counts of Gymnodinium breve are important in recognizing the onset of blooms and in following the course of organism concentrations at fish-killing levels found during red tides. Natural mobility of these organisms and the variety of presentations occasioned by viewpoint make direct counting of water samples cumbersome, low in precision, and of questionable accuracy. Physical (vortex stirring) and chemical (inhibitory drugs) means for non-disruptive immobilization of G. breve have been devised which significantly simplify counting procedures, leading to higher precision and accuracy. Unexpected stability of G. breve to the physical stress of vortex stirring raises questions about accepted ideas on cell fragility.

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.