Sometimes, everything old is new again. We just wanted to reminisce on research conducted by the late esteemed L.E.L. “Bets” Rasmussen (d. 2006) in the 1990’s, specifically:
Rasmussen, L.E.L.&M.J. Schmidt. 1992. Are sharks chemically aware of crocodiles? pp. 335–342. In: R.L. Doty & D. Muller-Schwarze (ed.) Chemical Signals in Vertebrates VI, Plenum Press, New York.
Her team found that crocodile exudates produced a repellent response in juvenile sharks, and this was suggested to be the first evidence of a true semiochemical signal in sharks. The exudates were cyclic imides (succinimides) with varied alkyl groups on the ring. They were proposed to give the young sharks a survival advantage by providing a chemical cue about their natural predator at that point in their life stage.
In 2008 through 2010, SharkDefense revisited some of this chemistry, particularly in Eric’s Ph.D. work. We also found cyclic imides in decomposing shark extracts, similar to Bet’s. Succinimide, maleimide, and methyl and ethyl substituted succinimides and a maleimide were studied in field tests at South Bimini using aerosol canisters. All were only weakly repellent compared to controls on adult sharks. We proposed that a synergist had to be present to be effective, and that the repellent was a binary or ternary mixture of actives.
More to come we are sure.