The effectiveness of sodium lauryl sulphate as a shark repellent in a laboratory test situation
Swim-through chemical repellency tests, using sodium lauryl sulphate (SLS), cupric acetate, and rotenone, were conducted in a specially-designed roundabout tank on horn sharks, Heterodontus francisci, swell sharks, Cephaloscylliun ventriosum, and leopard sharks, Triakis semifasciata. Effective concentration thresholds (EC50s) were calculated for two levels of response: (1) minimum noticeable and (2) strong. The SLS EC50s were: horn shark 43.6 and 174.5 ppm; swell shark 95.1 and 160.0 ppm; and leopard shark inconclusive and 113.1 ppm. No response was discernible from cupric acetate. Rotenone evoked a weak response with an EC50 of 5.7 ppm, but no strong response. The ratio of the minimum noticeable EC50: 24-hour lethal concentration (LC50) indicated the relative repellency (compared to toxicity) of the chemicals. The ratio for SLS was 19:1 and for rotenone 57:1. SLS did not provoke a repellency response at a low enough concentration to function effectively as a classical, surrounding-cloud type, repellent. The range of potency of SLS, however, does allow it to be used as a directional repellent.