SharkDefense is the leading researcher and developer of selective chemical and electrochemical shark repellents. Our shark repellent technologies are currently divided into three activity categories, described below.
Semiochemicals are chemical messengers or “clues” sharks may use to orient, survive and reproduce in their specific environments. Certain semiochemical extractions have the ability to trigger a flight reaction in sharks, but these trace chemicals present unique difficulties for isolation and detection. The possible use of semiochemicals as shark repellents was proposed by Baldridge (1990) and by Rasmussen and Schmidt (1992). In 2001, investigation of these possibilities led Eric M. Stroud and Michael Herrmann to begin qualitative analysis on semiochemical extractions using captive juvenile sharks. A variety of analytical instruments and techniques were employed to isolate possible candidates. The most promising semiochemical candidates were scaled up, and during 2003, with the help of Dr. Samuel Gruber, Grant Johnson, and the Bimini Biological Field Station, the team was able to document a number of successful field tests on wild feeding sharks. The results of these field tests were presented at the 2004 Joint Meeting of Ichthyologists and Herpetologists 26 – 31 May, 2004, in Norman, OK.
The detection of semiochemicals is hypothesized to be via olfactory pathways. Recent (2007) electro-olfactogram studies conducted by a major US university support that semiochemical extracts (diluted to10-4L) are detected by N. brevirostris. Dosages of 100uL (100×10-6L) directed towards the nares have been shown to terminate tonic immobility in juvenile N. brevirostris. Competitively feeding populations of C. perezi and C. acronotus respond to surrounding cloud dosages of 350-700mL of semiochemical extract by halting feeding activities and leaving visual range. This reaction draws some similarity to a schreckreaction (von Frich 1938).
Semiochemical extractions are selective to elasmobranchs. In teleosts studied to date including T. albacares, no flight reactions were observed when fish are directly exposed to the extract. In some instances, teleosts are observed feeding inside of the cloud of extract.
While the original semochemical extractions were made from decayed shark tissue, present work is focused on green synthesis pathways. Our time-release longline gel has been synthesized to contain one compound which is believed to act upon the shark’s olfactory system.
In the course of screening the biological activities of various fractions of semochemical extracts, certain compounds were modified in an attempt to increase potency (by substitution of active groups). Additional screening using the tonic immobity assay showed that these compounds terminated tonic immobility in N. brevirostris and G. cirratum, often violently, when in contact with the mouth and NOT the nares. Responses were observed at as low as a 50uL (50×10-6L) directed oral dose to the mouth. These compounds are hypothesized to act via gustation pathways in sharks. Continued studies in both G. cuvier (juvenile and
Gustation compounds are particularly effective on carpet sharks. Suction grip-bites are released when a gustation compound is introduced directly into the mouth. A clever bite-release experiment using juvenile G. cirratum demonstrated that these sharks would release their bite once gustation compounds were introduced.
In order to preclude possible respiratory irritation effects, we studied the movement of these compounds after delivery. In smaller sharks, we were able to observe if the compound was contacting the gill rakes using colored dyes. We have observed that the response occurs essentially on contact with the inner surfaces of the mouth/buccal cavity, before the compound is pumped through the rakes.
Teleosts, including T. albacares, responded similarly to semochemical extracts: No aversive behavior was observed, and breathing and swimming patterns were not disrupted. Captive cobia were observed to feed more aggressively in the presence of the gustation compounds.
Gustation compounds are green and are commercially sourced. To date, 15 compounds have been identified with gustatory activity in sharks. Our time-release longline gel has been synthesized to contain one compound which is believed to act upon the shark’s gustatory system.
Electrochemical repellents encompass strong permanent magnets and highly electropositive metals. This area of study represents the newest direction in SharkDefense’s research efforts. Electrochemical repellents exploit the use of the Ampullae of Lorenzini organ, found only in elasmobranchs, and thus ensures high selectivity. Electrochemical repellents have a much shorter range of effectiveness than chemical repellents, but these repellents do not have to be continually replenished and do not suffer from dispersive and dilutive losses in efficacy.
More information on this exciting new area of research can be found at Ocean Magnetics http://www.oceanmagnetics.com