SharkDefense is the leading researcher and developer of selective chemical and electrochemical shark repellents. Our shark repellent technologies are currently divided into four activity categories, described below.
Semiochemicals ( aka Necromones )
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 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 first 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 to 10-4L) 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 100mL 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 Thunnus albacares and Rachycentron canadum, 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 total synthesis pathways. A time-release longline polymer we named PolyShark 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 initially 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) when directed as an oral dose into the buccal cavity. These compounds are hypothesized to act via gustation pathways in sharks.
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 or buccal cavity, before the compound is pumped through the rakes.
Teleosts, including T. albacares and R. canadum, responded similarly to the semiochemical 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 improved time-release longline polymer, Super PolyShark, has been synthesized to contain one compound which is believed to act upon the shark’s gustatory system.
Click here to read our overview of magnetic shark repellents.
Electrochemical Shark repellents encompass highly electropositive metals. This area of study represents the newest direction in SharkDefense’s research efforts. Electrochemical Shark repellents exploit the use of the Ampullae of Lorenzini organ, found only in elasmobranchs, and thus ensures high selectivity. Electrochemical Shark 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.