Early Repellents Based on Decomposed Shark Meat
Around 1943 at Woods Hole, many compounds were screened for repellency using captive smooth dogfish (Mustelus canis). Many sinister materials were screened with a familiar outcome: Sharks were killed due to the toxicity of the materials, but none produced an instantaneous repellent response or worked at “practical” concentrations. Among those materials tested were rotenone, chlorine gas, sodium cyanide, hypochlorites, crystal violet, strychnine nitrate, MS-222 and quinaldine (narcotics), chemical stenches, and chemical warfare gases. In general, the early Wood Hole tests concluded that nearly any water soluble compound that was not normal prey reduced feeding responses in the captive dogfish.
A few candidates from the Woods Hole experiments, however, did show partial repellency: Maleic acid (fig. 1.4); malic acid (fig. 1.5); copper sulfate; and decomposing shark meat. Maleic acid and malic acid were eventually found to produce inconsistent results and were abandoned. The most consistent candidate was decomposing shark meat, which was prepared by allowing shark flesh to stand at 20°C for four to six days with “small concentrations of copper salts” (Gilbert). The presence of copper may have inhibited some putrefactive bacteria. The researchers found that the resulting raw decomposed shark meat produced feeding inhibitions more consistently than with ethanol extracts of the same meat.
Advances in Semiochemical Repellents 2001-2006
In 2001, SharkDefense, a small New Jersey-based company of which the author was a co-founder, began experiments with putrefied shark extracts in a collaboration with the Bimini Biological Field Station. In August 2004, an extract derived from putrefied shark carcasses that produced consistent repellent results was announced. This extract was efficacious for three coastal shark species of the Bimini Islands, namely Carcharhinus perezi, C. acronotus, and C. limbatus. Since that time, the use of the repellent has been featured extensively in shark related television programs and other media.
The extraction process developed by SharkDefense consists of allowing whole shark carcasses to aerobically decay for careful period of time. During this period, autolytic decomposition processes have completed, and bacteriological putrefaction has sufficiently progressed. Within this period, the carcass is extracted with polar solvents, thereby denaturating all enzymes and halting all bacteriological catabolism. The solvents thoroughly extract all soluble compounds from the putrefied tissue, cartilage and viscera. Following this period, the solution is assayed for a correct pH range and is filtered and containerized. This process was licensed to Repel Sharks, LLC in 2008, who currently produce aerosol canisters filled with the extract.
Species-specific dependencies on repellency were studied by Shark Defense between 2003 and 2006 to determine if the repellent had broad-spectrum efficacy. Shark tissue and viscera from four orders (Carcharhiniformes, Orectolobiformes, Squaliformes, and Lamniformes) all produced repellent material when tested against Carcharhiniform sharks (Table 1.1). A conspecific raw material was not required to produce a repellent for that species. One exception was found: Orectolobiformes sharks, namely Ginglymostoma cirratum, do not respond to putrefied shark extracts, regardless if the extract is from a conspecific or a heterospecific. The repellent extracts were not tested on Squaliformes and Lamniformes, as the research objective at that time focused only on Carcharhiniform sharks, which are responsible for the greatest number of investigatory bites along the Florida coast. (Source: The International Shark Attack File).
Table 1.2. Species-specific interpendencies for shark necromone, courtesy of SharkDefense.
Applicability to Longline fisheries
The shift of requirements from a chemical shark repellent as solely a human protection device to a conservation tool appears to coincide with increased awareness of sustainable fishing practices in the late 20th century. The Magnuson-Stevens Fishery Conservation and Management Act, as amended through October 11, 1996, is certainly a milestone in this transition. For the first time, a documented requirement to mitigate accidental shark capture in U.S. Commercial Fisheries existed. As quoted from section 101-627, 104-297 (3), the act [assures]:
“that the national fishery conservation and management program utilizes, and is based upon, the best scientific information available; involves, and is responsive to the needs of, interested and affected States and citizens; considers efficiency; draws upon Federal, State, and academic capabilities in carrying out research, administration, management, and enforcement; considers the effects of fishing on immature fish and encourages development of practical measures that minimize bycatch and avoid unnecessary waste of fish; and is workable and effective”.
The incidental capture of sharks and shark-like species is estimated at over 300,000 metric tons annually (Bonfil, 1995 ). A major contributor to the global population decline of large pelagic predatory sharks is exploitation pressure from the global multinational PLL fishing industry targeting tuna and swordfish (Falterman & Graves, 2002 ; Peel et al., 2003 ; Uozumi, 2003 ). Concern over declining shark populations is increasing due to their inability to sustain high rates of fishing mortality associated with commercial pelagic longline fishing (Myers and Worm, 2003; Meyers et al., 2007). Reports suggest population declines as much as 99% for some predatory shark species, including scalloped hammerheads (Sphyrna lewini), oceanic whitetips (C. longimanus), and tiger sharks (Galeocerdo cuvier) (Baum et al., 2003; Baum and Myers, 2004; Gilman et al., 2007). Beerkircher et.al. (2002) reports that Carcharhinid sharks comprise the largest portion of shark bycatch during U.S. commercial pelagic longline fishing with blue sharks (Prionace glauca), making up the most abundant bycatch species. Additionally, shark bycatch (and bycatch, in general) reduces fishing efficiency due to: (1) the inability of a deployed hook to capture a target species because it is occupied by a non-valuable species, (2) loss of fishing gear, and (3) loss of valuable time dealing with tangles, snarls, and/or the release of the animal. A discussion on longline fishing and the associated shark bycatch problem is provided in Chapter 6.
A true semiochemical shark repellent that meets the Johnson-Baldridge criteria would likely provide the high specificity needed to produce a significant reduction in shark catch without affecting the target bony fish catch. The semiochemical could be incorporated directly into baits, or formulated into a time release matrix, similar to the Shark Chaser of the past. The application of a selective shark repellent bait treatment will enable the fishermen to increase their target bony fish catch by making more hooks available (which would otherwise be occupied by sharks). This bycatch reduction technology will reduce the number of shark interactions which incur damage to tackle gear, thereby offsetting gear replacement costs. As long as the semiochemical can be synthesized or sourced in a practical manner, the capture of even a few market-value bony fish would offset the cost of the semiochemical repellent technology.