The emerging field of electrosensory and semiochemical shark ...

Ocean & Coastal Management xxx (2012) 1e10 

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Ocean & Coastal Management 

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The emerging field of electrosensory and semiochemical shark repellents: 

Mechanisms of detection, overview of past studies, and future directions 

Craig P. O’Connell a, *, Eric M. Stroud b , Pingguo He a 

a School of Marine Science and Technology, University of Massachusetts Dartmouth, New Bedford, MA 02740, USA 

b Shark Defense Technologies, LLC, P.O. Box 2593, Oak Ridge, NJ 07438, USA 

article 

Article history: 

Available online xxx 

info 

abstract 

Since the sinking of the USS Indianapolis (CA-35) and associated shark attacks in 1945, the quest to find 

an effective shark repellent has been endless. Early efforts were focused on finding a shark repellent 

which would minimize the probability of a shark attack. However, studies illustrate that shark populations 

are drastically declining which has led to calls for effective management policies and practices to 

reduce both directed catch and bycatch of various shark species. With increased need for shark 

conservation, the focus has shifted to protecting sharks from harmful anthropogenic pressures, such as 

fishing gear and beach nets. Current shark repellent technologies which aim to minimize elasmobranch 

mortality in fishing gears include: permanent magnets, electropositive metal (EPM) alloys, and semiochemicals. 

This paper will review present electrosensory and semiochemical shark repellents, the 

mechanisms of elasmobranch (e.g. shark, skate and ray) detection and repellency, species-specificity in 

elasmobranch response to the stimuli, and environmental and biological conditions which may influence 

repellent success. Future research to enhance our knowledge on electrosensory repellents and to 

improve the success of repellent implementation and application will be discussed. 

Ó 2012 Elsevier Ltd. All rights reserved. 

1. Introduction 

Fisheries and beach nets are major contributors to elasmobranch 

decline (Bonfil, 1994; Baum et al., 2003; Baum and Myers, 

2004; Cliff and Dudley, 1992; Dudley, 1997; Manire and Gruber, 

1990; Shepherd and Myers, 2005) and is an issue that urgently 

needs to be addressed. Elasmobranchs are often inadvertently 

caught (bycatch) on fishing gears that results in substantial adverse 

economic (Gilman et al., 2007) and ecological (Baum et al., 2003) 

effects. During fishing operations, fishers rarely retain sharks (dead 

or alive) due to little market for shark meat, trip limits, and/or 

management plans which prohibit the retention of certain species 

(Lewison et al., 2004; Harrington et al., 2005). These practices lead 

to high incidences of discards and associated mortality, and due to 

the K-selected nature of elasmobranchs (e.g. slow growth rate, late 

maturity, and low fecundity), the likelihood of shark population 

rebound is minimal if the present mortality rates continue (Pratt 

and Casey, 1990). From a fisherman’s standpoint, interactions 

with sharks during fishing operations cause considerable issues 

* Corresponding author. 

E-mail address: coconnell2@umassd.edu (C.P. O’Connell). 

including damage and loss of gear, reduced capture of marketable 

species, depredation, risk of injury to the mates, and loss of valuable 

time untangling and reconstructing the fishing gear (Gilman et al., 

2007). 

Approaches to reducing anthropogenic-associated elasmobranch 

mortality include the use of permanent magnets, electropositive 

metal (EPM) alloys, and/or semiochemicals as repellents. 

Several studies have been conducted that aim to evaluate the 

effectiveness of these repellents on different elasmobranch species 

(Brill et al., 2009; Rigg et al., 2009; Tallack and Mandelman, 2009; 

O’Connell, 2008; O’Connell et al., 2010; Stroud et al. submitted for 

publication). This paper will review present shark repellents, 

elasmobranch (e.g. shark, skate and ray) detection mechanisms, 

species-specificity in elasmobranch response to the stimuli, and 

environmental and/or biological conditions which may influence 

repellent success. Future research to enhance our knowledge on 

electrosensory repellents and to improve the success of repellent 

implementation and application will also be discussed. 

Permanent magnets and EPMs are hypothesized to overwhelm 

the acute electrosensory system, known as the ampullae of Lorenzini, 

of an interacting elasmobranch thus causing aversion 

behaviors (WWF, 2006; Rigg et al., 2009; Kaimmer and Stoner, 

2008). The ampullae of Lorenzini is a short-range detection 

0964-5691/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. 

http://dx.doi.org/10.1016/j.ocecoaman.2012.11.005 

Please cite this article in press as: O’Connell, C.P., et al., The emerging field of electrosensory and semiochemical shark repellents: Mechanisms of 

detection, overview of past studies, and future directions, Ocean & Coastal Management (2012), http://dx.doi.org/10.1016/ 

j.ocecoaman.2012.11.005

2 

C.P. O’Connell et al. / Ocean & Coastal Management xxx (2012) 1e10 

system, detecting bioelectric fields only centimeters away from 

prey to help the elasmobranch better pinpoint that prey prior to 

feeding (Kajiura and Holland, 2002; Kajiura, 2003). Evidence also 

supports that elasmobranchs use this sensory system to detect 

geomagnetic fields assisting in the determination of geolocation 

and navigation (Klimley, 1993; Klimley et al., 2002). The latter, 

semiochemicals, appear to target the olfactory senses of elasmobranchs 

and appear to function as a Schreckstoff, or chemical alarm 

signal (von Frisch, 1938; Stroud, 2008b), producing a Schreckreaktion, 

or flight reaction, that is highly selective. Each potential 

repellent; magnets, EPMs, and semiochemicals, are hypothesized to 

operate under different mechanisms, each of which are described 

below. 

1.1. Ampullae of Lorenzini 

Elasmobranchs differ from bony fishes (teleosts) in various 

ways, but a key difference is that an elasmobranch possesses an 

electrosensory system known as the ampullae of Lorenzini. The 

ampullae of Lorenzini were first discovered by Marcello Malpighi in 

1663, but described in detail by Stephano Lorenzini in 1678 

(Budker, 1971), after whom they were named. However, the function 

of these receptors remained unknown until Dijkgraaf and 

Kalmijn (1963, 1966; cited by Kalmijn, 1971, 1982) demonstrated 

the electrosensitivity of these receptors, with additional experimentation 

showing these receptors have mechanical and thermal 

sensitivities (Boord and Campbell, 1977; Brown et al., 2003; Murray, 

1957, 1960). 

The ampullae of Lorenzini are acute electrosensory organs 

composed of minute jelly-filled pores located around the cephalic 

region of elasmobranchs (Fig. 1). Each ampullae contains a pore at 

the surface of the skin, which connects to a subcutaneous canal 

filled with conductive jelly (Kalmijn, 1966, 1971, 1974, 2000; 

Bastian, 1994). As an elasmobranch encounters a weak electrical 

impulse, such as that associated with muscle contraction (e.g. 

a fish’s heartbeat) or the associated electrical charges originating 

from gill movement, the voltage external to the pores of the 

ampullae differs from the interior voltage potential. This voltage 

gradient is perceived and a sensory message is sent to the brain via 

an impulse from the afferent neurons. It has been suggested that 

elasmobranchs detect magnetic fields in a similar manner using 

this electrosensory system, but through a different mechanism 

known as indirect-based magnetoreception via electromagnetic 

induction (Kalmijn, 1973, 1974, 1982, 1984; Carey and Scharold, 

1990; Klimley, 1993; Holland et al., 1999) which will be described 

in more detail in the following section. 

1.2. Magnetic repellent concept 

Magnets vary by composition, strength, axis of polarization, size 

and shape. More specifically, the permanent magnets typically used 

in the current shark behavioral studies are ceramic magnets that do 

not degrade in seawater (e.g. bariumeferrite magnets-BaFe 12 O 19 ; 

Rigg et al., 2009; O’Connell et al., 2010, 2011a, 2011b) and rare-earth 

magnets that degrade in seawater (e.g. neodymiumeironeboron 

magnets-Nd 2 Fe 14 B; O’Connell et al., 2011b; Robbins et al., 2011). 

The magnetic flux associated with ceramic magnets is generally 

weaker (e.g. 3850 G) than rare-earth magnets (e.g. 14,800 G), 

whereas the axis of polarization exists in a variety of combinations 

regardless of magnet-type. 

The most current explanation as to how elasmobranchs detect 

magnetic fields is through the process of indirect magnetoreception 

by electromagnetic induction, or induced electric fields that arise 

when an object moves through a magnetic field (Kalmijn, 1973, 

1982, 1984). Through electromagnetic induction there are two 

proposed mechanisms on how elasmobranchs can detect magnetic 

fields: (1) active mode and (2) passive mode (Kalmijn, 1981, 1984; 

Montgomery and Walker, 2001). In active mode, as an elasmobranch 

is swimming with a horizontal velocity through the horizontal 

component of the Earth’s geomagnetic field, a vertical 

electromotive field is induced (Fig. 2a; Kalmijn, 1997; Montgomery 

and Walker, 2001). Paulin (1995) modified the concept of the active 

mode and stated that directional cues could originate from variations 

in induced electroreceptor voltage produced during turns 

(Montgomery and Walker, 2001). In passive mode, as electrically 

charged seawater moves through the vertical component of the 

Earth’s geomagnetic field, an electromotive field, which may be 

detected and utilized by an elasmobranch, is produced in the 

horizontal direction (Fig. 2b). 

The geomagnetic field on the Earth’s surface ranges from 0.25 to 

0.65 G (G). In comparison, the magnetic field associated with 

a bariumeferrite magnet (BaFe 12 O 19 ), produces a maximum flux of 

approximately 1000 G. It is hypothesized that a much stronger 

electromotive field will be induced by a permanent magnet and 

therefore will overstimulate the ampullae of Lorenzini of an 

approaching elasmobranch, thus producing a repellent response 

(WWF, 2006). 

Although electromagnetic induction is the current explanation 

as to how elasmobranchs detect the Earth’s geomagnetic field, firm 

evidence that this process governs magnetic field detection in 

elasmobranchs has yet to be presented and therefore further 

experimentation is needed. 

1.3. Electropositive metal concept 

Fig. 1. The ampullae of Lorenzini of a tiger shark (Galeocerdo cuvier). The ampullary 

pores are represented by the black dots located around the cephalic region of the 

shark. Ó Craig O’Connell. 

Electropositive metals (EPMs) can be found in Group I (e.g. 

Lithium), Group II (e.g. Magnesium), Group III (e.g. Yttrium), Group 

IIIA (the Lanthanides), and Group IIIB (the Actinoids) of the Periodic 

Table of the Elements. Magnesium and the lanthanide metals find 

the most practical application in shark bycatch reduction, 

producing standard reduction potentials of approximately 1.8 eV 

in water, a voltage that is orders of magnitude greater in strength 

than the bioelectric fields (i.e. nanovolts) that are encountered by 

elasmobranchs in search of prey. As an elasmobranch approaches 

the metal through the conductive seawater electrolyte, three 

potential scenarios exist: (1) the shark, whose skin is much more 

electronegative than the metal, completes a galvanic cell, or electrochemical 

cell that derives energy from spontaneous reductione 




C.P. O’Connell et al. / Ocean & Coastal Management xxx (2012) 1e10 3 

Fig. 2. a) ‘Active mode’ e Vertical induced electrical currents are produced as the shark swims through the horizontal component of the Earth’s magnetic field. The induced 

electrical current moves in a direction which opposes the change in magnetic field (Lenz’s Law). Illustration modified from Kalmijn (1974). b)‘Passive mode’ e Horizontal induced 

electrical currents are produced by the movement of ocean streams (i.e. currents) through the vertical component of the Earth’s magnetic field. Illustration modified from 

Montgomery and Walker (2001). 

oxidation (redox) reactions, to the metal and experiences a net 

charge increase that is detected by the ampullae and perceived as 

repellent, (2) the hydrated metal cation (aquo ion) is a weak Lewis 

acid, or electron pair acceptor, and therefore repellent to the shark 

purely on low pH/irritancy effects, and (3) a shark retreats due to 

induced currents which are generated perpendicular to the resultant 

electric field (Rice, 2008; Stroud, 2008a: Fig. 3). 

1.4. Semiochemical repellent concept 

Elasmobranchs are considered to have a highly developed sense 

of smell which is evidenced by their large olfactory epithelial 

surface area (Schluessel et al., 2008). Due to this, elasmobranchs are 

highly responsive to very small concentrations of odor molecules, 

particularly those of amino acids (Tricas et al., 2009). Beginning in 

1990, several studies aimed to take advantage of an elasmobranchs 

acute sense of smell and demonstrated that elasmobranchs are 

chemically aware of semiochemicals derived from decaying sharks 

(Stroud, 2008b) and predatory heterospecifics (Rasmussen and 

Schmidt, 1992). Semiochemicals are signals which animals may 

utilize to assist with mate selection (Nieberding et al., 2008), 

foraging (Tumlinson et al., 1993), aggregation (Verheggen et al., 

2010) or navigation within their respected ecosystems, but semiochemical 

derived from decaying shark tissue causes a reaction 

which is reminiscent of a “Schreckreaktion”, originally termed by 

von Frisch (1938) and is defined by the fright reaction of European 

minnows (Phoxinus phoxinus) when detecting the chemicals from 

an injured conspecific. Thus far, no published field work in the 

scientific literature exists on the newly discovered elasmobranchderived 

semiochemicals. 

2. Brief overview of electrosensory repellent studies 

To date, a total of eleven studies have been conducted which 

aimed to determine the effects of magnetic (Table 1) and EPM alloy 

(Table 2) stimuli on elasmobranch behavior. These studies can be 

classified into three categories based on the experimental focus 

and/or potential applications: (1) basic or proof-of-concept 

research, (2) recreational and commercial fishing applications, 

and (3) beach net applications. The findings from each of these 

eleven studies were highly inconsistent, which may stem from 

inexperience with using these materials. As with many new 

emerging fields, there is a learning curve, and the field of electrosensory 

repellents is in its infancy and requires substantially more 

field and laboratory investigations prior to the dismissal or 

implementation of any of these materials. 

2.1. Basic or proof-of-concept research 

Fig. 3. This figure represents the mechanism behind electropositive metal detection in 

elasmobranchs. When an electropositive metal is placed in seawater, it undergoes 

spontaneous hydrolysis generating hydrogen gas and metal hydroxide which precipitates 

out of solution. The hypothesized mechanism behind the repellent capabilities of 

the EPM alloys occurs as the cations transfer to the approaching electronegative shark 

(i.e. a galvanic cell). This build up of positively charged ions overwhelms the ampullae 

of Lorenzini and is the most current explanation for the observed deterrent capabilities 

of the repellents; however, another hypothesized explanation is that a shark may 

retreat due to the associated induced current which is produced from the electric field/ 

magnetic field. Illustration modified from Rice (2008). 

Four studies have been conducted which serve as proof-ofconcept 

experiments, or basic experiments exploring the efficacy 

of electrosensory repellents, on several elasmobranch species. In 

2008, a study was conducted which examined the behavior of 

Galapagos (Carcharhinus galapagensis) and sandbar (Carcharhinus 

plumbeus) sharks to NdePr (neodymiumepraseodymium) metal, 

a type of EPM (Wang et al., 2008). Results demonstrate that sharks 

fed more frequently from the lead-weight controls with a significantly 

greater quantity of aversive behaviors (e.g. sharp turns and 

cease feeding) toward the NdePr metal illustrating the potential 

utility of these electrosensory stimuli for recreational and 

commercial fishing applications (Fig. 4a). 

In a laboratory study, Rigg et al. (2009) evaluated the effects of 

ferrite magnets on five elasmobranch bycatch species; scalloped 

hammerhead shark (Sphyrna lewini), Australian blacktip shark 

(Carcharhinus tilstoni), gray reef shark (Carcharhinus amblyrhynchos), 

milk shark (Rhizoprionodon acutus), and speartooth shark 

(Glyphis glyphis), as well as the teleost species, the seabass (Lates 

calcarifer). Results from this study demonstrated that all elasmobranch 

species responded at distances ranging from 0.26 to 0.58 m 

from the magnets and no signs of habituation were observed, with 




4 


Table 1 

Description of all studies conducted from 2008epresent using magnets (NdeFeeB ¼ neodymiumeironeboron magnets; BaeFeeO ¼ barium ferrite magnets; Ferrite 

magnets ¼ used either strontium ferrite or barium ferrite magnets e study did not specify) as elasmobranch repellents. Elasmobranch species which were studied are listed in 

the appropriate column, along with the purpose of the research (i.e. application). If the researchers were just evaluating the effects of repellents, but not for a particular 

fisheries application, the term “proof of concept” was assigned. Additionally, success was ranked on a scale of “None” e no observed effects, “Yes” e induced some effect on all 

species tested, “Partial” e induced some effect on some, but not all species studied. Although Stoner and Kaimmer (2008) observed flinches by Squalus acanthias towards the 

magnets initially, when bait was present no deterrent effects were observed and therefore this study is categorized as “None” in the success category. 

Study Species studied Repellent tested Application Success 

Stoner and Kaimmer (2008) Pacific Squalus acanthias NdeFeeB Magnets Captive experiment None 

Rigg et al. (2009) 

Sphyrna lewini 

Ferrite Magnets Proof of concept Yes 

Carcharhinus tilstoni 

Carcharhinus amblyrhynchos 

Rhizoprionodon acutus 

Glyphis glyphis 

O’Connell et al. (2010) 

Ginglymostoma cirratum 

BaeFeeO Magnets Proof of concept Yes 

Dasyatis americana 

O’Connell et al. (2011a) Negaprion brevirostris BaeFeeO Magnets Captive experiment Yes 

O’Connell et al. (2011b) 

Carcharhinus limbatus 

BaeFeeO Magnets 

Recreational fishing 

Partial 

Carcharhinus plumbeus 

Dasyatis americana 

Mustelus canis 

Raja eglanteria 

Rhizoprionodon terraenovae 

NdeFeeB Magnets 

Longline fishing 

Robbins et al. (2011) Carcharhinus galapagensis Ferrite Magnets NdeFeeB Magnets Proof of concept Partial 

the teleost L. calcarifer, not showing any aversive reactions to the 

magnets illustrating the selectivity of this technology. Additionally, 

the distances with which the elasmobranchs responded to the 

magnets differed, with C. tilstoni, R. acutus and S. lewini reacting at 

similar distances from the treatments and C. amblyrhynchos and 

G. glyphis reacting at much closer distances from the magnets 

(Fig. 4b). These species-specific responses to the magnets were 

suggested to be due to differences in habitat and feeding ecology, 

with certain habitats (e.g. coastal/turbid environments) and associated 

feeding ecologies requiring greater electroreception capabilities 

leading to greater sensitivity to magnetic fields. 

O’Connell et al., 2010 conducted a baseline field experiment 

which examined the behavioral responses of wild southern stingrays 

(Dasyatis americana) and nurse sharks (Ginglymostoma cirratum) 

to grade C8 bariumeferrite (BaFe 12 O 19 ) magnets. D. americana 

and G. cirratum exhibited a significantly greater quantity of avoidance 

behaviors and significantly fewer feeding behaviors toward 

magnetic treatments. The results from this study demonstrated the 

potential utility of bariumeferrite magnets as benthic 

elasmobranch-deterrent devices and in conjunction with Rigg et al. 

(2009), suggested that futures studies should test these repellents 

in a more applied sense. 

2.2. Recreational and longlining applications 

2.2.1. Focal order: Squaliformes 

The spiny dogfish (Squalus acanthias), has been subjected to 

severe overharvesting causing great concern to many fisheries 

managers (MAFMC, 1998). In response to this overharvesting, Fisheries 

Management Plans have been implemented by the Atlantic 

States Marine Fisheries Commission, the Mid-Atlantic Fisheries 

Management Council and the New England Fishery Management 

Council, leading to the rebuilt status of the northwest Atlantic 

S. acanthias stock (Rago and Sosobee, 2009). Although population 

rejuvenation of S. acanthias has been successful in the northwest 

Atlantic, the development of bycatch reduction technology is of 

upmost importance to minimize future S. acanthias bycatch on 

a variety of commercial gears. In response to the need for effective 

bycatch technology, a variety of studies have been conducted which 

examine the potential use of electrosensory materials on S. acanthias 

behavior to determine their utility on longline gear. 

Stoner and Kaimmer (2008) conducted laboratory investigations 

on the effects of an EPM alloy (64.02% cerium, 34.22% lanthanum, 

0.55% neodymium, 0.11% praseodymium and impurities) and 

neodymiumeironeboron magnets on Pacific spiny dogfish 

Table 2 

Description of all studies conducted from 2008epresent using electropositive metal (EPM) alloys (CeeLaeNdePr ¼ alloy primarily composed of cerium, lanthanum, 

neodymium, and praseodymium; NdePr ¼ alloy primarily composed of neodymium and praseodymium; CeeLa ¼ alloy primarily composed of cerium and lanthium) or a pure 

EPM (Nd ¼ neodymium) as elasmobranch repellents. Elasmobranch species which were studied are listed in the appropriate column, along with the purpose of the research 

(i.e. application). If the researchers were just evaluating the effects of repellents, but not for a particular fisheries application, the term “proof of concept” was assigned. 

Additionally, success was ranked on a scale of “None” e no observed effects, “Yes” e induced some effect on all species tested, “Partial” e induced some effect on several, but not 

all species studied. 

Study Species studied Repellent tested Application Success 

Brill et al. (2009) Carcharhinus plumbeus CeeLaeNdePr Alloy Captive experiments Yes 

Brill et al. (2009) Carcharhinus plumbeus NdePr Alloy Longline fishing Yes 

Jordan et al. (2011) 

Squalus acanthias 

Nd Captive experiment Partial 

Mustelus canis 

Kaimmer and Stoner (2008) 

Squalus acanthias 

CeeLaeNdePr Alloy Longline fishing Yes 

Raja rhina 

Robbins et al. (2011) Carcharhinus galapagensis NdePr Alloy Proof of concept No 

Stoner and Kaimmer (2008) Squalus acanthias CeeLaeNdePr Alloy Captive experiments Yes 

Tallack and Mandelman (2009) Squalus acanthias CeeLa Alloy Captive experiments No 

Tallack and Mandelman (2009) Squalus acanthias CeeLa Alloy Longline fishing 

No 

Jigging 

Wang et al. (2008) 

Carcharhinus galapagensis 

Carcharhinus plumbeus 

NdePr alloy Proof of Concept Yes 





Fig. 4. a) Total aversion responses (p < 0.01) of Galapagos (Carcharhinus galapagensis) and sandbar sharks (Carcharhinus plumbeus) towards the lead weight control and electropositive 

metal (NdePr metal alloy). Modified from Wang et al. (2008). b) The mean reaction distance to turn from ferrite magnets for five elasmobranch species: gray reef shark 

(Carcharhinus amblyrhynchos), Australian blacktip shark (Carcharhinus tilstoni), milk shark (Rhizoprionodon acutus), scalloped hammerhead (Sphyrna lewini), and speartooth shark 

(Glyphis glyphis). The means for C. tilstoni, R. acutus, and S. lewini were not significantly different; however, both C. amblyrhynchos and G. glyphis were. Error bars represent 95% 

confidence limits. Modified from Rigg et al. (2009). 

(S. acanthias) and Pacific halibut (Hippoglossus stenolepis). Results 

demonstrated that metals significantly altered the feeding behavior 

of interacting S. acanthias and not H. stenolepis, whereas magnets 

were observed to have little effect during baited experimentation. 

Encouraged by the results of the laboratory studies, Kaimmer and 

Stoner (2008) conducted field investigations using an EPM alloy of 

same elemental composition as used in Stoner and Kaimmer (2008) 

to examine its deterrent capabilities in a commercial fishery targeting 

Pacific halibut (H. stenolepis), sablefish (Anoplopoma fimbria), 

and Pacific cod (Gadus macrocephalus) near Homer, Alaska. EPM 

alloy-associated hooks yielded a 19% reduction in S. acanthias 

bycatch and a 46% reduction of longnose skate (Raja rhina) bycatch in 

comparison to controls. Besides the catch of both S. acanthias and 

R. rhina, several teleosts species were captured in high frequency, 

including H. stenolepis and sculpins (unclassified); however, neither 

showed catch trends on EPM alloy-associated hooks demonstrating 

the selective characteristics of the metal. 

In contrast to the positive findings reported by Kaimmer and 

Stoner (2008) and Stoner and Kaimmer (2008), Tallack and 

Mandelman (2009) conducted a very similar study with contradicting 

results. Tallack and Mandelman analyzed the effect of an 

EPM alloy, composed mainly of cerium and lanthanide, on the 

Atlantic spiny dogfish (S. acanthias) in both laboratory and field 

studies. Laboratory results provided minimal evidence of deterrent 

success, with signs of deterrence being highly correlated with food 

deprivation level. Additionally, in both longline and jigging experiments, 

no observed reduction in S. acanthias capture was observed, 

and too few haddock (Melanogrammus aeglefinus), redfish (Sebastes 

fasciatus) and sea raven (Hemitripterus americanus) were captured 

to conduct any statistical analyses. 

Lastly, Jordan et al. (2011) conducted a comparative laboratory 

experiment examining the electro-sensitivities of two species of 

shark, S. acanthias and the smooth dogfish (Mustelus canis); 

however, the results pertaining to M. canis will be discussed in 

a later section. For the first part of this study, S. acanthias exhibited 

a sensitivity to weak electric fields (

6 


Fig. 5. The positioning at 1 s intervals (black dots) of one juvenile sandbar shark (Carcharhinus plumbeus) measured over a 2 h duration (1 h lead weight control and 1 h EPM). a) The 

positioning at 1 s intervals (black dots) of one juvenile C. plumbeus to three lead ingots (gray triangle) suspended in the tank for a duration of 1 h b) Experimental treatment 

examining the swimming pattern of one C. plumbeus at 1 s intervals in response to three EPM ingots (gray triangle) suspended in the tank for 1 h. Significantly fewer shark 

interactions occurred within 100 cm of the electropositive metal bars (b), in comparison to the lead ingots (a). Illustration taken from Brill et al. (2009). 

neodymiumeironeboron magnets significantly reduced total elasmobranch 

and capture of several elasmobranch species: Atlantic 

sharpnose shark (Rhizoprionodon terraenovae) and smooth dogfish 

(M. canis). For the inshore longline experiment, results demonstrated 

that neodymiumeironeboron magnets had no impact on elasmobranch 

capture whereas the bariumeferrite magnet significantly 

reduced total elasmobranch capture, in addition to the capture of the 

blacktip shark (Carcharhinus limbatus) andthesouthernstingray(D. 

americana). Teleosts, such as red drum (Sciaenops ocellatus), Atlantic 

croaker (Micropogonias undulatus), oyster toadfish (Opsanus tau), 

black sea bass (Centropristis striata), and the bluefish (Pomatomus 

saltatrix), showed no hook preference in either hook-and-line or 

longline studies. This study concluded that magnet-induced repellent 

behaviors may be a species-specific phenomenon and the magnetic 

characteristic known as the axis of polarization, similar to findings in 

Robbins et al. (2011), may be the key component to finding an effective 

magnetic shark repellent (Fig. 6b). 

2.3. Beach net applications 

Fig. 6. a) This illustration represents the 50 mm magnetic rare-earth magnetic discs 

which reduced Galapagos shark (Carcharhinus galapagensis) depredation rate by 50%. 

The magnetic flux along the bait ranged from 372 to 1474 G. Illustration taken from 

Robbins et al. (2011). b) This illustration represents the grade C8 bariumeferrite 

permanent magnet which significantly reduced overall elasmobranch capture in 

inshore longline trials. The axis of polarization extended vertically, over the entire bait 

and had a maximum flux of 3850 G. Illustration modified from O’Connell et al. (2011b). 

Neither image is drawn to scale. 

Beach nets are devices used to minimize the potential interaction 

between predatory shark species (e.g. great white shark- 

Carcharodon carcharias, tiger shark-Galeocerdo cuvier, and bull 

shark-Carcharhinus leucas) and beachgoers (Cliff and Dudley, 1992; 

Dudley, 1997). Although these nets are successful at minimizing 

this interaction, experimental evidence demonstrates that local 

elasmobranch populations have plummeted (Dudley, 1997; Stevens 

et al., 2000; Dudley and Cliff, 1993). 

As a means to examine the potential utility of ceramic magnets 

to exclude sharks from netted areas, O’Connell et al. (2011a) conducted 

a captive study where lemon sharks (Negaprion brevirostris) 

were individually subjected to a fence-like apparatus containing 

both a control (clay bricks) and magnetic (grade C8 bariumeferrite 

magnets) opening. Results demonstrated that ceramic magnets 

were efficient at manipulating the swimming behavior of 

N. brevirostris; however, barrier trials and tonic immobility trials 

demonstrated that habituation to the magnetic fields occurs due to 

repeated stimulation over a short duration (Fig. 7). It is uncertain 

how these results would relate to experiments conducted on wild 

sharks, but was deemed unlikely to be as high as the frequency of 





Fig. 7. The total behaviors from three lemon sharks (Negaprion brevirostris), with the treatment variables (C¼Control; M ¼ Magnet) listed on the x-axis. a) The total avoidance 

behaviors (p < 0.001) of the three sharks in trial one and trial two. b) The total number of entrances (p < 0.001) of the three sharks in trial one and trial two. Illustration taken from 

O’Connell et al. (2011a). 

interaction seen in this experiment and thus is unknown if sensory 

habituation would occur. 

3. Factors affecting repellent success 

Prior to drawing conclusions from the current body of research 

pertaining to electrosensory repellents and as a means to understand 

inconsistent results, it is imperative that scientists monitor 

a variety of biological and environmental parameters which may 

influence repellent success. Although it is important that scientists 

analyze the basic behavioral responses of elasmobranchs toward 

various electrosensory stimuli, studying parameters that may alter 

success will give scientists valuable insight as to methods and 

conditions which will yield the most successful implementation. 

3.1. Satiation 

The availability of prey can be influenced by a variety of factors, 

including: climate change (e.g. Loeb et al., 1997; Polovina, 1996), 

fisheries (e.g. Bearzi et al., 2006), and predator abundance (e.g. 

Connell, 1998). With changing prey densities, predator satiation 

may concurrently change which may greatly influence predator 

behavior (Williamson, 1980). To determine how the level of satiation 

could effect electrosensory repellent success, several laboratory 

studies were conducted (Stoner and Kaimmer, 2008; Tallack 

and Mandelman, 2009). Stoner and Kaimmer (2008) demonstrated 

that EPM repellent effectiveness on S. acanthias was found 

to be highly correlated with food deprivation where increasing 

levels of food deprivation (2 and 4 days) resulted in decreased 

repellent success. Similarly, Tallack and Mandelman (2009) 

demonstrated that the responsiveness of S. acanthias to EPM 

stimuli was inversely proportional to the level of food deprivation. 

Therefore one influential factor which may be pertinent to the 

success of electrosensory deterrents is animal satiation. It is unclear 

how these laboratory findings would translate to the field and 

future experimentation is needed; however, if these findings hold 

true, situations where the level of satiation may be highest (e.g. 

seasonality of prey abundance, lack of fishing pressure, healthy 

ecosystem) may increase the likelihood of repellent success and 

thus be pertinent to future implementation strategies. 

3.2. Water visibilityeturbidity and light intensity 

Little is known about the effect of water visibility on elasmobranch 

sensory allocation; however, preliminary experimentation 

with the bull shark (C. leucas) illustrates that increased turbidity 

and low water visibility conditions increase the repellent effectiveness 

of ceramic magnets (O’Connell et al., submitted for 

publication). Similar to where blind humans show enhanced 

auditory localization capabilities in comparison to sighted humans 

(Lessard et al., 1998; Muchnik et al., 1991; Rice, 1970), it may be 

possible that the electrosensory capabilities of elasmobranchs are 

altered in conditions when vision is compromised, therefore 

maximizing the effectiveness of electrosensory repellents. 

Upon further consideration, although turbidity may drastically 

alter the extent of the visual field of elasmobranchs and may yield 

differences in sensitivity to electrosensory repellents, the electrosensory 

differences due to variations in light intensity (e.g. day 

versus night) may be minimal due to the light-reflecting layer 

behind the retina known as the tapetum lucidum (Gruber and 

Cohen, 1985). This structure maximizes light available for lowlight 

conditions. Therefore although future studies should not 

neglect light intensity, turbidity may be a more influential factor in 

electrosensory repellent success and may provide pertinent information 

as to the locations which will yield the most success (e.g. 

turbid coastal environments). 

3.3. Presence of conspecifics and heterospecifics 

Intra- and inter-specific competition is highly reported in the 

literature (Crombie, 1947; Connell, 1961; Polis, 1981; Stiling et al., 

1984; Munday et al., 2001) and illustrates that the presence of 

conspecifics and/or heterospecifics induces a competitive 

mentality, often leading to an abrupt change in behavior. Brill et al. 

(2009) conducted a laboratory experiment which examined the 

feeding response of juvenile sandbar sharks (C. plumbeus) attwo 

different density levels (n ¼ 7; n ¼ 14) toward an EPM alloy. During 

high-density trials (e.g. 14 sharks), the deterrent effects were 

minimal and short-lived; however, C. plumbeus demonstrated 

a sensitivity to EPM alloys during low-density trials and therefore 

the researchers concluded that competition plays a role in the 

effectiveness of EPM alloys. (Brill et al., 2009). In a more recent 

study conducted by Robbins et al. (2011), the efficacy of seven rareearth 

(neodymiumeironeboron) magnet, two ferrite magnet, and 

two EPM (NdePr: neodymiumepraseodymium) alloy configurations 

on reducing the depredation rate of the Galapagos shark (C. 

galapagensis) on baited lines was examined. During high density 

levels (greater than 3 sharks) results illustrate that EPMs were 

ineffective; however, in low density trials behavior was exploratory 

and cautious. With these findings, this study concluded that 

conspecific density greatly impacted repellent success and suggested 

that these repellents may be better suited for recreational 




8 


and commercial fishing industries where shark densities are 

sufficiently low. Lastly, Jordan et al. (2011) examined the deterrent 

capabilities of an EPM stimulus (NeodymiumeNd) on the smooth 

dogfish (M. canis). When tested in groups, M. canis preferred to feed 

from EPM-associated baits, whereas individually tested M. canis 

were significantly deterred by EPM-associated baits. This demonstrates 

that the effectiveness of EPMs, or more specifically, 

Neodymium on M. canis, may be heavily influenced by conspecific 

density. Therefore, future studies should account for animal density 

as these studies illustrate that density-induced behavioral changes 

toward electrosensory deterrents is plausible. 

3.4. Salinity 

In regards to EPMs, the conductive medium is an essential 

component to the successful transfer of cations from the surface of 

the metal to the approaching electronegative shark. The lower the 

resistivity, or opposition of electric current, as seen in highly saline 

environments (Chave et al., 1991; Eidesmo et al., 2002), will result 

in the successful transfer of these cations and prove the metals to 

be more effective (Stroud, 2008a). It is essential that future studies 

monitor salinity, as deploying metals in open ocean regions (i.e. 

peak salinity) may produce drastically different results in 

comparison to estuarine or nearshore environments that are 

heavily influenced by freshwater input. 

It is uncertain how salinity may impact elasmobranch magnetoreception. 

In order for elasmobranch magnetoreception to occur, 

two key elements are required for active and/or passive electromagnetic 

induction: a magnetic field (B) and velocity (v) (Kalmijn, 

1982, 1984). For the active mode of electromagnetic induction, the 

velocity corresponds to movement of the organism through B h 

(horizontal portion of Earth’s geomagnetic field); however, in the 

passive mode, the velocity component refers to the velocity of the 

ocean currents through B v (vertical portion of Earth’s geomagnetic 

field). Although v and B are key elements required for elasmobranch 

magnetic field detection, another element is the conductive 

medium that the animal is swimming within (Kalmijn, 1974, 1984, 

1997). The resistivity of seawater and freshwater drastically differs, 

with freshwater being characterized of having a resistivity of 2e 

200 U m and seawater 0.3 U m(Pashley et al., 2005; Chave et al., 

1991; Eidesmo et al., 2002). In lower salinity conditions, the electric 

potential gradients between the pore (apical) and internal 

(basal) structures that are responsible for neural activity, tend to be 

minimal thus making the induction mechanism less efficient in 

freshwater (Kalmijn, 1974, 1981, 1984). Therefore, salinity may 

impact the magnetoreception capabilities of elasmobranchs and 

estuarine, brackish water, or even freshwater ecosystems may not 

be ideal ecosystems for magnetic deterrents (Kalmijn, 1974, 1984). 

3.5. Animal size/canal length 

Ontogentic shifts in electroreceptor sensitivity has been 

demonstrated with several elasmobranch species (Sisneros et al., 

1998; Sisneros and Tricas, 2002). It is suggested that these shifts 

or increases in sensitivity as an animal matures is directly related to 

increasing ampullary canal legnth. The ampullae of Lorenzini 

function on voltage gradients, with neurotransmitters being 

released to primary afferent neurons when a difference exists 

between the pore (apical) and internal (basal) potentials (Bennett, 

1971; Tricas, 2001). Thus enhanced sensitivity is a function of canal 

length since greater voltage gradients exist between the pore 

surface and internal ampullary canal as ampullary canals lengthen. 

In addition, previous studies pertaining to the Atlantic stingray 

(Dasyatis sabina) and clearnose skate (Raja eglanteria) demonstrate 

that with maturity there is a gain of electrosensory primary 

afferents and, presumably, neural sensitivity (Sisneros et al., 1998; 

Sisneros and Tricas, 2002). In R. eglanteria, the neural sensitivity 

was eight times greater in adults and five times greater in juveniles 

in comparison to embryos (Sisneros et al., 1998). Similarly, in 

D. sabina, the neural sensitivity was four times greater in adults and 

three times greater in juveniles when being compared to embryos 

(Sisneros and Tricas, 2002). Therefore, animal size which is related 

to ampullary canal length, and in some cases, an increase in the 

quantity of afferent neurons, may influence the success of electrosensory 

deterrents, with larger and more mature animals having 

enhanced sensitivity and thus a greater potential to be deterred. 

4. Commercial application 

Besides assessing the effectiveness of these repellents on 

interacting species, it is essential to also consider a variety of other 

characteristics/issues pertaining to these repellents, such as: cost, 

safety, pollution, and handling logistics. 

4.1. Cost of repellents 

The use of certain EPM and magnets may be prohibitively 

expensive when deployed in large quantities, such as for 

commercial fishing hooks. Jordan et al. (2011) proposed the use of 

neodymium metal due to its field strength and relative cost in 

comparison to other lanthanide metals, but it is likely that using 

a pure lanthanide metal in a commercial fishery is economically 

impractical. While the PEW Institute (Cosandey-Goden and 

Morgan, 2011) conclude that “significant cost” precludes EPMs as 

an “economically viable option”, the authors fail to consider 

abundant and cost-effective reactive metals. Metals with a higher 

reduction potential at a fraction of the cost of pure lanthanides have 

been shown to be effective (O’Connell et al., submitted for 

publication). Magnesium and certain magnesium alloys, at $0.05 

US/gram in quantity for 99% þ purity, are much more practical and 

easier to fabricate for fishing gear requirements. 

4.2. Magnet-associated issues 

Besides varying successes with magnetic repellents (Rigg et al., 

2009; O’Connell et al., 2010, 2011a, 2011b), there exists a variety of 

issues which one must consider prior to implementation and/or 

application. (1) When working in close proximity to neodymiume 

ironeboron and bariumeferrite magnets on a research vessel or 

platform, these magnets can be prohibitively difficult to work with 

and potentially very dangerous and cause bodily harm if a finger or 

other body part becomes trapped between two magnets. (2) These 

materials have the ability to permanently destroy electronic 

equipment (e.g. cameras and computers) and thus should be 

handled with care. (3) When applying magnets directly to a fishing 

hook, the presence of this large visual stimulus (e.g. the magnet) 

may potentially interfere with target catch unless hooks are 

magnetized thus removing the visual component. (4) If applying 

magnets directly to fishing hooks or for beach net-associated 

applications, it is inevitable that some magnets will be lost 

causing pollution. (5) Lastly, it is currently not understood how 

exposing organisms to strong magnetic fields may impact their 

electroreception of navigational capabilities and thus prior to 

commercial application this topic should be extensively studied. 

4.3. EPM-associated issues 

EPMs have shown promise in both laboratory (Stoner and 

Kaimmer, 2008; Brill et al., 2009; Jordan et al., 2011) and field 

experimentation (Kaimmer and Stoner, 2008; Wang et al., 2008). 





However, several issues arise when working with these materials: 

(1) These materials are flammable and this presents a variety of 

challenges both on land and at sea. (2) EPMs undergo rapid hydrolysis 

when placed in seawater. Although EPM degradation varies 

depending on reactivity, it is uncertain how cost-effective these 

materials will be if in constant need of replacement. (3) Similar to 

magnets, when applied to a hook an EPM ingot creates a large visual 

stimulus which may impact target catch. (4) The constant utilization, 

degradation and potential loss of materials in seawater is 

a source of pollution and must be taken into consideration. (5) Most 

importantly, it is unknown how these materials may physiologically 

affect interacting organisms in short and long term basis. 

4.4. Semiochemical-associated issues 

To date, little information exists pertaining to semiochemicals. 

Of the evidence that does exist, it was determined that very small 

quantities of semiochemicals, approximately 50 10 6 L are 

needed to evoke a repellent response while a shark is in tonic 

immobility (Stroud, 2008b). But, even with this minimal introduction 

of chemicals into seawater, a variety of issues can arise 

unless the chemicals are derived from natural sources. (1) The 

chemicals being introduced into the ecosystem are synthetic or 

superpotent and thus may serve as an environmental pollutant, 

although as stated in Stroud (2008b) components of chemical 

repellents are compliant with regulations pertaining to the United 

States Environmental Protection Agency, the Food and Drug 

Administration, the Department of Transportation, and the 

National Marine Fisheries Service. (2) In addition with chemicals, 

their success will be heavily dependent on currents and 

geographical features of the area. In situations where currents are 

slack or minimal, this will lead to minimal chemical dispersion and 

may make the chemical nearly ineffective at far distances. (3) In 

situations when sharks are approaching from the opposite direction 

from the source of the semiochemical, it may also minimize the 

effectiveness of the chemicals. (4) Lastly, it is unknown how the 

semiochemicals may affect the olfactory and/or gustatory receptors 

or other biological tissues of interacting organisms. Therefore 

extensive future research is needed on these aspects. 

5. Conclusion and future directions 

With the wide range of experiments examining the effects of 

electrosensory stimuli on elasmobranchs, evidence supports that 

elasmobranchs can detect the stimuli (e.g. Kaimmer and Stoner, 

2008; Rigg et al., 2009), but the species-specificity of the repellent 

responses (e.g. O’Connell et al., 2011b, Jordan et al., 2011) remains 

unclear. It is essential for future research to understand: (1) the 

environmental or physiological characteristics which may be most 

responsible for electrosensory sensitivity to magnetic or EPM 

repellents, (2) the best applications for each type of repellent with 

the recreational fishery being a possible candidate for future 

research due to minimal experimentation thus far, and (3) to 

understand the physiological effects of these repellents on interacting 

elasmobranchs. This field should no longer be solely assessing 

whether electrosensory repellents work as evidence now demonstrates 

the efficacy of repellents (Kaimmer and Stoner, 2008; Brill 

et al., 2009; Rigg et al., 2009; O’Connell et al., 2010; O’Connell 

et al., 2011a,b; Jordan et al., 2011), but this field may be enhanced 

through rigorous laboratory investigations, or field investigations 

when possible, which focus on what parameters maximize repellent 

effectiveness so future implementation will maximize the likelihood 

for success. Lastly, little evidence has been presented on the 

behavioral effects of current shark repellent technologies on teleost, 

mammalian, or chelonian species. Studies must be conducted on 

these species, as it will be essential prior to the final implementation 

of any repellents technology to fishing gears or beach nets. 

Acknowledgments 

We first would like to thank the School of Marine Science and 

Technology (SMAST) at the University of Massachusetts Dartmouth 

for their support. We thank Dr. Adrianus J. Kalmijn for sharing his 

invaluable knowledge pertaining to the mechanisms underlying 

elasmobranch magnetoreception. Lastly, we would like to thank Dr. 

John Mandelman, Dr. Laura Jordan and Dr. Steve Kajiura for their 

editorial comments as they greatly benefitted this manuscript. 

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