628 
Electrotaxis in American lobsters, 
Homarus americanus, and its 
potential use in sampling 
early benthic-phase animals 
Peter Koeller 
Invertebrates Division, Biological Sciences Branch 
Department of Fisheries and Oceans 
Bedford Institute of Oceanography 
PO. Box 1 006, Dartmouth, Nova Scotia, Canada B2Y 4A2 
E-mail address: koellerp@mar.dfo-mpo.gc.ca 
Gregory Crowell 
Department of Electrical Engineering 
Technical University of Nova Scotia 
PO. Box 1 000, Halifax, Nova Scotia, Canada B3J 2X4 
The American lobster, Homarus 
americanus , fishery is an important 
part of the economy in New En- 
gland and eastern Canada. A reli- 
able predictor of recruitment to this 
fishery would be useful in stock as- 
sessments and economic planning, 
yet no such predictors are avail- 
able. The best time for a prerecruit 
survey is just after the stage-4 
postlarva (approx. 5-mm carapace 
length) settles from the plankton to 
the benthos, after high larval mor- 
talities have established the size of 
the year class, but early enough in 
the growth cycle to allow prediction 
of recruitment 4-6 years before lob- 
sters are harvested. Unfortunately, 
this is also the period when lobsters 
are most difficult to capture. Stage-4 
lobsters prefer to settle into cobble- 
sized rock substrate, often several 
layers thick, where they remain 
until they begin to enter commercial 
traps at a carapace length of about 
40 mm (Lawton and Lavalli, 1995). 
Sampling this “early benthic phase” 
(EBP) of lobsters is laborious and 
costly. A team of divers must turn 
individual rocks and capture escap- 
ing animals with suction devices (e.g. 
Hudon, 1987, Wahle and Steneck, 
1992). This method is too time con- 
suming to permit synoptic prerecruit 
surveys such as are conducted for 
groundfish. Consequently, we sought 
a more efficient sampling method for 
EBP lobster stocks along the coast 
of Nova Scotia, Canada. 
Several previous studies sug- 
gested that electrofishing may be a 
useful approach. Saila and Will- 
iams (1972) developed an electric 
trawl system that increased catches 
of commercial-size American lob- 
sters. Stewart (1974) described the 
effects of electric fields on the Nor- 
way lobster ( Nephrops norvegieus), 
including an induced avoidance be- 
havior that caused animals to leave 
their burrows. Phillips and Scolard 
(1980) developed an electrofishing 
apparatus for juvenile rock lobsters 
( Panuliris cygnus) which looked 
promising, although it caught a size 
range similar to that taken by 
traps. Our approach was funda- 
mentally different from these stud- 
ies in that we intended to develop 
a sampling “quadrant” which elec- 
trified a small area (<1 m 2 ) of the 
substrate and took advantage of 
electrically induced behavior ob- 
served in our preliminary labora- 
tory experiments. This paper pre- 
sents results from these experi- 
ments and subsequent trials with 
several potential electrode arrange- 
ments and suggests avenues for 
further development. 
Methods 
Preliminary behavioral experiments 
were conducted in tanks of various 
sizes without shelters or substrate 
to determine if electrotaxis could be 
induced in lobsters and, if so, what 
pulse lengths and voltages would 
be most effective. Lobsters ranging 
in size from 5-50 mm carapace 
length were subjected to a wide 
range of electrical stimulation includ- 
ing voltages from 10 to 100 V and 
pulse frequencies from 2 to 200 Hz. 
Pulse lengths were varied indepen- 
dently of frequency during these 
observations, but it quickly became 
obvious that a square wave form 
(pulse duration 50% of cycle length) 
with a relatively high frequency 
was most effective in inducing the 
desired response. Consequently, all 
experiments with different elec- 
trode configurations and cobble 
shelters were conducted at a DC 
pulse frequency of 100 Hz, pulse 
duration of 20 milliseconds, and an 
input voltage of 50 V. All these ex- 
periments were also conducted in 
a 1.5 m 3 tank (1 m x 2 m x 0.75 m), 
large enough so that the walls did 
not distort the relatively localized 
electric currents produced by the 
apparatus. The tank was filled with 
sand to a depth of 10 cm, and a 
group of 15 cobble-size rocks (aver- 
age weight 2.5 kg) of various shapes 
obtained from known lobster habi- 
tat were placed in the central area 
of the tank so that they were sev- 
eral layers deep and entirely con- 
tained by a 0.35 m 2 quadrant. In- 
direct overhead fluorescent lighting 
was adjusted to the natural day 
length. The tank was kept filled 
Manuscript accepted 29 August 1997. 
Fishery Bulletin 96:628-632 (1998). 
