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Fishery Bulletin 107(3) 
0-5 45-50 95-100 145-150 195-200 245-250 
Distance bin (cm) 
Figure 2 
Frequency distributions (based on 5-cm bins) of the observed dis- 
tances in relation to lead fishing weights (filled circles) or electroposi- 
tive metal (open circles) calculated at 1-sec intervals from the video 
records of juvenile sandbar shai'ks ( Carcharhinus plumbeus, n = 10). 
When compared to the lead weights, significantly fewer (indicated 
by *, two-way repeated measures ANOVA, P <0.05) shark positions 
were recorded within 100 cm of electropositive meta, whereas more 
positions were recorded at distances more than approximately 200 
cm from electropositive metal. 
quently passed between the lead fishing 
weights and tank wall. In contrast, sharks 
generally avoided approaching electropositive 
metal bars, which precluded them from pass- 
ing between the electropositive metal bars 
and the tank wall. The locations of a single 
sandbar shark typifying these behaviors are 
shown in Figure 1. 
The frequency distributions of positions in 
relation to the lead fishing weights or elec- 
tropositive metal bars demonstrate avoidance 
of the latter by the sharks (Fig. 2). Signifi- 
cantly fewer positions were recorded within 
approximately 100 cm of the electropositive 
metal bars, and significantly more positions 
at the maximum distances (further than ap- 
proximately 200 cm from the electroposi- 
tive metal bars). The frequency distributions 
under both circumstances increased with 
distance and truncated sharply at the great- 
est distances because of simple positional 
geometry and the limitations imposed by the 
dimensions of the circular test tank. 
The swimming speed data were not nor- 
mally distributed and are therefore shown 
as box and whisker plots (Fig. 3). There 
appeared to be a tendency for swimming 
speeds to be greater in proximity to the 
electropositive metal bars than under the 
other circumstances. However, the small dif- 
ferences and extreme variability precluded 
statistically significant differences. 
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Figure 3 
Median swimming speeds in body lengths per second 
(BL/s) when juvenile sandbar sharks (Carcharhinus 
plumbeus) were within 100 cm of electropositive metal 
(A), more than 100 cm from electropositive metal (B), 
within 100 cm of lead fishing weights (C), and more 
than 100 cm from lead fishing weights (D). The high 
variability precluded statistically significant differences, 
but there appears to be a trend for fish to swim faster in 
proximity to electropositive metal than under the other 
circumstances. Limits of boxes show the 25 th and 75 th 
percentiles, the error bars the 90 th and 10 th percentiles, 
and the single points the 95 th and 5 th percentiles. 
Feeding deterrent experiments 
Bait pieces located approximately 30 cm from a stain- 
less steel bolt were generally attacked within 30 sec- 
onds of presentation (Figs. 4 and 5). In contrast, 
sharks did not attack baits located in proximity of an 
electropositive metal bar within three minutes, at least 
during the initial trials. When the repulsive effect was 
evident, sharks would rapidly approach the bait, flinch, 
turn sharply, and rapidly depart. Although we were 
not able to quantify these behaviors, they matched 
the responses of spiny dogfish sharks under simi- 
lar circumstances described by Stoner and Kaimmer 
(2008) and mirrored the apparent changes in swim- 
ming speeds of individual sharks near electropositive 
metal (Fig. 3). 
When 14 sharks were present in the tank (Fig. 4), 
the repulsive effect extinguished fairly suddenly during 
day 2, but reappeared during the initial trials on day 
4, and again during the initial trials on days 10 and 
21. Because it was impossible to identify individuals, 
it is unknown if only one or a few sharks overcame the 
deterrent effect of electropositive metal. The repulsive 
effect did not reappear after a one-week period where 
trials were not run; indicating that once tolerance of 
electropositive metal is learned it is retained at least 
over the short term. 
