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Fishery Bulletin 109(4) 
Figure 1 
Hook treatments used in the longline and hook-and-line experiments to examine the deterrent effects 
of permanent magnets on elasmobranchs. (A) Configuration of the magnetic treatment used on exper- 
imental longlines, (B) configuration of the control treatment used on experimental longlines, and 
(C) the magnetic, procedural control, and control treatments used for the recreational fishing experiment. 
Hook-and-line study 
The hook-and-line fishing experiment was conducted off 
Springmaid Pier (33°39'N, 78°54'W) in Myrtle Beach, 
South Carolina, between January 2008 and April 2009. 
Three medium-action rods and reel combinations were 
used in each trial. Rods were equipped with Penn Cap- 
tiva CLL4000 reels with 9.07-kg-test monofilament line, 
0.30-m steel leader, and egg-shaped sinkers weighing 
between 85 and 142 g. 
Because elasmobranch fauna varied with water tem- 
perature, 6/0 hooks baited with pink shrimp ( Penaeus 
spp.), squid ( Loligo spp.), or freshly caught pinfish (La- 
godon 7'hotnboides) were used during warmer months 
(April-October; mean sea surface temperature 24°C), 
and 2/0 hooks baited with 50 g pieces of Atlantic men- 
haden (Brevoortia tyrannus ) were used in colder months 
(December-March; mean sea surface temperature 11°C). 
At equally spaced locations along the pier, the rods 
were randomly arranged. Lines were cast, fished for 
fifteen minutes, and then retrieved. Each trial consisted 
of three hook treatments: 1) control, 2) procedural con- 
trol (sham magnet), and 3) magnetic treatment (Fig. 
1C). The control consisted of an untreated hook (i.e., 
no addition to the shank). The procedural control con- 
tained a lead weight of similar dimensions to those in 
the magnetic treatment and was attached to the hook 
shank with duct tape. The magnetic treatment con- 
tained a neodymium-iron-boron tube magnet (12-mm 
outer diameter, 5.5-mm inner diameter, and 25-mm 
height), magnetized through the height, and attached 
with duct tape to the shank of a hook. If any bait was 
removed or tampered with, all three treatments were 
rebaited with fresh bait of identical species. If a fish 
was found on any of the three lines, the remaining two 
lines were retrieved so that all three lines were in the 
water for the same duration. When a fish was caught, 
it was identified, measured (PCL, FL, TL, STL), the sex 
of elasmobranchs was determined, and treatment type 
was noted. Once the fish was de-hooked, all three lines 
were redeployed for the remaining minutes of the trial. 
Fishing occurred irrespective of tides and day or night. 
Statistical analysis 
For both the hook-and-line and longline experiments, 
total elasmobranch and teleost catches were analyzed 
separately. For the longline study, an individual chi- 
square analysis was used to compare the effectiveness of 
magnet type compared to the control. Also, a chi-square 
analysis was conducted on individual species if more 
than five individuals were caught during one treatment. 
For the hook-and-line study, a chi-square analysis was 
conducted to compare control and procedural control 
hook data in order to determine whether the presence of 
an object (sham-magnet) on a hook altered fish capture. 
If no statistical difference was observed, further analy- 
sis was conducted on catches of control versus magnetic 
treatments. As with longline analyses, if more than five 
individuals from one species were captured during one 
treatment, a chi-square analysis was conducted for that 
species to determine species-specific trends. 
Results 
Longline: neodymium-iron-boron magnets 
Five species of elasmobranchs were captured on long- 
lines during the neodymium-iron-boron magnetic trials 
