189 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
^ established in 1881 -<?. 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Efficacy of 2 common bait types in reducing 
bycatch of coastal sharks on bottom longline 
gear in the absence of choice 
Email address for contact author: william.driggers@noaa.gov 
Abstract-— A recent study determined 
that when simultaneously exposed to 
2 different commonly used baits, certain 
shark species demonstrate preferences 
for a specific bait on bottom longlines. 
To further investigate the value of bait 
type to reduce shark bycatch, we con¬ 
ducted single-bait-type bottom longline 
sets with standardized gear baited 
with either mackerel or squid. For 4 of 
the 5 shark species captured, there was 
no significant difference in catch rates 
with bait type. However, catch rates of 
Atlantic sharpnose sharks ( Rhizopri- 
onodon terraenovae) were significantly 
higher on mackerel-baited hooks. Our 
results indicate that the use of squid 
as bait can reduce the catch of at least 
one shark species in the northern Gulf 
of Mexico while not reducing the catch 
of a targeted species, in this case, the 
red snapper (Lutjanus campechanus). 
However, because some protected spe¬ 
cies, most notably sea turtles, have 
been shown to have higher catch rates 
on squid-baited hooks, it is necessary to 
assess the effect of a specific bait across 
all taxa directly or indirectly affected 
by a particular gear type before adopt¬ 
ing any bycatch reduction measure. 
Manuscript submitted 25 March 2019. 
Manuscript accepted 24 July 2019. 
Fish. Bull. 117:189-195 (2019). 
Online publication date: 1 August 2019. 
doi: 10.7755/FB.117.3.6 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
William B. Driggers III (contact author) 1 
Kristin M. Hannan 2 
1 Mississippi Laboratories 
Southeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
3209 Frederic Street 
Pascagoula, Mississippi 39567-41 12 
2 Riverside Technology Inc. 
Mississippi Laboratories 
Southeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
3209 Frederic Street 
Pascagoula, Mississippi 39567-4112 
Globally, shark populations are widely 
reported to be in decline (for a recent 
review, see Dulvy et al., 2014). Although 
a number of factors contribute to this 
trend, bycatch of sharks is a primary 
factor (Oliver et al., 2015). A number 
of potential shark bycatch mitigation 
measures have been considered, includ¬ 
ing time or area closures, gear modifi¬ 
cations, adaptive fishing practices, and 
use of repellents (Molina and Cooke, 
2012). Several studies have investigated 
the efficacy of bait type in reducing 
shark bycatch rates (e.g., Broadhurst 
and Hazin, 2001; Watson et al., 2005; 
Yokota et al., 2009); however, results 
of studies examining the relationship 
between catch rates and bait type on 
longline gear are often conflicting. For 
example, in studies with comparable 
gear comparing squid and mackerel 
baits, Watson et al. (2005) and Foster 
et al. (2012) found that catch of blue 
sharks ( Prionace glauca) was highest 
on pelagic longlines when squid (Illex 
spp.) was used compared with when 
bait of Atlantic mackerel ( Scomber 
scombrus ) was used, whereas Coelho 
et al. (2012) reported a higher catch of 
blue sharks on mackerel (Scomber spp.) 
bait than on squid bait. All 3 studies 
used a single bait type on each longline 
set. However, none addressed potential 
biasing factors of this experimental 
design in assessing bait preference of 
blue sharks, most notably the propen¬ 
sity for this shark species to form large 
aggregations in discrete locations (e.g., 
Kenney et al., 1985; Litvinov, 2006) 
where only a single bait type would 
have been used. 
Driggers et al. (2017) examined catch 
rates and bait preferences of fish spe¬ 
cies captured on bottom longline gear 
in the northern Gulf of Mexico using an 
experimental design alternating 2 bait 
types on individual bottom longline sets. 
The results of this study indicate that 
several shark species, including the lit¬ 
tle gulper shark ( Centrophorus uyato ), 
smooth dogfish (Mustelus canis), blac- 
knose shark ( Carcharhinus acronotus), 
sandbar shark (C. plumbeus), and Atlan¬ 
tic sharpnose shark (Rhizoprionodon 
terraenovae ), showed a preference for 
Atlantic mackerel over northern shortfin 
