230 
Fishery Bulletin 115(2) 
ed by the Coelho et al. (2012b) study (Atlantic Ocean: 
mean size=168.8 cm FL [SD 35.4], range=66-305 cm 
FL; Indian Ocean; mean size=193.9 cm FL [SD 24.6], 
range=138-228 cm FL), such differences could be a 
reason for the lower hooking mortality of the shortfin 
mako in the Indian Ocean. 
According to our results, there was not a significant 
difference in the VPUE, but it should be noted that our 
estimates were based on the average market price for a 
single month. A range of prices would, perhaps, better 
refiect market fluctuations. On the other hand, current 
perceptions of fishermen are that changing the bait 
from the more expensive squid to cheaper mackerel, 
is worthwhile in areas or seasons of high shark abun¬ 
dance (representing over 50% of the retained catch), as 
reported by Amorim et al. (2015) in a similar fishery in 
the southern Atlantic Ocean. Therefore, a thorough as¬ 
sessment (including the cost of replacing and repairing 
damaged gear) of the economic impact of banning wire 
leaders will be required if fisheries managers wish to 
consider such a measure to reduce unwanted bycatch 
in longline fisheries. 
The interaction of bycatch species with longlining 
gear raises a number of other concerns, namely their 
postrelease mortality (Gilman et al., 2008). Moyes et al. 
(2006), using a scientific crew, investigated postrelease 
survival of blue shark in longline fisheries in the Pa¬ 
cific Ocean, whereas Campana et al. (2009) conducted 
a similar experiment in the Atlantic Ocean but on com¬ 
mercial vessels. These authors used pop-up satellite ar¬ 
chival tags that recorded postrelease survival rates of 
blue shark of 100% (Moyes et al.) and 81%, (Campana 
et ah); the differences were attributed to the different 
study design, gear configuration (e.g., hook style and 
size, quantity of hooks and soaking time) and handling 
practices by the scientific crew in Moyes et al. (2006). 
It is known that the blue shark is a hardy shark spe¬ 
cies, and individuals are often recovered with one or 
more hooks in their bodies or mouth from previous cap¬ 
tures (senior author, personal observ.). However, it is 
not common to find reports of protected shark species 
or small sharks (or both), or commonly discarded bony 
fishes, with hooks embedded in their jaws from past 
interactions with longline gear. Therefore, we may as¬ 
sume that postrelease mortality rates are likely higher 
for those species. Campana et al. (2015) showed that 
porbeagles (Lamna nasus) and shortfin makos experi¬ 
enced much greater mortality than blue sharks in the 
Canadian pelagic longline fishery, and about one-half of 
the hooked porbeagles and shortfin makos died during 
or after fishing owing to hooking or postrelease mortal¬ 
ity. Additionally, we should note that Campana et al. 
(2015) used mainly circle hooks, whereas in our study 
we used J hooks that can affect the hooking location 
(mouth or jaw vs. deeply hooked) and consequently on 
the injuries of the discarded specimens. Apart from 
high mortality at haulback for many shark species 
(Coelho et al., 2012b), we also found high mortality 
rates at haulback with the use of nylon monofilament 
and wire leaders for commonly discarded species such 
as the longnose lancetfish (60% and 61%), and the 
snake mackerel (88% and 81%, respectively). 
The results of our work support banning wire lead¬ 
ers as an effective way of reducing shark bycatch in 
general, of lowering the number of sharks landed and, 
consequently, is an effective way of decreasing shark 
mortality in a fishery where the blue shark and the 
shortfin mako are currently the only shark species re¬ 
tained. At least some sharks are able to escape and 
survive by severing the nylon leaders, although their 
fate (delayed mortality) is still poorly known. The in¬ 
troduction of wire leaders in the southwest Indian 
Ocean swordfish longline fishery was a consequence of 
lower catch rates of the target species and a response 
to the increase in exploitation costs, with the objec¬ 
tive of increasing the revenues of fishermen. Fishery 
managers considering the banning of wire leaders in 
this swordfish fishery need to balance the potential 
beneficial effects on shark populations (particularly 
blue shark and shortfin mako) with the potential ad¬ 
verse effects on other species (particularly swordfish, 
as catches could increase). A reduction in the current 
catch levels of sharks should have a positive impact on 
the stocks, even though the current status of the shark 
stocks is unknown. According to the lOTC^, in the case 
of blue sharks, maintaining or increasing fishing effort 
will result in further declines in biomass, productivity, 
and catch rates in a stock whose current status is un¬ 
known but where the possibility of overfishing cannot 
be ruled out. For the swordfish, the most recent maxi¬ 
mum sustainable yield (MSY)-based reference points 
are uncertain for the Indian Ocean population as a 
whole, whereas the resource in the southwest Indian 
Ocean is overfished (lOTC^). Therefore an increase in 
effort or catch rates (or both) on swordfish target fisher¬ 
ies may exacerbate the problem because local depletion 
has been observed in the past decade and biomass still 
remains below the level that would produce MSY. Ad¬ 
ditionally, the human dimension (i.e., socioeconomics) 
should also be considered, because both species (i.e., 
swordfish and blue shark) are important to fishermen 
and represent over 90% of the overall retained catch. A 
combination of management measures (e.g., spatial or 
seasonal protection of critical habitats and good prac¬ 
tices in handling specimens to be released) may repre¬ 
sent a more appropriate solution to efficiently mitigate 
the incidental bycatch and mortality of species (namely 
sharks) captured in pelagic longline fisheries. 
Acknowledgments 
This study was funded by Project LL-SHARKs (ref. 31- 
03-05-FEP-44) funded through Programa Operacional 
das Pescas. R. Coelho was supported by an Investiga¬ 
tor contract (ref: IF/00253/2014) from the Portuguese 
Foundation for Science and Technology that is sup¬ 
ported by the European Union’s European Social Fund 
and the Programa Operacional Potencial Humano. We 
also thank the skipper and crew of the fishing vessel 
