Shark Depredation and Unwanted Bycatch in Pelagic Longline
Shark Depredation and Unwanted Bycatch in Pelagic Longline
Shark Depredation and Unwanted Bycatch in Pelagic Longline
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
<strong>Shark</strong> <strong>Depredation</strong> <strong>and</strong> <strong>Unwanted</strong> <strong>Bycatch</strong> <strong>in</strong> <strong>Pelagic</strong> Longl<strong>in</strong>e Fisheries<br />
If operators were <strong>in</strong>tent on l<strong>and</strong><strong>in</strong>g <strong>and</strong> process<strong>in</strong>g all sharks caught,<br />
the revenue from this was considered by half the respondents<br />
<strong>in</strong>significant when offset aga<strong>in</strong>st the time lost <strong>and</strong> crew safety<br />
compromise <strong>in</strong>volved. Time lost has the follow<strong>in</strong>g important<br />
consequences: (i) The longer it takes to haul a longl<strong>in</strong>e the more likely<br />
it is that target catch will die or be damaged, which reduces its value;<br />
<strong>and</strong> (ii) Increased time taken to haul a l<strong>in</strong>e can have a repercussion<br />
on subsequent fish<strong>in</strong>g effort potential <strong>and</strong>/or the appropriate tim<strong>in</strong>g<br />
of this to maximise target species catches.<br />
Here it is worthwhile to note that only one respondent operates <strong>in</strong><br />
a fish<strong>in</strong>g ground with a 500 hook per set limit imposition (a game<br />
fish catch <strong>and</strong> release alive, management strategy). As the average<br />
number of hooks set (which equates to time <strong>and</strong> this is thought to<br />
determ<strong>in</strong>e a fish’s likelihood of survival if discarded) <strong>in</strong> the fishery is<br />
nearly 50% more than this, it would be <strong>in</strong>terest<strong>in</strong>g to compare shark<br />
catch data here to quantify the relationship between the number<br />
of hooks set on a l<strong>in</strong>e <strong>and</strong> the survival or otherwise of sharks (<strong>and</strong><br />
other species). And, whilst there are obvious problems <strong>in</strong> compar<strong>in</strong>g<br />
species catch rates across different fish<strong>in</strong>g grounds, there can be (on<br />
average) more than twice this fish<strong>in</strong>g effort per l<strong>in</strong>e (<strong>and</strong> therefore<br />
time) elsewhere. The question here is whether species survival <strong>and</strong><br />
discard rates alter as a result of <strong>in</strong>creased hook numbers set (<strong>and</strong><br />
the <strong>in</strong>crease <strong>in</strong> total set time). Obvious economic <strong>and</strong> operational<br />
efficiency issues arise <strong>in</strong> relation to the impact of a change of this<br />
nature on target species catches.<br />
While all respondents agreed that more sharks can be caught if a<br />
wire trace is used, avoid<strong>in</strong>g sett<strong>in</strong>g hooks <strong>in</strong> certa<strong>in</strong> areas such as<br />
on the east coat cont<strong>in</strong>ental shelf, sett<strong>in</strong>g hooks at a greater depth<br />
or avoid<strong>in</strong>g especially oily (pilchards for example) or larger baits<br />
(especially squid) were all factors believed to help reduce sharks<br />
catches. Of all respondents, two had experience <strong>in</strong> us<strong>in</strong>g artificial<br />
baits <strong>and</strong> both considered them <strong>in</strong>effective for catch<strong>in</strong>g sharks<br />
compared to conventional baits. But, the suitability of such bait for<br />
target species catches is the other factor of importance.<br />
Respondents who considered that the use of light sticks (also<br />
referred to as “shark sticks”), caused higher rates of shark capture<br />
were strongly of this op<strong>in</strong>ion, but had different views about which<br />
color correlated most to high shark capture. Light sticks <strong>in</strong> blue,<br />
yellow <strong>and</strong> green were all suggested to be colors, which <strong>in</strong>creased<br />
shark catch, rates. But surpris<strong>in</strong>gly most did not consider the act of<br />
burley<strong>in</strong>g (to deliberately discharge offal <strong>and</strong> or spent bait) had any<br />
bear<strong>in</strong>g upon shark catches. In relation to this po<strong>in</strong>t it would be of<br />
value to ascerta<strong>in</strong> whether shark catch rates <strong>in</strong>crease as fish<strong>in</strong>g effort<br />
persists <strong>in</strong> the same location, potentially as a consequence of shark<br />
aggregation <strong>in</strong> response to persistent offal discharge. This may be<br />
of relevance <strong>in</strong> those fisheries where strategically discharg<strong>in</strong>g offal<br />
is actually a requirement, one entirely at odds with its objective of<br />
assist<strong>in</strong>g to m<strong>in</strong>imise seabird <strong>in</strong>teractions. Likewise, there is a<br />
relationship between hook box tangle decrease (hook box tangles<br />
cause more birds to be killed) <strong>and</strong> branchl<strong>in</strong>es configured with<br />
wire to a 45 g or 60g swivel at less than 1 metre away from the hook<br />
(a faster bait s<strong>in</strong>k rate to avoid birds). The logistics of reta<strong>in</strong><strong>in</strong>g fish<strong>in</strong>g<br />
gear whilst successfully discard<strong>in</strong>g live sharks is much improved<br />
too. Put simply, wire <strong>and</strong> an appropriate size swivel near each hook<br />
can be used to achieve several objectives, less birds killed for two<br />
reasons, more sharks released alive with more fish<strong>in</strong>g gear reta<strong>in</strong>ed<br />
<strong>and</strong> perhaps even fewer sea turtles killed because gear sets <strong>and</strong> stays<br />
set at a consistently greater depth (this too will keep shark catches<br />
down). One respondent also po<strong>in</strong>ted out that heavy swivels are too<br />
dangerous to use unless wire can be <strong>in</strong>corporated, an additional issue<br />
of specific relevance to management decision-mak<strong>in</strong>g with multiple<br />
not s<strong>in</strong>gle species bycatch reduction objectives <strong>in</strong> m<strong>in</strong>d.<br />
Even without a reduction <strong>in</strong> the <strong>in</strong>centive for operators to not catch<br />
<strong>and</strong> reta<strong>in</strong> sharks as a consequence of regulations to limit this, all<br />
operators believed that shark catches could be <strong>in</strong>creased by 100% or<br />
more if they chose to do so. This ability was thought to be relevant<br />
<strong>in</strong> the debate over the actual abundance of shark species as <strong>in</strong>dicated<br />
perhaps by catch rate on hooks set to target other species.<br />
Op<strong>in</strong>ions on how to m<strong>in</strong>imize shark captures <strong>in</strong> the first <strong>in</strong>stance,<br />
<strong>in</strong>cluded not re-sett<strong>in</strong>g <strong>in</strong> a location found to conta<strong>in</strong> a lot of sharks<br />
at that time, conf<strong>in</strong><strong>in</strong>g the set <strong>and</strong> haul to daylight, <strong>and</strong> <strong>in</strong>tervessel<br />
alerts to problem waters, (these areas be<strong>in</strong>g unpredictably<br />
changeable). In a locality where target species occur <strong>in</strong> addition to<br />
sharks, as is often the case, several respondents considered sharks<br />
could be avoided <strong>and</strong> target species still caught by sett<strong>in</strong>g the l<strong>in</strong>e at<br />
greater depth. The most prevalent op<strong>in</strong>ions amongst respondents as<br />
to how survival of sharks that are caught could be improved, <strong>in</strong>cluded<br />
keep<strong>in</strong>g l<strong>in</strong>e sets shorter, to not use wire (otherwise more will die on<br />
the hook before haul<strong>in</strong>g) <strong>and</strong> to not have guns aboard.<br />
Hook type, considered by most to be either an unknown or irrelevant<br />
factor for its impact on shark catches was by several respondents<br />
implicated <strong>in</strong> alter<strong>in</strong>g the way <strong>in</strong> which sharks are actually hooked<br />
(<strong>and</strong> therefore ease of release or for hook recovery). ‘J’ hooks catch<br />
<strong>and</strong> hold more sharks whereas circle hooks tend to mostly mouthhook<br />
sharks, mak<strong>in</strong>g these easier to release, hooks more likely to be<br />
recovered, <strong>and</strong> the survival prospects of the shark improved.<br />
Most respondents consider sharks to be responsible for their greatest<br />
gear damage <strong>and</strong> economic cost, giv<strong>in</strong>g average estimates of this<br />
to be around AU$100 per set but also estimate that target species<br />
economic loss could be up to 20% of catch. For those who considered<br />
sharks to be less problematic than other causes of gear or economic<br />
loss, pilot whales, lancet fish, snake mackerel, marl<strong>in</strong>, sunfish as well<br />
as crew were listed. Pilot whales were described as be<strong>in</strong>g considerably<br />
more destructive, but not so consistently as sharks. They were seen<br />
to be a greater potential problem locally <strong>and</strong> where this is so, no<br />
problem is greater!<br />
Most respondents considered the act of gaff<strong>in</strong>g sharks alongside<br />
either to reta<strong>in</strong> a shark, or recover fish<strong>in</strong>g gear <strong>in</strong> the process of<br />
discard<strong>in</strong>g the shark to be dangerous <strong>and</strong> unacceptably timeconsum<strong>in</strong>g.<br />
Similarly, it was considered <strong>in</strong>efficient to deal with sharks<br />
by try<strong>in</strong>g to use de-hookers or l<strong>in</strong>e-cutters, with these <strong>in</strong>creas<strong>in</strong>g<br />
safety risks by try<strong>in</strong>g to do so. Several respondents however do<br />
48