The study was done by the region's leading scientific assessment body - the Oceanic Fisheries Program at the Noumea-based Secretatriat of the Pacific Community.
The results will be presented to next month's meeting of the Western and Central Pacific Fisheries Commission, in Busan, in South Korea.
The Fisheries Commission brings the powerful distant water fishing nations together with the Pacific Island countries to decide on management regimes to protect marine resources.
Presenter: Jemima Garrett.
Speaker: Dr John Hampton, Manager of the Oceanic Fisheries Program, at the Secretariat of the Pacific Community
HAMPTON: The assessment that we have just conducted suggests that there has been a really, really substantial fall in the populations of oceanic white-tips over a long period of time. Right now they are down to a very low percentage of their pr-e-exploitation levels, probably of the order of less than 10 per cent, which is a very substantial level of depletion of that population.
GARRETT: So what is causing the decline in white-tip sharks?
HAMPTON: Well, it is primarily fishing pressure and mainly the longline fisheries that operate throughout the tropical and sub-tropical Pacific, that take oceanic white-tip and other shark species as a by-catch.
GARRETT: You also looked at silky sharks. How are their numbers faring?
HAMPTON: in a similar way to oceanic white-tips they have also undergone a very substantial decrease, perhaps not quite as dramatic as oceanic white-tips but still of substantial concern. We are probably talking levels of around 10 per cent mark of the unexploited levels, as well for silky shark.
GARRETT: And is that also a result of fishing effort?
HAPMTON: Yes, exactly! They are again one of the shark species that are commonly encountered by longlines. In the case of silky shark, they are also caught in relatively small numbers by other fisheries, such as the purse seine fishery, but even so, the main source of fishing mortality of silkies is longliners.
GARRETT: What action is needed from the Western and central Pacific fisheries commission to rescue the numbers of these sharks?
HAMPTON: Well, for oceanic white-tips there was a measure introduced at the most recent Commission meeting, held in March, and that basically requires fishing nations to not retain oceanic white-tips that are captured. So they must return them to the sea and they should do that in live condition, obviously, wherever possible so maximise their handling practices that would maximise their release in live condition. Unfortunately, we have some concerns about survival of these animals, particularly after they are brought on board the boat and there are some estimates of those. So it is unlikely I would think, that just those measures in themselves, will be effective in restoring oceanic white-tip populations.
GARRETT: What other measures could be introduced to help the white-tip sharks?
HAMPTON: Well, I think a couple of things. It is most important that longliners are able to avoid capturing them in the first place and one way to do that would be to regulate or limit the amount of targeted shark that occurs. Whilst tuna are the primary targets of longliners there are some longliners that actually go out and specifically target sharks so that is an activity that probably needs considerable regulation if we are going to avoid catching these animals in the first place. The second thing is, inevitably some sharks will get hooked up on longlines that are even targeting tuna. However, one way that you are able to maximise the way sharks are able to escape, once they are hooked, is to not use wire leaders on the longlines because sharks can't bite through that. So it would be preferable if longliners used exclusively monofilament leaders that sharks can more easily break away from. And that doesn't limit their ability to catch things like tuna but it does mean sharks have a greater chance of escaping.
GARRETT: As the fishing fleets are primarily targeting the tuna, would they be willing to take on board some of these suggestions which would help the sharks?
HAMPTON: Whether they are willing or not at an individual level, I think, would be quite variable. Historically, sharks have been a fairly valuable by-product of longline fishing operations, primarily through their fins, and shark-fining is quite a common practice. That is one thing that the existing measure adopted by the Commission, this year, addresses in terms of not being able to retain sharks that are caught or any part of the shark, including their fins. So, I guess there will need to be a realisation by longline operators that they can no longer just sort of take sharks as they wish and that these sorts of regulations will be required if they want to remain active in the fishery.