Fisheries
Whales Compete With Fishermen For Tuna
They take about 1.2% of hooked catch
Critics of Japan's penchant for whaling hoot with skepticism when Japanese experts claim that some species of whales are great competitors for the tuna and other fish species targeted by the Pacific's fishermen.
In fact some species of Toothe whales are frequently observed stripping catches from the hooks of fishermen.
- ADVERTISEMENT -
According to scientists of the New Caledonia headquartered Ocean Fisheries Programme (OFP), they are becoming smarter about doing it.
The technique for raiding hooked tuna from long line without getting hooked may even be passed from one whale species to another, according to scientists writing in an OFP newsletter Fork Length.
While sharks normally bite hooked fish about half way up from the tail, whales take nearly the entire fish by intelligently biting just short of the hook, leaving little more than the mouth and eyes, the scientists write.
Some whales use their teeth to grab a tuna and shake it violently from the line without becoming hooked themselves. They are thought to also use a sucking motion.
Observations between 1995 and 2000 indicated that whales were taking about 0.8% of all species of fish hooked by fishing vessels that trail lines up to 20 kilometres or more in length, with thousands of hooks dangling from them and about 1.2% of hooked tuna.
While sharks take about 2.1% of all hooked species, it is likely that the number taken by whales is greater than apparent since the number of observers watching them is small. "There are some concerns that the problem may be growing, although it is not clear if this is real or perceived," the scientists write.
"It is certainly true that many of the cetaceans ( whales) involved are intelligent enough to learn this behaviour from other cetaceans.
"Small cetaceans (dolphins) are said to even remove bait from the hooks, reducing the fisher's chance of ever catching a fish."
The Western Pacific tuna fishery is the world's largest, yielding an average of about one million tonnes of tuna year, of which about half is hooked and half netted. Since whales are rarely seen taking fish, it's not certain what whale species are mainly responsible for long line raids that cost fishermen tens of millions of dollars worth of lost fish annually.
"Some evidence suggests that they wait until a vessel starts hauling a line in before removing fish from it," the scientists write. Some of the main suspect species are the False killer whale, the Pygmy killer whale and the Melon-headed whale.
While the Killer whale is known to take fish from the tuna and swordfish in the South Atlantic, they haven't been spotted raiding Pacific lines. The Sperm whales also take the catch from lines in the Alaska and Patagonian fisheries but have also not so far been seen busy on Pacific lines.
