Wednesday, January 14, 2015
Monday, January 12, 2015
When we think of the ocean’s top predators, most of us are probably going to picture sharks. More specifically, we’re probably picturing the massive great white shark.
But a couple weeks ago we shared an article about an interesting way to scare sharks away from Australia’s beaches: playing recordings of killer whale ‘screams’. If the great white shark is truly the ocean’s top predator, why would it be so scared of killer whales?
Well, it turns out that killer whales have been known to prey on sharks.
Orcas have also been known to eat mako sharks and several other species. When hunting sharks, killer whales always end up flipping the shark upside down, regardless of how the attack starts. When flipped upside down, the shark goes into a paralyzed state known as ‘tonic immobility’ and can’t fight back, which suggests that the orcas understand a little something about shark biology. It doesn’t necessarily mean they understand the process, just that they know if the shark is upside down, they won’t get hurt.
Before we get into some examples, here’s what you need to know about our competitors:
Killer Whale, Orcinus orca:
- Size: Males can reach lengths of 32 feet (9.6 m) and weigh up to 9 tons. Females can reach 23 feet (8.2 m) in length and weigh up to 4 tons.
- Speed: They usually swim at speeds of 3 to 4 miles (5 to 6.4 km) per hour but can reach speeds of up to 30 miles (48 km) per hour in short bursts.
- Diet: Killer whales have 40-50 large conical teeth (3 in / 7.6 cm) that they use to capture and tear prey, not to chew. Their diets differ in based on population. In the North Pacific, resident killer whales eat fish, primarily salmon, while transient killer whales prey on marine mammals. In New Zealand waters, killer whales have been known to feed on stingrays and sharks.
Killer whale inspecting a Weddell seal before wave-wash attacks. Photo credit: R Pitman, NOAA/SWFSC.Hunting techniques: Killer whales are highly social animals and live in groups (pods) that range from 2 to 15 animals, but they have occasionally been seen hunting in groups of up to 40. Killer whales work together when hunting and they teach each other techniques. Mothers have been observed teaching their young how to beach themselves to hunt seals. In Antarctica, they make waves to wash seals off of floating ice, a behavior that isn’t seen anywhere else in the world.
Great White Shark, Carcharodon carcharias:
- Size: White sharks can reach lengths of more than 20 feet (6 m) and weigh more than 5,000 pounds (2,268 kg).
- Speed: They usually swim at speeds of around 15 miles (24 km) per hour.
- Diet: White sharks are the largest predatory fish in the world. Their razor-sharp, triangular teeth can measure more than 2.5 inches (5.7 cm) long and they use them to tear big chunks of flesh off their prey. They feed primarily on fish and actively hunt small marine mammals, including dolphins, seals and sea lions, but they also occasionally eat sea turtles, molluscs and crustaceans.
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Hunting techniques: Generally they are solitary animals, swimming alone or with one other shark. Sometimes, usually when feasting on a carcass, groups of about 10 or more have been spotted. Their hunting techniques vary based on the prey. When hunting brown fur seals, they ambush the seal from below, hitting the seal at high speeds. They often ambush from above or below to avoid being seen, but many Altantic great whites will hunt close to shore in shallow waters. They have also been known to scavenge on whale carcasses.
Read more: http://marinesciencetoday.com/2013/11/22/oceans-toughest-predators-great-white-shark-vs-killer-whale/#ixzz3OdGfs2ZO
Thursday, January 8, 2015
The Fisheries Minister Norman Moore has revealed charges have been laid over a shark slaughter on the north-west coast.Photos recently released to the media showed the mutilated remains of sharks scattered across 80 Mile Beach, they had been killed for their fins and dumped.
The photos were sent to the Department of Fisheries 10 months ago but the then Minister Jon Ford decided not to release them, fearing a backlash against the local fishing industry.
However the new Fisheries Minister Norman Moore has told the ABC a number of charges have been laid
"There is a listing for Broome Court sometime in February when this matter will come to trial," he said.
"I thought it was dreadful that someone could catch that number of sharks and simply dispose of them dump them on the beach.
"What offended me most was the wanton waste, of these fish, that they'd been left on the beach and not even buried."
Two WA fishermen operating in the area at the time of the offence have already had their licences revoked by the Department.
original article
December 4, 2008 -- Irin News - Kenya
Coastal communities in southwestern Madagascar, who risk their lives travelling long distances in dugout canoes to supply a lucrative demand for shark fins, face an uncertain future as unsustainable fishing practices threaten the survival of the marine resources on which they depend.
People in villages along the southwestern coast are reporting a dramatic decrease in all marine resources. "Around 2000 the decline really started here. The octopus catch fell and sea cucumbers disappeared. Some fish species also disappeared," Roger Samba, in the village of Andavadoaka, in Toliara Province, told IRIN.
"It is difficult to catch enough fish to sell. People go far away, fishing from early in the morning until late at night, to catch not even 10kg or 20kg of fish - just 5kg."
When shark fisherman Zoffe loads his nets into his pirogue (a dugout canoe, often with a sail) in the morning and sets out from his home in the coastal town of Morombe into the deep waters of the Mozambique Channel, he knows that he will be lucky if he catches anything.
"It is really hard to catch shark now," Zoffe told IRIN. "Things are not like they used to be; before, there used to be shark very near the shore - just five metres below the surface of the sea - now they are only found very far away, and are very deep. They are very difficult to catch."more
November 30, 2008 -- Brisbane Times - Australia
MARINE conservationists say the interception of a Papua New Guinea fishing boat laden with four tonnes of "de-finned" sharks in Australian waters shows illegal shark fishing has become a worldwide enterprise and the Great Barrier Reef could be its next target.
On Thursday, Australian Customs authorities escorted an illegal fishing boat to Cairns after it was spotted 6.6 nautical miles east of Ashmore Reef an Australian Nature Reserve west of Darwin.
The boat was first detected by a Customs Coastwatch aircraft last Sunday and was intercepted.
A search a revealed about four tonnes of sharks, with their fins cut off.
Twenty shark jaws, 20 tuna and 20 assorted large fish were also allegedly discovered on board. Customs could not confirm whether the vessel's 15 crew members had been charged.
Marine conservationist, researcher and Fox Shark Research Foundation director Andrew Fox said a shark finning industry in Papua New Guinea had previously been unheard of and the fact the vessel was from the region showed the industry had become truly internatio
Wednesday, January 7, 2015
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