California blue whales bounce back to near historic numbers

Researchers believe that California blue whales have recovered in numbers and the population has returned to sustainable levels.

A blue whale estimated to be around 20m long, swimming off Baja California

Scientists say this is the only population of blue whales to have rebounded from the ravages of whaling.

The research team estimate that there are now 2,200 of these giant creatures on the eastern side of the Pacific Ocean.

But concerns remain about their vulnerability to being struck by ships.

At up to 33m in length and weighing in at up to 190 tonnes, blue whales are the largest animals on the planet.

The California variety is often seen feeding close to the coast of the state, but they are found all the way from the Gulf of Alaska down to Costa Rica.

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Blast fishing destroying Tanzania's marine habitats

The rich marine life off Tanzania's coast is coming under threat because of blast fishing - a technique using explosives that some fishermen use to maximise their catch.

''Blast fishing destroys the fish habitats under water where fish reproduce and that has had a big impact, especially on us who use ring nets to fish," a 32-year-old fisherman says.

"The number of fish has drastically reduced we are not able to catch many fish like before," he said as prepared his wooden boat to go fishing in the calm and beautiful waters of the Indian Ocean.

Small fishing vessels like his dot the coastline that hugs Tanzania for thousands of kilometres.

Fisherman who use ring nets say their catches have been affected .Some say they face intimidation if they report those using dynamite

             Coral reefs in peril

According to Smart Fish, a fisheries programme funded by the European Union, Tanzania is the only country in Africa where fishing using explosives still occurs on a large scale.

Although it is illegal, it occurs along the entire Tanzanian coastline, from Mtwara to Tanga, and off nearby islands. There have also been reports of blast fishing off north Zanzibar.

Baraka Mngulwi, the assistant director of the government's Fisheries Resource Protection department, says the explosives are often taken from mines and demolition and road construction firms, or made at home.

The explosives are usually lit with small fuses and tossed overboard.

The underwater shock waves produced by the explosion stun the fish, rupturing their swim bladders - the organ which helps control their buoyancy.

So they float to the surface and are then scooped up by waiting nets.

People find it difficult to identify which fish have been caught using explosives

Experts say one blast is enough to kill all fish and other living organisms within a 20m (66ft) radius - up to 400 fish can be netted in each explosion.

In the process, the underwater coral systems, home to countless marine species, are reduced into rubble.

Michael Markovina, a SmartFish officer, says coral reefs left in the wake of a series of blasts resemble a shelled city.

"If this illegal practice is not stopped, gradually Tanzania could easily end up with a wasteland of ocean," he says.

Damaged coral reefs lead to an instant decline in fish species diversity and quantity - and in the long-term the ecosystem is unlikely to recover.

Blast fishing in Tanzania:

• Began in the 1960s, was brought under control in the 1990s but has surged in recent years
• 25% of all marine species are associated with coral reefs
• Each blast kills all fish and other living organisms within a 20m radius, completely destroying the coral reef habitat and there is no natural recovery
• Explosives are cheap and easily accessible, usually sourced from mining, demolition and road construction enterprises, or made using artificial fertilisers and diesel
• Banned in 2003 with a minimum sentence of five years for dynamite fishing and 12 months for possession of explosives

Source: SmartFish

It is very difficult to track down the illegal fishermen because there is a very secretive and apparently sophisticated network in place.

A former dynamite fisherman, Mwanya Sleiman, who now campaigns against the practice says he lost both his hands in an accident."They were ripped off when an explosive I was setting up blew off in my hands. I used to light the explosives with fuses and toss them into the ocean," Mwanya Sleiman, 50, told the BBC.

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Antarctic coastal waters 'rising faster'

Melting ice is fuelling sea-level rise around the coast of Antarctica, a new report in Nature Geoscience finds.

Parts of West Antarctica are undergoing significant change

Near-shore waters went up by about 2mm per year more than the general trend for the Southern Ocean as a whole in the period between 1992 and 2011.

Scientists say the melting of glaciers and the thinning of ice shelves are dumping 350 billion tonnes of additional water into the sea annually.

This influx is warming and freshening the ocean, pushing up its surface.

"Freshwater is less dense than salt water and so in regions where an excess of freshwater has accumulated we expect a localised rise in sea level," explained Dr Craig Rye from the University of Southampton, UK, and lead author on the new journal paper.

Globally, sea levels are going up, in part because of the contribution of the world's diminishing ice fields. This is well known.

But the Nature Geoscience report is the first to show the direct consequences to sea surface height (SSH) around Antarctica itself.

While the satellite data record indicates there has been a general upward trend in SSH in the Southern Ocean south of 50 degrees of up to 2.4mm per year, those satellites also indicate a more rapid rise in waters sitting on the continental shelf.

Mass losses

Modelling by Dr Rye's team suggests that this additional 2mm per year can be attributed almost exclusively to freshwater runoff from Antarctica, and not to some climatic oscillation that might make sea levels "breathe" up and down on decadal timescales.

"We can estimate the amount of water that wind is pushing on to the continental shelf, and show with some certainty that it is very unlikely that this wind forcing is causing the sea level rise," Dr Rye told BBC News.

"And because we can model the freshwater forcing, and the fact that this is so much more like what we see in the real world, we can come to the confident conclusion that the signal is driven by freshwater forcing."

Recent satellite studies have underlined the increased mass losses occurring in Antarctica.

Much of this accelerated ice discharge is occurring in the continent's western sectors, particularly in the Amundsen Sea Embayment and along the Antarctic Peninsula.

In contrast to land ice, the sea ice around Antarctica stands at record levels and is becoming more extensive.

The growth is small and very regional in character, but nonetheless significant.

Quite how the freshening of surface waters might be influencing this phenomenon is now a target for study.

"That's a really interesting question which I'd like to look into with further research," Dr Rye said.

From BBC Sci/Environment