Is overfishing a cause of mass marine stranding? Melon headed whales strand in Philippines.

21/04/2009 09:40:10 Mystery of the Melon headed Whales
By Jose Ma. Lorenzo Tan, WWF-Philippines Vice-Chairman and CEO

Over the last three months, two mass strandings of melon headed whales (Peponocephala electra) were reported in the Philippines. The first, reported in February, took place in the waters off Bataan, when 3-4 whales were reported to have died. The second, more recent mass stranding, reported in the first week of March, took place in the seas off Odiongan, in Romblon. Both cases involved some 100 - 200 whales.

Mass strandings of whales and dolphins are very rare in the Philippines. Melon-headed whales are deep-water feeders, and although this species has been involved in mass strandings throughout the world, it is unusual for them to gather so close to shore. These two instances are the first substantiated reports I have come across over the last fifteen years.

So, what's going on?

Well, one guess is that this is due to climate change or extreme weather. Another theory is that this behaviour is a reaction to the mid-frequency sounds emitted by the tactical active sonar used from submarines and other military vessels, as well as from helicopters. Sonar has been linked to abnormal behaviour among marine mammals - such as mass strandings - and is said by some to cause a temporary loss of their hearing. Other theories include undersea quakes, diseases such as parasite or viral infections, malnutrition, biotoxins from harmful algal blooms, traumatic injuries due to ship strikes or fishery entanglements, tidal fluctuations and who knows what else. In The United States, the NOAA Fisheries Service says that, in many case, scientists never learn the exact cause of most stranding events.

Sonar?
Much has been said about the effect of sonar on marine mammals - specifically, mass strandings of melon headed whales. However, as far as we know, there were no military exercises underway at that time.

Logically, active sonar could create havoc with animals that depend on echolocation for survival. Like many marine mammal scientists, I am convinced that cetaceans and sonar do not mix. This matter must be addressed directly, and a solution found. However, there were no military exercises, certainly no naval exercises taking place, when both strandings took place. One can speculate that a submarine may have been active, but that is pure speculation.

Undersea quakes - disease
There were no major undersea quakes either. The USGS website confirms this. The veterinarians who conducted necropsies on the dead animals did not report parasite or viral infections. Nor were there any reports of major algal blooms either in Bataan or in Romblon.

Fishing gear
The three or four animals which died in Bataan were reported to have died from drowning, probably as a result of entanglement in fishing gear. If sonar was not responsible, what other major factors could have driven the whales from their traditional deepwater habitats to the shallows?

Over fishing
In general, marine mammals only do a number of things out at sea: they eat, they sleep, they play and they mate. They can sleep, play or mate just about anywhere. However, they can only eat where there is food. Various scientific studies conducted here in the Philippines indicate that our seas are overfished. One study has estimated that, in certain fishing zones, we have consumed 90% of our fish stocks over the last 60 years.

A major study of coral reefs, undertaken some 15 years ago, indicated that less than 3% of Philippine reefs were in excellent shape. The greatest percentage was in poor condition. Mangrove forests, the nurseries of the coast, showed a 66% shrinkage 15 years ago, as well, and today the situation is probably worse. As a result of unregulated illegal logging and unwise land development, the great majority of coastal areas have suffered from severe silting. This phenomenon creates extensive zones of death, where no marine life can exist.

The situation is not much better in the high seas. As commercial fishing fleets benefited from the efficiencies of new technology, many previously well-stocked fishing zones - such as the Visayan Seas and Malampaya Sound -were badly over fished.

Causes
Why then did the whales swim into the shallows? There could be a number of reasons. And, if NOAA scientists can't pin it down, what chance do we have to explain what really happened in Bataan or Romblon? Before we start pointing fingers at the unusual and the extraordinary, or resort to speculation, maybe we should look at our own backyards, and use some common sense.

There are more than 80 species of whales and dolphins that populate the world's seas. Each one exists to feed on very specific prey, providing a regulatory function that keeps the oceanic food chain in balance. Here in the Philippines, we have consumed just about every form and size of seafood there is. We have fished down our food web. And, believe it or not, we continue to do so. When the normal prey of melon headed whales no longer exists in the abundance they need to sustain their own life, like you and I, they will simply move to another "supermarket".

Unlike the few remaining coral reefs that line our coasts, primary productivity in the deep seas of the tropics has been compared to a desert. When it's gone, unless we leave it alone for a long time, it will probably not come back to what it was. When their favourite deepwater "feeding holes" no longer provide sufficient food for the entire pod of whales, they move on.

Over the years, many people have asked me where they could find whales and dolphins. My answer has always been the same. Look for their food, and you will find them. I may be dead wrong, of course. But, I believe that the melon headed whales were simply looking for something to eat. It was a hunt, a family picnic that resulted in tragedy. And, unless we take the necessary steps to allow our natural fish stocks to come back, this could happen again, and again.

Unsustainable
Human population pressure, poverty and the fact that more than 50% percent of all Filipinos depend on the sea for their primary source of protein; make it very clear that most of our seas will continue to be fished intensively. If it is our intention to leave behind viable and productive seas for our children, it is imperative that each coastal community, and each commercial fishery, agrees to set aside a portion of their coastline, or specific tracts of ocean, as no-take zones - nurseries for the future. The seas must be allowed to recover.

We have 25,000 square kilometres of coral reefs. Once upon a time, they were more than sufficient to feed all of us. Once upon a time, they were all healthy. That is no longer the case. It is time for all of us to accept that reality, and take positive, strategic action. The government cannot do this alone. We have to learn how to work together for the greater good. Our seas are not bottomless. Nature has its limits.