Pinatubo Monsters- serpent or fish?

What were the Pinatubo Monsters that appeared in 2002?

Villagers appeal for scientists to explain 'monsters'

Filipino villagers are appealing for scientists to explain large unidentified creatures seen in the Tikis river. Five of the mysterious black creatures have been spotted in the river in Bhawen since November. They have baffled the Aeta tribe who live there. There is no account of such creatures in their oral history. Dubbed the Pinatubo Monsters, they are believed to be 7ft long and 3ft wide. Children have been ordered not to bathe in the river and fishing has also been banned in case the creatures are dangerous. They have never been seen in full form, but the elongated outlines can be seen when the wind blows over the river and ripples are made in the water. They have not produced any sound at daytime or night. Joel Serrano, a village councilman, told The Philippine Daily Inquirer: "We don't know if they are fishes or snakes or eels because they never show their heads or tails."He is also worried what effect the ban on fishing will have on the village, adding: "Frogs are our only source of protein."Villager Alfredo Banos said: "The children are afraid. When they come here to view those creatures, they wonder what those things really are. We don't have answers to their questions." Source:

http://web.archive.org/web/20050422192422/www.ananova.com/news/story/sm_494687.html

The story was reported from the Zambales region of the Philippine Island of Luzon.The  large creatures were said to be swimming in the Tikis River, near the former mining village of Buhawen. The first reported incident was on November 5, 2002,  an Aleta( local ) boy thought he saw  a floating log, when it moved, he was terrified and fled. The description he gave was that it looked like a cross between a catfish and a shark.  Then  on January 12, 2003, a group of  eyewitnesses claimed to have seen a 7 foot (just over 2 metres)long black creature approximately  3 feet(approx 1 metre)  wide, undulating silently down the river.
The local people , The Aetas, say that these creatures are unlike any eel, fish or snake that they are familiar with and unlike other rivers with monster sightings, there are no folklore tales locally of monsters in the river. However it upset the locals enough to almost force them into starvation as they would not fish in the river anymore.The fish being a staple diet.
The call for investigation persuaded  the Bureau of Fisheries & Aquatic Resources to send  Nelson Bien .According to reports he looked through a pair of binoculars at the river and saw nothing. Based on the descriptions provide by the local people he concluded that it  was most likely a school of the relatively common fish known as tilapia, that had gathered in a large group.
It seems unlikely that the locals would not recognise the local fish, nor know their habits. One of the more bizarre theories  that the creatures may be a mutation caused by the mercury  said to have been in the river from the gold mining. However if the mercury levels were that high local people who ate fish from the river would be ill ,but I couldn’t find any reports.
I wonder if it could be a species of Gnooch, a giant catfish, which has been known to eat humans. It would fit the description and it is a freshwater fish. Perhaps someone knows if they are found in the area, if so please post a comment.