The "sea" snake of Taal Lake

There's more to Taal Lake than just the spectacular breathtaking view

by Arvin C. Diesmos

We are standing on the windswept shores of Barangay Buso-buso in the town of Laurel in Batangas Province one lazy afternoon in February. Looming less than two kilometers from us is Volcano Island, better known as Taal Volcano. Although rising just a little over 1,000 feet from the waters of Lake Taal, it commands a forceful presence.

And it is not difficult to see why. Taal Volcano has inspired myths, legends, mystical and romantic tales, and—in the past 400 years of our written history—pure terror. Taal Volcano is, in fact, internationally recognized as among the most dangerous seismic localities in the world.

This breathtaking scenery is a welcome perk in our journey. Our main purpose here is to document the Lake Taal Sea Snake, a little-known species that lives in the waters of Lake Taal.

We won't, however, be diving in the lake to search for this snake—although we honestly wish we could. Instead, we hope to gather a variety of information about the snake through interviews with the local fisher folk of this community, keeping in mind that the Taaleños themselves are more knowledgeable about the workings of Lake Taal compared to us outsiders. But, who knows, perhaps if we get lucky enough, we could even catch a glimpse of this enigmatic snake.

Lake Taal

Lake Taal is one of the major freshwater lakes in the country. It places second to nearby Laguna de Bay for being the largest freshwater lake on the island of Luzon covering an area of about 26,000 hectares.

Taal Lake's environment rests in the hands of the communities around it.

Located in Batangas and right at the border of Cavite Province, Lake Taal lies less than 18 kilometers southwest of Laguna de Bay and around nine kilometers northeast of Balayan Bay off the coast of Batangas. Its waters flow into the sea through the Pansipit River, which is located at its southwest rim.

To ancient Taaleños, it is known as Lake Bombon. To volcanologists, it is a large caldera, the remains of a towering volcanic mountain that stood perhaps 6,000 meters tall until a series of turbulent volcanic eruptions nearly leveled the entire mountain.

To limnologists, it is an oligotrophic lake with a pH value ranging from 7.0 to 9.4 (this means its waters range from being neutral to being alkaline) and a bottom composed of loam and sand. And to most Filipinos, it is one of the most popular and picturesque tourist spots in the country.

Lake Taal has not always looked the way it does now. Volcanologists, geologists, and archaeologists claim that it was once part of the Batangas seas until cataclysmic volcanic forces 400 years ago shaped what we now recognize as Lake Taal. Like an umbilical cord to its mother, the narrow Pansipit River serves as Lake Taal's link to its past.

Lake Taal Sea Snake

The Lake Taal Sea Snake was described by Samuel Garman in 1881 and bears the name of its discoverer, Carl Semper, a noted naturalist who first collected the snake from the lake. To herpetologists, it is a hydrophine snake and bears the scientific name Hydrophis semperi. To Taaleños, it is most familiar as duhol.

Its color varies from black to deep blue with numerous white or (yellowish bands that encircle the body beginning from the neck) down to the base of the tail. The head and tail are usually colored black. Like all sea snakes, its tail is flat and paddle-shaped, an adaptation especially suited to living in a watery world.

The "sea snake" of Taal Lake

The Lake Taal Sea Snake is among the smallest species of sea snakes known. The total lengths of available samples of adult Hydrophis semperi range from 500 to a little over 750 millimeters.

By comparison, most other species reach lengths of well over 1,000 millimeters.

The Lake Taal Sea Snake is venomous as all sea snakes are. It belongs to the family Elapidae, which is comprised of cobras, kraits, coral snakes, and sea snakes. In fact, the venom of a sea snake is known to pack a deadlier punch than their earth-bound cousins: sea snake venom is known to be two to five times more lethal than cobras. A scary thought indeed, hut the good news is sea snakes are generally non-aggressive and do not readily attack. They also have tiny fangs and their gape is rather small. Unprovoked attacks on humans are unheard of.

Crucible of Evolution

One may ask then: "So, what's so special about this snake?" You see, in spite of being referred to as a "sea snake," Hydrophis semperi is a freshwater species and is the only known freshwater sea snake in the Philippines. More so, all available information indicates that Hydrophis semperi is found only in the waters of Lake Taal.

Scientists hypothesize that the volcanic forces that shaped Lake Taal played a major role in shaping the creatures that now inhabit the lake, resulting in the evolution of odd creatures unique to Lake Taal.

It is believed that a small population of the ancestor of Hydrophis semperi (which some herpetologists think may be the Blue-banded Sea Snake Hydrophis cyanocinctus) became landlocked and closed off from the ocean during heightened volcanic activities in the area. Through a process which evolutionary biologists call "Founder Principle," the trapped, isolated, and small population of the ancestral species (the "founder") eventually underwent an evolutionary change, evolving into a new species which is ecologically adapted to a new freshwater environment. And thus, Hydrophis semperi was born.

This scenario very probably set the stage for the evolution of other animals that are unique to Lake Taal (there is yet no final checklist of the strange creatures that lurk under its waters). For instance, another popular (and quite tasty) oddity is the Freshwater Sardinella Sardinella tawilis, the only freshwater sardine known in the world. And yes, found only in Lake Taal.

Threats

Recent studies have identified several factors that pose a serious threat to Lake Taal, the sea snake, and its many other inhabitants. Chemical pollution is a major threat. Toxic chemicals such as insecticides, pesticides, fertilizers, petrol wastes, and untreated sewage from the ever growing human population enter the lake every second of the day. The sources of these pollutants are commercial establishments, agricultural plantations, factories, processing zones, and resorts.

The burgeoning fish cages are a constant source of nutrients that can tip the balance of this ecosystem. In fact, there have been numerous documented fish kills in Lake Taal due to an overloading of nutrients (mostly coming from unutilized tilapia feeds), which lead to the uncontrolled proliferation of other organisms, especially microorganisms and benthos.

This plus the overcrowded fishes in the cages deplete oxygen present in the water (known as "dissolved oxygen"), the end result is a regular period offish kills.

Fishkills due to pollution and unsustainable use of the lake

In recent years, fishery authorities and the fishermen themselves have noticed a decline in harvest of several species of fish (especially those not cultured in cages). Over-harvesting is being blamed for the decline and scientists fear that the populations of some species (including the tawilis) may be plummeting.

You probably are not aware of it but the tilapia (such as the Blue Tilapia Oreochromis niloticus) is a big threat to the native fauna of Lake Taal. This much celebrated exotic species was introduced into the country from its native Africa. It is now practically found in almost all major rivers and lakes in the country. Scientific evidence have shown that the voracious and ecologically aggressive tilapia has caused the extinction of native species of fish in areas where it has been introduced. For example, the tilapia is being blamed for the demise of a number of endemic cyprinids in Lake Lanao, Mindanao.

An overlooked yet serious threat to the sea snake is human persecution. Like most snakes in the Philippines, H. . semperi is routinely killed. In fact, they are killed simply because they are snakes. Based on our studies, a fisherman on his usual routine will typically come across H. semperi in any given workday of the week. This encounter normally proves fatal on the

part of the snake: the snake gets killed. Thus, if one fisherman kills one snake per week and we multiply that to roughly 20% of the more than 10,000 fishermen making a living in the Lake (this is our estimated percentage of the number of persons who admitted that they have killed H. semperi), then account for the total number of weeks in a given year, only then will we begin to realize the magnitude of this impact. One can only hope that man and snake can live a peacefully in each other's presence.

The Future

The Lake Taal Sea Snake faces numerous threats, real and potential. Yet with the amount of information that is available about u this species, we can only guess what its future will be like.

A great deal needs to be known about its natural history and ecology. It is an irony that such a unique and striking creature could be so poorly known. Among the most pressing questions that need a immediate answers are the following:

• How long does it live?
• When a and where does it breed?
• How many young does a female produce?
• What is the maturity age?
• What is the survival rate?
• What is its preferred habitat?
• What does it eat?
• What is its home range?
• Do populations exist outside of Lake Taal?
• How many are left?

The communities around the lake must work to preserve it

Studies on these topics could provide valuable information in order to assess its present conservation status with great confidence. Furthermore, the information can be used to identify appropriate conservation and management interventions that might be needed for the species and for Lake Taal in general. Using the snake and tawilis as flagship species, conservation measures will benefit the whole of Lake Taal ecosystem.

The government in partnership with civil society groups had already taken initial action to manage Lake Taal; this is a very important step to safeguard this unique, fragile, and very vital ecosystem in the southern Tagalog region of Luzon. But there has to be more. More than ever, there is a great need for a sustained research, management, and conservation program for Lake Taal. For this will benefit its many dependents: people, animals, and plants.

Our country is facing very tough problems: unrelenting poverty, political upheaval, social unrest—just to name a few. Yet scientists and naturalists observe that we, as a nation, seem to be overlooking an equally important challenge that we have to confront right now: a full-scale ecological meltdown.

All these things we pondered as we strode on the shores of Lake Taal. Under a mid-day sun, some groups of men, women, and children are fishing from the shores. We approached them, curious to investigate the day's harvest. A wispy old man in his late '70s handed us a rusty tin plate with a dozen sweet-smelling tawilis, grilled fresh from an open fire. We gladly accepted.

We hope to come here again and study this snake more actively. When we return, we hope to learn more details about its life. We also wish to discover more of the charms, secrets, and other strange animals of Lake Taal. And perhaps when we come back, we can even learn to dive.

This work was funded by the conservation and environmental grants of the Ford Motor Company Philippines through the Project HerpWatch Luzon 2000 awarded to Arvin C. Diesmos.

Arum C. Diesmos is an ecologist and Researcher at the Herpetology Section, National Museum of the Philippines and the current president of the Wildlife Conservation Society of the Philippines, Inc. He is presently based at the National University of Singapore.

Marefe C. Lagda and Norydel F. Tresnado are biology graduates of De La Salle University-Dasmariñas and are presently undertaking field research and a conservation awareness program on Hydrophis semperi and the Lake Taal ecosystem.

Rafe M. Brown is an evolutionary biologist and Ph.D. candidate at the University of Texas, Austin, USA. He has been collaborating with Filipino herpetologists for the past 10 years on field studies of Philippine amphibians and reptiles. He is presently based at the University of California, Berkeley.