A Fishview on the Fish Kills

Fish kills stink. Like the rancid fish oil going through the decay process, the main reason for the massive deaths of fish in fish cages and natural lakes is MISMANAGEMENT and GREED. It is not the lack of oxygen that every Juan de la Cruz have been told. Lack of oxygen is a manifestation that nature is reacting to human intervention of a natural system. Let us analyze in greater detail what was happening and use Taal lake to represent all the natural lakes (there are man-made lakes, e.g. result of open pit mining) of the country.

Taal lake is a classic oligotrophic lake example which is deep, with very little circulation because its exit to the sea through a river is very shallow. Because of this character, only the top portion has circulation that go as deep as its sill. Now, if you put there large number of cages and without any consideration on its natural circulation pattern, these made made structures hinder or changes the circulation pattern, disrupting the replenishment of nutrients from the sea etc and more importantly its vertical circulation. Ecological disruption #1.

Now the fish needs to be fed because oligotrophic lakes is not very productive. The excess feeds (arising from poor culture practices) and the fish droppings would initially contribute to the fertility in form of increased total N. Many of these excess food and droppings accumulate on the bottom and never rot because of lack of oxygen at the bottom and, partly also because of the high sulfur dioxide content, rendering the bottom layer, anoxic. Over time as these excess food and droppings continue to settle and accumulate, the anoxic portion of the lake becomes higher and higher. Ecological disruption #2.

The vertical temperature profile of Oligotropic lakes is highly stratified. This stratification normally disappears or get reduced when cold, dense water from rain settles to the bottom displacing the anoxic warm water layer to the surface. This happens only very seldom, perhaps once every two or three years.

What probably happened last week was that the anoxic part was almost at the surface where small amount of rain triggered the vertical circulation. On normal situation where the anoxic part is just a small percentage of the lake water, these layer, when coming up are oxidized by the upper water layers. But this time when a huge part of the lake water is already without any oxygen, the oxidized water at the surface is not enough to maintain a dissolve oxygen level sufficient for fish in the cages to survive.

What are the consequences of the fish kill? The investments and loss of livelihood in the fisheries sector represent a minor cost to the overall loses that media failed to account for. These are:

1. Loss of biodiversity. what we are seeing are fish in the cages. what about other fish species like the tawilis, an endemic sardines. what about the fishes that have no bladder that sink at the bottom, the other organisms, the snails, the insects that need the lake for their young to survive, the algae, the primary producers that start the food chain, all these could not function because of our greed to make profits?
2. Collapse of the ecosystem integrity. This by far is the most serious impact of mismanaged fish cages. the whole process of life cycle in the lake is disturbed and we do not know its consequences.
3. Land based impacts - tourism sector, a major source of livelihood is just one of the directly hit by the fish kill, the boat that ferries, resorts, horse rides, and thenumerous peddlers, suppliers of goods and services.
4. Health - impacts to health could run up to millions as bans on sale of fish reached the markets.

Our local managers need to understand that normality is not restored when bangus would not die in the cages, or when water clears up, or when the foul odor disappears. The impacts on the lake will be felt on the land, by humans and non humans,not just by fishers but by farmers, tourists, and all those that support and dependent on the lake.

Normality returns only after we see that human activities like rearing fish obeys the laws of nature, that profit is not the main governing policy but respect of nature.

When fish kills occur, it means that nature complains and fights back. Its consequences is wide and could be long lasting. Nobody gains and everybody loses.