Rotting fish: More food for thought
Most fishkills in lakes and coastal waters occur where fish farming activities are excessive. A common suspect is pollution build-up—industrial and domestic wastes, agricultural fertilizers and pesticides and fish feces and excess feeds. These dissolved nutrients can trigger phytoplankton or algal blooms and subsequent decay (using oxygen). The decay may be blown by wind in one area or settle at the bottom, and brought up by upwelling caused by wind or temperature changes. Algal blooms in coastal waters may also involve poisonous phytoplankton that, in high concentrations, cause red tide. The specific causal pollutant or factor in these environmental changes or fishkills is largely unknown.
What is known, however, is that organisms have a capacity for tolerance to environmental changes, like pollution. The tolerance is limited and varies among organisms and with the kind of change or pollution. The tolerance is widest for survival, less for growth, and least for reproduction.
A given level of water pollution, for instance, may prevent an organism from reproducing, but allows it to grow. A higher level may arrest growth but allows it to survive. At the limit of tolerance for survival, any factor of environment, man-made (e.g. pollution) or natural (e.g. temperature), can trigger fishkill, affecting all species with similar tolerance properties.
Let me relate a story about fish pens in Laguna Lake, which in the 1980s was the site of fish diseases and deaths. It shows how the unregulated practice of aquaculture has given rise to conflicts of interest, which caused serious ecological, social, economic and political problems.
In 1961-1964, when there were no fish pens, the annual fish catch was 80,000-82,000 tons. In 1968, a survey showed that some 10,000 fishers used the lake as a communal fishing ground. Harvest of shrimps and mollusks was about 240,000 tons; the bulk was used for animal feeds in the duck-raising industry.
There were 23 species of fish caught in Laguna Lake, with the goby (biyang puti) and perch (ayungin) as the dominant species. Carp, catfish (hito and kanduli), snakehead (dalag) and tilapia were also caught, in addition to migratory species from Manila Bay, through the once unpolluted Pasig River.
In 1971, the Laguna Lake Development Authority (LLDA) introduced fish pen culture with a 38-hectare pilot project. Milkfish (bangus) was chosen because of its market value, and it fed on phytoplankton, abundant in the lake. The project gave encouraging results, producing 3.5 times more fish per hectare than in open waters. The potential of the lake fish pen aquaculture was estimated at 20,000 hectares and annual production valued at P320 million. This prompted businessmen and entrepreneurs to enter into fish pen culture. Development expanded to 4,800 hectares by the end of 1973; gross annual value was P77 million.
Data in 1982 showed that fish pens—then 31,000 hectares or one-third of the lake—produced 62,000 tons. And the small fishers’ harvest from the open waters dropped to only 19,000 tons. They added up to a total lake harvest of 81,000 tons, same as the yearly catch of the small fishers in 1961-1964 without the fish pens. This result was easily predictable from the start because the culture milkfish and wild fishes both depended on the lake’s natural food.
As would be expected (because of competition for natural food), the uncontrolled growth of the fish pen industry led to longer rearing time, stretching the usual four months to 8-15 months. This led to supplemental feeding, which also allowed increases in the fish stock. Note that water circulates in and out of the fish pens, bringing in natural food and taking out fish feces and excess feed to pollute the open waters, or settle at the bottom.
The conflict was between the community of poor fisherfolk (in the 1980s, more than 15,000 families) and the group of a few hundred rich fish pen operators. In a report published in the newspapers, the LLDA identified an elite group of fish pen operators owning 10 of the largest fish pens that added up to over 4,000 hectares (the law said no person or corporation can own more than 50 hectares of fish pen concessions). The list showed members of prominent families, including politicians and ranking military officers.
What the fish pens industry did was rob the small fishers of their traditional rights—by reducing their fishing areas and navigation lanes, competing for the lake’s budget of natural food, polluting the waters and reducing their fish catch. Further, they ruined the resource, important not only for fisheries but also for its other uses, like water supply, irrigation, navigation, etc.
A true “Tragedy of the Commons.” In his essay, Garrett Hardin points out that “the Tragedy of the Commons is an example of the class of problems with no technical solution … Therefore, any solution requires that we, as a society, change our values of morality.” (Hardin 1968).
Dr. Flor Lacanilao obtained his PhD from the University of California at Berkeley. He served as professor of marine science, chancellor of UP Visayas and chief of SEAFDEC in Iloilo. Email: firstname.lastname@example.org
Subscribe to INQUIRER PLUS to get access to The Philippine Daily Inquirer & other 70+ titles, share up to 5 gadgets, listen to the news, download as early as 4am & share articles on social media. Call 896 6000.