Fish Kill - Estimation

Estimation

Estimating the magnitude of a kill presents a number of problems.

1. Polluted waters are often very turbid or have low transparency making it difficult or impossible to see fish that have sunk
2. Rivers and streams can move fish downstream out of the investigation area.
3. Small fish and fry can decompose or become buried in sediments very quickly and are lost from the count.
4. Predators and scavengers remove and eat fish.
5. Stressed fish may swim up tributaries and die there
6. Many kills are reported only when dead fish resurface due to decompositional gas formation, often several hours after the kill has occurred.

Some very large fish kills may never be estimated because of these factors. The discharge of red aluminium sludge from a reservoir in Hungary into the Marcai River is acknowledged as causing environmental devastation, The loss of adult fish also can have long term impacts on the success of the fishery as the following year's spawning stock may have been lost and recovery of the pre-kill population may take years to recover. The loss of food supplies or recreational income may be very significant to the local economy.