7170 - Laserfiche WebLink

Home Browse Search

i 2 FRED P. MEYER No fish kill is without a cause. The cause can usual- ly be determined and corrective action taken to pre- vent future losses. However, determining the cause is often difficult, and a valid determination requires careful observation, accurate recording of data, and the proper use of sampling procedures. Further- more, because many fish kills may lead to litigation or court action, the investigators must understand rules of evidence, custody of samples and data, valid record keeping, and other factors that may affect the admissibility of evidence. Because fish kills can be caused by a wide array of factors, one must be careful not to reach pre- mature conclusions. Although many people believe that toxic substances are the only causes of fish kills, many natural causes, including infectious disease agents, can sometimes lead to large-scale losses. Depletion of dissolved oxygen, excessive water tem- perature, toxic algal blooms, bacterial and viral infections, and parasitic infestations all have the potential for inducing widespread mortalities of fish in an ecosystem. However, each cause is usually ac- companied by a distinctive set of characteristics that provides insight into the source of the fish kill. It becomes the responsibility of the investigator to make a complete assessment of the situation asso- ciated with a fish kill and to collect appropriate samples to ensure that the role of each potential fac- tor can be identified or eliminated. In the 10-year period 1970-79, an estimated 3.6 million fish died in 409 documented fish kills in the State of Missouri (Czarnezki 1983). The incidence of the types of causes is typical of that in many States, and the Missouri data thus provide useful insight into the most likely sources of fish kills (Fig. 1.1). In Missouri, municipal-related sources were the most common cause (26.407o) of fish kills, followed by agricultural operations (17.407o), and in- dustrial operations (10.8%). Less important sources of fish kills were transportation accidents (7.607o), oxygen depletion (7.307o), other nonindustrial opera- tions (6.807o), mining (6.607o), disease (3.707o), and others (2.707o); undetermined causes accounted for 10.707o of the kills. Although sewage-related causes Thirty-eight million Americans go fishing each year. The competition for places to go fishing is becoming more intense and it is vital that waters be protected from contamination.