PW11 Integrating Sublethal Responses and Ecologically Relevant Endpoints
Exhibit Hall
8:00 AM - Wednesday
(PW186) Effects of four types of discharges on fish populations in a New Zealand river.
West, D. W.1, Van Den Heuvel, M. R.2, Ling, N. 1, Tremblay, L. 3, Hicks, B. J.1, 1 Centre for Biodiversity and Ecology Research, University of Waikato, Hamilton, New Zealand2 Forest Research, Rotorua, New Zealand3 Landcare Research/CENTOX, Lincoln, New Zealand
ABSTRACT- The Waikato River is the longest (425 km) and most intensively used river in New Zealand. It receives numerous point source discharges and it has 8 hydroelectric impoundments in its upper reaches. Resident populations of the exotic brown bullhead catfish (Ameiurus nebulosus), indigenous shortfin eel (Anguilla australis), and common bully (Gobiomorphus cotidianus) were sampled from paired sites upstream and downstream of point-source discharges (a geothermal power station, Bleached Kraft Mill Effluent (BKME), municipal sewage, and thermal power station), and from uncontaminated sites elsewhere in the river system. Population parameters (relative abundance, age structure, and number and size of eggs per female), and physiological indices (condition factor, organ to somatic weight ratios, gonadosomatic index (GSI), blood cell counts) were measured. Biochemical and chemical indicators of exposure to toxins such as hepatic ethoxyresorufin-O-deethylase (EROD) activity, plasma steroids and bile chemistry were also assessed. Although physiological and chemical measurements show evidence of contaminant (eg. BKME) exposure differences in relative abundance, population structure, growth rates and condition factors of fish from sites downstream of some discharges suggest populations of catfish particularly benefit from factors (nutrients and higher temperatures) associated with the discharges. Changes in fish population parameters were strongly influenced by habitat variables such as flow, temperature, and exploitation. Resident fish populations appeared to be most influenced by near field point source discharges and local conditions and cumulative influences were not manifest. Some observations, such as recruitment failure at one site, remain unexplained Care needs to be taken in the assessment of the overall effect of discharges as beneficial factors associated with discharges may be masking toxic effects especially on higher metabolic levels such as reproduction.
Key words: fish health, fish populations, pollution, reproduction