A SIMPLE MODELING APPROACH TOWARDS HYDROPERIOD EFFECTS ON FISH DYNAMICS IN A NORTHERN TAIWAN WETLAND ECOSYSTEM

Abstract

In this paper we develop a simple dynamic model to describe the seasonality of fish population subjected to the pattern of water level fluctuations (i.e., hydroperiod) in a northern Taiwan wetland ecosystem, Kuandu Natural Reservation. We use a harmonic oscillation to characterize hydroperiod quantitatively by obtaining the amplitude and timing of the dominant periodic component in a time series of water levels. The model illustrates the temporal pattern of fish dynamics through the year that can result in very high density of fish at the end of a hydroperiod as well as the importance of ponds and other depressions that both are refuges and sinks during dry periods. We suggest that a 9-mon effective threshold in the length of the hydroperiod must be exceeded to produce high fish population densities. Our results also indicate that the large, piscivorous fish appear to have a major impact on smaller fish in the marsh habitat. Simulation results reveal that the recovery of small fish populations in the marsh following a major drought requires up to two years. The collective results imply that human activities such as drainage or other alterations of the hydrology can exacerbate natural cycles and results in detrimental stresses on fish production and the higher trophic levels dependent on this production.

Keywords:

• Dynamic model
• Ecosystem
• Fish
• Hydroperiod
• Wetland

ACKNOWLEDGMENTS

The authors wish to acknowledge the financial support of the Chung-Cheng Agricultural Science and Social Welfare Foundation of Republic of China.