Migration and Metabolism in a Temperate Stream Ecosystem

Abstract

Fish migration, total stream metabolism, and phosphous were studies in New Hope Creek, North Carolina, from April 1968 to June 1970. Upstream and downstream movement of fish was monitored using weirs with traps. Most of the 27 species had a consistent pattern of larger fish moving upstream and smaller fish moving downstream. Both upstream and downstream movements were greatest in the spring. For example, in the spring of 1969, a daily average of seven fish weighing a total of 1,081 g were caught moving upstream, and 17 fish weighing a total of 472 g were caught moving downstream. Although more moved downstream than up, the larger average size of the fish moving upstream resulted in a large transfer of fish upstream. Diurnal oxygen series were run to measure the metabolism of the aquatic community. Gross photosynthesis at the principal sampling station ranged from 0.21 to almost 9 g O 2 m—2 day—1, and community respiration from 0.4 to 13 g O 2 m—2 day—1 (mean of 290 and 479 g O 2 m—2 yr—1). Both were highest in the spring. Area values of metabolism were often similar for different parts of the stream, but both production per volume and respiration per volume were always much larger near the headwaters than farther downstream. Migration may allow populations to take advantage of such differences in productivity by maintaining young fish in areas of high productivity. Other effects of migration may include: prey control, recolonization of defaunated regions, genetic exchange, and mineral distribution. An energy diagram was drawn comparing energies of insolation, leaf inputs, currents, total community respiration, fish populations, and migrations. About 1% of the total respiration of the stream was from fish populations, and over 1 year about 0.04% of the total energy used by the ecosystem was used for the process of migration. If it is assumed that upstream migration is necessary to maintain stocks, which may be periodically decimated by droughts, each Calorie invested by a fish population in migration returns at least 25 Calories (kilocalories). Even without that assumption returns are 3—fold. Analysis of phosphorus entering and leaving the watershed studied indicated that flows were very small relative to storages and that this generally undisturbed ecosystem is in approximate phosphorus balance. Upstream migrating fish were important in maintaining phosphorus reserves in the headwaters of New Hope Creek.