Seasonal migration of elvers (anguilla spp.) into lake pounui, New zealand, 1974–1978

Abstract

The migration of elvers of Anguilla australis Richardson and A. dieffenbachii Gray into Lake Pounui, Wairarapa, was monitored from November 1974 to July 1978 by installing a trap on the outlet stream. The trap was cleared regularly— daily from November 1976 to March 1977—to provide data for a migration periodicity model. The number of elvers caught each season (August‐July) varied from 6754 to 190 009, the largest migrations coinciding with the greatest seasonal rainfall and the smallest migrations with the least rainfall. A. australis dominated all samples: 99.4% of all elvers (n = 372 082) were this species. Glass‐eels (Age Class 0) and Age Class 1 elvers predominated, although relative age class strengths varied considerably between seasons. Most elver activity occurred at dusk and dawn, but movement in daylight was observed during large migrations. Of various meteorological variables considered as possible influences on migration, water level was the most important and affected both periodicity and size of the migration. A delay of several days occurred between the peak water level of a flood and the peak of the following migration; for the mathematical model a delay of 5 days was the most appropriate to explain variations. The water temperature and number of elvers on the preceding day were also incorporated into the final model, which accounted for 76% of the error sum of squares. To test the predicatibility of the model, daily values for water level, water temperature, and the number of elvers for Day 1 were supplied. The resulting series was in good agreement with both the observed and the calculated number of elvers. © 1983 Taylor & Francis Group, LLC.