Temporal aspects of juvenile pink salmon (Oncorhynchus gorbuscha Walbaum) emergence from a simulated gravel redd

Abstract

The temporal pattern and daily timing of sibling pink salmon fry emerging from a simulated gravel redd were examined in the laboratory under a 12 h light: 12 h dark cycle and at temperatures ranging from 3.4 to 15.0 °C. The distribution of sibling fry emergence was generally unimodal in time, but differed significantly from normality. The rate of emergence decreased as temperature increased, owing in part to a positive relationship between the duration of the emergence period and mean temperature. Timing of 50% emergence was correlated negatively with mean temperature. Emergence was mainly nocturnal at all temperatures except 15.0 °C. However, the fry's tendency to emerge during daylight increased progressively during the course of the emergence period for all redds except the one at 5.0 °C. The onset of darkness appeared to be the major time cue for emergence at temperatures ≤ 12.3 °C. In general, the daily peak of fry emergence occurred within 3 h after the onset of darkness.