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The early life history and ecology of Columbia Lake burbot Taylor, Joshua L.

Abstract

This thesis examines aspects of the early life history and ecology of the Columbia Lake burbot population in southeast British Columbia. Growth was examined using otoliths from burbot sampled in shoreline habitats, a recreational ice fishery, and the spawning population. Columbia Lake burbot begin to recruit to the fishery, and no longer inhabit shoreline habitats, by age 2 or 3 (39 cm in length). The mean density of age 0 burbot per km of shoreline on 12 sites sampled from 1997 to 1999 ranged from 400 in 1997 to 62 in 1999. This suggests that recruitment is not seriously depressed and, thus, the decline in the burbot population may be best explained by changes in environment that affect post settlement life stages. Recruitment, as estimated by shoreline surveys of juvenile abundance and the age distribution of adults in the fishery and spawning population, varied greatly among cohorts. This variation is not well explained by spawner numbers and, presumably, is partly driven by environmental fluctuations. Reduced lifespan, as occurs with decreasing latitude and increasing fishing pressure, should reduce the survival of adults over periods when conditions are unfavorable for recruitment and, thus, reduce population stability. Egg development and early larval life were investigated under laboratory conditions. Egg survival peaked about 3°C and all embryos died at temperatures above 6°C. This narrow temperature tolerance during incubation may cause density independent mortality, especially when egg incubation temperatures are variable and borderline for survival. The minimum time to hatch at 5, 4, and 3°C was 28, 32, and 38 days, respectively. Newly hatched larvae averaged 3.47 mm in length and were positively phototactic. The mouth and swimbladder form between 5 and 10 days after hatching. After 27 days (mean length 4.25 mm) all larvae were neutrally buoyant and feeding exogenously. Habitat use by juvenile burbot was modeled statistically. Juveniles use crevices, especially the interstitial spaces between substrate particles, as cover. Because much of the shoreline habitat suitable for juvenile burbot is above water from late fall to early spring, competition for cover may regulate recruitment in Columbia Lake.

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