White Sturgeon Spawning Habitat in an Unregulated River: Fraser River, Canada

Abstract

Spawning habitat used by white sturgeon Acipenser transmontanus in the lower Fraser River, British Columbia, is described based on field sampling in 1998 and 1999. Fraser River flow is unregulated and, within our study area, its channel morphology is largely unaltered by land use activities. The study area consisted of (1) the wandering reach (river km 98–143), which had side channels, wooded islands, and gravel bars; and (2) the confined reach (river km 145–181), which was naturally restricted by mountains, producing a single‐thread and simple channel. Six spawning sites were identified in the study area, five in side channels of the wandering reach and one in the main channel of the confined reach. Within the wandering reach, eggs and larvae were collected only from side channels despite sampling efforts in main‐channel areas. Multiple lines of evidence, including radio‐tracking of prespawning adults and visual observations, substantiated the use of side channels by white sturgeon for spawning. A total of 3 unfertilized and 80 fertilized eggs were captured at water velocities averaging 1.8 m/s, whereas 101 larvae were found in velocities averaging 1.0 m/s. Water depths averaged 2.9 m at capture locations for all life stages and were shallow compared with depths of egg and larval captures reported from most regulated rivers. Turbidity, which averaged 42 nephelometric turbidity units during the spawning period, was notably higher than in regulated rivers. We hypothesize that reduced light attenuation due to turbidity may substantially influence habitat suitability for spawning within the range of available water depths and velocities. Our observations of white sturgeon spawning activity outside of main‐channel habitats are unique, and we have demonstrated that spawning may occur over a wider range of habitat conditions than previously reported. Our observations of white sturgeon spawning in an unregulated river in which fluvial processes and channel morphology are relatively unaltered, albeit increasingly threatened by river engineering, are also unique.

A Riparian Habitat Hypothesis for Successful Reproduction of White Sturgeon

“…One of the most significant losses is shallow, off-channel habitat, which is recognized from studies in the Fraser River to be habitat that is heavily used by early life stages of white sturgeon (Lane and Rosenau, 1995;Perrin et al, 2003).…”

Effect of incubation temperature on green sturgeon embryos, Acipenser medirostris

“…Studies with the Caspian beluga, Huso huso, ship, A. nudiventris, Russian sturgeon, A. gueldenstaedtii, and sevruga, A. stellatus, revealed generally similar temperature effects on the early life stages (Nikol'skaya & Sytina 1978, Igumnova & Dubinin 1987, Sytina & Shagaeva 1987. Observations on natural spawning, documented by the collection of eggs and larvae, indicate that the majority of sturgeons reproduce within the temperature range of 10-20°C, including Eurasian (Dettlaff et al 1993) and North American (McCabe & Tracy 1994, Bruch & Binkowski 2002, Perrin et al 2003 species.…”

Population viability analysis of the Endangered shortnose sturgeon

“…We note that the first suitable site moving upstream occurs near the confluence of the Black River and Ogeechee River, near 83 km. Interestingly, tributary confluences are known to be used for spawning by sturgeon species including shortnose sturgeon (Collins et al 2000b) and white sturgeon (A. transmontanus) (Perrin et al 2003). Coarse substrates inputs can characterize these depositional areas.…”