Before impacts of forest harvesting can be identified, the
natural physical and biological influences on incubation processes
must be understood within interior British Columbia watersheds. The
early Stuart stock of sockeye salmon {Oncorhynchus nerka) utilize
the most northerly nursery habitat of the Fraser River sockeye
stocks. This has led to speculation that production may be limited
by high overwinter incubation mortality. An in situ incubation
study was conducted on four adjacent tributaries of the Stuart Takla
watershed (Kynock, Forfar, Gluskie, Bivouac creeks), during
the 1993 and 1994 broodyears.
The study objective was to estimate overwinter survival of
sockeye salmon embryos within various redd micro-environments. It
was hypothesized that spawning salmon select incubation sites based
on environmental cues to optimize egg to fry survival. Egg to
pre-emergent , fry bioassays, in conjunction with microhabitat
environmental monitoring, were implemented to define a range of
natural spawning conditions and their relative contribution to fry
recruitment.
Results demonstrate that high quality, relatively invariant
incubation environment resulted in the lack of classical relations
observed in previous studies between incubation parameters and
survival.. Physical processes (i.e. hydraulic regime, bedload
characteristics) and biological processes (i.e. mass cleaning by
high densities of spawning adults) result in uniformly high quality
gravel conditions with permeabilities, surface water interchange,
and intragravel dissolved oxygen levels associated with high
incubation success. Alternative hypotheses of random egg deposition
and unlimited high quality habitat were rejected due to;
1) observed spatial preferences and, 2) expansion/contraction of
range under different annual population sizes.
Sockeye salmon successfully spawned over a wide range of
habitats. High density spawning habitat was the downstream end of
pools at the pool riffle interface. Habitats utilized to a lesser
degree included; riffles, stream margins, intermittent side
channels and portions of the off-channel habitat. Survival rates
between these habitat types were not significantly different in
contrast to predictions generated from optimality models. This was
due to the definition of "marginal" habitat. In situ redd
simulations showed similar intragravel conditions, in both low
density (i.e. assumed marginal) and high density (i.e. assumed
preferred) areas. Spawning adults avoided truly marginal areas with
intragravel dissolved oxygen levels below 3.0 mg/1.
A number of adaptations which would optimize incubation
success in northern environments were identified within the early
Stuart stock of sockeye salmon. Early Stuart sockeye risk energy
depletion and seasonal maximum temperatures during migration and
spawning. By spawning early in the season (Jul. - Aug.), early
Stuart sockeye enjoy advanced embryological development prior to
the onset of low water temperatures. Embryos rapidly accumulate the
thermal units necessary to hatch, thereby becoming mobile in time
to avoid freezing and desiccation as water-levels decline and reach
seasonal minima. Embryos and alevins of the early Stuart stock can
apparently tolerate temperature conditions previously considered
lethal. Fry successfully emerge in the spring after accumulating
less thermal units than any other Fraser river stock. The trade off
against this strategy is the effect of unusually stressful
migration conditions on the quality and viability of the gametes.
Evidence of this trade off was obtained in 1994, when egg survival
rates were very low for spawners that arrived late and had suffered
severe thermal stress during migration.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/4448 |
| Date | 05 1900 |
| Creators | Cope, R. Scott |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
Page generated in 0.0021 seconds