Newly emerged steelhead fry (Oncorhynchus mvkiss) of hatchery and
wild origins were studied in laboratory stream channels and natural
streams. Objectives of the study were to determine if and how earlier
emerging hatchery fry influence the emigration, realized densities,
growth, habitat use, social structure, and activity patterns of
localized populations of wild steelhead fry when the hatchery fry have
a competitive advantage conferred by larger size and prior residence.
During 1986 and 1987, the above variables were observed daily among
hatchery and wild steelhead fry in laboratory stream channels for 8
weeks following emergence in June. The habitat use and social
activities for fry of both origins were observed weekly in natural
stream reaches from June through August in 1987 to corroborate lab
findings. In lab channels, both hatchery and wild fry received 2
treatments: living alone (allopatry) and living together (sympatry).
In the lab, fry of hatchery origin emerged 7 to 10 d prior to wild fry
and remained larger in size during the 8 weeks of study both years.
In natural stream reaches, fry of each origin were observed only in
allopatric situations. Wild fry in the field emerged from natural redds
while hatchery fry were released in stream reaches as unfed, newly
emerged (swim-up) fry.
Hatchery and wild fry in lab sections were found to be very similar
in their emigration rates, distances to nearest neighbor, growth rates,
and use of habitat. Both fry types, regardless of treatment or
environment (lab or field), established similar stable social structure
and used the same types of aggressive acts. Among all lab groups, once
a fry became dominant, it retained that social status to the end of the
study period.
Significant differences (P<.05 both years) among comparison tests
were: 1) in allopatric lab sections, wild fry maintained larger
densities than hatchery fry, 2) in sympatry, hatchery fry had a greater
tendency to establish stable focal points and social hierarchies more
readily, defend larger areas, have better condition, prefer pools with
overhead cover more frequently, be more aggressive, and reach stable
densities more quickly than the wild fry, 3) fewer hatchery fry in
sympatry maintained nomadic positions than wild fry in both treatments,
4) in sympatry, hatchery fry directed more acts of overt aggression
toward wild fry than other hatchery fry, 5) wild fry in sympatry usually
used defensive or less offensive acts of aggression when interacting
with other fry, 6) fry of both origins in natural stream reaches
maintained greater distances to their nearest neighbor than fry in
allopatric lab sections, 7) dominant hatchery fry in both treatments
maintained larger focal areas than subdominant fry, 8) hatchery fry
maintained longer lengths than wild fry through the duration of the
study, and 9) hatchery fry were more aggressive in sympatry than in
allopatry.
Potential differences (P<.05 in one year and P<.1 in the other
year) were: 1) wild fry in sympatry had lower realized densities,
maintained smaller focal areas, had greater proportions of nomadic
individuals, and established stable social hierarchies slower than wild
fry in allopatric lab sections, 2) wild fry in sympatry had poorer
condition than all other fry groups in lab sections, 3) in sympatry,
wild fry were the recipients of the majority of aggressive acts
perpetrated by hatchery fry and other wild fry and usually assumed the
subordinate positions within the social hierarchy, 4) all fry in the lab
showed a high preference for pools with overhead cover and low
preference for gravel and fines and run areas, and 5) wild fry in
allopatric lab sections were more socially active than hatchery fry
while the reverse was observed in the natural streams.
Any influences that could be attributed to inherent differences between stock origins were probably masked by size differences between
fry types. The study would have been more complete had I included
sympatric lab sections where wild fry emerged first and where fry types
emerged simultaneously, and sympatric reaches in natural streams.
Results were further confounded by the limited number of wild adults
used for broodstock in the lab segment of this study. Progeny produced
from so few adults (5 adults of each sex each year) would have very
limited genotypic variation compared to what occurs in natural streams.
This may partially explain why some findings from lab sections and
natural stream reaches differed. Likewise, genotypic expression among
wild fry in lab sections may have varied greatly between years. This
could explain differences found between years in behavior of wild fry
in similar lab treatments.
Although this study does not simulate all possible scenarios,
results support suspicions that introductions of hatchery fry of larger
size and earlier emergence into streams containing wild stocks could
disrupt the social structure and negatively influence the realized
densities, spatial distribution, growth, and behavior of wild juveniles
in recipient streams. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/38072 |
| Date | 24 January 1991 |
| Creators | Noble, Sandra M. (Sandra Marie) |
| Contributors | Li, Hiram W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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