Studies were conducted during late winter and spring of 1970 to
establish the extent of spawning of Pacific herring (Clupea harengus
pallasi Valenciennes) in the Yaquina estuary, and to define the degree
of egg mortality on certain substrates. Routine surveillance of the
north shore of the estuary provided information on the length of the
spawning season, the number of separate spawnings which occurred,
the extent of spawning into brackish water, and the types of substrates
utilized for spawn deposition.
Random sampling of egg deposits at specific locations within the
estuary, and at frequent intervals following deposition provided estimates
of spawn mortality on two commonly used plant substrates,
Fucus sp. and Zostera sp. These included estimates of the amount of
eggs removed from the substrates prior to commencement of hatching,
and estimates of the mortality among eggs which remained attached
to the substrates. One series of samplings of a deposit of eggs on
Fucus was designed to establish the extent of bird predation on the
eggs.
Results from the spawn survey indicated that at least five
separate spawnings occurred during the season. Initial spawning took
place on February 5 in the lower estuary (from the south jetty to a
point three miles upriver from the mouth). Subsequent spawnings
occurred in the third, fifth, sixth, and seventh weeks following this
initial deposition, and appeared to take place exclusively in the middle
and upper estuary (from three and one half miles to ten miles upriver
from the mouth). Among the substrates observed with eggs Fucus
appeared to be the most extensively utilized, while localized deposits
were noted on Zostera, bare rocks and pilings. Spawning was predominantly
located on substrates lying above mean lower low water.
Analysis of the samples collected from four populations of eggs
deposited on Fucus, and one population deposited on Zostera revealed
that egg removal was extreme during the period of incubation. Recorded
losses from initially sampled populations of eggs on Fucus
ranged from 78% to 1OO% based on sample means. A 9l% loss was recorded
for the one Zostera population sampled.
A comparison of a protected with an unprotected segment of a
sampled population on Fucus indicated that birds contributed at least
80% to the removal of eggs from the unprotected segment. The observed
presence of birds on all of the sampling areas when eggs were
present suggests that predators accounted for the extensive losses
from these areas.
Analysis of the ratios of dead eggs to the total number of eggs in
samples collected from Fucus substrates provided estimates of natural
mortality. Low rates of mortality (about 20%) were recorded for two
populations sampled during a period in which the weather was cool and
moist, while considerably higher rates (about 50%) were observed in
samples from a population exposed to a dry and relatively warm climate.
Dessication of eggs was therefore indicated as a significant
cause of mortality of eggs remaining attached to substrates exposed to
drying conditions in the atmosphere.
In addition to these field studies, a study was conducted in the
laboratory to define the effects, on the survival of herring eggs to
hatching, of combinations of three environmental parameters: temperature,
salinity, and exposure to air. Groups of artificially fertilized
eggs were incubated in the 18 test environments provided by the different
combinations of three temperatures, three salinities, and exposure
and non-exposure to air. Survival of eggs to hatching remained
high (from 60% to 86% of total eggs in each environment) except for
eggs incubated in the highest temperature ( 11 °C.) and subjected to
eight hour exposure periods. Average survival in these environments
was 5.2% and 24.2% (for two replicates). These observations lend
support to the findings from the field sampling studies that survival
of herrings eggs can be tenuous when subjected to exposure to air. / Graduation date: 1972
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37242 |
| Date | 02 September 1971 |
| Creators | Steinfeld, James David |
| Contributors | McNeil, William |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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