Graduate Thesis Or Dissertation

 

Distribution of Pacific herring spawn in Yaquina Bay, Oregon, and observations on mortality through hatching Public Deposited

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  • 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.
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