Interactions of cattle and chinook salmon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hh63t1768

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  • Spring chinook salmon spawning occurs in late summer when it is common for cattle to be present in pastures that have streams where fish spawning occurs. This two-year study addressed three main objectives relative to behavioral interactions between cattle and spring chinook salmon during the spawning life history stage. These objectives were 1) to determine cattle distribution and behavior within the riparian pasture, 2) to determine if cattle disrupt the spawning behavior of salmon by their presence near the redd and 3) to determine the likelihood of a cow coming into direct contact with a redd. This study did not measure the changes in redd structure or egg survival if contacted by the cattle. The study area was a 41 hectare riparian pasture along an Eastern Oregon stream with cattle stocked at a rate of 0.82 ha/aum and spring chinook salmon spawning at densities of 4.6 redds per kilometer in 1996 and 6.1 redds per kilometer in 1997 in areas accessible to cattle. The pasture contained 2.6 kilometers of stream with approximately 50% of the 2.6 kilometers of stream excluded from cattle since 1978. From mid-August through early-September in each of the two years, cattle and salmon distribution and behavior were recorded every minute for two out of three four-hour periods per day. Cattle preferred the terrestrial habitats by spending 94% of their time in those habitats, approximately 5% in the gravel bar habitats, and <1.0% of their time in direct contact with the aquatic habitat. During the observations of active salmon redds, cattle were visible from the redd location an average of 12% of the time. While visible, cattle spent 96% of the time out of the stream and 84% of the time greater than 3 meters from the redds. There were no encounters of cattle contacting redds during the cattle distribution and behavior observations. However, during the 2 years of observations of the redds, out of 50 cows over the 56 days in the pasture a redd was contacted two different times. This calculates into <0.01% of the time that cattle contacted redds. Spawning activities were not equally distributed, resting in the redd was the dominant activity and spawning was one of the least frequent activities. The majority (83%) of the time spent by salmon spawning, constructing the redd and burying the eggs laid in the redd occurred within the first 2 days of occupying each redd. Salmon continued preexisting patterns of behavior while cattle were within visible range of a redd. When cattle were present, salmon spent 64% of their time resting in the redd and 26% of their time under cover. This pattern of salmon behavior was consistent with spawning season averages where 45% of the time was spent resting in the redd and 30% of the time was spent under cover. The salmon carcasses surveyed in the study area were 100% spawned in both 1996 and 1997 indicating egg loss from retention due to harassment by cattle was not a problem. Cattle were rarely close to a redd so consequently, there was very little opportunity for cattle to interact with salmon or step on redds. Likewise, there was little chance for salmon to change their behavior in response to the presence of cattle.
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