Geology topics

R.K. Steinhorst

Publications and source records attributed to R.K. Steinhorst.

4 recordsLinked to original sources

USGS2011

Two alternative juvenile life history types for fall Chinook salmon in the Snake River basin

Fall Chinook salmon Oncorhynchus tshawytscha in the Snake River basin were listed under the Endangered Species Act in 1992. At the time of listing, it was assumed that fall Chinook salmon juveniles in the Snake River basin adhered strictly to an ocean-type life history characterized by saltwater entry at age 0 and first-year wintering in the ocean. Research showed, however, that some fall Chinook salmon juveniles in the Snake River basin spent their first winter in a reservoir and resumed seaward movement the following spring at age 1 (hereafter, reservoir-type juveniles). We collected wild and hatchery ocean-type fall Chinook salmon juveniles in 1997 and wild and hatchery reservoir-type juveniles in 1998 to assess the condition of the reservoir-type juveniles at the onset of seaward movement. The ocean-type juveniles averaged 112-139 mm fork length, and the reservoir-type juveniles averaged 222-224 mm fork length. The large size of the reservoir-type juveniles suggested a high potential for survival to salt water and subsequent return to freshwater. Scale pattern analyses of the fall Chinook salmon spawners we collected during 1998-2003 supported this point. Of the spawners sampled, an overall average of 41% of the wild fish and 51% of the hatchery fish had been reservoir-type juveniles. Males that had been reservoir-type juveniles often returned as small "minijacks" (wild, 16% of total; hatchery, 40% of total), but 84% of the wild males, 60% of the hatchery males, and 100% of the wild and hatchery females that had been reservoir-type juveniles returned at ages and fork lengths commonly observed in populations of Chinook salmon. We conclude that fall Chinook salmon in the Snake River basin exhibit two alternative juvenile life histories, namely ocean-type and reservoir-type. ?? Copyright by the American Fisheries Society 2005.

Idaho, Oregon, Washington↗

USGS2009

Behavioural thermoregulation by subyearling fall (autumn) Chinook salmon oncorhynchus tshawytscha in a reservoir

This study investigated behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir on the Snake River, Washington, U.S.A. During the summer, temperatures in the reservoir varied from 23?? C on the surface to 11?? C at 14 m depth. Subyearlings implanted with temperature-sensing radio transmitters were released at the surface at temperatures >20?? C during three blocks of time in summer 2004. Vertical profiles were taken to measure temperature and depth use as the fish moved downstream over an average of 5??6-7??2 h and 6??0-13??8 km. The majority of the subyearlings maintained average body temperatures that differed from average vertical profile temperatures during most of the time they were tracked. The mean proportion of the time subyearlings tracked within the 16-20?? C temperature range was larger than the proportion of time this range was available, which confirmed temperature selection opposed to random use. The subyearlings selected a depth and temperature combination that allowed them to increase their exposure to temperatures of 16-20?? C when temperatures <16 and >20?? C were available at lower and higher positions in the water column. A portion of the subyearlings that selected a temperature c. 17??0?? C during the day, moved into warmer water at night coincident with an increase in downstream movement rate. Though subyearlings used temperatures outside of the 16-20?? C range part of the time, behavioural thermoregulation probably reduced the effects of intermittent exposure to suboptimal temperatures. By doing so, it might enhance growth opportunity and life-history diversity in the population of subyearlings studied.

Journal of Fish Biology↗

USGS2001

Early life history attributes and run composition of PIT-tagged wild subyearling Chinook salmon recaptured after migrating downstream past Lower Granite Dam

Seaward migration timing of Snake River fall chinook salmon ( Oncorhynchus tshawytscha ) smolts is indexed using subyearling chinook salmon passage data collected at Lower Granite Dam. However, not all of the subyearlings are fall chinook salmon. For six years, we recaptured wild subyearling chinook salmon smolts, which had been previously PIT tagged in the Snake River, to genetically determine if the fish were offspring of spring and summer (hereafter, spring/summer), or fall chinook salmon. Springfall chinook salmon comprised over 10% of the samples of recaptured smolts in five of six years. For these five years, we used discriminant analysis to determine run membership of PIT-tagged smolts that were not recaptured (i.e., not sampled for genetic identification). Accuracy of the discriminant analysis models, based on genetically identified smolts, varied between 75 and 85%. After using discriminant analysis to classify run membership for each PIT-tagged smolt that was not genetically identified, we compared early life history attributes between fall and spring/summer chinook salmon and calculated annual run composition. The life history attributes we studied overlapped, but spring/summer chinook salmon reared along the shoreline of the free-flowing Snake River earlier, were larger, and began seaward migration earlier than fall chinook salmon. Spring/summer chinook salmon made up from 15.1 to 44.4% of the tagged subyearling smolts that were detected passing Lower Granite Dam. As a result, the presence of spring/summer chinook salmon makes migration timing for the fall chinook salmon seem earlier and more protracted than is the case. If wild subyearling spring/summer chinook salmon smolts are not considered, fall chinook salmon abundance at Lower Granite Dam will be overestimated.

Washington↗

USGS1989

Sightability adjustment methods for aerial surveys of wildlife populations

Aerial surveys are routinely conducted to estimate the abundance of wildlife species and the rate of population change. However, sightability of animal groups is acknowledged as a significant source of bias in these estimates. Recent research has focused on the development of sightability models to predict the probability of sighting groups under various conditions. Given such models, we show how sightability can be incorporated into the estimator of population size as a probability of response using standard results from sample surveys. We develop formulas for the cases where the sighting probability must be estimated. An example, using data from a helicopter survey of moose in Alberta (Jacobson, Alberta Oil Sands Research Project Report, 1976), is given to illustrate the technique.

Biometrics↗