Document Type

Capstone Project

Degree Name

Bachelor of Science (B.S.)


Science & Environmental Policy


South-Central Coast Steelhead have recently been listed as threatened by the National Marine Fisheries Service. As a result, many studies are being undertaken to examine habitat, populations, and the effects of land use on steelhead (Oncorhynchus mykiss irideus) throughout the central coast of California. The primary aim of this study was to conduct and inventory of steelhead habitat and population within the Gabilan Creek watershed in Monterey, California. The specific objectives of this study were to address the following quesions: Is there suitable habitat for steelhead in the Gabilan Creek watershed? Have populations existed there in the past? Do populations currently exist, and if not, why? This was accomplished by researching the life cycle and characteristics of steelhead, performing a reconnaissance survey, assessing rearing and spawning habitat, and conducting a population survey. The purpose of the reconnaissance survey was to locate perennial water, note important features related to the survival and spawning of steelhead, and to map accessible portions of the creek. The survey was conducted along much of the length of the creek and grouped into three reaches totaling approximately 21 km. The habitat assessment involved using a Rearing Index for Young-of-the-Year Method to measure the quality and quantity of surveyed rearing habitat and to then calculate a rearing index. The rearing index was used to predict steelhead young-of-the-year population density per unit length of stream. This method was performed for five sections located within the headwaters of Gabilan Creek. Additionally, selected sites throughout the watershed were monitored for stream factors such as temperature, dissolved oxygen concentrations, total dissolved solids, and suspended sediment concentrations. Finally, population assessment involved visually observing adult steelhead, if present, during upstream migrations. Interviews were also conducted with several local residents regarding historical anecdotal steelhead sightings. The results of this study indicated that suitable rearing and spawning habitat does exist in the headwaters of Gabilan Creek. It was also determined lower reaches of Gabilan creek could be problematic for the migratrion of adults due to lack of cover, woody debris, and uniform flow structure. It remains inconclusive as to whether or not steelhead currently exist in Gabilan creek. However, rainbow trout were observed in the headwaters. Rainbow trout have a polymorphic life-history structure enabling them to assume anadromy. Therefore, even if steelhead do not currently exist in Gabilan creek, there is a potential for a steelhead run during years with adequate rainfall and stream flow.


Capstone Project (B.S.) Earth Systems Science & Policy Institute