Publication Date

Spring 2010

Degree Type


Degree Name

Master of Science (MS)


Biological Sciences


Jerry J. Smith


estuary, growth, lagoon, steelhead, temperature, water quality

Subject Areas

Biology, Ecology; Biology, Animal Physiology; Biology, Zoology


To better understand the temporal and spatial relationships of water quality parameters, as well as steelhead (Oncorhynchus mykiss) habitat use and growth in San Gregorio Creek estuary / lagoon, water quality and steelhead at San Gregorio Creek estuary / lagoon were studied over a period of two years. During both years, there was above-average rainfall, and during the dry seasons of both years the lagoon was repeatedly artificially breached. In spite of the breaching, variations in growth and population size relative to variable sandbar dynamics were measured both within and between years. Data showed that repeated artificial breaching of the sandbar prevented complete destratification, causing hot (up to 29.5°C) and hypoxic / anoxic conditions at the bottom of the water column. Nevertheless, steelhead that reared in the lagoon in both 2005 and 2006 were abundant and grew substantially larger than those in two stream reaches. Coho (O. kisutch) did not rear in the lagoon, but passed through as smolts in spring 2006. Sizes of juveniles in the lagoon were more related to time spent in the lagoon than to their age. In 2005 the estimated steelhead population declined 15% from 2,365 ± 598 to 2,005 ± 715 from July to October. The 2006 population decreased substantially from 2,802 ± 354 to 1,373 ± 610, and age 0+ grew slower, possibly due to impacts of breaching. A majority (55-64%) of a sample (n=22) of adult steelhead had reared in the lagoon. Most of the remaining adults and most spring smolts reared 2 years in the stream.