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Because of the success of this initial effort, this strategy was expanded into mark-recapture efforts during the spring and fall of 2001 (Van Haverbeke and Coggins 2002), 2002 (Van Haverbeke 2003), and 2003 (Van Haverbeke 2004). In 2004, GCMRC again contracted the USFWS to conduct two additional mark- recapture efforts in the LCR. One important element of these efforts is that they were designed to be comparable to the closed historical abundance estimates of HBC in the LCR provided by Douglas and Marsh (1996). Like Douglas and Marsh (1996), our approach is to obtain closed abundance estimates in the LCR via fishing the entire lower 13.6 km of the LCR with hoop nets deployed from three separate camp locations. However, largely because of funding constraints, our efforts only provide closed estimates during the spring and fall of each year, rather than on a monthly basis year round as was obtained by Douglas and Marsh (1996). Nevertheless, within a given set of spring and fall months, and within a given size class of fish (~ 150 mm), our estimates are considered comparable to the estimates of Douglas and Marsh (1996). Our spring estimate is timed to coincide with the peak of HBC spawning within the LCR and therefore provides GCMRC with a reliable measure of the annual spawning magnitude. Our fall estimate is aimed primarily at providing an estimate of the abundance of sub-adult fishes rearing in the LCR. OBJECTIVES The primary goal of the 2004 sampling trips was to obtain information for the stock assessment of HBC. In addition, these trips provide information for characterizing the natural history and ecology of the LCR fish community. Therefore, all species of native and non-native fish were monitored. The specific objectives for 2004 were: 1. Obtain spring and fall 2004 population estimates of HBC ~ 150 mm in the lower 13.6 km of the LCR. 2. Collect data in support of GCMRC stock assessment models. Specifically, our data and results will be incorporated into Age-Structured Mark- Recapture (ASMR) models that make full use of the historical database to estimate long-term population and recruitment trends of HBC (Coggins et aI., In prep.). In addition to the above stated objectives, information is also presented on physical parameters of the LCR, effort and catch compositions, species compositions, length frequencies, sexual conditions, predation, and parasites. 12