(Equation (1)), then Equation (1) can be used to 

 easily estimate the catch per trap day that would 

 prevail at a standardized soak time. Comparing 

 catch per trap day at a standardized soak time will 

 provide a more accurate measurement of relative 

 abundance. The relative fishing power of a trap as 

 estimated by Equation (1) yields the same results 

 as the computations of adjusted traps in Table 2, 

 column 5. 



Conclusions 



When the soak time is variable in trap fisheries, 

 trap days may not be an accurate index of fishing 

 effort. Furthermore, there is evidence that as the 

 exploitable stock declines the profit-maximizing 

 soak time declines, which can result in a measured 

 catch per trap day that will not reflect the declin- 

 ing relative abundance. It is possible to adjust trap 

 days or catch per trap day according to the soak 

 time to more accurately reflect fishing effort (catch 

 per unit of effort). The calibration of this ad- 

 justment requires data on the relationship be- 

 tween the catch and soak time. It is recommended 

 that in the future soak time be documented to 

 facilitate this calibration. 



Acknowledgments 



Data collected by R. E. Warner, University of 

 Florida Cooperative Extension Service, Key West, 

 on trap fishing in the Florida Keys and D. 

 Simmons, Southeast Fisheries Center, National 

 Marine Fisheries Service, NOAA, on Bahama trap 

 fishing were helpful. D. Simmons also provided 

 review and recommendations in developing the 

 model. 



Literature Cited 

 Robinson, R. K., and D. E. Dimitriou. 



1963. The status of the Florida spiny lobster fishery, 1962- 

 63. Fla. State Board Conserv. Tech. Ser. 42, 30 p. 



Thomas, j. C. 



1973. An analysis of the commercial lobster (Homarus 

 americanus) fishery along the coast of Maine, August 

 1966 through December 1970. U.S. Dep. Coramer., NOAA 

 Tech. Rep. NMFS SSRF-667, 57 p. 



C. Bruce Austin 



Department of Economics, School of Business 

 and Division of Biology and Living Resources 

 Rosenstiel School of Marine and Atmospheric Science 

 University of Miami, FL 33149 



SPECIES COMPOSITION AND 



RELATIVE ABUNDANCE OF 



LARVAL AND POST-LARVAL FISHES IN 



THE COLUMBIA RIVER ESTUARY, 1973 



Few ichthyoplankton surveys of northern Pacific 

 coast estuaries exist: Waldron (1972) and 

 Blackburn (1973) surveyed larvae in northern 

 Puget Sound; Eldridge and Bryan (1972) con- 

 ducted a 1-yr survey in Humboldt Bay, Calif; 

 Pearcy and Myers (1974) conducted an 11-yr sur- 

 vey in Yaquina Bay, Oreg. No data on 

 ichthyoplankton are available for the Columbia 

 River estuary. 



In 1973, the National Marine Fisheries Service 

 conducted a survey of zooplankton in the Colum- 

 bia River estuary to study productivity and 

 seasonal variation of zooplankton populations. 

 The survey also captured larval and post-larval 

 fishes. This paper reports species composition, size 

 range, and seasonal and horizontal occurrence of 

 larval and post-larval fishes within the Columbia 

 River estuary. Substrate was provided for egg 

 deposition as an additional technique to deter- 

 mine if spawning was occurring in the estuary. 

 Such investigations are valuable to assessing the 

 importance of the estuary as a spawning and 

 nursery ground. 



Methods 



Seven stations from the Columbia River's 

 mouth to Tongue Point upstream 29 km were 

 sampled once a month with a 0.5-m plankton net 

 January to December 1973 (Figure 1). A single 

 station was sampled monthly from March to 



FIGURE 1. — Columbia River estuary, showing location of sampl- 

 ing stations. 



218 



