Perrin and Irvine 1990

Perrin, C.J., and J.R. Irvine. 1990. A review of survey life estimates as they apply to the areaunder-the-curve method for estimating the spawning escapement of pacific salmon.  Canadian Technical Report of Fisheries and Aquatic Sciences 1733.

Accurate estimates of Pacific salmon spawners are needed to set spawning escapement goals and regulate harvests. Estimating the number of pink salmon Oncoryhnchus gorbuscha spawning in Prince William Sound, Alaska, is difficult since annual runs have ranged between have ranged between 2.2 million and 19.6 million and spawning occurs in over one thousand individual freshwater systems. Escapement monitoring is accomplished by surveying a collection of 208 index creeks several times over a period of weeks from fixed wing aircraft. Unadjusted survey counts are used to monitor escapements during the commercial fishing season, while estimates of the total number of spawners are calculated after the season using the area-under-the-curve methods. We examined the accuracy of the area-under-the-curve estimates by using information obtained on creeks with intertidal weirs: 3 creeks in 1990 , 7 creeks in 1991, and 7 creeks in 1992. Aerial observer efficiency and stream-life values, calculated for each study creek each year of the study, used in conjunction with aerial observations, produced pink salmon escapement estimates that were on average within 10% o weir counts for these same creeks. Currently used methods, using only the area-under-the-curve and a constant stream life of 17.5 days produced escapement estimates that were on average less than 50% of the corresponding weir counts. The use of a correction for aerial observer efficiency provided the greatest improvement in escapement estimates, although the adjustment for stream life also provided substantial improvement. An investigation of the effect of survey frequency on area-under-the-curve estimates indicated that accuracy deteriorated when the survey interval exceeded 7 days.