Estimates of Recreational Catch of Reef Fish Updated

PIFSC researchers in the Hawaii Marine Recreational Information Program (MRIP) and colleagues from the Coral Reef Ecosystem Division fish team have produced new estimates of recreational reef fish catch. Estimates in catch in weight were generated for the period 2004-2011 using data from the Hawaii Marine Recreational Fishing Survey (HMRFS).

For every two-month survey period (wave), HMRFS estimates of the catch for individual species were derived based on the catch rate (number of fish per angler- trip) from the onsite Angler Intercept Survey and fishing effort (number of fishing trips) from a Fishing Effort Telephone Survey. The estimation scheme is illustrated in the following graphic. The catch rate estimates from the onsite intercept survey were post-stratified according to three fishing areas: inland (bays, estuaries, and sounds); ocean 3 miles or less from shore; and ocean more than 3 miles from shore. The fishing effort estimates were partitioned into the three different fishing areas according to the proportions of fishing trips recorded within the areas in the onsite intercept survey. The catch estimates were calculated as the product of catch rate and fishing effort in the estimation domain (combination of fishing mode and fishing area). Currently HMRFS covers two fishing modes, shoreline fishing and fishing from private boats.

Catch estimation scheme for the HMRFS surveys.
Catch estimation scheme for the HMRFS surveys.

For each HMRFS wave, estimates were derived for (1) catch in numbers of fish, (2) mean weight of fish measured during the intercept surveys, and (3) catch in weight as the product of catch number and the mean weight of the fish. In Hawaii surveys, approximately two-thirds of the records used to estimate catch in number by species have no corresponding weight estimate. In these cases, the mean weight of fish landed in the State of Hawaii during that wave (including all fishing modes and fishing areas) is substituted. At least two measurements are required for the substitution. (When similar estimates are calculated for states on the U.S. mainland, weight measurements from nearby states can be used as substitutes, but of course this option is not available in Hawaii.) In addressing this problem PIFSC scientists Ivor Williams and Hongguang Ma used a variety of methods to acquire appropriate substitution weights for catch records with missing weights, including (1) deriving mean weight from the entire 8-year (2004-2011) sample, (2) estimating weight from length using length-to-weight conversion formulas, and (3) using substitution weights from other sources when there were no weight or length measurements for the entire 8 years. The updated catch weight estimates indicated that annual catch weights for surgeonfish, parrotfish, and goatfish were >2 to >13 times the original estimates with missing weights.