The use of acoustic measurements for in-season management of marine fishes

                                    Gary. L. Thomas

   Prince William Sound Science Center, P.O. Box 705, Cordova, Alaska 99574 USA

     In recent years, acoustic surveys  have been used to determine the prespawning 
biomasses of herring  and pollock before and/or after  the commercial fisheries in the 
Prince William Sound  region.  These surveys  have provided repeatable measures  of 
backscatter  which  is   converted  into  biomass  using  published  target   strength 
relationships.  The major source of error in repeating the biomass estimates has been 
founded to  be unequal truncation of  the fish concentration  by the survey coverage.   
With the truncation  problem solved, the repeatability of biomass  estimates from this 
approach  is a  major  argument for  use  of  acoustics.   Low  costs and  speed  of 
sampling  make  the  application  of   the  procedures  practical.    The  speed  and 
repeatability of the measurements suggest that in-season regulation  of these fisheries 
in  the prespawning  areas  maybe  possible.   The  key  to applying  the  acoustics 
correctly is  to understand  the behavior  of the  fish in  the region.   We have  had 
success using commercial  fishermen for this source of  information.  Many economic 
and  environmental  arguments   support  the  adoption  of   in-season  management 
strategies for marine fishes.