GUNDERSON: POPULATION BIOLOGY OF SEBASTES ALUTUS 



fecundity must be discussed separately for the 

 QCS and WVI stocks. 



Migrations and Availability Within 

 the Study Area 



Availability of S. alutus fluctuates widely over 

 short periods of time. Short-term fluctuations in 

 availability were quite evident during a series of 

 2- to 3-wk research cruises off the Washington 

 coast (Gunderson 1974), and masked any long- 

 term changes in biomass that occurred during 

 1968-72. 



For this reason, catch and CPUE data can be 

 used to study migration patterns and seasonal 

 availability only if they are based on a large quan- 

 tity of trawling effort, carried out more or less 

 continuously. The data from the Washington 

 trawl fleet seem well suited to this purpose, since 

 these trawlers spend a great deal of time searching 

 out and catching Pacific ocean perch. Sebastes 

 alutus is frequently the target species for this fleet, 

 and made up 29% of its total coastal landings dur- 

 ing 1967-71. 



In this section, catch and effort data from the 

 Washington trawl fleet will be used to describe 

 migration patterns and seasonal trends in the 

 availability of S. alutus. Data on sex and length 

 composition of the catch will also be brought into 

 the analysis, since it is difficult to interpret trends 

 in availability without them. 



Queen Charlotte Sound 

 Seasonal Patterns for the Region 



The continental shelf is steep and untrawlable 

 seaward of 150 fm (274 m) in Queen Charlotte 

 Sound, so the fish in this area are inaccessible to 

 trawlers when they move into deep water 

 (January-April). Examination of gonads indicates 

 that spawning occurs in March (Gunderson 1971), 

 but there is no certainty as to where this occurs. 

 Few fish are caught during January-April, and 

 virtually all of these are males (Figure 5) that do 

 not participate in the spawning migration. 



Males precede females in their return from win- 

 tering areas, and when the fishery first begins in 

 earnest (May), males constitute 68% of the catch. 

 The availability of females increases sharply after 

 May, and by July they dominate the catches. 



During June- August, Pacific ocean perch are at 

 the shallowest point in their bathymetric cycle. 

 Catches are low during this period, and large 

 quantities offish 35 cm or smaller are landed (Fig- 

 ure 6). 



Both catch and CPUE rise in September, and 

 although the mean depth of catch is about the 

 same as in July and August, there is a sharp in- 

 crease in the proportion offish larger than 35 cm in 

 the catch. Aggregations of large adults must sud- 

 denly become available during September, prob- 

 ably because mating activities are beginning. 



QUEEN CHARLOTTE SOUND 



WASHINGTON -VANCOUVER [S 



| 500- J05- 

 i * 



FIGURE 5. — Mean monthly catch, catch 

 per hour, mean depth of catch, and sex 

 ratio for the Washington trawl fleet dur- 

 ing 1967-71. Data for the QCS and WVI 

 stocks of Pacific ocean perch are pre- 

 sented separately. 



Jon-Apr Moy Jun Jul Aug. Sep Oct Nov Dec Jon Feb Mor Apr May Jun Jul Aug Sep Od Now Dec 



373 



