FISHERY BULLETIN: VOL. 80, NO. 2 



operation from the acoustic vessel on the basis of 

 target abundance from the echograms in an 

 attempt to approximate optimal sampling 

 allocation (Cochran 1977). 



The net employed was a four panel midwater 

 trawl with 9.2 m headrope and footrope and 9.2 

 m sides designed to open 6.1 m vertically and 

 horizontally; meshes tapered from a 7.6 cm 

 stretch mesh in the wings to a 1.27 cm stretch 

 mesh cod end liner. Head rope floats and chain on 

 the foot rope were used to aid the vertical 

 opening. Trawl doors were metal, V-type, and 

 weighed 31 kg; 55 m dandylines extended from 

 the doors to the side panels. Trawl depth was 

 monitored with a bathykymograph and in 1977, 

 by third wire telemetry to one of the trawl doors. 



A typical survey included three to five 30-60 

 min tows. The number of tows was limited by 

 hours of darkness. Catches were sorted on board 

 by major species, normally herring, dogfish, cod, 

 and smelt, and by incidentals; each species 

 aggregate was weighed separately. Two sub- 

 samples of herring were collected from each tow. 

 One subsample was processed on board to 

 determine maturity (prespawning, spent, and 

 immature). The other was returned to the 

 laboratory for length, weight, age, sex, and 

 sexual maturity data. 



Spawning Ground Surveys 



The herring lay adhesive eggs on lower 

 intertidal and upper subtidal vegetation. The 

 biomass of herring which have spawned can be 

 estimated from the intensity and extent of spawn 

 deposition in conjunction with fecundity, sex 

 ratio, and average weight data (Hourston et al. 

 1972). The basic procedure is to sample 

 vegetation along the shoreline and note the 

 intensity (number of egg layers) of deposition. A 

 spawning ground survey crew used a small (4-5 

 m) boat with outboard motor to maneuver 

 nearshore, and a grappling rake to retrieve 

 vegetation at 350-500 m spacing along the 

 spawning grounds. Observations on spawning 

 intensity and extent are then converted to an 

 estimate of the spawning escapement (Trumble 

 et al. 1977; Meyer and Adair 1978). The survey 

 intensity during the spawning period is typically 

 twice weekly for each of four major spawning 

 areas in the Strait of Georgia. During the 2-mo 

 period (April-May) that encompasses the ex- 

 tremes of the spawning period, 15-20 spawning 

 ground surveys are conducted for each of the four 



areas. The objective to maximize number of sur- 

 veys to reduce the time between spawn deposition 

 and survey is limited by available personnel. 



Catch Records 



The Washington Department of Fisheries has 

 a computerized data retrieval system for pre- 

 liminary catch statistics. Telephone reports of 

 daily estimated catch (soft data) are required 

 from each buyer by noon of the day following the 

 catch. These telephone reports are replaced and 

 updated when fish receiving tickets (hard data) 

 arrive. Management during the fishery used 

 both soft and hard data; this report used final 

 data. Summary reports of daily and cumulative 

 landings by treaty and nontreaty fishermen, and 

 totals for the combined fleet, are available 

 through the catch data retrieval system. 



RESULTS 



A point estimate of sac-roe herring abundance 

 was made the day following each hydroacoustic 

 survey by incorporating cumulative spawning 

 escapement estimates and cumulative catch up 

 through the date of each hydroacoustic survey. 

 This procedure assumed that acoustic-trawl 

 estimates represent maturing adult fish remain- 

 ing to spawn, while cumulative catch and escape- 

 ment account for adult fish removed from the 

 spawning population. The point estimates should 

 be similar once the stock has fully recruited to 

 the area, and will then represent total biomass; 

 as acoustic estimates decline through the season, 

 compensating increases in catch and escapement 

 occur. 



1976 Surveys 



The total acoustic biomass estimates in the 

 study area during 1976 ranged from an initial 

 value of 1,920 tons 5-8 April to a peak of 21,000 

 tons on 21-22 April (Table 1). Trawl catches were 

 predominately herring (about 90% by weight). 

 However, a large proportion of the herring 

 biomass was often either juvenile or spawned out 

 fish. Only 58% of the total biomass estimates was 

 maturing herring at the time of the peak 

 estimate. The acoustic-trawl estimates of matur- 

 ing herring increased from 1,480 tons during the 

 first survey on 5-6 April to a maximum of 12,240 

 on 21-22 April, and decreased to tons on the last 

 survey, 3-4 June (Fig. 2). 



384 



