HEALEY: UTILIZATION OF THE NANAIMO RIVER ESTUARY 



During April and May 1975, samples of 

 downstream migrant chinook salmon were mea- 

 sured for fork length (millimeters) and wet pre- 

 served weight ( iO.Ol g) to provide an estimate of 

 the body size of downstream migrants. 



During 1975 and 1976 the temperature of the 

 river near the trapping site was measured morn- 

 ing and evening. Daily discharge of the river was 

 available from Inland Waters Directorate, Envi- 

 ronment Canada, Ottawa. The measurements 

 were made about 12 km upstream from the traps. 



Estuary- Sampling 



In the intertidal area of the estuary most sam- 

 pling was by beach seine ( 18 m long x 3 m deep of 

 12 mm mesh I. Stream channels crossing the inter- 

 tidal mud flat and the delta front were sampled at 

 low tide, and the edges of the tidal marshes at high 

 tide. During March and April 1975 widely scat- 

 tered locations on the estuary were sampled, but 

 during the latter half of April and May. sampling 

 was concentrated in the east channel of the river 

 and Holden Creek (Figure 1) at low tide. During 

 1976 and 1977 four specific sampling sites were 

 established in the east channel of the river and 

 Holden Creek and these were fished weekly (Sta- 

 tions 28-31; Figure 1) except that Station 28 was 

 not fished until June 1976, and fishing at Stations 

 30 and 31 was discontinued after the chinook 

 salmon disappeared from these stations. Sampling 

 at other locations at high and low tide was per- 

 formed occasionally, as time permitted, to deter- 

 mine the distribution of chinook salmon in the 

 estuary. In addition to beach seining, five sets with 

 a 90  7 m hand-hauled purse seine were made 

 over the intertidal mud flat at high tide on 12 May 

 1976 to determine if juvenile chinook salmon re- 

 mained over the mud flat at high tide. Catch data 

 are presented as average catch-per-set (CPUE) in 

 this report. 



Estuary sampling began during the second or 

 third week of March of each year. In 1975, sam- 

 pling terminated in early June; in 1976, in mid- 

 July; and in 1977, at the end of June. In 1975. 

 samples of chinook salmon for analysis of length, 

 weight, and stomach contents were preserved in 

 only 6 of 12 sampling weeks. In 1976 and 1977. 

 however samples of 20 or more were preserved 

 each week. 



In 1977, temperature (°C) and salinity (per mil) 

 were measured at the time of beach seining at each 

 sampling location in the east channel of the river 



and Holden Creek with a Yellow Spring Instru- 

 ments Model 33 Thermister/Salinometer*. 



In 1977 the total population of chinook salmon 

 in the estuary was estimated twice by mark and 

 recapture techniques. Between 18 and 21 April, 

 3,187 chinook salmon were captured along the east 

 channel of the river and Holden Creek, mainly at 

 Stations 30 and 31, marked with a left pelvic fin 

 clip, and released at the point of capture. Catch 

 and recaptures were recorded on 19-22 April, and 

 on all subsequent sampling days. Between 16 and 

 19 May, 1,554 chinook salmon captured mainly at 

 Stations 28 and 29 were marked with a right pel- 

 vic fin clip. Recaptures of these marks were re- 

 corded on 17-19 May. 22 May. and all subsequent 

 sampling days. 



Recaptures after the final mark release for each 

 fin clip provided an estimate of the rate of disap- 

 pearance of marked fish from the sampling area. 

 This rate was assumed constant for each mark and 

 was calculated as the slope of the regression of loge 

 (CPUE marks) on days since marking. In calculat- 

 ing the rate for left pelvic clips, catches during the 

 second marking period were ignored since sam- 

 pling on these days was performed in a way to 

 maximize catch, and was different from our nor- 

 mal sampling procedure. The number of marks 

 released was reduced each day in accordance with 

 these estimated rates of disappearance to give an 

 estimate of the total marks present on each sam- 

 pling day. Population estimates for each day were, 

 therefore, the product of total catch and estimated 

 marks present divided by recaptures. Left pelvic 

 marks were still present at the time of the second 

 marking, so that it was possible to make two inde- 

 pendent estimates of population size at this time. 



A sample of chinook salmon was preserved from 

 those captured each day for marking, and these 

 provided an estimate of the average size of marked 

 fish at the time of release. Marked fry captured 

 after the last release of each fin clip were pre- 

 served and their fork length and weight measured 

 to provide an estimate of growth rate. 



Marine Sampling 



Up to 18 different locations within a 10 km 

 radius of the river mouth were sampled in 1975 

 and 12 locations in 1976 (Figure 2). In 1975 nine 



'Reference to trade names does not imply endorsement by 

 Fisheries and Oceans, Canada, or by the National Marine 

 Fisheries Service, NOAA. 



655 



