BARRACLOUGH and ROBINSON: LAKE FERTILIZATION. III. 



of migration may not occur until the first week 

 in September. It takes between 2 and 5 days 

 for the sockeye to migrate up the Stamp River 

 into Great Central Lake, depending on the water 

 levels in the river. The fish remain in the lake 

 but do not commence to spawn until the latter 

 part of September. Great Central Lake is one 

 of the few lakes in British Columbia where most 

 of the spawning occurs in areas along the lake- 

 shore rather than in tributary streams. Only 

 a few hundred sockeye spawn in tributary 

 streams a short distance away from the lake. 

 Drinkwater, Lindsay, and Fawn Creeks (Fig- 

 ure 1) receive most of the stream spawners. 

 Lakeshore spawning commences in the last 

 week of September, reaches a series of peaks in 

 three principal locations during October, and 

 ends in November. About 50% of the spawning 

 occurs along 4.63 km of lakeshore between Lind- 

 say Creek and Forestry Creek, 30 '^r along 1.1 km 

 of shoreline west of Fawn Point, and 20 '^'r along 

 1.6 to 4.8 km of lakeshore off" North Creek. Redds 

 were found at depths between 0.6 and 24 m but 

 most were between 12 to 15 m. Spawnings were 

 observed by scuba divers at depths as great as 

 41 m. It is now realized that the location of 

 separate major in-lake spawning areas is im- 

 portant in providing the potential basis for the 

 immediate and rapid distribution of juvenile 

 sockeye throughout the lake, shortly after the 

 fry emerge from the gravel and commence to 

 feed. Two spawning areas are adjacent to the 

 lake area where fertilizer was applied (see Par- 

 sons et al., 1972). 



METHODS 



LOCATION AND DISTRIBUTION OF 

 JUVENILE SOCKEYE SALMON 



A high frequency (200 kHz) moist paper re- 

 cording echo sounder (Furuno model No. FNV- 

 3000)' was used to locate the young sockeye in 



^ Reference to trade names in the publication does 

 not imply endorsement of commercial products by the 

 National Marine Fisheries Service. 



the lake and monitor their horizontal and vertical 

 distribution. During the day, young sockeye are 

 generally distributed throughout the lake at 

 depths between 45 and 90 m, but are most abund- 

 ant at about 65 m. They commence to migrate 

 toward the surface about half an hour before 

 sunset. In the summer months at civil twilight, 

 when the sun is 96° from the zenith (or 6° be- 

 low the horizon) they are distributed irregularly 

 in density between 5 and 30 m. At nautical twi- 

 light when the sun is 102° from the zenith (or 

 12° below the horizon) the juvenile sockeye form 

 a layer between the depths of 10 and 20 m, with 

 a maximum density of about 14 m. At night 

 during the winter months they are distributed 

 more uniformly between 20 and 60 m. In sum- 

 mer the downward migration commences shortly 

 before sunrise and is usually complete 15 to 30 

 min after sunrise. 



The young sockeye were sampled with mid- 

 water trawls. Sampling commenced at night 

 when the fish were in a layer between 10 and 

 20 m. Samples were also collected during day- 

 light at diff"erent depths throughout the depth 

 range of the young sockeye. The depth of 

 trawling was adjusted to coincide with the depth 

 of maximum fish concentration as shown by the 

 echo sounder traces. 



FISHING GEAR 



A trawl net with a mouth opening 3 m wide, 

 6.1 m deep, and 17.7 m long was towed at 2.7 

 to 3.2 km/hr by a single vessel, the Decihar, to 

 sample the sockeye between the depths 5 and 

 25 m. Three mesh sizes of knotless nylon netting 

 were used in the construction of the net: 5 cm 

 and 2.5 cm stretched mesh in the body and 1.3 

 cm in the cod end. The cod end measured 1.2 m 

 wide by 1.8 m deep at the mouth and it tapered 

 to a blunt end about 76 cm in diameter. A 

 standard Henson plankton net (350/x mesh) 

 76 cm in diameter at the mouth, was secured to 

 the blunt aft end of the cod end to retain the 

 smallest juvenile sockeye and minimize the loss 



39 



