DAUBLE ET AL.: SPATIAL DISTRIBUTION OF JUVENILE SALMONIDS 



= 375) yearling-sized salmonids collected by 

 electroshocking during the spring 1984 studies. 

 Only one juvenile sockeye salmon was collected 

 by boat electroshocking. 



Overall, 3,982 0-age chinook salmon and 1 

 juvenile sockeye salmon were collected by beach 

 seining. Almost all of the chinook salmon cap- 

 tured with seines originated from upstream 

 spawning areas near Vernita Bar. Catches 

 peaked on 17 May with 178 fish/seine haul. Num- 

 bers declined in June despite the large numbers 

 of hatchery fish present. The size of 0-age 

 chinook salmon collected with seines (Fig. 9) was 

 similar to those collected with fyke nets in April 

 and May. However, fish collected with barge 

 fyke nets in .June (see Figure 5) were generally 

 larger than those collected with seines. No ju- 

 venile spring chinook salmon or steelhead were 

 collected with beach seines. 



70 



^ m 



40 



•s 30 — 



^. 20 



10 



o 



I- 





 50 



40 



30 



20 



10 



20 



10 



i^ 



April 

 n = 48 



n 



May 

 n = 100 









 30 40 



June 

 n = 86 



50 



60 



70 



80 90 



Fork Length (mm) 



Figure 9. — Length-frequency of 0-age fall chin- 

 ook salmon captured by beach seine in spring 

 1984. 



Diel Patterns In Salmonid Migration 



Principal movement of all salmonids occurred 

 between the hours of 2200 and 0400, based on 

 barge fyke net collections: however, differences 

 in peak movement among species were evident 

 from the barge catches (Fig. 10). For example, 

 only 0-age fall chinook salmon (wild and hatch- 

 erj' populations) were collected during daylight 

 hours. For these populations, peak catches oc- 

 cun-ed just after darkness (2200 to 2400). In con- 

 trast, fyke net catches of sockeye salmon, spring 

 chinook salmon, and steelhead smolts peaked be- 

 tween 2400 and 0400. Although nocturnal move- 

 ment was also evident based on shoreline fyke 

 net catches, a higher proportion (—229c) of the 

 0-age chinook salmon were collected in shoreline 

 nets during dayhght hours (Fig. 11). 



Diel patterns of distribution based on electro- 

 shock catch totals contrasted among the differ- 

 ent groups of chinook salmon (Fig. 12). Peak 

 numbers (55%) of the 0-age fall chinook salmon 

 in April and May were collected fi'om the hours 

 of 1600 to 2200;" 44% of the 0-age hatcheiy fall 

 chinook salmon (June fish) were collected from 

 0400 to 1000: and 80% of the hatcheiT spring 

 chinook salmon and late summer migrant 

 chinook salmon were collected diu-ing the night 

 fi-om 2200 to 0400. 



DISCUSSION 



Our studies showed that distributional pat- 

 terns were different for each of the three most 

 abundant gi'oups of juvenile salmon (i.e., fall 

 chinook, spring chinook, and sockeye salmon). 

 Our hypothesis that fish distribution was inde- 

 pendent of barge station and depth was rejected, 

 suggesting that different gi'oups acted differ- 

 ently at different barges and at different depths. 

 Salmonid outmigrants in the Hanford Reach ex- 

 hibited patterns of proportional distribution that 

 were mainly size related (Table 8). Larger out- 

 migi'ants (i.e., chinook salmon, sockeye salmon, 

 and steelhead) occuiTed near the bottom, mid- 

 channel zone of the river, while the smaller wild 

 and hatchery 0-age fall chinook salmon pre- 

 feiTed the shallower shoreline areas. 



The relatively high contribution of fall chinook 

 salmon to the total catch during the spring re- 

 sulted primaiily from the large numbers of wild 

 fish emerging in the Hanford Reach and the 

 hatchery fish released there. About 90% of the 

 salmonids collected were 0-age chinook salmon. 

 Collectively, this gi'oup comprised about 70% of 



785 



