FISHERY BULLETIN: VOL. 72, NO. 1 



sizes caught at Buoy 29 in the three nets during 

 the 1970 larval season is shown in Figure 6. 

 Little difference is apparent in the proportion 

 of different sizes of larvae in the different nets. 

 All curves show that the number of larvae 

 caught between 6 and 8 mm was less than be- 

 tween 8 and 10 mm. This is probably explained 

 by hatching of some larvae at lengths over 8 

 mm, and hence is a true reflection of relative 

 abundance, rather than lack of retention of 

 the smallest larvae by the nets. Larvae larger 

 than 20 mm were not caught at all in the CB 

 samples, presumably because of the capability 

 of large larvae to avoid this gear. 



TIDAL-DIEL VARIATIONS 



Figure 7 illustrates the variations in CB 

 catches of fish eggs and larvae during several 

 diel sampling periods at Buoy 21. In Figure 7A, 

 peaks in both egg and larval abundance occurred 

 during periods of low water (Mann-Whitney U 

 test. P <0.01). Similarly, highest catches of 

 herring larvae coincided with times of low 

 water in Figure 7B {P = 0.06). In neither of 

 these figures is a day-night difference evident 

 (P > 0.2). In Figure 7C, however, catches of 

 herring larvae were not correlated with tidal 

 stage (P >0.2), but highest catches coincided 

 with darkness (P <0.01); all but one of the 9 

 nighttime catches exceeded the 14 daytime 

 catches. 



Therefore, both tidal and diel factors may 

 influence catches. We believe the high catches 

 associated with low water were caused by tidal 

 excursion of water with high density of eggs 

 or lai-vae. In other words, the center of abun- 

 dance of L. lepidus larvae and fish eggs (Figure 

 7A) and C. h. pallasi (Figure 7B) was up the 

 estuary from Buoy 21 at high tide. The ability 

 of larger larvae to avoid plankton nets during 

 the daytime (see Figure 6; Tibbo et al., 1958; 

 Bridger, 1956; and Colton, Honey, and Temple, 

 1961) was thought to explain the high catches 

 after dark in Figure 7C, but this interpretation 

 was not supported by the similar size-frequency 

 distributions of day- and night-caught larvae. 



Q 

 UJ 

 CE 



LiJ 



I 



E 



UJ 



a. 

 (r 



LJ 

 CO 



72 



10 



0.1 



0.01 



01 



OOI 

 0[ 



10- BUOY 15 



0.1- 



0.01 

 



BUOY 39 



• CB 233 



 BONGO 233 



• BONGO 571 



BUOY 29 



0.1 



0.01- 



Of 1 \ 1 1 1 r 



BUOY 21 



T 1 1 r 



n 1 1 r 



"T — ji 1 r 



T 1 r 



1 1 1 r 



1969 



1970 



THE ESTUARY AS A NURSERY 



The results of this study on the i)lanktonic 

 fish larvae tentatively support McHugh's (1966, 



Figure 5. — Number of Pacific herring per m^ caught in 

 Clarke-Bumpus nets with 0.233 mm mesh, the bongo net 

 with 0.233 mm mesh and the bongo net with 0.571 mm 

 mesh at five stations in Yaquina Bay, June 1969-June 1970. 



208 



