FISHERY BULLETIN: VOL. 78. NO. 2 



Kramer (1979) suggested, but the irregularity of 

 the isotherms defining these tongues off Newport 

 Beach implies local shifting of temperatures. 

 Comparison of time as well as temperature differ- 

 ences along and adjacent to the cruise track for 20 

 March indicates, in fact, that notable temperature 

 differences between closely located tows were 

 probably more a matter of change over time than 

 of static gradients between locations. Tows 15 and 

 20 are of particular interest because they both had 

 a high incidence of emaciated larvae and were 

 close together, but differed in temperature by 1.5° 

 C. However, tow 20 was taken 24 h later than tow 

 15, and the thermograph record showed that the 

 higher temperature applied to tow 15, as well as to 

 the tow 19 and tow 20 positions, at the later time. 

 Such short-term temperature shifts indicate that 

 there was water mass instability or movement in 

 the area. 



Plankton Volume 



Plankton volume averaged appreciably lower 

 for the four tows with a high proportion of 

 emaciated larvae than for either the inshore or the 

 offshore set of tows (Table 4). The average number 

 of larvae was also relatively low in these four tows, 

 being about half the average for all tows off New- 

 port Beach, or in the San Pedro Channel area 

 (inshore set). Number of larvae and plankton vol- 

 ume, in fact, tend to be associated for the inshore 

 set (Figure 17), and while the four tows with high 

 incidence of emaciated larvae do not show the low- 

 est values, they are among the tows with low val- 

 ues. 



Plankton volume did not relate to temperature 

 in the inshore area, but there were some interest- 

 ing changes with time (Figure 18). From 17 March 

 to midnight of 20 March all volumes were 11 ml or 

 less. This includes the four tows with a high inci- 

 dence of emaciated larvae, one of which (tow 20) 



Table 4. — Mean plankton displacement volume (milliliters) for 

 different sample arrays in the study of northern anchovy larvae 

 off southern California. 



Plankton 



Item 



No. of 

 tows 



Larvae/ 

 tow 



Volume/ 

 tow 



SD 



0.5 



9.3 



9.0 

 20 1 



15.6 



was the last taken in this time period. Twenty-four 

 hours later tow 21, the first tow with a markedly 

 higher volume (21 ml), was taken at a nearby 

 position (Figure 14). Three more tows of progres- 

 sively higher volume were taken during night 

 hours over the next few days, but there were also 

 several tows with lower volumes (3-14 ml) taken 

 during this period, some at night. This pattern 

 indicates that there was a striking change in the 

 plankton regime off Newport Beach starting on 2 1 

 March, with volume tending to be higher, espe- 

 cially at night, than it had been during the preced- 



< 

 > 



< 



U. 



o 



CO 



3 



300 - 



200 



10 20 30 



PLANKTON VOLUME (ml) 



40 



Figure 17. — The regression of number of anchovy larvae on dis- 

 placement volume of plankton (larvae excluded) for the inshore 

 tows, 1-37. The solid circles indicate the four tows with a high 

 incidence of emaciated larvae. 



40 



30 



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 3 



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a. 



20 



10 



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—I — I — I — I — I I I — 1 — I — f— 1 — I I I I I I I I I I I — I I I I I I — I — I — I I I — I I I I 



06 13 18 \0€ 12 IB \ 06 12 18 \ 06 12 18 \ 06 12 W \ 06 12 18 \ 06 12 '8 \06 12 W \ 06 12 18 \ 06 



17 18 19 20 21 22 23 24 25 26 



DATE a MOUff OF TOW 



Figure 18. — Displacement volume of plankton on date (March 

 1977) and hour of tow. Dots indicate the four tows with a high 

 incidence of emaciated larvae. Dates are in bold type and located 

 at midnight points on the hour scale. 



486 



