FISHERY BULLETIN: VOL, 77. NO 2 



METHODS 



Ichthyoplankton samples were collected from 

 the Southern California Bight in March 1976, 

 May 1976, and March 1977 with the NOAA ship 

 David Starr Jordan. The sampling gear consisted 

 of a CalCOFI (California Cooperative Oceanic 

 Fisheries Investigations) ring net (1 m mouth 

 diameter), MARMAP (Marine Resources, Moni- 

 toring, Assessment, and Prediction Program) 

 Bongo net (60 cm mouth diameters), and a Manta 

 neuston net: all with 505 ;um mesh. Oblique tows 

 were made from the depth indicated in Table 1 to 

 the surface. Samples were drained of excess sea- 

 water and preserved in 85% ethanol. (Recently we 

 found that preservation is greatly improved if the 

 alcohol is changed at least once after initial pres- 

 ervation; the otoliths may dissolve in poorly pre- 

 served samples with large plankton volumes. We 

 change it once within 24 h and again within a few 

 weeks.) Surface temperatures were measured 

 with a bucket thermometer, and vertical tempera- 

 ture profiles were obtained with expendable 

 bathythermographs. 



The 12 samples analyzed in this study are from a 

 limited part of the spawning range of the northern 

 anchovy, but the Southern California Bight in 

 March is an important spawning area for the cen- 

 tral population of the anchovy (Smith 1972). Sam- 

 ples A1-A3 and Bl were collected near Los 

 Angeles and the Channel Islands in 1976 (Figure 

 1 ) and were selected because of the wide size range 

 of anchovy larvae found in each. Samples CI and 

 C2 were collected in this same region in March 

 1977. They were selected to represent the widest 

 temperature range possible. Samples D1-D6 were 

 collected in March 1977 along a transect extend- 

 ing seaward from San Diego and were the only 

 samples containing anchovy larvae on this tran- 

 sect. Additional station data are in Table 1. 



All fish eggs and larvae were sorted from the 

 plankton samples chosen for analysis and anchovy 

 larvae were processed in a manner similar to that 

 described by Brothers et al. ( 1976). The standard 

 length, tip of snout to tip of notochord or hypural 

 plates, of each larva was measured to the nearest 

 0.1 mm. Sagittae were removed and placed on a 

 microscope slide with the lateral (flat) side up. A 

 polarizing filter and analyzer in the dissecting 

 microscope made the otoliths more visible during 

 dissection. The slide was air-dried and the otoliths 

 were mounted under a coverglass with a clear 

 mounting medium iPro-texx'M. Daily growth in- 

 crements were counted in otolith images on a 

 video screen; the total magnification by the micro- 

 scope and video camera was 600 ^ or 1 ,500 x . Each 

 otolith was counted by 1-3 observers until the 

 range of accepted counts for the two otoliths was 

 =s2. Accepted counts were averaged over all ob- 

 servers and both otoliths. 



The shrinkage of sea-caught larvae in preserva- 

 tive (Blaxter 1971) and the lag between hatching 

 and first increment formation must be considered 

 before comparing the size at age of sea-caught 

 larave with laboratory-reared larvae. Shrinkage 

 of anchovy larvae depends upon the elapsed time 

 between death and preservation (Theilacker''). 

 There is no shrinkage when live larvae are placed 

 directly into ethanol but a 5-15 mm larva could 

 shrink about 0.6 mm if dead throughout the 6 min 

 duration of the net tow. No shrinkage correction 

 was applied because the elapsed time between 

 death and preservation probably was <6 min and 

 highly variable. Anchovy larvae tend to stay 

 above the thermocline ( Ahlstrom 1959) so are cap- 



^Reference to trade names does not impl.v endorsement by the 

 National Marine Fisheries Service. NOAA. 



"H^heilacl^er. G. H, Preservative shi'inltage of larval anchovy. 

 Engrauhs mordax: laboratory versus field. Paper presented 

 Nov. 1, 1978 at CalCOFI Conference, USC, Idyllwild, Calif. 



Table l — Data on samples of larval northern anchovy taken from the Southern California 

 Bight, spring 1976 and 1977. 



414 



