FISHERY BULLETIN: VOL. 72, NO. 2 



parachute silk attached to a wooden frame, creat- 

 ing three intersecting planes normal to each 

 other; each plane covers about 9 m^) set at depths 

 in or near the thermocline (about 15-m depth). 

 During the field studies surface temperatures 

 were measured by bucket thermometer to the 

 nearest 0.1°C, and the vertical distribution of 

 temperature was measured by mechanical 

 bathythermograph (BT) or salinity-temper- 

 ature-depth recorder (STD). Tidal heights for the 

 time of particular events are taken from tide cal- 

 endars for predicted tides by the U.S. Coast and 

 Geodetic Survey for La JoUa. 



For studies of the offshore and seasonal dis- 

 tributions of P. bachei two types of nets were 

 used. The net to collect postlarval ctenophores 

 (i.e., ctenophores larger than 0.5 mm in diameter) 

 is a ring net of 0.5 m diameter and 0.363-mm 

 mesh apertures. This net was used for oblique 

 sampling. The second net is a 0.17-m diameter 

 ring net of 0.035-mm mesh apertures equipped 

 with a 20-cm metal collar that attaches the net 

 onto the wire. This net was towed vertically, and 

 it was used for sampling the eggs and larvae of 

 Pleurobrachia and the smaller zooplankters 

 which were available as prey but not sampled 

 quantitatively by the 0.363-mesh net. Both nets 

 were equipped with a calibrated TSK (Tsurumi- 

 Seiki Kosakusho) flowmeter^ to measure volumes 

 of water filtered. 



Two studies of the vertical distribution of P. 

 bachei were made, the first during 3-6 November 

 1969 and the second during 22 May-1 June 1970. 

 In both cases, 0.7-m diameter paired, 

 opening-closing bongo nets with mesh apertures 

 of 0.053 and 0.153 mm were used. In each vertical 

 profile of abundance, four to six depth intervals 

 were sampled at 10- to 20-m intervals for shal- 

 low depths and at greater intervals below 50 m. 

 Thus, a set of four to six pairs of samples com- 

 prised each vertical profile. The volumes of water 

 filtered were between 5 and 50 m^, as determined 

 from calibrations of numerical settings on the net 

 release gear against the calculated cubic meters 

 of water filtered using a TSK flowmeter. 



In all cases net samples were preserved with 10 

 ml of 40% formaldehyde solution, buffered with 

 calcium carbonate, in about 750 ml of seawater. 

 This solution is about 0.5% formaldehyde. Pre- 

 liminary experiments with preservation of 



Pleurobrachia showed this to be the best concen- 

 tration and type of preservative. Relatively small 

 changes occur in length frequencies of P. bachei 

 after 27 mo in this preservative (Table 3). 



A preliminary survey of the horizontal, offshore 

 distribution (the distribution of numerical abun- 

 dance of Pleurobrachia in samples taken at in- 

 creasing distances from the shore) was made on 28 

 August 1969. Samples were taken at 10 stations 

 with closely spaced intervals out to 11 km from 

 shore off Scripps Institution. Results of this study 

 showed that the ctenophores occurred in highest 

 abundances within 3 km of shore. 



Samples were taken in the following manner 

 during the two field studies of the vertical and 

 offshore distributions of P. bachei mentioned 

 above. In both studies of vertical distributions, 

 about 10 sets of four to six pairs of samples were 

 taken alongside or between parachute and vane 

 drogues. Each sample set permitted the descrip- 

 tion of abundances at various depth intervals for 

 one time of the day. In the study of November 1969 

 the offshore distribution sampling consisted of six 

 transects of stations perpendicular to shore. The 

 transects were about 3-8 km apart, beginning off 

 Del Mar and ending off Point Loma. Each transect 

 consisted of three or more stations located between 

 1 and 13 km from shore. In the second study the 

 offshore distribution sampling consisted of two 

 transects of seven and nine stations out to 50 km 

 from shore. In all offshore distribution studies rep- 

 licate samples were taken at each station except 

 in five cases where time prohibited it or second 

 samples were lost. 



Table 3. — Changes in size-frequency distribution of Pleuro- 

 brachia with duration in 2% Formalin-seawater preservative. 

 Samples A and B were analyzed 16 and 12 days after sampling, 

 respectively, and a second time after 27 months as indicated in 

 columns A' and B'. The variable indicated is the number of 

 occurrences of each size class. One specimen in sample A was 

 lost. 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service. 



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