iiT'ig 



32"'56 



FISHERY BULLETIN: VOL. 72, NO. 2 



II7°I7' 15' 



Date Time Height, cm 



3 1630 134 



2324 2 1 



0606 146 



1200 67 



1730 137 



2354 21 



0630 159 



1236 46 



1818 140 



0018 24 



0648 175 



1306 21 



1906 143 



32° 52 



32° 52 



117° 19 



32° 56 



- 54 



52 



50 



II7°I9 



Figure 5. — Trajectories of two drogues during the field study of 3-6 November 1969. Observed 

 positions of the drogues are indicated by the open circles, and the date and time of the triangulation are 

 indicated by the one-four digit sequence of numbers near the circles. The date and predicted times 

 (Pacific standard time) and heights of tides in centimeters are given in the inset. 



Estimates of the standing stocks of food avail- 

 able to P. bachei were obtained from counts of prey 

 taxa in subsamples of the 0.035-mm mesh net 

 samples at station 3, the centrally located station 

 (Figure 4). These pairs of replicate samples were 

 treated in a manner similar to the counts of 

 ctenophore eggs and larvae, except that counts of 

 all zooplankters were made in a 5-ml subsample 

 of a 500-ml sample. Over 100 specimens were 

 counted in each subsample. The counts of numbers 

 were converted to mass of organic carbon using 

 the data from six species (Table 2) which fre- 

 quently occur in these waters, data in the litera- 

 ture, and approximations by proportions of body 

 volumes relative to the known mass of species for 

 which data exist. 



Counts of ctenophores in samples for vertical 

 distribution studies were made as follows. First, 

 all large ctenophores which could be seen by the 

 unaided eye were removed with pipets from one of 

 the pair of bongo net samples selected at random. 

 When no further specimens could be found by eye, 

 subsamples of 5-12.5% of the whole sample were 

 taken by Stempel pipet or Folsom splitter and 

 examined under 12-25 x magnification for all 



sizes of ctenophores, including larvae and eggs. 

 The diameters were measured as described above. 

 Numbers per cubic meter were calculated by ap- 

 propriate corrections for subsample fraction and 

 volume of water filtered. 



Results 



Physical Parameters and Distribution 

 of Pleurobrachia 



Patterns in the currents of La Jolla Bight ap- 

 pear to be affected by: 1) the configuration of the 

 coastline (especially in the Point La Jolla-La Jolla 

 Cove complex, 2) the bottom topography and 

 bathymetry in the La Jolla Canyon-Scripps Can- 

 yon complex, and 3) the surface tides. During the 

 first field study in November 1969 a pair of 

 drogues drifted toward Point La Jolla, paralleling 

 the axis of La Jolla Canyon during an ebb tide 

 (Figure 5). Both changed directions several times 

 over La Jolla Canyon and made a complete coun- 

 terclockwise rotation before moving northward 

 nearly parallel to shore. Note that the rotational 

 motion and major changes in direction occur over 



304 



