AREA COVERED 



The area covered on survey cruises made during 1956 is shown in figure 

 1. The north-south extent of the coverage was from Cape Mendocino, off nor- 

 thern California (station line 40), to below Cape San Lucas, Baja California 

 (station line 157); the offshore coverage extended 250 miles seaward or more 

 on some lines. The survey area was not completely covered on any one cruise. 

 The number of stations occupied during each monthly cruise is summarized in 

 text table 1, by sub-areas. The most intensive coverage was obtained during 

 April through July (178 to 239 stations per cruise). The sub-area off northern 

 California (lines 40-57) was occupied during May and June only, that off cen- 

 tral California (lines 60-77) between April and July, and the sub-area off 

 southern Baja California (lines 140-157) on three cruises between January and 

 April. No sub-area was covered on every cruise. The sub-area off southern 

 Cplifornia (lines 80-93) had the most repeated coverage (10 cruises), while 

 the sub-areas off central Baja California (lines 110-137) were covered con- 

 tinuously between January and September. 



There were three cruises into the Gulf of California in 1956, made in 

 February, April and December. Data from the Gulf cruises will be reported 

 in a separate publication. 



One to four vessels participated on each cruise. The "Black Douglas" 

 made eight survey cruises (February through September). The following vessels 

 operated by the Scripps Institution of Oceanography participated in the cruises 

 indicated: "Stranger": 5 cruises (January through May), "Horizon": 2 cruises 

 (January, December), "S. F. Baird": 4 cruises (February, April-June), "Paolina 

 T.": 2 cruises (June, July), "Orca": 4 cruises (July, October-December). 



METHODS OF SAMPLING 



The plankton nets used during 1956 were either constructed of No. 30xxx 

 silk grit gauze or nylon bolting cloth of fairly similar mesh size (Refer to 

 Ahlstrom and Kramer 1957:4 for more detail). Plankton hauls are made obliquely 

 from approximately 140 meters deep to the surface (2(X) meters of wire out at 

 greatest depth), at all localities where depth of water permits. The hauls 

 are made at a vessel speed of between one and two knots. During a haul, an 

 inclinometer is suspended from the boom, riding freely on the towing wire. 

 The angle of stray of the towing wire from the vertical is recorded at inter- 

 vals, and the inclinometer readings also are closely watched in order to main- 

 tain favorable vessel speeds during the period of hauling. The depth of the 

 net at any instant during a haul can be approximated by multiplying the amount 

 of tow wire out by the cosine of the angle of stray of the towing wire from the 

 vertical. The amount of water strained during each haul is determined from 

 the revolutions registered during the haul by a current meter fastened in the 

 mouth of the net. For more details concerning sampling procedures refer to 

 previous reports in this series. 



