temperatures aboard vessels were used in cliart- 

 ing isotherms between station positions. The data 

 for cruises TO-59-2 (considered as part of Cal- 

 COFI cruise 5908), 6608, TO-64-1, and TO-64-2 

 have been publislied (Scripps Institution of Ocean- 

 ography, 1961, 1968, 1969). The data for cruises 

 TO-65-1 and TO-66-1 are available from the 

 Scrijjps Institution of Oceanography. 



SURFACE CHLOROPHYLL A 



On cruise TO-59-2, concentrations of chloro- 

 phyll a were determined by spectrophotometric 

 measurement of optical density of acetone extracts 

 by use of the equations of Kichards with Thompson 

 (1952). These data have been published (Black- 

 burn, Griffiths, Holmes, and Thomas, 1962). On 

 cruises TO-64-1 and TO-64-2, concentrations were 

 determined by mesisuring the fluorescence of ace- 

 tone extrax-ts ( Holm-Hansen, Lorenzen, Holmes, 

 and Strickland, 1965; Lorenzen, 1966). The data 

 have been published (Scripps Institution of 

 Oceanography, 1969). On the other three cruises, 

 determinations were made by measuring the fluo- 

 rescence of acetone extracts or in vivo suspensions 

 (Lorenzen, 1966) or both. The data for these 

 cruises are available at tlie Scripps Institution of 

 Oceanography. All available surface measure- 

 ments were used in this study, irrespective of the 

 time of day or night at which the material was 

 collected. Concentrations are given in mg./m.' 



PELAGIC RED CRABS 



The jielagic red crab was collected or observed 

 and its concentration in the water estimated in sev- 

 eral ways. Tables 1-6 list stations and localities be- 

 tween stations where red crabs were collected or 

 observed on the six cruises and give the estimated 

 concentrations in milliliters (displacement vol- 

 ume) /1,000 m.^ These data refer to adults and 

 juveniles (iM)stlarvae), but not larvae. 



One method of collection (M in tables 1-6) was 

 the standard micronekton net haul, which was 

 made usually once eacli niglit. Tlie net wa.s the 1.5- 

 m. (5-foot) net described by Blackburn (1968); 

 it was hauled obliquely at a ship speed of 5 knots 

 (9.3 km./hour). On cruises TO-59-2, TO-65-1, 

 and TO-66-1, the hauls were made to a deptli of 

 about 90 m. with 350 m. of wire. On cniises TO- 

 64-1 and TO-64-2 they were made to about 140 m. 

 with 500 m. of wire. Wire was paid out at speeds of 



20 to 30 m./minute and retrieved at speeds of 10 to 

 15 m./minute. This method was not used on cruise 

 6608; other methods, mentioned below, were em- 

 ployed on that cruise. The volume of water strained 

 on each haul was estimated from the distance 

 traversed in meters, the mouth area of the net in 

 square meters, and an empirical filtration coeffi- 

 cient, 0.76 (Blackburn, 1968). Crab volumes were 

 measured directly. 



Another method (Z in tables 1-6) was the stand- 

 ard zooplankton net haul with the CalCOFI 1-m. 

 net, which was usually made at each station. These 

 hauls were made obliquely to a depth of about 140 

 m. at a ship speed of less than 2 knots (3.7 km./ 

 hour). Thrailkill (1956) described the net and 

 hauling procedure. A flowmeter measured the 

 volume of water strained on each haul. Volumes of 

 red crabs were measured directly for cruises TO- 

 64-1, TO-64-2, and TO-65-1. For the other three 

 cruises the volumes were estimated from counts of 

 crabs, using an empirical average volume of 3.0 

 ml. per crab, or 1.0 ml. per crab if they were re- 

 corded as small. Some crabs probably avoided these 

 slowly moving nets, even at night. At 46 night 

 stations both standard micronekton hauls ajid 

 standard zooplankton hauls were made and red 

 crabs collected. Volumes per 1,000 m.= were equal 

 in the two hauls at 3 stations, gi-e<ater in the micro- 

 nekton hauls at 31 stations (including 18 when the 

 zooplankton haul was negative) , and greater in the 

 zooplankton haul at 12 stations (including one 

 with a negative micronekton haul) . 



A third method (H in tables 1-6) was the high- 

 speed micronekton net haul described by Black- 

 burn (1968). This net is hauled horizontally at 

 about 10 m. below the surface at the ordinary 

 cruising speed of the ship. Such hauls were made, 

 usually at night, on all cruises except TO-64-1. 

 Their duration was from 2 to 3 hours on cruise 

 TO-59-2, from i/o to II/2 hours on cruise TO-64-2, 

 and 1 hour on other cruises. The volume of water 

 strained was estimated from the distance traversed, 

 the mouth areu of the net, and an empirical filtra- 

 tion coefficient, 0.94 (Blackburn, 1968). Crab 

 volumes were measured directly. I showed earlier 

 (Blackburn, 1968) and found again in this study 

 tliat volumes per 1,000 m.^ from these hauls aver- 

 age much smaller than those from standard micro- 

 nekton hauls made at about the same time and 

 place; the ratio, high-speed net volume/standard 



DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA 



153 



