FISHERY BULLETIN: VOL. 69, NO. 3 



lower for preserved than for fresh material. 

 These groups were prominent in the inimp sam- 

 ples, and dry weight determinations were made 

 after long Formalin preservation. The pump 

 samples undoubtedly contained a higher propor- 

 tion of small copepod forms than the net samples 

 of Ahlstrom and Thrailkill (1963) , and it is pos- 

 sible that dry weight loss in Formalin is less 

 for the smaller than for the larger individuals 

 of this group. 



As a basis for estimating the contributions 

 of different species groups to dry weight con- 

 centration, dry weight factors were determined 

 for large copepods, euphausiids, and chaeto- 

 gnaths by sorting known numbers of each from 

 a few representative samples for drying and 

 weighing. The resulting values are given in 

 Table 8. The factor given for small copepods, 

 which would have been difficult to separate in 

 sufficient numbers and purity for a direct de- 

 termination, was inferred from data given by 

 Marshall and Orr (1955) for Calanus finmarchi- 

 ctis and C. helgolandkiis in eastern Atlantic 

 waters. They showed that Calamis stage V, at 

 an average length of 2.5 mm, have a dry weight 

 of about 300 mg 1000 organisms, and that ac- 

 cording to Bogorov (1938) one stage V organism 

 is equal in dry weight to two stage IV, 11 stage 

 III, 42 stage II, and 60 stage I organisms. The 

 average lengths of these stages are given as 

 2.1 mm, 1.65 mm, and 0.94 mm, and the average 

 length of nauplii is given as 0.585 mm, which 

 is the same as that of small cojiepods in the 

 present study. Large copejjods from the present 

 study show an average length intermediate be- 

 tween those given for stages IV and III above. 



Table 8.— Dry weight (DW) and ash weight (AW) 

 determinations (mg/1000 organi,sms) for species groups 

 in selected samples. 



AW 



suggesting a ratio of six large copepods to one 

 stage V, or a dry weight of 50 mg 1000 organ- 

 isms, which is very close to the actual determina- 

 tions. No dry weight equivalent is given by 

 Bogorov for nauplii, but extrapolation of his 

 series against average lengths suggests that 120 

 nauplii per stage V Calanus, or 2.5 mg 1000 

 nauiJJii, would be a conservative estimate. 



Dry weight concentrations were calculated 

 for each species group in each block from the 

 dry weight factors and from the medians of nu- 

 merical estimates for the blocks. The values 

 for sjjecies groups were summed to produce a 

 "calculated" dry weight concentration for each 

 block. These are compared to the measured dry 

 weight concentrations in Figure 8. All the data 

 together tend to cluster around the line of equal 

 value (slope 1.0), and each of the different 



80r 



• Not determined by direct meoiurenienl. See text. 



10 20 30 40 50 

 MEASURED DRY WEIGHT (mg/m') 



FiGL'RK 8. — The relation of calculated to measured dry 

 weight concentration for all sampling blocks. Calcu- 

 lated dry weights were derived from species group 

 density estimates and dry w^eight factors (Table (>). 

 The line indicates equality of the two scales C Cruise 1; 

 O Cruise 2; A Crui.se ;i; ▲ Cruise 4; • Cruise 5. 



692 



