WHITLKDCK: REGENERATION OF NITROOEN BY NEKTON 



centration changes of any of the measured 

 parameters greater than the standard precision 

 of the chemical methods (=5%). 



Other Measurements 



The wet and dry weights were determined for 

 all specimens except for P. glaueas where only 

 wet weights were estimated by displacement 

 volume. The wet and dry weights determined for 

 all other specimens (Fig. 4) were linearly related 

 by the least squares equation, dry weight = 0.284 

 wet weight + 1.5, with an r 2 of 0.96. 



The percentage body carbon content in all 

 dried specimens ranged from 33.7 to 48.9. The 

 mean and standard deviation for the 34 samples 

 was 41.6+4.24% C. Fresh D. senegalensis speci- 

 mens contained a mean of 42.59% C (Table 2) 

 while specimens starved 1 and 2 d had 43.08 and 

 36.6% C. The mean percentage body nitrogen de- 

 termined for all specimens was 9.35 with a stan- 

 dard deviation of ±1.49%. Fresh D. senegalensis 

 specimens contained 10.36% N while specimens 



100 150 



WET WEIGHT (g) 



250 



Figure 4.— Wet weight vs. dry weight plot for all fish speci- 

 mens. 



starved 1 and 2 d had 9.79 and 7.41% N. Carbon to 

 nitrogen ratios (by atoms) calculated from these 

 data were 4.85 for fresh D. senegalensis and 5.18 

 and 5.90 for specimens starved 1 and 2 d. These 

 ratios show a larger loss of nitrogen than carbon 

 during starvation and the ratios bracket the 

 value of 5.17 measured as the mean C:N of 10 

 Peruvian anchoveta, Engraulis ringens, and cor- 

 respond to the C/N values reported for phyto- 

 plankton and zooplankton (Walsh and Howe 

 1976). When changes in body nitrogen content 

 are calculated from changes in C/N values and 

 are compared with measured nitrogen excretion 

 losses, assuming defecation is approximately 

 equal to excretion (an assimilation efficiency of 

 50%), then about 67% of the observed C/N 

 changes in D. senegalensis are explained. 



The absolute rates of nitrogen loss by excretion 

 were calculated for the various nitrogen frac- 

 tions. The sum of ammonium and urea losses 

 were then compared with body nitrogen content 

 to determine percentage body nitrogen loss per 

 day which ranged from 1.2 to 1.5%. These nitro- 

 gen loss rates would require from 65 to 85 d for 

 turnover of body nitrogen. These nitrogen turn- 

 over estimates are quite reasonable for fish of 

 this size range so the nitrogen excretion rates 

 should not be grossly overestimated due to the 

 stress of capture and handling. Of course, loss of 

 scales, mucus, and reproductive losses would de- 

 crease this turnover time and, if they were 

 known, would represent a refinement of thisesti- 

 mate. 



Nekton Biomass 



Nekton biomass was determined in the study 

 area by acoustic mapping surveys on the RV 

 Atlantis II and bottom trawls during the cruise 

 period. Results of the acoustic surveys that were 



Table 2.— Mean and standard deviation of experimental measurements for Diplodus senegalensis. Octopus vulgaris, and 



Prionace glauca. 



'Number of specimens as in Table 1. 



331 



