FISHERY BULLETIN: VOL. 80. NO. 1 



""1 



RING BOB 



STATION I 



MOC 10-27 D 



MOC 1-63 N 

 n-K>9 



P 2 



MOC 10 28 N 



APRIL 1977 KNORR 65 



RING AL 



STATION 2 

 MOC 1-72 D 



MOC 10-35 

 



SLOPE WATER 



STATION 3 

 MOC I 73 a 



MOC K> 36 D 



STATION 4 

 MOC I 75 N 



MOC 10-38 N 



OCTOBER /NOVEMBER KNORR 71 



O 



CO 



coo 



RING EMERSON 

 STATION 6 

 MOC I 99 MOC 1-98 N 



n.27 n-58 



MOC K) 59 



STATION 7 



MOC t 102 



r-|i 





MOC 10 61 D 



'ii.ii i i i  



50 100 150 



MOC K) 58 N 



  . i i i i i i i i  i 



RING FRANKLIN 



MOC I 103 N 



J 



MOC K) 62 N 



MOC 1-117 



L J 



...... 



LU 



MOC 10 65 D 



STATION 9 



MOC K> 67 



' 



MOC H09 



WET WEIGHT (mg) 



SLOPE WATER 



MOC 1116 N 



MOC 10 68 N 



MOC 10 66 N 



I ' ' I ' ' I 



50 100 150 



STATION 5 

 MOC I 97 N 



50 K>0 



D = DAY 



N  NIGHT 



FIGURE 4. — Comparison of the composite size-frequency distribution (expressed as No./l,000 m 3 for a given wet weight interval)of 

 Nematoscelis megalops caught by the MOC NESS 1 (shaded) and the MOC NESS 10 (crosshatched) for tows taken on the same day or 

 night, n = the number of individuals used to construct the histogram. 



Application of Barkley Avoidance Theory Catch 



Since it is likely that N. megalops avoids both 

 net systems, it must detect the approach of either 

 net at some distance in front of the net, resulting 

 in a response which permits a certain percentage 

 of the population to avoid capture. Determina- 

 tion of the avoidance percentage and reaction 

 distance requires an indirect approach, since no 

 other means are available. The theoretical 

 framework on the process of net avoidance devel- 

 oped by Barkley (1964, 1972) provides a means 

 for estimating these parameters according to a 

 quantitative theoretical model. Barkley (1972) 

 formulated the problem in the following way: 



(volume sampled) X 



(no. of organisms unit volume ) X 



(probability of capture) — (losses) 



(1) 



"Losses" refers to individuals which are enclosed 

 by the net but escape through the net meshes. 

 For the size range of individuals which consti- 

 tute our "catch," the "losses" term is essentially 

 zero. Since the volume of water sampled has been 

 rather carefully measured, the "probability of 

 capture" (Pc) is of greatest concern. Pc is related 

 to the mean reaction distance (.r<>), the radius of 

 the net mouth (R), the net's speed (U), and the 

 organism's mean escape speed (u,) by the equa- 



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