APRIL 1977 KNORR 65 



FISHERY BULLETIN: VOL. 80, NO. 1 



60 

 40 

 20 







40 - 

 BO 



MOC 1-62 D 



RING BOB 



STATION 1 



MOC I- 63 N 



MOC 10-28 N 



RING AL 

 STATION 2 



MOC t-72 D 



lH 



MOC 10-35 D 

 ' 



SLOPE WATER 



STATION 3 

 MOC 173 D 



M 



TF~ 



MOC 10-36 



'  ' ' ' ' 



STATION 4 

 MOC 1-75 N 



ru e 



MOC 10-38 N 



' ' i ' i  ' ' 



3 



L^ MOC 1-99 D 



O 60 - 

 J? "0 



I 



£ 



1 



OCTOBER /NOVEMBER KNORR 71 



RING EMERSON 



STATION 6 



MOC 1-98 N 



MOC 1-117 



•J~\A^ 



27 



Vf°~ 



42\ 



MOC 10 59 D 



MOC 10 58 N 



MOC 10 67 D 



SLOPE WATER 



STATION 9 



' i i i i i i i i i i i I i i i l i l l l l i I i i l 



MOC 1-116 N 



_ ; "< 



31 



81 

 51 



01 



MOC 10 68 N 



STATION 5 



MOC I 97 N 



„ y*"*. 



II ™^ 64 

 33 

 06 



MOC 10 57 N 



I I I I I I I II I I I I I I 



- 60 



- 40 



- 20 



- 



- 20 



- 40 



- 60 



50 100 150 



MOC 1-102 D 



1 07 I 



L 



62 



I ° 3 



STATION 7 



50 100 150 



MOC 1-I03 N 



5 82 73 



4 4 



RING FRANKLIN 



MOC 10 62 N 



i i i ' ' ' ' 



50 100 150 



STATION 8 



MOC 1-109 D 



55 



pg™ 



22 



MOC 10-65 D 



' 



50 100 150 



WET WEIGHT tmg) 



MOC 1-110 N 



4 43 



MOC 10-66 N 







50 100 150 



= DAY 

 N = NIGHT 



NOTE VALUES < 10"/. 



ARE NOTED ON PLOTS 



FIGURE 6.— Comparison of the difference between paired MOCNESS 1 and MOCNESS 10 tows in the percent of the catch in a 



given wet weight interval. 



where a?io and X\ refer to the reaction distance 

 for the 10 m 2 and 1 m 2 net systems, where we 

 have approximated the radius of the large net as 

 150 cm and the small net as 50 cm, and where 

 both nets were towed at approximately 100 cm/s. 

 We are also assuming that the mean swimming 

 speed of the individuals (u.) is the same for both 

 nets. Solving for the ratio of the reaction dis- 

 tances we find: 



■Tip 

 Xi 



= 3.0. 



That is, in order for the two net systems to pro- 

 vide numbers of N. megalops per volume filtered 

 which are approximately the same, the reaction 

 distance for the 10 m 2 MOCNESS must be three 

 times greater than for the 1 m 2 MOCNESS. 



Since we do not know the absolute abundance 

 of N. megalops independent of our net tow esti- 

 mates for any sampling period, we cannot di- 

 rectly estimate the absolute magnitude of the re- 

 action distance or the minimum probability of 

 capture for either net. It is possible to derive 

 those estimates by a method described by Bark- 

 ley (1972:808) which involves making a best fit of 

 theoretically derived curves which relate P c , 

 u,./U, and X /R to observations of u,./U and the 

 catch/volume filtered for each size class of indi- 

 viduals caught by the nets. In order to make 

 these comparisons, we must have an estimate of 

 the mean escape velocity of an individual ( u,) in a 

 given size class, and ultimately we must make 

 some assumption about population structure, 

 i.e., abundance versus size class of the population 

 sampled. 



84 



