FISHERY BULLETIN: VOL. 85, NO. 3 



1979 



1980 



10 15 211 



25 3D 35 40 4S 50 SS 60 65 



SIGHTING PtHGLE IM DEGREES 



70 75 BO 85 30 



ttn 



[HIM 



i 



10 IS 20 25 30 35 40 45 50 55 60 65 70 75 



SIGHTING flMGLE IM DEGREES 



ml 



kfl 



Ik 



0.5 l.O 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 G.O 6.5 7.0 7.5 8.0 

 RflDIflL DISTflriCE m nflUTICFIL HILES 



15 

 14- 

 12- 



I 



JUl 



0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 S.S G.O 6.5 7.0 7.5 8.0 



RFIDIflL DISTflnCE IM MHUTICflL nlLES 



2.00 

 1.75- 



> 1. so- 



ul 



u 



l.ZS- 



f 1.00 



-I 



m 



S o.so- 



p- 



0.25 



0.00 



0.0 



Hfn 



_ji_p ^ 4i^_ 



OS 10 l.'S 2^0 2.5 5.0 5.5 



PERPEMDICULflR DISTflnCE In nflUTICFIL MILES 



f 1.00 



_J 



5 0.75- 



a: 

 at 

 o 



K 0.50 



o- 



0.25- 



M 



nn^ nn r^Hq 



0.5 1.0 1.5 2.0 2.5 5.0 3.5 



PERPEnDICULfiR DISTRnCE in nflUTICRL niLES 



FK'.URE 2.— Distribution of sighting angle, radial distance, and perpendicular distance from 1979, 1980, 



With this system, the rounding to convenient val- 

 ues was not as evident (Fig. 2); hou'ever, mea- 

 surements may still be inaccurate. 



ANALYTICAL METHODS 



Vessel data for area, sea state, sun glare, and 

 observer performance strata were compared 

 using rates of detection for all schools encoun- 

 tered within 2.13 km perpendicular distance of 

 the ship (schools/1,000 km searched) and esti- 

 mates of density of schools (schools/1,000 km^). 



Similar comparisons of aerial data were com- 

 pleted using rates of detection for all schools en- 

 countered within 1.85 km perpendicular distance 

 of the trackline, rates of detection for trackline 

 schools, and estimates of school density. 



Density estimates were made using line tran- 

 sect (LT) theory (Burnham et al. 1980). The basic 

 equation (Seber 1973) is 



D 



n fiO) 

 2L 



422 



