(observed < theoretical) in hook 10 that is twice 

 as large. 



In a case where the gear is skewed toward 

 one side, one would expect hook 7 to have a nega- 

 tive mean difference and a standard deviation 

 somewhat smaller than hook 10. Because this 

 is not so (table l)it is likely that the error with 

 depth shown by the sounding tubes in figure Z 

 must be unduly influencing the analysis. The 

 data presented in the lower half of table 1 were 

 obtained after an adjustment to the theoretical 

 slope was made. The results were those 

 anticipated; accompanied by a reduction of 

 significance to the 5-percent level. 



CAUSES OF SKEWNESS 

 AND EXCESSIVE READINGS 



The results show that generally the 

 conformation of baskets of longline fished by 

 POFI was not a catenary. It is thought that the 

 sounding tubes were accurately recording the 

 depths of the gear. Therefore, the cause of 

 skewness noted inthe baskets mustbe related to 

 the environment or operative procedures. The 

 relatively moderate environmental conditions 



encountered on longline stations during all 

 seasons of the year suggest the latter was 

 responsible (table 2). 



However, a more detailed analysis of 

 environmental factors was obtained by deter- 

 mining a measure of skewness, or the difference 

 in feet between the depths of hooks 4 and 10 of 

 the bookless baskets. In order that each set be 

 comparable, only the bookless basket placed 

 between baskets 25 and 26 or close t o that 

 position^.' was used in the analysis. Omitted 

 from analysis were data from each bookless 

 basket whenever, on the model, the mainline 

 did not reach, or i t overshot the buoy line. 

 Skewness was then compared with a measure 

 of current velocity (the mean longline drift), 

 with possible decrease in current speed at the 

 thermocline resulting in a shearing effect (the 

 ratio of the depth of hook 7 of the bookless bas- 

 ket to the depth of the top of the thermocline) 



■i/ 



— In Hugh M. Sn-iith cruise 29 and Charles 



H. Gilbert cruise 23 the bookless basket was 



placed at times between 24 and 25 or 26 and 27. 



Table 2. --The average and range of certain physical conditions of longline 

 stations during albacore fishing cruises in the central North Pacific 



1/ 



— Coded; for values in feet see Hydrographic Office Observers' Manual, 

 U. S. Navy Hydrographic Office, H. O. Pub. No. 606-c, 1951. 



2/ ^. 



— This mean was computed with the omission of station 28 because the drift 



was undetermined. 



3/ 



— This mean was computed with the omission of stations 13 and 17 because 



the drifts were undetermined. 



