Five-fathom floatline gear was set first on 

 station 17whereas 15-fathom gear was set first 

 on station 18; a like sequence was followed on 

 stations 32 and 33. Thus, to compare similar 

 gear types along the sets, stations 18 and 33 

 were plotted in the reverse of stations 17 and 

 32. The paired stations show considerable con- 

 sistency and, with the exception of station 33, 

 probably are fairly accurate descriptions ofthe 

 "lay" of the gear in the water. The ends and 

 center of the sets were deep and separated by 

 two plateaus. This configuration is undoubtedly 

 related to the alternation of a 5-fathom and 15- 

 fathonn floatline gear in groups of 10 baskets. 

 Station 33 shows an additional trough and, in 

 general, is considerably deeper throughout than 

 station 32, ^ 



Line hauler trouble developed at basket 2 1 

 of this set and continued throughout the retriev- 

 ing to the extent that parts of the gear were 

 hauled by hand. Possibly the line was retrieved 

 primarily from astern and the gear allowed to 

 sink below the maximum fishing depth; or the 

 hauling was so slov/ as to permit an effect 

 similar to creating another end in the set. 

 Figure 6 shows that the ends of the sets sank 

 deeper than the center. Presumably this oc- 

 curred because at the center a basket of gear 

 has more or less equal tension applied on either 

 side. However, toward the end of the set there 

 are less baskets and thus less tension on one 

 side of an individual basket thanthe other. This 

 allows the buoys of the baskets near the ends of 

 the set to close in toward the center dropping 

 their mainline to depths greater than that of 

 the same floatline gear in the center ofthe set. 

 Operations with POFIlongline gear in the equa- 

 torial Pacific show that an interruption of 30 

 nninutes during hauling, at which tinne the gear 

 is freed from the vessel, is sufficient to allow 

 the newly formed end to register depths con- 

 siderably greater than those shown by tubes on 

 the gear hauled just before the break. V/hen 

 mainline breaks occur the new end formed must 

 be retrieved rapidly to avert a deepening of the 

 gear. Usually, the new ends caused by breaks 

 were retrieved within 5 to 20 minutes during 

 POFI albacore cruises. 



Mechanical troubles are not alone 

 responsible for such discrepancies because re- 

 trieving of the gear is sometimes delayed for 

 varying periods of time during stornny weather 

 and for the removal of large numbers of fish. 

 Large fish may sound when captured on the 

 longline and could increase the readings of 

 sounding tubes if they were attached to the sanne 

 dropper as the fish. The effect of the capture 



of a large number of tuna on longline gear was 

 described by BuUis (1955, fig. 15b). He shows 

 Echograph depth records of 10 baskets of long- 

 line in which 9 of the baskets approximated 

 complete catenaries. The fifth basket was 

 distorted with only a portion of the basket being 

 recorded. This basket contained one yellowfin 

 and four "blackfin tuna" while the others had no 

 catch. It is noteworthy that the capture of fish 

 on this one basket did not affect the adjoining 

 baskets. 



CONCLUSIONS 



It is concluded that the maximum fishing 

 depths of POFI longline, during albacore 

 survey cruises, were recorded by sounding 

 tubes with sufficient accuracy to locate the 

 general depths at which the various sets of gear 

 fished. They also showed the configuration of 

 the baskets to deviate from a catenary. This 

 deviation is thought not to have occurred during 

 the fishing period but rather during retrieving 

 operations when slack formed in hauling allowed 

 a portion of the gear to sink below the maxi- 

 nnum fishing depth. Also, deepening of gear 

 below the maximum fishing depth presumably 

 occurred when operational breakdowns or re- 

 quirements formed a new end to a set. The 

 above analysis is relatively simple and it can- 

 not be ascertained whether the results obtained 

 would be applicable to the longline operations 

 of others. But, possibly most of the error in 

 the catenary could be avoided merely by 

 placing two tubes on a basket of gear on a pair 

 of the shallower hooks, such as 3 and 11 in 

 albacore gear, and accepting only the shoalest 

 reading of the two. In this case, the estimation 

 of individual hook depths from sounding tube 

 readings nnight be reliable in areas where the 

 physical environment did not distort the "hang" 

 of a basket of gear. 



Figure 7 shows the ideal relation of hook 

 depths to the distance between buoys for hooks 

 number 2 and 12, 4 and 10, and 7 without drop- 

 pers and with 5- and 15-fathom floatlines. The 

 curves were deternnined empirically using the 

 scaled chain and plotting board described above 

 (fig. 4). With these curves it would be possible 

 to derive theoretical buoy distances from a 

 given sounding tube reading for the above hooks. 

 The scale model of a longline basket could then 

 be pinned at the appropriate buoy interval on 

 the plotting board and the theoretical depths for 

 all hooks of that basket estimated. Reasonable 

 extrapolation between baskets bearing sounding 

 tubes would pernnit estimation of hook depths 

 for an entire set of longline gear. 



