" sekiyama ", a 22-foot section constructed of 12 strands of No. 8 Irish linen whipped with No. 6 

 cotton located between the cotton line and the wire leader of each dropper. The sekiyama is used 

 to provide a good gripping surface on the part of the line nnost often handled in fighting fish, and 

 also perhaps to resist abrasion of the line on the hull when fish go under the boat. Because it is 

 one of the more expensive components of the longline gear (about $2. 25 each), an experiment was 

 conducted to ascertain whether the 261 -thread cotton line used in the balance of the gear could be 

 substituted for it. 



On Manning cruise 13, 10 baskets of longline gear in which 261 -thread cotton line was 

 substituted for the sekiyama were fished in addition to 40 baskets of standard gear. A comparison 

 of the catch on this gear with the catch of the 10 adjacent baskets of standard gear is given in 

 table 18. The capture of 56 fish on each type of gear is a good indication that the efficiency was 

 not changed by the elimination of the sekiyama. Insofar as durability is concerned, five droppers 

 were broken on each of the two types of gear. During the cruise both scientists and fishermen 

 were in agreement that the absence of the sekiyama did not cause undue difficulty in handling fish. 



Table 18. --Analysis of catch of experimental 

 baskets with 10 adjacent standard 

 baskets. Manning cruise 13 



1/ Catch includes all species except sharks. 



SHARK DAMAGE TO THE CATCH 



Varying fractions of the catch were damaged by sharks. This damage usually takes 

 the form of one or more bites from the body of the tuna while it is being hauled in. The problem 

 is of considerable importance to a commercial fishery because severely bitten fish are unsuitable 

 for canning. In considering the data it should be borne in mind that: (1) our records of shark- 

 bitten fish did not include estimates of the severity of the damage to each fish (about one-half of 

 the fish recorded as bitten are probably unsuitable for the cannery); and (2) no particular effort 

 has been made during the course of POFI experimental fishing to reduce shark damage. For 

 these reasons our estimates of the severity of the problem can be considered as maximal. 



During the course of six cruises 21 percent of all yellowfin landed were damaged by 

 sharks (table 19). If half of these were unsuitable for canning, the net loss would be about 10 

 percent of the catch. It is of interest to note that the percent of loss to sharks appears to be re- 

 lated to the size of the fish. For instance, bigeye, the largest species in the catch, sustained 

 the highest rate of shark damage; and skipjack, the smallest species, sustained the lowest rate. 



