39 



backing down until all live porpoise were released (42 of 4~> sets). These efforts 

 in conjunction with the "super apron" and doulile-depth safety panel of 1-V4" 

 streteh-mesh webbing have allowed this vessel to achieve a record low kill rate. 



The "super apron" 



The apron-type appendage to the backdown area of purse seine nets was first 

 tried on an NMFS^chartered vessel in the fall of 1974 and subsequently led to 

 the development and successful testing of the apron-chute complex known as the 

 "Bold Contender" system. 1 year later. It includes a porpoise safety panel of 

 I-14" mesh webbing 12 fathoms deep and 180 fathoms long. A 10-vessel mass 

 test of the "Bold Contender" system in 1976 resulted in mortality rates sub- 

 stantially below the 1976 fleet averages for vessels using conventional nets, i.e., 

 2" stretch mesh in the safety panel. However, the mass testing revealed two 

 generally recognized problems with its use. First, the smaller mesh size of the 

 safety panel and apron-chute complex caused considerably greater drag when 

 being pulled through the water during backdown than did the normal 2" 

 safety panel. This caused the corkline perimeter of the backdown channel to 

 submerge in the early stages of backdown, thus increasing the danger of loss 

 of fish and necessitating a slower-than-normal backdown. Secondly, several 

 vessels reported that the inability to sink the corkline at the apex of the 

 backdown channel in the later stages of the procedure caused greatly increased 

 need for hand rescue and longer backdown times. 



To alleviate these problems the two-stage taper employed in the "Bold 

 Contender" system (five mesh, two bar on the apron and one mesh, two bar 

 on the chute) was changed to all five mesh, two bar. This straight taper 

 allowed more even distribution of the downward pull on the corkline as back- 

 down proceeded. Although the corklines did tend to sink slightly in the early 

 stages of backdown, and backdown still had to begin slowly, no fish were lost 

 at this stage during the charter and it was generally agreed that there was no 

 problem. 



With the "super apron" modification, the topmost strip of 1-%" webbing 

 (designated as the chute in the "Bold Contender" system) is approximately 

 200 meshes shallower at the backdown apex than its predecessor. The fish 

 captain was able to sink the backdown apex to release the porpoise at will 

 during all stages of the procedure. The re-surfacing of the corkline after 

 sinking was probably slightly slower than for nets with the 2" porpoise safety 

 panel. Two or three speedboats were deployed at the backdown channel apex 

 on every set to help prevent accidental fish loss and to hand-release porpoise 

 as needed. The chief scientist estimated that approximately 18 tons of tuna 

 were accidentally backed out of the net during porpoise release in the 45 

 porpoise sets during the cruise. In general, the fish captain and the alternate 

 fish captain were pleased with the porpoise-saving characteristics of the "super 

 apron." 



Observations from the inflatable raft during backdown on the charter of the 

 M/V Bold Contender (fall 1975) showed that spotted porpoise sometimes 

 become passive and pile up on the bottom of the backdown channel where they 

 can be mistaken for dead. The removal of the extra webbing in the chute 

 (discussed above) eliminated the two-step shelf formed with the "Bold 

 Contender" system. Thus, as backdown proceeded with the "super apron," the 

 channel became progressively shallower and ramp-like, raising the "passive"' 

 spotters up and flushing them out of the net. This reduced the necessity for 

 hand rescue considerably. Of the 146 animals hand-released from the raft 

 during backdown, the rescuer was quite certain that most of them would have 

 been backed out anyway. No porpoise were killed in the six porpoise sets for 

 which the raft was not used. 



The use of the "super apron" atop the small-mesh, double-depth safety panel 

 is not without operational faults, primarily because of the increased drag of 

 the small mesh as it is moved through the water or as it is held against a 

 current. In each of the porpoise sets which caught 50 tons of tuna or more 

 the corkline tended to sink after backdown in the area just outboard of the 

 third bow bunch. Though only a few tons of tuna were lost in porpoise sets, 

 approximately 35 tons were lost in set 36 (schoolfish on a log) in this area. 

 Underwater observation of the net in that area showed that as the net is 

 hauled in after backdown the small mesh squeezes the entrapped water against 



