38 



,< D ■'■MM Ml NT OF Commmmk. NATIONA1 < "»' r.ANIC AND ATMOSPHERIC 



Ai,\iiMsiiaiiii\, National .m auim: Fisheries Service, La Jolla, Calif. 



I Bl WE REPORT (OEAB Rl BEABCH) 



Vi • ■• i and Equipment 



Chartered tana purse seiner M/V Elizabeth C.J. (Nicholas L. Lavalouis, 

 Master; Manuel Jorge, Fish Captain; Joe Jorge, Alternate Fish Captain). 

 NMPS Cruise No. 208, Contracl No. 03-6 208 35483. The vessel is 252 feel Long 

 with a 12 fool beam and a draft <»r 21 feet. She can carry up to 1700 tons of 

 fro/en tuna in 10 pairs of brine wells. Propulsion is provided by a twin screw 

 system wiili two 2800 horsepower main engines giving a top cruising speed of 

 18 knots and a 400 horsepower bowthruster aids in maneuverability. The net 

 ased during the cruise was Too fathoms long by 13 standard 4-%" mesh strips 

 deep. The experimental "super apron" and double-depth safety panel of i-V 

 mesh webbing (Fig. l) were installed in the backdown area of the net 



Cruise Period 



October 7. 1076 to December 9, 197G. 



.1 .■■' a of Operation 



Yellowfin tuna Ashing grounds off Mexico and Central America within the 

 Inter-American Tropical Tuna Commission's regulatory area (CYRA). 



Purpose of Charter 



TO test a modification of the "Bold Contender" system, termed the "super 

 apron" and to develop techniques f«r its efficient use in reducing incidental 

 porpoise mortality during commercial tuna purse-seining operations. This w 

 to be performed in partial conjunction with tuna-porpoise behavioral studies 

 during a portion of the same cruise period. 



Objectives 



1. To evaluate the effectiveness of the "super apron" modification of the 

 "Bold Contender" system in reducing incidental porpoise mortality. 



•J. To adjust notation and deployment techniques during backdown to reduce 

 the incidence of a prematurely submerged corkline and the resultant accidental 

 lo<s of lish. 



3. To adjust flotation and apron structure to permit controlled sinking of the 

 backdown apex. 



4. To conduct further tests of the use of a small, one-man inflatable raft to 

 assist in porpoise removal during and after backdown. 



Results 



During the cruise 30,233 porpoise were captured and 913.3 tons of yellowfin 

 tuna were taken in 45 net sets on yellowfin tuna associated with porpoise. One 

 set was a water set and two sets were made on tuna associated with floating 

 objects dogs) in which 90 tons of yellowfin and 5 tons of skipjack tuna were 

 landed. Table 1 presents a summary of the catch and kill data for the behavioral 

 research and gear research sets. Table 2 presents the date, location, catch, kill 

 and raft-use statistics by set with subtotals for the gear and behavioral sets. 



Porpoise mortality occurred on only five of the 43 sets made on tuna-porpoise- 

 associated schools. Sixteen porpoises were killed on these five sets, four during 

 the course of regular fishing operations and 12 during the activities of the 

 scientific party. Excluding mortality during scientific activity, the mortality 

 rates were 0.09 per set, 0.004 per ton of yellowfin caught in association with 

 porpoise and 0.013% of the porpoise captured. 



Fourteen net sets were made for the purpose of studying porpoise behavior 

 in detail. As many as three skiffs and six divers were inside the net prior to 

 and during backdown. In three of these sets (numbers 4. 5, 12) the presence of 

 the divers and tagging efforts during backdown hampered porpoise release and 

 resulted in 12 of the 16 deaths. The remaining four deaths occurred during 

 backdown in two gear experimental sets that had no operational malfunctions. 

 The animals became folded into the side of the backdown channel at a depth 

 that precluded hand rescue. 



The extremely low porpoise mortality rate experienced during this cruise is 

 the result of the fishing captain and crew members - care and efficiency in setting 

 and hauling their net, using speedboats to adjust the corkline (IS sets) and in 



