FISHERY BULLETIN, VOL. 72. No. 1 



before the meeting. The report of the meeting 

 may be considered as a summary of these pa- 

 pers, which indicated that increases in size at 

 recruitment would probably increase yield per 

 recruit but not by more than about 10% . 



The special ICCAT working group also ex- 

 amined available evidence on the practicability 

 of minimum size regulations. Scientists of the 

 group were concerned that since the gears that 

 fish for yellowfin in the Atlantic supposedly 

 kill most fish that are captured, a minimum 

 size regulation would reduce the number of 

 small yellowfin that are landed but would not 

 have the desired effect of reducing mortality 

 rates of small yellowfin. This, of course, as- 

 sumes that schools of yellowfin containing yel- 

 lowfin less than any minimum size would actual- 

 ly be set upon. In this connection the group 

 noted that the conditions which must be met 

 before minimum size regulations can be effec- 

 tive are: (1) the fishermen must be able to 

 estimate the size of yellowfin in a school, and 

 (2) there must be little or no mixing of small 

 yellowfin with large yellowfin within schools. 



Very little evidence is available from the At- 

 lantic on these subjects. Ten sami)les were pre- 

 sented at the Abidjan meeting that indicated 

 considerable mixing of small yellowfin (<5 kg) 

 with large yellowfin (>5 kg) within schools. 

 The working group also took note of a study on 

 the subject by Calkins (1965) when size regula- 

 tions were being considered by the lATTC 

 (Inter-American Tropical Tuna Commission) 

 for the yellowfin fishery in the eastei'n tropical 

 Pacific. Calkins, working with only one hypo- 

 thetical minimum size out of a range of 12.7 to 

 25.0 kg, concluded that a 12.7-kg size regulation 

 would be seriously complicated by size varia- 

 tion within sets. He also noted that a consid- 

 erable amount of small yellowfin are often cap- 

 tured in sets that include skipjack. Thus it ap- 

 pears that it would not be possible to fish for 

 skii)jack without killing some small yellowfin. 

 Evidence based on the few samples from the 

 Atlantic indicated that sets would include 

 yellowfin tuna larger and smaller than 5 kg; 

 thus even if a minimum size regulation were set 

 at this value it would be difficult to prevent 

 the capture offish smaller than 5 kg. 



The working group recommended that more 

 data should be collected on the subject from 

 the Atlantic. The working group also noted 



that a reduction in the size at first recruitment 

 should be prevented and that minimum size 

 regulations of 3.2 kg that have been passed by 

 several African nations should help prevent a 

 reduction in size at recruitment. 



The population dynamics of Atlantic yellow- 

 fin tuna are complex because the fishery is 

 prosecuted by several types of gear: bait boats, 

 small purse seiners, large purse seiners, and 

 longliners. These gears tend to capture differ- 

 ent sizes of fish and thus affect the population 

 in different ways. FAO (1968) noted that long- 

 line gear tends to capture large yellowfin while 

 the other gears capture small yellowfin. Lenarz 

 (1970).'' with more recent data, showed that 

 American" purse seine gear tends to capture 

 relatively more large yellowfin — in significant 

 quantities — than was indicated for the earlier 

 surface fishery. Joseph and Tomlinson (1972, 

 see footnote 4) presented data that indicated 

 small purse seiners of France-Ivory Coast- 

 Senegal (FIS) tend to capture relatively more 

 small yellowfin than the large FIS and Ameri- 

 can purse seiners. The differences among size 

 selectivity of the four gears necessitates con- 

 sideration of the physical makeup of the fleet 

 when e.xamining size regulations. Therefore, 

 considerable attention was paid to this aspect 

 of the problem during the study. 



The above paragraph might be taken to imply 

 that adequate data are available respecting the 

 relative quantities and size distributions of fish 

 caught by the various gears. It is our feeling 

 that the adequacy of the data needs to be dem- 

 onstrated. We cannot place much faith in the 

 details of the relative size distributions per 

 unit effort among the various fishing units, but 

 we do feel that the general orders of magnitude 

 are essentially correct. We should also point 

 out that with the improvement in data over the 

 last several years, the interpretations which 

 accrue from the data and our appreciation of 

 the considerable complexity of the fishery are 

 more evident. 



Definitions of Minimum Size 



Because this paper discusses minimum size, 

 it is necessary to define the term explicitly to 



" Lenarz, W. 1970. Estimates of yield per recruit of 

 Atlantic yellowfin tuna. Southwest Fisheries Center, 

 National Marine Fisheries Service, La Jolla, Calif. Un- 

 published manuscript. 



" Refers to vessels registered in Canada, Panama, and 

 the U.S.A. 



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