results apply to the fastest growing, 

 rather than the average, individuals. 



Rivas (1954) and Mather and 

 Schuck (1960) presented very simi- 

 lar curves of estimated linear growth 

 for the first eight months of life of 

 bluefin tuna collected in the western 

 North Atlantic. Mather and Schuck's 

 curve (Figure 7) was based on a lim- 

 ited number of measurements, includ- 

 ing those of Rivas, from various ar- 

 eas along the Atlantic coast of the 

 United States and in the Gulf of 

 Mexico. The date of spawning was 

 assumed to be May 15. Although 

 spawning probably occurs earlier in 

 the western Atlantic than in the Medi- 

 terranean (see Section V), the esti- 

 mated mean sizes attained by the 

 young of the year by mid-October 

 are about the same in both areas — 38 

 cm or 1 , 1 00 g. Data for age bluefin 

 caught off the Atlantic coast of Mo- 

 rocco (Fumestin and Dardignac 1962, 

 Aloncle 1964) are similar. Individu- 

 als taken in the first half of October 

 were 3 1 to 34 cm long, in November, 

 39 to 43 cm, and at the end of De- 

 cember, 44 to 45 cm. 



80 



CALENDAR MONT HS AN OYEARS OF AGE(BIRTH IS ASSUMED TO OCCUR IN MID-MAVI 



Figure 8. Estimated growth of young bluefin tuna. Broken lines indicate estimated 

 lengths in periods for which data are lacking. The lower scale shows ages 

 assuming that hatching occurs at mid-May (Mather and Schuck 1 960). 



In all three areas, growth is ex- 

 tremely rapid in the spring, summer 

 and early fall, and considerably 

 slower during the first winter of life. 

 At twelve months of age, eastern and 



to** 



NIO JEIISEV-C«I>ECOO 

 MMTLANO-CAROLINAS 

 yiAMr AHEA 

 GULFOFWXICO 



I tlWiItt |W>TtytH| gitfam I Hovtme* I occiiittn I j«tiu«>r' 



40p 



z 



so; 



2S 1 



z 

 20 u 



15 ' 



10 



Figure 7. Lengths of bluefin tuna less than 50 cm long (young of the year) 

 collected in the western Atlantic and the Gulf of Mexico. The curve of estimated 

 growth was fitted by inspection (Mather and Schuck 1 960). 



western Atlantic fish are about 50 

 cm long, according to Fumestin and 

 Dardignac (1962) and Mather and 

 Schuck (1960). Larger sizes are re- 

 ported for 1 -year-old tuna by 

 Rodriguez-Roda (1960) for eastern 

 Atlantic fish (55 cm) and Sella 

 ( 1 929a) for specimens from the Medi- 

 terranean Sea (64 cm). 



3. Growth of Young Bluefin Tuna 



Westman and Seville (1942) 

 were the first to show that young 

 bluefin tuna grow much more rap- 

 idly during the summer than during 

 the winter. They reached this conclu- 

 sion by tracing the growth of young 

 fish taken off Long Island, New York, 

 through the period July I -October 

 16, 1 94 1 , from length frequency data. 



Mather and Schuck ( 1 960) stud- 

 ied this matter in greater detail. Their 

 data included some specimens taken 

 during both summer and winter in 

 their first year of life (age 0), but data 

 were available for ages 1-4 for the 

 period July-October 16 only. The 

 growth rates in the latter period were 

 very rapid (about 3.8 cm per month), 

 and it was evident that their average 



II 



