GROWTH OF BLUEFIN TUNA OF THE WESTERN NORTH ATLANTIC 



By Frank J. Mather III and Howard A. Schuck 



Information on the growth of bluefin tuna 

 {Thunnus thynnufi) of the western North Athintic 

 Ocean is incomplete, and limited to the smaller 

 sizes for which age-with-length studies are pub- 

 lished (Westman and Gilbert, 1941; Westman and 

 Neville, 1942). Only fragmentary data are avail- 

 able on specimens longer than 46 inches. As a 

 result of the growing interest in bluefin tuna by 

 sport and commercial fishermen, we began a co- 

 operative project, in 1950, to accumulate material 

 for an age-determination study of the bluefin 

 throughout its entire size range. The present 

 paper is an account of our interpretation of this 

 material to date. 



In the preparation of this paper, we received 

 valuable advice from Dr. Lionel A. Walford of the 

 U.S. Bureau of Commercial Fisheries, and Dr. 

 Henry B. Bigelow and Dr. William C. Schroeder, 

 both of the Woods Hole Oceanographic Institution 

 and Harvard University. Dr. James R. Westman 

 of Rutgers University made available to us his 

 extensive data on bluefin tuna. Other material 

 was collected and measurements were obtained 

 through the kindness of several Cape Cod com- 

 mercial fishermen, notably Capts. John Vetorino, 

 Adam Rupkus, Mike Goulart, and Nathaniel 

 Wixon of Barnstable; also John A. Worthington of 

 North Truro, Joseph Francis and Stuart Joseph of 

 Provincetown, as well as through the cooperation 

 of many sport fishermen and charter boat captains. 

 Many of the length measurements were made by 

 Frank Riley of the U.S. Bureau of Conunercial 

 Fisheries at Provincetown, Mass. Several other 

 people contributed length measurements as noted 

 in the frequency tables. Assistance in obtaining 

 and processing data and in preparing this paper 

 was received from members of the U.S. Bureau of 

 Commercial Fisheries at Woods Hole, including 



I Regression formula with a correlation coefficient of 0.997 computed from 

 155 specimens, 29 to 270 centimeters long, where X is fork length, Y is caudal 

 spread— Log X=O.7271+0.8642 Log Y. 



Note.— Frank J. Mather HI. Woods Hole Oceanographic Institution, 

 Woods Hole, Miiss.; Howurd A. Schuck, Alaskan Air Command, Anchorage, 

 Ahiska, formerly fishery biologist, U.S. Bureau of Commercial Fisheries, 

 Woods Hole, Mass. 



This project was supported in part by grants from the National Science 

 Foundation. 



Approved for publication March 11, 1960. Fishery Bulletin 179, 



Donald M. Allen who worked 4 years on this study, 

 also from several members of the Woods Hole 

 Oceanographic Institution. Their assistance is 

 gratefully acknowledged. 



READINGS OF ANNULI 



As in other species of fishes, including several 

 other tunas, annuli are formed on the scales, and 

 also on the centra of the vertebrae (Sella, 1929; 

 Aikawa and Kato, 1938; Westman and Gilbert, 

 1941; Westman and Neville, 1942; Partlo, 1955). 

 Because these annuli are not consistently distinct 

 in either of these two structures, and for other 

 reasons which will be explained later in the text, 

 we examined both. In the beginning we assumed 

 that the annuli which we counted were formed once 

 each year and therefore indicated the age in 

 years. For verification of this assumption we 

 depend on the internal evidence furnished by our 

 material, including consistency of the age de- 

 terminations with analysis of length-frequency 

 data. 



Most of our data are from fish caught in the 

 vicinity of Cape Cod in pound nets or by hook and 

 line. We took scales or vertebrae (or both) from 

 as many specimens as time and opportunity per- 

 mitted. There was rarely any difficulty in obtain- 

 ing scales from fishermen's catches. This was less 

 true for vertebrae, for frequentlj- we were per- 

 mitted to take them only from the tail, which is 

 usually cut ofF in dressing the fish. Owing to 

 unfavorable working conditions, it was not always 

 possible to measure the fish from which the tails 

 were cut. In such cases, we estimated the length 

 from a regression of fork length against caudal 

 spread ' or, if the weight of the fish could be ob- 

 tained, from a length-weight curve based on 778 

 specimens from 34 to 270 centimeters long. 



We prepared celluloid impressions of the scales 

 (Arnold, 1951), and studied them with the aid of 

 a magnifying projector. Figure 1 shows the annuli, 

 zones of crowding, or discontinuity of the circuli, 

 which research workers consider to be formed 

 annually. We also counted the rings on the centra 

 of the vertebrae (fig. 2). These rings were marked 



39 



