Prince et aL Otolith analysis of Makaira nigricans age and growth 



457 



Interspecific comparisons of linear growth rates can 

 be misleading if differences in body shape and resul- 

 tant patterns of growth in body weight are not con- 

 sidered. Juvenile blue marlin are very elongate fishes, 

 and the very high rates of growth in length correspond 

 to only moderate rates of increase in weight. For ex- 

 ample, the maximum calculated relative growth rate 

 is 1.8% body weight per day at an age of about 70 days. 

 This value is well within the typical range exhibited by 

 teleosts (Weatherley 1972). Extraordinary consump- 

 tion rates or conversion efficiencies would not be re- 

 quired to support the growth rates predicted in this 

 study. Furthermore, since swimming speed usually in- 

 creases with body length, this early growth period no 

 doubt is advantageous for survival and sets the stage 

 for the fast-swimming and wide-ranging capabilities of 

 adults. 



While sexual dimorphism in linear growth was not 

 evident from our samples (perhaps due to small sam- 

 ple size), significant differences in the length-weight 

 relationships were found above 140cm. Our weight-at- 

 age equations indicate small differences in growth rates 

 between sexes for both length and weight may begin 

 at about 110-120cm. 



Ageing adults 



In order to evaluate the usefulness of the ageing meth- 

 ods used in this study on adult blue marlin (2 13-367 cm 

 LJFL), SEM and light microscope analysis of the 

 microstructural increments between presumed annual 

 marks were examined on whole otoliths and transverse 

 sections of 23 fish. Although the presumed annual 

 marks (as described by Wilson 1984) were clearly visi- 

 ble in both the dorsal and ventral lobes of sagittae in 

 adult fish over 300 cm LJFL (Fig. 10), the microstruc- 

 tural increments between these marks could not be 

 clearly distinguished for accurate counts. Conversely, 

 the presumed annual marks could not be distinguished 

 on sagittae from the largest young adults (200-212 cm 

 LJFL) while the microstructural increments were still 

 visible. Therefore, this approach could not offer con- 

 clusive evidence for validating either daily or annual 

 periodicities in blue marlin otolith deposition. 



Incidental observations of relative otolith size (dimen- 

 sion and mass) in Atlantic and Pacific blue marlin in- 

 dicate that individuals with relatively larger otoliths 

 also have many more presumptive annuli in their 

 otoliths compared with similar-sized fish (Wilson 1984, 

 Hill et al. 1989). The coefficients of determination for 

 linear regressions of these parameters are strong 

 (range in R 2 , 0.70-0.91; Wilson 1984). Further explor- 

 ation of the relationships between fish size, otolith size, 

 and increment counts coupled with validated ages for 



younger fish could lead to more robust regression 

 techniques (Boehlert 1985) to estimate the age of adult 

 blue marlin. 



Acknowledgments 



The authors would like to thank all NMFS port sam- 

 plers, Miami Laboratory billfish survey personnel, and 

 employees of Pflueger Marine Taxidermy, Inc., J.T. 

 Reese Taxidermist, Inc., Gray Taxidermy, Inc., and 

 New Wave Taxidermy, Inc., for their assistance in ob- 

 taining and collecting biological samples for our age and 

 growth research. We are especially indebted to the 

 following individuals who acted as cornerstones for our 

 "save it for science" program, which resulted in the 

 acquisition of some of the most important juvenile 

 samples: Dr. Guy Harvey and Chris Maxwell (Jamai- 

 ca), Captain Larry Dukehart (Florida), and Captains 

 Mike and Erin Benitez and other members of Club 

 Nautico de San Juan (Puerto Rico). We would also like 

 to express our appreciation to Drs. Alex Wild, Gary 

 Sakagawa, Cynthia Jones, and Nelson Ehrhardt for 

 their constructive reviews of our manuscript. We wish 

 to thank Thomas Potthoff (Florida), Joe Ebel (New 

 York), and the staff of Specialty Testing and Equip- 

 ment (New York) for their technical assistance. 



Citations 



Beamish, R.J., and D.A. Fournier 



1981 A method for comparing the precision of a set of age 

 determinations. Can. J. Fish. Aquat. Sci. 38(8):982-983. 

 Beamish, R.J., and W.N. McFarland 



1983 The forgotten requirements for age validation in fisheries 

 biology. Trans. Am. Fish. Soc. 112(6):735-743. 

 Boehlert, G.W. 



1985 Using objective criteria and multiple regression models 

 for age determination in fishes. Fish. Bull., U.S. 83(2): 

 103-118. 



Brothers, E.B. 



1979 Age and growth studies on tropical fishes. In Saila, S.B., 

 and P.M. Roedel (eds.), Stock assessment for tropical small- 

 scale fisheries, p. 119-136. Proceedings of an international 

 workshop held at the University of Rhode Island, Kingston, 

 RI, Sept. 19-21, 1979. Int. Cent. Mar. Resour. Development, 

 Univ. Rhode Island, Kingston. 

 1987 Methodological approaches to examination of otoliths in 

 ageing studies. In Summerfelt, R.C., and G.E. Hall (eds.), The 

 age and growth of fish, p. 319-330. Iowa State Univ. Press, 

 Ames. 



Brothers, E.B., and C.P. Mathews 



1986 Application of otolith microstructural studies to age deter- 

 mination of some commercially valuable fish of the Arabian 

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