NOTE Davis and West: Growth and mortality of Lutjanus vittus 



403 



to channeling energy into gonadal growth at the ex- 

 pense of somatic growth at a relatively early age (Davis 

 1984). 



Length-frequency distributions did not show the 

 modal structure one would expect knowing the age 

 structure of the population. The length-frequencies 

 showed three modes, whereas direct ageing suggested 

 there should be at least six. Length-based methods of 

 ageing work best with fish that spawn over a short 

 period of time, have short life spans, and are fast grow- 

 ing; characteristics not typical of lutjanids (Manooch 

 1987). 



A preponderance of females at larger sizes has been 

 reported in studies of other lutjanids, e.g., L. synagris 

 (Rodriguez Pino 1962, Erhardt 1977), Etelis carbun- 

 culus (Everson 1984), E. coruscans, Aprion viriscens 

 (Everson et al. 1989), and Rhomboplites aurorubens 

 (Grimes and Huntsman 1980). The latter authors at- 

 tributed the preponderance to differential mortality 

 and longevity. L. vittus goes against this trend: males 

 predominate the larger size-classes, as is the case for 

 Lutjanus mnabilis (Loubens 1980) and Lutjanus buc- 

 canella (Thompson and Munro 1983). The preponder- 

 ance of males at larger sizes appears to be due largely 

 to a reduction in growth rates of mature females. 



No significant differences were found in the instan- 

 taneous rate of annual mortality (Z) between male and 

 female L. vittus. One of the assumptions of estimating 

 mortality using the catch curve method of Gulland 

 (1969) is that the mortality rate is constant for all years 

 used in the estimation. This may not be the case for 

 female L. vittus after 6 years of age. However, the data 

 points in the oldest age-groups are based on smaller 

 sample sizes, so the mortality curve at this stage should 

 be interpreted with caution. Using the relationship be- 

 tween natural mortality (M) and the growth coefficient 

 (K) for snappers and groupers determined by Ralston 

 (1987) from published data provides us with estimates 

 for M of 0.59 for males and 0.92 for females. The value 

 for males seems reasonable, but that for females is 

 unlikely if total mortality is about 0.98. Clearly, regres- 

 sion methods to produce estimates of M such as those 

 used by Pauly (1980) and Ralston (1987) should be ap- 

 plied with caution. 



Acknowledgments 



This paper is dedicated to the memory of Mr. Otto 

 Augustine, a technician with the CSIRO Division of 

 Fisheries. He was responsible for the ageing of many 

 fish species in the Division's programs from the late 

 sixties up until his death in 1990. He determined the 

 age and marginal increment data used in this paper. 



We wish to thank W. Thomas for laboratory assistance 

 and all people who assisted in the fieldwork on the 

 Northwest Shelf Program. We are grateful to K.J. 

 Sainsbury for providing length-frequency and catch 

 data from his research program, and K. Haskard for 

 statistical advice. S. Blaber and J.S. Gunn reviewed 

 the manuscript. 



Citations 



Carlander, K.D. 



1981 Caution on the use of the regression method of back- 

 calculating lengths from scale measurements. Fisheries 

 (Bethesda) 6:2-4. 

 Claro, R. 



1983 Ecologia y ciclo de vida del caballerote, Lutjanus grisevs 

 (Linnaeus), en la plataforma Cubana: 2. Edad y crecimiento, 

 estructura de las poblaciones, pesquerias. Rep. Invest. Inst. 

 Oceanol. Acad. Cienc. Cuba 8, 26 p. 



Davis, T.L.O. 



1984 A population of sexually precocious barramundi, Lates 

 calcarifer, in the Gulf of Carpentaria, Australia. Copeia 1984: 

 144-149. 



Draper, N.R., and H. Smith 



1981 Applied regression analysis, 2d ed. Wiley, NY, 407 p. 

 Erhardt, H. 



1977 Beitrage zur biologie von Lutjanus synagris (Linnaeus 

 1758) an der Kolumbianischen Atlantikkuste. Int. Rev. 

 Gesamten Hydrobiol, 62:161-171. 

 Espinosa, L., and E. Pozo 



1982 Edad y crecimento del sesi {Lutjanus buccanella Cuvier, 

 1828) en la plataforma suroriental de Cuba. Rev. Cubana 

 Invest. Pesq. 7(1):80-100. 



Everson, A.R. 



1984 Spawning and gonadal maturation of the ehu, Etelis car- 

 bunculus, in the Northwestern Hawaiian Islands. In Grigg, 

 R.W., and K.Y. Tanoue (eds.), Proc, Second symposium on 

 resource investigations in the northwestern Hawaiian Islands, 

 vol. 2, p. 128-148. UNIHI-SEAGRANT-MR-84-01, Univ. 

 Hawaii. Honolulu. 



Everson, A.R., H.A. Williams, and B.M. Ito 



1989 Maturation and reproduction in two Hawaiian eteline 

 snappers, uku, Aprion virescens, and onaga, Etelis coruscans. 

 Fish. Bull., U.S. 87:877-888. 



Francis, R.I.C.C. 



1990 Backcalculation of fish length: A critical review. J. Fish 

 Biol. 36:883-902. 



Grimes, C.B., and G.R. Huntsman 



1980 Reproductive biology of the vermilion snapper, Rhom- 

 boplites aurorubens, (Cuvier) from North and South Carolina 

 waters. Fish. Bull. U.S. 78:137-146. 

 Gulland, J.A. 



1969 Manual of methods for fish stock assessment. Part 1. 

 Fish population analysis. FAO Man. Fish. Sci. 4:1-154. 

 Jernakoff, P.. and K.J. Sainsbury 



1990 CSIRO's northern demersal finfish stock assessments: 

 1980 to 1990. Bur. Rural Resour., Dep. Primary Ind. Energy 

 Aust. Inf. Pap. IP/6/90, Canberra, A.C.T.. Aust., 169 p. 

 Kimura, D.K. 



1977 Statistical assessment of the age-length key. J. Fish. 

 Res. Board Can. 34:317-324. 



