V JONES: DETERMINING AGE OF LARVAL FISH 



applied to larval field populations of many species 

 of fish (Table 5). Most applications have been based 

 on laboratory validation of daily increment deposi- 

 tion for the individual species studied. Some have 

 not. Methot and Kramer (1979), based on validation 

 of daily increment deposition by Brothers et al. 

 (1976), obtained growth rates for wild populations 

 of Engraulis mordax by fitting a Gompertz function 

 to length-at-age data. Various other field applications 

 of the increment aging technique are listed in Table 

 5. Of special interest is a comparison of growth 

 estimates for Parophrys vetulus from modal progres- 

 sion of length frequencies and otolith increments 

 (Laroche et al. 1982). Growth based on the increment 

 count method was 2-3 times faster. If the increment 

 count method proves to be accurate, then mortality 

 estimates could be considerably changed. 



For at least four species listed in Table 5, labora- 

 tory validation was not conducted. These applica- 

 tions assume a given age at initial deposition and 

 daily increment deposition thereafter. The validity 



of these assumptions depends on the species and on 

 the sensitivity of the application to inexactness in 

 the age estimation. For example, controversial results 

 have been obtained for larval herring, Clupea 

 harengus. Geffen (1982) showed that growth rates 

 could be overestimated by as much as three times 

 the actual rate However, analysis of Gulf of Maine 

 herring data (Jones 1985) showed that differences 

 in growth between larvae hatched early and late in 

 the season could be drawn. Until sensitivity analyses, 

 laboratory verification, or other evidence exists to 

 assure daily increment formation as a universal 

 phenomenon under suboptimal conditions, there will 

 be some doubt about the accuracy of aging field- 

 captured larvaa 



Transition from the Laboratory 

 to the Field 



A question that remains to be answered when 

 applying laboratory-derived increment deposition 



Table 5.— Continued. 



Species 



Source 



Based on prior 



validations 



(validations in 



Table 1) 



Validation 

 source 



Sample 

 size 



yes 



no 



Barkman (1978) 



105 

 (lab) 



Application 



Compare growth in lab and field. 

 Calculate hatching dates. Compare 

 growth between early and late 

 hatched larvae. 



Correspondence between increment 

 estimated age and spawning 

 season. Growth through lifetime of 

 juvenile. 



Relationship between fish weight 

 and otolith size. Use daily in- 

 crements as time marker. 

 Determine growth of aged field lar- 

 vae and fit Gompertz and von Ber- 

 talanffy functions. Compare length- 

 frequency and otolith techniques. 

 Growth during metamorphosis. Re- 

 late to age and transformation in 

 morphology. 



Comparison of length-frequency and 

 increment-frequency histograms for 

 field larvae. Daily growth rate calcu- 

 lated. Compare growth rates over 

 time. 



Built growth curves based on age. 

 Discussion of relationship to feeding. 

 Preliminary study of growth rate dif- 

 ference between areas. 

 Determine daily increment deposi- 

 tion. Calculate pattern of settlement 

 based on age estimate. 

 Determine length of larval life prior 

 to recruitment. Examine otoliths 

 for marker between postlarvae to 

 juvenile. 



99 



