GROWTH OF LARVAL ATLANTIC COD, GADUS MORHUA, 



AND HADDOCK, MELANOGRAMMUS AEGLEFINUS, ON 



GEORGES BANK, SPRING 1981 1 



George R. Bolz and R. Gregory Lough 2 



ABSTRACT 



A study of the otoliths of larval Atlantic cod and haddock collected on Georges Bank in spring of 198 1 pro- 

 vided information on growth and development during the first 2 months of life for these species. Exponential 

 growth curves of length at age were fitted based on daily increment deposition which agreed with prior 

 laboratory results and the few reported field studies. The faster growth rate (3.4% per day) of haddock larvae 

 collected in May compared with that of cod larvae (2.6% per day) collected in April appeared to be due to the 

 higher water temperature rather than to species- specific differences in rate of growth. Based on the micro- 

 structure of the otoliths, it was estimated that both species remained in the yolk-sac phase for 2-8 days 

 followed by an 8-11 day period of slow growth during the transition to successful active feeding. 



One of the major hypotheses of fisheries biology is 

 that the extent of mortality during the larval phase 

 greatly influences the size of a year class (Moser 

 198 1). Since mortality is best described as a function 

 of age and abundance, it is very important to be able 

 to determine accurately the age of the larvae. Until 

 Pannella (1971, 1974) demonstrated that the 

 otoliths found in the semicircular canals of larval fish 

 are composed of daily rings or increments, the only 

 methods available for aging field- caught larvae were 

 indirect ones based on inference, e.g., cohort analysis 

 or growth curves generated by laboratory rearing 

 experiments. Although the mechanisms controlling 

 the rhythmic secretion of calcium and carbonate ions 

 into the protein matrix of the otolith are as yet incom- 

 pletely known (Watabe et al. 1982), many recent 

 studies have demonstrated that the periodic 

 increments formed are of a daily nature for the most 

 part (Taubert and Coble 1977; Wilson and Larkin 

 1980; Schmidt and Fabrizio 1980; Tanaka et al. 

 1981; Mugiya et al 1981; Townsend and Graham 

 1981; Rosenberg and Laroche 1982; Laroche et al. 

 1982; Campana and Neilson 1982; Lough et aL 

 1982). 



In addition to containing an age record, otoliths can 

 provide other information on the life history of larval 

 fish (Radtke 1980; Brothers 1981; Brothers and 

 McFarland 1981). Physiological changes or growth 

 disturbances often are indicated on the otolith by 



'MARMAP Contribution MED/NEFC 82-64, Northeast Fisheries 

 Center Woods Hole Laboratory, National Marine Fisheries Service, 

 NOAA, Woods Hole, MA 02543. 



2 Northeast Fisheries Center Woods Hole Laboratory, National 

 Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 



thick, dark bands or check rings (Radtke and 

 Waiwood 1980; Geffen 1982). An examination of the 

 area and the number of increments enclosed by these 

 checks can provide insight on the duration and 

 related environmental conditions of the early stages 

 of larval fish. The relative width of individual 

 increments, or small groupings of increments, pro- 

 vides a possible index to the daily or weekly feeding 

 success of the larvae (Methot 1981). By knowing the 

 precise age, hatching dates can be established and 

 analyzed to assess yearly or population differences in 

 the survival of larvae in relation to spawning time 

 and location. 



The work reported here was undertaken to derive 

 accurate growth curves for larvae of Georges Bank 

 Atlantic cod, Gadus morhua L., and haddock 

 Melanogrammus aeglefinus L., from the field based 

 on an analysis of their increment formation. Also, 

 from the standpoint of understanding their larval 

 ecology, it was important to determine what addi- 

 tional information might be revealed in the micro- 

 structure of cod and haddock otoliths on species 

 differences and on stage of development in relation 

 to environmental conditions. This study was conduct- 

 ed as part of the MARMAP program of the Northeast 

 Fisheries Center, which measures long-term changes 

 in the variability of the fish- stock abundance off the 

 northeast coast of the United States (Sherman 

 1980). 



METHODS 



Cod and haddock larvae were collected on two lar- 

 val fish dynamics, cruises (Lough and Laurence 1 982) 



Manuscript accepted March 1983. 



FISHERY BULLETIN: VOL. 81, NO. 4, 1983. 



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