Age and growth of larval cod and haddock from the '95 and '96 broad-scale program

J. Green, S. Brownell, R. Jones and A. Chute

Typically, relative age structure of larval fish populations is inferred from the change in length over time. Daily growth ring deposition in larval fish otoliths provides a means of obtaining an independent source of age information. This along with length data can be used to develop age-length relationships and estimate growth in the field. Daily growth increment analysis has been completed for larval cod and haddock from the 1995 and ’96 broad-scale cruises. The number of concentric rings counted under a compound microscope at 1000x in the two most visible otoliths, the sagittae and lappilli of cod and haddock were used to age larvae in days from hatching. Age and standard length of preserved fish were used to generate age-length relationships for both species as shown below. The estimated growth rate for cod was approximately 3.1% per day for both years and similar for haddock in 1995. The numbers of haddock available for otolith increment analysis from 1996 was low and the size range was limited, essentially 2-6 mm, which provides a poor representation of growth. On the other hand, cod larvae, which were reasonably abundant in ’96, were aged over a wide range of sizes and included some fish that were substantially larger at age than found in ’95.

Cod growth curve

Haddock growth curve