Family relationships and effective population size in a natural cohort of Atlantic cod (Gadus morhua) larvae

Sibship relationships within a naturally spawned cohort of Atlantic cod (Gadus morhua) larvae on the Western Bank of the Scotian Shelf were investigated by a likelihood ratio method that estimates relationships is among individuals using microsatellite (DNA fingerprint) information. We found no evidence of any temporal or spatial family structure among the larvae from seven different sample collections taken at sequential time intervals during a 21-d period of sampling the larval cohort. There was no evidence that larvae were more related within sample collections than across sample collections. Within each sample collection, there was no evidence of a family structure within or among the depths sampled. Similarly, there was no apparent change in the potential occurrence of sibship with time (successive sample collections), or in association with the passage of a storm during the sampling period. This cohort of cod larvae appears to have been a fairly homogeneous mixture of larvae that were not siblings and came from a large genetic pool. The minimum estimate of the inbreeding effective population size is 2800 individual spawners.