In general, the relationship between frequency and abundance is not linear. Group I contains species that are the most frequent and most abundant in the survey travels. Representing roughly 9% of the ichthyofauna, this group contains most commercial species such as Atlantic cod, Atlantic herring, deepwater redfish and rainbow smelt. The species in group II (33% of the ichthyofauna) are generally as frequent as those in group I, but significantly less abundant. Group III consists of many relatively rare species (23% of the ichthyofauna). Group IV is made up of many very rare species (31% of the ichthyofauna); usually only one or two individuals are caught at a time. Lastly, group V also consists of a few very rare species (4% of the ichthyofauna); but usually a dozen individuals are caught at one time.

The following map shows the distribution of the rare species (groups III, IV and V). A rarity index was calculated to measure the importance of rare species, putting more weight on species in groups IV and V, less weight on species in group III and not any weight on species in groups I and II. The index for each unit is the total of the weight of the species present divided by the maximum value (calculated for all species). Rare species were found mainly in the estuary and northern Gulf. Areas like the maritime estuary, the western Gulf, the shelf break south of Anticosti Island and the Lower North Shore received high scores for richness.