Determining the stock structure of Atlantic cod

Atlantic cod make up one of the most culturally and economically important fisheries in the North Atlantic. Currently, populations in the Gulf of Maine are at a fraction of their carrying capacity and fishing quotas have been drastically cut to promote the recovery of populations. The decline has in large part been due to an inadequate understanding of the population structure and dynamics of cod in the region, and a slow translation of science into management practices.

As part of an interdisciplinary research collaboration between scientists, fishermen and fisheries managers, I am assessing the biological structure of Atlantic cod in the Gulf of Maine. To date, the fishery has been managed as two stocks separated geographically, yet initial research suggested that there are actually multiple populations which overlap geographically but breed at different times of the year.

To investigate differentiation and gene flow amongst populations, I am using RADseq to generate genome-wide molecular data. I will determine the fine-scale population structure of the remaining populations and determine whether there are adaptive differences amongst them using the recently updated cod reference genome. I will also determine the genetic diversity of the remaining populations, as genetic diversity within and amongst populations is likely to promote resilience to environmental change and over-fishing in the future.

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Cod otoliths which we can extract high quality DNA from. Photo credit: NEFSC/NOAA.

Using cod otoliths (ear bones) from collections dating back to the 1960s, I am also going to investigate the genetic diversity of populations which have now been lost to overfishing, to determine whether any genetic diversity has been lost for good.

This work is part of a formal cod stock structure working group, which will feed results back to fisheries managers to aid in assessment and re-evaluation of management practices.

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