Kinship-based assessment of Norwegian coastal cod to determine sustainable harvest levels and protect genetic diversity in fisheries

Overfishing has been greatly reduced in the last 50 years by splitting fish populations into manageable ‘stocks’ and counting them in fisheries catch and large scientific surveys to determine sustainable fishing levels. This works well for big, valuable populations, such as Northeast Arctic cod (skrei). However, this approach is too inefficient for smaller populations with complex structure, such as coastal cod, and has led to overharvest and biodiversity loss. Our project further develops a fundamentally different monitoring method, close kin mark recapture (CKMR), which costs far less and can estimate population size with greater precision than is currently possible with traditional methods. CKMR applies modern genomics to identify related individuals (parents-offspring and siblings) in tissue samples, and then uses these kinship data to estimate key quantities for management, such as population size and survival. We will establish the method for southern Norwegian coastal cod (62-67N), and then combine the genetic kinship data with traditional fisheries and survey data in the same model framework. Our aim is to transform management of coastal cod in Norway from the current data-limited paradigm to one that sustains both harvest and genetic diversity in the long-term. The methods developed here address several big challenges to fisheries assessment and thus also have great potential to improve management of other commercial fish stocks.

Splitting fish populations into manageable "stocks" and counting them in large scientific surveys to determine sustainable fishing levels has greatly reduced overfishing in the last 50 years. Yet, complex population structure and inefficient, costly monitoring methods challenge this approach and have led to overharvest and biodiversity loss of vulnerable subpopulations. Our project further develops a powerful new monitoring method, close kin mark recapture (CKMR), which can estimate population size with far greater precision than currently possible. CKMR relies on modern genomics to identify related individuals (e.g. parent-offspring and sibling pairs) in tissue samples. These kinship data are then fit in a population model to estimate key values such as population size and mortality. CKMR data have great potential to improve management of coastal cod and other Norwegian fish stocks by simultaneously addressing several big challenges to assessment. Our work to integrate genetic kinship data into the same model framework as fisheries and survey data is at the leading-edge of developing "next-generation stock assessment models" and is anticipated to revolutionize the field by estimating previously intractable parameters (e.g. natural mortality), reducing our reliance on questionable assumptions, and greatly improving precision of abundance estimates used by managers and policy makers.