Genetic variation and local differences in Pacific cod Gadus macrocephalus around Japan.

Area of Science:

• Marine Biology
• Population Genetics
• Fisheries Science

Background:

• Understanding population structure is crucial for effective fisheries management of Pacific cod (Gadus macrocephalus).
• Previous studies on Pacific cod genetics in Japanese waters are limited, necessitating further investigation into population differentiation.

Purpose of the Study:

• To investigate the population genetic structure of Pacific cod (Gadus macrocephalus) in waters around Japan.
• To estimate the effective population size (N_e) for different genetic groups.
• To identify potential barriers to gene flow.

Main Methods:

• Analysis of 15 microsatellite loci and mitochondrial DNA (ND2 region) from 274 Pacific cod individuals.
• Sampling conducted across 16 locations surrounding Japan.
• Employed pairwise F_ST, analysis of molecular variance (AMOVA), and Bayesian clustering analyses.

Main Results:

• Identified two genetically distinct populations of Pacific cod in Japanese waters.
• The eastern population exhibited a significantly higher effective population size (N_e) compared to the western population.
• Genetic differentiation suggests limited gene flow between the identified groups.

Conclusions:

• The Pacific cod population in Japanese waters is structured into at least two distinct genetic groups.
• Oceanographic features, such as the Tsushima Warm Current and associated temperature differences, likely act as barriers to gene flow, restricting migration between western and eastern populations.