Declining population sizes and loss of genetic diversity in commercial fishes: a simple method for a first diagnostic

Exploited fish species may have or are experiencing declines in population sizes coupled with a decrease in genetic diversity. This can lead to the loss of adaptive potential to face current and future environmental changes. However, little is known about this subject while research on it is urgently needed. Thus, this study aims to answer a simple, even naive question, given the complexity of the subject: Could we use a simple method to obtain information on the loss of genetic diversity in exploited fish species? We investigated the use of the levels of genetic diversity in the widely used genetic marker Cytochrome C Oxidase subunit I (COI) mitochondrial gene. Estimates of genetic diversity in COI were obtained for populations of seven fish species with different commercial importance from the East China Sea. These estimates were contrasted against a large dataset of fish species distributed worldwide (N=1426), a dataset of East-Asian fish species (N=118), two farmed species with expected low genetic diversity, and four long-term managed species from the Mediterranean Sea. We found that estimates of genetic diversity in COI match the expectations from theoretical predictions, known population declines, and fishing pressures. Thus, the answer to our question is affirmative and we conclude that estimates of genetic diversity in COI provide an effective first diagnostic of the conservation status of exploited fish species. This simple and cost-effective tool can help prioritize research, management, and conservation on species with suspected loss of genetic diversity potentially eroding their adaptive potential to global change.