Long-Term Change of a Fish-Based Index of Biotic Integrity for a Semi-Enclosed Bay in the Beibu Gulf

The Beibu Gulf in the northwestern South China Sea is one of the world's most productive fishing grounds, yet its biotic resources appear to be in rapid decline because of overexploitation. Assessments of the health status of the fisheries' resources in the gulf provide a foundation for their conservation and management. As fish accounted for 84% to 97% of the total catch in the Beibu Gulf in the period 1962-2017, a Fish-based Index of Biotic Integrity (F-IBI) was developed for the Beibu Gulf, and data from otter trawl surveys during the period 1962-2017 were used to measure variations in the fish community. The assessment revealed a generally downward trend in total fish catch density (kg/km(2)), catch density of 12 traditional commercial demersal fish species, and percentage of nektonic-feeding species, but an upward trend for the percentage of fishes with a planktivorous or detritus diet, percentage of pelagic species, and percentage of the dominant species. The dominant species varied greatly over the 50 year period and showed a tendency towards small-sized species. The synthetic F-IBI variable showed a downward trend and has indicated a 'fair' state since 1998. The decline in the F-IBI over the last three decades suggests that anthropogenic disturbances, especially overfishing, have had a serious impact on the fish community of the Beibu Gulf. The F-IBI is currently at risk of becoming 'poor.' Consequently, we suggest that rigid and enforceable fishery management measures should be taken by both China and Vietnam to prevent further deterioration of the fisheries' resources in the gulf.

Automated summary

The Beibu Gulf, one of the most productive fishing grounds in the world, is experiencing rapid decline in its biotic resources due to overexploitation. The study assesses the health status of its fisheries' resources and reveals that anthropogenic disturbances, particularly overfishing, have had a serious impact on the fish community. It suggests that strict and enforceable fishery management measures should be implemented by China and Vietnam to prevent further deterioration of the resources in the gulf.