The increase of pelagic fish spawning triggered by typhoon in the Western Pacific

Abstract

The marine ecosystem is sensitive to natural changes, including an episodic event like the typhoon. Nutrient enrichment occurs along the track after the storm passes, which leads to a surge of primary production. While there is considerable research on the typhoon's effect on phytoplankton bloom and fish aggregation, the study on fish reproduction responding to the storm is minimal. To assess the typhoon’s influence on fish spawning, we sampled fish eggs just before and after typhoon Mangkhut (2018) and Ling-ling (2019) in the Philippine Sea, Western Pacific and compared the abundance and species richness of the eggs. Fish egg samples were collected using continuous underway fish egg sampler (CUFES), DNA extracted from each egg, and its species identified by the DNA barcoding method. Then, species richness was estimated using the Chao1 index. At the 2018 Mangkhut event, a total of 16 eggs and 115 eggs were collected before and after the storm, respectively. The species richness showed an increase from 7(1.24) to 11(2.24) after the storm. Through the 2019 Ling-ling event, 3 eggs and 38 eggs were collected before and after the typhoon, respectively. Nine additional species were identified after the typhoon, augmenting the species richness from 2 (0.94) to 13 (4.38). Interestingly, eggs of two tuna species and one mesopelagic fish were found in abundance in both 2018 and 2019 samples collected after the typhoons. Katsuwonus pelamis (Skipjack tuna) eggs had increased from 2 to 92 in the 2018 typhoon event and from 2 to 10 in 2019. Thunnus alunga (albacore tuna) eggs were found only after the storms in both years: three after Mangkhut and four after Ling-ling. Likewise, a mesopelagic fish Vinciguerria nimbaria (light marine fish) also experienced an upward in the number of collected eggs from 8 to 14 after Mangkhut, and from null to 6 after Ling-ling. The enhancement of fish egg abundance and species richness after the typhoons in both 2018 and 2019 indicates that typhoons could trigger pelagic fish spawning especially of tuna and mesopelagic fishes.