The effects of ENSO on spatial-temporal distribution and growth rate of three cryptic mullet species in Taiwan

Abstract

This study investigates the impact of ENSO on the species composition and growth during the early-life history of three cryptic mullet species (NWP1-3) in the estuaries around Taiwan. Juvenile mullets were identified using genetic method, and their growth rates were analyzed using generalized additive models (GAMs) based on biological and environmental variables. The results found that NWP2 was the most abundant species, dominating several months and estuaries. NWP1 had lower abundance than NWP2, but its proportion was relatively higher in La Nina and rarer in El Nino. NWP3 exhibited the lowest abundance, but expanded spatially during El Nino. Moreover, the growth of juvenile mullet was influenced by multiple factors annually, especially sea surface temperature (SST) and drifting growth rate (DGR). The environmental changes induced by ENSO and species-specific traits simultaneously impact both the distribution and growth patterns of cryptic mullet species. Both these factors directly influence species composition and indirectly affect species abundance by modifying growth and mortality rates. Consequently, lower SST during La Nina year benefited the abundance and growth of NWP1, while higher SST during El Nino year benefited NWP3 population. Although NWP2 maintained high abundance annually, rising SST may impact the growth of this species. These findings underscore the critical role of interannual environmental variability in regulating the distribution, abundance, and growth during the early life stages of cryptic mullet species in subtropical estuarine systems.