Environmental drivers of skipjack tuna, Katsuwonus pelamis (Actinopterygii, Scombriformes, Scombridae), catch variability in tropical coastal waters: Insights from physical and biogeochemical oceanography

Skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758), is an economically important pelagic species that supports small-scale fisheries in Palabuhanratu Bay, West Java, Indonesia. This study aimed to examine the relationship between physical oceanographic parameters {sea surface temperature (SST), salinity, sea surface height (SSH), and current speed} and biogeochemical parameters {chlorophyll- a (CHL), pH, and silicate} with skipjack catch per unit effort (CPUE) using a Generalized Additive Model (GAM) based on data collected during 2019–2023. The results indicate that variations in skipjack CPUE are associated with a combination of physical and biogeochemical oceanographic conditions. The best-performing model explained 70.7% of the deviance, with an adjusted R 2 of 0.623 and an AIC (Akaike Information Criterion) value of 743.26. Response curves indicated that higher CPUE tended to be associated with lower sea surface temperature (marginally significant; P = 0.068), lower salinity, higher chlorophyll- a concentrations, and variation in pH, while several other oceanographic variables exhibited non-linear relationships with CPUE. Model selection results further showed that the model integrating both physical and biogeochemical parameters outperformed models based on either group of variables alone. These findings highlight the importance of considering multiple environmental factors simultaneously when examining CPUE variability in small-scale skipjack fisheries. However, the results represent statistical associations between environmental variability and fishery-dependent catch rates and should not be interpreted as definitive evidence of skipjack tuna habitat suitability.