Effects of freshwater replenishment on the Fenneropenaeus indicus CPUE along the west coast of Madagascar based on structural equation modeling

To conserve fisheries resources and achieve sustainable fisheries development, having an understanding of the relationship between fisheries resources and environmental factors, as well as how population distributions respond to environmental changes, is fundamental. However, variations in fisheries resources are influenced by multiple complex interrelated environmental factors. Current research primarily focuses on the direct impacts of environmental factors on population distribution and resource abundance, often overlooking the interactions between these factors. This study investigated the mechanisms and pathways by which different environmental factors and their interrelationships affect Fenneropenaeus indicus stock on the west coast of Madagascar. A structural equation model (SEM) was used to analyze data from 2014 to 2019. This analysis was used to assess the relationships between F. indicus CPUE (Catch Per Unit Effort) and environmental variables such as precipitation, runoff, sea surface temperature (SST), sea surface height anomaly (SSHA), and chlorophyll a concentration (Chl-a). The SEM model provided a good fit and indicated that the runoff, SST, SSHA, and Chl-a all directly affected F. indicus CPUE. Specifically, the runoff, SST, and Chl-a all correlated positively with the CPUE, while the SSHA correlated negatively. Precipitation indirectly influenced the CPUE by affecting the SST and SSHA, while runoff influenced the CPUE through its impact on the SSHA. These findings reveal the potential mechanisms by which freshwater replenishment and other marine environmental factors directly or indirectly affect the variability of the F. indicus population resources along Madagascar's west coast.