Size-based, seasonal, and multidirectional movements of an estuarine fish species in a habitat mosaic

To improve understanding of uni- versus multidirectional movement, seasonal dynamics, and the role of body size in tropical and sub-tropical nursery habitat, we conducted a 4 yr study on 1917 tagged juvenile common snook Centropomus undecimalis in 4 mangrove creeks. We detected 86% of individuals marked with autonomous passive integrated transponder (PIT) tag antennae. Marked fish were divided into 2 size classes (SC) for analysis: SC1 (approximately age-0) and SC2 (approximately age-1). A higher percentage of SC2 than SC1 snook migrated, SC2 made longer movements, and the 10 d probability of migration was 2.4-fold higher in SC2 than SC1. For both size classes, migration probabilities varied seasonally, with lowest rates in the coldest months. Furthermore, migration events during fall and winter tended to be temporary movements, while migration in spring and summer was more often permanent. Increased catch proportion of late-stage SC1 and early-stage SC2 individuals outside the creeks in spring/summer temporally aligns with increased permanent migration, suggesting a large-scale seasonal movement away from the study creeks. During this potential seasonal transition to alternative habitats, increased mortality at the end of the first year, as implied by proportionally fewer SC1 than SC2 individuals returning to the creeks in the following year, may act as an early population bottleneck. Alternatively, some individuals may lack fidelity and instead move to habitat not studied here. This work suggests that movement from nursery habitat can be bidirectional, size dependent, and seasonally dependent, and that the studied habitat functions as part of a habitat mosaic.