Regional Variation in Growth and Mortality of Spotted Seatrout in the Western Gulf of Mexico

The Spotted Seatrout Cynoscion nebulosus, a year-round estuarine resident throughout the Gulf of Mexico, is a common mid-trophic predator across its range and is one of the most popular game fish in Texas. In 1998, the Texas Parks and Wildlife Department initiated long-term collections of otoliths from Spotted Seatrout encountered in fishery-independent samples. Here, we use data from those collections (1998-2018) to generate a coastwide growth function and assess regional and temporal variation in growth and mortality. Key findings from this work include (1) sexual dimorphism in Texas that is consistent with previous studies across the species' range, with females exhibiting faster growth rates (growth rate parameter k) and having a greater asymptotic length than males based on coastwide sex-specific growth functions; (2) relatively fast growth in northern estuaries, as evidenced by estuary-specific patterns of deviation from a coastwide growth function as well as variability among k-values from regionalized growth functions; and (3) higher estimates of natural mortality and total mortality in northern estuaries based on regional variation in k and catch-curve analysis. The third finding was supported by an increase in estuary-specific mean age of Spotted Seatrout from north to south, suggesting that older fish are more common in southern estuaries. Broadly, significant regional variation in age, growth, and mortality implies a complex underlying demographic structure. Clinal variation in important life history phenotypes of Spotted Seatrout in the western Gulf is consistent with previous studies that have described clinal genetic variation for the species, implying the potential for overlapping but independent subpopulations in the western Gulf of Mexico.

Automated summary

The Spotted Seatrout is a common predator in the Gulf of Mexico and a popular game fish in Texas. The study found regional and temporal variation in the species' growth and mortality, including sexual dimorphism with females growing faster and bigger than males, faster growth in northern estuaries, and higher mortality in northern estuaries. These findings suggest a complex demographic structure and the presence of independent subpopulations in the western Gulf of Mexico.