Rapid changes in age structure, mortality, and escapement accompanied stock recovery of the estuarine Red Drum population of Texas

Abstract

Objective

We analyzed a fishery-independent catch time series in the context of predicted historical age structure of Red Drum Sciaenops ocellatus for the years 1980–2019. This time series roughly coincided with closure of the commercial fishery in Texas (in 1981) and federal waters (in 1987). Changes in size and age were used to estimate changes in mortality and offshore escapement.

Methods

Otoliths collected from Red Drum between 1997 and 2015 in Texas were used to create seasonal length-at-age growth functions, which were then used to estimate ages (based on total length) of all Red Drum encountered in fishery-independent gill-net samples collected by the Texas Parks and Wildlife Department during 1980–2019 (total n = 311,150). Temporal changes in observed body size and overall catch were used to predict annualized changes in mean age, mortality, and offshore escapement of the estuarine population.

Result

The initial 14-year period (1980–1993) was characterized by rapid increases in mean catch per hour and mean total length (mm) in fishery-independent samples, followed by relative stability for the remainder of the time series. There was a 55% increase in estimated mean age of Red Drum when comparing 1980 (mean age = 0.84 year) to 2019 (1.30 years). There were also rapid and significant declines in total mortality (Z; estimated via catch curves) and increases in offshore escapement (estimated indirectly from mortality) in the initial recovery period.

Conclusion

The current estuarine population of Red Drum in Texas is significantly larger and older than it was at the onset of fishery management measures, and offshore escapement is annually well above the current target level of 30% set by the federal fisheries management plan. These findings suggest that regulations put into effect starting in the 1980s have succeeded in recovering the estuarine Red Drum population in Texas.