Effects of Variation in Settlement and First-Year Processes on Productivity of Red Drum at Northern Distributional Limits

The red drum (Sciaenops ocellatus) supports valuable fisheries throughout the southeastern US.  At the northern edge of the distribution, variation in recruitment of newly settled individuals is high relative to more southern latitudes.  A range of hatch times, as well as variable estuarine growth rates, typically produces a broad range of red drum body sizes at the onset of the first winter, combining with winter severity to cause considerable overwinter loss and size-selective mortality among juveniles.  Empirical evidence supported higher first year survival for individuals that had been hatched earlier and achieved faster fall growth.  Laboratory results found age-0 red drum to be intolerant of even brief exposure to temperatures ≤3°C, with variation in the frequency of cold front events responsible for the largest deviation in survival.  Size-dependent mortality was only evident for fish exposed to moderate winter conditions, with larger fish surviving longer.  A matrix projection model was then used to explore the influence of variable recruitment and variable size-dependent survival during the first winter on red drum population growth rate near the northern edge of the range.  Model analysis revealed that increased variation in age-0 and age-1 abundance had lasting impacts on fishery recruitment and overall population growth rates.