Stewart, DR, JM Long, and DE Shoup. 2015. Spatial structuring within a reservoir fish population: implications for management. Marine and Freshwater Research 66:202-212.
Spatial structuring in reservoir fish populations can exist because of environmental gradients, species-specific behavior, or even localized fishing effort. The present study investigated whether white crappie exhibited evidence of improved population structure where the northern more productive half of a lake is closed to fishing to provide waterfowl hunting opportunities. Population response to angling was modeled for each sub-stock of white crappie (north [protected] and south [unprotected] areas), the entire lake (single-stock model), and by combining simulations of the two independent sub-stock models (additive model). White crappie in the protected area were more abundant, consisted of larger, older individuals, and exhibited a lower total annual mortality rate than in the unprotected area. Population modeling found fishing mortality rates between 0.1 and 0.3 resulted in sustainable populations, (spawning potential ratios [SPR] > 0.30). The population in the unprotected area appeared to be more resilient (SPR > 0.30) at the higher fishing intensities (0.35 – 0.55). Considered additively, the whole-lake fishery appeared more resilient than when modeled as a single-panmictic stock. These results provide evidence of spatial structuring in reservoir fish populations, and we recommend model assessments used to guide management decisions should consider those spatial differences in other populations where they exist.