Fishing and Natural Mortality of Bluegills and Redear Sunfish at Lake Panasoffkee, Florida: Implications for Size Limits

Abstract

Growth, annual exploitation (u), and natural mortality (v) of bluegills Lepomis macrochirus and redear sunfish L. microlophus were investigated on Lake Panasoffkee, Florida, during 1998 and 1999 to assess the potential benefits of several minimum size limits. The average u of 15.0-cm total length (TL) or larger fish was 0.14 for bluegills and redear sunfish during the 2-year period. For both species, exploitation increased up to threefold as fish size increased (e.g., u = 0.37 for bluegills ≥23.0 cm TL in 1999). Total annual mortality (A) was 0.64 for bluegills and 0.68 for redear sunfish. Natural mortality estimates were 0.50 (78% of A) for bluegills and 0.55 (81% of A) for redear sunfish. Simulations predicted that minimum size limits would decrease average total yield and harvest for both bluegills and redear sunfish, but that a 20.3-cm minimum length limit could slightly increase the number of fish harvested over 20.0 cm TL. A 22.9-cm minimum length limit was predicted to greatly reduce yield without creating a measurable increase in the harvest of fish over the size limit. Lake Panasoffkee sunfishes incurred record levels of estimated effort and harvest in 1998–1999, but size-selective exploitation acted essentially as a minimum size limit, resulting in no predicted benefit for a 20.3-cm limit. Separation of fishing mortality and natural mortality allowed us to conclude that natural mortality had a greater influence on Lake Panasoffkee sunfish population abundance and fishing quality than did fishing mortality, so a minimum size limit was not recommended. Estimates of exploitation, natural mortality, and growth rates are more valuable than measures of size structure and angler catch when considering or evaluating harvest restrictions.