Date of Award

Winter 1999

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

Cynthia M. Jones

Committee Member

Kent Carpenter

Committee Member

Michael J. Doviak


Spot were sampled from the Chesapeake Bay commercial fishery from 1993–1995 to determine if spot are overfished. Transversely sectioned otoliths were determined to be the most appropriate structure for ageing spot. It was determined that spot have a high natural mortality rate (M = 0.9) and fast growth (K = 0.6). This combination of M and K makes spot relatively impervious to growth overfishing as determined by yield-per-recruit modeling. Because spot are nearly impervious to growth overfishing, management thresholds based on yield-per-recruit modeling may be inappropriate. In addition, the combination of high M and fast K makes it possible to completely fish out a cohort before it reaches its first potential spawning event and still not growth overfish the stock. Spawner Potential Ratios (SPR) per recruit were developed to assess the potential of recruitment overfishing spot. At current levels of fishing mortality (F), less than 20% of the potential reproductive effort of a cohort is available for spawning. Levels of F should be reduced to F = 1, to allow SPR = 20%. Levels of F should not, however, be reduced much below F = 1 to avoid under-utilizing the potential cohort biomass.