3.4 Link to Mortality Estimates
The stock-recruit (S/R) relationship is described as biomass of spawning stock in year t in relation to biomass of year class age 1 in the following year. In conjunction with mortality estimation, it drives forward projections of the status of the shell resource. Oysters are protandric hermaphrodites, maturing first as males and subsequently as females. Thus any spawning stock biomass estimate that assumes sexual parity may be influenced by age structure of the population and age of transition from male to female. There is remarkable consistency in the sex ratio with size for oysters in both the Delaware Bay and the Virginia portion of the Chesapeake Bay as reported in recent contributions by Powell et al. (2013) and Harding et al. (2013) respectively. These reports suggest that the male to female transition starts at ~60 mm and 1.5 y and that larger oysters are at least 70-80% female. There are no discussions of egg versus sperm limitation in reef forming oysters so no modification is proffered of the biomass-based estimates of broodstock at this time in this report. This does not exclude such consideration in future discussions.
Link to Mortality Estimates