Density Impacts on Biological Reference Points and Management

Biological reference points (BRPs) are used to determine stock status and set management regulations.  BRPs rely on equilibrium life history data, though conditions are not static and density dependence can play a role.  Our objective was to determine the relationship between recruitment strength (i.e., density) and mean length and weight at age for Atlantic Menhaden in order to assess the impacts on BRP calculations and management.  Recruitment was tested for autocorrelation and related to time varying mean lengths and weights at age.  Spawning potential ratio (SPR) and yield per recruit (YPR) benchmarks were calculated across a range of fishing mortality rates, F, and recruitment.  Recruitment was autocorrelated and negatively related to mean lengths and weights at age.  Both SPR and YPR weren’t static under non-equilibrium assumptions about recruitment.  To maintain SPR with recruitment increased above equilibrium, F would decrease; while maintaining YPR would require increased F to maintain yield.  Tracking recruitment gives managers the ability to track the population and its ability to withstand F in the short term and to make timely management decisions.  Time varying information should be incorporated into BRP calculations and benchmarks should change over time, as opposed to being equilibrium based.