The Effect Of Reduced Data On The Ability To Monitor Rebuilding Of Overfished Fish Stocks

Several rockfish stocks off the U.S. west coast are below target biomass and are managed under rebuilding plans that severely limit the allowable harvest. Limited harvest, however, reduces the opportunity to collect fishery-dependent data, which are the primary source of information on changes in abundance for species poorly sampled by fishery-independent methods. A simulation study was conducted by using an operating model to evaluate the effect of reduced data on estimation of spawning biomass and biological parameters during rebuilding of a stock. Decreased availability of data during rebuilding resulted in increased among-simulation variation in estimates of spawning biomass. Additionally, decreased data resulted in reduced average catches and increased interannual variation in catches during rebuilding compared with averages of and variation in catches when data collection was maintained at higher levels. The presence of time-varying parameters in the operating model that were not accounted for within the estimation method resulted in increased among-simulation variability in spawning biomass than with the time-invariant case, and the largest increase in variability occurred during stock rebuilding when data were reduced or eliminated. Retaining data collections at historical levels allowed improved parameter estimation during rebuilding, resulting in reduced variability in estimated stock size, increased average catches during rebuilding, and in reduced frequency of stocks being prematurely estimated as rebuilt.