Future Directions for Stock Assessment Models

Stock assessment models estimate the dynamics of a single species in response to a time series of catch and an indicator of the trend in stock abundance over time. More complete assessments also include size/age composition data which provides direct information on the level of total mortality being experienced by the stock.  Where there are sufficient data, the models estimate the time series of absolute stock abundance and fishing mortality and productivity parameters that determine sustainable harvest rates. These estimates are conditioned on simplifying assumptions about the constancy of parameters that govern the productivity and natural mortality of the stock. From an ecological perspective, a stock’s carrying capacity, productivity and natural mortality are not just functions of the stock’s characteristics.  These factors are functions of a stock’s interactions with its predators, prey, competitors, habitat and environment.  In a fished ecosystem, many stocks are fished and reduced in abundance, so these interactions will change over time. From this perspective, the need for coordination of single species models and ecosystem models emerges. Ecosystem models can provide more comprehensive evaluation of the effects of fishing and sustainable rates, single species models can provide better estimation and short-term forecasting of stock abundance.