Uncertainty in Stock Assessments Impacts Harvest Rates

Dr. John Wiedenmann, Dr. Olaf P. Jensen

Research Abstract

Overfishing continues for many stocks in the New England groundfish complex despite efforts to constrain harvest rates and rebuild populations. We evaluated the magnitude and sources of scientific uncertainty in catch targets for groundfish and found that since 2004 annual harvest rates have been 151% above the target while catches have been 29% below the target catch, on average, resulting from overly optimistic catch targets for the majority of stocks. Multiple sources of scientific uncertainty contributed to this overestimation, but the largest contributor was overestimated abundance. By evaluating sequential assessment estimates, we found previous assessments frequently overestimated terminal abundance. Additional uncertainty in catch targets resulted from recent recruitments often being below historical levels. The net effect of overly optimistic catch targets and declining recruitment is that rebuilding has been sluggish and potential yield (and revenue) has been forgone for many stocks. The causes of the overestimation of stock abundance and declines in recruitment remain unknown, but because these patterns were widespread, there may be common mechanisms in the region influencing assessment estimates and stock productivity.

The research was funded through the New England Fishery Management Council’s budget.

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