Changes in Abundance and Certain Population Parameters of American Plaice on St. Pierre Bank off Newfoundland during 1972-1994, with Implications for Fisheries Management

摘要

Changes in abundance and certain population parameters of American plaice Hip-poglossoides platessoides in Northwest Atlantic Fisheries Organization (NAFO) subdivision 3Ps, south of Newfoundland, were examined over the period 1972-1994. During these years, there has been a substantial reduction in population size and in more recent years, there has been a redistribution of the remaining population to deeper, warmer water than previously observed. Despite the substantial changes in stock size and distribution, there is no clear evidence that growth patterns have changed nor has there been any truncation of the age structure of the population, both of which commonly occur if overexploitation takes place. On the other hand, age and size at 50% sexual maturity for both males and females declined over the same period. This stock has been managed through quota regulation since 1974; however, the quota rarely restricted the fishery. During the 1980s, when the greatest declines in stock abundance occurred,the commercial exploitation rate was far too low to have been an important contributor to the observed decrease in population size. It is concluded that management measures during this period were ineffective in maintaining stock size at the target level because the stock decline was not the result of fishing. The reasons for such substantial reductions in the stock remain unknown. During the 1990s, however, as this and other groundfish stocks were declining rapidly, a substantial increase in fishing effort was directed towards this stock in an attempt to fully utilize existing quotas. Annual catches thus were maintained at a moderate level despite a rapidly declining population, producing exploitation rates much higher than those of the 1980s. By 1995, the stock was estimated to be so reduced that a total fishing moratorium was introduced for American plaice in NAFO subdivision 3Ps. The result of this measure is yet to be evaluated.