Causes of Decline and Potential for Recovery of Atlantic Cod Populations

Abstract

The large declines in abundance and failure to recover in many Atlantic cod populations has been the subject of numerous papers and the continued low abundance of several Canadian cod populations has become an icon for failed fisheries management. It has been argued that many stocks failed to recover after declines, despite reduced fishing pres- sure. A range of complex mechanisms have been invoked to explain failure to recover, including decreased age-at- maturity, vulnerability to by-catch, fishing induced evolution, depensatory predation and habitat change caused by fishing gear. We show that, for all North East Atlantic cod populations, continued high fishing pressure is sufficient to explain the failure of stocks to recover and the stocks would increase at 40-60% per year in the absence of fishing. This is also true for four out of nine North American cod stocks. The other five North American stocks, located in the Gulf of St Lawrence and around the Grand Banks and Labrador, show no net productivity (would not increase in the absence of fishing) since the late 1980s or early 1990s. Four of the Canadian stocks show a rapid shift in the mid 1980s, from being highly produc- tive to low or negative net productivity, despite having been at relative high abundance. We conclude that for most Atlan- tic cod stocks (13 out of 18) no mechanism other than excessive fishing is required to explain their failure to recover. Fishing pressure cannot lead to the sudden decrease in productivity in the four Canadian stocks which flipped from high to low productivity; environmental change seems the likely cause, although continued fishing drove these stocks to very low abundance and likely impaired their ability to recover.