The potential of marine reserves for the management of northern cod in Newfoundland

Marine reserves (areas closed to exploitation of marine life) should allow better resilience to management errors such as overestimation of stocks, in adequate control of fishing effort, and inaccurate catch statistics. We emp loyed a detailed population model to explore the use of marine reserves to protect cod populations from overexploitation. The northern cod of the east coast of Newfoundland in the 1980s, at low biomass but prior to the major collapse, was used, as a case study. We asked two questions: Would marine r eserves have prevented the 1992 collapse, and how would reserves compare wi th other management measures? The model is age- and spatially-structured an d includes a recruitment function (Beverton and Holt type). Migrations were simulated by inclusion of target cells (attraction sites), which were spec ific for each age and month of the year. Random movements around target cel ls determined how fish spread to form a spatial distribution that moved alo ng the seasonal trajectory defined by the target cells. Fishing was calibra ted from historical data on temporal and spatial distribution of effort for three types of gears (trawl, gill net, trap). Marine reserves were modeled alone or in conjunction with temporal closures. For the 1980s low cod biom ass, if used alone, only large reserves (80% of the fishing grounds) would have prevented the collapse and allowed the cod stock to rebuild. However; these very large reserves would have reduced the catch per unit effort on t he remaining fishing grounds and possibly triggered an increase in investme nt in gear, defeating the purpose of the reserve. At low cod biomass, reser ves must be accompanied by a reduction in fishing capacity. When used with reserves of moderate size (20%), temporal closures to trawls and gill nets succeeded in preventing a collapse and rebuilding the stock.