How Effective Are Marine Protected Areas for Managing Stocks with Maternal Effects in Larval Survival?

Recent studies have indicated that the viability of larvae for some species, including Pacific rockfish (genus Sebastes) and Atlantic cod (Gadus morhua), may depend upon spawner age. Because even moderate amounts of fishing mortality can dramatically affect spawner age structure, closed areas have been proposed as a management tool that would allow old spawners to accumulate. In this study, we examine how the effect of marine reserves upon yield, recruitment, and mean age for stocks with maternal effects varies as a function of the spatial density-dependent recruitment process and adult movement.  Under the assumption of only larval movement between areas, marine reserves help ameliorate the loss of equilibrium yield associated with maternal effects at high fishing rates, and generally increases the mean age of the population. However, for some density-dependent spatial recruitment processes, marine reserves lowered the maximum sustained yield (MSY). For stocks with substantial adult movement, the effect of marine reserves on mean age and yield is slight at fishing mortalities near those that produce MSY (F_msy).  An effective way to address concerns regarding reduced production due to maternal effects may be to fish at F_msy, where the loss of equilibrium yield associated with maternal effects is reduced.