Fishery-Management and Stock-Rebuilding Prospects Under Conditions of Low-frequency Environmental Variability and Species Interactions

Interdecadal climate variability complicates fishery science and management. On the U.S. west coast, periods of favorable and adverse conditions may last 30 yrs each. A constant-harvest-rate policy may work for long-lived fishes (those with life spans comparable to or exceeding the duration of adverse conditions). Exploitation of short-lived fishes (species with life spans shorter than the duration of adverse conditions) benefits from policies that link harvest rate to environmental conditions, but a delayed response can be desirable. Therefore, rapid identification of regime shifts is not necessary but could provide advance notice of long-term changes in expected harvests. Planning horizons, especially for stock rebuilding, may have to be much longer than has been typical, even a century or more. During adverse periods little rebuilding may occur even after total cessation of fishing. Adverse species interactions like intraguild competition or 'cultivation effects' may prolong rebuilding or reduce sustainable yields. Management reference points like F_msy and B_msy can be strongly influenced by abundance of competitors. Importantly, B_msy of large predators may be well above half the unfished biomass if their removal releases smaller competitors. Although adverse interactions may be reversible, rebuilding of apex predators may require decades to centuries.