(2) measuring the actual total catch with at-sea observer coverage or verifiable logbook data.
Total allowable catch is a management measure that limits the total output from a fishery by setting the maximum weight or number of fish that can be harvested. TAC-based management requires that landings be monitored and that fishing operations stop when the TAC for the fishery is met. A TAC is based on stock assessments and other indicators of biological productivity, usually derived from both fishery-dependent (catch) and fishery independent (biological survey) data (see NRC, 1998a). Data collected from fishermen, processors, or dockside sampling can be combined with at-sea observations and independent fishery survey cruises to provide information about the total biomass, age distribution, and number of fish harvested. Typically, the TAC is determined on an annual basis, but then partitioned across seasons. To the extent that a TAC is well estimated and enforced, it can control total fishing mortality on a stock (e.g., Pacific halibut). However, experience shows that management by a TAC alone is insufficient to eliminate the race for fish and incentives for capital stuffing. In the long run, without other management controls, management under a TAC leads to dissipation of all fishery rents (Rettig, 1991; OECD, 1997).
The relationship between recruitment and stock size, which is a key part of TAC calculations, is usually difficult to measure reliably because recruitment is often highly variable and, for some species, seemingly independent of parental stock size. Hence, it is extremely difficult to guarantee that conservation objectives will be satisfied by a given numerical TAC or by an IFQ program based on such a TAC. However, stochastiscity and uncertainty about the relationship between recruitment and stock size does not preclude the development of a TAC; it may be possible to develop a risk-compensated TAC based on precautionary principles. The risk of overfishing is greater with no TAC than with a precautionary TAC. Recent National Research Council (NRC) studies have stressed the need to address stochasticity in the development of TAC recommendations (NRC, 1998a,b).
Trip limits and bag limits are measures that pace landings by limiting the amount of harvest of a species in a given trip. Trip limits are applied in commercial fisheries when there is interest in spacing out the landings over time or a desire to specify maximum landings sizes, and they are usually accompanied by a limit on the frequency of landings. For example, many Pacific groundfish species are restricted in terms of pounds landed per week or month (PFMC, 1993). The Pacific groundfish trip limit system was adopted for the purpose of