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Setting Catch Ceilings

For catch ceiling management, the simulation period is divided into two time segments. The base period includes the years 1979 to 1984 (i.e., years prior to enactment of the PST). The simulation period includes year 1985 and beyond.

Catch ceilings are established in two steps. During data entry, base period (1979-1984) catches for each fishery (from the *.cei file) are summed and averaged. Catches for the remaining years are divided by the average to get scalar values relating observed catches to average base period catches. During model execution, preterminal and terminal catches for each fishery are summed and averaged. At the end of the base period, the scalars computed during data entry are multiplied by the average preterminal and terminal model catches to get the catch ceilings for the remainder of the simulation period. Thus, the model catches during the ceiling management period are not equal to the catches given in the *.cei file, but have the same relative value compared to the base period catches. Table 4.6 illustrates how the catch ceilings are computed.

Table 4.6 Computation of catch ceilings. For example, in 1985 the ceiling scalar = 212,827/272,500; the model preterm ceiling = 216,667*.781; the model terminal ceiling = 64,833*.781.
Year Observed Catch (*.CEI file)
Model PreTerm Catch Model Terminal Catch Model Total Catch
1979 338,000 250,000 75,000 325,000
1980 300,000 235,000 70,000 305,000
1981 248,000 198,000 65,000 263,000
1982 242,000 202,000 64,000 266,000
1983 271,000 235,000 55,000 290,000
1984 236,000 180,000 60,000 240,000
Average Base Period 272,500 216,667 64,833 281,500
Year Observed Catch Ceiling Scalars Model PreTerm Ceiling Model Terminal Ceiling Model Total Ceiling
1985 212,827 .781 169,217 50,635 219,852
1986 229,980 .844 182,867 54,719 237,586
1987 230,901 .847 183,517 54,915 238,432
1988 216,427 .794 172,034 51,477 223,511
1989 220,966 .811 175,717 52,580 228,297

The algorithm used to keep model catches for each fishery below ceilings (or equal to quotas, if forcing is specified) depends on whether or not any ceilinged fisheries have both preterminal and terminal harvests. If a fishery has only preterminal harvests, the model simulates the effects of ceiling management policies by calculating catches in two passes. The first pass calculates catch as if no ceiling were present. The ratio of the ceiling divided by the total catch of all stocks in the fishery is then calculated. This ratio is the basis for adjustment during the second pass. If the ratio is less than one (i.e., the ceiling is less than the computed catch), the catch is reduced by multiplying the age-specific catch of each stock by the ratio. If the ratio is greater than one and the user specifies quota management, the catch is increased to meet the quota; if the ratio is greater than one and ceiling management is specified, no adjustment to catch is made.

Fisheries that are "terminal" for one or more stocks must use an iterative procedure to compute the appropriate adjustment ratios. This is because preterminal catches are computed prior to the calculation of mature run sizes and terminal catches. For each fishery, the procedure is as follows:

In instances where a fishery is (1) terminal for a particular stock and (2) the terminal run size after fishing exceeds the specified spawning escapement goal, any catch ceilings specified for that fishery will not include the harvest of fish in excess of the spawning escapement goal.

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CRiSP Harvest Manual, Chapter 4. Theory
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