Ecological and single-species reference points

2024-07-01

Evaluation of equilibrium MSY reference points from EwE user manual

• Single-species FMSY (stationary FMSY)
  • Run the Ecosim model to equilibrium for a range of F values while holding biomasses of all other groups constant (except other life history stanzas for the same species in split and multi-stanza cases)
  • Examine predicted compensatory responses by the group caused by the foraging arena functional response and related foraging time adjustment parameters
• Ecological FMSY (compensatory FMSY)
  • Allows all groups’ biomass to change in response to the biomass changes of the focal FMSY groups
  • The assessment usually produces a more optimistic estimate of MSY for each group
  • Increases in food species abundances and decreases in predator abundances when any one group is harvested harder

Output comparison

Run model to get compensation FMSY vs stationary FMSY

• Mean relative differences between compensation and stationary FMSYs across 7 age classes from scenarios S1 and S2 = 0.01446

Run model by functional group vs by fleet

• FMSYs by functional group are identical to FMSYs by fleet

Run model to equilibrium for a range of F values vs run to depletion

• FMSYs from the two searching methods are identical

Single FMSY vs multiple FMSYs

• EwE default summary output files (e.g., FMSY_FullCompensation.csv or FMSY_StationarySystem.csv) show the estimate of FMSY for each functional group (Table 1-4).
• EwE also produces the catch of each functional group over a range of F values in F.menhaden_Catch_FullCompensation.csv or F.menhaden_Catch_StationarySystem.csv. To extract reference points, we can get a vector of fishing effort multipliers that correspond to the maximum catch of the case stock, and them multiply the fishing effort multipliers with seven base fishing mortality rates from 1985 to obtain seven FMSY values by age.

Table 1. Base scenario S1 compensation FMSY output from EwE

Group TL Fbase Cbase Vbase FmsyFound Fmsy Cmsy Vmsy Case stock 0 2.562 0.0187 0.0054 0.0010 0 0.1868 0.0500 0.0095 Case stock 1 2.722 0.0698 0.0675 0.0129 0 0.6967 0.5610 0.1071 Case stock 2 2.722 0.2230 0.1681 0.0321 1 1.3220 0.5888 0.1124 Case stock 3 2.882 0.1462 0.0461 0.0088 0 1.4598 0.2580 0.0492 Case stock 4 2.882 0.3177 0.0347 0.0066 0 3.1773 0.1424 0.0272 Case stock 5 2.882 0.2001 0.0080 0.0015 0 1.9979 0.0447 0.0085 Case stock 6+ 2.882 0.1464 0.0045 0.0009 0 1.4643 0.0190 0.0036

Table 2. Base scenario S1 stationary FMSY output from EwE

Group TL Fbase Cbase Vbase FmsyFound Fmsy Cmsy Vmsy Case stock 0 2.562 0.0187 0.0054 0.0010 0 0.1868 0.0495 0.0094 Case stock 1 2.722 0.0698 0.0675 0.0129 0 0.6967 0.5524 0.1054 Case stock 2 2.722 0.2230 0.1681 0.0321 1 1.3029 0.5750 0.1097 Case stock 3 2.882 0.1462 0.0461 0.0088 0 1.4598 0.2531 0.0483 Case stock 4 2.882 0.3177 0.0347 0.0066 0 3.1773 0.1402 0.0268 Case stock 5 2.882 0.2001 0.0080 0.0015 0 1.9979 0.0442 0.0084 Case stock 6+ 2.882 0.1464 0.0045 0.0009 0 1.4643 0.0187 0.0036

Table 3. Environmental forcing scenario S2 compensation FMSY output from EwE

Group TL Fbase Cbase Vbase FmsyFound Fmsy Cmsy Vmsy Case stock 0 2.562 0.0187 0.0054 0.0010 0 0.1868 0.0500 0.0095 Case stock 1 2.722 0.0698 0.0675 0.0129 0 0.6967 0.5610 0.1071 Case stock 2 2.722 0.2230 0.1681 0.0321 1 1.3220 0.5888 0.1124 Case stock 3 2.882 0.1462 0.0461 0.0088 0 1.4598 0.2580 0.0492 Case stock 4 2.882 0.3177 0.0347 0.0066 0 3.1773 0.1424 0.0272 Case stock 5 2.882 0.2001 0.0080 0.0015 0 1.9979 0.0447 0.0085 Case stock 6+ 2.882 0.1464 0.0045 0.0009 0 1.4643 0.0190 0.0036

Table 4. Environmental forcing scenario S2 stationary FMSY output from EwE

Group TL Fbase Cbase Vbase FmsyFound Fmsy Cmsy Vmsy Case stock 0 2.562 0.0187 0.0054 0.0010 0 0.1868 0.0495 0.0094 Case stock 1 2.722 0.0698 0.0675 0.0129 0 0.6967 0.5524 0.1054 Case stock 2 2.722 0.2230 0.1681 0.0321 1 1.3029 0.5750 0.1098 Case stock 3 2.882 0.1462 0.0461 0.0088 0 1.4598 0.2531 0.0483 Case stock 4 2.882 0.3177 0.0347 0.0066 0 3.1773 0.1402 0.0268 Case stock 5 2.882 0.2001 0.0080 0.0015 0 1.9979 0.0442 0.0084 Case stock 6+ 2.882 0.1464 0.0045 0.0009 0 1.4643 0.0187 0.0036

Table 5. FMSY output from catch over F output

	compensation_fmsy_s1_CatchVec	stationary_fmsy_s1_CatchVec	compensation_fmsy_s2_CatchVec	stationary_fmsy_s2_CatchVec
Case stock 0	0.0569	0.0559	0.0569	0.0559
Case stock 1	0.2392	0.2352	0.2392	0.2352
Case stock 2	0.6849	0.6722	0.6849	0.6722
Case stock 3	0.3592	0.3550	0.3592	0.3550
Case stock 4	0.6309	0.6264	0.6309	0.6264
Case stock 5	0.3201	0.3173	0.3201	0.3173
Case stock 6+	0.2259	0.2280	0.2259	0.2280
Apical FMSY	0.6849	0.6722	0.6849	0.6722

Table 5. MSY output from catch over F output

	x
Compensation MSY s1	609478
Stationary MSY s1	595712
Compensation msy s2	609485
Stationary MSY s2	595716

Table 6. SBMSY output from catch over F output

	x
Compensation SBMSY s1	586271
Stationary SBMSY s1	569183
Compensation SBMSY s2	586284
Stationary SBMSY s2	582363

Table 7. Bratio output from catch over F output

	x
compensation_bratio_s1	0.1496
stationary_bratio_s1	0.1538
compensation_bratio_s2	0.8045
stationary_bratio_s2	0.8105
compensation_bratio_s3	1.3951
stationary_bratio_s3	1.4055

Table 8. SBratio output from catch over F output

	x
compensation_sbratio_s1	0.1134
stationary_sbratio_s1	0.1168
compensation_sbratio_s2	0.7228
stationary_sbratio_s2	0.7277
compensation_sbratio_s3	1.2514
stationary_sbratio_s3	1.2598