This Scoping Document Is Divided Into Two Sections
Tab B, No. 6a
10/27/06
PRELIMINARY SCOPING DOCUMENT FOR GAG REGULATORY AMENDMENT TO STOP OVERFISHING AND SET SFA PARAMETERS
This scoping document is divided into two sections:
-Alternatives to set status determination criteria and management targets
-Alternatives to end overfishing of gag and to address discard and discard mortality
Purpose and Need
The 2006 (SEDAR 10) stock assessment of the gag fishery in the Gulf of Mexico indicated that the stock is undergoing overfishing, but overfished status relative to biomass benchmarks could not be determined. NOAA Fisheries issued a formal determination that the gag stock is undergoing overfishing on October 11, 2006[1]. Under the Magnuson-Stevens Act National Standard Guidelines, once a Council is notified that overfishing is occurring, it must take action within 1 year to end overfishing.
The average recent (2001-2004) annual fishing mortality rate (F) on this stock is estimated as 0.40 (Table Gag-1, F annual mortality rate all removals). The fishing mortality rate has increased every year from 1999 (when F = 0.30) to 2004 (when F = 0.49). This increase in F has occurred despite the implementation in June 2000 of an increased minimum size limit, a February 15 – March 15 commercial closed season, and the establishment of two marine reserves established in part to protect gag spawning aggregations. Relative to both the current proxy for FMSY (F30% SPR= 0.25, NMFS 2006) and the estimate for actual FMSY (FMSY = 0.23, NMFS 2006), overfishing of the Gulf of Mexico gag grouper is occurring, and the fishing mortality rate needs to be reduced.
Despite the finding of overfishing, inconsistencies in the assessment results were noted by the SEDAR 10 Assessment Review Panel. The Review Panel suggested that a maximum fishing mortality threshold (MFMT) of F = 0.25 is not consistent with the recent dynamics of gag grouper: fishing mortality has been fluctuating around F = 0.36 for more than twenty years, yet the stock biomass is near its historical maximum (Figure Gag-1). Therefore, the Review Panel advised that it would be prudent to reduce fishing mortality below F = 0.36 (NMFS 2006).
The gag spawning stock biomass (SSB) was high in the early 1960s, declined more or less regularly until the early 1990s, and then started to increase (Gag-Figure 1). For the most recent year’s data (2004), the SSB in the Gulf of Mexico appears to be almost 60% above average, and close to the maximum observed in the early 1960s. However, the stock recruitment relationship has a large variation in recruitment (1 to 6 million fish) over a moderate range of spawning stock sizes, resulting in a high degree of uncertainty about the stock recruitment relationship and estimates of biomass benchmarks (MSY, SSBMSY, and MSST) (Gag-Figure 2). Because of this uncertainty in biomass benchmarks, the Review Panel felt that current stock status with respect to overfished status could not be determined.
The purpose of this document is to provide potential alternatives to set or modify status determination parameters (MFMT and MSST) and optimum yield, to set a TAC (or series of TACs) that will end overfishing, and to establish management measures that will implement the TAC while minimizing to the extent practicable discards and discard mortality.
ALTERNATIVES TO SET STATUS DETERMINATION CRITERIA AND MANAGEMENT TARGETS
Fishing mortality rates in this section are for total removals, including both landed and dead discards.
Action 1. Maximum Fishing Mortality Threshold (MFMT)
Alternative 1. No action – MFMT remains at F30% SPR (currently estimated at F = 0.25)
Alternative 2. MFMT is set to FMSY (currently estimated at F = 0.23)
Alternative 3. MFMT is set to just under F1980-2004 (F = 0.35)
Alternative 4. MFMT is set to average recent F2001-2004 (F = 0.40)
Alternative 1 retains the MFMT definition of F30% SPR. This is currently estimated to be F = 0.25, and would require a reduction in fishing mortality of about 38 percent (from the recent 4-year average F).
Alternative 2 sets MFMT at the actual estimate of FMSY. This is currently estimated to be F = 0.23, and would require a reduction in fishing mortality of about 43 percent (from the recent 4-year average F). This is similar to the 2001 recommendation of the Reef Fish Stock Assessment Panel (RFSAP). The RFSAP recommended that FMAX rather than F30% SPR be used as an FMSY proxy for protogynous species such as gag. In the current assessment, FMAX = FMSY, which would seem to support the RFSAP’s recommendation that it is a superior FMSY proxy for gag. The statement of the RFSAP was (RFSAP 2001):
RFSAP Recommendation for FMSY Proxy
The fishing mortality rate of F30% SPR is frequently used as a proxy for FMSY, and usually works well with fish that do not change sex, since egg production remains fairly proportional to biomass throughout a fish’s life. However, gag is a protogynous hermaphrodite, and this relationship between egg production and biomass does not hold. The F30% SPR proxy is based on the potential number of eggs produced by each age class, which decreases rapidly after a peak at age 8 because older fish turn into males. The Fmax proxy, on the other hand, is based on the average weight of each age class, which increases a great deal after age 8. Thus, allowing a substantial fraction of the population to survive much beyond age 8 offers little in terms of egg production, but much in terms of potential yield. Under the selectivity scenarios estimated for the fishery, F30% SPR turns out to be a higher fishing mortality rate than Fmax. This means that a policy based on achieving F30% SPR would not only lead to growth overfishing (foregone yield), but also a lower SPR than would be obtained with an Fmax policy (and therefore a greater potential for recruitment overfishing). Moreover, the use of the F30% SPR proxy implies that sperm is not limiting, which may not be the case at very low levels of male biomass. Thus, it seems clear that, for gag, an Fmax policy is more compatible with the concept of MSY than is an F30% SPR policy.
Efforts should be undertaken to maintain a harvest strategy that maintains F at FMAX, or moves toward FOY. This strategy allows higher yields than fishing at F30% SPR, allows male biomass to be about 10% of its unfished biomass, and reduces harvest costs to the fishery.
Alternative 3 sets MFMT at F = 0.35, which is just under the long-term average fishing mortality rate during 1980-2004 (F = 0.36). This would require a reduction in fishing mortality of about 13 percent (from the recent 4-year average F). This level was recommended by the SEDAR 10 Review Panel, which stated (NMFS 2006):
For the Gulf of Mexico, a MFMT of 0.25 (current value of F30%SPR) is not consistent withthe recent dynamics of gag grouper: fishing mortality has been fluctuating around F =0.36 for more than twenty years (1985-2004) and the stock biomass is near its historicalmaximum. The Review Panel could not provide advice on target F and biomass referencepoints, but noted that the stock has apparently increased as a result of good recruitmentunder estimated fishing mortality rates that have fluctuated around an average value of F= 0.36 since the early 1980s. The Review Panel advised that it would be prudent toreduce fishing mortality below F = 0.36.
Alternative 4 sets MFMT at the recent 4-year average F2001-2004 = 0.40. This would not require any reduction from the recent 4-year average F. Only the single year estimate of F for 2004 is above this level (F2004 = 0.49, Table Gag-1, F annual mortality rate all removals) but gag stock biomass appears to be declining in the most recent two years (Figure-Gag 1). This suggests that stock status may not be sustainable at current fishing rates.
Action 2. Minimum Stock Size Threshold (MSST)
The current (2004) gag female biomass is estimated at 40.55 mp (Table Gag-1)
Alternative 1. No action – MSST is undefined post-SFA (or = 20% SPR pre-SFA)
Alternative 2. MSST is 20 mp female SSB (SEDAR recommendation)
Alternative 3. MSST is (1-M)* BMSY = female SSB of 32.3 mp*
Alternative 4. MSST is the female equilibrium SSB at F30% SPR(34.6 mp)
Alternative 5. MSST is the female equilibrium SSB at FMSY (37.6 mp)
* The stock assessment used a natural mortality vector that varied M with age, but averaged out to M = 0.14 across all ages. The estimate of BMSYin terms of female SSB is 37.6 mp, from the equilibrium SSB at FMAX reported in the Advisory Report. FMAX = FMSY, therefore equilibrium SSBMAX = SSBMSY. Using the formula in Alternative 3: (1-0.14)*37.6 = 32.3 mp.
The National Standard Guidelines state the following when defining minimum stock size threshold: To the extent possible, the stock size threshold should equal whichever of the following is greater: On-half the MSY stock size, or the minimum stock size at which rebuilding to the MSY level would be expected to occur within 10 years if the stock or stock complex were exploited at the maximum fishing mortality threshold. (50 CFR 600.310(d)(2)(ii).
Alternative 1, status quo, leaves MSST for gag undefined. The 1999 Generic SFA Amendment did not attempt to define an MSST for reef fish, but instead stated, “The overfished threshold (MSST) will be implemented for each stock by framework measure as estimates of BMSY and MSST are developed by NMFS, the RFSAP, and Council” (GMFMC 1999).
Note: An alternative interpretation of Alternative 1 is that it leaves MSST at the pre-SFA level of 20% SPR adopted in Amendment 1. According to the Advisory Report, female equilibrium female SSB at F20% SPR = 23.1 mp. This would make Alternative 1 slightly more conservative than Alternative 2.
Alternative 2 is the recommendation by the SEDAR Review Panel to set MSST at 20 mp female SSB, the lowest observed spawning stock size on a temporary basis until better estimates of spawning stock biomass benchmarks can be developed. The Review Panel recommended this level because they had no confidence in the benchmark estimates of SSB, and they observed that the SSB had historically been down to this level (Figure Gag-1) and had subsequently recovered, implying that there was no impairment of recruitment. The Standing and Special Reef Fish SSC felt that this recommendation was too non-conservative, and it might bring the stock to the brink of recruitment failure. The SSC could not agree on a specific alternative, but recommended that MSST be set above 20 mp.[2]
Alternative 3 sets MSST using the formula (1-M)*BMSY recommended by the NMFS Technical Guidance document as a default proxy for MSST (Restrepo et al. 1998), estimated to be 32.3 mp female SSB. This is the most commonly used definition of MSST by the Council. However, the SEDAR Review Panel felt that this was to close to SSBMSY and would result in stock biomass falling below MSST with a relatively high frequency.
Alternative 4 sets MSST to the equilibrium biomass associated with fishing at F30% SPR, which is estimated to be a female SSB = 34.6 mp. This corresponds to the expected long-term female SSB if the stock is fished at the current MFMT of F30% SPR.
Alternative 5 sets MSST to the equilibrium biomass associated with MSY, which is estimated to be a female SSB = 37.6 mp. This is similar to Alternative 4 except that it uses the actual MSY estimate rather than a proxy.
Action 3. Optimum Yield (OY)
Recent average yield (2000-2004) = 14.57 mp total removals, or 7.20 mp landed yield.
Alternative 1. No action – OY is undefined post-SFA (or = 20% SPR pre-SFA)
Alternative 2. OY is the yield at 75% * MFMT (appox. 94% of MSY).
Alternative 3. OY is fixed at 75% of MSY
The NMFS National Standard Guidelines state, “Target reference points, such as OY, should be set safely below limit reference points, such as the catch level associated with the fishing mortality rate or level defined by the status determination criteria”. The NMFS Technical Guidance document further states, “In setting a precautionary target control rule by means of the “frequentist” approach, we recommend that the probability of exceeding MFMT be not greater than 20%-30%, and certainly smaller than 50%” (Restrepo at al. 1998). The recommended default target is to set the fishing mortality rate associated with OY at 75% of FMSY, which would result in equilibrium yields of 94% of MSY or higher, and equilibrium biomass levels between 124% and 131% of BMSY (Restrepo et al. 1998).
Alternative 1 leaves OY undefined. In the absence of an OY target, management will continue to be focused on keeping the stock within threshold (MFMT and MSST) criteria.
Note: An alternative interpretation of Alternative 1 is that it leaves OY at the pre-SFA level of 20% SPR adopted in Amendment 1.
Alternative 2 sets OY equal to the yield associated with fishing at a fishing mortality rate equal to 75% of MFMT. This is approximately 94% of the yield at MFMT. Yield based on F will vary with stock size. Based on the MFMT alternatives in Action 1, this would produce OY yields of:
Yield at2008 OY Yield2008OY Yield at Equilibrium
75% of:Total RemovalsLanded YieldTotal Removals
F20% SPR8.45 mp4.26 mp7.75 mp
F30% SPR6.95 mp3.54 mp8.12 mp
FMSY6.55 mp3.53 mp8.14 mp
F = 0.35*8.22 mp4.15 mpn/a (close to 7.75)
F = 0.408.60 mp4.32 mpn/a
*Note: SEFSC has provided yield streams through 2010 for fishing at F0.35. Based on these values, the MSY and Alternative 2 OY annual yields would be:
YearMSYMSYOYOY
Total RemovalsLanded YieldTotal RemovalsLanded Yield
at F0.35at F0.35at 75% of F0.35 at 75% of F0.35
20088.74 mp4.42 mp8.22 mp4.15 mp
20098.63 mp4.35 mp8.11 mp4.09 mp
20108.57 mp4.29 mp8.06 mp4.03 mp
Alternative 3 sets OY at a fixed yield equal to 75% of the MSY level. Since this level of harvest is based upon equilibrium stock levels, it is a constant value regardless of biomass levels. Fishing at this yield level could result in overfishing at lower stock sizes. Depending on how MSY is defined, this would be:
MSY OY YieldOY
ProxyTotal RemovalsLanded Yield
(75% of MSY)(75% of MSY)
F20% SPR6.18 mp4.26 mp
F30% SPR6.48 mp3.54 mp
FMSY6.50 mp3.53 mp
F = 0.35n/an/a
F = 0.40n/an/a
ALTERNATIVES TO END OVERFISHING OF GAG AND TO ADDRESS DISCARD AND DISCARD MORTALITY
Action 4. Total Allowable Catch (TAC)
Alternative 1. No action – do not set a TAC for gag
Alternative 2. Set TAC at the yield corresponding to MFMT in 2008 (or year of implementation) – see table below.
Alternative 3. Set TAC at the yield corresponding to OY in 2008 (or year of implementation) – see table below.
Alternative 1 takes no action to reduce TAC. The total fishing mortality rate has been rising every year from 1999-2004, and for the most recent year (2004) it is at 0.49 (Table Gag-1, F annual mortality rate all removals). Thus, overfishing is occurring under all definitions of MFMT. However, under the assumption of a constant stock-recruitment relationship equal to the geometric mean recruitment for 1984-2004, Fcurrent is projected to be reduced to F = 0.392. If MFMT is set to F2001-2004 = 0.40 (Action1, Alternative 4), overfishing will end with no action needed. However, at this level of F, SSB is projected to continue to decline at least in the near future (Table Gag-1, SSB mature female wgt. all removals), and may enter an overfished condition depending on the definition of MSST selected in Action 2.
Alternative 2 ends overfishing by setting TAC in 2008 (presumed to be the first year of implementation) at the yield corresponding to MFMT. Depending on the MFMT alternative selected in Action 1, this would be:
MFMT2008 Yield
Total RemovalsLanded Yield
F30% SPR7.39 mp3.77 mp
FMSY6.97 mp3.75 mp
F = 0.35*8.74 mp4.42 mp
F = 0.409.15 mp4.60 mp
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*Note: SEFSC has provided yield streams through 2010 for fishing at F0.35. Based on these values, the Alternative 2 annual TACs would be:
YearMSYMSY
Total RemovalsLanded Yield
at F0.35at F0.35
20088.74 mp4.42 mp
20098.63 mp4.35 mp
20108.57 mp4.29 mp
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TAC can be specified either in terms of total removals (landed plus dead discards) or landed yield. In the past, TAC has usually been in terms of landed yield, with the estimated dead discards incorporated into the overall mortality rates. Dead discards are usually considered to be some constant proportion of the total discards depending upon average depth fished or other characteristics of the fishery. If TAC is specified in terms of total yield, a method of monitoring dead discards will need to be developed that accounts for changes in the discard mortality rate due to changes in fishing methods or regulations. Also, because the selectivity of dead discards differs from the retained catch (most of the dead discards are likely undersized gag), and increase or decrease in discards will not necessarily correspond to a one-to-one change in allowable landed harvest. The stock will need to be periodically reassessed, incorporating changes in discard rates in order to set subsequent TACs.
Under MFMT definitions of F30% SPR or FMSY, the stock SSB is projected to increase, which may allow or increases in TAC in future years. Under an MFMT of F=0.35, SSB will initially increase but then decrease, possibly requiring a future reduction in TAC. Under an MFMT of F=0.40, SSB will continue to decrease, requiring future reductions in TAC.
Alternative 3, TAC would be set at the OY level instead of the MFMT level. This would hasten rebuilding of the stock to OY and provide a measure of protection against the fishing mortality rate rising back above MFMT. OY yields are estimated to be about 94% of the corresponding MFMT yield, so depending on the MFMT alternative selected in Action 1, this would be:
MFMT2008 OY Yield
Total RemovalsLanded Yield
F30% SPR6.95 mp3.54 mp
FMSY6.55 mp3.53 mp
F = 0.358.22 mp4.15 mp
F = 0.408.60 mp4.32 mp
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*Note: SEFSC has provided yield streams through 2010 for fishing at F0.35. Using OY based on these values, the Alternative 3 annual TACs would be:
YearOYOY
Total RemovalsLanded Yield
at 75% of F0.35 at 75% of F0.35
20088.22 mp4.15 mp
20098.11 mp4.09 mp
20108.06 mp4.03 mp
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Action 5. Allocation between commercial and recreational sectors
Alternative 1. No action – do not establish an allocation for gag. Changes to landings levels will be based on equal percent reductions (or increases) to each sector from the most recent four-year average (2001-2004 average = 59.5% recreational, 40.5% commercial).
Landed yield alternatives
Alternative 2. Allocate the landed yield based on historical landings: 61% recreational, 39% commercial (1986-2004 average) (or some other base years)
Alternative 3. Allow the landed yield allocation to fluctuate such that recreational portion stays within 58%-75% of total landings, and commercial harvest stays within 25%-42% of total landings. If landings fall outside these bands for two consecutive years, action will be taken to restore the allocation to the center of the historical bands (66.5% recreational, 33.5% commercial). Changes to harvest levels to adjust TAC will be based on equal percent reductions (or increases) to each sector, except when asymmetric changes are needed to restore allocations.
Total removals alternatives
Alternative 4 Allocate the total removals TAC based on historical catches and discards 78% recreational, 22% commercial (1991-2004 average) (or some other base years)
Alternative 5. Allow the total removals allocation to fluctuate such that recreational portion stays within 67%-82% of total removals, and commercial removals stay within 18%-33% of total landings. If landings fall outside these bands for two consecutive years, action will be taken to restore the allocation to the center of the historical bands (74.5% recreational, 25.5% commercial). Changes to harvest levels to adjust TAC will be based on equal percent reductions (or increases) to each sector, except when asymmetric changes are needed to restore allocations.