Purpose and Need

In response to the national standards established in the Magnuson Act and advisory guidelines, the Council developed an objective and measurable definition of overfishing and, in 1991, implemented that definition under Amendments 16 (BSAI) and 21 (GOA) to the FMPs. In the years since implementation of that definition, fishery scientists had the opportunity to evaluate the efficacy of these definitions of ABC and overfishing. In light of that experience and with the increased understanding of the reference fishing mortality rates used to define ABCs and overfishing, fishery scientists had raised several concerns about the definitions and the extent to which they reflect and account for levels of uncertainty about fish populations. Consequently, NMFS’s Overfishing Definitions Review Panel and the Council’s Scientific and Statistical Committee recommended redefining ABC and overfishing to facilitate more conservative, risk-averse management measures when stock size and mortality rates are not fully known. The purpose of this Amendment was to revise the ABC and overfishing definitions to be consistent with these recommendations.

Analysis

A 60-page EA (final draft dated January 6, 1997) was prepared for this amendment. Two alternatives including the status quo were considered. The alternative chosen was more conservative for several reasons. First, the overfishing rate varies with biomass. Second, the ABC fishing rate is reduced when biomass is below levels that produce maximum sustainable yields. Lastly, more caution is incorporated into establishing fishing rates when less information is available; this is particularly true of tier 1.

Tiers used to determine ABC and OFL for BSAI

groundfish stocks under Amendment 44.

(1) Information available: Reliable point estimates of B

and BMSY and reliable pdf of FMSY .

1a) Stock status: B/BMSY > 1

FOFL = mA , the arithmetic mean of the pdf

FABC ≤ mH , the harmonic mean of the pdf

1b) Stock status: a < B/BMSY ≤ 1

FOFL = mA × (B/BMSY - α)/(1 - α)

FABC ≤ mH × (B/BMSY - α)/(1 - α)

1c) Stock status: B/BMSY ≤ α

FOFL = 0

FABC = 0

(2) Information available: Reliable point estimates of B,

BMSY , FMSY , F30% , and F40% .

2a) Stock status: B/BMSY > 1

FOFL = FMSY

FABC ≤ FMSY × (F40% /F30%)

2b) Stock status: α < B/BMSY ≤ 1

FOFL = FMSY × (B/BMSY - α)/(1 - α)

FABC ≤ FMSY × (F40% /F30%)×(B/BMSY - α)/(1 - α)

2c) Stock status: B/BMSY ≤ α

FOFL = 0

FABC = 0

(3) Information available: Reliable point estimates of B,

B40% , F30% , and F40%.

3a) Stock status: B/B40% > 1

FOFL = F30%

FABC ≤ F40%

3b) Stock status: α < B/B40% ≤ 1

FOFL = F30% × (B/B40% - α)/(1 - α)

FABC ≤ F40% × (B/B40% - α)/(1 - α)

3c) Stock status: B/B40% ≤ α

FOFL = 0

FABC = 0

(4) Information available: Reliable point estimates of B,

F30% , and F40% .

FOFL = F30%

FABC ≤ F40%

(5) Information available: Reliable point estimates of B

and natural mortality rate M.

FOFL = M

FABC ≤ 0.75 × M

(6) Information available: Reliable catch history from 1978

through 1995.

OFL= the average catch from 1978 through 1995,

unless an alternative value is established by the SSC

on the basis of the best available scientific information

ABC ≤ 0.75 × OFL

Regulation Summary

Amendments 44/44 provided for more conservative definitions of ABC and OFL. The fishing mortality rate used to calculate ABC was capped by the overfishing rate. The maximum allowable fishing rates were prescribed through a set of 6 tiers which are listed in descending order of preference, corresponding to descending information availability. These tiers are shown in the adjacent table. Harvest rates used to establish ABCs are reduced at low stock size levels, thereby allowing rebuilding of depleted stocks. If the biomass of any stock falls below Bmsy or B40% (the long-term average biomass that would be expected under average recruitment and F=F40%), the fishing mortality is reduced relative to stock status. This serves as an implicit rebuilding plan should a stock fall below a reasonable abundance level.

Results

The amendment resulted in lower (more conservative) ABCs; consequently, total allowable catch levels were reduced for many species. The definitions adopted under Amendments 44/44 were further revised under Amendments 56/5