ASMFC 2013 Striped Bass Stock Assessment Summary

NOTE: Underlined passages

The 2013 Striped Bass stock assessment summary has been released, as expected it showed a stock on the edge of problems.   It can be found here: http://nefsc.noaa.gov/publications/crd/crd1314/

The introduction of the assessment is as follows:

State of the Stock:

In 2012, the Atlantic striped bass stock was not overfished or experiencing overfishing relative to the new reference points from the 2013 SAW/SARC57 (Figure B1-B3). Female spawning stock biomass (SSB) was estimated at 61.5 thousand mt (136 million lbs), above the SSB threshold of 57,904 mt, but below the SSB target of 72,380 mt. Total fishing mortality was estimated at 0.188, below the F threshold of 0.213 but above the F target of 0.175.

When compared to the biological reference points currently used in management (ASMFC

2008), the stock is neither overfished nor experiencing overfishing. Female SSB in 2012 is above both the target (46,101 mt) and the threshold (36,000 mt), and F2012 is below both the target (0.30) and the threshold (0.34).

There are several important caveats to this assessment, the most important of which is the fishing mortality reference points (F) have changed.  A little background here is necessary.  When the stock was declared recovered in 1995, the estimated SSB at that point became the SSB  threshold (36,000 mt) and the target 125% of that (46,101 mt).   The last assessment used these SSB, but developed F separately (largely due to an internal disagreement on the Stock Assessment Committee (SAC).

As an aside, CCA has argued for a lower F, if for no other reason than striped bass are a long-lived, late-maturing species that, by definition, cannot withstand a high fishing mortality rate.

In the 2013 assessment, the SAC agreed with that philosophy and used a conventional stock-recruit relationship and basically devised the Frate which, over the long term, would produce the designated SSB (increased from the 1995 number by using a different Natural Mortality Rate but consistent).

It turns out that this is the right track. The current F threshold that produces the SSB threshold is F=0.213 and an F target of F=0.175. 

Using the current fishing mortality threshold, we have been overfishing for five of the last eight years.  Using the old fishing mortality threshold, we have not (see page 29 of the summary).   However, it would be difficult to point fingers here; this is a case of not really knowing the stock status largely due to an internal scientific disagreement.

The projections are important:

Projections:

Five-year projections of female spawning SSB and fishing mortality (Figure B4) were made by using a standard forward projection methodology. If the current fully-recruited F (0.188) is maintained during 2013-2017, or if it increases to the threshold or decreases to the target, the probability of being below the SSB threshold increases until 2015-2016, but declines thereafter. If action to reduce F is delayed until 2014 or 2015, the probability of being below the SSB threshold increases (Figure B5).

If the current removals, meaning landings and dead discards of 3.59 million fish, are maintained during 2013-2017, the probability of the full recruited F being above the F threshold increases rapidly starting in 2013 and reaches near 1 by 2014 (Figure B6). If constant removals equal to 50% of the 2012 removals are taken during 2013-2017, the probability of fully recruited F being above the F threshold is near zero.

Basically, this says that if removals are maintained where they are, the fishery will likely be pushed to an overfishing condition.  If removals are reduced by 50%, that most likely can be avoided.

The Striped Bass Board will have to adopt the stock assessment, which is expected, and then consider adopting the new F reference points, which is less certain.  Given the evidence and the underlying reasons for this situation, it would be my recommendation that we maintain our position calling for F to be reduced in order to increase abundance and age structure for this critically important recreational fish.