HOW TO THINK ABOUT MARYLAND'S 2019 JUVENILE STRIPED BASS ABUNDANCE INDEX

By now, the word is out.

Maryland’s striped bass juvenile abundance index for 2019, announced last Thursday, is 3.37, less than one-third of the long-term average of 11.6.  Given that the striped bass stock is already overfished and is also experiencing overfishing, the biggest question out there is what poor spawning success in 2019 means for the striper’s future.

It’s impossible to gauge the impact of the 2019 abundance index figure on the striped bass stock without putting the number in context.  Maryland’s Department of Natural Resources took a struck a measured tone when it noted that

“Weather, river flows, and abundance of food for newly-hatched fish are all important factors in the spawning success of fish such as striped bass.  Although the specific cause of this year’s poor spawning has not yet been determined, large variations in annual reproductive success are normal for the Bay’s striped bass population.  Typically, several years of average reproduction are interspersed with high and low years.  While three of the past five years have produced strong numbers of young-of-the-year striped bass, the department is recommending continued monitoring and conservation measures.”

Bill Anderson, Maryland’s Assistant Secretary for Aquatic Resources, also noted that

“The Chesapeake Bay spawning stock is still capable of high reproductive success under the right conditions.”

That’s an important point, because some Striped Bass Management Board members have also argued that the Chesapeake Bay’s productivity has declined in recent years.  Maryland’s statement that the Bay is still capable of “high reproductive success” goes a long way to put the reduced productivity arguments to rest.

Of course, we can’t ignore the qualification “under the right conditions.”

There is good evidence that striped bass spawning success is highest in years that feature wet winters and cool springs.  On the other hand, when winters are dry with little snow, and spring brings quick warming, spawns are likely to be sub-par.  Spawning success is associated with a phenomenon known as the Atlantic Multidecadal Oscillation, which is a long-term climate pattern that sees large areas of the Atlantic Ocean alternately warm and cool.

When the Oscillation brings favorable spawning conditions, bass thrive.  When it brings unfavorable conditions, spawns are often poor, and bass populations decline.  About 80% of the variation in striped bass spawning success can theoretically be attributed to this long-term climate pattern.

If 2019’s low juvenile abundance index is associated with the Atlantic Multidecadal Oscillation, we could be looking at a long string of relatively poor spawns, similar to what we saw during the period 2004-2010, which helped to bring the striped bass spawning stock down to its current overfished state.  The Striped Bass Management Board’s failure to promptly reduce fishing mortality inorder to compensate for those poor spawns helped assure that the stock would become depleted.

Thus, it’s important that the Management Board act to reduce fishing mortality to the target level when it meets on October 30.  That’s when it will make a final decision on Addendum VI to Amendment 6 of the Interstate Management Plan for Atlantic Striped Bass, which is expected to impose needed cuts in harvest.  

If fishing mortality isn’t adequately constrained, and striped bass go into another long period of below-average spawns, the stock could find itself in real trouble.

Even if fishing mortality is reduced to the target level next year, there is less than a 10% chance that the stock will rebuild by 2023; if fishing mortality is significantly above target, even if overfishing does not occur, there is virtually no chance at all that the stock can be rebuild by that date.  At the August Management Board meeting, the time required to rebuild the stock, assuming that fishing mortality was reduced to target, was estimated to be about 13 years.

And that assumes that the striped bass enjoy average spawning success.  Again, depending on conditions, that could be a big assumption.

As mentioned earlier, the 2019 Maryland abundance index of 3.37 is relatively meaningless unless put in context.  Maryland’s recent announcement notes that “three of the past five years have produced strong numbers of young-of-the-year striped bass,” and putting this year’s figure into a historical context is probably the right way to begin evaluating just what that figure really means.

Taking a historical approach, we note that an average of the Maryland juvenile abundance indices for the past three years—2017, 2018, and 2019—would be a little over 10.4, somewhat below the long-term average of 11.6.

Extending that average back another two years would capture the large 2015 year class, and result in a 5-year average of 11.5—just below the long-term average, and close enough to consider the five-year average to equal the long-term figure.  Go back 10 years, to capture not only the 2015s, but the 2011 year class as well, and you end up with a number that equals the long-term average of 11.6.

From that perspective, this year’s abundance index doesn’t seem to signal anything dire.  However, it also isn’t enough to spur recovery.  Remember that the 2011 and 2015 year classes were already figured into the projection that the stock will still be a long way from recovered in 2023.

But, again, the big question is what happens next.  Is the 2019 juvenile abundance figure an outlier or, like the 2016 juvenile abundance number, a seeming interruption in what could be a trend of increasing spawning success?  Or is it the first in a string of bad years?

Remember that the average index for the seven-year period 2004-2010 was around 9, not too far below the long-term average. Yet the small difference between a seven-year average of 9 and the long-term average of 11.6 was enough to cause the spawning stock, which peaked in 2004, to slip into a steady decline beginning in 2011, and eventually to become overfished.

Thus, if the 2019 juvenile abundance index is the harbinger of a similar period of below-average recruitment that began when the stock was already overfished, it is easy to see how the stock could end up in serious trouble unless management measures far more restrictive than those in Addendum VI are promptly implemented.

So it’s reasonable to say that the 2019 juvenile abundance figure doesn’t foreshadow anything good.

It might still turn out to be a relatively meaningless number, if a few large year classes are produced in the near future.  But such production is no guaranteed.

Perhaps the most rational comment on the 2019 number came from the American Saltwater Guides Association, which noted

“The press release yesterday does not spell the end for stripers.  They do spawn in boom and bust cycles.  Cold, wet springs are the recipe for good recruitment.  It should be noted that the spring of 2019 was one of the wettest on record.

“Our plea to the managers up and down the coast is simple.  If a robust [2011] year class gave you the wiggle room to ease reductions in 2012, then the equal and opposite reaction would be that this [young-of-the-year] report should cause you to take a precautionary approach.”

Because when you don’t know where you’re going, and you see a warning sign, it makes sense to slow down.

Otherwise, you could find yourself driving right over the edge of a cliff, with no time left to avoid a crash.