STRIPED BASS: ANOTHER POOR SPAWN IN MARYLAND

 

Earlier this week, Maryland released the 2022 striped bass juvenile abundance index, and the news is not good.  This year’s JAI was 3.6, well below the long-term average of 11.3; it marked the fourth year in a row when the index did not rise above 4.0, something that has never before happened in a time series stretching all the way back to 1957.

The Maryland JAI represents the average number of juvenile striped bass caught in a series of samples taken throughout the summer.  All samples are taken with a 100-foot-long, hand-operated beach seine, deployed at 22 established sampling points in the upper Chesapeake Bay, and on the Potomac, Choptank, and Nanticoke rivers.  Each site is sampled three times during the summer, and two sweeps of the seine are made at each site during each sampling session.

Since the time series began in 1957, the annual index reached a high of 59.39 in 1996, and a low of 0.89 in 2012.  Typically, the index fluctuates widely from year to year with no apparent pattern.  The record high index of 59.39 was bracketed by slightly below-average years, when the indices only reached 9.27 and 7.98; the record low index of 0.89 was preceded by the highest JAI in the past 20 years, 34.58 in 2011.  In that context, it is somewhat disconcerting that the index has been stalled in a low and very narrow range, between 2.48 and 3.60, since 2019.

The four-year average for 2019-2022, 3.16, ties the lowest average for any 4-year period in the entire 65-year time series; the previous low occurred during the years 1983-1986, when the stock was just beginning to recover from its collapse in the late 1970s and early 1980s.

The question on many anglers’ minds is what the continued poor recruitment might mean for the recovery of the overfished stock, and on future regulations.

The answer to that question isn’t clear.

The first thing to remember is that striped bass recruitment isn’t dependent on the size of the spawning stock biomass.  There is no clear stock/recruitment relationship; the scientists who performed the last benchmark stock assessment set the “steepness” variable at 1, which implies that there is no stock/recruitment relationship at all.  A very small spawning stock biomass can produce a very large year class; a very large spawning stock can and has produced disappointlingly low JAIs.

Instead, striped bass recruitment seems to be driven largely by environmental conditions in the spawning rivers.  When the winter has been cold and wet, and spring comes late, there is a very good chance that a large year class will emerge.  Under such conditions, more nutrients are washed into the spawning rivers, feeding blooms of zooplankton large enough to sustain unusually strong numbers of juvenile bass.  Warm, dry winters paired with early springs minimize nutrient runoff, and what runoff occurs enters the rivers too early in the year to benefit the newly-spawned fish.

Thus, fishery management is less a matter of keeping the spawning stock biomass large enough to assure a healthy spawn, and more about making sure that the population retains enough older, larger females to be able to take advantage of favorable spawning conditions when they finally recur, even if it might take many years for such conditions to come about.  

In a paper published more than 20 years ago, “Spawning in the nick of time?  Effect of adult demographics on spawning behavior and recruitment in Chesapeake Bay striped bass,” Dr. David H. Secor argued that

“Through a moratorium on Maryland State harvests in the Chesapeake Bay, the 1982 year-class was effectively protected and became a dominant one.  Ironically, most egg production in 1982 was attributable to striped bass >10 years of age.  Old remnant females produced during the 1960s were a hedge against a long period of recruitment overfishing which occurred during the 1970s.  [citation omitted]”

In the same paper, Dr. Secor noted the advantage of having a well-stratified spawning stock, which includes both young and old females, because striped bass of different ages enter the rivers at different times, with the older, larger fish entering sooner.  Such a reproductive strategy makes it more likely that, even in years when environmental conditions are not generally favorable, some portion of the spawning stock will enter the rivers during a time when conditions are relatively good, and thus prevent a spawning failure.

The current 28- to 35-inch recreational slot limit, which protects older, larger fish, would seem fairly well suited to supporting such a reproductive strategy, although commercial fisheries in a number of states may still harvest older, larger striped bass, and Maryland’s spring “trophy” season allows the continued landing of even the largest females—fish that may not be retained by anglers anywhere else—in the heart of the Chesapeake Bay. 

The recently adopted Amendment 7 to the Interstate Fishery Management Plan for Atlantic Striped Bass also includes provisions intended to address periods of low recruitment.  It provides,

“If any of the four JAIs used in the stock assessment model to estimate recruitment (NY, NJ, MD, VA) shows an index value that is below 75% of all values (i.e., below the 25^th percentile) in the respective JAI from 1992-2006 (which represents a period of high recruitment…) for three consecutive years, than an interim [fishing mortality] target and interim [fishing mortality] threshold calculated using the low recruitment assumption will be implemented, and the [fishing mortality]-based management triggers…will be reevaluated using those interim reference points.  If [a fishing mortality]-based trigger is tripped upon reevaluation, the striped bass management program must be adjusted to reduce [fishing mortality] to the interim [fishing mortality] target within one year.

“The lower interim [fishing mortality] reference points will remain in place at least until the next stock assessment update or benchmark assessment is approved for management use.  Upon reviewing the results from the next assessment, the Board will determine which [fishing mortality] rate (target or interim target) to manage towards moving forward by considering factors such as current stock status, recent JAI data, and [Technical Committee] input.”

That all sounds fairly straightforward, but putting it into practice may not be all that simple.

The “low recruitment assumption” is based on Age-1 recruitment for the years 2008-2017 which, because survival of Age-0 fish can vary from year to year, doesn’t necessarily correspond to the annual JAIs (e.g., the 2011 Maryland year class was the highest in the last 20 years, yet its Age-1 recruitment was significantly less than that of the 2015 year class, which had a JAI roughly two-thirds the size of the 2011).  However, if we just look at the JAIs in order to more easily accommodate the recent Maryland indices, the average JAI for the years 2007-2016 was 10.9, not too far below the long-term average.

Thus, the average Maryland JAI for the years used to calculate the “low recruitment assumption” was more than triple the average JAI for the past four years.  If we extend the recent JAI out a little farther—say, out 6 and 8 years, to capture fish maturing into the spawning stock—things get a little better, with the average JAI for the past six years being 6.77 and the average for the most recent eight years being 8.38.  Still, even such 6- and 8-year averages fall below the average JAI for the years used to determine the low recruitment scenario, which suggests that the interim fishing mortality reference points used in the low recruitment assumption might not be low enough to capture what is actually happening with the striped bass stock (although the lower Year-1 recruitment of the 2011 year class may at least partially offset the higher average JAI for the low recruitment base years).

Then there is the question of setting interim reference points.

In August, the Management Board was advised that the Maryland JAI for 2019, 2020, and 2021 tripped the new recruitment trigger, but took no action to set interim fishing mortality reference points, perhaps because many Board members assumed that new management measures would be required pursuant to a rebuilding plan.  However, even if the Management Board had initiated action on interim reference points, the release and likely acceptance of a stock assessment update at the Board’s November meeting would relieve the Management Board of its absolute obligation to adopt such interim reference points, although it must still determine whether such interim reference points are needed.

The new Maryland JAI numbers would seem to trip the recruitment trigger again, and start the clock running on a new requirement to adopt interim reference points, but with a benchmark stock assessment scheduled for next fall, that requirement, too, will seemingly not survive long enough for any interim reference points to be put into effect, although the Board could set interim reference points if it felt that doing so would best benefit the stock.

As far as rebuilding goes, if the opinions expressed atrecent Technical Committee meetings hold, the striped bass stock has a goodchance of attaining its target level by the 2029 deadline.  That view incorporates a low recruitment assumption (although that assumption is still based on a recruitment level higher than what we’ve seen in the most recent years).  Most of the recent low JAIs have been incorporated into that projection.  

Because it takes striped bass a while to mature, the great majority of the fish spawned after this year will not enter the spawning stock until after 2029, making future recruitment irrelevant to rebuilding, although such recruitment will be very relevant to maintaining the stock at the target level.

Thus, whether or not the stock rebuilds by 2029 will not be determined by the 2022 JAI.

Even if the stock rebuilds by the 2029 deadline, continued low recruitment could threaten the long-term health of the striped bass resource.  Until the Maryland JAI returns to more typical levels, conservative management will be required to prevent an eventual decline in abundance.  

Although we can hope that the Management Board will be willing to maintain a conservative management regime until recruitment rebounds, whether it will actually do so remains an open question.