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Spawning Striped Bass: Oldies but Goodies

There’s been some great science coming out about fish lately.  The findings are eye opening because scientific studies have shown us that bigger, older, and fatter female fish are better reproducers. A recent study in the journal Science supports this theory, finding that larger females produce disproportionately more eggs.  Scientists have even come up with an acronym for these fish.  Affectionately known as BOFFFF, for Big Old Fat Fecund Female Fish, these fish are getting harvested at an alarming rate. In fact, in 31% to 42% of fish populations, the magnitude of decline in BOFFFFs is over 90%.

The Washington Post article about the study notes, “The authors of the new research say it contains an important message for the fishing industry. ‘Most classic fisheries models don’t account for the massively disproportionate contribution that larger fish make, yet these are the first individuals to disappear under even a moderate fishing pressure,’ Barneche and Marshall wrote in a joint email. ‘So, fisheries scientists, despite the best of intentions, have been using models that inadvertently recommend overharvesting [emphasis added].’”

The research included 394 species.  In the case of vermillion snapper, a small female will lay 4,000 eggs.  A large female will lay millions.  It is the same with cod.  The scientists found that one large cod will lay 28x the eggs of a female that just reached sexual maturity.  But the story goes even further.  As the BOFFFF grows, the ovaries grow disproportionately larger.  This not only makes more eggs per pound of fish, but the eggs are also richer in fat and larger in size.  So, instead of 28 times more baby cod per BOFFF, the real number is about 37.

Research done on striped bass shows the same hyperallometry, that is, one part of the body grows disproportionately larger with age.  Research is telling us that fish become infinitely more valuable to the overall spawning potential with time. Local scientists have found the same to be true of striped bass eggs, according to a 1990 study by Doreen M. Monteleone and Edward D. Houde. A study published in 2000 found that there is an increase in egg production of about 200,000 eggs per kg (2.2lbs) of female striped bass. Furthermore, small females tended to produce smaller larvae and the eggs from a large striped bass are larger and richer in fat.

First and foremost, I hope this helps dispel the myth that giant female striped bass produce “bad eggs.”  This is an argument that lacks any shred of evidence and yet another old wives’ tale that plays a part in how we approach the striped bass fishery.  My hope is that by reading this, it empowers you with the correct information to make the right decision on which fish you harvest.

This biology has been largely ignored in the past.  But, as the data accumulates, it is hard to deny the facts.  BOFFFFs across all species are the most important members of the stocks, and we are killing them faster than they are being replaced.  Fish can be managed on slot limits or egg production rates vs. a minimum size.  We are simply putting too much pressure on the most important segment of the population.

But wait, there’s more!

If you are a striped bass fisherman, you have probably seen this chart.

It shows a straight-line growth/weight relationship.  While hyperallometry is common across species, straight line growth is not.  Most species will grow to a certain size quickly and experience a reduction in growth rates.  This slowdown in growth rate is common.  Here’s an example of a redfish that grew only a foot in 22 years.

So, how old are stripers?  Dr. Dave Secor from UMCES has done some research on the subject and let’s just say, the graph above is not as accurate as we think.

Here’s a sample of fish taken in May of 1992.

 

You see a range of fish with the oldest being over 31 years old.  There’s also a large segment of fish that are between 21 and 27 years old.  How could this be?  Dr. Secor aged the fish by using the otolith.  That’s an inner ear bone that provides researchers with a very accurate age of the fish.

Here’s a quote from “Longevity and resilience of Chesapeake Bay striped bass.” (Secor, D. H. 2000. “Longevity and resilience of Chesapeake Bay striped bass.” – ICES Journal of Marine Science, 57: 808–815.)

“The longevity of Chesapeake Bay striped bass found in our study surpassed that reported in the literature. Investigators have long suspected that large striped bass (e.g. >30 kg) were quite old but were not confident in using scale annuli for age determination. Merriman (1941) reported difficulty in assigning ages after 8 years using scales yet estimated that a 40-kg striped bass captured in Massachusetts coastal waters was 29–31 yr old. The two females I observed to be 31 yr old were 20–24 kg in weight. Because a systematic error occurred with scale ageing. (Secor et al., 1995)”

Dr. Secor’s research was noted in the most recent update of the striped bass stock assessment.  On page 995, appendix b-10, the paper notes that scale aging has fallen out of favor because SCALE AGING CAN UNDERESTIMATE THE AGE OF STRIPED BASS.  The age/length chart shown in the first chart was done with scale aging, and its accuracy should absolutely be called into question.

In layman’s terms, striped bass could live longer than the scale studies show.  As Dr. Secor suggests, this is a survival strategy that allows the stock to persist even with a long-term recruitment failure (a series of nonproductive spawns). The spawning stock biomass has most certainly fallen below the threshold.  We’ll know for sure when the benchmark stock assessment comes out in early 2019.  Managers are banking on the 2011-year class to recruit in high numbers.  That’s fine and dandy, but these small females have less impact on spawning success.  We won’t see true increases in spawning until the 2011-year class is about 22 years old.  So, maybe we can up the harvest in 2033, but it isn’t a great idea right now.  The ramifications on this information are certainly interesting.  Knowing this, how can we continue to remove these fish from the population?

In Maryland’s Chesapeake Bay, the blame falls squarely on the shoulders of recreational fishermen.  Commercial anglers are not allowed to harvest striped bass over 36”.  If I were a waterman, I’d be screaming from the highest towers.  We are solely responsible for removing fish from the spawning stock.  The coastal regulations target the spawning stock.  Does this make any sense when we know that these fish are the best hope we have for a resilient population?

John McMurray did a great recap of the most recent Atlantic States Marine Fisheries Commission meeting where the topic of harvesting more stripers was a big part of the management discussion.  Why in the world would ASMFC be talking about lowering the reference points (increasing harvest) on striped bass when the best science available shows us that we need to keep the oldest females in the population to ensure spawning success?   Why do we encourage the harvest of the largest fish through our regulations?  The BOFFFFs are nothing short of an insurance policy that can protect the species from low spawns and environmental shifts.  It’s time we became smarter about leaving our best reproducers and future of the stock in the water.  What’s the worst thing that could happen if we protected the BOFFFFs?  We would have more fish?  What’s the worst thing that could happen if we don’t start protecting them?  Well, I think we saw that in the 80s.  I’m too old to go through that again.

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    May 26, 2018 at 2:59 am

    Spawning Striped Bass: Oldies But Goodies - Moldy Chum