The Boffff Principle: Do Big Stripers Make Better Spawners? - The Fisherman

The Boffff Principle: Do Big Stripers Make Better Spawners?

2018 11 Do Bigger Stripers Make Better Spawners SNAPSHOT
Fin Chasers’ Capt. Frank Crescitelli and Sean Gros of Navionics grab a quick snapshot before letting this striped bass free to spawn again. As she ages, the BOFFFF principle shows her ability to produce more eggs grows.

Big, Old, Fat, Fecund, Female Fish!

For over a decade, fishery biologists have acknowledged the crucial role that older, larger female fish play in maintaining healthy stocks.  Known as the Big Old Fat Fecund Female Fish (BOFFFF) hypothesis, researchers have documented several instances where the continued harvest of larger older females has resulted in truncation of the size and age structure of fished populations leaving them comprised of predominantly younger, smaller spawners.

Subsequently, these age truncated fish stocks experience greater variability in spawning success and year class strength through time and become more susceptible to collapse than populations with a more intact age structure that includes older, more mature individuals.  In short, these studies provide evidence that old-growth age structure fosters population stability, whereas age truncation often destabilizes population dynamics.

BOFFFF Biology

In most fishes, the ability to produce an abundance of offspring, referred to as fecundity, generally increases with female age as a function of body size.  BOFFFs can produce significantly more eggs than younger fish because their larger body cavity allows development of larger ovaries.

Accordingly, a single 4-pound fish would have a greater reproductive output than two 2-pound fish.  This relationship increases disproportionately with increased body size.  For example, scientists have estimated that a single 66-pound female Atlantic cod produces more eggs than about 28 females weighing approximately 4 pounds would.  In another study of rockfish species along the California coast, researchers determined that a 31-inch Bocaccio rockfish could produce nearly 10 times more eggs per year than an individual half that size.

The scientific evidence available also suggests that offspring of BOFFFFs typically perform better than those of smaller females.  Their eggs and the subsequent larvae are often larger, grow faster, and are better provisioned and more capable of withstanding starvation.  The higher vitality or fitness of the eggs and larvae produced by older adults is due to older fishes having more metabolic reserves enhancing their ability to invest more energy in each offspring.  The greater fitness and survival of their offspring appears to be related to the increased volume of the nourishing larval oil globule they are provisioned with at birth, the size of which is strongly related to maternal age.

2018 11 Do Bigger Stripers Make Better Spawners STRIPED BASS FECUNDITY
While older fish might sometimes skip a year, the spawning potential in terms of numbers of eggs produced during a spawn increase significantly as striped bass age.

There is also evidence that in addition to being more fecund than smaller fish, BOFFFFs provide the population with a longer spawning season by spawning at different times or in different locations. This spread of reproductive effort over time and space provides a bet-hedging life history strategy helping to ensure that some larvae are produced at times of favorable environmental conditions.

Therefore, elimination of larger, older age females through fishing will eventually shorten the spawning season, reduce the number of high quality larvae produced and decrease the chance that some larvae will encounter favorable environmental conditions, lowering the potential for larvae to survive to the next stage in their life history.

BOFFFFS and Bass

The striped bass is a species where fecundity and offspring fitness fit the BOFFFF model.   Regrettably, some striped bass anglers continue to harvest larger stripers thinking that it does little damage to the resource, or even believing that it enhances the growth and survival of smaller fish in the long run. Contrary to these views, anglers that value taking larger, older female bass strip them away from the reproductive population. Therefore, selective harvesting of older individuals by recreational anglers contributes to impacts on the long-term sustainability of these fisheries.

Striped bass are extremely fecund and available data on fecundity clearly indicate that larger females produce disproportionately more eggs than smaller females.  As with other BOFFFs, the number of eggs produced by mature female striped bass increases based on size {length and weight} and age.

Several studies have estimated the mean number of eggs produced by mature female striped bass per pound of body weight in East Coast spawning grounds.  A study of spawning potential in striped bass conducted in Chesapeake Bay estimated fecundity at 62,000 to 112,000 eggs/pound of body weight while fecundity for females in the Hudson River was estimated to average 78,500 eggs/pound of body weight.

A study of fecundity of striped bass in North Carolina’s Roanoke River yielded a value of approximately 80,000 eggs/pound of body weight.  In another study of maturation and fecundity of Roanoke River – Albemarle Sound striped bass, researchers estimated that fecundity of female striped bass increased about 100,000 to 200,000 eggs with each year of growth.

A number of studies along the east coast have also reported fecundity estimates that illustrate the increasing production of eggs by adult female stripers as they grow larger and older.  For example:

  • Fecundity estimates for 6-year-old stripers sampled in the Roanoke River – Albemarle Sound system of North Carolina ranged between 612,000 – 702,422 eggs (estimated by weight and age).
  • In Chesapeake Bay, a 6-year-old, 28-inch female weighing 13 pounds yielded 856,267 eggs.
  • Fecundity estimates for 8-year-old stripers sampled in the Roanoke River – Albemarle Sound system of North Carolina ranged between 1.04 million to 1.16 million eggs (estimated by age and weight).
  • In Chesapeake Bay, an 8-year-old, 32-inch female weighing 16 pounds yielded over 1.6 million eggs.
  • Fecundity estimates for 10-year-old stripers sampled in the Roanoke River – Albemarle system ranged between 1.37 million and 1.83 million eggs (estimated by age and weight).
  • A 10-year-old, 36-inch female weighing 21 pounds sampled in Chesapeake Bay yielded over 2.5 million eggs.
  • A 12-year-old, 38-inch female weighing 29 pounds sampled in Chesapeake Bay yielded over 2.9 million eggs.

Perhaps even more astonishing is that during the study of spawning potential of striped bass in the Chesapeake Bay, an age 14 female sampled (which was 43 inches and 35 pounds) produced over 4.5 million eggs!

2018 11 Do Bigger Stripers Make Better Spawners GOOD FISH By JDB
There’s a lot to be said about releasing a few good stripers for the future, especially those big, old, fat, fecund, female fish. Photo by John DeBona.

In addition to having greater fecundity, older larger female striped bass also exhibit greater fitness than their smaller counterparts, a measure of the contribution of an individual to future generations. They tend to be more experienced and successful spawners providing the population with an earlier and longer spawning season and spreading their reproductive outputs across many years. They produce larger fitter eggs that produce fitter larvae that grow faster and are more likely to survive during periods of unfavorable environmental conditions.

The higher fitness of eggs and larvae produced by older, larger females results from them having more metabolic energy reserves that allow them to invest more energy in each offspring.  They provision larvae with significantly more nourishment via larger oil globules than those produced by smaller females.  Larger oil globules aid larval growth and survival including making larvae more resistant to starvation.

It should also be noted that there is a misconception among some anglers that these larger old females will halt spawning at some point in their life. While there is evidence of skipped-spawning behavior in mature stripers (i.e., not spawning in each successive year) tied to the overall condition of individual fish (e.g., deficient diet, poor nutritional condition, resulting in decreased residual body weight and low energy reserves) or unfavorable environmental conditions, there is no documented evidence that females reach a point where they halt spawning altogether. In fact, female striped bass are extremely fecund, fecundity increases with age, and older fish produce large numbers of eggs and spawn multiple times during their life.

So, continued removal of older, larger individuals from the striped bass stock may lead to large reductions in the number of eggs and larvae produced, shortening of the reproductive season, decreased chances that larvae will encounter favorable environmental conditions and lowered average survival potential of larvae produced. Potential lowering of genetic diversity over time is also a concern.  Stocks with high genetic diversity are more likely to produce offspring with high fitness especially in a variable environment.  The harvest of older, larger striped bass strips away these individuals from the reproductive population and their value to the overall success of the stock.

As striped bass anglers, it’s all about the choices we make.  By practicing selective harvest of fish of various sizes and releasing BOFFFFs, recreational anglers can contribute to the conservation of striped bass and the long-term stability of the fishery.

The author is Assistant Dean at the Monmouth University School of Science and Director of the Marine and Environmental Biology and Policy Program.  He specializes in marine ecology, coastal zone management, environmental science, marine recreational fisheries, and marine and environmental education.

 

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