Want more fish? Throw back big females.

If we were talking about humans, the acronym, BOFFFF would be a horribly inappropriate term.

But we’re talking about fish, and the term represents the most valuable and important members of the school—animals that are big, old, fat, female, fecund (or fertile) fish.

(Image: Bluefin trevally in the Northwestern Hawaiian Islands. You want to save the big ones. Credit: Dwayne Meadows, NOAA/NMFS/OPR)

And what’s important about them is that they reproduce more, have healthier and bigger eggs, have young more likely to survive, they may spawn at different times than younger fish so they increase species’ chance of success, and they are more likely to survive hard times than smaller, skinnier fish.

And what does that mean for the fishing community? They’re the ones you ought to throw back.

“Increasingly, fisheries managers are realizing that saving some big old fish is essential to ensure that fished populations are stable and sustainable,” said Mark Hixon, the University of Hawai`i researchers who was the lead author in a new paper, BOFFFFs: on the importance of conserving old-growth age structure in fishery populations.

 

His co-authors are Darren W. Johnson of California State Long Beach and Susan M. Sogard of the National Marine Fisheries Service. Theypublished in the ICES Journal of Marine Science.

“The loss of big fish decreases the productivity and stability of fishery stocks,” Hixon said.

The big old fat females have been shown to be important in a broad range of fish, both in fresh and salt water. They have the resources to survive periods of low food. They produce enormously more eggs than smaller fish. Their eggs are bigger and more likely to produce successful young. 

And the difference in egg production is amazing. A 27-inch ‘ōmilu or bluefin trevally, as an example, produces 84 times more eggs than a 12-inch fish. The increase with age is not the case with every fish species, but it seems to be the case with most of them.

And yet, we are removing them from the fish population faster than others. 

“Fishing differentially removes BOFFFFs, typically resulting in severe truncation of the size and age structure of the population. In the worst cases, fishing mortality acts as a powerful selective agent that inhibits reversal of size and age truncation, even if fishing intensity is later reduced,” the authors write.

Another way of saying that: If you keep taking the big, fat, females out of the population, you’re likely to end up with few fish overall, and fewer big, fat fish.

One of the solutions to this issue is slot limits—you keep the fish in the middle size slot, while releasing keiki as well as the biggest fish. But there are other ideas for fishery enhancement, as well.

“A growing body of knowledge dictates that fisheries productivity and stability would be enhanced if management conserved old-growth age structure in fished stocks, be it by limiting exploitation rates, by implementing slot limits, or by establishing marine reserves, which are now known to seed surrounding fished areas via larval dispersal,” the authors wrote.

A University of Hawai`i press release on the paper is here. 

© Jan TenBruggencate 2014