Fat fish could save the fishing industry!

Written by Abby Fournier

Imagine a world without fish… Fish are one of the only sources of protein for many island communities. They help maintain healthy coral reefs, which provide coastal protection against hurricanes, typhoons, and cyclones4. Additionally, they provide income for the fishing community – for some, the only source of income. So, what does the world look like without fish? Fish populations have been decreasing rapidly. Since 1950, fishing has killed 90 percent of all tuna and sharks in the ocean5. Scientists even expect there to be more plastic than fish in the ocean by 20505!

Fishing doesn’t always harm the ocean; however, if everyone in the fishing community overfishes (catches fish faster than the fish can reproduce), it becomes a problem6. Fortunately, researchers are trying to find ways to help fish populations replenish so the billions of people that rely on fish can continue to do so. 

One way to help fish populations replenish is to protect BOFFFFs – Big, Old, Fat, Fecund (fertile), Female Fish. 

An image of a BOFFFF from Hixon et. al, 2014.

Fish are often measured in “biomass.” Biomass is how much mass – or the amount of “stuff” – is in a defined space. This means that three fish that weigh the same amount as one big fish have the same biomass. However, not all biomass is created equal – many young, small female fish do not produce the same number of baby fish as an equivalent mass of BOFFFFs3. BOFFFFs are particularly good reproducers for 5 reasons:

1. Big, fat fish make better baby fish

The bigger fish are, the more fertile they are. Bigger bodies allow bigger ovaries, and better quality eggs. Because BOFFFF eggs are larger and in better condition, their offspring grow faster, have better swimming capabilities, a greater ability to detect predators and prey, and higher survival rates3. These better quality eggs are more likely than younger fish’s eggs to survive harsh environmental conditions2.

2. Old fish care more about reproducing…

            Rougheye rockfish can live to be 205 years old2! As BOFFFFs get older, they put more and more energy into spawning than growth3. Spawning is when eggs and sperm are released into the water for fertilization. When trying to rebuild a population, you want fish that prioritize reproduction – young females will even skip spawning some years3!

3. … and they reproduce at different times

            BOFFFFs spawn earlier in the season and for longer, and often in different locations than smaller female fish3. Because BOFFFFs reproduce at different times and locations than smaller fish, they will produce eggs at different times, so that even when habitat conditions vary, at least some of the eggs produced by smaller and larger females combined will survive.

4. BOFFFFs are like seed banks2

Fish of different ages are sensitive to different environmental factors, so age diversity increases resilience during environmental variation1. BOFFFFs have a storage effect: they live through periods with difficult reproduction conditions and then can continue to reproduce when “favorable conditions return”3.

5. The benefits are disproportionate

            Even after accounting for body size, BOFFFFs produce significantly more eggs than smaller female fish3. The quality of eggs also increases disproportionately with size and maturity2. The image below shows this significant increase in the number of offspring as size increases.

This picture shows how the average numbers of young per fish increases disproportionately with size. For example, the second fish weighs about twice as the first fish in weight, but produces almost three times as many fish! Image from Goeden, 1978.

So, in order to prevent fish populations from declining – which protects the billions of people that depend on them – we must protect the BOFFFFs. Protecting the old fish in a fish population is called conserving old-growth age structure, or limiting age truncation. Without this protection, fisheries remove the BOFFFFs and leave the younger, smaller fish because bigger fish sell for more money. In order to protect BOFFFFs, scientists typically focus on three conservation methods: (1) Limit exploitation rates, (2) Implement slot limits, and (3) Establish marine reserves3. Establishing marine reserves is the best way to both protect the fishing industry and BOFFFF populations.

  • Limit exploitation rates – This protection method reduces fishing pressure for all species of fish and allows more fish to reach old age, but significantly reduces the ability for fishers to maintain their livelihood.
  • Implement slot limits – This protection method has fishers release fish that are above the size limit, specifically reducing the fishing of BOFFFFs and allowing fishing to continue. However, most BOFFFFs do not survive after they have been caught even when they’re released due to catching injuries.
  • Establish marine reserves – This protection method designates specific areas as “no-catch” zones and it is the best way to both protect BOFFFFs and promote sustainable fishing. The BOFFFFs protected in the marine reserve release eggs that disperse and replenish populations outside of the reserve, which is called the seeding effect3.

            Protecting the BOFFFFs will also protect the fishing industry. Therefore, it is important to support marine reserves and follow the rules for those that exist. If you respect the reserve, your fish can be served!

This diagram summarizes the benefits of BOFFFFs for the health and growth of fish populations, from Hixon et. al, 2014.

References

1. Barnett, Lewis, Trevor Branch, R. Anthony Ranasinghe, Timothy Essington. “Old-Growth Fishes Become Scarce under Fishing.” Current Biology, vol. 27, 2017, pp. 2843-2848. https://www.cell.com/current-biology/pdf/S0960-9822(17)30973-9.pdf

2. Berkeley, Steven A., Mark A. Hixon, Ralph J. Larson & Milton S. Love. “Fisheries Sustainability via Protection of Age Structure and Spatial Distribution of Fish Populations.” Fisheries, vol. 29, no. 8, 2004, pp. 23-32. https://afspubs.onlinelibrary.wiley.com/doi/abs/10.1577/1548-8446%282004%2929%5B23%3AFSVPOA%5D2.0.CO%3B2

3. Hixon, Mark, Darren Johnson, Susan Sogard. “BOFFFFs: on the importance of conserving old-growth age structure in fishery populations.” ICES Journal of Marine Science, vol. 71, no. 8, 2014, pp. 2171-2185. https://academic.oup.com/icesjms/article/71/8/2171/748104

4. Holmlund, Cecilia and Monica Hammer. “Ecosystem services generated by fish populations.” Ecological Economies, vol. 29, 1999, pp. 253-268. https://www3.epa.gov/region1/npdes/schillerstation/pdfs/AR-211.pdf

5. Johnson, Dr. Ayana Elizabeth. “How to use the ocean without using it up.” TED Residency. July 2016. https://www.ted.com/talks/ayana_elizabeth_johnson_how_to_use_the_ocean_without_using_it_up#t-391400

6. World Wildlife Fund. (n.d.). Overfishing. Retrieved December 4, 2020, from https://www.worldwildlife.org/threats/overfishing

7. Featured Image: Alaska Halibut Forever: https://akhalibutforever.wordpress.com/2015/04/19/boffffs/

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