Quantcast
Animals
Atlantic cod is one of hundreds of fish species in which larger females lay more, and healthier eggs. OCEANA / Carlos Minguell

Old, Fat Fish Have the Most Offspring, Sustainability Study Finds

By Annie Roth

It might seem smart to eat the big fish and throw the little ones back. But a recent study in the journal Science says just the opposite. Big fish are the ones to throw back, especially if they're female.

That's because bigger females have disproportionately more babies than their smaller counterparts.


Biologists from Monash University in Australia and the Smithsonian Tropical Research Institute in Panama came to this conclusion after comparing size and fecundity across 342 fish species. In 95 percent of the species, larger mothers produced far more offspring, pound for pound, than smaller mothers. The authors point to Atlantic cod, for instance, where one 30-kilogram (approximately 66-pound) female can lay more eggs per spawning event than 28 smaller, 2-kilogram females.

Scientists already knew this for some species, "but we didn't know it was so widespread," said ecologist Diego Barneche of the University of Sydney, who co-authored the study. Until recently, it was widely believed that for most fish, fecundity scaled linearly with size, meaning that 15 2-kilogram cod could lay the same number of eggs as one 30-kilogram cod. But this assumption is not only false, it may also severely underestimate the contributions of larger moms.

The new study looked at 342 fish species, including mackerel. Here a school swims in Bimini Island, Bahamas. OCEANA / Houssine Kaddachi

The Bigger, the Better

The study also found that hefty females lay bigger, more nutrient-rich eggs than small females. Previous research has shown that hatchling survival increases with both egg size and nutrient content. So, even if several small cod lay the same number of eggs as one large one, more of the larger cod's eggs are likely to survive to adulthood.

When calculating the amount of fish that can be sustainably harvested, fishery managers rarely factor the importance of big mothers into their equations, "and that may explain why some populations have declined," said Barneche.

However, some scientists are skeptical of that conclusion. Ray Hilborn at the University of Washington in Seattle, and Michael Sissenwine, a Massachusetts-based member of the New England Fishery Management Council, agree that large females disproportionately contribute to the reproductive pool, but hesitate to blame overfishing of large females for past population declines.

Populations of many commercially harvested species, including tuna, mackerel and bonito, did decline by as much as 74 percent between 1970 and 2010, according to a report published by the World Wildlife Fund and the Zoological Society of London. In roughly one-third of all fish populations, the largest, and therefore most valuable, fish have declined by 90 percent or more, one recent study found. That's even true for so-called sustainable fisheries, said Trevor Branch, a fishery scientist with the University of Washington in Seattle, who co-authored the study.

"We should think about how we can change our fishing to increase the big, old fish," Branch said. The Pacific rockfish fishery, and a few others, are already protecting big moms, he said, but more fisheries need to get on board—and fast.


Overfishing big females could be a factor in population declines, the authors say. But not all researchers agree. OCEANA / Enrique Talledo

Bringing Big Moms Back

Protecting important habitats is one way to make sure female fish get bigger.

One study found fish living within marine protected areas, or MPAs, are on average 28 percent longer than those living in unprotected areas. For the West Coast's formerly overfished populations of widow rockfish, a size increase of this magnitude would bolster a mother's reproductive output by 74 percent, according to Barneche's calculations.

But creating MPAs isn't the only way fishery managers can bring back big mothers. Limiting allowable catch size and temporarily closing some fishing areas can increase fish size across the board.

For fishery managers, the science is clear. Global fish stocks in decline will have a better chance of bouncing back if we leave more big fish in the ocean.

Show Comments ()

EcoWatch Daily Newsletter

Sponsored
Climate
350 .org / Flickr / CC BY-NC-SA 2.0

Taking Your First Steps Into Local Climate Action

Yes, yes—it can feel daunting. The climate crisis is more urgent than it's ever been. Some days we feel like we're making good progress, when we hear of countries powered by 100 percent renewable energy or a big commitment to take on fossil fuel corporations from a city like New York. But other days, it's a heavy burden knowing there's so much more that needs to be done to unseat the fossil fuel industry and move to a just, Fossil Free, renewably-powered world.

Keep reading... Show less
Food

'Eating Animals' Drives Home Where Our Food Really Comes From

It started with a call from actress and animal rights activist Natalie Portman to author Jonathan Safran Foer. The latter had recently taken a break from novel-writing to publish 2009's New York Times best-selling treatise Eating Animals—an in-depth discussion of what it means to eat animals in an industrialized world, with all attendant environmental and ethical concerns. The two planned a meeting in Foer's Brooklyn backyard, and also invited documentary director Christopher Dillon Quinn (God Grew Tired of Us) over. The idea was to figure out how to turn Foer's sprawling, memoiristic book into a documentary that would ignite mainstream conversations around our food systems.

Keep reading... Show less
Food

A Ghanaian Chef Feeding His Country and Combating Food Waste

Ghanaian chef Elijah Amoo Addo is on a mission to feed his nation on the excesses the food industry creates. Since 2012, he has been collecting unwanted stock or food nearing its use-by date from suppliers, farmers and restaurants in Ghana to redistribute to orphanages, hospitals, schools and vulnerable communities through his not-for-profit organization Food for All Africa. They provide meals through a Share Your Breakfast program in addition to donating stock to be used later. The organization supports and encourages communities to farm and works with stakeholders within Ghana's food industry on ways to combat waste.

Keep reading... Show less
Animals
Tucuxi Amazon river dolphins (Sotalia fluviatilis). Projeto Boto

Hunting, Fishing Cause Dramatic Decline in Amazon River Dolphins

By Claire Asher

Populations of two species of river dolphin in the Amazon are halving every decade, according to the results of a twenty-two year survey.

The Amazon rainforest is home to the Amazon river dolphin, or Boto (Inia geoffrensis) and the Tucuxi (Sotalia fluviatilis). But the results of a long-term study published in PLoS ONE show that both of these once abundant aquatic mammals are now in rapid decline in the Brazilian Amazon, likely due to hunting and fishing.

Keep reading... Show less
Sponsored
Energy

'Historic First': Nebraska Farmers Return Land to Ponca Tribe in Effort to Block Keystone XL

By Jessica Corbett

In a move that could challenge the proposed path of TransCanada's Keystone XL pipeline—and acknowledges the U.S. government's long history of abusing Native Americans and forcing them off their lands—a Nebraska farm couple has returned a portion of ancestral land to the Ponca Tribe.

Keep reading... Show less
Business

Sustainable Fashion Innovator Makes Fiber From Pineapple Leaves

In 1960, 97 percent of the fibers used in clothing came from natural materials. Today that number has fallen to 35 percent. But sustainable fashion veteran Isaac Nichelson wants to reverse that trend.

His company, Circular Systems S.P.C. (Social Purpose Corp.), has developed an innovative technology for turning food waste into thread, according to a Fast Company profile published Friday.

Keep reading... Show less
Sponsored
Politics
EPA Administrator Scott Pruitt at the U.S. House Committee on Energy and Commerce Subcommittee on Environment on April 26. EPA / YouTube

Chair of Senate Environment Panel to Call Scott Pruitt to Testify on Scandals

The Republican chairman of the Senate committee with oversight of the U.S. Environmental Protection Agency (EPA) plans to call the agency's embattled chief Scott Pruitt to testify, specifically in response to multiple scandals and investigations surrounding the administrator.

Through a spokesperson, Sen. John Barrasso, R-Wyo., informed Reuters of his decision to compel Pruitt to come before the Environment and Public Works Committee to answer questions about his alleged abuse of his office.

Keep reading... Show less
Politics
Pexels

Senate’s Farm Bill Moves Forward—But What Is It, Anyway?

By Shannan Lenke Stoll

The Senate Agriculture Committee just passed its version of a farm bill in a 20-1 vote Thursday. It's one more step in what has been a delayed journey to pass a 2018–2022 bill before the current one expires in September.

Keep reading... Show less
Sponsored

mail-copy

The best of EcoWatch, right in your inbox. Sign up for our email newsletter!