Our directory of things of interest

University Directory

Where have all the old fish gone?

Older fish have been proven to be more useful to the ecosystem than juveniles Older fish have been proven to be more useful to the ecosystem than juveniles Shutterstock
21 Sep
A study of various fish populations has found dramatic reductions in the proportion of older fish, something that spells trouble for the overall stability of population

Industrial-scale fishing practices have reduced the number of older individuals in around 80 per cent of fish populations around the world, according to scientists at the University of Washington. In fact, a third of populations have experienced a loss of 90 per cent since the beginning of large-scale, commercial fishing.

The fear is that fewer older fish will put whole populations at risk. ‘More age complexity among species can contribute to the overall stability of a community,’ explains Lewis Barnett, a post-doctoral researcher in fisheries and climate at the University of Washington. ‘If you trim away that diversity, you’re probably reducing the marine food web’s ability to buffer against change.’ Because fishing is usually unscrupulous about age, it follows that older fish are disproportionately in danger of being caught.

rockfishA copper rockfish (Image: Shutterstock)

‘Old’ is relative to the species in question – some species of rockfish can live as long as 200 years, while herring are lucky to last a decade. However, across all species, older fish are more successful breeders. They spawn more reliably, at different times of year and in different locations, often with bigger offspring. This increases the chance that hatchlings will emerge with the bloom of algae or zooplankton and survive. Juvenile fish, on the other hand, are less reliable breeders, they are vulnerable to predation and changes in environment such as water temperature and habitat.

‘The success rate of producing baby fish is extremely variable,’ says Trevor Branch, co-author of the study and an associate professor of aquatics at the University of Washington. He describes the older breeders as ‘an insurance policy’ saying that ‘they get you through those periods of bad reproduction by consistently producing eggs.’

The data was collected from 63 populations of fish across five ocean regions. Though it is not the first time fishing has been linked to removing older fish, it is the first study to demonstrate the global spread of the problem.

red line


Geographical Week

Get the best of Geographical delivered straight to your inbox by signing up to our free weekly newsletter!

red line

Related items

Geographical Week

Get the best of Geographical delivered straight to your inbox every Friday.


Subscribe to Geographical!

Adventure Canada


Aberystwyth University University of Greenwich The University of Winchester




Travel the Unknown


Like longer reads? Try our in-depth dossiers that provide a comprehensive view of each topic

  • National Clean Air Day
    For National Clean Air Day, Geographical brings together stories about air pollution and the kind of solutions needed to tackle it ...
    The Air That We Breathe
    Cities the world over are struggling to improve air quality as scandals surrounding diesel car emissions come to light and the huge health costs of po...
    Hung out to dry
    Wetlands are vital storehouses of biodiversity and important bulwarks against the effects of climate change, while also providing livelihoods for mill...
    When the wind blows
    With 1,200 wind turbines due to be built in the UK this year, Mark Rowe explores the continuing controversy surrounding wind power and discusses the e...
    The true cost of meat
    As one of the world’s biggest methane emitters, the meat industry has a lot more to concern itself with than merely dietary issues ...


NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...


So much photographic theory is dedicated to image sharpness that…


Changing temperatures in East Africa are set to upset a delicate…


As the planet warms and tensions rise, Marco Magrini finds that…


A deep-sea mission in the ocean around Bermuda confirms the…


An oxygen-deprived ‘dead zone’ in the Arabian Sea is much…


Scientists working with new drone technology are hoping to reveal…


A new virtual reality experience, ‘BBC Earth: Life in VR’,…


Faced with protecting a country more than 30 times the…


As Chile’s president leaves office, the country designates large expanses…


More than two years after first being announced, the International…


The winner of the 2018 Whitley Gold Award is Pablo…


Celebrate World Penguin Day with this selection of penguin-related stories…


It takes a lot more than the latest research data…


NGOs shine a light on the underreporting of wildlife crime…


Pioneering laser photography is being used by scientists on the…


Annual competition looks to celebrate island life in all its…


Increasing interest in offshore aquaculture is dividing environmentalists


Well-meaning promises don’t always have positive outcomes. Marco Magrini finds…


The RSPB introduces a new hotline for reporting the unlawful…


With the death earlier this week of the world’s last…