Seals could be hit by shrinking portion sizes as scientists warn climate change will cause substantial prey like cod to die off, forcing them to hunt harder for smaller fish

• Climate change will shrink the size of certain fish that seals feed on, forcing them to eat less fulfilling fish  
• Popular seal prey in the Hudson Bay – such as Arctic cod – could see their population figures slump in the next few years
• Cod will decline between 18-35% in size and Pacific sand lance will decline between 45-82%   
• It’s unclear what the consequences would be to eating less fulfilling fish 
• All fish species declined in body size according to the model

Climate change will deplete stocks of fish that Arctic predators, such as ringed seals, feed on, forcing them to go after smaller, less nourishing prey, a new study warns.

The study, put together by researchers at the University of British Columbia, suggests that changes to both fish numbers and their size in the Hudson Bay in Canada will accelerate by 2025. 

Cod stocks will decline between 18 and 35 percent and Pacific sand lance will decline anywhere between 45 and 82 percent.  Those species body size will also shrink, meaning seals which find them won’t have as nourishing a meal. 

Climate change will shrink the size of certain fish that seals feed on, forcing them to eat less fulfilling fish

The size and population of fish in the Hudson Bay — such as the Arctic cod — will accelerate by 2025 and population figures could drop by 50%

Cod will decline between 18-35% in size and Pacific sand lance will decline between 45-82%

They estimate that if the atmosphere continues to be impacted by greenhouse gasses, such as carbon dioxide and methane, all varieties of fish in the study will shrink in size.  

‘This decrease in body size, along with a shift from the energy- and lipid-rich Arctic cod to smaller forage fishes, may result in seals feeding on more on ‘junk food’ with un-known demographic consequences, but perhaps including reduced energy reserves (stored as blubber),’ the authors wrote in the study.  

All fish species declined in body size according to the model, but there was a 29 percent increase in total prey biomass, meaning that smaller fish, such as capelin and sand lance, may become more prevalent. 

‘It costs energy to forage,’ the study’s lead author, UBC student Katie Florko, said in a statement.  

‘Does that mean the seals will need to spend more energy to get a larger number of these smaller fish for the same amount of energy as capturing a bigger fish?’ 

Florko continued: ‘It’s not unlike how the burgers in fast food restaurants seem to get smaller and smaller every year, and you’re getting less bang for your buck.’ 

With Arctic waters heating up due to climate change, the cod will head north and decline in numbers, the researchers said

It’s unclear what the consequences would be to eating less fulfilling fish and not cod (pictured)

All fish species declined in body size according to the model, but there was a 29 percent increase in total prey biomass, meaning that smaller fish, such as capelin and sand lance (pictured), may become more prevalent

With Arctic waters heating up due to climate change, the cod will head north and decline in numbers, the researchers said. 

The findings are not unexpected. Several other studies in recent memory have suggested that fish will get smaller as the world warms, because they will have to increase their metabolism and will need more oxygen to sustain their bodily functions. 

A study published in February looked at fish size and bottom sea temperatures over the past 30 years and concluded that the size of adult fish, including cod, haddock and whiting, are shrinking. 

In August, a separate study suggested that other fish, such as sardines, pilchards and herrings, are shrinking and at risk of extinction due to climate change. 

Last month, a report from the United Nations said the planet will heat up by 2.7 degrees Fahrenheit by 2040, a decade earlier than forecast.   

As larger fish have greater energy reserves to call upon in comparison with smaller fish, a reduction in size will reduce the distances over which fish can travel, and limit their ability to seek out more suitable environments as the climate changes.

For other animals, the situation is more complex, Florko noted. 

Beluga whales feast on capelin in the summer, but dine on Arctic cod in the fall to store body fat.   

‘We’ve never seen such drastic change so quickly,’ said Travis Tai, a co-author of the study.

‘We’re rolling the dice, and we don’t know what exactly will happen. 

‘When we have dramatic shifts in food web structures, we can expect large changes not only to how species such as ringed seals use the oceans, but also how people use the oceans.’

The study was published last month in the journal Ecology Letters. 

A recent study in Canada found that over the last century, the beetles in the region have shrunk.

By looking at eight species of beetle and measuring the animals from past and present they found that some beetles were adapting to a reduced body size.

The data also showed that the larger beetles were shrinking, but the smaller ones were not. 

Around 50 million years ago the Earth warmed by three degrees Celsius (5.4°F) and as a result, animal species at the time shrunk by 14 per cent. 

Another warming event around 55 million years ago – called the Paleocene-Eocene Thermal Maximum (PETM) – warmed the earth by up to eight degrees Celsius (14.4°F).

In this instance, animal species of the time shrunk by up to a third. 

Woolly mammoths were a victim of warming climate, shrinking habitat and increased hunting from a growing early-human population which drove them to extinction – along with many large animals

Shrinking in body size is seen from several global warming events.

With the global temperatures set to continue to rise, it is expected the average size of most animals will decrease. 

As well as global warming, the world has seen a dramatic decrease in the amount of large animals. 

So called ‘megafauna’ are large animals that go extinct. With long life-spans and relatively small population numbers, they are less able to adapt to rapid change as smaller animals that reproduce more often. 

Often hunted for trophies or for food, large animals like the mastadon, mammoths and the western black rhino, which was declared extinct in 2011, have been hunted to extinction. 

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