How will sharks respond to climate change? It might depend on where they grew up

How will sharks respond to climate change? It might depend on where they grew up
The smaller egg to the left is from Port Jackson sharks near Adelaide, while the right egg is from sharks in Jervis Bay. Credit: Connor Gervais, Author provided

They may have been around for hundreds of millions of years—long before trees—but today sharks and rays are are among the most threatened animals in the world, largely because of overfishing and habitat loss.


Climate change adds another overarching stressor to the mix. So how will sharks cope as the ocean heats up?

Our new research looked at Port Jackson sharks to find out. We found individual sharks adapt in different ways, depending where they came from.

Port Jackson sharks from cooler waters in the Great Australian Bight found it harder to cope with rising temperatures than those living in the warmer water from Jervis Bay in New South Wales.

This is important because it goes against the general assumption that species in warmer, tropical waters are at the greatest risk of climate change. It also illustrates that we shouldn’t assume all populations in one species respond to climate change in the same way, as it can lead to over- or underestimating their sensitivity.

But before we explore this further, let’s look at what exactly sharks will be exposed to in the coming years.

An existential threat

In Australia, the grim reality of climate change is already upon us: we’re seeing intense marine heat waves and coral bleaching events, the disappearance of entire kelp forests, mangrove forest dieback and the continent-wide shifting of marine life.

The southeast of Australia is a global change hotspot, with water temperatures rising at three to four times the global average. In addition to rising water temperatures, oceans are becoming more acidic and the amount of oxygen is declining.

Any one of these factors is cause for concern, but all three may also be acting together.

One may argue sharks have been around for millions of years and survived multiple climate catastrophes, including several global mass extinctions events.

To that, we say life in the anthropocene is characterised by changes in temperature and levels of carbon dioxide on a scale not seen for more than three million years.

Rapid climate change represents an existential threat to all life on Earth and sharks can’t evolve fast enough to keep up because they tend to be long-lived with low reproductive output (they don’t have many pups). The time between generations is just too long to respond via natural selection.

Dealing with rising temperatures

When it comes to dealing with rising water temperature, sharks have two options: they can change their physiology to adapt, or move towards the poles to cooler waters.

Moving to cooler waters is one of the more obvious responses to climate change, while subtle impacts on physiology, as we studied, have largely been ignored to date. However, they can have big impacts on individual, and ultimately species, distributions and survival.

We collected Port Jackson sharks from cold water around Adelaide and warm water in Jervis Bay.

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Finland’s third quarter GDP grew 3.3%, more than expected

FILE PHOTO: People walk past Stockmann shopping center in Helsinki, Finland, May 6, 2017. REUTERS/Ints Kalnins

HELSINKI (Reuters) – Finland’s third-quarter economic output rose 3.3% from the second quarter, Statistics Finland said on Friday, outstripping an earlier flash estimate of a rise of 2.6%.

The new estimate prompted Danske Bank chief economist Pasi Kuoppamaki to call it “an encouraging sign of the Finnish economy’s corona resilience”.

Statistic Finland also revised its estimate of the decline in Finnish second-quarter gross domestic product to 3.9% quarter-on-quarter, from a previous estimate of a 4.5% drop.

The earlier estimate of the second-quarter GDP drop caused by the COVID-19 pandemic was already the smallest among euro zone economies, according to estimates collected by Eurostat in September.

Year-on-year, Finland’s GDP fell 2.7% in the third quarter, Statistics Finland said.

Finland’s consumer confidence index recovered in November to -4.8 points but remained below its long-term average level of -1.8 points, Statistics Finland said.

“The corona epidemic has a clear impact on consumers’ sentiments, and thus the news on the coming vaccines have likely cheered up the expectations,” Kuoppamaki said in a statement.

Even so, the industry confidence indicator increased just one point from October’s figure, to -14 in November, well below its long-term average of +1. Production expectations for the coming months remained pessimistic among manufacturers, the Confederation of Finnish Industries said.

Reporting by Anne Kauranen, editing by Larry King

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How Megalodon Sharks Grew Up to Become Apex Predators of the Sea, According to Scientists

Researchers have uncovered evidence to suggest that the largest sharks to ever roam the seas commonly raised their young in nursery areas where juveniles could grow up in a safe environment.

The scientists identified five potential megalodon nurseries—one off the eastern coast of Spain, two in the United States and two in Panama—in a study published in the Royal Society journal Biology Letters.

Megalodon (Otodus megalodon) is an extinct shark species that lived between 23 million and 3.6 million years ago.

The shark is considered to be one of the largest and most powerful predators ever to have lived on Earth, with some estimates suggesting that it could have grown up to around 60 feet in length.

Despite its gigantic size, young megalodon would have been vulnerable to attacks by other predators.

In order to overcome this problem, the sharks gave birth to their young in shallow, warm water nurseries near coastlines where the juveniles would have had plentiful access to prey while also facing relatively few predators.

“Our results reveal, for the first time, that nursery areas were commonly used by the O. megalodon, reducing early mortality and playing a key role in maintaining viable adult populations,” the authors wrote in the study.

These nurseries would have provided the the young with a “perfect place to grow” as they matured into adults—a process that took around 25 years.

“Many of them were quite small for such a large animal,” two of the authors, Carlos Martinez-Perez and Humberto Ferron from the University of Bristol, U.K., told AFP.

An analysis of megalodon teeth found in nine locations around the world revealed the sites of the five potential prehistoric nurseries, according to the study.

Examining the size of these teeth, the researchers concluded that these locations contained a high density of sharks that likely had body lengths within the typical range of newborns and young juveniles, suggesting the presence of prehistoric nurseries.

The nursery off Spain’s east coast would have been a “shallow bay area of warm waters, connected to the sea and with extensive coral reefs and plenty of invertebrates, fish species, marine mammals and other sharks and rays,” the authors said.

But the scientists note that megalodon’s apparent reliance on the existence of suitable nursery areas may have been a key factor in the demise of this iconic predator as the world cooled during the Pliocene period (around 5.3 million to 2.5 million years ago) and sea levels declined, leaving fewer of these safe havens.

megalodon
Stock image showing megalodon teeth.
iStock

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