Can a Salmon Shark Live in Freshwater?

It lives in the cold waters of the North Pacific and is called the salmon shark (Lamna ditropis). As their name suggests, salmon are a major part of their diet. But this shark only lives in salt water. Can a salmon shark live in lakes and rivers with fresh water?

The short answer is no. Salmon sharks are unable to live for extended periods in freshwater environments. Read on to learn more about why salmon sharks can’t live in fresh water and must stay in the ocean and seas.

Salmon Shark Habitat and Range

Salmon sharks have a wide range in the northern Pacific Ocean. They are found from the Gulf of Alaska down to Baja California. Some individual sharks have even been recorded as far south as Hawaii.

However, this species always sticks to marine habitats. They prefer cooler offshore waters but can be found closer to shore, especially during salmon runs.

Common salmon shark environments include

• Open ocean
• Coastal areas
• Inshore zones around islands
• Nearshore waters during salmon migration

Within their oceanic habitat, salmon sharks dive to depths of over 1,000 feet But they rarely enter enclosed bodies of freshwater

Why Salmon Sharks Cannot Survive in Freshwater

There are a few key reasons salmon sharks are unable to live for long periods in freshwater:

• Osmoregulation difficulties – Sharks maintain internal salt levels higher than the surrounding water. This is disrupted in freshwater.

• No gills adapted to freshwater – A salmon shark’s gills are designed to filter out salt from seawater. They cannot properly extract oxygen from freshwater.

• Reproduction issues – Sharks use internal fertilization and give live birth. The change to a freshwater environment could disturb their reproductive cycle.

• No food sources – Salmon sharks feed on marine organisms like salmon, squid, and herring. Freshwater ecosystems do not contain their prey.

• Temperature – Salmon sharks thrive in cold saltwater. Warm freshwater temperatures could overheat and stress the shark.

• Oxygen levels – Freshwater tends to have lower dissolved oxygen levels than seawater. Salmon sharks require highly oxygenated water.

Let’s look at these factors in more detail:

Osmoregulation Challenges

Like all elasmobranchs, the salmon shark maintains internal salt levels higher than the surrounding seawater. This saltier shark blood allows them to retain water and avoid dehydration in the ocean.

However, in freshwater environments, the reverse happens. The lower salt content of the water causes water to flow into the shark’s body. This disrupts their electrolyte balance.

While salmon sharks can survive short stints in freshwater, their osmoregulation system cannot adapt to permanently live in these conditions.

Gills Designed For Saltwater

A key reason salmon sharks cannot osmoregulate well in freshwater is their specialized gill structure.

Their gills are evolutionarily adapted to filter out and excrete excess salts from seawater. Salmon shark gills cannot properly extract oxygen from freshwater since there are minimal salts to excrete.

The gills would also have trouble eliminating the excess water brought in by osmosis in a freshwater habitat.

Reproductive Concerns

Salmon sharks use internal fertilization and give live birth to pups rather than laying eggs. The embryos start out feeding on yolk sacs before moving on to eating unfertilized eggs from the mother (oophagy).

This complex reproductive strategy relies on specific conditions tuned to a saltwater environment. If a pregnant female salmon shark entered freshwater, it could interfere with her pup’s development and ability to feed on the uterine eggs.

Since newborn salmon sharks are not well developed, giving birth in freshwater would likely not be survivable for the pups.

Lack Of Suitable Freshwater Prey

Salmon sharks feed on fast swimming, migratory marine species like salmon, herring, and squid. Occasionally they take seabirds as well.

But freshwater lakes and rivers do not contain these prey sources. The shark would need to adapt to hunting completely new types of slower freshwater fish and animals, like trout and frogs.

Finding adequate nutrition to sustain their large size would be a challenge in the freshwater food web. Their marine adapted hunting skills would also be ineffective in a lake or river.

Warm Water Temperatures

Salmon sharks thrive in cold North Pacific waters with temperatures ranging from 43 to 60°F. However, freshwater lakes and rivers tend to be significantly warmer during summer months.

Extended time in water above 60°F could cause heat stress in salmon sharks. Their bodies are designed to conserve heat, not dissipate excess warmth.

Until the water cooled down in winter, the warmth could become fatal if the shark could not return to the temperature regulated ocean habitat.

Lower Oxygen Content

Salmon sharks require lots of dissolved oxygen to maintain their active, fast swimming lifestyles. While cold water holds more oxygen, freshwater actually has lower oxygen content than seawater.

Stagnant lakes and backwater areas off major rivers can be especially low in oxygen content. This could suffocate the gills of salmon sharks used to highly oxygenated saltwater.

In combination with their difficulties extracting oxygen in freshwater, the lower oxygen levels create a major survival hurdle.

Can Salmon Sharks Enter Freshwater At All?

Given all the above factors, salmon sharks clearly cannot live for long in freshwater or migrate between oceans and lakes like salmon. However, brief excursions into freshwater are possible.

During the salmon run, salmon sharks may follow prey upriver for short distances. But they ultimately have to return to the ocean before the disruptions to their salt balance and other systems becomes fatal.

There are also no reports of salmon sharks entering other types of freshwater bodies like lakes. While not impossible, this species sticks to the domain of oceans it is superbly adapted for rather than freshwater habitats.

Unusual Freshwater Sighting In Idaho River

In a viral news story from 2023, a deceased salmon shark mysteriously appeared on the banks of the Salmon River in Idaho. Since salmon sharks only inhabit saltwater, it caused quite a stir!

While shocking, the shark almost certainly did not swim up the Salmon River on its own. Experts believe the 3 foot long dead shark was caught by fishermen at sea, transported inland, and dumped along the freshwater river as a prank.

So while interesting, this case does not show salmon sharks can migrate into and survive in freshwater systems. They are still bound to their marine habitat.

Brief stints near river mouths may be possible during the salmon run. But remaining permanently in freshwater would disrupt a salmon shark’s osmoregulation, respiration, hunting ability and ultimately prove fatal. These powerful sharks remain masters of the temperate ocean habitats they have long evolved to dominate.