Tag Archives: Pacific Salmon

Osmoregulation in Salmon

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Osmoregulation is the process of maintaining salt and water balance across the body’s membranes. Any fish faces a challenge to maintain this balance. A freshwater fish struggles to retain salt and not take on too much water, while a saltwater fish tends to lose too much water to the environment and keeps a surplus of salt. Fish have developed behaviors and physiological adaptations to survive in their environments, whether fresh or marine water, but how do fish manage to thrive in both fresh and saltwater?

A catadromous fish spends most of its life in freshwater and then migrates to the ocean to breed. Eels of the genus Anguilla represent catadromous organisms. Anadromous fish begin life in freshwater, spend most of their lives in saltwater, and then return to freshwater to spawn. Pacific salmon and some species of sturgeon are anadromous fish.

How does a salmon maintain the composition of its body fluids within homeostatic limits? How does it reverse its osmoregulation physiology when it swims from a freshwater environment into the ocean or from the ocean to freshwater?

In the ocean, a salmon swims in a fluid nearly three times more concentrated than the composition inside its cells. In such an environment, the fish tends to take on salt from the water and lose water to the denser ocean. This exchange would result in severe dehydration and quickly kill the salmon if the fish did not adequately deal with the issue.

A Salmon faces the opposite problem in freshwater, where it lives in a solution nearly devoid of salts. In this case, the fish has more salt in its body than in its environment, presenting the problem of losing salt to the environment while flooding its body with water.

How does a salmon deal with these two warring issues of osmoregulation? The salmon has evolved behavioral and physiological adaptations to allow it to live in both fresh and saltwater habitats.

In the ocean, a salmon drinks several liters of water a day to maintain its water volume, but in freshwater, it does not drink at all, except for what it takes on during feeding. In freshwater, a salmon’s kidneys produce a large volume of very dilute urine to offset the excess water diffusing into its body fluids. In the ocean environment, though, a salmon’s urine is highly concentrated, consisting mostly of salt ions, and it excretes very little water.

A salmon also has a remarkable adaptation that allows osmoregulation by the fish in both marine and freshwater environments. A salmon uses energy to actively pump Na and Cl ions across the gill epithelial cells against their concentration gradients. In saltwater, the fish pumps NaCl out of its blood and into the surrounding ocean. In freshwater, the pump works in reverse, moving NaCl out of the water, over the gills, and into the blood.

These amazing behavioral and physiological adaptations allow a salmon to move from fresh to saltwater when the fish leaves its nursery area to travel to its ocean feeding grounds and then back from its marine habitat to freshwater when the salmon returns to spawn. The critical changes in osmoregulation are not immediate, though. When a salmon smolt first leaves its home stream, it must rest in brackish water for several days or weeks while it adjusts, and then it will slowly move into water with higher salt concentrations. As the smolt adjusts, its kidneys begin producing more-concentrated urine while the NaCl pumps in its gills reverse direction and start pumping NaCl out of the blood. When the salmon returns to its natal stream to spawn, it must again remain in brackish water for a period while its kidneys adjust, and the NaCl pump changes direction to pump NaCl out of the water and into the blood.

I am always amazed by how animals and plants adjust to the demands of their environment. Anadromous and catadromous fish, however, must adapt to two environments with opposite physiological requirements, and to do this, they flip the switch on osmoregulation from one extreme to the other.

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Robin Barefield is the author of four Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter, and Karluk Bones. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.

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What is the difference between Atlantic and Pacific Salmon?

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How are Atlantic and Pacific salmon related to each other, and how do their lifecycles differ?

As their names suggest, Atlantic salmon are originally from the Atlantic Ocean, while Pacific Salmon are from the Pacific Ocean. Atlantic and Pacific salmon belong to the family Salmonidae, but Pacific salmon belong to the genus Oncorhynchus while Atlantic salmon (Salmo salar) are the largest members of the genus Salmo. Atlantic salmon are more closely related to certain species of trout, such as brown trout (Salmo trutta), than they are to Pacific salmon.

There is only one species of Atlantic salmon, and members of this species are silvery with large, black spots on their gill covers and back. The five species of Pacific salmon are pink salmon, also known as humpies; chum salmon, also known as dog salmon; red salmon, also known as sockeyes; silver salmon, also known as coho; and king salmon, also known as chinook. Pacific salmon, like Atlantic salmon, are sleek and silvery in their marine phase, but once they enter fresh water, they go through significant physical changes, and each species has distinctive markings. The photos below show a sockeye salmon in the marine phase and in the spawning phase when the salmon returns to freshwater.

The lifecycles of natural populations of Atlantic and Pacific salmon are similar. Atlantic salmon spend one to four years in the ocean before returning to spawn in the freshwater stream where they were born. One big difference, though, is Atlantic salmon don’t always die after they spawn. Pacific salmon are semelparous, meaning they die after they spawn. Atlantic salmon are iteroparous which means they might recover, return to the sea, and repeat the migration and spawning pattern. Spawning takes a huge physiological toll on a salmon, though, and most Atlantic salmon do not survive to spawn a second or third time.

Are Atlantic or Pacific salmon healthier to eat?

Controversy swirls over the health benefits of eating Atlantic and Pacific salmon. This debate has nothing to do with wild Atlantic salmon, though. Most salmon sold in the U.S. are farmed Atlantic salmon. Salmon sold as “wild” salmon are Pacific salmon. Sadly, most wild Atlantic salmon stocks were wiped out or severely depleted years ago by over-fishing, but in a few places, these wild stocks are recovering.

The question then becomes is farmed or wild salmon healthier to eat, or does it matter?

What are the health differences between eating a wild or farmed salmon?

Salmon is good for you. Both wild and farmed salmon are high in Omega-3 fatty acids, a fat with many health benefits. Farmed salmon, though, also have other fats which are not as good for humans. A half-pound filet of wild salmon has 281 calories, while a half-pound fillet of farmed salmon contains 412 calories. Farmed salmon is loaded with twice as much fat as wild salmon and three times more saturated fat. Wild salmon packs more calcium, iron, potassium, and zinc and less sodium than farmed salmon. Depending on the farm, farmed salmon might have higher levels of contaminants than wild salmon, but biologists believe farmed salmon is safe to eat.

Most experts agree if you have a choice, eat wild salmon, but farmed salmon is better than no salmon, and farmed salmon is more readily available, can be found year-round, and usually costs less.

I think the biggest difference is taste. Wild Pacific salmon has a rich, robust flavor, while farmed salmon often tastes bland.

Could farmed fish threaten native species?

One of the biggest concerns biologists have about farmed salmon is that the salmon will escape their pens and become an invasive species. How these farmed salmon might affect wild salmon populations, no one knows, but biologists fear farmed salmon might spread parasites and diseases. Atlantic and Pacific salmon can’t interbreed because they belong to different genera, but these salmon have similar lifecycles. Would escaped farmed fish compete with native fish for habitat and food?

In 2017, 300,000 Atlantic salmon escaped from a farm in the San Juan Islands in Puget Sound, Washington, and alarmed Alaska Fish and Game biologists sent out an alert to all anglers to be on the lookout for invasive Atlantic salmon.

What is the difference?

Atlantic salmon are large trout, but Pacific and Atlantic salmon look similar and have comparable life cycles. Atlantic salmon don’t necessarily die after they spawn, but Pacific salmon always die after they return to a freshwater stream to spawn.

Atlantic salmon are rare in nature because over-fishing has decimated their stocks. Atlantic salmon fillets you find in the grocery store come from farmed salmon. If you see a Pacific salmon fillet in a store or restaurant in the U.S., it almost certainly originated from a wild salmon.

Both wild and farmed salmon are high in Omega-3 fatty acids, but farmed salmon contains other fats not good for you. Farmed salmon fillets appear paler than wild salmon, and they are not as flavorful as wild Pacific salmon.


Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. If you like audiobooks, check out her audiobook version of Murder Over Kodiak. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.

 

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Why Do Salmon Jump And Other Questions

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Why do salmon jump?

This is the question our guests most frequently ask about salmon as they watch fish pop out of the water around them. The answer is: no one knows. Some speculate salmon jump to loosen their eggs from the membrane encasing them, but males also jump, so this reasoning doesn’t work. Another explanation is they jump to catch flying insects, but their jumping behavior increases in frequency as they near their spawning stream at the same time their digestive system is shutting down and they stop feeding, so this explanation also is not valid.

I like to tell our guests the salmon they see jumping are teenagers. As a salmon prepares to spawn, its hormones rage and its body changes color and shape. These jumping fish are the equivalent of a human teenager, so they act like teenagers. While this explanation is always good for a laugh, there is no scientific evidence to support it.

My opinion, for what it’s worth (and not much, since there is also no scientific evidence to support this), is salmon have evolved to jump because jumping is beneficial to their survival. Salmon that have inherited the genetic characteristic to jump when they near their home stream are more likely than those who cannot jump to make it upstream and spawn. They then pass along this trait to jump to their offspring. Evolution has selected this jumping trait. Most salmon spawn in small streams and they must navigate shallow water, rapids, and sometimes even waterfalls. If they couldn’t jump, many salmon would never make it to their spawning grounds. Again, this explanation is only my opinion, but I believe it has some merit.

The correct answer to the question, “Why do salmon jump?” is: no one knows.

Do all salmon return to spawn in the same river or stream in which they were born?

No. A small percentage of salmon spawn somewhere other than where they were born. This behavior is called “straying,” and it is adaptive because it allows salmon to colonize streams that do not currently have a salmon population. It also allows salmon to spawn somewhere if the stream where they were born no longer exists. Pink salmon and chum salmon both often spawn close to the mouths of small streams. If these streams are diverted by winter storms, as often happens, the returning salmon will stray to a nearby stream.

When a salmon returns from the ocean, how does it find its spawning stream?

Salmon must navigate a long distance from the open ocean to their spawning stream. Evidence shows they use magnetic cues, the position of the sun, and day length to know when to begin their migration back to their natal stream and how to get there. Once salmon near and enter fresh water, scientists think they use their sense of smell to find not only their home stream or river but the specific tributary or area of the river where they were born. Juvenile salmon imprint on the unique chemical signatures of the waters where they were born and occupied as fry as well as on the waters they migrated through to get to the ocean. When they return to spawn, they follow this chemical smell back to where they were born.

How many salmon eggs hatch, develop, and return as adults to spawn?

Salmon have tough lives. From the egg stage, until they spawn and die, they are a food source for a wide variety of fish, birds, and mammals, including man. Biologists estimate 1 in 1000 eggs will develop, find their way to the ocean, swim back to their natal stream, and spawn. Depending on the species and the age of the fish when she spawns, a female salmon lays between 1000 and 6000 eggs, so the survival rate is not good.

I hope I’ve answered a few of your questions about the amazing Pacific salmon. Next week, I will tackle a big question. What is the difference between Atlantic and Pacific salmon?

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If you haven’t seen my webinar on how I became an author and why I write Alaska wilderness mysteries, this is the link: http://bit.ly/2pcCOo6. If you like it, please share it with your friends. The free book offer is sincere, and there is no catch. Also, please sign up for my free, monthly newsletter about true murder and mystery in Alaska. This month I am writing about the Fairbanks Four. Four young men spent 18 years in prison for a murder they didn’t commit. 

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Which Salmon Is It?

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Over the past several weeks, I’ve been writing about Pacific salmon, so this week, I want to pause a minute and review. In their marine phase, the five species of Pacific salmon are hard to tell apart. Their life cycles are similar, and sometimes all five species spawn in the same river/lake system. What are their differences, and how do you tell one species from another?

Perhaps you are thinking, why should I care if I can differentiate between salmon species? Let’s pretend you are fishing in Alaska on a river where all five Pacific salmon species are present. It is legal to keep pink salmon, chums, and cohos, but you must release sockeyes and kings. You catch a beautiful, silvery salmon. You know right away it hasn’t been in fresh water long enough for its color and body shape to change. You also know if it is still silver in color, its flesh will be firm, and it will be good to eat. Is this one of the species you can keep, or must you release this fish?

The size of the fish is a clue, but often, different year classes of a species return to the same river, so size is not definitive. Does the fish have spots, and if so, where and how big? Spots are more visible when a salmon gains its spawning coloration, but if you look closely, the spots are visible in the silvery marine phase. Pink salmon have large, oval spots on the back and both lobes of the tail. Cohos have small black spots on the back and the upper lobe of the tail. Kings have spots on the back and both lobes of the tail. Sockeyes and chums have no spots on their backs or tails.

While you are looking at the tail, do you see any silver streaks? Cohos and kings have silver streaks radiating along the rays of the tail. Chums also have silver streaks but only on half the tail.

The mouth is another distinguishing characteristic. King salmon have a black mouth with a black gum line and a black tongue. Pinks also have a black gum line, but they have a white mouth. The other three species all have white mouths and white gum lines.

A chum salmon has a white tip on the anal fin, an important characteristic to note when trying to differentiate a chum from a sockeye.

Other distinguishing characteristics you can use include the size of the eye, scale size, and the shape of the tail, but none of these are easy to employ unless you are comparing one salmon to another.

Take a look at the salmon you caught. It weighs about four pounds and has spots on the back and both lobes of the tail. You think you see silver streaks in the tail, but you’re not certain, so you check the mouth and note a black gum line and a black mouth. You are allowed to keep the fish if it is a pink,  chum, or silver salmon, but you must release it if it is sockeye or king. Will you be able to grill this salmon for dinner, or should you carefully release it back into the stream?

The size of the fish, and the spots on the back and both lobes of the tail may lead you to jump to the conclusion you caught a pink salmon, and you can keep it. Only pinks and kings have spots on both lobes of the tail, so you can quickly rule out the other three species. The silver streaks in the tail may be hard to see, so you wisely check the mouth. Both pinks and kings have black gum lines, but only king salmon have a black mouth, including a black tongue. Take a closer look at the fish. Are the spots small or are they large and oval? If you said small, you have your answer. You caught a small, probably a mature 3-year-old king salmon, and you must release it.  

It takes practice to identify a silvery Pacific salmon in its marine phase. Commercial fishermen can quickly differentiate one species from another, but if you only occasionally fish for salmon, one silver salmon looks much like the next. If you can’t identify the salmon you caught, you must release it, so if you plan to go salmon fishing in Alaska without a guide, you should do your homework first.

Next week, I’ll write about some of the questions we are commonly asked about salmon, and I will do my best to answer them.

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I am excited to announce the webinar I told you about last week explaining how I became an Alaska wilderness mystery writer and where I get some of my ideas for my novels, has now been released. To see the webinar, follow this link: http://bit.ly/2pcCOo6. I used many of Mike’s photos and my friend, Ryan Augustine’s photos and videos in the webinar, so I think you will enjoy it. Please share the webinar link with your friends and family. If you stay until the end, you can get a free e-book of one of my novels. The purpose of the webinar is to introduce myself and my books to a wider audience, so the more you share this link, the happier I will be! Thank you!

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King (Chinook) Salmon (Oncorhynchus tshawytscha)

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King salmon, also called Chinook salmon (Oncorhynchus tshawytscha) are the largest Pacific salmon, and they are also the least abundant of the Pacific salmon species. Adult kings average 24 to 36 inches (61 to 91 cm) in length but may be as long as 58 inches (150 cm). They average 10 to 50 lbs. (4.5 to 22.7 kg) but sometimes grow much larger. The world record sport-caught king, caught on May 17th,1985 in the Kenai River in Alaska, weighed 92.25 lbs. (44.11 kg.), and the largest king salmon caught by a commercial fisherman weighed 126 lbs. (57 kg). This fish was caught near Rivers Inlet, British Columbia in the 1970s.

King salmon can be distinguished from other Pacific salmon species by the black spots present on their head and on both the upper and lower lobes of the tail and by their black gums. In their marine phase, kings are dark green to blue on the top of the head and back and silver to white on the sides, belly, and tail. When they return to fresh water to breed, they turn olive brown, red, or purple in color. Males are more brightly colored than females. In the ocean, kings are torpedo-shaped with a heavy mid-section and a blunt nose. During their breeding phase, males develop a hooked nose and enlarged teeth. Fry can be identified by well-developed parr marks extending below the lateral line. When they become smolt and are headed for the ocean, they have bright, silver sides, and the parr marks recede to above the lateral line.

In North America, king salmon range from Monterey Bay in California to the Chukchi Sea in Alaska. On the Asian coast, kings occur from the Anadyr River in Siberia to Hokkaido, Japan. In Alaska, they are most abundant in the Yukon, Kuskokwim, Nushagak, Susitna, Kenai, Copper, Alsek, Taku, and Susitna Rivers. Kings have been introduced to many areas, including the Great Lakes of North America, Patagonia, and New Zealand. King salmon are raised in pens in New Zealand and are an important export for the country.

King salmon spawn in fewer rivers than other Pacific salmon because they require larger, deeper rivers and spawn only in areas with good water flow through the gravel. They migrate from the ocean back to their birth streams in the winter and early spring, and while some enter fresh water as early as May, most enter streams in late June or early July. Most Alaska rivers receive only a single run of kings each year. Usually, those entering the streams first are the ones that will travel the furthest. Yukon River kings may travel more than 2000 miles (3219 km) to the headwaters of the Yukon River to spawn.

When a female king arrives in the spawning area, she selects a spot for her nest. She swims to the bottom of the stream, turns on her side and gives several powerful thrusts with her tail to remove gravel from the stream bottom. She continues to dig, resting occasionally, until she has a long, deep nest. While she is digging her nest, she drives off any other females that approach but pays little attention to the males. She is usually accompanied by a dominant male and one or two subordinate males. The dominant male, and occasionally one of the subordinate males, drive off any other male intruders. The males do not help with the nest digging, but the dominant male may court the female by resting beside her and quivering or by swimming over her and touching her dorsal fin with his body and fins.

When the nest is finished, the female drops into it followed by the dominant male and sometimes one or more of the subordinate males. The fish open their mouths, quiver, and release their eggs and sperm. The female then swims to the upstream end of the nest and begins digging a second nest, covering the eggs in the first nest with the gravel she unearths for the second nest. She continues digging four or five nests or more over the next several days and lays between 3,000 and 14,000 eggs. Even after all her eggs are laid, she continues digging in a haphazard manner until she weakens and dies. The male may mate with another female, but he also will soon die.

In Alaska, king salmon eggs hatch in the late winter or early spring, depending both on when they were laid and the temperature of the water. The hatchlings are called alevins, and they live in the gravel for several weeks, receiving nutrition from their attached yolk sac. Two to three weeks later, the young fry, as they are now called, wiggle up through the gravel and begin to feed on their own. Fry in fresh water feed on plankton and insects. Some kings, called “ocean-type,” migrate to saltwater during their first year. “Stream-type” kings remain in fresh water for one or even two years. In Alaska, most kings remain in fresh water one year and then migrate to the ocean as smolts the following spring.

In the ocean, king salmon eat herring, pilchard, sandlance, squid, crustaceans, and other organisms. They are voracious feeders, and they grow rapidly in the ocean, often doubling their weight in just one summer. Most king salmon have pink or red meat, but 3% of all kings have white meat. In Southeast Alaska, as many as 40% of the kings in some runs have white flesh. Biologists are unsure whether the variable meat color is due to genetics or to what the fish eat.

Kings become sexually mature anywhere from their second to their seventh year, so they vary greatly in size when they return to spawn. A mature three-year-old king, called a “jack,” would weigh less than four pounds (1.8 kg) while a mature seven-year-old would probably weigh more than fifty pounds (22.7 kg). Males mature earlier than females, so most jacks are males, and in many spawning runs, males outnumber females in all but the six-and-seven-year age groups.

King salmon are considered relatively uncommon but not rare in Alaska, but in some rivers their numbers have dropped drastically in the past few years. Over the next two weeks, I’ll write about the various fisheries for kings and the controversies swirling around them.

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Sockeye (Red) Salmon (Oncorhynchus nerka)

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Sockeye salmon also called red salmon and sometimes blueback salmon, are larger than pink salmon but average smaller in size than other Pacific Salmon species. Sockeyes measure between 18 and 31 inches (45.7-78.7 cm) in length and weigh between 4 to 15 pounds (1.8-6.8 kg). In their marine phase, sockeyes have iridescent silver sides, a white belly, and a metallic green-blue back. Due to this marine coloration, sockeyes are sometimes called blueback salmon. While they can have fine, black speckles on their backs, they lack the large spots found on other species of Pacific Salmon. The flesh of a sockeye in the marine phase is bright orange and firm. This beautiful, firm flesh with its rich flavor makes sockeyes highly prized and a culinary favorite.

When sockeyes return to their natal streams to spawn, their bodies turn bright red, and their heads become green. They are called red salmon because of this spawning coloration. In addition to changing color when they return to spawn, males develop a humped back, and hooked jaws called a kype. Breeding females are paler in color than males.

Unlike pinks, chums, and cohos that can spawn close to the mouths of small streams, sockeye salmon usually spawn in large, complex river/lake systems. Most sockeyes spawn either in streams connected to lakes or along the lakeshore in areas of upwelling. Because a sockeye requires unimpeded access to a lake to complete its life cycle, it is susceptible to habitat manipulation or degradation. Not only man but also beavers can alter a river system by building dams, effectively blocking a river or stream and denying salmon access to the lake.

The natural range for sockeyes is from the Klamath River in California and Oregon north to Point Hope in Alaska. In the western Pacific, sockeyes range from the Anadyr River in Siberia south to Hokkaido, Japan. Sockeyes are most numerous in the Fraser River system in British Columbia and the Bristol Bay system, including the Kvichak, Naknek, Ugashik, Egegik, and Nushagak rivers. Some populations of sockeyes do not migrate to the ocean but spend their entire lives in freshwater. These landlocked salmon are called kokanee salmon. Kokanees are found from Siberia to Japan on the Asian side of the Pacific and In North America from the Kenai Peninsula to the Deschutes River in Oregon. Kokanees have been widely introduced to lakes in the U.S., including the Great Lakes.

In Alaska, sockeye salmon return from the ocean to spawn from July to October. Like other Pacific Salmon species, sockeyes spawn in the streams where they were born. Some sockeyes spawn in streams not connected to lakes and others spawn near the lakeshore, but most spawn in streams attached to a lake. A female digs a nest in the stream bottom by giving several, powerful strokes of her tail. Once she finishes digging the nest, she rests while a dominant male courts her by nudging her side with his snout and then coming to rest beside her and quivering. The female then drops into the nest, and the male follows, stopping beside her. Both fish arch their bodies, open their mouths and quiver, releasing their eggs and sperm. Other males may also enter the nest and release sperm. The female will continue to dig nests until she has deposited all her eggs. She usually digs three to five nests over the course of three to five days, and she may breed with several dominant males. A female deposits between 500 to 1,000 eggs in a nest and lays a total of 2,500 to 4,300 eggs. A male sockeye may breed with several females, and both male and female sockeyes die within a few weeks after spawning.

Sockeye eggs hatch in the winter, and the young alevins remain in the gravel, gaining nutrition from their yolk sacs until spring when they emerge into the stream. At this stage of their lives, the young sockeyes are called fry and have dark, short, oval parr marks on their sides. Fry move out of the stream and into the lake where they spend one to three years in fresh water, feeding on zooplankton and small crustaceans. As they prepare to leave the lake, sockeyes lose their parr marks and turn silvery. They are now called smolts. Smolts weight only a few ounces when they enter the ocean, but they begin to grow quickly, mostly feeding on plankton, insects, and small crustaceans. A sockeye’s beautiful orange flesh comes from eating plankton and krill in the ocean.

Sockeyes spend one to four years in the ocean where they travel nearly continuously, covering as many as 2300 miles (3700 km) in one year. As it begins the return trip to its spawning stream, a mature sockeye swims even faster, covering 28 to 35 miles (45-56 km) per day during its last two months at sea. Sockeyes are prey for nearly every animal they encounter that is bigger than they are, and they are a valuable species for commercial fishermen.

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Next week, I will cover the commercial and sport fishery for sockeyes as well as the status of sockeye populations and threats to their survival, including the controversial proposed Pebble Mine in Bristol Bay, Alaska.

I would love to hear your opinions and ideas about the Pebble Mine as well as about anything else related to salmon conservation or any of my other posts.

My novel, The Fisherman’s Daughter, is now available for sale at Amazon and other online booksellers, as well as on my page at www.authormasterminds.com

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Coho or Silver Salmon (Oncorhynchus kisutch)

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Coho salmon, often called silver salmon due to their beautiful bright chrome color, are the most aggressive of the Pacific Salmon species. There aren’t as many cohos as there are pink salmon, chum salmon, or sockeye salmon, but coho salmon manage to spawn in tributaries and small headwaters inaccessible to other salmon species. A Coho can leap vertically six feet (1.8 m) to overcome obstacles such as rapids or waterfalls on its return journey to its spawning stream, and cohos usually migrate to their spawning streams later than other salmon species at a time when fall floods allow them to access areas not available during lower water levels.  Even young cohos are aggressive, and they often eat the young of other salmon species. This aggressive nature of coho salmon makes them excellent fighters on a rod and reel and an important species for the sportfishing industry in Alaska.

Range

The natural range of coho salmon is from Monterey Bay, California north to Point Hope, Alaska, west across the Bering Sea to the Anadyr River in Siberia, and south along the coast of Asia to Japan. Cohos have been introduced to the Great Lakes and other lakes in the Continental U.S. Cohos spawn in ponds, lakes, and pools within streams and rivers.

Description

Coho adults usually weigh between 8 and 12 lbs. (3.6-5.4 kg) and range from 24 to 30 inches (61-72 cm) in length, but fish weighing up to 31 lbs. (14.1 kg) have been caught. During their marine phase, adults are bright silver and have small, black dots on the back and the upper lobe of the tail fin. In their marine phase, cohos look very similar to king (Chinook) salmon, but king salmon have spots on both lobes of the tail, while cohos only have spots on the upper lobe. Another way to distinguish the two species is cohos have white gums, while king salmon have black gums.

When cohos return to freshwater to spawn, males turn dark to bright green on the head and back, bright red on the sides, and dark on the belly. Breeding females are not as brightly colored as males. Spawning males develop a hooked jaw called a kype.

Life Cycle

In Alaska, coho salmon return to their spawning streams from July to November, usually during periods of heavy rain and high runoff. On Kodiak, most cohos return from late August through October. A female coho selects a suitable spot and then begins to dig a nest, or redd. She turns on her side and gives several powerful flips of her tail to remove silt and other debris and then continues to dig for two to five minutes until she has a shallow nest. While she is digging her nest, she aggressively drives away other females. Meanwhile, a male coho stays near the female while she digs the nest, occasionally swimming close to her. He may also stop beside her and quiver, swim over her and touch her dorsal fin, or nudge her side with his snout. When the female has finished excavating the nest, she drops into the deepest part of the depression, and the male immediately joins her. The two fish remain side by side in the nest while they open their mouths, quiver, and release eggs and sperm. The female then moves upstream and begins digging a new nest, covering the eggs in the first nest with the gravel she dislodges from the second nest. Nest digging and spawning may continue at intervals over the next several days, until the female deposits all her eggs. The male might then leave and seek another female, but the female will continue the digging process until she grows weak and dies.

A female coho lays between 2,400 and 4,500 eggs. The eggs develop over the winter and hatch in the early spring. The alevin, with the yolk sac attached, remains in the gravel until May or June before emerging. Young silver salmon fry usually spend between one and three winters in fresh water, but some spend as many as five years in a lake before migrating to the ocean. Young silver salmon in Karluk Lake on Kodiak Island often stay two, three, or even four years in fresh water before migrating to sea. The length of time spent at sea also varies for coho salmon. Some males, called jacks, mature and return after only six months at sea, but most cohos remain in the ocean for 18 months to three years and return as full-size adults.

Prey and Predators

Cohos are aggressive feeders. In freshwater, they eat a wide range of aquatic insects and plankton. They also eat salmon eggs, and as they grow, the fry also consume smaller fry. In the ocean, cohos eat herring, sand lance, other fish, and squid.

Young coho are eaten by birds, larger fish, and a variety of other predators. Killer whales, sharks, sea lions, seals, bears, humans, and other land mammals prey on adult cohos.

Next week, I will cover commercial and sport fisheries for cohos as well as threats to coho salmon populations.

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Announcements

The publication date has changed for my novel, The Fisherman’s Daughter. Now, both the e-book and print versions of the novel will be released on November 1st. You can still pre-order the e-book, and it will be delivered to your device as soon as it is released. If you pre-ordered my novel, thank you!

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Chum Salmon (Oncorhynchus keta)

Fish, Kodiak Wildlife, , ,


Chum salmon (Oncorhynchus keta) are the most widely distributed Pacific Salmon species and can be found throughout Alaska. They range along the east and west coasts of the North Pacific Ocean, from the Mackenzie and Anderson Rivers in Canada to the Lena River in Russia.

Chums are often called dog salmon, but experts disagree about the origin of this nickname. Some believe chums are called dogs because, in the Arctic, Northwestern, and Interior parts of Alaska, chums were and still are traditionally dried and used as a winter food supply for both humans and dogs. Others argue they are called dog salmon because of the enlarged “canine” teeth the males develop during the spawning season.

Chum salmon are the second-largest Pacific Salmon species. Only Chinook (King Salmon) grow bigger. An average adult chum salmon weighs between 8 and 15 lbs. (3.6 to 6.8 kg), but they can grow as large as 45lbs. (20 kg). During their marine phase, chums are dark metallic blue on the back and silver on the sides and belly. Tiny dark specks may be present, but chums do not have large spots like those on Chinook, coho, and pink salmon. The tail of a chum salmon is highly forked, lacks spots, and has silver streaks along the fin rays.

When chums enter fresh water on the return to their spawning streams, males darken to what is often described as a calico pattern. They turn a dark olive brown and have red to purple, wavy, vertical stripes. They also develop hooked jaws called a kype lined with large, sharp teeth. Females turn brown and have a dark, thick, horizontal bar running along the lateral line. Females also develop a hooked jaw with large teeth, but the jaw is less pronounced than it is in males.

There are two, distinct races of chum salmon that spawn at different times. Summer chums spawn in early to mid-summer, and fall chums, as their name suggests, spawn later in the autumn. Chum salmon usually spawn at the mouth or in the lower sections of a stream or river, but in large river systems, they may travel as far as 2000 miles (3219 km) upriver to spawn.

When spawning, a female chum digs a nest in the gravel of the streambed. She then deposits her eggs in the nest while one or more males release sperm to fertilize the eggs. The female may dig more nests upstream from the first nest, depositing her eggs in the nests until her eggs are gone. A group of nests is called a redd, and a female guards her redd until she becomes weak and dies.

Chum salmon eggs hatch after three to four months. The alevin that emerges from the egg remains in the gravel, receiving nutrients from its yolk sac for 60 to 90 days. When it emerges, a chum salmon fry is dark greenish-brown on the back and iridescent green below the lateral line. It also has 8-12 vertical, spaced parr marks on the upper half of its body, not extending below the lateral line.

Fry begin migrating downstream to the ocean within a few days to a few weeks after emergence when they are only one to two inches long. Young chums spend several months near shore before traveling to the open ocean. They stay in the ocean three to four years where they grow to a size of 8 to 15 lbs. (3.6-6.8 kg) or larger. They grow the fastest during their last year in the ocean. Like other Pacific Salmon, chums return to spawn in the stream or river where they were born, and after spawning, they die.

Juvenile chum salmon eat crustaceans, insects, and young herring. Adults feed on copepods, tunicates, mollusks, and fish. When adults return to fresh water to spawn, they stop eating, and their digestive tract deteriorates.

Chum salmon rank second to pink salmon in average annual catch in Alaska’s commercial fishery. Chum-salmon meat is commercially the least valued of the salmon species, and commercial fishermen are paid less or the same for chums as they are for pink salmon. Chum-salmon eggs, though, are the largest and most valuable of any salmon eggs and are sold in Japan as ikura salmon caviar. Chums are not usually targeted by sports anglers because they rarely aggressively attack a lure.

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Pink Salmon (Oncorhynchus gorbuscha)

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Pink salmon (Oncorhynchus gorbuscha) are also sometimes known as humpback salmon, or “humpies,” due to the hump males develop on their backs before they spawn. Pink salmon are the smallest of the five species of Pacific salmon found in Alaska. They average between 3.5 and 5 lbs. (1.6-2.3 kg) in weight and are usually between 20 and 25 inches (51-63 cm) long.

Young pink salmon are completely silver with no parr marks or spots. In their ocean phase, adult pink salmon are steel blue to blue green on the back and have silver sides and a white belly. As they get closer to fresh water, males develop large, black spots on the back, the adipose fin, and on both lobes of the caudal fin (tail). When they return to fresh water to spawn, males turn dark on the back and are red with olive blotches on the sides. They have a bright white belly. Females are similarly but less-distinctly colored. In their ocean phase, pink salmon have an elongate, fusiform shape, but when a male returns to fresh water, he develops a large hump on his back, an enlarged head with big teeth, and hooked jaws called a kype. These morphological changes allow a male to fight off other males once he has chosen a breeding partner.

Pink salmon are the most numerous Pacific salmon. They occur naturally throughout the coastal waters of the North Pacific Ocean, Arctic Ocean and nearby seas. In North America, pink salmon have been found in small numbers as far south as north-central California, but they are more common from Puget Sound northward. They also occur to the west from the Lena River in Siberia south to Korea and Kyushu, Japan. Pink salmon have been introduced to the Great Lakes. In Alaska, pink salmon are abundant along the coast.

Pink salmon complete their entire life cycle within two years, the shortest life cycle of any Pacific salmon. Because the life span is two years, fish born in an odd-numbered year do not interbreed with fish born in an even-numbered year, creating genetically distinct odd-year and even-year populations. Even if salmon spawn in the same stream, odd-year and even-year fish will never interbreed, and often, either the odd-year or even-year population in a stream will produce more fish.

Salmon eggs incubate in the gravel of a stream over the winter and hatch either in the late winter or early spring. The alevin that emerges from the egg remains under the gravel, receiving nutrients from the large yolk sac attached to its belly. Once it depletes its yolk sac and emerges from the gravel, the fry swims downstream to the ocean and begins eating plankton and larval fishes.

Eighteen months later, the adult salmon returns to the stream or river where it was born to spawn. It arrives back at the stream sometime between late June and mid-October, depending on the stream and the population. Once they reach their spawning stream, both males and females stop eating, and they change from their sleek, silver marine phase to their spawning coloration and morphology. A male develops hooked jaws and a hump on his back, and his head and teeth enlarge.

A spawning female chooses a suitable nesting spot in the gravel and prepares a nest by turning on her side, pressing her tail against the stream bottom, and giving several vigorous flaps with her tail. She repeats this action several times to dig a shallow hole. She then settles into the hole to deposit her eggs, and her male partner joins her to fertilize them, using his hooked jaw and large teeth to fend off any other would-be suitors. A female may dig as many as four nests. She digs the second nest upstream from the first nest, covering the eggs in the first nest with the gravel she dislodges while digging the second nest. A group of nests is called a redd. The female defends her redd until she dies, usually two weeks after spawning. All pink salmon die after they spawn.

A female pink salmon lays between 1200 and 1900 eggs. Pink salmon have a tough life. If a fry is lucky enough to make it downstream to the ocean, it faces a mortality rate of 2% to 4% per day for the first forty days. Young salmon provide food for birds, fish, invertebrates, and other predators. Studies show after forty days, the mortality rate drops to .4% to .8% per day. Once a salmon heads back to coastal waters and its natal stream, it must avoid humans, sharks, killer whales, seals, sea lions, river otters, eagles, and every fish larger than it is. When it reaches its birth stream, it becomes prey for bears, eagles, human anglers, and other predators.

Pink salmon mostly spawn in small streams and rivers near the coast, and most do not travel more than forty miles upstream to spawn. In large river systems, though, they sometimes travel further. Pink salmon have been documented swimming 130 miles (209 km) up the Susitna River in Southcentral Alaska, and they have been seen spawning 250 miles (402 km) up the Mulchatna River.

In the ocean, pink salmon eat plankton, small fish, squid, and an occasional aquatic insect. Their flesh gains its pink color from the tiny marine crustaceans they eat.

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Next week, I’ll write about the commercial and sports fisheries for pink salmon. While pink salmon may be the least flashy of the salmon species, they are known as the bread and butter of the salmon commercial fishing industry.

I will soon be releasing my next novel, The Fisherman’s Daughter, so check back often for updates on its release. Also, be sure to sign up for my monthly mystery newsletter. Newsletter subscribers will be the first to hear about the release of my new novel.

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Pacific Salmon

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Five species of Pacific salmon return each summer to breed in Alaskan streams, rivers, and lakes. I will admit salmon are confusing fish. Not only do they have some of nature’s most complicated life cycles, but each species of Pacific salmon is known by two different common names. Are Atlantic and Pacific salmon the same fish? Which species of Pacific salmon is worth the most money to commercial fishermen? Do the various species taste different? Which species of salmon freezes the best? Why do some species grow larger than others, and why do salmon jump when they return to spawn?

Over the next few weeks, I hope to answer the above questions while I profile each of the five species. In this post, I will give you a generic overview of salmon and describe the life cycle of a Pacific salmon.

Pacific salmon and Atlantic salmon belong to the same family but not to the same genus. Atlantic salmon are more closely related to some species of trout than they are to Pacific salmon. One big difference between Pacific and Atlantic salmon is Pacific salmon only breed once, and then they die. Atlantic salmon return to freshwater to breed many times before they die.

The five species of Pacific salmon are pink salmon, also known as humpies; chum salmon, also known as dog salmon; red salmon, also known as sockeyes; silver salmon, also known as coho; and king salmon, also known as chinook. The five species look very similar to each other in their marine ocean phase, but once they enter fresh water, salmon go through significant physical changes, and each species has distinctive markings.

Fertilized salmon eggs incubate in the gravel of a river or lake bed for a length of time that varies depending on the species as well as other factors. Once the egg hatches, it is called an alevin. An alevin is small and has a relatively large, orange yolk sac attached to its body. The alevin receives its nutrients from the yolk sac and remains hidden from predators in the safety of the gravel bottom of the stream or lake. As the alevin grows, it depletes the nutrients in the yolk sac and begins to develop mouth parts.

Once the yolk sac is depleted, the young salmon leaves the safety of the gravel bed and must search for its food. At this point in its life cycle, the fish is called a fry. Except for pink salmon, a fry has parr marks along each side of its body. These marks provide camouflage to protect the fry from predators. Fry eat food such as insect larvae and plankton.

This is where the life cycle begins to get complicated. Fry remain in fresh water for a length of time which not only varies between species but may also vary between populations of the same species. Sockeye and silver salmon usually remain in fresh water for one or two years, while pink and chum salmon migrate to sea soon after they emerge from the gravel. King salmon fry usually stay in fresh water for one year.

Before salmon migrate to the ocean, they lose their parr marks and turn silver in color. At this stage of their lifecycle, they are called smolt. Once smolt leave their freshwater stream, they spend a great deal of time in brackish water where freshwater streams flow into the ocean. They feed and grow in the brackish water until they reach a certain size, and then they migrate to the ocean. Once they enter the marine phase of their lifecycle, they are considered adult salmon.

Adult salmon remain in the ocean for a variable amount of time, depending on the species and the population. King salmon can stay in the ocean for as long as six years, but pink salmon return to freshwater to spawn when they are only two-years-old. Once adult salmon return to freshwater, they undergo a dramatic physical change. Sockeye salmon, king salmon, and silver salmon turn dark red, while chum salmon develop calico bands on each side of their bodies. Pink salmon turn dark, and males develop a hooked jaw and a large hump on their back.

Salmon return to the stream or lake where they were born to spawn and die. At this point in their lifecycle, they are called spawners. Once the salmon reach their spawning grounds, a male and female form pair bond. The female digs a bed, called a redd, for the eggs in the gravel. She deposits her eggs in the redd, and the male swims over the eggs and fertilizes them with his sperm. She then brushes a light coating of gravel over the eggs. Once they spawn, all species of Pacific salmon slowly deteriorate and die, their bodies left to fertilize the stream or lake where they were born, ensuring the birthing grounds will remain rich in nutrients for future generations.

Every year, I watch salmon return to their natal streams to spawn. This summer, we had a huge return of pink salmon to the many streams on Kodiak Island, and at times when I sat on our boat, salmon surrounded me, jumping out of the water as far as I could see, reminding me of popcorn. I am always amazed by the incredible life cycles of Pacific salmon and how the many animals and plants on Kodiak Island depend on salmon to survive and thrive. As they return from the ocean, salmon are chased by humans, bears, eagles, seals, sea lions, sharks, and any fish big enough and fast enough to catch them. It is a wonder any salmon survives the gauntlet it must swim to reach its birth area and reproduce. Once it spawns and dies, the body of a salmon provides nutrients for the stream or lake bed and the plants and trees growing in the vicinity. It is impossible to imagine a Kodiak riparian ecosystem without salmon.

Next week, I’ll write about pink salmon, the smallest but one of the most important of the five Pacific salmon species.

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