Category Archives: Kodiak Wildlife

Wildlife of Kodiak Island including biology, behavior, and news

In Conclusion

June 20, 2021Bald Eagle, Birds, Fin Whale, Gray Whale, Harbor Seal, Humpback Whale, killer whale, Kodiak Bear, Kodiak Wildlife, Mountain Goat, Orca, Porpoise, Red Fox, River Otter, Sea Otter, Sitka black-tailed deer, Steller Sea Lion, WeaselBald Eagle, Conclusions, Kodiak Bear, Kodiak Island, Kodiak Island wildlife, Robin Barefield, whales, Writingadmin

When I reach the end of a manuscript, I dread writing the conclusion because a conclusion requires a great deal of thought and effort. Just as we were nearly done polishing my non-fiction book, Kodiak Island Wildlife, the editor said he believed the book needed a conclusion, and I groaned, but I also agreed with him.

I don’t know how long I stared at a blank computer screen, but I could think of nothing to write. How do you sum up a book about wildlife? Then, as I stood on our boat one morning, watching giant fin whales with our guests, the conclusion for my book popped into my mind, fully formed. When I read it to my husband, tears came to my eyes, and I knew I had done my best work. My editor agreed, and he said it was the perfect ending. The following is the conclusion for my recently released book, Kodiak Island Wildlife.

Emerald cliffs plunge into the gray ocean, and only a slight breeze stirs the surface of the water. In front of our boat, three huge fin whales feed, frequently surfacing to breathe. Their exhalations sound like cannon shots, and our guests capture every moment with their cameras. A sea otter bobs placidly a short distance from our boat, and a bald eagle circles overhead. I have seen all of this many times, but still, it takes my breath away, and a chuckle escapes my lips. How have I managed to live my life in one of the most beautiful places on the planet? To me, Kodiak is paradise. Sure, the weather here throws frequent tantrums, and mistakes in the hostile wilderness do not go unpunished, but I have found nowhere else I would rather live.

One of my greatest joys is to guide visitors into the Kodiak wilderness. I love the look on a newcomer’s face the first time she sees a Kodiak bear or watches a sea otter eat a crab. I wrote this book to honor the wild animals we’ve watched over the years and to thank the many folks who have visited our lodge. I know they would tell you that Kodiak is a special place. The island is mysterious and magical.

It is a short conclusion, but it sums up how I feel and accurately describes my motivations for writing the book. I am grateful for the many experiences I’ve enjoyed. My life is an adventure filled with wonder in the Kodiak wilderness, and I can’t imagine living anywhere else.

Speaking of wildlife, I hope to return to regular and more frequent posts soon. The past two months have been hectic. I’m writing this while I sit on our boat. We are cruising 100 miles around Kodiak Island from our lodge to the town of Kodiak, where we will have our boat lifted out of the water so that we can clean and paint the bottom. As soon as we return home, we have endless jobs awaiting us before our summer season begins. Meanwhile, I am trying to promote my new book and keep up with my scheduled newsletters and podcasts. I realize I’ve let my blog posts fall through the cracks, and I vow to make my posts more of a priority in the future. Thank you for your patience.

Kodiak Island Wildlife is now Available

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

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Big Skate

April 4, 2021Fish, Kodiak WildlifeBig Skate, Kodiak Island wildlife, Robin Barefield, Skates in Alaskaadmin

The aptly named big skate (Raja binoculata) is the largest skate in the waters off North America. Big skates range along the Pacific coast from Alaska to Baja California. They inhabit a variety of habitats, from bays and estuaries to the continental shelf. They prefer sandy or muddy bottoms and seem to prefer depths shallower than 390 ft. (120 m). They inhabit shallower water in the northern part of their range.

The largest big skate ever captured measured 7.9 ft. (2.4 m) in length, but they typically reach a maximum of 5.9 ft. (1.8 m) in length and weigh as much as 201 lbs. (91 kg). An average big skate weighs less than 110 lbs. (50 kg).

A big skate has a diamond-shaped, flattened pectoral fin disk. It has a pointed snout, and the eyes are small and sit just ahead of the spiracles. The tail has two small dorsal fins but no anal fin, and the caudal fin is only a simple fold. A juvenile has smooth skin, but an adult’s skin has small prickles on the dorsal surface, the underside of the snout, between the gill slits, and on the abdominal region. An irregular row of approximately 33 middorsal thorns runs down the back and tail to the first dorsal fin. A single thorn protrudes from behind each eye. The back of a big skate ranges in color from mottled reddish-brown to olive-brown to grey, and it is covered with small, pale white spots or dark blotches. The ventral surface ranges from white to gray.

A large dark spot with pale borders appears on each wing of a big skate, and biologists suspect these “eyespots” appear to predators as the eyes of a much larger animal, making a shark or another predator much less likely to attack the skate.

A big skate camouflages itself by partially burying its body in the sand and silt on the seafloor. Between its submerged position and its mottled coloration, a skate appears nearly invisible to predators and prey. When partially buried, it breathes with the aid of the spiracles on the top of its body. It takes water in through these spiracles and pushes it out through the gills on its dorsal surface.

Big skates differ from Alaska skates in that their egg cases may contain as many as seven eggs each. The big skate produces the largest egg case of any skate species, measuring 9 to 12 inches (23-31 cm) long and 4 to 7 inches (11-19 cm) wide. Big skates have a maximum lifespan of 26 years, but most big skates in Alaska don’t live past 15.

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Skates in Alaska

March 14, 2021Fish, Kodiak WildlifeAlaska Skate, Kodiak Wildlife, Robin Barefield, Skates and Rays, Skates in Alaskaadmin

Skates are mysterious creatures, and scientists still know little about them. We often catch skates when we sportfish for halibut. The angler usually thinks he has a halibut when the heavy fish hits the lure, but we soon know it’s a skate when the animal exerts long, steady pulls instead of the head-jerking motions of a halibut.

“What is it?” The angler asks when he reels the strange creature up to the side of the boat.

“It’s a skate,” I say.

“What’s a skate? Is it like a stingray?” He asks.

“It’s related,” I reply, “but skates and rays belong to different families.”

Skates in the family Rajidae differ from rays in the family Myliobatidae mainly because skates lay eggs, while rays give birth to live young. Both skates and rays are cartilaginous fish (they have no bones) and are related to sharks.

Biologists have identified 14 species of skates in Alaska, and eight of these species are considered common in the Gulf of Alaska and the Bering Sea. Two of the most abundant species in Kodiak Island’s waters are the Alaska Skate and the Big Skate.

The Alaska Skate ranges from the Gulf of Alaska to the Bering Sea and the Aleutian Islands and west to Japan. They live at depths from 56 to 1286 ft. (17-392 m) and prefer soft bottoms of sand, silt, or mud. They grow to 53 inches (135 cm) in length.

Alaska skates are long-lived and do not reach sexual maturity until they are ten years old. A female lays 20 to 40 eggs per year, and each egg is enclosed in a tough case to protect the embryo as it grows. Since a female skate has dual uteri and shell glands, she can form two single encased embryos at a time. The embryo grows for an average of 3.7 years before it emerges from its case as a fully developed young skate. In certain areas, skate egg cases litter the ocean floor, and beachcombers who find them on the shore call them mermaids’ purses or devils’ purses. Biologists have identified several skate nursery areas in Alaska’s waters. Some of these nursery areas have egg densities of over 100,000 eggs per square kilometer.

A skate’s exceptionally long gestation period and its prolonged maturation until it can reproduce concern biologists. Skate populations are potentially fragile, and if targeted by commercial or sport fisheries, they could easily be overfished. Once considered a trash fish, skate wing is now presented as gourmet food in some regions. The Monterey Bay Aquarium lists skate as seafood to avoid because several North Atlantic species are now in decline from overfishing.

Juvenile Alaska skates eat mainly crustaceans such as amphipods and hermit crabs. As they grow, they begin to eat fish. While enclosed in their tough egg casing, skates remain protected from most predators, but hairy triton snails can prey upon a developing embryo by drilling through the case. Once they hatch, young skates are vulnerable to predation by any larger fish. Steller sea lions and other sea mammals sometimes feed on adult skates.

In my next post, I will profile the big skate, the largest species of skate in the waters off of North America.

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Pacific Sleeper Shark (Somniosus pacificus)

January 31, 2021Fish, Kodiak WildlifeKodiak Wildlife, Pacific Sleeper Shark, Robin Barefield, Sharks, Sharks in Alaska, Somniosus pacificus, Steller Sea Lionsadmin

The reclusive, deep-dwelling Pacific sleeper shark (Somniosus pacificus) remains an enigma to biologists. Once believed to be sluggish bottom-dwellers that scavenged or fed on small fish and slow-moving prey, researchers now think Pacific sleeper sharks play a pivotal role in the North Pacific’s food web. Biologist Lee Hubert with the Alaska Department of Fish and Game studies Pacific sleepers, and he has learned the sharks spend little time on the bottom but instead move continually through all depths and are stealth predators of fast-moving prey.

I can understand how Pacific sleepers earned their reputation as sluggish sharks. We occasionally catch immature Pacific sleeper sharks when we halibut fish, and when reeled up to the boat, they look dead and move very little. I was surprised to hear these sharks are voracious predators. This shark’s ability to remain still, though, is one of the reasons it is such a successful predator. When it glides through the water, barely moving its body, it minimizes hydrodynamic noise, allowing it to elude acoustic detection by its prey.

Pacific sleeper sharks dive to depths exceeding 6500 ft. (1981 m). They typically remain deep during the day and then move to the surface at night, where they feed under cover of darkness. These sharks probably have poor eyesight, but they are extremely sensitive to electromagnetic fields. They can detect even minute electrical signals, such as the beating of an animal’s heart or its diaphragm’s movement. The shark does not need vision to detect these signals and attack its prey. Its dark grey body and stealth movements make it an efficient predator under the cloak of darkness.

The mouth of a Pacific sleeper shark is large and acts as a vacuum to inhale prey. Fish, such as salmon and cod, can be swallowed whole, but the shark uses its teeth to aid in eating larger prey items. Its upper jaw has small, sharp conical teeth used to hold the prey, while the teeth in the lower jaw interlock, forming a serrated blade used for slicing. A Pacific sleeper shark’s bite resembles the shape of a three-quarter moon.

Because they make little noise when traveling, a sleeper shark attacks with little warning. It might slowly swim up underneath a seal resting on the surface and attack the seal’s midsection, inflicting a fatal wound. Researchers know Pacific sleeper sharks eat fish, squid, octopuses, and marine mammals, but they are still trying to discern how much impact these sharks have on the their ecosystem. The number of Pacific sleeper sharks has increased dramatically in the North Pacific since the 1980s. Because they live very deep much of the time, it is difficult for biologists to estimate their population size. Still, in many areas where commercial fishermen caught few sleeper sharks in the 1970s, they now catch many.

Investigators are particularly interested to learn how many marine mammals Pacific sleeper sharks kill and eat. Pacific sleepers can grow to twenty feet (6.1 m) in length and weigh more than 8000 lbs. (3600 kg). They grow nearly as large as an adult orca, and recent evidence suggests these sharks might eat endangered Steller sea lions, especially sea lion pups.

In a 2014 study, biologists inserted “life-history transmitters” into the abdomens of 36 juvenile Steller sea lions.These transmitters record temperature, light, and other properties during the sea lions’ lives. When a sea lion dies, the tags either float to the surface or fall out onshore and transmit the data by satellite to researchers. After 17 of the original 36 tagged sea lions died, researchers noted that 15 of the transmitters indicated that predators killed the sea lions. Usually, when a predator kills a sea lion, the tag is ripped from the body and floats to the surface, recording a rapid temperature change and exposure to light. Three of the transmitters relayed data that suggested a very different type of predator, though. They recorded an abrupt drop in temperature, but they did not float to the surface and sense light, indicating that tissue surrounded them. The apparent explanation is that a cold-blooded animal, such as a shark, had eaten them. Other than sleeper sharks, great white and salmon sharks are the only other candidates living in the area near where the sea lions died. But both great white sharks and salmon sharks have counter-current heat exchangers in their bodies, giving them higher body temperatures than those recorded. Biologists think a Pacific sleeper shark is the only predator in the area that is large enough to eat a sea lion and has a body temperature as low as those recorded.

Pacific sleeper sharks live in polar and sub-polar regions year-round. They range from Baja California north to the Bering, Chukchi, and Beaufort Seas and the Okhotsk Sea off Japan. Biologists know little about Pacific sleeper shark reproduction and only recently learned they give birth to live young. Their social structure is also unknown, but researchers have photographed them feeding together in large numbers on whale carcasses.

Pacific sleeper sharks probably have a lifespan of more than forty years. Their tissue is toxic to humans and believed to be toxic to many other animals, so they have few natural predators except perhaps for other sharks.

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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Salmon Shark (Lamna ditropis)

January 12, 2021Fish, Kodiak Wildlife, UncategorizedAlaska wildlife, Lamna ditropis, Lamnid Sharks, Robin Barefield, Salmon Shark, Sharks in Alaskaadmin

I am always thrilled when I see the dorsal fin of a salmon shark protruding from the water as it swims near the surface. I love seeing any apex predator, but sharks conjure an air of mystery and fear. I wonder if the shark is chasing prey or if it is just watching and waiting for a fish to make the fatal mistake of swimming into its strike range.

Salmon sharks (Lamna ditropis) are some of the fastest fish in the ocean, and their high metabolism makes them voracious eaters. Salmon sharks are closely related to great white sharks, makos, and porbeagle sharks. Because their body shape so closely resembles a great white shark’s shape, people sometimes mistake salmon sharks as juvenile great whites.

Like other species of lamnids, salmon sharks have a conical snout, dark, round eyes, and a keeled, lunate tail. The salmon shark and porbeagle shark can be distinguished from great whites and makos by their smaller secondary caudal keel below the primary keel at the base of the tail. While the porbeagle shark inhabits the Atlantic and Southern Pacific, the salmon shark lives in the North Pacific.

A salmon shark has a bluish-black to dusky gray back, fading to white on the stomach. It has long gill slits and large teeth. Salmon sharks can grow to over 10 ft. (3 m) in length, but they average 6.5 to 8 ft. (1.9 – 2.4 m). They can weigh more than 660 lbs. (300 kg). Females grow larger than males.

Like other lamnid sharks, salmon sharks manage to sustain elevated body temperatures, even in the cold North Pacific. Their core body temperature measures approximately 80°F (26.7°C). They maintain this warm body temperature because they have a counter-current heat exchanger of blood vessels, directing heated blood through their core and dark musculature. This elevated body temperature permits the shark to live and hunt in a wide range of depths and water temperatures. The warm blood flow allows their brain, eyes, and muscles to function at peak performance.

A salmon shark is a big marine animal with no fur or blubber to keep it warm. To maintain its body heat, it must consume a large amount of food each day. Like a great white shark or a mako, a salmon shark aggressively chases its prey and sometimes even explosively breaches out of the water while in pursuit. Salmon sharks feed on fish, squid, other sharks, seals, sea otters, and marine birds. A study done in 1998 determined that salmon sharks consumed twelve to twenty-five percent of the total annual run of Pacific salmon in Prince William Sound.

While salmon sharks are most abundant in the North Pacific Ocean near Alaska, they travel as far south as northern Mexico and the Hawaiian Islands. Researchers have recorded salmon sharks dives as deep as 2192 ft. (668 m). Although biologists do not entirely understand salmon shark migrations, they believe the sharks spend the summer in the northern part of their range, and then they migrate south to breed. In the western North Pacific, salmon sharks migrate to Japanese waters to breed, and in the eastern North Pacific, they migrate south to the Oregon and California coasts. Their migrations are complicated, though, and they segregate by size and sex. Their migrations also depend upon available prey species in various areas. Scientists have determined that although many salmon sharks migrate south in the winter, some remain in the Gulf of Alaska and Prince William Sound year-round.

Male salmon sharks mature at five years of age, while females do not reach sexual maturity until they are eight to ten years old. They breed in the late summer or early autumn. Embryos develop inside their mother for nine months until she gives birth to between two to five pups. The developing embryos consume any unfertilized eggs in the womb. The mother provides no parental care to her young after birth, and they must fend for themselves. Females usually produce a litter every two years.

Male salmon sharks have a maximum lifespan of 25 years, while females can live 17 years. Other sharks sometimes eat salmon sharks, but humans pose the biggest threat. In Alaska, no commercial fishery exists for salmon sharks, but some sport fishing companies specialize in shark charters. Salmon sharks are big, strong, aggressive fish, and they pose a challenge and thrill for sport anglers. Each angler is limited to two salmon sharks per year. Salmon shark meat reportedly tastes similar to swordfish.

In my next post, I’ll describe another species of shark common in Alaska. Pacific sleeper sharks were long ignored as large, sluggish fish, but research over the past few years suggests Pacific sleeper sharks might play an essential role in the North Pacific’s food chain.

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Pacific Spiny Dogfish Shark (Squalus suckleyi)

December 20, 2020Fish, Kodiak WildlifeDogfish Shark, Pacific Spiny Dogfish, Pacific Spiny Dogfish biology, Robin Barefield, Sharks in Alaska, Sharks near Kodiak Island, Spiny Dogfish, Squalus suckleyi, Wildlife of Kodiak Islandadmin

One of the most abundant sharks globally, Pacific spiny dogfish belongs to the family Squalidae (the dogfish family). Pacific spiny dogfish range from the Bering Sea to Baja California to Japan and the Korean Peninsula. They are most common off the west coast of the U.S. and British Columbia. Dogfish are typically bottom dwellers and inhabit depths from shallow coastal waters to 4,055 ft. (1,236 m). They prefer water temperatures ranging from 44.6° F to 59° F (7-15° C).

Pacific spiny dogfish are small, streamlined sharks. Males can grow to 3.3 ft. (1 m), while females measure a maximum length of 4 ft. (1.2 m). A dogfish has a distinctive snout, large eyes, and a flattened head. The body has a cylindrical shape. The top half is dark gray with scattered white spots, and this color fades to light gray or white on the underneath side of the fish. The teeth of a dogfish have sharp edges, but they are specialized for grinding instead of tearing. Dermal denticles comprise the scales of a dogfish. These denticles are the same rigid material found in their teeth, and they make the skin very tough.

A dogfish does not have an anal fin, but it has two dorsal fins, with a spine in front of each fin. These spines are venomous, and the shark uses them as protection against potential predators, such as other sharks or humans. The dogfish employs its two dorsal fins in different ways. The first dorsal fin helps it maintain stability while swimming, and the second dorsal fin provides thrust. The large caudal fin (or tail) allows the shark to maneuver quickly and efficiently through the water.

A dogfish has five gills on either side of its body, but unlike bony fish, a dogfish does not have gill covers. To breathe through these gills, the shark must remain in constant motion, so it either must continually swim or rest in a current where water rushes past its gills. A dogfish has an adaptation called spiracles, aiding it to breathe in calm water. These specialized gills, located behind the eyes, allow the shark to breathe when resting or eating.

Dogfish earned their common name from fishermen who observed them hunting in packs like dogs. Schools of hundreds of dogfish swim close together during the day, hunting herring, capelin, other small fish, squid, octopus, and even jellyfish. The dogfish uses its teeth and not its spines when feeding. It uses its spines for protection. Scientists think dogfish eat less in the winter when they migrate to great depths. They are preyed upon by larger sharks, seals, orcas, and some larger fish.

Spiny dogfish can live 100 years, and females do not reach sexual maturity until they are approximately 35 years old. Males can reproduce at an average age of 19. Males internally fertilize females in October or November. Dogfish are ovoviviparous, meaning females give birth to live young, and they have a gestation of nearly 24 months, the longest of any vertebrate. They give birth to up to 22 pups, and the newborns range in length from 8 ½ to 12 inches (21.6 – 30.5 cm).

Pacific spiny dogfish stocks remain stable and are carefully managed. In some areas of the world, a commercial market exists for dogfish, and they are considered a good food fish, but they are not yet in demand as a food source in the United States.

We usually catch a few dogfish each year during our sportfishing trips, but this past summer, we landed as many as 20 per day while halibut fishing. Dogfish are tricky to release because while you try to get the hook out of its mouth, the shark attempts to whip its body into a position to stab you with one of its venomous spines. I was not pleased to encounter so many dogfish this past summer, but more importantly, I wondered why we were catching so many dogfish. I speculate that the dramatic decrease in the Pacific cod population led to an increase in small fish species typically eaten by cod. Dogfish probably are exploiting an opening in the food chain. Will their presence affect the abundance of other fish species in this region of the North Pacific? Only time will tell.

Happy holidays, and I wish us all a nicer, brighter 2021!

Mystery Newsletter

Sharks in Alaska

November 30, 2020Fish, Kodiak WildlifeDogfish Shark, Pacific Sleeper Shark, Robin Barefield, Salmon Sharks, Sharks in Alaskaadmin

Our guests are often surprised to learn sharks feed and swim in the frigid North Pacific. We catch spiny dogfish sharks when halibut fishing, and large salmon sharks terrorize commercial salmon gillnetters by ripping enormous holes in their nets when stealing fish from the mesh. Pacific sleeper sharks also live in Alaska’s waters, but sleeper sharks remain elusive, and biologists do not know much about their biology, diet, and habits. These three species fascinate me, and I think you will enjoy learning about their longevity, reproductive biology, and the mechanisms each species employs to stay warm in the frigid waters surrounding Alaska. I will cover each shark in detail in future posts, but for now, let me give you an overview of sharks in Alaska.

The three shark species I listed above are the most common but not the only sharks trolling the North Pacific. Over the past several years, ocean waters in the region have warmed, encouraging other shark species to venture into these nutrient-rich areas. Great white sharks began exploring Alaska in the 1970s, but recent, more frequent sightings suggest an increasing number of great whites have discovered the North Pacific’s fertile feeding grounds. Most of these visiting sharks only stay during the warm summer months, but researchers believe a small percentage find enough to eat to keep them in Alaska year-round.

Great whites are related to salmon sharks. Like salmon sharks, great whites have a highly developed countercurrent heat exchange mechanism that allows them to maintain a body temperature several degrees warmer than the ambient temperature. Sharks in this family represent some of the few species of endothermic fish in the ocean. Unlike their cold-blooded cousins, great whites and salmon sharks can produce bursts of speed to chase down prey, even in frigid ocean temperatures.

In recent years, Alaskans living and working in the far north regions of the Bering Strait and the Chukchi and Beaufort Seas have reported sightings of marine mammals with unusual wounds. Researchers noted that several ice-associated seals and Steller sea lions in the area suffered injuries from an uncommon predator.

Reports of seals with amputated flippers alerted biologists because killer whales have pegged teeth and don’t cause a slicing-type laceration. In some instances, scientists noted penetrating stab wounds and circular bite marks. Flesh torn by sharp, triangular teeth convinced researchers they were looking at the bite marks of a very large shark. Are the warming water temperatures and melting sea ice inducing great white sharks to travel further north where they can find a bounty of sea mammals to eat?

When great white sharks reach adulthood and grow very large, they seem to prefer eating marine mammals over fish, probably because marine mammals have a high energy-rich fat content. Observers have watched great whiles kill beluga whales in Cook Inlet, and biologists suspect they may even take walruses in the Bering Sea and the Arctic Ocean. Are great whites, at least in part, responsible for the diminishing numbers of Beluga whales? If the number of great whites increases in Alaska, will they affect other marine mammals’ population densities? Much more research is needed to answer these questions.

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I’ll take a closer look at my nemesis, the spiny dogfish shark, in my next post. We used to catch one or two of these nasty little critters a year during our summer fishing trips, but we caught as many as twenty per day this past summer. Is this increase in spiny dogfish a trend, or was this past year only an anomaly?

Osmoregulation in Salmon

July 5, 2020Fish, Kodiak WildlifeKodiak Wildlife, osmoregulation in salmon, Osmoreulation, Pacific Salmon, Robin Barefieldadmin

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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Mystery Newsletter

Incredible Spot Shrimp

June 14, 2020Kodiak Wildlife, ShrimpKodiak Wildlife, Robin Barefield, Shrimp, Shrimp in Alaska, Spot Shrimpadmin

Spot shrimp are the largest wild species of shrimp found in Alaska, with females reaching more than 12 inches (30 cm) in length. Because of their large size, marketers often refer to them as “spot prawns,” but they are not prawns.

What is the difference between a prawn and a shrimp? They might look similar, but shrimp differ from prawns in many ways. Prawns and shrimp are both decapod crustaceans, but they belong to separate sub-orders. Shrimp have plate-like gills and a set of claws on their front two pairs of legs, while prawns have branching gills and claws on three sets of their legs. Shrimp have three body segments, with the middle segment overlapping the front and rear sections, causing their bodies to curve. Prawns, however, lack the body segmentation and have straighter bodies than shrimp. Shrimp and prawns vary in many other ways too, including their reproductive habits. Prawns release their progeny into the water to survive on their own, while a female shrimp carries her eggs on her abdomen for five months.

Spot shrimp range from Southern California to the Aleutian Islands to the Sea of Japan and the Korea Strait. They occupy a variety of habitats and water depths from very shallow to 1510 ft. (460 m), but they most commonly live at approximately 300 ft (90m.). They usually remain close to the bottom and stay near rock piles, crevices, under boulders, or in other areas where they can seek protection from predators. Juvenile spot shrimp remain in shallow, inshore areas and migrate offshore when they mature.

Spot shrimp appear reddish-brown to tan and have horizontal bars on the carapace. The distinctive white spots, from which they derive their common name, are located on the first and fifth abdominal segments. The slender body of a spot shrimp has five pairs of swimmerets on the underside of its abdomen. A spot shrimp repeatedly molts throughout its life and grows larger with each molt.

The most amazing fact about spot shrimp is, like some other shrimp species, spot shrimp are protandric hermaphrodites. They mature as males and later transform into females. They reach sexual maturity at age three when they can produce sperm and spawn as males. As they grow, they pass through a transitional stage and become females capable of producing eggs. Research indicates not all spot shrimp follow this pattern, though. Some skip the male-phase of the life cycle and develop directly into females.

Before mating, a female molts into a shell specialized for carrying eggs. Each egg attaches to her abdomen by a hair-sized structure called a seta, and she carries the eggs from October to March. Biologists believe each spot shrimp spawns once as a male and one or more times as a female. They spawn at depths of 500-700 ft. (152.4 m to 213.4 m).

Spot shrimp are bottom feeders, and they feed at night. They eat a wide variety of bottom organisms, including worms, diatoms, dead organic material, algae, mollusks, and even other shrimp. Fish such as halibut Pacific cod, pollock, flounders, and salmon pursue and eat spot shrimp. Spot shrimp can live seven to eleven years.

Due to destructive fishing methods used to catch shrimp in many areas of the world, biologists consider the commercial harvest of shrimp to be one of the most unsustainable of all global fisheries. Bottom trawls destroy everything in their path. In Alaska, the shrimp harvest is mainly restricted to pot fisheries in certain areas.

In Southeastern Alaska, the Alaska Department of Fish and Game closed the spot shrimp fishery to commercial and sport fishermen in 2013, but the spot shrimp population in the area has continued to decline. Biologists wonder if recent warmer, more-acidic ocean waters could be the cause for dwindling spot shrimp numbers, and they are beginning to research the issue. Shrimp remain most vulnerable to acidification during early life stages when they rely on calcification to build their exoskeletons.

Robin Barefield is the author of four Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter, and Karluk Bones. You are invited to watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. 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.

Alaska Wilderness Mystery Novels by Author Robin Barefield: Big Game, Murder Over Kodiak, The Fisherman's Daughter, and Karluk Bones.

Mystery Newsletter

Whale Season

May 24, 2020Fin Whale, Humpback Whale, killer whale, Kodiak WildlifeFin Whale, Grey Whale, humpback whale, Minke Whale, Robin Barefield, Sei Whale, Whale Biology, Whale Evolution, whales, whales in Alaska, Wildlife of Kodiak Islandadmin

Spring marks the beginning of whale season here in Alaska. The humpbacks and grey whales begin arriving from their long migrations north from their wintering grounds, and the north Pacific Ocean teems with life as the waters warm and phytoplankton blooms. Swarms of krill and other zooplankton feast on the abundant plant life, and fish such as herring, eulachon, and similar species follow the zooplankton into the bays on Kodiak Island. In turn, huge baleen whales, including fin, sei, and humpback, gather to eat the krill and small fish. I am thrilled any time I see a whale, but I think it’s a special treat to stand in my front yard and watch these magnificent creatures feed and blow.

Sea mammals evolved from land mammals, and they resemble us in many ways. Whales, like humans, have lungs and must breathe air to survive. They are warm-blooded, and they bear live young. Whales nurse their young with milk, and while you might not think of a whale having hair, all whales do have hair at some stage in their development. All members of the order Cetacea evolved 45 million years ago from hoofed mammals, such as cows, sheep, and camels. Comparisons of specific milk protein genes indicate the hippopotamus is the closest, living, land relative to whales.

The order Cetacea contains more than eighty species; although, taxonomists debate the precise number. Biologists have recorded thirty-nine cetacean species in the North American Pacific.

Cetacea comes from the Greek word “ketos,” which means “whale.” All cetaceans have forelimbs modified into flippers and no hind limbs. They have horizontally flattened tails, and they breathe through a nostril, or blowhole, located on the top of the head. A blowhole has a nasal plug that remains closed except when forced open by muscular contractions to breathe. This plug seals when the whale dives. A whale has internal sensory and reproductive organs to reduce drag while swimming, and they do not have external ears but instead have a complex internal system of air sinuses and bones to detect sounds.The lungs of a cetacean are relatively small, highly elastic, and elongated. A whale has a muscular diaphragm, allowing the animal to purge a large amount of air in a short time. With each respiration, a whale replaces 80% to 90% of the air in its lungs. During a deep dive, a cetacean slows its heart rate and decreases blood flow to peripheral tissues.

Cetaceans living in the cold ocean waters of the North Pacific must somehow maintain a body temperature nearly the same as a human’s body temperature. A whale uses several mechanisms to accomplish this feat. First, it has a thick layer of blubber with few blood vessels, reducing the heat loss at the body surface. A whale has a counter-current heat exchanger, with arteries surrounding veins at the periphery. Hence, vessels flowing from the cold periphery to the warm core partially absorb heat lost by vessels flowing from the core toward the surface. A cetacean also has a high metabolic rate to produce heat, and it has a low body surface to volume ratio, which conserves heat. Finally, a whale has a slower respiration rate than a land mammal, so the whale expels warm air less frequently.

Most cetaceans produce large calves, and the large body volume relative to surface area minimizes heat loss in the calf. Calves are born tail first, and as soon as the calf emerges from the birth canal, the mother or another whale nudges it to the surface for its first few breaths.^[3]Cetacean mothers nurse their calves with a pair of teats concealed in slits along the body wall. The milk has a high-fat content, and the calves grow at a rapid rate. Whale mothers tend and guard their calves closely, and a calf often rides the bow wave or the convection currents produced by its mother or another adult when the whales travel. This method of travel is so efficient that the calf barely needs to move its flukes to keep up with the group.

Two suborders comprise the order Cetacea: The Mysticeti or baleen whales and the Odontoceti, or toothed whales. We most commonly see fin whales in Uyak Bay, but we also spot sei, humpback, minke, and killer whales. No matter the species, whenever I see a spout of water, excitement buzzes through me while I watch one of the largest animals on the planet.

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