Category Archives: Kodiak Wildlife

Wildlife of Kodiak Island including biology, behavior, and news

Mammals Introduced to Kodiak Island

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Man has introduced every mammal species on Kodiak Island other than the six endemic species (Kodiak bear, red fox, river otter, short-tailed weasel, little brown bat, and tundra vole). We humans have a sketchy history of introducing mammals into ecosystems where they did not evolve. Sometimes these introductions are harmless, but often, they are not. Ecosystems are complicated, and it is impossible for us to fully understand how the plants and animals in a particular habitat have worked together to survive over thousands of years. When we introduce mammals not native to that environment, we change the balance.

It is tricky to introduce a mammal into a habitat where it did not evolve. For example, if an island has birds that nest on the ground and man introduces an egg-eating or chick-eating predator to this habitat, the predator will soon wipe out the ground-nesting birds. Of course, most introductions do not cause such an obvious impact, but the harm is often subtle and occurs slowly over time.

New Zealanders have waged an all-out war on introduced mammals in their country. New Zealand has lost 42% of its terrestrial birds since humans settled the country 700 years ago. Many of these birds were flightless and provided easy prey for introduced mammals such as rats, stoats (weasels), and dogs. New Zealanders are trying very hard to save the few species of flightless birds they have left, including kiwis and penguins, but at this point, it is an uphill battle.

While the mammal introductions to Kodiak Island have not had the disastrous consequences of those in New Zealand, introduced mammals have had an impact on the habitat here. Beavers have altered some watersheds on the island. Their dams can divert rivers and block salmon-spawning streams. In areas where beavers are native, their activity may be beneficial to other wildlife, but in an ecosystem where beavers did not originally exist, they can have a negative effect on riparian habitat. If beavers construct a dam on a small salmon stream, they can destroy the salmon-spawning grounds in that stream.DSC_53

Mountain goats on Kodiak are over-grazing their alpine habitat, and these impacts are now being studied. Sitka black-tailed deer have nearly decimated high-bush cranberries, a species that was abundant before deer were introduced to Kodiak. Other introduced mammals have also impacted the endemic flora and fauna of the island, but most mammals were introduced in the first half of the twentieth century, and those species that survived their initial introduction, are now thriving and are considered part of the complex ecosystem of the Kodiak Island Archipelago.

Over the next few weeks, I will write about several of the introduced wild mammal species on Kodiak Island. These include Sitka black-tailed deer, mountain goats, Roosevelt elk on Afognak Island, reindeer, beavers, and snowshoe hare. I will discuss how the species are doing and how their introductions have impacted the island.

I would love to hear your comments and opinions about mammal introductions. Are they good, bad, or a little of both?

 

 

Little Brown Bat (Myotis lucifugus)

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The little brown bat (Myotis lucifugus) is one of the six species of mammals endemic to Kodiak Island. The species ranges from Alaska to Labrador and south into central Mexico. It is more prevalent in the northern part of its range and is absent from much of Florida and Texas. It is the most common and widespread bat species in Alaska and lives in a variety of habitats, from the temperate rainforests of southeastern Alaska to the spruce/birch forests of the interior to treeless areas dominated by shrubs in western Alaska. While four other bat species are found in Southeast Alaska, the little brown bat is the only species of bat that lives in the Interior and South Central Alaska, and it is the only species that exists on Kodiak Island.

As their name implies, little brown bats are small mammals. They weigh between .18 and .32 ounces (5-9 grams) and are 3-4.5 inches (7.62-11.43 cm) in length. Their wingspan is 8 to 9 inches (20.32-22.86 cm) wide. They have cinnamon to dark brown fur on their backs, while their undersides are buff to pale gray. The hairs on their backs have long, glossy tips. The tragus, a fleshy projection that covers the ear canal, aids bats in echolocation. The shape and length of the tragus are sometimes used to identify bat species. In little brown bats, the tragus is half as long as the ear and has a blunt tip.

Little brown bats are efficient in the air and can fly at speeds ranging from 4 to 21 mph (6-34km/h). At an intermediate rate of speed, their wings make 15 strokes per second. They are most active at night, and their flight patterns are erratic. If knocked to the ground, they are clumsy crawlers, but if they land on the water, they can flap across the water for several hundred feet before getting tired. When roosting, bats hang upside down, and they achieve this position by flying up to a perch and grasping it with the long, clawed toes on their hind feet.

Little brown bats in Alaska mate between August and October, but fertilization is delayed until spring. After a gestation of 50 to 60 days, a female gives birth to a single pup. It is unusual for a small mammal to have only one baby at a time. Voles and mice give birth to large litters, and sometimes produce many litters per year. Voles and mice only live for one or two years, though, while bats may live 10 to 20 years. Pregnant or nursing females congregate together in maternity roosts. This clustering helps raise the temperature in the roost, speeding growth and development of the young. While bats normally hang with their heads down, a female gives birth with her head up, allowing her to catch the newly born pup with her tail membrane. A baby is born with deciduous incisors that along with its thumb and hind feet, allow it to cling to its mother. Pups are naked and blind at birth. They are weaned and able to fly on their own when they are three weeks old.

Little brown bats eat insects and feed at night, and this can be a problem in Alaska where the short amount of darkness at high latitudes in the summer reduces the amount of time bats can spend feeding. Bats use echolocation to find and capture prey, and they often hunt over lakes, ponds, and slow-moving streams and rivers. Bats drink while flying near the surface of the water. In Alaska, little brown bats eat moths, mosquitos, beetles, a variety of flies, and even spiders. They capture prey with their teeth, by netting them with their tail membrane, or by batting an insect with the tip of a wing and deflecting it into the tail membrane. They can then transfer prey from their tail membrane to their mouth while still in flight. During the day when not feeding, bats rest in roosts, and they conserve energy while roosting by going into torpor. A torpid bat reduces its metabolic rate and temperature, thereby decreasing its energy demands.

Little brown bats communicate with chemical signals produced by the nasal gland. These glands enlarge during the breeding season. Bats also use tactile signals when mating, and while they produce few vocalizations, they do make a honking sound, which may help to prevent mid-air collisions when foraging. Echolocation calls probably help bats locate roosts and hibernation sites.

It is not known how many little brown bats live in Alaska, and not much is known about where they hibernate, or if bats in the interior and far north migrate to warmer coastal areas before hibernating. Biologists hope to learn more about the migration and hibernation of bats in Alaska through ongoing research and bat-monitoring programs.

Bats face many threats, including wind farms. For some reason, bats are more susceptible than birds to being hit by windmill blades. Pesticides are bad for bats for two reasons. They can directly poison bats, and they reduce the number of insects that bats depend on for food. Habitat loss and disturbance can also affect bats, but at present, the greatest threat to bats, especially little brown bats, is a disease called white-nose syndrome. This disease is caused by a fungus that appears white around the nose and on the wing membranes. Biologists believe this fungus, or something associated with the fungus, causes bats to wake and move around when they should be hibernating, forcing the bats to use up all their stored energy and causing them to starve to death. White-nose syndrome has killed more than six million bats in northeastern North America since 2006, and the disease is slowly moving westward.

I have now written posts about the six mammal species endemic to Kodiak Island, and next week, I will begin a series of posts about some of the mammals that have been introduced to Kodiak.

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Tundra Vole (Microtus oeconomus)

Kodiak Wildlife, , , ,

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Tundra Voles are one of the six mammal species endemic to Kodiak Island. Seven species of voles live in Alaska. Two belong to the genus Muridae, and the other five belong to the genus Microtus. The name Microtus means “small ear,” referring to the tiny ears that are nearly hidden in the fur. The tundra vole or root vole, (Microtus oeconomus) is the only species of vole that lives on Kodiak Island. Microtus oeconomus has the northernmost distribution of any Microtus species and exists on all northern continents. In North America, tundra voles are only found in Alaska and northwest Canada.

Tundra voles live in colonies of a few to as many as 300 individuals. They live in a variety of habitats from tundra to sedge meadows, but they favor areas with abundant cover. In grassy meadows, they build distinctive runways that crisscross the ground. They also dig burrows, complete with food and nesting chambers. Tundra voles do not hibernate and are active all winter. In areas covered with snow, voles make extensive tunnel systems, sometimes hundreds of meters long, under the snow where they feed on snow-flattened grass and plants. Research has shown that they memorize their tunnel routes and become so accustomed to them that if a rock is placed in the middle of a tunnel, the vole will probably run into the rock.

Voles are highly dependent on their sense of smell, and scents are probably used to identify individuals or to determine age, sex, and reproductive condition of other voles. Voles have scent glands and display common scent-marking behaviors such as scratching or rubbing. Tundra voles also have a well-developed sense of hearing, and it is believed that they may use vocalizations for communicating.

Tundra voles breed from late April through September. The gestation period lasts 20 to 21 days, and females can produce three litters a year. Females give birth to between four and eight offspring, and when they are born, the babies are naked and blind. After five days, the young are covered with hair, and they open their eyes 11 to 13 days after birth. The young develop quickly and are weaned after 18 days. They attain their maximum size approximately two months after they are weaned. Females reach sexual maturity at an age of only three weeks, but males are not sexually mature for six to eight weeks. Biologists think this delay in sexual maturation for males guards against inbreeding since females are usually fertilized before their males siblings are ready to mate. Tundra voles may live as long as two years but rarely live longer than one year in the wild.

Tundra voles are vegetarians and eat sedges, grasses, mosses, lichens, small woody shrubs, and other plants. Voles play a critical role in the food chain in Alaska. They are the primary food source for many small mammals and birds, including weasels and foxes. Even bears will sometimes eat voles. Vole populations cycle through boom and bust periods. During the high point of a cycle, the vole population may be 50 to 100 times higher than it is at the low point of the cycle. These boom times occur every four to five years, and predators that depend on voles for food also cycle in response to the size of the vole population.

Next week, my post will be about the little brown bat, another mammal endemic to Kodiak Island. Don’t forget to sign up for my free monthly mystery newsletter to read about true crime in Alaska.

 

End of Summer

Kodiak Wildlife, Living in the wilderness on Kodiak Island, , , , , ,

 

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Our summer wildlife-viewing and sport-fishing trips ended three days ago. It was time for them to end because summer is over here on Kodiak Island, and a fall storm broadsided us with our last group of bear viewers. They were good sports as we fought through the wind and rain to watch bears. The bears didn’t seem to mind the weather and put on a fantastic show, and while our guests loved watching sows chase salmon while their cubs played, we were all very wet by the end of the day. I love our September bear-watching trips, but I am tired of fighting boats in the wind, and I admit I am ready for a break. It is time to let my bruises heal and curl up with a blanket on a rainy, windy day instead of pulling on my foul-weather gear and heading out on a boat. dsc_0590b

We had a great season this year. No two days of our summer trips are ever the same, and every minute is as much of an adventure for us as it is for our guests. In July, we enjoyed great salmon fishing, and halibut fishing was good most of the summer. We saw bears in July, but they weren’t concentrated in any one place. As the summer progressed, the bear viewing steadily improved, and by September, we enjoyed phenomenal bear viewing every day. We watched several sets of sows and cubs this summer, and while our guests crouched behind fallen trees on a riverbank, they were thrilled by bears that fished only a few feet from them. They were so close; they could hear bones snap when a bear bit into a salmon.dsc_0204-2

We saw whales nearly every day of our summer season. Huge fin whales surfaced beside our boat, while humpbacks raised their flukes in the air. We saw killer whales a few times, and once, they swam over to us when we were in our 19-foot whaler, jumping beside the boat and playing in our wake. We saw dozens of sea otters and countless bald eagles every day, and we watched Sitka black-tailed deer prance along the beach while red foxes dug for clams.dsc_0287-2

On the sport-fishing front, our guests caught 17 halibut over 40 lbs. (that’s what it takes to make the Munsey’s Bear Camp halibut club) and many more halibut between 20 and 40 lbs. The largest halibut of the summer weighed 128 lbs. We enjoyed great pink salmon fishing in July, but we had a poor silver salmon run.

Michael Acela and his 128-lb. halibut
Michael Acela and his 128-lb. halibut

As always, we had guests from around the world, and we shared many laughs on ouradventures with them. Summer always seems to fly by too quickly. Sure, by mid-September I’m tired, but come next June, I’ll be excited for our summer season to begin again.

Visit our Munsey’s Bear Camp website for more information about our summer trips. If you haven’t signed up for my free Mystery Newsletter yet, head over to my home page and do that now. My newsletters chronicle true crime stories from Alaska.

Gordy Sexton with his 87-lb. halibut
Gordy Sexton with his 87-lb. halibut

Kodiak Short-tailed Weasel (Mustela ermine kadiacensis)

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Short-tailed weasels are one of the six mammals native to Kodiak Island.  Weasels are known by three common names. In their summer phase in the U.S., they are called weasels, but in their white, winter phase, they are known as ermine, and in many other countries, the same animal is called a stoat.  Two species of weasels exist in Alaska: the short-tailed weasel or ermine (Mustela ermine) and the least weasel (Mustela rixosa). The least weasel does not occur on the Kodiak Archipelago. Seven subspecies of Mustela ermine can be found in Alaska, and six of these are endemic to the state, including Mustela ermine kadiacensis, which is only found on the Kodiak Archipelago.  Weasels belong to the family Mustelidae.  Other Alaskan mustelids include river otters, sea otters, mink, marten, and wolverines.

Short-tailed weasels are found in North America, Europe, Siberia, Greenland, and Canada and have been introduced to other parts of the world.  In North America, they range from Alaska and Canada south to central California, northern Arizona, northern New Mexico, Iowa, the Great Lakes, Pennsylvania, and northern Virginia.  Short-tailed weasels occur throughout most of Alaska, except on the offshore islands of the Bering Sea and the Aleutian Islands west of Unimak Island.ermin

A Short-tailed weasel has an elongated body, short legs, a long neck, and a triangular head with long whiskers and round ears.  In the summer, a weasel’s fur is reddish-brown on the back and creamy white on the stomach, but in the winter, the fur is completely white except for the tip of the tail, which remains black all year.  A short-tailed weasel can reach 15 inches (38 cm) in length and weigh seven ounces (198 g). A weasel’s long narrow skull and slender body allow it to squeeze into vole tunnels to chase its prey of choice.

Weasels mate in mid- to late summer in Alaska, and a female may breed with more than one male.  In the southern part of their range a female produces three litters per year, but in Alaska, females give birth to only one litter a year.  Like many other animals, weasels experience delayed implantation.  After an egg is fertilized, it does not implant on the uterine wall for six to seven months.  Once it does implant, the remaining gestation period lasts only four weeks. Females give birth from early May through June to litters of three to ten young.

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Weasels nest under old buildings, in stumps, in rock outcroppings, or in rodent burrows.  They often line their nests with mouse or vole fur.  Young weasels remain in the den for 30 to 45 days after they are born, and after they first emerge, they stay near the den for a week or two before following their mother on foraging trips.  They are full grown in the early fall when they are 80 to 85 days old, and at this time, they leave their mother.  Weasels reach sexual maturity when they are one year old.  Female weasels may survive three years, but males usually do not live that long.

Weasels eat a variety of animals, including birds, insects, fish and young rabbits, but rodents, especially mice and voles, are their food of choice.  On Kodiak Island, weasels mainly eat tundra voles (Microtus oeconomus).  Weasels have a very high metabolic rate and must eat at least 40% of their body weight every day.  A pregnant female consumes an average of four voles per day.  Weasels do not hibernate but hunt all year long.  Their white fur provides them camouflage against the snow in northern climates, allowing them to sneak up on prey more easily.  They hunt both night and day, and they locate their prey mainly by scent. A weasel usually pounces on its prey with its forefeet and then kills it by biting the back of its neck.

Weasels have few natural enemies; their speed and ability to squeeze into narrow spaces help them avoid most predators.  Humans sometimes trap weasels in their white, winter phase and use this “ermine fur” as a trim on parkas and other clothing.  In some western societies, ermine fur was once considered a badge of royalty.  In Alaska, not many weasels are trapped, and only about 300-500 weasel pelts enter the fur market every year.

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Kodiak River Otter ( Lontra canadensis kodiacensis)

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The Kodiak river otter (Lontra canadensis kodiacensis) is a sub species of the North American river otter and is found only on the Kodiak Archipelago. North American river otters range throughout much of Canada and the United States.

River otters are stocky, with short legs, webbed hind feet, a thick neck, a flattened head, small ears, and a muscular body. A strong tail that is more than one-third as long as the head and body helps propel them through the water when they swim. Adult river otters weigh 15 to 35 lbs. (6.8-15kg) and are 40 to 60 inches (102-152 cm) long. Females are usually about 25% smaller than males. An otter’s fur is black-brown in color on the legs and back fading to a slightly lighter shade on the belly. The chin and throat are gray. The fur consists of a dense undercoat and longer guard hairs. Several sets of strong whiskers sprout from beneath the nose.

A river otter is well adapted for living both on land and in the water. Its thick fur helps keep it warm when swimming in cold water, and its webbed hind feet, narrow body, and flattened head allow for streamlined movement through the water. An otter swims by paddling or vertically flexing its hindquarters and strong tail. It can swim 6 mph (9.7 km/hr) and even faster over short distances by “porpoising.” An otter can dive at least as deep as 60 ft. (18 m) and stay underwater for as long as eight minutes. On land, an otter can run up to 15 mph (24 km/hr).

River otters have well-developed senses of smell and hearing. Their vision on land is not good, but they may see better under water. An otter uses its whiskers to detect prey in murky or dark water, aid in navigation, and to avoid obstructions.

River otters can live in any water habitat, including ponds, marshes, lakes, rivers, estuaries and coastal areas. They can tolerate both cold and warm environments and can live at any elevation as long as the habitat provides an adequate food source. On Kodiak, river otters live in timbered habitat next to the coast. They often travel long distances overland between bodies of water and use the same trails year after year. While more common at sea level, river otters on Kodiak are sometimes found high in the mountains.

River otters reach sexual maturity at age two, and females produce one litter per year. In Alaska, otters breed in the spring, and breeding can take place in or out of the water. A female may give birth to as many as six pups, but two or three are more common. Due to delayed implantation of the fertilized egg in the uterine wall, pups may be born from late January to June after a gestation of nine to thirteen months.

Pups are born in a den, and at birth, they are toothless and blind. They open their eyes when they are seven weeks old, and at two months of age, they begin to leave the den and start to swim and eat solid food. Pups do not innately know how to swim but must be taught by their mother who sometimes has to force and even drag them into the water. Pups are weaned when they are five months old, but they stay with their mother until just before her next litter is born.

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River otters are usually found in groups. Often these groups are related individuals, such as a mother and her pups, with or without an adult male. The female is normally the dominate member of such a group and will drive other animals away from the area around her den. Other groups may consist of siblings who have left their mother, a male and female otter, or a group of bachelor males. While otters live together in social units, they do not hunt together or share their catch with other members of their group. River otters may live for more than twenty years, but a lifespan of eight to nine years is more common.

In Alaska, river otters hunt on land and in fresh and salt water. They are opportunistic feeders and eat mussels, clams, sea urchins, snails, crabs, shrimp, octopi, fish, insects, birds, small mammals, and even plants. Otters normally eat their aquatic organisms on shore, and it is not unusual for us to find the remains of a river otter’s breakfast on our dock. If an otter catches a fish or other organism that is too big to eat in one meal, it eats what it can and abandons the rest of the food. River otters have a high metabolism and must eat often.

River otters spend half of their time sleeping. Both adults and pups are playful and like to slide on snow and mud. They wrestle, chase their tails, dunk each other in the water, and play with rocks and sticks. This playful behavior strengthens social bonds and aids pups in learning how to hunt.

River otters communicate with each other in a variety of ways. They use several vocalizations, including whistles, yelps, growls, and screams. When they are alarmed or upset, they emit a loud “hah” sound, and when two or more otters are together, they may mumble to each other as if in conversation. They chirp like a bird to express anxiety, and this sound is often heard when members of a group become separated from each other.[3] Otters also communicate by body posturing and by touch. They use the scent produced by the glands at the base of their tail to mark their territories or to create scent trails to communicate where they have been.

 

 

 

Red Fox

Kodiak Wildlife, Red Fox, , , ,

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The red fox (Vulpes vulpes) is a member of the Order Carnivora and the dog family Canidae. Red foxes occupy the largest geographic range of any member of the Carnivora, across the entire Northern Hemisphere, Central America, and Asia. The European red fox is the same species as the American red fox. There are currently 45 recognized subspecies of Vulpes vulpes, and while the classic image of a red fox may be a medium-sized canine with orange-red fur on its head, back, and sides; white fur on its chest and neck; black legs and feet; pointed black ears; and a long, bushy tail tipped in white, the reality is that the 45 subspecies differ greatly in size and color. Only the white tip on the tail distinguishes the red fox from other fox species. In addition to the differences in physical appearance between subspecies, members of the same red fox subspecies may have different color morphs. The three most common color morphs are red, silver/black, and cross. Color variations are more common in colder regions than they are in the southern parts of the range.

Red foxes are one of only six mammal species that are native to Kodiak Island, and the Kodiak red fox is a separate, distinct subspecies (Vulpes vulpes harrimani). Members of this subspecies are very large with a huge tail, coarse, thick fur on the lower back and tail, and a thick ruff around the neck and shoulders, especially in the winter. Most Kodiak red foxes are either cross foxes with a black/brown cross on the back and shoulders, or they are red in coloration. Silver foxes make up a smaller percentage of the population and are striking with black fur and silver-tipped guard hairs.

The red fox is the largest member of the true foxes. It has a head and body length that measures approximately 22 – 32 inches (56-82 cm), relatively short limbs, and a fluffy tail that is approximately 14 – 16 inches (36-43 cm) long. Adults weigh between 6 and 15 lbs. (2.7-6.8 kg), but the size and weight vary depending on the subspecies. The front paws of a red fox have five digits while the back feet have only four. Red foxes are capable of jumping over a six ft. (2 m) high fence and they can run nearly 30 mph (48.28 km/h).

The red fox has extremely good hearing and unlike other mammals, can hear low-frequency sounds very well, allowing it to detect small animals digging underground so it can dig the prey out of the dirt or snow. Although not as acute as its hearing, the red fox has a good sense of smell and binocular vision that reacts mainly to movement.

DSC_0168Anal and supra-caudal glands, as well as glands around the lips, jaws, and on the pads of the feet, allow foxes to leave and detect scents that may mark a territory or a food cache. Foxes use urine to mark their territories and food caches. A male raises one hind leg and sprays urine in front of him, while a female squats and sprays urine between her hind legs.

Red foxes are considered solitary, and they do not form packs like wolves. They often do live in family groups, though, with a dominant male and female and often a few subordinate foxes all sharing the same home range. Subordinate females may help guard, feed and care for the kits.

In Alaska, voles appear to be the food of choice for foxes, but the red fox is an omnivore and will eat fruits, berries, vegetation, insects, birds, rabbits, squirrels, and other small mammals. On Kodiak, it is common to see foxes on the beach feeding on sea urchins and other invertebrates and digging for worms. Red foxes are considered nocturnal or crepuscular (active at dawn and dusk), but they may be active at any time of the day, and on Kodiak, they are often most visible on the beaches during the morning and evening low tides. When hunting a vole, a fox locates the vole by sound and then jumps in the air and lands on its target much like a cat does. An adult red fox will eat between one and two pounds (.5 to 1.0 kgs.) a day.

 

 

 

 

 

Mammals Endemic to Kodiak Island

Kodiak Bear, Kodiak Wildlife, , , , ,

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How can any mammal be endemic to an island in the North Pacific? That mammal did not evolve on that island, so it had to arrive on the island at some point. I guess the answer depends on your definition of endemic. Most biologists believe that if a species was present on an island when the island became separated from nearby land masses, and if that species continued to survive on the island, then the species is endemic or native to the island. In other words, the species was not transported to that island by man. Experts list six mammals they consider endemic to Kodiak Island. These are the Kodiak Bear, the red fox, the river otter, the short-tailed weasel, the tundra vole, and the little brown bat. Over the next few weeks, I will discuss each of these mammals. I have already written several posts on Kodiak Bears, so I will mention them briefly here, and then in subsequent posts, I will focus my attention on the other five mammals.

At the end of the Pleistocene epoch, 12,000 years ago, ice sheets covered the North Pacific, connecting Kodiak Island to the mainland. At this time, bears and other mammals could roam freely between the mainland and Kodiak, and we assume that this was when the six mammals we consider native to Kodiak Island arrived on the island. When the ice receded and water levels rose, these mammals were trapped on Kodiak Island, where they adapted, evolved, and thrived. Humans would not arrive for another 4500 years.

After the ice receded, vegetation was scarce, but conditions slowly improved. Vegetation grew and became the jungle-like growth we know on the island today, and salmon runs became established in the many rivers and streams here. More than 3500 bears presently inhabit the Kodiak Island Archipelago, the largest number to have ever lived here. The bears thrive on prolific berry crops and rich salmon runs. Many mammals have been introduced to Kodiak over the years, and while some have negatively impacted the vegetation here, none seem to have affected brown bear abundance and vigor.DSC_0040

Kodiak brown bears exist only on the islands of the Kodiak Archipelago. The archipelago is located in the western Gulf of Alaska, approximately 250 miles (408 km) southwest of Anchorage. The island group is 177 miles (283.2 km) long and 67 miles (107.2 km) wide at its widest point. Kodiak, the most prominent island in the group, has a land mass of 3,588 square miles (8,975 km²) and is the second largest island in the United States.

In 2005, the brown bear density on Kodiak Island was estimated at 0.7 bears/square mile (271.2 bears/1000 km²), making it one of the densest brown bear populations in the world. This density estimate is a bit misleading, however, since bears are not evenly distributed across the archipelago. In the spring, summer, and fall, the bear density is much greater along the coast and salmon streams, while there are fewer bears in alpine regions. During the past decade, the Kodiak bear population has been slowly increasing. Recent genetic research has shown that while Kodiak brown bears are closely related to Alaska Peninsula brown bears and brown bears in Kamchatka, Russia, Kodiak bears have been isolated since ice sheets receded at the end of the Pleistocene epoch 10,000 to 12,000 years ago.

Over the next few weeks, I’ll write posts about red foxes, river otters, short-tailed weasels, tundra voles, and little brown bats.

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Moon Jelly

Kodiak Wildlife, Marine Invertebrates, , , ,

You probably have seen moon jellies at an aquarium. They are the small, round, nearly- transparent jellies most of us picture when we think of jellyfish. The common name moon jelly refers to all species in the genus Aurelia. Species in this genus are so similar to each other they can only be differentiated by DNA analysis. Scientists do not know how many species belong to the genus Aurelia because more are being discovered all the time.

Moon jellies are found worldwide but are most prevalent in the Atlantic, Pacific, and Indian Oceans. They tolerate a wide range of temperatures and salinities and may even inhabit brackish water. In brackish water, the bell of a moon jelly is much flatter due to the decreased salinity. Moon jellies usually stay near the surface and are capable of moving upward on their own but are dependent on wind, tides, and currents for horizontal movement. Currents sometimes bring together thousands of moon jellies in a small area, and these groupings are called a bloom, a swarm, or a smack.

A moon jelly is typically 4 to 5 inches (10 to 15 cm) in diameter. It has a shallow bell that is colorless, except for the horseshoe-shaped gonads that may be tinted violet, pink or yellow. Since the gonads are near the bottom of the stomach, they often take on the color of the prey the jelly has just eaten. The margin of a moon jelly is divided into eight lobes that are fringed by numerous, thin tentacles. Each lobe is divided by a shallow cleft housing a sensory organ that aids the jelly in maintaining its equilibrium. The radial canals of the digestive system are clearly visible and repeatedly branch as they move toward the margin of the jelly. The oral lobes or arms are short and thick.

Moon jellies are carnivorous and feed mainly on zooplankton. They are eaten by lion’s mane jellies, sea urchins, crab, some sea anemones, sea turtles, and shorebirds. Like other jellies, moon jellies have tentacles with stinging nematocysts, but their stings are relatively harmless to humans.

Moon jellies have a lifecycle similar to other jellies. In the medusa or free-floating phase, the male releases a strand of sperm which the female takes through her mouth, fertilizing her eggs. The fertilized eggs develop into larvae in pockets in the oral arms that surround the mouth. The female then releases the larvae, and they settle and develop into polyps. A moon jelly may remain in the polyp stage of its lifecycle for 25 years until conditions are right for the polyp to reproduce asexually by budding. The buds float free and develop into medusae. In the wild, moon jellies only survive about 6-months in the medusa stage, but they may live up to a year as medusae in an aquarium.

Moon jellies are the most commonly kept species in both public and private aquariums. Their wide tolerance of both salinity and temperature make them a good choice as an aquarium species.

 

 

Lion’s Mane Jellyfish

Marine Invertebrates, , , ,

The lion’s mane jelly (Cyanea capillata) is the largest known species of jelly. The largest specimen ever recorded was longer than a blue whale; it had a bell diameter of 7 ft. 6 in. (2.3 meters) and tentacles that were 121.4 ft. (37 meters) long. Lion’s mane jellies near Kodiak Island are not nearly that large; a large specimen here would have a bell diameter of 20 inches (50.8 centimeters) and tentacles 29.5 ft. (9 meters) long. Lion’s mane jellies are gorgeous animals that range from red-brown to yellow to white in color. Larger individuals are often red to dark purple while smaller jellies are a lighter orange or tan.

The lion’s mane jelly has a bell that is flattened and thick in the center and thin at the margins. The margin of a lion’s mane jelly is divided into eight, deep lobes, and each lobe is divided by a shallow cleft. A sensory organ called a rhopalium is located in each cleft, and these organs aid the jelly in determining its orientation. Although a jelly does not have a brain, it does have a central nervous system that receives input from sensory organs. Large, sticky tentacles emanate from the margin of the jelly. These tentacles are grouped into eight clusters with each cluster containing over 100 tentacles. Colorful oral arms that are much shorter than the tentacles extend from the center of the bell.

A lion’s mane jelly uses its long tentacles to capture and pull in prey to its mouth in the center of the bell. As with other jellies, the tentacles contain stinging nematocysts. When the tentacles touch a human’s skin, they cause temporary pain, itching, and localized redness. The pain is more intense if these nematocysts get into a cut or sore, or if the contact is around the eyes and nose. I frequently touch the tentacles when cleaning a fouled fish hook, and the tingling, burning sensation usually lasts only a few minutes. The pain is more severe if a person comes into contact with a large number of tentacles, but the stings are not fatal to humans who are in good health.

Lion’s mane jellies eat zooplankton, small fish, and moon jellies. They are preyed upon by anemones, some crab, shrimp, and nudibranchs. Leatherback sea turtles feed almost exclusively on lion’s mane jellies in the summer around Eastern Canada.

Some fish species, such as juvenile Pollack, and some amphipod species are immune to the sting of the lion’s mane jelly and form a symbiotic relationship with the jelly by swimming in the protection of its tentacles.

Our summer guests are often surprised to see an abundance of jellies in the frigid waters of the North Pacific, but lion’s mane jellies are a cold-water species that cannot tolerate warmer water.

Lion’s mane jellies inhabit the open ocean and stay near the surface, usually no more than 65 ft. (20 meters) deep. They can move forward with slow, weak pulses, but they are mostly dependent on wind and currents to move great distances.

Lion’s mane jellies have a one-year life span. The female jelly in the medusa stage carries its fertilized eggs in its tentacles until they grow into larvae. She then deposits the larvae on a hard surface, such as a rock, where they grow into polyps. The polyps reproduce asexually, creating a stack of individuals called ephyrae. Each individual ephyra then buds and breaks away from the stack, developing into the medusa stage.

I never grow tired of watching a beautiful lion’s mane jelly pulsing near the ocean’s surface, often with one or two small fish swimming in its tentacles. This gorgeous creature with its complicated lifecycle is one of nature’s most amazing creations.

My post next week will be about the moon jelly, the most common jelly seen near Kodiak Island. While not as showy as a lion’s mane jelly, it is a fascinating animal that often forms blooms of thousands of individuals.

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