Monthly Archives: August 2016

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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