Category Archives: Wildlife

Interpretive Blogs about Wildlife and Plants

Albacore TUNA (Thunnus alalonga)

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Where does the tuna in your sandwich come from?
               That can over there.
Is that where it lives?  
                      Mmmm it seems a little small.
How does the tuna get into the can?
                               I don’t know but probably angry.

What you know may not be what’s important.

If you have only seen something in a little can it may be difficult to envision it as a top level, hard hitting ocean predator. Tuna is more than what you see in the can.

Dressed like a rock star

Albacore Tuna are handsome fish with torpedo-shaped bodies, smooth skin, and long, streamlined fins. The pectoral fins may be at least half the length of their bodies. Their metallic, dark blue back and silvery white sides make them nearly invisible in the water.

They can grow up to nearly four feet in length and weigh almost 80 pounds. In our waters they average 20- to 30-inches and up to about 35 pounds. These fish belong to the North Pacific stock and are generally juvenile or sub-adult fish that have not spawned.

Eats like an athlete

Albacore can swim over 50 miles per hour which facilitates long annual migrations and successful predation. They have a high metabolism and thus may consume as much as 25 percent of their own weight every day. 

Albacore tuna are unique among the tunas because their primary food sources are octopus and squid, versus fish. As a top ocean carnivore, they prey on schooling stocks such as squid, sardines, anchovy, crabs, lobsters, shrimp.

Albacore predators include larger species of billfish, tuna, sharks, and humans.

Hunting and Hunters

This fish has a highly evolved circulatory system that regulates body temperature, increases muscle efficiencies, supports high metabolism, and high blood pressure, volume and hemoglobin.

All of this helps tuna increase their ability to absorb oxygen. They lack structures needed to pump oxygen rich water over their gills. To compensate they must constantly swim and keep their mouths open to breathe.

Going to School

Similarly-sized Albacore swim together in a school. Each school is very large and can be up to 19 miles wide. Migrating Albacore may cover over 50 miles each day when migrating. Migration timing and distance vary based on oceanic conditions.

There are six distinct Albacore stocks that generally do not mix (North Pacific has two groups one that heads for Baja California and the other for the coasts of Oregon and Washington). Other stocks include Atlantic and Indian oceans, and the Mediterranean Sea.

Migrations

North Pacific 2- to 4-year old Juveniles begin in spring and early summer from waters near Japan. They spawn between March and July. Females broadcast eggs near the surface for fertilization. They may release between 800,000 and 2.6 million eggs every time they spawn.

By July, they move into inshore waters 15-200 miles off the U.S. Pacific coast and hang out through September. They spend fall and winter in the western Pacific Ocean.

Management of

The migration across several international boundaries complicate specie management along with its economic importance. The gross national product of several countries depends on the tuna.

In the U.S., the National Oceanic Atmospheric Administration (NOAA) Fisheries have been tagging and studying the fish and recommending management actions to avoid overfishing. Several stocks are in significant decline and the species’ overall population trend is decreasing. Albacore are considered to be ‘Near Threatened.’

Bait and Switch

Albacore demand is sometimes fraudulently met through substitution.  Escolar (Lepidocybium flavobrunneum) has been frequently substituted, or ‘confused,’ with Albacore.

Escolar are known to create potential health problems when consumed. While it is not toxic per se it has caused enough concern for several countries to ban it.

REFERENCES:
–Oregon Dept. of Fish and Wildlife (https://myodfw.com/fishing/species/albacore-tuna, commercial landing statistics, and 2018 Albacore Annual Reports)
–NOAA Fisheries (https://www.fisheries.noaa.gov/species/pacific-albacore-tuna)
–Wikipedia Albacore (https://en.wikipedia.org/wiki/Albacore)
–The Atlantic, 59% of the tuna Americans eat is not tuna (https://www.theatlantic.com/business/archive/2013/02/59-of-the-tuna-americans-eat-is-not-tuna/273410/

Orca (Orcinus orca)

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Wolves of the Sea

Orca, or Killer Whales, are sometimes called ‘wolves of the sea.’ Orcas have no natural predators and often hunt in packs like wolves.

Killer Whales (royalty free image by Bart Van Meele on Unsplash)

Killer whales can be found in all oceans, most seas, and even in some rivers. They are also tolerant of most water temperatures.

Range

Orcas can be seen on the Oregon coast in several locations, particularly in mid-April when the gray whales are returning.

Generally, they are found along the Pacific west coast from California north into Alaska. Killer whales have also been seen at Depoe and Yaquina bays, and Newport.  

Orcas have been spotted on large rivers (as in 100 miles upstream on the Columbia most likely hunting seals).

Diet

Their diet will vary depending on food productivity. As the level of productivity goes down, their diet becomes more generalized.  Some specialize and focus on a particular (most likely abundant) prey species in a particular region.

They hunt fish, squid, octopi, mammals (otters, seals, swimming deer), seabirds, squid, octopus, cuttlefish, sharks, nautilus, and other whales. Killer whales eat around 100 lbs of food each day.

Maternal Groups

Some orca populations, or pods, have complex and stable social groups and may include 50 individuals.  Several generations will travel together, and with only short separation periods (for foraging and mating).

An Orca may live with its mother as part of a pod for their entire life. Orca form matrilineal (matriarch, or eldest female) family groups.

Matrilineal family structures are the most stable. No other species has such a complex social structure.

Pod members help teach young Killer whales how to hunt and parent through apprenticeship, among other skills. 

Social Structures

A pod can contain several family groups. Males nearly always mate with females from other pods.

Pods may co-mingle to create a clan. Clans typically share similar dialects or vocalizations and potentially older Maternal lineages.

Clans can also regularly commingle to create a ‘community.’  Communities, however, may not share the same vocal patterns.

Vocalization, or dialects, can be specific to a particular clan. A lack of shared dialect suggests that there may be more than one species of Killer whale.

Identification

Orca pod (royalty free image by Lachlan Gowen at Unsplash)

You have probably seen pictures of a Killer whale. They are very identifiable due to their size (huge), color (black and white warning colors), teeth (big and sharp), and similar to dolphins. All white orcas have been found.

This apex hunter is often significantly larger than most great white sharks. The arrival of orcas in an area can cause white sharks to flee and forage elsewhere.

Killer whales are the largest members of the dolphin family. Males can grow up to 26 feet long and weigh over six tons. Females are generally a bit smaller growing up to 23 feet long and weighing about three to four tons.

These giant dolphins are born large weighting in about 400 pounds at birth and already nearly eight feet long. Even so, nearly half of all newborns die before their first birthday.  

Unlike other dolphin species, this animal has a well-developed protective dermal (skin) layer that includes a dense network of collagen fibers. Beneath the skin, orcas have a nearly four-inch layer of insulating blubber.

Hunting

Killer whales are amazing apex hunters. Orcas typically swal­low small prey whole and tear up larger prey. A few facts about orcas:

  • They are so­cial hunters, similar to wolves, that work as a pack to hunt large prey. They use coordinated behaviors and communication which may be specific to a particular pod.
  • Orcas have very sophisticated echolocation abilities (like other dolphins). They can identify the location and characteristics of prey or objects in the water.
  • These dolphins also have good eyesight above and below the water. They also have excellent hearing and a good sense of touch.
  • Typically, they spend most of their time in shallow waters but will occasionally dive several hundred feet to reach prey. As they dive, they are able to reduce their heartbeat per minute from 60 to 30 which helps them conserve energy.

Humans

Killer whales have been a part of many indigenous cultures and widely regarded with respect. This has not always been true.

For some time, orcas were hunted for entertainment (shows, zoos, etc.). This practice is being dramatically discontinued.

Several elements make these animals difficult to maintain in captivity (social structure, size, etc.). Generally wild orcas have not killed or harmed humans. This is not the case for stressed-out captive whales.

A lack of knowledge affects our ability to measure populations, identify different species, and track them. See Oregon Whale Watching!  

REFERENCES:
–Oregon Dept. of Fish and Wildlife, Orca (https://myodfw.com/wildlife-viewing/species/killer-whale)
–Animal Diversity (https://animaldiversity.org/accounts/Orcinus_orca/)
–Wikipedia, Killer Whales and several other terms like ‘Cephalopoda’ (https://en.wikipedia.org/wiki/)

Opossum (Didelphis virginiana)

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Playing Possum….

You might have heard about ‘playing possum.’ Opossums will fake apparent death in order to escape a predator.

They are pretty convincing because the animal falls over and lies motionless for up to six hours! They also often release a very nauseating odor when threatened.

Opossum or possum….both bite. Photo courtesy of ODFW.

Opossums are not the only animal that will fake apparent death or tonic immobility. Evidently this technique is also used by fish, sharks, reptiles, rabbits, chickens, and ducks.

Description

The Virginia Opossum is a cat-sized gray and white animal with a pointed nose, beady eyes, and a naked scaly tail. This mammal will reach up to 40 inches long.

This nocturnal species has several adaptations that help make it successful, including:

  • Five toes and opposable thumbs on all feet make them agile climbers. Humans, gorillas, chimps, orangutans, gibbons also have opposable thumbs.
  • Extra keen eyesight–they have more than twice the number of rod-to-cone ratios compared to humans (50:1 vs. 20:1). Color recognition is limited.
  • They have very sensitive whiskers that assist their nocturnal movements.
  • The prehensile, rat-like tail is great for grasping plant materials and bedding material.    
  • Females have a pouch for holding newborns similar to a kangaroo. 

Origins

Opossums originated in South America. There are different theories about how opossums became established in the U.S. including migrations, as pets, for farming, and more.

What we do know is that this mammal is found in many parts of the U.S. and northwestern Canada. It is the only marsupial north of Mexico.

These mammals arrived in California and Oregon in the early 1920’s. Opossum were also farmed for their pelts and meat (considered a substitute for rabbit and chicken).

“I’ll be back and eat anything (almost).”
Photo royalty free, unsplash.

Diet

This opportunistic omnivore will eat almost anything. Much of their diet includes scavenged foods, like carrion. Other foods often include plant materials, insects, mammals, and reptiles, fish, amphibians, and more. 

Human activities have provided excellent opportunities for opossums by inadvertently providing shelter, food, and water. Recommendations for minimalizing problems include sealable waste containers, securing pet food and water inside at night, and cleaning up agricultural waste (such as dropped fruit).  

A Pest and Friend

Opossums are successful colonizers and survive in a wide variety of environments. They favor dark, secure areas and are active at night for potentially nine or more hours. Typical habitats include agricultural lands, forest communities, areas with small streams, and wherever humans are.

They are an invasive species in most places, but they do have a redeeming trait. Many large opossums are immune to rattlesnake venom and will regularly prey upon these snakes.

Fun Facts:

–The word “opossum” (borrowed from the Powhatan language) was first recorded by John Smith and William Strachey between 1607 and 1611.
–Opossums are finicky groomers.
–They can be trained to use a cat box.
–The species has a tendency towards cannibalism, particularly in over-crowded conditions.
–Juveniles swing from branches with their tails.
–It is illegal to keep this species as a pet (see State regulations).
–When threatened they will growl, hiss, strike, and attempt to bite. With approximately 50 teeth, it has the ability to hurt you and your pets.  If you have an infestation, call a professional.

REFERENCES:
–Oregon Dept. of Fish & Wildlife (https://myodfw.com/wildlife-viewing/species/virginia-opossum and https://myodfw.com/articles/furbearer-trapping-and-hunting)
–LafeberVet (https://lafeber.com/vet/basic-information-sheet-virginia-opossum/)
–Wikipedia, Apparent death and Opossum (https://en.wikipedia.org/wiki/Apparent_death and https://en.wikipedia.org/wiki/Opossum