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Behavior

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Juvenile opossum in Minnesota hissing defensively

"Playing Possum"

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When injured or threatened (e.g., by a dog), the Virginia opossum is known to feign death or "play possum".

If threatened, an opossum will either flee or take a stand. To appear threatening, an opossum will first bare its fifty teeth, snap its jaw, hiss, drool, and stand its fur on end to look bigger.[1] If this does not work, the Virginia opossum is noted for feigning death in response to extreme fear.[2] This is the genesis of the term "playing possum", which means pretending to be dead or injured with intent to deceive.[3] The reaction is involuntary and triggered by extreme fear.[2] In this inactive state it lies limp and motionless on its side, mouth and eyes open, tongue hanging out, and feet clenched.[1] Fear can also cause the opossum to release a green fluid from its anus whose putrid odor repels predators.[2][4] Heart rate drops by half, and breathing rate is so slow and shallow it is hardly detectable.[1] Death feigning normally stops when the threat withdraws, and it can last for several hours.[1][4] Besides discouraging animals that eat live prey, playing possum also convinces some large animals that the opossum is no threat to their young.[2] "Playing possum" in response to threats from oncoming traffic often results in death.[5]

Diet

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Opossums are omnivorous and eat a wide range of plants and animals such as fruits, grains, insects, snails, earthworms, carrion, snakes, birds, mice, and other small animals.[6] Insects such as grasshoppers, crickets, and beetles make up the bulk of animal foods.[7] Small animals include meadow voles, mice, rats, birds, and frogs.[8] Attracted to carrion on the side of the highway, opossums are at an increased risk of being hit by motor vehicles.[4] Plant foods are mainly eaten in late summer, autumn, and early winter.[7] These include raspberries, blackberries, apples, acorns, beechnuts, and vegetables.[7] Opossums in urban areas scavenge from bird feeders, vegetable gardens, compost piles, garbage cans, and food dishes intended for dogs and cats.[7][8] Opossums eat up to 95% of the ticks they encounter.[5][9] Opossums are estimated to eat up to 5,000 ticks per season and help prevent the spread of tick-born illnesses, including Lyme disease and Rocky Mountain spotted fever.[9] The Virginia opossum has been found to be very resistant to snake venom.[10][9] Persimmons are one of the opossum's favorite foods during the autumn.[11] Opossums in captivity are known to engage in cannibalism, though this is probably uncommon in the wild.[12] Because of this, placing an injured opossum in a confined space with its healthy counterparts is inadvisable.

Seasonal Behavior

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The Virginia opossum is most active during the spring and summer.[7] It does not hibernate but reduces its activity during the winter.[6][13] It may not leave its den for several days if the temperature drops below -7 to -4 degrees C.[7] Both males and females are at greater risk of injury during breeding season.[14] Males extend their range in search of mates which puts them at greater risk of injury from motor vehicles and predators due to unknown territory.[14] Females carrying young are slower moving and have to forage earlier in the evening and later into the night, also increasing their risk of injury from motor vehicles and predation.[14]

Reproduction

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The breeding season for the Virginia opossum can begin as early as December and continue through October with most young born between February and June.[14] A female opossum may have one to three litters per year.[14] During the mating season, the male attracts the female by making clicking sounds with his mouth.[14] The female's estrus cycle is 28 days and lasts 36 hours.[14] Gestation lasts 11-13 days and the average litter size is 8-9 infants, although over 20 infants may be born.[14] Opossums have a very high mortality rate of their young; only one in ten offspring survive to reproductive adulthood.[15] Newborns are the size of a honeybee.[7] Once delivered through the median vagina or central birth canal, newborn opossums climb up into the female opossum's pouch and latch onto one of her 13 teats.[14] The young remain latched for two months and in the pouch for 2 1/2 months.[14] The young then climb onto the mother's back where she carries them for the remainder of their time together.[14] It is during this time that the young learn survival skills.[14] They leave their mother after about four or five months.[16] Like all female marsupials, the females reproductive system is bifid, with two lateral vaginae, uteri, and ovaries.[17] The male's penis is also bifid, with two heads, and as is common in New World marsupials, the sperm pair up in the testes and only separate as they come close to the egg.[17]

 
Carrying its young

Life span

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Virginia opossum in northeastern Ohio

Compared to other mammals, including most other marsupials except dasyuromorphians, opossums have unusually short lifespans for their size and metabolic rate.[18][19] The Virginia opossum has a maximal lifespan in the wild of only about two years.[20] Even in captivity, opossums live only about four years.[21] The rapid senescence of opossums is thought to reflect the fact that they have few defenses against predators; given that they would have little prospect of living very long regardless, they are not under selective pressure to develop biochemical mechanisms to enable a long lifespan.[22] In support of this hypothesis, one population on Sapelo Island, 5 miles (8 km) off the coast of Georgia, which has been isolated for thousands of years without natural predators, was found by Dr. Steven Austad to have evolved lifespans up to 50% longer than those of mainland populations.[22][23]

 
Yellowmouth Rockfish
Threatened(COSEWIC 2010).
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Scorpaeniformes
Family:
Scorpaenidae
Genus:
Sebastes
Species:
S. reedi
Binomial name
Sebastes reedi
 
Domestic fancy rats in a double critter nation cage.



Sebastes reedi (Yellowmouth Rockfish)

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Species Information

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Out of over sixty species of rockfish found in the Pacific Ocean along North America, Yellowmouth rockfish are one of over thirty-five species found along the coast of British Columbia.[24] Its common name, Yellowmouth rockfish, comes from the characteristic yellow markings found on the inside of its mouth,[24][25][26] whereas its scientific name, Sebastes reedi, originally comes from Queen’s University Professor G. B. Reed, the Fisheries Research Board of Canada’s chairman from 1947 to 1955.[25] Yellowmouth rockfish are also frequently referred to as “red snapper,” “redeye,” “reedi,” and “rockcod."[24] Yellowmouth rockfish are often confused with Pacific ocean perch, Sebastes alutus.[27] Both species are so similar that, before the 1970s, they were interchangeably referred to as “red rockfish” or “ocean perch."[24][28]

Description and size

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The inside of the mouth has yellow, black, and red blotches, which make Yellowmouth rockfish distinguishable from other rockfish.[24][28][29] The mouth itself is pinkish white.[27][29] The body of adults is primarily red, with a mix of orange and yellow.[26][27][29] Black mottling on the dorsal side is also present in smaller rockfish of less than 40 cm.[27][29] The head has three distinct dark bands.[27] The lateral line sports a thin pink-red line down its length.[25][26] The peritoneum is silver with black dots.[29] The lower jaw is long and has a moderate to small symphyseal knob.[27] Individuals have thirteen dorsal and three anal spines.[24] The mean weight of Yellowmouth rockfish is 1.467 kg.[25] Yellowmouth rockfish have been known to live up to 99 years,[24][25][27] and reach a maximum length of 54 to 60 cm.[24][26][27]

Distribution and habitat

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Yellowmouth rockfish are an east Pacific saltwater species that range from the Gulf of Alaska to San Francisco, California, and are commonly found from southeast Alaska to Oregon.[24][25][26][27][28] Yellowmouth rockfish are widely distributed along the west coast of Canada, with highest densities in Queen Charlotte Sound.[25][26][28] Yellowmouth rockfish are estimated to inhabit 11,000 to 34,000 of the estimated 48,000 square kilometers of potential habitat available to them in Canada.[24][28] Yellowmouth rockfish occur along the continental slope at depths of 100 to 431 meters, with a preferred range of 180 to 275 meters.[24][25][26][27][28] Juvenile Yellowmouth rockfish are pelagic whereas adult Yellowmouth rockfish are benthic[24][26] and are frequently found inhabiting hard substrates such as bedrock and gravel.[24]

Biology

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Yellowmouth rockfish are viviparous.[24] In British Columbia, fertilization events occur in February and females bear live young from early spring through June.[24][25][26] Immature Yellowmouth rockfish are pelagic for up to one year.[24] During the pelagic stage, immature Yellowmouth rockfish larvae mature into juveniles, and then into adults.[24] Juvenile Yellowmouth rockfish are vulnerable to predation by other fish, such as Pacific Hake and Chinook Salmon, as well as by seabirds.[24] Once they reach adulthood, Yellowmouth rockfish become benthic and settle on rocky substrates along the ocean floor.[24][26] Yellowmouth rockfish achieve 50% maturation when the average lengths of females and males average 38 and 37 cm, respectively.[25][26] On average, it takes them 10 years to reach these lengths.[24] Yellowmouth rockfish are slow-growing, and have a generation time of 30 years.[24]

Interspecific interactions

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Yellowmouth rockfish are social, and are typically found in multispecies complexes.[24] In British Columbia, Yellowmouth rockfish are frequently caught along with Pacific Ocean perch, Arrowtooth flounder, and Redstripe rockfish.[24][28] Deepwater Yellowmouth rockfish assemblages along the west coast the the US and the Gulf of Alaska typically consist of a variety of rockfish species, including Chilipepper and Darkblotched rockfish.[24]

Commercial Importance

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Yellowmouth rockfish support the third largest rockfish fishery in British Columbia, after Pacific Ocean perch and Yellowtail rockfish, with an annual total allowable catch of 2,444 t.[26] From 2007 to 2008, the total Canadian catch of Yellowmouth rockfish was valued at $1.5 million.[24][26] Bottom and midwater trawlers are the preferential method used to catch this species.[24][28]

Threats

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The primary threat to Yellowmouth rockfish is commercial fishing.[24][28] Bottom trawling is the preferred method of catching Yellowmouth rockfish along the continental slope in British Columbia, and very little of this area receives habitat protection.[24] In 2006, the Seafood Watch Program of Monterey Bay Aquarium classified all slope rockfish as high conservation concern and inherently vulnerable.[24] In 2010, the Committee on the Status of Endangered Wildlife in Canada officially declared Yellowmouth rockfish along the Pacific coast of Canada as threatened.[24][26][28] Rockfish traits of slow growth, delayed maturity, and longevity make them vulnerable to overfishing, habitat loss from bottom trawling, and environmental change.[24][28]

Yellowmouth rockfish are susceptible to infection by common marine fish pathogens.[24][30] Out of the Yellowmouth rockfish surveyed for pathogens off of the coast of Oregon in 2001, 10% were found to be infected with Ichthyophonus and 2% with Mycobacterium.[24] The spleens and kidneys of rockfish infected with these pathogens contained multiple, discrete nodules of cartilaginous metaplasia.[30]

Like other rockfish, Yellowmouth rockfish have swim bladders that are unable to adjust to rapid pressure changes.[24] Consequently, Yellowmouth rockfish are extremely vulnerable to injury when caught from deep water, and bycatch mortality for most rockfish species is close to 100%.[24]

  1. ^ a b c d "Virginia Opossum". www.psu.edu. Retrieved 2020-09-28.
  2. ^ a b c d "Opossum Defense Mechanisms | Opossum Society of the United States". Retrieved 2020-09-28.
  3. ^ "PLAY POSSUM | definition in the Cambridge English Dictionary". dictionary.cambridge.org. Retrieved 2020-09-28.
  4. ^ a b c "Give opossums a break". Cary Institute of Ecosystem Studies. Retrieved 2020-09-30.
  5. ^ a b "Why you should brake for opossums". Cary Institute of Ecosystem Studies. Retrieved 2020-09-28.
  6. ^ a b "Virginia opossum". Smithsonian's National Zoo. 2018-01-05. Retrieved 2020-09-28.
  7. ^ a b c d e f g "Opossum | Adirondack Ecological Center | SUNY ESF | College of Environmental Science and Forestry". www.esf.edu. Retrieved 2020-09-28.
  8. ^ a b "Opossum Management Guidelines--UC IPM". ipm.ucanr.edu. Retrieved 2020-09-28.
  9. ^ a b c Maurer, Steph. "The Helpful Opossum | Wildlife Medical Clinic at Illinois". Retrieved 2020-09-28.
  10. ^ Sharon A. Jansa; Robert S. Voss (2011). "Adaptive evolution of the venom-targeted vWF protein in opossums that eat pitvipers". PLOS ONE. 6 (6): e20997. doi:10.1371/journal.pone.0020997. PMC 3120824. PMID 21731638.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  11. ^ Sparano, Vin T. 2000. The Complete outdoors encyclopedia. St. Martin's Press. ISBN 0-312-26722-3
  12. ^ Cannibalism in the Opossum. Opossum Society. Accessed May 7, 2007.
  13. ^ "Virginia Opossum Didelphis virginiana". eNature.com. Shearwater Marketing Group. Archived from the original on 2011-05-17. Retrieved 2009-03-24.
  14. ^ a b c d e f g h i j k l "Reproduction – Life Cycle | Opossum Society of the United States". Retrieved 2020-09-30.
  15. ^ Tyndale-Biscoe, Hugh (2008). Life of marsupials ([New.] ed.). Collingwood: CSIRO. pp. 105–138. ISBN 9780643092204.
  16. ^ "Reproduction – Life Cycle - Opossum Society of the United States". opossumsocietyus.org.
  17. ^ a b Krause, William J. (2005). The Opossum: Its Amazing Story. Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri, Columbia, Missouri. ISBN 0-9785999-0-X.
  18. ^ Krause, William J.; Krause, Winifred A. (2006).The Opossum: Its Amazing Story Archived 2012-12-11 at the Wayback Machine. Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri, Columbia, Missouri. 80 pages.
  19. ^ Fisher, Diana O.; Owens, Ian P. F.; Johnson, Christopher N. (2001). "The ecological basis of life history variation in marsupials" (PDF). Ecology. 82 (12): 3531–3540. doi:10.1890/0012-9658(2001)082[3531:TEBOLH]2.0.CO;2.
  20. ^ Virginia Opossum. Didelphis virginiana Archived 2007-10-24 at the Wayback Machine. Great Plains Nature Center. accessed Oct. 15, 2007
  21. ^ The Life Span of Animals Accessed Oct. 15, 2007
  22. ^ a b Karen Wright Staying Alive. Discover Magazine. November 6, 2003 Accessed Oct 15, 2007.
  23. ^ "State Of Tomorrow™ - Rising Challenges. Higher Education Solutions". www.stateoftomorrow.com.
  24. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai COSEWIC. 2010. COSEWIC assessment and status report on the Yellowmouth Rockfish Sebastes reedi in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 57 pp. http://publications.gc.ca/collections/collection_2011/ec/CW69-14-605-2010-eng.pdf
  25. ^ a b c d e f g h i j Haigh, R., and P. Starr. A Review of Yellowmouth Rockfish Sebastes Reedi Along the Pacific Coast of Canada: Biology, Distribution, and Abundance Trends. DFO, Ottawa, ON (Canada), 2008. https://waves-vagues.dfo-mpo.gc.ca/Library/335708.pdf
  26. ^ a b c d e f g h i j k l m n Recovery Potential Assessment for Yellowmouth Rockfish (Sebastes Reedi) Along the Pacific Coast of Canada. Science Advisory Report 2011/060 Vol. Ottawa: Fisheries and Oceans Canada, 2011.https://waves-vagues.dfo-mpo.gc.ca/Library/345104.pdf
  27. ^ a b c d e f g h i j “Yellowmouth Rockfish Sebastes Reedi.” Bottomfish Identification Guide: Rockfish (Sebastes), Washington Department of Fish & Wildlife. https://wdfw.wa.gov/species-habitats/species/sebastes-reedi
  28. ^ a b c d e f g h i j k Government of Canada, Fisheries and Oceans Statistical Services (2016-12-19). "Yellowmouth Rockfish". www.dfo-mpo.gc.ca. Retrieved 2019-04-07.
  29. ^ a b c d e Orr, J. W., M. A. Brown, and D. C. Baker. 2000. Guide to rockfishes (Scorpaenidae) of the genera Sebastes, Sebastolobus, and Adelosebastes of the Northeast Pacific Ocean, second edition. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-117, 47 p. https://www.afsc.noaa.gov/publications/AFSC-TM/NOAA-TM-AFSC-117.pdf
  30. ^ a b Heidel, Jerry R., et al. “Visceral Nodular Cartilaginous Metaplasia in Rockfishes (Sebastes Spp.) in the Eastern North Pacific Ocean.” Journal of Veterinary Diagnostic Investigation, vol. 14, no. 6, Jan. 2002, pp. 495–497. https://journals.sagepub.com/doi/pdf/10.1177/104063870201400608
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