Feature Species: Salmon Shark (Lamna ditropis)

This week’s featured species is a member of the family Lamnidae from the Northeastern Pacific Ocean. The Salmon Shark (Lamna ditropis) is kissing cousin to the great white (Carcharodon carcharias) and the shortfin mako (Isurus oxyrinchus) (Skomal, 2016). And like the great white and mako shark, they have a heavy body with a short snout and large gills. They have counter shading camouflage with dark gray above and stark white bellies. The salmon shark also has a distinct white patch over the pectoral fin base that is not seen on other members of Lamnidae (Ebert, Fowler, & Dando, 2015). To the ancient Greeks, “Lamna” signified a horrible monster with man-eating tendencies that was often invoked to scare children who misbehaved (Tricas et al, 1997).

Salmon shark
Idol, J. (Photographer). (2018). Salmon Shark in Alaska [Digital Image]. Retrieved from https://biganimals.com/

The salmon shark is closely related to another Lamnidae species, the Porbeagle shark (Lamna nasus). The two species are so similar in body size, morphology, and appearance that until 1947 these two species were considered one-in-the-same (Tricas et al, 1997). However, there are some notable differences between these two species. Both species demonstrate counter shading camouflage with dark gray dorsally with white bellies. However, the salmon shark has a distinct white patch above the pectoral fins over the gills (Ebert, Fowler, & Dando, 2015). These two species also appear to be geographically separated. The salmon shark resides in the northern Pacific Ocean; while the porbeagle shark resides in the northern Atlantic Ocean (Tricas et al., 1997; Weng et al, 2005; Weng, Foley, Ganong, Perle, Shillinger, & Block, 2008).

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Left: Washington Department of Fish and Wildlife (Author). (n.d.). Salmon Shark [Digital Image]. Retrieved from https://wdfw.wa.gov/ Right: Ocean Research & Conservation Ireland (Author). (n.d.). Porbeagle Shark [Digital Image]. Retrieved from https://www.orcireland.ie/

The salmon shark is a high speed, opportunistic, apex predator known for catching fast oceanic fish like mackerel, spiny dogfish, and, as their name suggests, Pacific salmon (Compagno, 2001; Fowler & Cavanagh, 2005). To catch their prey, the salmon shark has several adaptations to give them the edge over their prey. Their teeth and strong jaws are also perfectly designed for gripping slippery prey items. Unlike the great white, the salmon shark has smooth teeth with a large central cusp which are accompanied by two smaller cusplets laterally (Tricas et al, 1997).

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M. Sid Kelly (HumboltMike) (Videographer). (2011). Salmon Shark Teeth [Screen Capture]. Retrieved from https://www.youtube.com/

 

The salmon shark also have strong bodies that are built to keep up with their high speed prey. Sharks and rays can have two different types of pectoral fins: aplesodic or plesodic. Aplesodic fins are composed of cartilaginous radials that extend less than 60% through the pectoral fin. This means they are very flexible compared to plesodic fins, which have radials extending further outwards, providing more support to the fin. This makes plesodic fins stiffer and more rigid at great speeds (Klimley, 2013). Lamnidae sharks like the salmon shark have plesodic pectoral fins that give them more support when they explode into a high speed chase. The salmom shark also has a very strong caudal keel. In fact, both the salmon shark and the porbeagle shark are the only two sharks in the Lamnidae family that have a secondary keel along the base of the tail (Tricas et al, 1997).

Skeletal-structure-of-the-pectoral-fins-in-aplesodic-sharks-such-as-leopard-bamboo-and_W640
FIGURE 5.10 Skeletal structure of the pectoral fins in aplesodic sharks, such as leopard, bamboo, and dogfish (left) and plesodic sharks, such as lemon, blacktip, and hammerhead  (right). The left pectoral fin for each species is shown in dorsal view. Dark gray elements are propterygium, mesopterygium, and metapterygium from anterior to posterior; light gray elements are radials; dotted line delimits extent of ceratotrichia into the fin web. Muscle insertion extends to the end of the third row of radials in aplesodic sharks and to the end of the second row or middle of the third row of radials in plesodic sharks (Wilga & Lauder, 2004).

 

The salmon shark, unlike other members of Lamnidae, is known to form schools of 20 to 30 individuals when feeding (Tricas et al., 1997). They have even been observed cooperatively hunting in these schools. Working together, the sharks her the salmon into tighter and tighter groups towards the surface of the water. The salmon sharks then charge in at high speeds, sometimes breaching the surface, as they capture their prey (Nat Geo WILD, 2018)!

 

 

Nat Geo WILD (Videographer). (2018 May). Alaska’s Deadly Sharks | Alaska’s Deadliest [Video Clip]. Retrieved from https://youtu.be/

 

The salmon shark is ovovivparous, otherwise known as placental viviparity. This means that they give birth to live pups that develop inside the mother’s uterus. However, unlike aplacental viviparity, these sharks are not linked to their mother via an umbilical cord. Each embryo has its own yolk sac, which it will get all its nutrients throughout its 9 month gestation. Salmon shark embryos have another method of supplementing their nutrient: oophagy, or the act of consuming other embryos. As soon as these little sharks develop little jaws and teeth, they are practicing their hunting skills in utero but consuming other eggs in the womb. You may be thinking, “I thought the sand tiger shark (Carcharias taurus) was the only species known to perform intrauterine cannibalism?” And you are correct, in that the sand tiger is the only species known to actively hunt and consume other developing embryos in the womb until only one pup emerges from each womb. This is called embryophagy. Salmon shark pups have not been documented consuming their developing brothers and sisters, but rather the unfertilized eggs produced by the mother.

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Alaska Department of Fish and Game (Author). (n.d.). Salmon Shark (Lamna ditropis) embryo [Digital Image]. Retrieved from http://www.adfg.alaska.gov

Another incredible adaptation of the salmon shark is their ability to maintain and even elevate their body temperature above the ambient water temperate (Klimley, 2013). Unlike most sharks, which are ecotherms or cold blooded, sharks in family Lamnidae are endotherms or warm blooded (sort of). Endothermic sharks have a modified circulatory system that allows them to elevate the temperatures of certain organs (such as the eyes, brain, heart, stomach, and trunk muscles) through a process called counter-current heat exchange. The arteries and veins run parallel over the trunk muscles. The incoming cold blood in the veins is warmed by the outgoing warm blood in the arteries (Frederico & Hassall, 1998). The salmon shark is the most amazing example of a warm blooded shark. Studies have shown they can maintain a body temperate as high as 38°F above ambient water temperature (Goldman, Kohin, Cailliet, & Musick, 2009). In comparison, the shortfin mako can maintain a body temperature 14°F above the surrounding water and the great white can maintain 26°F above (Skomal, 2016).

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Counter-current heat exchange (n.d.). [Digital Image]. Retrieved from http://bio1152.nicerweb.com/

 

 

The salmon shark’s ability to keep its body temperature warmer than the ambient water temperature allows it to have a a wide ranging habitat throughout the northern Pacific. Typically, this species demonstrates extremely sexual segregation, with males dominating the western side of the Pacific and females dominating the eastern (Nagasawa, 1998). They also segregate by size, with larger, more mature sharks being found further north, and smaller, immature sharks being found south and in deeper waters than adults (Nagasawa, 1998). The salmon shark can venture into waters far too cool for its cousins, the great white and the shortfin mako; however, the habitats of all three species overlap along the western coast of the United States. The salmon shark’s habitat spans approximately 30° of latitude from 60°N to 30°N, ranging in temperature from 3°C to 24°C (37°F to 75°F). The shortfin mako’s habitat also spans approximately 30° of latitude from 45°N to 15°N, ranging in temperature from 10°C to 30°C (10°F to 86°F). The great white shark’s habitat covers that smallest range in this region, spanning approximately 40° of latitude from 40°N to 20°N in waters ranging from 5°C to 28°C (41°F to 82°F) (Klimley, 2013). Below, you can see the habitat ranges from these species along the Northeast Pacific. The salmon shark is shown in blue, the shortin mako in red, and the great white in black.

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Figure 14.10 The spatial distributions of salmon shark (blue symbols), what shark (black symbols), and the shortfin mako shark (red symbols) in the northeastern Pacific Ocean. With the map is a plot of the distribution of the daily average water temperatures encountered by members of each species over annual periods (Klimley, 2013).

 

The salmon shark is currently categorized as Least Concern by the International Union for the Conservation of Nature (IUCN). Historically, salmon sharks were often bycatch in gillnets set for salmon (Oncorhynchus spp.) by Russian, Canadian and Japanese fisheries (Goldman, Kohin,  Cailliet, & Musick, 2009). However, since the elimination of open water driftnet fishing by the UN in 1992, there have been significantly fewer accidental catches of the salmon shark by these fisheries (Nagasawa, Azumaya, & Yoshida, 2002). The salmon shark is still taken in U.S. water as bycatch in other fisheries such as trawl, gillnet and seine (Camhi, 1999). These catches have been poorly documented so it is difficult to fully assess the risk of these fisheries; but at this time it is thought the threat to the population is low as analysis of the populations in both the western and eastern Pacific suggest that populations are stable (Goldman, Kohin,  Cailliet, & Musick, 2009). Commercial fishing for the salmon shark in Alaskan waters has been illegal since 1997.

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Hough, K. SST (Photographer). (n.d.). Salmon shark (Lamna ditropis) caught in a trawl [Digital Image]. Retrieved from https://commons.wikimedia.org/

Shark Stats

Authority: Hubbs & Follett, 1947

Family: Lamnidae; 5 species

Length: Maximum of 10 feet (3.05 m)

Weight: Upwards of 485 lbs (220 kg); reports of 990 lbs (450 kg) are unsubstantiated

Habitat: Inshore continental shelves

Depth: Surface to 1968 feet (600 m)

Reproduction: Ovoviviparous with oophagy stage

Gestation: 9 months

Litter Range: 2 – 5 pups

Home Range: Northern Pacific Ocean

Diet: Pacific salmon, bony fishes, spiny dogfish, squid

IUCN Status: Least Concern

(Compagno, 2001; Goldman, Kohin, Cailliet, & Musick, 2009; Ebert, Fowler, & Dando, 2015; Skomal, 2016)

Thanks so much for checking out the wonderful Salmon Shark! If you missed last week’s featured species, please be sure to check out the endangered Broadfin Shark! If there is a species of elasmobranch you’d love to know more about, leave me a comment or send me a message! I would love to do a feature on your favorite species. So connect with me on Instagram and Facebook for even more elasmo fun!

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Conservation legislation needs public support in order to become law and help protect the environment and wildlife. Tell your representatives that you care about environmental and wildlife conservation.  It only takes a moment to make a change that will last a lifetime. Until next time finactics!

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Featured Image Source

AnimalSpot (Author). (2017). Salmon Shark [Digital Image]. Retrieved from http://www.animalspot.net/

Literature Cited

Camhi, M. (1999). Sharks on the line II: an analysis of Pacific state shark fisheries. National Audubon Society.

Compagno, L. J. (2001). Sharks of the world. An annotated and illustrated catalogue of shark species known to date, vol 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). FAO species catalogue for fishery purposes1, viii+-1.

Ebert, D. A., Fowler, S. L., & Dando, M. (2015). Sharks of the world: a fully illustrated guide. Wild Nature Press.

Fowler, S. L., & Cavanagh, R. D. (Eds.). (2005). Sharks, rays and chimaeras: the status of the Chondrichthyan fishes: status survey (Vol. 63). IUCN.

Frederico, L., & Hassall, G. (Eds.). (1998). Reader’s Digest Explores: Sharks (1st ed.). Reader’s Digest.

Goldman, K., Kohin, S., Cailliet, G.M. & Musick, J.A. (2009). Lamna ditropisThe IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/39342/10210228

Klimley, A. P. (2013). The biology of sharks and rays. University of Chicago Press.

Nagasawa, K. (1998). Predation by salmon sharks (Lamna ditropis) on Pacific salmon (Oncorhynchus spp.) in the North Pacific Ocean. N. Pac. Anadr. Fish Comm. Bull.1, 419-433.

Nagasawa, K., Azumaya, T., & Yoshida, Y. (2002). Impact of predation by salmon sharks (Lamna ditropis) and daggertooth (Anotopterus nikparini) on Pacific salmon (Oncorhynchus spp.) stocks in the North Pacific Ocean (No. 4). Report.

Nat Geo WILD (Videographer). (2018 May). Alaska’s Deadly Sharks | Alaska’s Deadliest [Video Clip]. Retrieved from https://youtu.be/

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.

Weng, K. C., Landiera, A., Castilho, P. C., Holts, D. B., Schallert, R. J., Morrissette, J. M., … & Block, B. A. (2005). Warm sharks in polar seas: satellite tracking from the dorsal fins of salmon sharks. Science310, 104-106.

Weng, K. C., Foley, D. G., Ganong, J. E., Perle, C., Shillinger, G. L., & Block, B. A. (2008). Migration of an upper trophic level predator, the salmon shark Lamna ditropis, between distant ecoregions. Marine Ecology Progress Series372, 253-264.

Wilga, C. A., & Lauder, G. V. (2004). Biomechanics of locomotion in sharks, rays, and chimeras. Biology of sharks and their relatives5, 139-164.

Next Post

The IUCN Announced Conservation Status Update on 58 Elasmobranch Species, Including the Shortfin Mako

Previous Post

Featured Species: Broadfin Shark (Lamiopsis temminckii)

 

 

 

 

 

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