Featured Species: Birdbeak Dogfish (Deania calcea)

The ornate wobbegongs are the family Orectolobidae, which contains 12 species of wobbegongs. Like all “wobbies,” the ornate wobbegong has a flattened body with a broad head and back that quickly narrows towards the tail. They have long, slender teeth that have been adapted for grasping small, benthic fishes. What differentiates the ornate wobbegong are the black bordered, saddle-like markings along its back side. It has 5 to 6 dermal lobes on each side of its head and a single barbel attached to its nostril. Other species of wobbegongs like the tasseled wobbegong (Eucrossorhinus dasypogon) can have dermal lobes covering the lower jaw and chin and several barbels instead of one (Tricas, Deacon, Last, McCosker, Walker, Taylor, 1997).This week’s featured species is another wonderfully bizarre species from the deep sea. The Birdbeak Dogfish (Deania calcea), also known as the Brier Shark or the Shovel-nose Shark,  is a relatively small shark species, reaching lengths of 4 feet (1.22 m) (Parker, 2008; Ebert, Fowler, & Dando, 2015). They have extremely long, flattened snouts with large, bulging eyes. Their dorsal fins are proceeded by sharp spines, with the second dorsal fin and spine being longer and higher than the first (Ebert, Fowler, & Dando, 2015).

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Sharkwater Extinction (Author). (n.d.). Birdbeak Dogfish [Digital Image]. Retrieved from https://www.sharkwater.com/

The birdbeak dogfish is a deep water species that is typically observed between 230 to 4820 feet (70 to 1470 m) in bathypelgaic or bathyl zone.  This region of the water column is characterized by its lack of light and photosynthetic organisms; for this reason, this zone is sometimes called the “midnight zone” (NOAA, 2017). The birdbeak dogfish has been encountered along continental and insular slopes and shelves in the Eastern Atlantic Ocean and scattered regions in the Pacific Ocean (Ebert, Fowler, & Dando, 2015). Juveniles and adults appear to segregate by depth. There also appears to be segregation by sex once males and females mature (Stevens, 2003). Though more research is needed to understand this dynamic as well as many other behaviors. Due to the great depths of their habitat, the birdbeak dogfish isn’t a well studied species. However, this species does appear to be one of the more abundant deep water, mid-slope dogfish species based on catch data (Clark, Anderson, Francis, & Tracey, 2000).

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IUCN (Author). (2012). Geographic range in detail for Deania calcea [Digital Image]. Retrieved from https://www.iucnredlist.org/

Living in the bathypelgic zone, food can be scarce. The birdbeak dogfish has evolved a set of jaws that can easily prey upon whatever it may come across. Whether it be a slippery bony fish, like a lanternfish; or a soft, squishy cephalopod, like a squid or an octopus; or the hardened bodied of a crustacean, like a shrimp or crab, the birdbeak dogfish has the tools to handle the job (Parker, 2008).

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OceanLab (Photographer). (2008). Birdbeak Dogfish at approximately 900m water depth off the west coast of Ireland in the Rockall Region [Digital Image]. Retrieved from http://eu-fp7-coralfish.net/

The birdbeak dogfish has a set of jaws that exhibits heterodonty, or having different morphologies of teeth (Valenzuela, Bustamante, & Lamilla, 2008).  The teeth in the upper jaw have a straight, wide root with a single cusp. The teeth in the lower jaw have a recurved cusp, meaning the tooth curves towards the side. The teeth in both jaws have sharp, smooth edges (Valenzuela, Bustamante, & Lamilla, 2008).

 

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Fig. 2. Frontal teeth of upper (left) and lower (right) jaws of Deania calcea. Scale bar (in mm) is indicated on each photograph (Valenzuela, Bustamante, & Lamilla, 2008).

 

A shark eye is remarkably similar to a human or cat eye. In the most basic terms, light enters the eye through a pupil where the image is focused by the lens before coming to rest on the retina. The retina is the lining of the back of the eye which is made up on the cells that see. The retinal cells transmit information to the optic nerve, where the information is then passed along to by interpreted by the brain (Stein, Stein, & Freeman, 2006). Both sharks and cats also have a layer called the tapetum lucidum which provides the retinal cells with a second opportunity for photon-photoreceptor stimulation, enhancing their visual sensitivity in low light (Klimley, 2013).  Within the retina there are two types of photoreceptors: rods and cones. Rods are the most common photoreceptor cell in the retina. These cells have an oval base and long inner and outer segments. These cells allow elasmobranchs to distinguish light from dark objects in twilight and low light situations (Klimley, 2013). Cone cells, on the other hand, are less common within the retina. These photoreceptor cells have a conial base with thick inner segments attached to thinner outer segments which taper at the end. These cells are thought to allow elasmobranchs to distinguish colors during the daytime, as well as distinguish an object from the background with a slightly different brightness (Klimley, 2013). These cells are more abundant in the retinas of shark species that inhabit shallow waters and are active during the day. Deep dwelling, nocturnal species tend to have to rods than cones. The birdbeak dogfish shark has a rod to cone ratio of over 100:1 (Klimley, 2013). Below, you can see the overall structure of the shark eye (a), as well as the structural differences in the retina between a darker adapted species (b) and a light adapted species (c).

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Fig. 8.3 (a) Anatomy of the eye of a shark. Structure of the retina when adapted to (b) dark and (c) light (Klimley, 2013).

 

The birdbeak dogfish is currently categorized as a Least Concern species by the International Union for the Conservation of Nature (IUCN). Currently, evidence suggests that populations are trending stable, and the birdbeak dogfish continues to be one of the most abundant mid-slope species throughout its region (Clark, Anderson, Francis, & Tracey, 2000). However, there are targeted fisheries for the birdbeak dogfish and they taken as bycatch by trawl, hook, and gillnet fisheries (Stevens, 2003). They are taken specifically for their livers, which comprises about 70% of their body by weight (Bakes & Nichols, 1995). Shark livers store high levels of oils, which are believed to keep their bodies buoyant, as oil is less dense than water (Parker, 2008). Within the livers are several oils that have been harvested by humans, one of which is squalene. Squalene can be found in many skin care products and cosmetics because its fatty, richness does wonders for keeping our skin soft, supple, and moisturized. However, shark liver is not the only available source for squalene, as it is also found in wheat germ, amaranth seeds, and even olives (Parker, 2008). These alternative sources are referred to as “plant based” Squalane. In 2002, fisheries in Australia prohibited the landings of shark livers unless accompanied by the entire carcass in an effort to curb harvesting sharks at sea for livers alone in a similar manner to the fin trade (Stevens, 2003).

As a consumer you have several options available to you to help sharks, like the birdbeak dogfish and the tope shark (Galeorhinus galeus), stay out of your skincare and cosmetics:

  1. Examine your favorite products. Avoid any that list Squalene or Squalane that is not specified as “plant based.”
  2. Change up your routine! Switch to a cosmetic and skin care company that is cruelty free (no animal testing) or vegan certified (no animal testing and no animal product/by products used). Here is a list of cruelty free companies.  Here is a list of vegan companies.  I personally use E.L.F. and Tarte cosmetics and Shea Moisture skin care products.
  3. You can write letters/emails to the cosmetic companies demanding accountability and transparency. You have a right to know what you are putting on your skin and absorbing into your body.
  4. You can write to your government representatives. Demand that the cosmetics industry be held to higher standard of accountability. Your government officials can pass laws to regulate the industry, but the call to action needs to come from the constituents: YOU.
Squaleane
100% Pure (Author). (2019). Squalane V Squalene [Digital Image]. Retrieved from https://www.100percentpure.com/

I’m delighted to announce a partnership with the wonderfully talented Julius Csotonyi! Julius creates stunning shark coloring sheets that are fun and educational for all ages. From time to time you’ll see Julius’ work featured right here and on my other social media platforms! You can find more coloring sheets in the store! You are welcomed to download these beautiful sheets and enjoy them with family and friends.

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Shark Stats

Authority: Lowe, 1839

Family: Centrophoridae (Gulper Sharks); 17 species

Length: 4.0 feet (1.22 m)

Weight: Up to 15 lbs (6.8 kg)

Habitat: Continental and insular slopes and shelves

Depth: 230 to 4820 feet (70 to 1470 m)

Reproduction: Ovoviviparous

Gestation: Unknown

Litter Range: Up to 12 pups; average litter size is 7 pups

Home Range: Patchy distribution throughout the Atlantic and Pacific Oceans

Diet: Deep sea bony fishes like lanternfish, as well as cephalopods, mollusks, and crustaceans

IUCN Status: Least Concern

(Stevens, 2003; Parker, 2008; Ebert, Fowler, & Dando, 2015)

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. Proceeds benefit shark research and conservation with a donation to Project AWARE!

Thanks so much for checking out the bizarre Birdbeak Dogfish! If you missed last week’s featured species, please be sure to check out the wonderfully weird Winghead 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. Also connect with me on Instagram and Facebook for even more elasmo fun!

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

OceanLab (Photographer). (2008). Birdbeak Dogfish at approximately 900m water depth off the west coast of Ireland in the Rockall Region [Digital Image]. Retrieved from http://eu-fp7-coralfish.net/

Literature Cited

Bakes, M. J., & Nichols, P. D. (1995). Lipid, fatty acid and squalene composition of liver oil from six species of deep-sea sharks collected in southern Australian waters. Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology110(1), 267-275.

Clark, M. R., Anderson, O. F., Francis, R. C., & Tracey, D. M. (2000). The effects of commercial exploitation on orange roughy (Hoplostethus atlanticus) from the continental slope of the Chatham Rise, New Zealand, from 1979 to 1997. Fisheries Research45(3), 217-238.

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

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

NOAA. (2017, February 7). Layers of the Ocean. Retrieved from http://www.srh.noaa.gov/jetstream/ocean/layers_ocean.html

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

Stein, H. A., Stein, R. M., & Freeman, M. I. (2006). The ophthalmic assistant: A text for allied and associated ophthalmic personnel(8th ed.). Philadelphia, PA: Elsevier Mosby.

Stevens, J. (SSG Australia & Oceania Regional Workshop, March 2003) (2003). Deania calceaThe IUCN Red List of Threatened Species. Retrieved from https://www.iucnredlist.org/species/41798/10549437

Valenzuela, A., Bustamante, C., & Lamilla, J. (2008). Morphological characteristics of five bycatch sharks caught by southern Chilean demersal longline fisheries. Scientia Marina72(2), 231-237.

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