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Posts tagged ‘shark’

Sharks Among Us – The Brown Cat Shark

Here’s a mystery shared (and solved) by Farlyn Campbell.

This was found in May of 2018 north of Port Hardy.

Photo: Jared Towers. Brown Cat Shark egg case found on May 30, 2018 near Doyle Island off NE Vancouver Island, British Columbia. Found by Jared and Farlyn when they came upon a rope with buoy drifting in the ocean. They removed the rope due to its potential to entangle animals and of course placed the egg case back in the ocean. 

It’s the egg case of a Brown Cat Shark (Apristurus brunneus) with an embryo developing inside and it’s mind-blowing how long it takes before it hatches. Read on!

The Brown Cat Shark is a common species of shark off British Columbia’s coast but, here we go again . . . very little is known about it.

Most sharks (about 60%) have “viviparous” reproduction where the young develop inside the female and hatch out when fully developed.

However, Brown Cat Sharks have “oviparous” reproduction where the eggs hatch outside the body of the female. The embryo develops inside the egg, feeding on the yolk. Yes, this is how birds develop too. The egg cases of oviparous sharks are not shelled however, as you can see above. They have distinct shapes per species but all have this tough “leathery” membrane. The egg cases are also known as a “mermaid’s purses”. (See the end of this blog for further information on reproductive strategies in sharks).

Female Brown Cat Sharks lay one egg case at a time that contains a single embryo. Each egg case is around 5 cm long and 2.5 cm wide. In the case of Brown Cat Sharks, the embryo develops inside for more than 2 years! In our cold waters, maximum known incubation period is 27 months. The size of the hatched pup is 7 to 9 cm. (Source: Love). Development is shorter where temperature is warmer.

The distinctive “tendrils” on the egg cases of Brown Cat Sharks are believed to help anchor them to hard surfaces.

In British Columbia, the females carry (and deposit) between 1 to 16 mature eggs most often between February and August. (Source: Love and McFarlane). Further to the south in their range, they females apparently lay egg cases year round.

Little is known about what feeds on the egg cases but bore holes suggest that gastropods like whelks drill into them.

Brown Cat Shark – Details 

See below for more information on the 16 species of shark known to be off the coast of BC. Image source:  Fisheries and Oceans Canada, Sharks of British Columbia. 

Cat sharks (Scyliorhinidae) are the most diverse and largest family of living sharks. There are ~157 species worldwide. Their common name may be in reference to their cat-like eyes.

Brown Cat Sharks are harmless to humans. They feed on small true shrimps, pelagic red crabs, euphausiids, mysid shrimps, isopods, squids, and small fishes (Source: Love) Off the coast of BC, maximum documented size for the Brown Cat Shark is 70.4 cm for males and 65.1 cm for females (Source: Wallace et al).

The Brown Cat Shark is a cold water species, found in waters from 5 to 8°C in the Eastern Pacific. They appear to be most common from British Columbia to northern Baja California, Mexico with their known range extending from Alaska to Columbia in South America. They are probably also off Panama, Ecuador, and Peru.

Known global range of the Brown Cat Shark. Source: IUCN. 

 

Brown Cat Sharks are a deep-dwelling species, often over mud/sand and on the outer continental shelf. Known depth range is 33 to 1,298 m. They are most often found at depths of 137 to 360 m in the cold waters off the coast of British Columbia. Where it is warmer, they are likely to be deeper e.g. most often at depths of 656 – 932 m off southern California (Source: IUCN).

Distribution of Brown Cat Shark off the west coast of Canada from 1965 to 2007. Source: McFarlane.

As aforementioned, the Brown Cat Shark is one of the most common shark species off the coast of BC but so little is known about it and there have not been the recommended efforts to fill knowledge gaps.

Risks to the Brown Cat Shark include that it is commonly taken as bycatch in deepwater trawl fisheries (Source: IUCN). The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) reported in April 2007 that there was not enough information known about the species to evaluate how at risk it was =  Data Deficient. MarFarlane et al, 2010 determined that the Brown Cat Shark was among those shark species off the coast of BC that was a high priority for further study.  This has not yet happened. Reportedly, there are no management measures currently in place for the Brown Cat Shark anywhere in the world (Source: IUCN).

Shark Reproduction 

Unlike most fish, sharks have internal fertilization, where the eggs are fertilized inside the female’s body. The males have reproductive structures known as “claspers” (modified parts of the pelvic fins). Claspers are appropriately named as, not only do they transport sperm into the female’s oviduct, they also anchor into the female.

Most sharks are viviparous, giving birth to fully developed young. As mentioned above, Brown Cat Sharks are not. They are oviparous.

Shark egg development modes in further detail:

Oviparity = egg-laying. After fertilization, the egg cases are deposited into the ocean. There is no development of the embryo inside the female. The embryo develops inside the egg case feeding on the yolk. The only oviparous shark off the coast of BC is the Brown Cat Shark. The skates off our coast are oviparous as is the Spotted Ratfish. (See the image at the end of this blog contrasting their egg cases / mermaid’s purses).

Viviparity = after fertilization, the embryo develops inside the mother and the young are fully developed when born. There are two types of viviparity:

  1. Placental viviparity:
    We humans and most other mammals and reptiles also developed via placental viviparity. The embryos develop inside the mother, attached to her placenta (in the case of viviparous sharks, the umbilical cord is between the pectoral fins). Through the placenta, the mother’s blood delivers nutrients and oxygen to the embryo and waste is transported away. Examples of sharks off the coast of BC who develop by placental viviparity: Sixgill Shark, Sevengill Shark, Blue Shark, Pacific Sleeper Shark, Spiny dogfish.
  2. Aplacental viviparity (Ovoviviparity): In this case, there is no placenta to nourish the embryo. The young develop inside the eggs while in the mother’s oviduct and are born fully developed. They feed from the yolk as well as from glands in the oviduct walls (there are varied ways this “uterine milk” is delivered). The embryos hatch into the oviduct and finish development feeding from gland secretions and unfertilized eggs (known as being “oviphagous”). In some species, the first pup to hatch eats their developing siblings. This is referenced as being “embryophagic” or “adelphophagic” (translates literally into “eating one’s brother”) and is not known in any other animals other than some species of sharks. You can imagine that final litter size is small in sharks with this “intrauterine cannibalism”. Examples of sharks off the coast of BC who develop by aplacental viviparity are: Tope (Soupfin) Shark, Pacific Angel Shark, Spiny Dogfish, Common Thresher Shark, Bigeye Thresher Shark, Shortfin Mako Shark, Basking Shark and Salmon Shark. Those whose embryo development is known to include embryophagy are the: Common Thresher Shark, Bigeye Thresher Shark, Shortfin Mako Shark, Basking Shark and Salmon Shark (Source: Elasmo-Research).


Sharks off the Coast of British Columbia

Image source:  Fisheries and Oceans Canada, Sharks of British Columbia. Click to enlarge.

In BC waters there are 16 species of shark from 11 families.

Brown Cat Shark (Apristurus brunneus)
Spiny Dogfish (Squalus acanthias)
Sevengill Shark (Notorynchus cepedianus)
Salmon Shark (Lamna ditropis)
Blue Shark (Prionace glauca)
Pacific Sleeper Shark (Somniosus pacificus)
Common Thresher Shark (Alopias vulpinus) ICUN status: Vulnerable
Bigeye Thresher Shark (Alopias superciliosus) ICUN status: Vulnerable
Shortfin Mako Shark (Isurus oxyrinchus) ICUN status: Endangered
Green-Eye Shark (Etmopterus villosus)

Protected under Canada’s Species at Risk Act:
Basking Shark (Cetorhinus maximus) – Endangered (and ICUN status: Vulnerable)
Sixgill Shark (Hexanchus griseus) – of Special Concern 
Tope (or Soupfin) Shark (Galeorhinus galeus) – of Special Concern (and ICUN status: Vulnerable)

Incidental:
Great White Shark (Carcharodon carcharias) ICUN status: Vulnerable
Hammerhead Shark – 2 known sightings up to 2016 (Source: Royal BC Museum)
Pacific Angel Shark  – 1 known sighting up to 2016 (Squatina californica) ICUN status: Near Threatened

Contrast of egg cases commonly found along coastal British Columbia. Only the Big Skate can have more than one embryo per egg case. Reported to be up to a maximum of 7 embryos but more often 3 to 4.

Sources:

 

Sharks Among Us #3 – Meet the gang – From Rat Fish to Sixgills! (Video)

Great thanks to Rendezvous Dive Adventures for sharing this video with me! 

It’s a fantastic (7.5 minute) interview with Dr. Chris Harvey-Clark of the University of British Columbia and the Greenland Shark and Elasmobranch Education and Research Group (GEERG).

He discusses the shark species found in our cold-rich waters in the Pacific Northwest: “We have some of the largest species of sharks in the world swimming in these waters”.

Great video of sharks and I particularly appreciated Dr. Harvey-Clark’s explanation of the ecological link between rat fish and bluntnose sixgill sharks and, related to this, the latest research on the “ocean wanderings” of sixgills. 

I learned too about the Shark Observation Network where divers’ observations can help research. 

Basking in History – The Story of B.C.’s Basking Sharks

If you ever see a Basking Shark in British Columbia: call 1-877-50-SHARK (1-877-507-4275) or, if less urgent, email sharks@dfo-mpo.gc.ca.
Please see info below to aid ID. 

Photo by Chris Gotschalk
(Wikimedia Commons)

It’s a first. Canada has now (2011) acknowledged the endangerment of a marine fish species – the Basking Shark (Cetorhinus maxiumus). 

Basking Sharks used to be common in the coastal waters of British Columbia.  As the second largest fish species in the world, they could be half the size of a city bus (12 m and 4 tonnes) and could be seen at the surface of the ocean, “basking” there to feed on plankton. It’s a long-lived species too, believed to be able to reach 50 years of age.

However, even the most seafaring fisher is now unlikely to ever see one off the B.C. coast. There have been less than 25 sightings of Basking Sharks since 1996. So what happened?

We slaughtered them.

These sharks were put on the Canadian fisheries “Destructive Pests” list in 1949, and from 1955 to 1969 there was a federal eradication program directed at these benign, plankton-eating giants. In these years, the federal fisheries patrol vessel, the Comox Post, even had a blade mounted on its bow, designed specifically to slice Basking Sharks in half.

This species of shark has only the tiniest of teeth and does not compete for a commercial fishery like the sea lions, seals and Killer Whales that were also culled in that time period. The motivation for the “pest control” of these gentle giants was that they got trapped in gill nets, causing damage to fishing gear.

Click here for this annotated Basking Shark colouring sheet by Romney McPhie who is not only a shark scientist but clearly also an artist (and very skilled educator)!

Who we used to be. Blade on the front of the Comox Post. Source: Popular Mechanics 1956.

As an indicator of how far we have come since then, imagine the social outrage today if a magazine celebrated the ingenuity of the Comox Post’s blade, illustrating how the executioner’s tool was used accompanied by the text “Huge 30-foot basking shark is almost cut in two by sharp-edged ram. The sharks, floating lazily near the surface of the water, are no match for this skillfully handled vessel, which heads directly into a school and catches an individual shark before it is aware of its plight”.  November 1956’s edition of Popular Mechanics featured just that and the June 22,1955 front page of the Victoria Times included a photo with the text “This is a basking shark, basking and leering. But the smirk will soon be wiped off its ugly face by the fisheries department, which is cutting numerous sharks down to size” (from The Slaughter of B.C.’s Gentle Giants by Scott Wallace and Brian Gisborne).

Further: “After the initial flurry of press commentary on the shark blade in 1955 and 1956, the Comox Post went about its daily job, firing bullets into the occasional sea lion, seal, or merganser and slicing sharks when seasonally abundant. At the end of each fishing season an annual report was written, and over the years the entries for basking sharks appear to diminish. The blade was used over a period of 14 years in the Barkley Sound region, during which time 413 kills were recorded.” In 1956 alone, 105 Basking Sharks were reported to have been killed.”

Basking Sharks survived as a species for at least 30 million years but have been pushed to the brink extinction in B.C. by just a couple of decades of human intolerance, misunderstanding and mismanagement.

But as a testament to how quickly human social evolution can occur, we have gone from being executioners to acknowledging the species’ endangerment in just over 40 years.  In February 2010, the Pacific population received legal protection by being listed as “endangered” under Canada’s Species at Risk Act. The Recovery Strategy was finalized at the end of July, 2011. 

Only history will tell if our evolved enlightenment is enough or if it came too late for the Basking Shark and many other marine species. The fact that you care enough to read this blog item is every reason for hope.

Above: Basking Shark sighting July 17, Caamano Sound, BC. Video by Archie Dundas of the GitGa’at Guardians via Fisheries and Oceans Canada.


 

 

Sources:

Fisheries and Oceans Canada. 2011. Recovery Strategy for the Basking Shark (Cetorhinus maximus) in Canadian Pacific Waters [Final]. Species at Risk Act Recovery Strategy Series. Fisheries and Oceans Canada, Ottawa. v + 25 pp.

Fisheries and Oceans Canada. 2019. Action Plan for the Basking Shark (Cetorhinus maximus) in Canadian Pacific waters [Proposed]. Species at Risk Act Action Plan Series. Fisheries and Oceans Canada, Ottawa. iii + 16 pp.

Species at Risk Act (SARA) Species Profile 

The Tyee, December 7, 2016, How BC Killed All the Sharks – Hysteria and a knifelik ram helped us slaughter the benign basking giants by Scott Wallace and Brian Gisborne

Wallace, Scott, and Brian Gisborne. 2006. Basking sharks: the slaughter of BC’s gentle giants. Vancouver: New Star Books.

Sharks Among Us #2 – The Bluntnose Sixgill Shark

[Update February 2019 – Another pregnant female Bluntnose Sixgill Shark has been found – February 5th, in Coles Bay, North Saanich, southern Vancouver Island, British Columbia. Original blog about a pregnant female found in 2011 follows after the first two photos.]

Photo #1: Dead pregnant Bluntnose Sixgill Shark, found  – Coles Bay, February 5th, 2019 ©Ron DeVries.

Photo #2: Dead pregnant Bluntnose Sixgill Shark, found  – Coles Bay, February 5th, 2019 ©Ron DeVries.


Original blog:

The awe-inspiring images below are of a pregnant female Bluntnose Sixgill Shark (Hexanchu griseus) that was found dead on a beach in Alberni Inlet on low tide in February of 2011. She was necropsied by Department of Fisheries and Oceans staff and there were no obvious indications of how or why she died.

The information has been generously shared by federal shark biologist with the Pacific Biological Station, Romney McPhie. 

4.2 m pregnant female Sixgill Shark – February 2011.

This female Sixgill was 4.2 metres and was estimated to weigh 569 kg (1254 lbs).  As a viviparous shark species, she carried her embryos through the entire 12 to 24 month gestation period (species does not lay eggs / egg cases).  She may have given birth to some prior to her death and still had 28 pups inside her.  If she did indeed give birth, these pups would likely survive.

Sixgill Sharks have been reported to be up to 4.8 metres in length with females being larger than males (females to 4.8 m and males to 3.5 m).Age fo sexual maturity is estimated to be between age 11 to 14 for males and between 18 to 35 years for females. It is believed that life expectancy may be up to 80 years of age. 

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) 2007 assessment report on the Bluntnose Sixgill puts into perspective how rare an opportunity it is to learn about a pregnant Sixgill.  It relates that the number of pups carried by females is known from only three previous credible accounts (ranging from 47 to 108 pups which are 61 to 73 cm in size).

The Bluntnose Sixgill Shark is an extremely cryptic species that can dwell at depts up to 2,500 m.  So little is known about them and (sigh)  they are “near threatened” globally and are a species of “special concern” in Canada.

I have had the incredible privilege of seeing a Bluntnose Sixgill Shark while diving and felt like I was in the presence of greatness. They are living fossils, perfected by 200 million years of adaptation. They are amazingly graceful with large, luminous and intensely green eyes.

They are of absolutely no threat to humans and, like all sharks, have an essential role in marine ecosystems.  As top-level predators, sharks strongly shape food webs and the loss of such predators has proven to have profound effects on the number and diversity of other species.

The unique teeth of Bluntnose Sixgill Sharks. Photo by Romney McPhie.

We however are a threat to them.  It is reported that in just three years (2006 to 2009), 1,341 Sixgills were bycatch in longline fisheries. There is no information on the survival rates from bycatch nor is population size and reproductive rate known for this species.

Please read more about the biology, threats and conservation of Bluntnose Sixgill Sharks:

  • Government of Canada Management Plan for the Bluntnose sixgill shark (Hexanchus griseus) and tope shark (Galeorhinus galeus) at this link. 
  • Species at Risk Public Registry at this link.

Sixgill Shark eye. This one died as a result of longline bycatch and was brought into Alert Bay in July of 2007. It was rumoured to be one of 12 sharks caught by only one local fishing boat. Photo: Jared Towers.

 

Sharks Among Us #1 – The Blue Shark

The image below is of a Pacific Blue Shark (Prionace glauca) being rescued by Lindsey Pattinson of Tiderip Grizzly Tours on July 15th, 2010 in Glendale Cove, British Columbia.

Lindsey Pattinson rescuing a blue shark. Photo: Nick and Sue Spiller. 

Many British Columbians are unaware that we have at least 13 species of shark among us, ranging from the smaller species such as the Spiny Dogfish up to the 6-gill shark (5 m+) and the very, very rare Basking Shark (9 m+). The beautiful Blue Shark reaches a maximum of 3.8 meters and is distinct in its deep blue colouration and slender shape.

The Slue Shark is common in B.C. and is, in fact, extremely far ranging and widespread. It is found from Alaska to Chile in the Pacific but is also present in the Atlantic and Indian Oceans.  It has been found in waters from 7 to 16°C, latitudes of 60°N to 50°S and from the shallows to depths of 350 m (being more often at depth in warmer waters).

In researching the species after Lindsey’s find, I discovered that Blue Sharks undertake very large migrations, reportedly up to 9,200 km, moving north in the summer months.  More females than males move to the higher latitudes.

But, of course a sighting like this in Glendale Cove is an enormous rarity. Even with the Blue Shark being common in B.C., they are more often oceanic, on the continental shelf . . . not on the beach in Glendale!

For whatever reason, the animal stranded there and Lindsey cared enough to do what he could to save it.  Many shark species need to keep swimming in order to have oxygen-rich water pass over their gills. Knowing this, Lindsey moved the stranded shark back and forth in the water, forcing water over its gills and indeed, he revived it. He and the tourists he was guiding on the Grizzly Bear (and shark) watching trip had the joy of watching the animal swim to depth.

Thanks to Lindsey, this Blue Shark will be able to have more days of feeding on anchovy, mackerel, salmon, hake, dogfish, crustaceans and squid. It may also scavenge here and there and even feed on aggregations of krill by straining the water in the way a baleen whale would.

I suspect the Glendale Cove shark was a female and with Blue Sharks being a very prolific species, now saved, she could go on to bear 25 to 50 pups at a time (apparently even as many as 135)!  These young would grow inside her as the blue shark is “viviparous”, meaning they bear fully formed young. The pups are 35 to 44 cm at birth.

I was fascinated to learn that blue shark females can apparently “get pregnant” up to 20 months AFTER mating. They can store sperm packets in special glands in their reproductive tract called “shell glands” (aka nidamental glands) and pass their eggs through these glands to get fertilized.

If the rescued Blue Shark was indeed female, she may not have been able to feel much of Lindsey’s caring touch since the females are up to 3 times thicker skinned that the males! This adaptation is believed to allow the females to deal with the males since there is a lot of biting during courtship.

Unfortunately, the fate of Blue Sharks can also be to become the bycatch of longline and driftnet fisheries. One source reported that in one year alone (1990) “it is conservatively estimated that by-catch of blue sharks taken by the Japanese squid fleet in the North Pacific totalled 700,000.”

Further life history: Males sexually mature at 4–6 and females at 5–7 years. Believed to live to age 20.

For more photos of the blue shark rescue, click here.

Great thanks to Nick and Sue Spiller for sharing these photos.

Sources include: