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Posts from the ‘Sharks’ category

Sharks Among Us #4 – The Salmon Shark

Salmon shark found dead on Port Hardy beach on November 23, 2011. Photo: Mandy Norrish.

This is a salmon shark (Lamna ditropis) that washed up dead on a beach in Carrot Park in Port Hardy, B.C. on November 23rd. 

Local Department of Fisheries and Oceans staff conducted an external examination and collected the unfortunate shark so that a full necropsy could be done at a later date.  Although salmon sharks are common in the North Pacific, examining the body may allow science to find out more about the species and how this individual died. 

The dead salmon shark was just over 1.5 metres (length from the nose to fork in the tail = fork length). The species can be 3.7 m and weigh up to 454 kg.

Cut in the pectoral fin suggesting the shark died as a result of by-catch in the longline fishery. Photo: Mandy Norrish.

Salmon sharks are of no threat to humans, however, the species does suffer impacts from humanity. 

The Port Hardy salmon shark had external injuries that suggest it may have been caught in a fishing net and possibly even shot.  It had a large cut on its tongue and on one of its pectoral fins and there was a circular hole behind the dorsal fin.  Many shark species suffer the threat of  by-catch in nets since they are targeting the same species we humans are fishing for.  

If it is determined that this shark indeed was caught in a net, this may be particularly interesting since I believe there are no openings for net fisheries at this time of year. 

Cut also found on the shark’s tongue. Photo: Mandy Norrish.

Although the salmon shark feeds on many species of fish,  it is indeed a very successful predator of salmon.

Salmon sharks can regulate their body temperatures to be higher than the temperature of the surrounding water. The salmon shark, in fact, has a higher body temperature than any other shark species. Apparently, even when the water is 2 °C, their internal temperature can be 16 °C.

This ability to thermoregulate is why, in part, salmon sharks can be incredibly fast. The US Navy has recorded speeds of up to 80 km/hr.  

I was heartened by the response of the majority of people to the death of this shark. It seems society might be moving beyond the “Jaws Effect” where we demonized sharks because we have bought into their fictitious portrayal.  

Many of us now seem to embrace shark fact rather than fiction, realizing that sharks pose little threat to humans; that they have been shaped by some 200 million years of evolution; that globally they are struggling to survive; and that they have an essential role in marine ecosystems.

Hole behind the dorsal fin. Photo: Mandy Norrish.

Sharks, as top-level predators, strongly shape food webs.   Loss of such predators has proven to have profound effects on the number and diversity of other species.   

The unenlightened are still out there though. It may be an inevitability that sharks get caught in fishing nets but they need not then be shot or butchered. Locally, I have seen evidence of both. 

[Update: December 22nd, 2011 – The necropsy revealed that this was a female shark. It is also now known that the shark was caught in a hook and line sable fish fishery and that the hole behind the dorsal was the result of a hook. It is rare that there is shark bycatch in this type of non-net fishery.]

For further information on salmon sharks, please refer to the natural history information from ARKive below.

Click here for two ARKIve videos showing salmon sharks hunting.

Skin parasite (ectoparasite). I have no expertise here but had suggested that this a copepod from the Caligidae family.

Click here for the petition to ban shark fin products in Canada and here for video by astounding 18-year-old Madison Stewart about the vilification of sharks and the atrocities of shark-finning . . . 73 million sharks killed/year for their fins = 190 sharks killed/minute.   

Click here for video of the shark found on the beach in Port Hardy.

Click here to follow tagged salmon sharks in our waters. 

Click here for a scientific paper reviewing the biology of salmon sharks and evaluating their “status” as predators of salmon.

 

Salmon shark image from ARKive site. Click image for two ARKive videos of salmon sharks hunting. Credit: BBC Natural History Unit.

Salmon Shark Information
from ARKive

Description

A formidable hunter, the salmon shark (Lamna ditropis) is sometimes mistaken for the white shark (Carcharodon carcharias), but can be distinguished by its shorter snout and the dusky blotches that mark the white abdomen of adults (3) (4). The rest of the salmon shark’s stocky, spindle-shaped body is dark bluish-grey or blackish, with white blotches around the base of the pectoral fins. The first dorsal fin is large, while the second dorsal and anal fins are tiny and are able to pivot. Its crescent-shaped tail gives it impressive propulsion through the water (2) (3), while its large, well-developed eyes enable it to spot potential prey (2), and its large, blade-like teeth are well suited to gripping slippery fish(2) (3).

Range

The salmon shark occurs in the North Pacific Ocean. From Japan, North Korea, South Korea and the Pacific coast of Russia, its distribution extends east to the Pacific coast of the U.S.A., Canada, and probably Mexico (3).  See this species on Google Earth.

Habitat

The salmon shark is a coastal and oceanic shark, inhabiting waters between 2.5 and 24 degrees Celsius, generally from the surface down to depths around 152 metres, although one individual has been recorded at 255 metres (3).

Biology

Occurring singly or in schools of several individuals (3), salmon sharks are long distance, high-speed predators (2), occasionally seen at or near the surface in some areas. They can maintain their body temperature well above that of the surrounding cold water of the North Pacific, and may have the highest body temperature of any shark (3). This allows them to maintain warm swimming muscles and internal organs, so they can still hunt effectively in cool waters (2).

The salmon shark is considered to be one of the main predators of the Pacific salmon, and its voracious feeding on this fish has earned it its common name (3). However, it is an opportunistic feeder that consumes a wide variety of fish that also includes (amongst many others) herring, sardines, pollock, Alaska cod, lanternfishes and mackerel. It also feeds on some squid and is sometimes attracted to by-catch dumped back into the ocean by shrimp trawlers (3).

After spending the summer in the north of their range, the salmon shark migrates south to breed. In the western North Pacific they migrate to Japanese waters whereas in the eastern North Pacific, the salmon shark breeds off the coast of Oregon and California, USA. The young are born in spring after a gestation period of around nine months (3). The salmon shark is ovoviviparous (young hatch inside the female; they are nourished by their yolk sac and then ‘born’ live), and oophagy (when the growing embryos eat unfertilized eggs to gain nutrients) has been recorded in this shark (4). Most litters contain between two and five young. Male salmon sharks are thought to mature at about five years and live to at least 27 years; females reach maturity at eight to ten years and are known to live to at least 20 years (3).

Threats

The salmon shark is often caught as by-catch in Japanese, United States and Canadian fisheries. When caught, often just the fins are taken for shark fin soup and the rest is discarded, although sometimes the flesh may be sold for consumption in Japan and the United States (4). Many fishermen view salmon sharks as pests, as they often damage fishing gear, making them more likely to be killed if captured (4). In addition to the threat of by-catch, some recreational fishing for this shark occurs in Alaskan and Canadian waters (4), and some commercial fishing has taken place in the past, such as in Prince William Sound, Alaska (5).

Conservation

In 1997, the Alaska Board of Fisheries closed all commercial shark fishing in state waters and implemented strict regulations in the state sports fishery for salmon sharks (4). Measures such as these are vital in protecting this species’ future, until further research can determine the conservation status of this magnificent predator.

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

Photo by Chris Gotschalk (Wikimedia Commons)

It’s a first. Canada has 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 15 sightings of basking sharks since 1996. So what happened?

Click here for the annotated basking shark colouring sheet by Romney McPhie. She’s not only a shark scientist – she’s an artist and very skilled presenter and educator!

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.

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).

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. 

If you ever see a basking shark in BC call: 1-877-50-SHARK (1-877-507-4275). 

See:

Basking Sharks – The Slaughter of B.C.’s Gentle Giants by Scott Wallace and Brian Gisborne 

How BC Killed All the Sharks – Hysteria and a knifelike ram helped us slaughter the benign basking giants by Scott Wallace and Brian Gisborne

David Suzuki Foundation blog; April 2014; What’s bigger than a bus but has prey smaller than a grain of rice

Final Recovery Strategy for the Basking Shark (Cetorhinus maximus) in Canadian Pacific Waters (2011-07-26)

Photos of basking sharks

Species at Risk Act (SARA) Species Profile– summary of natural history, threats, etc. 

Sharks Among Us #2 – The Bluntnose Sixgill Shark

4.2 m female sixgill shark.

The awe-inspiring images here are of a pregnant female bluntnose sixgill shark (Hexanchu griseus) that was found dead on a beach in Alberni Inlet on low tide. She was necropsied by Department of Fisheries and Oceans staff on February 11th 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 (click images to see at larger size).

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 -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.

Romney McPhie, DFO shark biologist examining pups.

Examination of the pups in one uterus. Yes, 6-gill sharks have two uteri.

Sixgill sharks have been reported to be up to 4.8 metres in length with females being larger than males and reaching sexual maturity only between age 18 and 35. It is believed that they may reach 80 years in 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 six gill.  It relates that the number of pups carried by females is known from only three previous credible accounts (ranging from 47 to 70 pups of size 61 to 73 cm).

The bluntnose six gill 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 six gill 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 six gill 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 by-catch in longline fisheries. There is no information on the survival rates from by-catch nor is population size and reproductive rate known for this species.

Please read more about the biology and conservation of bluntnose sixgill sharks in the Species at Risk Public Registry. Click here.

See the Alberni Valley News for coverage on this sixgill. 

 

See the Draft Management Plan for the bluntnose six gill shark and tope shark in Canada for natural history information and a summary of threats. 

Sixgill shark eye. This one died as a result of longline by-catch 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 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 12 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 blue 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 totaled 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: