Month: March 2022

By: Mahé Colas and Joanne Carney

The Bay of Fundy is home to 7 species of sharks, and 3 of them are in the Mackerel Family with hundreds of individuals, including the impressive Great White shark, and its close relatives the Porbeagles and the Mako Shark. Although mackerel sharks are large and heavy, they are very agile and active fishes that are fast swimming. They typically have long conical pointed snouts, spindle shaped bodies, huge gill openings and they generally have a white ventral surface from the head to the tail.

*FUN FACT: you can track recently tagged sharks at the website ‘Ocearch.org’.

MACKEREL SHARK DIFFERENTIATION:

PORBEAGLE SHARK (Lamna nasus:) can measure up to 3.5 metres (~11.5 feet) and weigh 230kg (~507 lbs). They are mainly recognizable for their distinctive white rear tip on their first dorsal fin. They also have a crescentic/lunate caudal fin with two keels, which is used for easier movement in the water and strength. Finally, their pointed blade-like teeth with smooth edges and lateral cusplets (small bumps on either side of the tooth) are all identical through the entire jaw.

Porbeagle shark: note white on dorsal fin.

Porbeagle sharks are coastal species and found in temperate and cold-temperate waters but can be found to 700 metres underwater (2300 ft). Due to their large size porbeagle sharks do not have any known natural predators however their meat is highly valued by target fisheries. They are not only threatened by commercial fishing activities but also bycatch, which is the unintentional capture of species during fishing. In addition to the enormous fishing pressure, the late age of reproductive maturity and few offspring per pregnancy, (around 4 to 5 pups), they have been listed vulnerable to extinction since 2006.

* FUN FACT, all sharks must swim constantly forward to breathe and gain a constant uptake of oxygen.

2) MAKO SHARKS: can be divided into two species the Shortfin Mako (Isurus oxyrinchus) and Longfin Mako (Isurus paucus). The Mako sharks are slightly larger than porbeagles and can reach a maximum size of 4 metres (~13 feet). They have a deep blue to purple skin color and a large caudal fin with only one keel on the caudal peduncle. Mako’s are highly migratory and capable of withstanding significant temperatures changes due to their specialized blood vessel structure called counter current exchanger. It allows them to maintain a body temperature higher than the surrounding water giving them a lot more flexibility to hunt in colder waters. They have a white underside that covers their slender body and an acutely conical pointed snout. This hydrodynamically efficient body shape and their ability to orient their scales (dermal denticles) makes them the fastest shark in the world, also known as the peregrine falcon of the sea because it can reach 43 mph (70 km/h). Their large U-shaped mouth hold large awl-like teeth that present no cusps or serration, and the lower teeth protrude outside of the mouth even when closed.
The shortfin mako which is classified as vulnerable due its popularity for shark fin soup and bycatch in longline fisheries.

*FUN FACT: There are around 470 species of sharks in the world with the oldest one being a 400-year-old Greenland shark recently discovered by scientists.

3) GREAT WHITE SHARK: (Carcharodon carcharias): They are notable for their large size, with larger female individuals growing to 6.1 m (20 ft) in length and 1,905–2,268 kg (4,200–5,000 lb) in weight at maturity. They have a muscular and heavy spindle-shaped body, a moderately long conical snout, long gill slits, large and triangular dorsal fin without a white rear tip and only one keel on the caudal peduncle of the crescentic caudal fin. The name is thought to have come from their stark white undersides. They have a grey dorsal area (sometimes in a brown or blue shade) that gives an overall mottled appearance.

Great white shark (eating a seal..). Note extensive size.

The lifespan of great white sharks is estimated to be as long as 70 years or more. Great white sharks can swim at speeds of 25 km/hr (16 mph) for short bursts and to depths of 1,200 m (3,900 ft). Great white sharks, like many other sharks, have rows of serrated teeth behind the main ones, ready to replace any that break off. When the shark bites, it shakes its head side-to-side, helping the teeth saw off large chunks of flesh. These sharks, like other mackerel sharks, have larger eyes than other shark species in proportion to their body size. The iris of the eye is a deep blue instead of black.

Great white sharks are known to spend increased amounts of time near the seal rookeries along the Atlantic Coast with seals being one of their food sources. It is not recommended to swim near a seal haul-out or rookery! (see photo!). They are arguably the world’s largest predatory fish, preying on mammals as large as baleen whales.

The species faces numerous ecological challenges which has resulted in international protection and is listed as a vulnerable species. They should be afforded protection because of their ecological role in the ecosystem as an apex carnivore in the food web.

The diversity is immense and there is so much more to learn about these predatory fish to protect them as they play an important role in the balance of the ecosystem.

By: Mahé Colas and Joanne Carney

Four species of seals, including grey, harbour, harp and hooded seals, are commonly observed on shorelines around the Maritime provinces.

On our whale watching tours, the seals are often spotted lazing about on the rocky islands in the middle of the Bay of Fundy. These seal haul out locations are called ‘seal rookeries’ or ‘seal haul-outs’.

The term ‘rookery’ can be applied to a colony of breeding animals such as seabirds, marine mammals, and turtles. While the term rookery originally came from the nesting habits of rooks (a species part of the crow family). Here in the Bay of Fundy, there are many seal rookeries where large aggregation of harbour seals and grey seals can be observed between two high tides cycles.

The behavior of temporarily leaving the water between foraging (hunting) periods to spend time on land is typically associated with pinnipeds. Pinnipeds are a group of marine mammals that include seals, sea lions, fur seals and walrus.

These individuals haul themselves out of the water at low tide on these rocky ledges. These seal rookeries are used for reproduction, mating and giving birth. They are also used for avoiding predators, thermoregulation, socializing, moulting, nursing, resting and removing parasites.

Different seals species may have different haul-out patterns depending on physical constraints like air temperature, wind speed and time of day. In addition to these, there are also biological constraints such as moulting, age and sex and geographical limitations that could affect the range and number of individuals at one location.

Seals are known to be extremely agile in the water and super clumsy on land. They take full advantage of these rocks up until the last second. They can be found laying in a banana shape balancing themselves on the rocks until they get pushed off by the incoming tide. Once the tide is high and covers these rocks, the seals are usually out hunting but at a higher risk to be preyed on by great white sharks and other predators in the surrounding waters.

The newborn seal babies, are generally born on these rookeries in the spring. They are born at low tide and must learn to swim with hours of birth before the tide rises again! Mothers will typically nurse the pups for 4-6 weeks. In their early weeks of life, the mother harbour seal may carry the pup on her back while swimming and diving.

The rookeries are also used for moulting once a year, when a seal sheds their old coats and grow new skin and hair. During this time, the seals spend a particularly large amount of time ashore on these rocky rookeries and spend little or no time feeding in the water. By staying ashore, they minimize heat loss and maintain a relatively high temperature, which encourages blood flow close to the skin, thus accelerating the molting process. More seals will be seen hauled out at low tide on the rocks during the moulting period generally last summer to early fall.

Contrary to popular belief, the seals, when hauled out, are not simply “basking in the sun”. We know this because seals in temperate regions haul out regularly even on the coldest winter days, and seals in polar regions remain hauled out on the ice, even during the most ferocious storms.

Come and enjoy watching the seals hauled out on the rookeries of the Bay of Fundy!