Informative

Mackerel Sharks Pt.2: The Makos

“What you lookin’ at?”     http://www.factzoo.com/fish/shortfin-mako-fast-bright-eyed-open-water-shark.html

“What you lookin’ at?”

http://www.factzoo.com/fish/shortfin-mako-fast-bright-eyed-open-water-shark.html

Nature’s purpose-built torpedo is the mako shark. The mako is the fastest of all sharks, capable of powering through the water at speeds of up to 27 to 38 knots – that’s 50 to 70 kilometres per hour! Makos are divided into two species: the short-finned (Isurus oxyrhincus) and the long-finned (Isurus paucus) mako, which look very similar to each other bar the size of their pectoral fin (as their names suggest). Both species are global in their distribution, but in our Victorian waters, you’re more likely to come across the short-finned species.

 

Makos are clearly identified by their slender fusiform body, which is coloured by a brilliant, indigo blue dorsal side and a white underside. They also possess large black eyes and rows of long needle-like teeth that often protrude from the mouth. Like the other mackerel sharks, sexual maturity is relatively late in life, with males and females reaching maturity at approximately 8 and 18 years respectively. The average number of pups born to a female is 12 following a gestation period of up to 18 months in a three-year reproductive cycle.

Although approximately half the size (about 2.8 metres) of their bigger cousin, the great white (Carcharodon carcharias), makos are formidable hunters, chasing down medium to large-sized fish, such as tuna and small cetaceans (whales and dolphins). The mako has a unique arrangement of red muscle (which is fatigue-resistant) in the centre of its body, which is linked to the tail by long tendons. These allow for rapid, powerful and repeated contractions to occur with maximal transfer of energy to the tail. Funnily enough, tuna also have a similar muscle arrangement, illustrating the beauty of evolution - although two very different kinds of fish, they’ve both evolved a similar way to solve the same problem: to eat and to avoid being eaten! Using its speed to chase down prey, the mako is even capable of launching itself six metres into the air if it means securing dinner! If the chase is successful, the mako ensures its prey cannot escape using its perfectly-designed teeth like rows of spears to puncture and hold.

Makos are considered aggressive sharks, readily chasing and attacking baited lines. Despite this, there have only been three fatal attacks globally since 1980. Many non-fatal incidences with makos have occurred when harassing the animal whilst on the fishing line or when it has been landed in the boat. The tenacity of the mako and its prized flesh has made it a very popular target for sport fishers, which has unfortunately placed increased pressures on their already declining populations. The International Union of the Conservation of Nature (IUCN) red list has makos listed as ‘vulnerable’. 

The Importance of Upwelling

 

Upwelling: many of you may have heard of it, and many of you may have no idea what it is. Regardless of what you may know, upwelling is extremely important in creating and sustaining life within all oceans. It is so important that, if missing, we might not be around much longer either.

Upwelling is the process where cool water is brought up from the depths of the ocean, full of delicious nutrients ready for consumption by tiny phytoplankton. This cool water replaces the warm, barren and ‘stale’ water that sits at the surface layer, giving the phytoplankton the food they need to produce the energy that is then bestowed upon the rest of the marine food web. Phytoplankton sit in the water and suck up all the nutrients surrounding them, which they then use to power growth.

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-->    A nudibranch off Blairgowrie pier: one of the
many creatures within Port Phillip Bay that benefits from upwelling in Bass
Strait.

A nudibranch off Blairgowrie pier: one of the many creatures within Port Phillip Bay that benefits from upwelling in Bass Strait.

Phytoplankton fill the niche space (a ‘sciencey’ word for a position in the food web) of a plant, as they are primary producers. Primary producers use sunlight to create energy using photosynthesis, as well as utilising the nutrients brought up from the depths of the ocean to move this energy up the food chain, allowing life to bloom. Phytoplankton therefore sequester the nutrients and convert sunlight into energy, and are in turn eaten by zooplankton, which are then eaten by larger and larger organisms, eventually reaching the apex predators, such as killer whales, dolphins and, my favorite, SHARKS! This process of nutrient acquirement makes up something you might have heard of before: the food chain!

If that description confuses you a little or doesn’t seem clear, we can use the analogy of a plant. Imagine any plant that has roots in the soil: the roots sit in the soil so that the plant can access the nutrients found there. Each root pulls in nutrients essential for life processes, such as phosphorus, nitrogen and potassium. These nutrients are then used to power the plant. Primary consumers then eat these plants, moving the nutrients up the food chain. Predators then chase these consumers and subsequently eat them, thus moving the nutrients up to the apex of the food chain.

In a nutshell, if you can’t get your nutrients, you can’t exist. For example, carbon is used in the construction of a plant by forming the backbone of most essential biomolecules, such as cellulose and starches. As many of you may already know from basic chemistry, carbon is pretty much the most essential element on earth, as it allows life to exist!

Now back to upwelling and why it is so important. Upwelling doesn’t occur all the time, as in the terrestrial environment there are seasons when not much food is available, and other times when there is. For Victoria in particular, the greatest period of upwelling is springtime. That’s right - NOW!

As a result of this huge upwelling, we see large marine animals visiting our coasts. Most would be aware that we have recently had humpback whales passing through our waters. You might be surprised to know that we also have the largest animal in the world moving into our waters during this period: the blue whale! It is amazing to think that microscopic phytoplankton can bring the biggest animal in the world to Australia’s own shores. Such an event truly draws attention to how influential these little critters are in the oceans of the world. It is even more amazing that something so small and (almost) invisible can be so integral to keeping the oceans afloat.

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-->      Australasian Gannets hanging out at Pope’s Eye. These are among the many seabirds that benefit from
the upwelling in Bass Strait.


Australasian Gannets hanging out at Pope’s Eye. These are among the many seabirds that benefit from the upwelling in Bass Strait.

 

So even though all the nature we can see with our eyes is both beautiful and vital when it comes to the survival of life, it’s the things that we maybe can’t see directly that are even more important. If you wish to witness the changes that upwelling can bring to the marine environment, jump in the water somewhere during the middle of winter, and you’ll find that it’s pretty quiet. Then go and have another look around early summer, sometime near Christmas, and experience the change in activity - you will be amazed!

Platypus Magic

Did you know that one of Australia’s most unique and charismatic animals lives right on Melbourne’s doorstep? With a duck’s bill, egg-laying ability, a mammal’s fur and a poison barb on their foot, of course I’m talking about the famous Platypus (Ornithorhynchus anatinus). The platypus is about as iconic an animal as you can get, featuring on television shows such as Blinky Bill (who could forget ‘Flap’ the platypus?), in aboriginal dreamtime stories, and even in a song by Green Day.

However, the platypus also plays an important ecological role in addition to its plethora of cultural significance. Being a carnivore, the platypus generally sits atop the food chain in our freshwater rivers and streams. Therefore, it plays a vital role in keeping species such as freshwater crustaceans and aquatic invertebrates in check.

 

PLATYPUSweb1.jpg

Unbeknownst to many in Melbourne, one can go in search of this fantastic creature without spending longer than an hour in the car. Many of the Yarra River’s freshwater tributaries, as well as the Yarra itself are home to the platypus. Most active during the early morning and late evening, these are the best times to sneak up quietly to the water’s edge and peer into the depths in search of the splash of their thick tail. If you’re lucky enough to spot one frolicking in the shadows, it makes for a truly unforgettable experience.

For an extended introduction to the art of platypus spotting, head to the Australian Platypus Conservancy (APC).

Whilst this beloved animal is listed under ‘Least Concern’ by IUCN (International Union for Conservation of Nature), there is sufficient evidence to show that platypus numbers have decreased in the past decade. The cause of this decline has been linked to two or three different reasons, namely water quality, the use of opera house nets and increased river temperatures as a result of climate change.

 

The platypus is incredibly sensitive to the quality of the river it lives in, particularly in terms of pollution levels and the degree of bank erosion. However, 80% of platypus deaths reported between 1989 and 2009 were related to humans. Specifically, the use of opera house nets to catch freshwater crustaceans and fishermen leaving behind tackle in which animals get caught have been particularly damaging.  

The illegal opera house net, the unfortunate cause of death to hundreds of our special platypuses. 

The illegal opera house net, the unfortunate cause of death to hundreds of our special platypuses. 

As a result, the use of opera house nets in Victorian public rivers and streams is now illegal (carrying a fine of up to $11,000, or even jail). This is due to platypuses continually becoming caught in them whilst looking for food and subsequently drowning (they can only hold their breath for 30 to 40 seconds). On various occasions, three or more dead platypuses have been found in a single, abandoned opera house net. These deaths are completely preventable, and it is up to the wildlife loving public to help ensure these nets do not end up in our waterways.

So, when venturing out around Greater Melbourne in search of your own platypus experience, keep an eye out for opera house nets or fishing line in and around our waterways. Removing and reporting any opera house net use to the Department of Environment and Primary Industries could literally mean the difference between life and death for one of Australia’s most special creatures.

 

 

To report the use of illegal opera house nets in our waterways, call 13 FISH (136 186)