The shortfin mako is the fastest species of shark. Photo: Istockphoto.

The tragic disappearing act of Mediterranean sharks

Conservationists trying to save the shortfin mako are working blind. UBC researcher Madeline Cashion is changing that.

By Madeline Cashion, UBC Institute for the Oceans and Fisheries

The fastest shark in the ocean is also among the tastiest and most threatened.

The shortfin mako (Isurus oxyrinchus) is a large shark of the Lamnidae family, which also contains the great white. It’s the cheetah of the seas, swimming in bursts of up to 68 kilometres per hour as it cruises the North Atlantic looking for fish to eat, sometimes jumping several meters out of the water in hot pursuit. Shortfin mako is common in European seafood markets, usually in the form of steaks, but many people don’t realize they’re eating shark meat. It’s often marketed as swordfish. Overfishing and changing oceans have rendered the shortfin mako vulnerable to extinction globally and critically endangered in the Mediterranean Sea. This is where I come in.

My master’s degree at the University of British Columbia focused on tracking down and improving shark and ray fisheries data. Coming from a background in marine biology and sustainability, I’ve always been rooted in the natural sciences, but this project emphasized just how crucial it is to understand the human side to ocean issues, even if it means straying from my comfort zone into social research. Conservation issues begin and end with people and in the Mediterranean Sea, humans have altered ecosystems beyond recognition.

Shortfin mako, also known as marrajo. Photo: Flickr, José Antonio Gil Martínez

Large sharks like the shortfin mako were once common in the Mediterranean. But Mediterranean catches became less selective and more destructive after World War II. Fishing holds, nets and lines grew in size at an exponential rate. Foreign fishing fleets began exploiting the fertile fishing grounds. Giant industrial fishing vessels started unselectively catching the valuable fish, like mackerel, tuna and swordfish, undesirable species like sea turtles and dolphins, and sharks like the shortfin mako (which tend to fall somewhere in between).

At the time, fishers considered makos pests — the mako gobbled up catches and got tangled in lines and nets in the process. Today, overfishing has nearly depleted the Mediterranean Sea’s large shark populations, with up to 70 per cent of all sharks and rays now estimated to be threatened with extinction, according to the International Union for the Conservation of Nature. My research is helping uncover which species have been fished and in what amounts–essential information for designing conservation plans.

Fisheries in the Mediterranean are now dubbed ‘multispecies’ — they target vaguely and market much of what they catch. The number of species categories reported in fisheries landings — catches brought back to shore as opposed to those discarded at sea — has nearly doubled since the United Nations began collecting fisheries data. In the 1950s, 95 catch categories were recorded. By the 1970s there were 140 categories, and by 2014 it was up to 274. It is difficult to disentangle the species that are new in the data because they haven’t been caught before from those that are just now being reported (but were perhaps also caught historically). Are the catches new? Or is the information new?

Overfishing has nearly depleted the Mediterranean Sea’s shark populations. Photo: Istockphoto.

To some extent, researchers know that it’s both — more species are exploited, and reporting is improving, but which fish are which? A lot of new species catch records are of species that used to be included in vague categories like ‘sharks and rays’ but are now being identified by species. This distinction is essential. Think of it like this: you wouldn’t report killing a ‘mammal’ if you went deer hunting. Detailed data is especially critical for understanding the history of shark fishing because many species are threatened and are often not reported by fishers or governments — whether self-preservation, ignorance, or inadequate capacity is behind these omissions is a different discussion.

Madeline Cashion holds a juvenile dark shyshark (Haploblepharus pictus), raised at the South African Shark Conservancy from an egg.

My research indicates that since fisheries reporting began in 1950, only three per cent of the shark and ray catch reported from domestic Mediterranean fleets has been identified by species. We don’t know what species make up 97 per cent of the reported catch. We have a ton of work to do.

But there’s good news: We know what needs to be done. My master’s research provides a first estimate of what species make up that 97 per cent of the catch, including where and how they were caught. I’m publishing the results to help conserve the remaining sharks that are so vital to Mediterranean ecosystems and livelihoods. With the new information, scientists and conservationists can tailor marine conservation to better protect the mako.

Please share this story with your friends and hit the applause button.

Follow UBC Science on Twitter, Facebook and subscribe to our newsletter.