The silver-cheeked toadfish.

Shipping lanes have always formed artificial routes for certain species to take advantage of and invade new habitats. Traditionally, ship hulls were wooden and the rock, iron or lead ballast was laid along the inside of the keel. This meant that the marine life that could take advantage of these routes were limited to fauna and algae, which were able to encrust on or bore into the external parts of the hull. The quantity and frequency of ships along these lanes was fairly sparse and this helped to reduce the influx of invasive species.

The silver-cheeked toadfish.

The addition of ballast water into large tankers allowed these ships the flexibility to choose exactly how much extra weight they needed depending on the cargo that they were carrying. This resulted in docking times being vastly reduced, but it brought with it an unintended consequence. Many marine species are pelagic spawners; the fertilised eggs simply develop freely in the water column until they have grown enough to settle in an area. The lack of food availability in the open ocean usually takes care of plankton trying to traverse oceans as starvation makes it practically impossible to cross. The introduction of ballast water however, created a ready-made taxi service for these organisms who would be picked up in one part of the world and dumped at a container port somewhere else.

By proxy, this increased the chances of a species establishing itself in a foreign environment, and hence, becoming invasive. For the sake of clarity, as local species are typically better adapted to local conditions, this event is pretty rare. A species which becomes invasive typically has some type of advantage in that foreign ecosystem (e.g. no natural predators due to venom, toxicity etc.) and this gives it a competitive advantage over the local species.

Fast forward further and we see the opening of direct shipping channels between major oceans and seas; the Suez Canal in 1869 and the Panama Canal in 1914. These amazing feats of human engineering cut costs and travel times massively, not only for merchant shipping but in the case of the latter for the wildlife too. For the first time in human history, marine animals could potentially swim through the channel or, at the very least, pass through in a pelagic stage and develop on the other side. And that is exactly what they have done.

One such invasive species to the Mediterranean is Lagocephalus sceleratus or the silver-cheeked toadfish. Its name is derived from the Greek, lagos meaning hare and kephale meaning head. It forms part of the ray finned fish and is a member of the pufferfish family Tetraodontidae.

A species common to the Indo-Pacific, the first recorded sighting of the fish within the Mediterranean was in 2002 when it was caught off the Turkish coast at a depth of 15 metres by a trammel net. Some previous reports placed the species within the Mediterranean as early as 1977 but these sightings are unconfirmed or disputed as being a different species altogether.

Unlike the Lionfish, the silver-cheeked toadfish does not make good eating. In fact, its flesh contains a powerful trodotoxin strong enough to kill humans through muscular paralysis and circulatory failure. The famous explorer Captain James Cooke apparently had a near death experience when he consumed it whilst in Australia in 1774.

The invasion of the Mediterranean basin by this species is now complete, although the lowest population densities are found in the western region close to Gibraltar. Its spread through the basin has been helped by the fact that the Toadfish is a pelagic spawner. This has allowed the fertilised eggs to be distributed by current flows within the sea. Although the species is established it is fair to say that it is not as destructive to ecosystems as other invasives. Part of the reason for this is that it feeds on benthic invertebrates which are in plentiful supply.

Considering its distribution, is there any point even trying to control its numbers? With this particular species one would suggest that it is no longer possible. It is fortunate that the biggest problem we face with respect to the invasion is that the fish cannot be eaten. However, there is a considerable amount of scientific study attempting to understand how populations are doing. In order to determine the continued pressure exerted on the Mediterranean it is important to understand if populations are growing, and indeed how quickly? The evidence being released suggests that populations are growing in the Western Mediterranean whilst they appear to be stable in the east; a lucky escape indeed.

Whilst the removal of this species is highly unlikely to take place, its presence should serve as a warning that there are other species which could follow through similar routes. The detrimental impacts by these potential invasive species could be much more severe and dramatic and this highlights the importance of controls on shipping and the regulations governing them; otherwise the next ‘hare head’ of this type could leave us with a bit of a ‘hair-less’ head.