‘Bounty’ on the heads of invasive species could keep nuisance fish at bay

Maltese scientists say direct measures might be needed to control the Mediterranean populations of invasive speices like the toadfish and the lionfish, in a study that of the species and their native predators.

The landmark study by marine biologists from Greece, Turkey, Cyprus, Libya, Italy, Tunisia, the UK, the US and even Malta, documented instances where native Mediterranean species have preyed upon two highly invasive marine fish – the Pacific red lionfish and the silver-cheeked toadfish.

In Cyprus, for example, the direct removal of both silver-cheeked toadfish and Pacific red lionfish individuals was incentivised by authorities through the provision of financial ‘bounties’ and through the organisation of spearfishing competitions known as ‘derbies.’

Prof. Alan Deidun, coordinator of the Spot the Alien Fish citizen science campaign and resident academic within the Department of Geosciences of the Faculty of Science, is a co-author of the extensive study.

The Pacific red lionfish and silver-cheeked toadfish are amongst the most invasive of non-indigenous fish species to enter the Mediterranean in recent years, posing both ecological and socio-economic hazards. The effects of the lionfish on fish populationsin the Caribbean and in the Gulf of Mexico led to calls for the active removal and even consumption of the species by conservation biologists.

Lionfish also pose risks to humans as the venom in their 18 spines can cause cardiovascular and neuromuscular effects, ranging from mild reactions, including swelling, to extreme pain and paralysis in upper and lower extremities. First recorded from the Mediterranean in 1991 within Israeli waters and even reaching the central Mediterranean in Italy and in Tunisia, it has not yet reached Maltese waters, to date.

The silver-cheeked toadfish was first recorded from the Mediterranean from Turkish waters in 2003, and has even been caught a number of times from Maltese waters as of 2016. This is an extremely toxic species due to the high concentrations of the potent neurotoxin tetrodotoxin (TTX) in its tissues, responsible for a number of human mortalities each year.

It also disrupts fishing lines, tears fishing nets and predates on fished stocks, including cephalopods (squid, cuttlefish, octopus.

The study has documented only one native predator of adult silver-cheeked toadfish – loggerhead turtles – and a number of native predators for juvenile toadfish, including dolphinfish (lampuki) and garfish (msell). Interestingly enough, cannibalism was also observed within the species. As for the Pacific red lionfish, documented native predators included the dusky grouper (ċerna), the white grouper (dott tal-faxxi), the common octopus (qarnit) as well as the silver-cheeked toadfish itself. 

But the relative scarcity in natural, native predators of these two highly invasive non-indigenous fish species suggests that direct human management measures will need to be implemented in order control their Mediterranean populations.