Author: Oscar Ward
As humanity transitioned from being a scattered species of isolated populations into the global community we know today, the natural world was changed forever. Species that were before confined to a particular area due to physical obstructions or biological barriers, were suddenly provided the opportunity to cross over these obstacles by piggybacking on new routes formed by mankind. Species which may have been naturally regulated in their own environment could cause chaos in another due to more favourable conditions, a lack of competition, an absence of predators, or any combination of the three. Species that make this jump are as invasive species. Of all the invasive species we see today few come as close in terms of prevalence or volition, to the red lionfish, Pterois volitans.
The red lionfish is a venomous reef fish that was originally confined to the Indo-Pacific. However since the mid-1990s their range has extended far beyond this native boundary, with invasive populations in the West Atlantic continuing to swell in size even today. The primary suspect for the introduction of the red lionfish to much of the south east coast of North America and the Caribbean is the aquarium trade. Lionfish are undeniably stunning fish, with their long feather-like dorsal spines drawing the eye of any keen aquarist. This allowed sellers to easily profit by importing large numbers of the species to the US market. As with any trend, lionfish eventually became commonplace in aquariums, and people began to grow bored of them. Rather than killing their once loved pets, many owners went for the more humane option and released them into local waters. In addition Hurricane Andrew destroyed a large private aquarium 1992 which may have provided the boost in numbers that the population needed to stabilise and spread. Regardless of how the lionfish arrived in the West Atlantic, it seems they are here to stay unless new methods for removal or control are developed in coming years. But what is it about this fish that we should be concerned about, and what has allowed it to expand its territory so rampantly?
The diet of the lionfish is made up of anything it can find on the reef, with small fish making up a significant part of their nutritional intake. With the ability to consume forty fish an hour and expand their stomach by over 30 times, they can quickly decimate a reef. These factors allow them to out compete many other local carnivorous species with similar diets, resulting in these populations also decreasing causing what is called a trophic cascade. As lionfish continue to consume fish on the reef, other species such as sharks and grouper who also consume these organisms begin to struggle to maintain the same calorific intake they had previously, and their populations begin to decline despite the lionfish rarely interacting with them directly.
It is likely that the greatest contributing factor to the rapid rise of lionfish numbers in the Atlantic is a lack of natural predators. In the Pacific, lionfish are consumed by a range of apex species including eels, shark and grouper. Although all of these species are found in West Atlantic and Caribbean waters, they have not had the time to associate this new and unusual looking species as a prey item. That is not to say that the Atlantic relatives will refuse to eat lionfish all together. Opportunistic consumption of lionfish by these predators has been observed by spear fishermen who have wounded or killed individuals only to have them be stolen by hungry individuals. This suggests that there may be a chance for Atlantic natives to learn and adapt to this new intruder. However as of now, this unwillingness for local predators to hunt lionfish has allowed for their numbers to increase without being hindered, and for the species range to increase in a seemingly unstoppable fashion. This lack of natural population control alongside the voracious feeding habits of the lionfish population has also had a noticeable impact on local economies. Species such as snapper and grouper are very important to fisheries in many of the affected areas, and their juveniles are ideal prey items for lionfish. This is likely to be one of the most influential factors in bringing about serious action towards mass population control.
Bringing control back to the West Atlantic will be no easy task. Despite appearances, lionfish are nutritious and tasty, and their appearance on menus has slowly increased in recent years. Currently Lionfish Derbies are popular events on many islands in the Bahamas. Whole communities spend one day a year catching as many lionfish as possible to try and make a dent in their numbers – no easy task considering the female lionfish is capable of laying up to 2 million eggs a year. Despite the commendable effort, it sadly seems that these events are not frequent or impactful enough to be making a significant difference on lionfish populations. In Honduras, local divers have been attempting to teach shark populations to recognise lionfish as a viable prey item. The most viable action at this time seems to be through the changing of fisheries regulation. By increasing regulations on grouper landings (a potential lionfish predator) and providing incentives to local fishers to target lionfish, their population may feel a noticeable drop.
Lionfish are, for a number of reasons one of the most impactful of all invasive species across the globe. Their high fecundity, low predation rates and widespread presence across the Western Atlantic have resulted in a seemingly untameable population. Many attempts have been made to slow or stop this invasion, but at current rates of population growth these solutions are unlikely to be restorative. At best they will act to slow the ever-increasing range of the species until a more effective solution can be found. For a real impact to be made in the slow but sure advance of the Red Lionfish, Pterois volitans, government responsibility and hard hitting changes to current fishing regulations need to be made as soon as possible.
Oscar started working for Sea Fans after finishing his degree in Applied Marine Biology at Bangor University in North Wales. He leaned to dive when he was 14 and has been hooked on the ocean ever since! He completed his Divemaster in 2014 during work on a coral conservation programme in the Philippines and has since been able to dive at some amazing places around the world. He spent a year working for the Australian Institute of Marine Science during his degree. Here he worked alongside researchers investigating the potential for coral on the Great Barrier Reef to adapt to the rising temperatures and acidity that our oceans are currently experiencing as a result of climate change.