Non-native species invasions occur most often because of human activities and tend to have deleterious effects, as they can significantly alter the ecology of ecosystems, from the individual level to community structures (Ruiz et al, 1997). Species that become invasive typically have traits that allow them to be successful in their new environment, such as being generalists of habitat (Cassey, 2004) and allowable environmental conditions, occupying a broader niche (Higgins & Richardson, 2014), and undergoing rapid reproduction (Ruesink, 2005). Marine habitats are susceptible to anthropogenic invasions via many routes of entry, including aquarium releases and the taking up, transport, and dumping of ship ballast water (Whitfield et al, 2002). The lionfish, Pterois volitans and Pterois miles, (Schultz, 1986) are opportunistic generalist carnivorous fish (Peake et al, 2018) that are native to the Indo-Pacific region (Hamner et al, 2007). They are also present on the western Atlantic Ocean as an invasive species via what is believed to have been an anthropogenic introduction (Whitfield et al, 2012) in the 1990s (Albins & Hixon, 2008). An event, or series of events, that lead to their introduction was unlikely to be natural dispersion, and was most likely an aquarium release, but it is also possible the founding individuals were dumped with ballast water from ships coming from the Indo-Pacific (Whitfield et al, 2002). The populations were found to be very low in genetic diversity, pointing towards the fact that when they were introduced, a founder effect occurred in which the population came from a few initial individuals (Belancur et al, 2011). As many scientists have noted, this voracious piscivore has the potential to cause severe problems for effected regions (Albins & Hixon, 2011; Bumbeer et al, 2017; Côté & Maljkovic, 2010). They pose a threat to the biodiversity and success of fisheries of the western Atlantic coast (Ballew et al, 2016). As an invasive species that can cause severe deleterious effects, and the case of the Lionfish appears to be one that warrants serious cause for concern. These concerns, as well as potential solutions, will be presented over the course of this work.
The effects of lionfish are due to many compounding factors. They have many of the characteristics that make for a successful invader (Albins & Hixon, 2011), including unique predation methods (Albins & Lyons, 2012), hardiness (Fishelson, 1997), high consumption (Fishelson, 1997), rapid growth, high fecundity, habitat generality, and cryptic form (Albin & Hixon, 2011). They have been described ecologically as opportunistic feeders and generalist carnivores (Peake et al 2018) with the potential to cause significant changes in the structure and function of ecosystems (Green et al, 2012). They consume an abundant amount of fish. It was found that adult P. volitans consumed 14.6g/day under a lab setting, and only lost 5-16% of their body mass when starved for three months (Fishelson, 1997). They blow a jet of water at their prey, a unique predation technique, that the evolutionarily naïve Atlantic reef fishes have no protection from (Albins & Lyons, 2012). They also complete with natural predators efficiently, and prey on local fishes and invertebrates voraciously (Albins & Hixon, 2008), having been shown to make an average of 1.44 kills per hour conservatively (Côté & Maljkovic, 2010).These invasive species, like any other, are additional stressors on marine ecosystems, and it has been shown that their interactions with other stressors are significant and necessary to consider (Ruiz et al, 1999). The effect of the lionfish compounds with other current stressors on our oceans, such as pollution, climate change, and overfishing (Albins & Hixon, 2008).
Lionfish have negative effects on native fish populations (Lesser, 2011) for many reasons. They have been shown to be a significantly more effective predator than a comparable predator that is native to the western Atlantic (Albins, 2012). Significantly more than this predator, they effected abundance of native reef fish, reduced their species richness, and the lionfish themselves were found to grow six times faster (Albins, 2012). It has also been found that lionfish caused a significant decline in recruitment, an average of 79% over a five-week duration (Albins & Hixon, 2008). This was believed to be due to their high rate of predation which, as previously mentioned, was shown to be 1.44 kills per hour conservatively (Côté & Maljkovic, 2010). Lionfish presence reduced the diversity of fish populations, and the community shifted to algal-dominated alongside a decline in local herbivores (Lesser, 2011). If the problem of lionfish invasions were to spread to Southern Brazil, lionfish would reduce the local prey populations, leading to reduced food availability for native predators, and they would have potentially deleterious cascading effects down the trophic levels (Bumbeer et al, 2017). An increase in lionfish coincided with a 65% decrease in prey fishes over two years, an effect that has the ability to affect the structure and function of ecosystems (Green et al, 2012). Clearly, these invasive species are a severe issue on the Western Atlantic Coast.
The ideal model of repair for the lionfish invasion of the western Atlantic is one that maximizes the cost efficiency of removing lionfish while minimizing ecological damage done and preventing harmful ecological effects (Green et al, 2014). It is highly unlikely that we can completely remove lionfish in their invasive range (Barbour, 2011), and because of this it has been recommended by many scientists that lionfish control measures be focused on strategic locations and individuals (Albins & Hixon, 2008; Barbour, 2011) such as vulnerable, economically and ecologically important areas (Albins & Hixon, 2008). It is also recommended that larger fish are targeted, to produce a shift towards shrimp, rather than a fish dominated diet by the remaining smaller lionfish (Frazer et al, 2012) It has been shown that it is not necessary to eradicate lionfish altogether to minimize ecological harm, as reducing their population density anywhere from 25-92% is enough to prevent a decline in prey population (Green et al, 2014).Targeted removals is a viable option for improving the state of the seas, as the lionfish do not disperse to new areas when others are removed (Frazer et al, 2012). A 90% reduction of lionfish abundance is possible with pole-spears in fewer than 2.5 diver hours per 1000m² (Usseglio et al, 2017). In the worst-case scenario, most reef fish biomass gets converted into lionfish biomass, leaving behind barren reefs (Albins & Hixon, 2011). A proposed, good target for management of this problem is to remove just enough fish to see increases in native populations effected (Barbour, 2011), although it would be ideal if biological controls such as diseases, and native predators learning to prey on them were to come in place (Albins & Hixon, 2011). Currently, there are local efforts by divers in place, and inflicted nations are encouraging lionfish fisheries to help decrease population numbers (Albins & Hixon, 2011). In some places, such as no take zones or areas that are too deep, it is not possible to undergo targeted fishing, in which it is more effective to SCUBA dive to remove individuals (Anderson et al. 2017) It has been proposed that volunteer efforts can reach wider ranges than professionals can (Anderson et al. 2017). Efforts of the public on this issue would be a cost effective, but potentially only short-term solution. I recommend that we follow the direction of the scientific literature on this management problem and encourage all kinds of fishing of these lionfish in their invasive range. Public outreach for volunteer and recreational SCUBA diver hunters could be effective at eliminating some of the population below harmful levels, especially if targeted in areas that are economically and ecological important and where the population is most vulnerable. We can also encourage the start-up of commercial fisheries to deal with the problem, although there are some challenges to this, I believe they are ones that can be overcome. The positioning of lionfish in the sea presents to managers a problem, they are most abundant at depths of greater than 20m, making manual removals difficult (Ballew et al, 2016). And with consumption of lionfish come some health concerns, as lionfish possess harmful ciguatoxins (Hardison, 2018). The FDA guideline is 0.1 ppb of ciguatoxin, and it has been recommended that consumption should be governed by thorough control and risk assessments (Hardison, 2018). Although this will likely not completely eradicate the invasive lionfish problem of the Atlantic coast, if implemented it could significantly reduce the ecological damage done to the ecosystems currently impacted. One thing that is certain in that we must consider the ecology of the animals we are trying to eradicate, before removing them (Barbour, 2011). This is what will prevent us from simply throwing money into solutions that are not maximally cost effective for whatever benefit we attain.
The case of the lionfish appears to be a case in which fisheries management is role reversed. As opposed to a fisheries problem that can be solved with management, it presents a management problem that can potentially be solved with fisheries.
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