Academics

Introduction 

The presence of exotic organisms is often viewed with negative connotations; however, whether the introduction of a species is worthy of concern is based on the extent of damage they can cause. Such a basis can be used to determine whether introduced organisms are successfully invasive. A prime example of a successful invader is Petromyzon marinus. Petromyzon marinus, more commonly known as the sea lamprey, is one of the most notorious aquatic invasive parasites, and rightfully so (Lennox et al. 2020). It is a type of jawless, anadromous fish that is native to the North Atlantic Ocean (Bjerselius et al. 2000). Over the past several years, especially since their first official documentation in the mid-19th century, these fish have been considered an invasive pest within the Great Lakes in North America. The traits that allow the successful invasion of these parasites are those that aid in their ability to adapt and spread all across the Great Lakes’ aquatic environments (Hubbs and Pope 1937); their wide range of selectivity of hosts (Silva et al. 2014), parasitic behavior, and adaptations for migration have gone on to cause immense damage to native fish and fisheries (Szalai et al. 2005). Although management efforts to control populations have been put forth, they have not been nearly enough (Szalai et al. 2005). Without a doubt, the sea lamprey is one of the worst ecologically and economically damaging invasive species within the Great Lakes that requires more immediate investigation and investment in management.  

Sea lamprey invasion range and invasive success 

The success and cause of concern in documenting the presence of invasive species has long been attributed to the alien organism's ability to spread and establish itself within its area of introduction. As aforementioned, the parasitic sea lamprey, Petromyzon marinus, is a prime example of a successful invader that has gone on to take over the Great Lakes region. These native Atlantic Ocean fish (Bjerselius et al. 2000) were first spotted in the waters of Lake Ontario below Niagara Falls. Thanks to the establishment of canals, they were able to pass into the other Great Lakes, thereby bypassing natural barriers of entrance (Hubbs and Pope 1937). Sea lampreys have spread and are continuing to spread and grow in numbers within the Great Lakes region (Hubbs and Pope 1937). Within their invasive range among all five of the Great Lakes, P. marinus has been found to display highly adaptive behavioral traits that have aided in their dispersal and establishment. These traits include an extensive migration range, adaptive migration behavioral traits, and a capacity for feeding on a broad scope of hosts, all of which are traits that have allowed for their successful invasion. Their great ability to spread should be one of the immediate focus in efforts to manage their population.  

Sea lampreys are anadromous species that can live in a substantial range of aquatic environments during the different portions of their life (Bjerselius et al. 2000). Such a capacity aids in their widespread, invasive distribution within the Great Lakes region of the United States (Bryan et al. 2005), and thus merits immediate attention. Petromyzon marinus has been found within both fresh and saltwater environments (Silva et al. 2014). While they have been noted to be present in sea waters during their adult-feeding stage, the lampreys also inhabit freshwater regions, such as the Great Lakes and streams, in order to spawn during their larval stage (Silva et al. 2014). Sea lampreys have also been found to feed in freshwater. Studies investigating P. marinus feeding patterns, particularly during their parasitic stage, have also found a widespread distribution amongst fresh, marine, and even brackish water in correlation with their use of a broad range of fish hosts (Silva et al. 2014). The parasitic attachment of sea lampreys onto host fish further aids in their widespread migration, as it helps them move across long distances while attached to their hosts (Bryan et al. 2005). A closer, in-depth investigation of the alleles within a population of sea lampreys has shown that small micro-evolutionary changes over the years have also aided the expansion of their invasive trajectory (Bryan et al. 2005). Such research suggests that P. marinus naturally migrates over large trajectories and does not home in one area (Bryan et al. 2005); however, further investigations regarding more recent trajectories should still be completed. This ability to distribute back and forth within a wide range of environments is what helps make these parasites a problem within the Great Lakes and is thus an area that merits further, in-depth research for management.  

The capacity of P. marinus populations to extend across such a broad distribution of aquatic environments is also thanks to efficient migratory behavioral traits that aid in their spread and establishment. Adaptive migratory behavioral traits have been observed amongst invading sea lampreys within the Great Lake regions and should thus be another main focus in research for population control efforts. Existing investigations have shown that during spawning seasons, the migration of adult sea lampreys occurs in response to pheromones which consist of larval odors with bile acids unique to P. marinus (Bjerselius et al. 2000). The lampreys are attracted to the lakes where the pheromones are present; this behavioral response therefore affects selection of spawning streams, in turn affecting population distribution (Bjerselius et al. 2000). Due to this adaptive attraction, sea lampreys do not require going back to natal spawning streams; rather they can simply depend on migratory-pheromone cues to find suitable streams (Bjerselius et al. 2000). One study has gone on to show that mature sea lampreys do stop responding to larval odors in order to expend their energy on finding mates to reproduce, yet more in-depth investigation regarding this change is required (Bjerselius et al. 2000). Aside from using larval odors, the lampreys have evolved to respond to other cues which aid in their ability to migrate. For example, it has been hypothesized that lampreys can utilize riverine odor cues to select streams for adequate spawning; however, not enough is known about this (Bjerselius et al. 2000). It has also been demonstrated that sea lampreys have evolved and adapted to finding suitable streams through use of not only migratory pheromones, but also extreme current flow sensitivity (Bjerselius et al. 2000). This great ability to migrate has proved fruitful to their reproductive success. With their ability to migrate, P. marinus has even been found to successfully breed alongside lakes in creek tributaries (Hubbs and Pope 1937). Considering such breeding success, more research regarding how sea lampreys locate suitable spawning areas would be of great importance in controlling their populations.  

The invasive success of sea lampreys can also be attributed to their broad range of hosts for feeding. Adult parasitic sea lampreys are hematophagous feeders that can feast upon an extensively broad range of hosts (Silva et al. 2014). As this diverse feeding trait helps contribute to their invasive success, it thus also requires immediate investigation for the purposes of population management. Sea lampreys have been observed to have low degree host selection (Silva et al. 2014). One study has gone as far as to show that they are capable of preying upon 54 confirmed host species within fresh, brackish, and open sea ecosystems. Despite this, the lampreys have been found to have a preference for larger hosts like lake trout (Silva et al. 2014). This preference could be an area of focus that can be exploited to figure out better ways to control sea lamprey presence. Other studies have shown that sea lampreys even have the capability of latching onto sharks and their tough dermal denticle armor thanks to P. marinus’s salivic ability to deaminate amino acids and attach itself onto said host (Silva et al. 2014). This interesting aptness to latch onto hosts could be investigated and targeted when creating new methods of population management.  

Overall, the sea lamprey's broad dispersal capabilities, migratory behavioral traits, and widespread, adaptive feeding behaviors are all traits that effectively contribute to their invasive success within the Great Lakes (Silva et al. 2014). These traits additionally serve in helping them take the spot as one of the worst aquatic invasive species within the Great Lakes, effectively allowing them to damage native fish biology and contribute to the collapse of fishery economies; thus, sea lampreys’ broad range of hosts, host dispersal, and feeding behaviors should be areas meriting further investigation. Despite the extent of what is already known, further examination and management is urgently required in order to understand and control the extensive damage that they partake in, beginning with their effect to native fish and the economic injury they contribute to.  

Damage to native fish and fishery economy caused by sea lampreys 

When determining whether an introduced species will be of significant concern, investigations regarding its behavior and effects in its invasive range are conducted. Research pertaining to Petromyzon marinus behavior in its invasive range within the Great Lakes determined that the sea lamprey’s destructive feeding is of primary and significant concern as it causes considerable harm to the health of native fish (Lennon 1954). Sea lamprey parasitism also triggers disruptive economic problems relating to monetary value losses in fishery harvesting (Stewart et al. 2003). In turn, significant costs have also resulted from establishing management programs that attempt to control and prevent further increase in the abundance of the lampreys (Szalai et al. 2005); however, the cost of continued lamprey invasion is greater than the price of spending on population management, and the current expenditure is still not enough to effectively manage these parasites. 

The main concern regarding sea lamprey invasions has to do with the extensive damage they bring about via their parasitism. The invasive presence of sea lamprey has led to a drastic decline of native fish in the Great Lakes thanks to the lamprey’s deleterious feeding (Harvey et al. 2008), a trait that earns them the title as one of the most awful aquatic invaders. In their parasitic life stage, sea lampreys actively use their highly adaptive suction-cup-like mouths with pronged tongues, teeth, and anticoagulant lampredin secretions, to effectively attach and feed off hosts (Lennon 1954). This brutal feeding method can lead to host mortality or risk of fungal infections within the wounds (Lennon 1954). One study investigating P. marinus’ parasitic efficiency calculated that the presence of a single lamprey resulted on an average of 1.32 and 0.75 lake trout deaths in Lake Huron and Lake Michigan, respectively (Bence et al. 2003). Additionally, fish that are not killed immediately by the parasite are still likely to experience fatality due to secondary infections in wounds or, for some fish (like Brook trout), due to negative reactions to P. marinus’ secreted lampredin (Lennon 1954). The amount of native fish lost can worsen if effective management is not placed forth.  

Damage caused by lamprey feeding behavior does not stop with fish populations; another area that is hurt is the fishery economy as the damage sea lamprey parasitism imposes on local fish populations in turn damages the economy of important fisheries that depend on harvests of the parasitized fish. Petromyzon marinus destructive feeding on native fish triggers economic problems such as monetary loss in fishery harvesting businesses (Szalai et al. 2005). The Great Lakes commercial fisheries statistics found that in just ten years since P. marinus' exploding population in the mid-20th century, native lake fish populations had dropped drastically (Lennon 1954). This was of particular concern for lake trout populations where fisheries' highly important catches had dropped from 8,600,000 pounds to less than 26,000 pounds (Lennon 1954). In more recent studies, economic injury level analysis (EILs) has shown that the damage that sea lampreys are causing fisheries is greater than the level of investment placed on control efforts (Szalai et al. 2005). For instance, in Lake Huron, control efforts fail to reach EILs calculated optimal investments of around $2.12 per harvested lake trout (Szalai et al. 2005). This is primarily due to the fact that there are limited resources which must only be allocated to areas where control would be most efficient (Szalai et al. 2005). These same calculations, however, also provide corroboration that despite management investments being lower than optimal level, the funding expended on managing the populations of these parasites continues to be of great cost. This is seen in the statistics for expenditure on control programs in 2002 where more than two million dollars were spent in management (Szalai et al. 2005).  

The damage that Petromyzon marinus parasitism causes to fisheries’ becomes more prominent when considering the financial investments that management programs must go through to control the sea lamprey. Ultimately, Petromyzon marinus is cause for great concern to the Great Lakes native fish and fishery economy; consideration of all that is being spent as well as of the limited amount of resources that can go around make clear that more research regarding what would constitute effective management strategies is urgently required. The damage that sea lamprey have caused within its invasive range still requires further investigation that can bring to light more recent economic injury level statistics. Additionally, more research regarding other alternative effects that the presence of sea lamprey has in its invasive range is required. In particular, investigations concerning the role of P. marinus in spreading pathogens is of prime concern. This new focus arises from reference to recent studies that have discovered that sea lampreys can potentially carry and transmit the pathogen Aeromonas salmonicida when feeding (Diamanka et al. 2014). Aeromonas salmonicida is a dangerous bacterial disease that causes significant harm to Salmonids, so much so that its presence can deteriorate fishery business (Diamanka et al. 2014). Because of such, further research on the sea lamprey’s possible additional role in pathogen transmission would be of considerable importance given the heightened risks the transmission poses to the Great Lakes native fish and fisheries. This research can be further implemented to figure out better strategies of control. 

Current control strategies and the future of management  

Effective control of invasive species should not just require removing populations, but rather depend on the efficiency of management protocols, especially when dealing with costly control of terrible invaders. Petrmyzon marnius’ extensive damage to the Great Lakes has earned them the title of one of the worst aquatic invaders whose invasive biology requires more investigation for effective application to control efforts. Given that complete elimination of sea lamprey populations is not feasible, the need for efficient management is crucial to properly control populations (Bravener and McLaughlin 2013). The current efforts that are being expended on sea lamprey control do not involve one simple approach, but rather require a culmination of a variety of methods. Despite these good efforts, more research asserting the effectiveness of control and prospects of future management barriers like global warming must seriously be considered.   

Over the last 45 years, management has undergone substantial changes in attempts to better manage sea lamprey populations in the Great Lakes (Guo et al. 2017). The attempt to control populations began in Lake Huron during the 1950's with placement of barriers to lessen spawning migration (Guo et al. 2017). This was then followed with the application of electrical barriers, traps, lampricide, sterilization of males, and natural chemosensory repellent cues (Guo et al. 2017). Despite this wide variety of control methods, management programs still require continual monitoring of their success to seek ways to make them more effective. One of the most recent programs adopted to measure damage has been the Integrated Management of Sea Lampreys (IMSL) that is based on estimate injury level costs (EILs) (Stewart et al. 2003). Despite its use in estimating damage, it is still not being effectively allocated to control populations, evident by how EILs continue to be below optimum level (Stewart et al. 2003). Furthermore, it has even been suggested that reliance on EIL's be considered carefully given that the implied value of fish could change for each lake (Stewart et al. 2003). Variance in damage depends on the fishes targeted as host by the lampreys and changes in the fishing community value of select local fish (Stewart et al. 2003). This implies that each lake requires different options for efficient management and thus further in-depth research in each lake is required. Ultimately, sea lamprey control efforts must be set out resourcefully, all depending on differing, specific local circumstances (Stewart et al. 2003).  

One of these areas that requires further investigation for efficiency is the use of traps. Trapping success is greatly dependent on the behavior of sea lampreys and whether they encounter placed traps or not (Bravener and McLaughlin 2013). Although traps had been placed accordingly in areas with high flow and appropriate upstream barriers in St. Mary’s River, no high efficiency in lamprey trappings was found. Trapping success lacks efficiency not only because the encounter rate is low, but also because even when sea lamprey do happen to be near traps, they do not spend much time at them before leaving. While it is suggested that traps be modified in location, design, abundance, and attraction, limits in resources are preventing efficient advancement in these trap-based control methods (Bravener and McLaughlin 2013). The allocation of resources, as seen in trapping control, is another consideration to take crucially, especially when regarding the future of management success in response to global climate change.  

The development of management efforts must be increasingly considered in the light of current global issues regarding climate change. It has been predicted that continued changes to the Great Lakes ecosystem thanks to climate change will significantly affect the presence of sea lampreys (Lennox et al. 2020). One of the main predictions is that sea lamprey will benefit from global warming; however, it is still not known whether control efforts will benefit or suffer (Lennox et al. 2020). Climate change may prove positive for sea lampreys by accelerating larval growth and allowing for larger lampreys (Lennox et al. 2020). It is also estimated that more lampricide will be required to control sea lamprey larval populations due to increased water levels caused by warmer temperatures (Lennox et al. 2020). Bigger populations may also increase the possibility of host fish wound infections (Lennox et al. 2020), showing how this pest will continue to have a terribly damaging presence. Additionally, climate change may change locations of suitable spawning waters, thus resulting in the need for new assessments and resources for management efforts (Lennox et al. 2020).  

Ultimately, although methods for management have continually been changing, continued development of control efforts would be of considerable importance to control these parasites that have become one of the worst pests in the Great Lakes. Considering that continued increased presence of the invasive parasite has led to decline of hosts fish and has impacted commercial fisher and biological food webs, additional research would be quite beneficial. Interestingly enough, the invasive biology of these pests is of crucial importance not just for management in the Great Lakes but also for the surprising need of conservation for their populations in native waters. One particular study notes that within its native waters in the North Atlantic region of Europe, sea lampreys are actually considered endangered (Guo et al. 2017). There, they are threatened due to water pollution and habitat loss (Guo et al. 2017). This same research acknowledges that the study of the sea lamprey's invasive biology and management efforts is of great importance when determining conservation efforts in its native range (Guo et al. 2017). These types of findings further show just how important more research regarding the critical invasive status of P. marinus in the Great Lakes would be. Additionally, it also suggests how it may be possible that investigations of why sea lamprey are in danger in native waters could be beneficial to configuring methods to continue to push for better management of these species that will otherwise continue to be an awful pest in the Great Lakes.  

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