Emily L. Mensch and Ellen M. Weise
With a mouth that pays homage to horror movies, sea lamprey have become an infamous invasive species in the Great Lakes. Their invasion through the expansion of the Welland Canal in 1919 decimated the valuable Great Lakes fisheries and caused remarkable harm to the economy and the ecosystem. In response, a multi-million-dollar, multi-national, annual control and assessment program was deployed to keep their numbers in check. There is now extensive research into sea lamprey biology and behavior aimed at bolstering control techniques and assessing their populations.
The villainous reputation lent to sea lamprey does not extend outside the Great Lakes. For thousands of years, sea lamprey were regarded as a delicacy by English Royals. King Henry I even reportedly died from an overdose of lamprey pie. Beyond sea lamprey populations in Europe, there are closely related species in the Pacific Northwest imperiled by migration blockages and habitat fragmentation. Between industrialization in the 19th century and overexploitation of lamprey, their numbers have plummeted.
From a research perspective, sea lamprey represent an important evolutionary species. Along with other fish like gar, coelacanths, and lake sturgeon, they are an example of a ‘living fossil’ — a species whose body and behavior encode important evolutionary events. Records indicate that this jawless organism’s morphology (the study of an organism’s size, shape and structure) has been largely unchanged for nearly 400 million years. Living fossil species are often the surviving lineage of a mostly extinct evolutionary trait, in this case the jawless vertebrate. Therefore, understanding sea lamprey traits can provide a unique insight into vertebrate evolution as a whole, making studies of this species interesting and informative beyond exclusive management purposes.
Sea lamprey are at the crossroads of conservation and invasive species management due to their varied history in different parts of the world. These opposing goals seem incompatible but results of sea lamprey research provide insight for both scenarios. From genomic assessments to sea lamprey deterrents, methods designed to keep invasive populations in check in the Great Lakes can be used to conserve counterparts in Europe and the Pacific Northwest. Here, we’ll explore how studies which aim to control a ‘monstrous’ invasive species can also be used to generate interesting science and conserve imperiled populations, leaving it up to the reader to decide if these creatures are true monsters of the deep, or organisms complex and misunderstood.
FEAR AND SEX IN THE MIGRATING LAMPREY
One current research project in the lamprey realm aims to understand and exploit how these fish use their sense of smell. More specifically, how they use smell to navigate a gauntlet of “fear” during their migration
Many fishes have a mechanism to smell when another member of the same species is injured or killed. This enables them to accurately assess the presence of a predator and the likelihood of a potential attack. These macabre odors, dubbed “alarm cues”, are used throughout the sea lamprey’s complex lifecycle but are especially important during their upstream spawning migration. Sea lamprey are semelparous, which means they migrate upstream after they stop feeding in the lakes (or the ocean, in their native range), and then mate, essentially uninterrupted, until they die. This means finding suitable mating habitat is immensely important because sea lamprey only have one chance to produce offspring and pass their genes on to the next generation.
By unlocking the chemistry of this powerful “fear” cue, lamprey behavior and movement could be manipulated which could have broad implications in management and conservation. In the Great Lakes ecosystem, alarm cues could be used as a repellent to guide fish into traps or to habitats not suitable for mating. In the Pacific Northwest, where Pacific lamprey are facing population constraints, alarm cues could be used to guide fish through fish pass systems to reach suitable mating grounds. And finally, understanding the chemistry of this alarm cue could assist in deciphering the evolution of this fear response in vertebrate species.
USING GENOMICS TO ASSESS SEA LAMPREY POPULATIONS
Population genetics data is becoming increasingly valuable in a management context due to the plummeting costs of sequencing and an explosion of resources related to population genetics research. The cost of sequencing a human-length genome has decreased from over a hundred million dollars in 2000 to under a thousand dollars in 2015. This cost decrease is largely due to improvements in sequencing technologies, including the development of next-generation sequencing, where thousands of short DNA fragments are sequenced in parallel. As genomics research has become financially viable, databases of genetic sequences like NCBI and open access bioinformatics software make it accessible.
Population genomics studies provide an in-depth look at the population history and abundance of any group of individuals. Metrics related to genetic diversity and population size are needed for assessments in both control and conservation contexts. In the Great Lakes, these metrics can assess the effectiveness of traditional control techniques, including lampricides and barriers, and supplemental control techniques like pheromone and alarm-cue methods and sterile-male release. In systems where lamprey are endangered, these same metrics can be used to evaluate spawning success and look for ‘red flags’ that indicate risk of extinction spirals.
Sea lamprey are an important model species in population genomics. Their genome was sequenced in 2013, and a germline (DNA in reproductive cells) genome was released in 2018. For a large-scale population study, short sections of variable DNA in thousands of individuals can be sequenced and aligned to the genome rather than sequencing the whole genome. Recently developed methods allow specific regions of the genome to be targeted for sequencing, further improving our ability to generate genome-wide data for a large number of individuals at minimal cost. This method, known as RAD sequencing, is a cost-effective way to generate the precise data needed to assess a population. These approaches are currently being utilized for sea lamprey in the Great Lakes region.
While sea lamprey may be the closest thing to a sea monster in the Great Lakes, they are also a unique and valuable species that provides insight into evolutionary processes and can be used to transfer knowledge for conservation studies. Because they are both invasive and imperiled, depending on where they are, managers need a variety of techniques to regulate these populations. In the Great Lakes, there is a ‘kings ransom’ of research devoted to sea lamprey behavior and biology to better control population numbers, and this research can also be used by managers in Europe to conserve dwindling lamprey populations. This provides a clear example of how researchers can harness their creativity to exploit a problem and use it to construct meaningful endeavors in science and conservation.
ALL PHOTOS: EMILY MENSCH