Investigating New Methods to Improve Ageing and Study Movement Patterns of Larval Great Lakes Sea Lamprey (Petromyzon Marinus) Populations

Abstract

Sea lampreys (Petromyzon marinus) are parasitic pests in the Great Lakes which have negatively impacted game fish populations. Management efforts to control sea lamprey populations throughout the Great Lakes began in the 1950s and continue today. The primary control technique used is the application of lampricides to streams to kill larvae before they become parasites. A better understanding of larval sea lamprey growth rates, age determination, and habitat preference is greatly needed to improve both selection of streams for lampricide application and to inform models of sea lamprey population dynamics. Otoliths have been used to estimate age in teleost fish through annuli counts and otolith size metrics. Lampreys do not have otoliths, having instead an analogous structure called a statolith. Determining age based on statolith annuli counts has been found to be imprecise and inaccurate. Therefore, I evaluated whether statolith size is correlated with sea lamprey larva, also known as ammocoete, age using known-age populations of ammocoetes from two contrasting Great Lakes streams. Statolith width was found to be the measurement that better distinguished the age-classes within the populations. When combining length-frequency and statolith width data into a likelihood-based statistical model I was able to more accurately assess ammocoete population age composition for one known-age population than when using only length-frequency data. Studies of the biology and ecology of Great Lakes sea lampreys (Petromyzon marinus) may require an effective means of tagging larvae to track individual movements to better control this pest species. I evaluated the feasibility of using passive integrated transponder (PIT) and visible implant (VI) Alpha tags in larval sea lampreys at least 100 mm and 85 mm in length, respectively. The use of PIT tags in lampreys as small as 100 mm in length is not suggested unless a tag burden of less than 5% can be achieved. Until a better method of wound closure is found to limit VI Alpha tag loss in lampreys, the use of these tags is not suggested in lampreys as small as those used in this study. If habitat preference, depth distribution, or in-stream distribution changes as larvae approach metamorphosis, as anecdotal evidence suggests, there is a potential for bias in the current ranking surveys which make the assumption that larval lampreys occupy habitat in the same proportion irrespective of size. To monitor the movement and preferred habitats of large larvae, I marked and released larvae approaching metamorphic size and subsequently tracked their movements. I used three different tagging methods, including passive integrated transponders (PIT) tags, visible implant (VI) Alpha tags, and visible implant elastomer (VIE) tags to mark larvae. Using PIT telemetry and electrofishing, I was able to locate 11% of our released ammocoetes. It was found that the larger ammocoetes moved further distances downstream from release locations than the smaller ammocoetes.