Short-term outcomes of juvenile sea lamprey feeding on lake trout vary among parasite–host number combinations in a controlled laboratory setting

Abstract

The parasitic juvenile stage of the invasive sea lamprey ( Petromyzon marinus ) causes host injury and mortality in the Laurentian Great Lakes, yet laboratory feeding studies have generally used single-host or simple host-choice designs. We conducted controlled 7-d trials to quantify lake trout ( Salvelinus namaycush ) wounding, sea lamprey recovery, positive net mass change, growth, and wound location across four lamprey–host number combinations: 1:3, 6:6, 6:3, and 18:9. Candidate models evaluated whether outcomes were better explained by number combination, lamprey abundance, lamprey:host ratio, or separate lamprey and host effects. Across 27 trials, 70 of 135 lake trout (51.9%) were wounded, producing 113 wounds. Wounding was lowest in 1:3 (sea lamprey:host) and highest in 18:9, where 72.2% of hosts were wounded, and wound intensity was 1.33 wounds per host. In pooled descriptive models, each additional stocked sea lamprey was associated with a 13% increase in the odds that an exposed lake trout was wounded and an 8.3% increase in wound intensity per host. Among 173 recovered sea lamprey, 104 (60.1%) exhibited positive net mass change. This probability varied among number combinations, whereas candidate predictors provided little improvement over constant-mean models for continuous growth. Among lamprey exhibiting positive net mass change, intercept-only models were best supported, indicating little evidence that growth magnitude varied systematically among combinations. Wounds were distributed non-randomly among host body regions relative to proportional surface area. Short-term outcomes, therefore, varied among the tested parasite–host number combinations.