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

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.