Marine biology of the pacific lamprey Entosphenus tridentatus

Pacific lamprey Entosphenus tridentatus has an anadromous life cycle that begins with larvae that filter-feed in freshwater, followed by transformation into juveniles that migrate to the ocean where they parasitize hosts, and adults that migrate into freshwater to spawn and die. The marine-phase (i.e., juvenile life stage) is important yet poorly understood, and is associated with growth opportunities to achieve maximum body size and recruitment. The four goals of this paper are to: (1) synthesize the literature to identify patterns in the marine biology of Pacific lamprey; (2) develop hypotheses to explain these patterns; (3) identify limiting factors and threats, and (4) identify research needs. We hypothesize that recruitment of adult lamprey to spawning populations is influenced by oceanographic regimes through impacts on host abundance. Three marine factors that may be limiting lamprey abundance include: (1) predation and fisheries bycatch; (2) host availability; and (3) host contaminant loads. Four potential marine-related threats to lamprey include: (1) pollution; (2) climate change; (3) unfavorable oceanographic regimes; and (4) the effects of interactions between climate and regimes. Pacific lamprey is not philopatric and the extent to which host migrations and other factors influence lamprey entry into rivers is unclear. Research is needed to fill information gaps on how, when, why, and where lamprey move, feed, and grow in the ocean. Their widespread distribution, parasitic life history, diverse hosts, and multiple predators suggest that Pacific lamprey is integrated into diverse marine ecosystems.