Stream and Ocean Hydrodynamics Mediate Partial Migration Strategies in an Amphidromous Hawaiian Goby
Here, we use spatiotemporal variation in partial migration across populations of an amphidromous Hawaiian goby to test whether stream or ocean conditions favor completing its life cycle entirely within freshwater streams.
Partial migration strategies, in which some individuals migrate but others do not, is widely observed in populations of migratory animals. Such a pattern could arise via variation in migratory behaviors made by individual animals, or genetic variation in migratory predisposition, or simply by variation in migration opportunities mediated by environmental conditions.
Across 35 watersheds, microchemical analysis of otoliths revealed that most adult Awaous stamineus are freshwater residents but we found considerable variation among watersheds. We then tested the hypothesis that the prevalence of freshwater residency increases with the stability of stream flows and decreases with the availability of dispersal pathways arising from ocean hydrodynamics.
We found that streams with low variation of daily discharge were home to a higher incidence of freshwater residents in each survey year. The magnitude of the shift in freshwater residency between survey years was positively associated with predicted interannual variability in the success of larval settlement in streams on each island based on passive drift in ocean currents. We built on these findings by developing a theoretical model of goby life history to further evaluate whether mediation of migration outcomes by stream and ocean hydrodynamics could be sufficient to explain the range of partial migration frequency observed across populations.
The model illustrates that the proportion of larvae entering the ocean and differential survival of freshwater-resident versus ocean-going larvae are plausible mechanisms for range-wide shifts in migration strategies. Thus, we propose that hydrologic variation in both ocean and stream environments contribute to spatiotemporal variation in the prevalence of migration phenotypes in A. stamineus. Our empirical and theoretical results suggest that the capacity for partial migration could enhance the persistence of metapopulations of diadromous fish when confronted with variable ocean and stream conditions.
Lisi P, Hogan J.D, Holt G, Moody K, Wren J, Kobayashi D, Blum M, McIntyre P. 2022. Stream and ocean hydrodynamics mediate partial migration strategies in an amphidromous Hawaiian goby. Ecology, e3800. https://doi.org/10.1002/ecy.3800.