Metapopulation structure of a semi-anadromous fish in a dynamic environment

Abstract

The Sacramento splittail (Pogonichthys macrolepidotus) is a relatively large (400 mm), long-lived (8 years) demersal cyprinid of conservation importance endemic to the San Francisco Estuary (SFE), California, USA. It exhibits a semi-anadromous life cycle spending adult life in low to moderate salinity (0-12) habitat with migrations into upstream freshwater rivers and floodplains for spawning during winter-spring. The species persists as two genetically distinguishable populations -one dominant and one subordinate -separated by discrete spawning habitats that we suggest resemble an island-mainland metapopulation structure. The populations overlap in distribution in the SFE, yet segregation is maintained with individuals tending to aggregate or school with others of similar population heritage and natal origin. The populations are spatially connected via dispersal of the dominant population into the subordinate population's spawning habitat when climate patterns produce freshwater outflow sufficient to form a bridge of suitable low salinity habitat across the upper SFE. Habitat affinities of the two populations, hydrodynamic modeling studies, and historical outflow records together suggest such conditions occur in approximately 1/3 of years overall with an irregular frequency. This dynamic pattern of spatial connectivity controlled by climate variability may be an important driver of gene flow between the two populations.Résumé : Pogonichthys macrolepidotus est un cyprinidé démersal longévif (8 ans) relativement grand (400 mm) d'importance pour la conservation et endémique de l'estuaire de San Francisco (SFE; Californie, États-Unis). Il présente un cycle biologique semianadrome, passant sa vie adulte dans des habitats de salinité faible à modérée (0-12) avec des migrations dans des rivières d'eau douce et des plaines alluviales situées plus en amont pour frayer à l'hiver et au printemps. L'espèce persiste en deux populations génétiquement distinctes, une dominante et l'autre subordonnée, séparées par des habitats de frai distincts qui ressemblent, selon nous, à une structure de métapopulation de type île-continent. Si les aires de répartition des populations se chevauchent dans le SFE, une ségrégation est maintenue, les individus tendant à se regrouper ou former des bancs avec d'autres individus provenant de la même population et de la même origine natale. Les populations sont connectées dans l'espace par la dispersion de la population dominante dans l'habitat de frai de la population subordonnée quand les aléas du climat produisent des débits sortants d'eau douce assez importants pour former un pont d'habitats d'assez faible salinité de part en part du SFE supérieur. La combinaison de l'affinité des habitats des deux populations, d'études de modélisation hydrodynamique et des registres historiques des débits sortants indiquerait que de telles conditions se produisent environ une année sur trois, à une fréquence irrégulière. Ce motif dynamique de connectivité spatiale contrôlée par la variabilité du climat pourrait...

An Evaluation of Three Fish Surveys in the San Francisco Estuary, 1995–2015

“…We restricted our Striped Bass analysis to age-0 fish to minimize the potential effects of ontogenetic changes in habitat use and distribution and because older age classes are likely much less vulnerable to these sampling methods. In contrast with the other focal species, Sacramento Splittail is a littoral species (Feyrer et al 2005(Feyrer et al , 2015 and likely not as vulnerable as the pelagic species to the sampling methods used in the three surveys.…”

Inter-population differences in salinity tolerance and osmoregulation of juvenile wild and hatchery-born Sacramento splittail

“…2 ). Also taken into consideration were environmental salinity measurements at seine and trawl locations when capturing the wild fish used in the experiments reported here and published observations during wild capture suggesting that splittail are not found at salinities >16‰ in the wild ( Feyrer et al ., 2015 ).…”

Isotopes and genes reveal freshwater origins of Chinook salmon Oncorhynchus tshawytscha aggregations in California’s coastal ocean

“…If the ocean spatial associations found in this study are also found in other migratory species that exhibit philopatry to feeding or breeding grounds, then maintaining an association with individuals from the same genetic or natal origin during migration may represent an underappreciated process that aids in the successful return of individuals to habitats that confer fitness benefits (Feyrer et al 2015). The ability to recognize and associate preferentially with individuals from the same genetic or natal group is common across animal taxa (mammals, Porter et al 2001;birds, Senar et al 1990;reptiles, Bull et al 2000;insects, Clark et al 1995) and is particularly prevalent in fishes (Griffiths 2003).…”

“…To the extent that membership in such aggregations is stable, understanding the number, size and distributions of aggregations, could help predict the influence of stock-specific fishing mortality. The rich literature on models of predator encounter with fish prey schools may play a more pivotal role in improving fisheries management and conservation than previously recognized (Czaran 1998).…”

“…These techniques can be used to understand migratory ecology and spatial structure in fishes at fine spatial scales, because all individuals potentially carry 'tags' that can identify their origin (Milton & Chenery 2001, Miller et al 2005, Sturrock et al 2012. There is growing appreciation that these techniques, when applied together, can provide a greater understand-ing of place of origin and connectivity than either alone (Barnett-Johnson et al 2010, Collins et al 2013, Feyrer et al 2015. Molecular techniques can detect restricted gene flow and the resultant genetic divergence among groups over evolutionary time scales (Waples 1991, O'Connell & Wright 1997, Banks et al 2000, whereas banding patterns and isotopes in otoliths reflect growth rate and environmental differences recorded by individuals on ecological time scales (Campana & Thorrold 2001, Barnett-Johnson et al 2007).…”