Behavior of early life intervals of Klamath River green sturgeon, Acipenser medirostris, with a note on body color

Abstract

SynopsisWe studied ontogenetic behavior, migration, and wintering behavior of young Klamath River green sturgeon, Acipenser medirostris, in the laboratory to provide insight into likely behavior of wild sturgeon. Hatchling free embryos preferred cover but were poor swimmers and could not move farther than a few centimeters to cover. The poor swimming ability and cover preference of hatchlings suggests evolution for habitat selection of females to place eggs in habitat with cover for eggs (and hatchlings), and for egg characteristics (large, dense, and weakly adhesive) to cause rapid sinking into cover without drifting. A day or so after fish developed into larvae (first life interval feeding exogenously), day-12 larvae initiated a 12-day downstream nocturnal migration. A totally nocturnal migration is unlike other Acipenser migrants yet studied. Migrant larvae had a dark-colored body typical of other Acipenser species that migrate as larvae. Tail color was a dark black (black-tail phenotype) only during the early larva period, suggesting a morphological adaptation for migration, foraging, or both. Post-migrant larvae and early juveniles to day 84 foraged diurnally with a nocturnal activity peak. Day 110-181 juveniles moved downstream at night until water temperature decreased to about 8°C, indicating wild juveniles migrate downstream to wintering habitat. Habitat preference of month 9-10 wintering juveniles suggests wild juveniles are in deep pools with low light and some rock structure. Wintering juveniles were only active at night. Initiation and cessation of daily activity was at dusk and dawn during illumination changes of <1.0 lx. This sensitivity to illumination has not been found before in sturgeons. During the first 10 months of life, nocturnal activity of early life intervals is a dominant feature of migration, foraging, and wintering.

Effects of rearing practice on post-release young-of-the-year behavior: Acipenser sturio early life in freshwater

“…This is consistent with a previous study of this species under controlled conditions (Charles et al 2009), and with observations of the closely related Atlantic sturgeon A. oxyrinchus (Fredrich et al 2008) and Gulf of Mexico sturgeon A. oxyrinchus desotoi (Kynard & Parker 2004), as well as for other less related acipenserids such as lake sturgeon A. fulvescens (Benson et al 2005) and green sturgeon A. medirostris (Kynard et al 2005). In the tidal area and the saline estuary, Acolas et al (2012) found no differential diel movements in 10 mo old European sturgeon.…”

“…Development of salinity tolerance has not been studied in YOY European sturgeons. Nevertheless, all anadromous sturgeon species must develop such tolerance (Altinok et al 1998, Bain et al 2000, Kynard & Horgan 2002, Allen et al 2011, which is age-dependent (Magnin 1962, Altinok et al 1998) and as far as it is known, occurs between 9 and 12 mo old at the earliest (Kynard et al 2005). Hatin et al (2007) pointed out that habitat use in Atlantic sturgeon juveniles is controlled by salinity and distance to the salt wedge where YOY use freshwater zones only.…”

European sturgeon (Acipenser sturio L.) young of the year performance in different rearing environments –study within a stocking program

“…For example, body pigmentation may provide with good camouflage within the environment, reducing predation risk and increasing survival (Svanbäck and Eklöv 2011). In sturgeons, it is believed that body pigmentation is linked to behavioral traits and early life foraging and migration (Kynard et al 2005). We observed differences in pigmentation that may be caused by the light differences between both methods and they could have a significant influence on habitat-specific fitness of individuals after release.…”

Movements of green sturgeon, Acipenser medirostris, in the San Francisco Bay estuary, California

“…This is contrary to what was expected based on the apparent nocturnal activity of captive-reared green sturgeon juveniles (J.J. Cech Jr., Department of Wildlife, Fish & Conservation Biology, University of California, Davis, personal communication). Kynard et al (2005) also reported nocturnal activity peaks in both larval green sturgeon and 9-to 10-month-old juveniles, attributing it as an adaptation for avoiding predation during dispersal migration and first-year wintering. The reported nocturnal behavior of reared fish may be specific to younger individuals, who would normally still be inhabiting the river environment, or it may be an artifact of captive rearing.…”