Spawning Site Selection and Potential Implications of Modified Flow Regimes on Viability of Gulf Sturgeon Populations

Abstract

Rapid human population growth and an associated increase in consumptive water demands within the ecologically diverse Apalachicola-Chattahoochee-Flint (ACF) River basin of the southeastern United States have led to a series of highly publicized water wars, exacerbated by recent drought conditions, between the states of Alabama, Georgia, and Florida. A key issue is how managing riverine flows to meet human water needs will affect the viability of species that are federally listed as threatened or endangered, including the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi. Our present understanding of Gulf sturgeon ecology within the Apalachicola River basin indicates that altered riverine flow regimes may affect spawning success and possibly the recruitment patterns of the population. Through intensive field work, we documented Gulf sturgeon spawning site selection in the Apalachicola River and then evaluated the relationship between river stage and the available spawning habitat at these sites. We then used an agestructured simulation model to assess the effects of changes in recruitment patterns on population viability using hypothetical scenarios based on changes in flow regime and its effect on available spawning habitat. Over 3 years we were able to collect almost 500 Gulf sturgeon eggs in the Apalachicola River at three different spawning sites. We observed that the depths and flows where eggs were found were similar across years and sites despite varying river conditions. River discharges of less than 142 m 3 /s at Jim Woodruff Lock and Dam significantly reduced the spawning habitat available to Gulf sturgeon at all known spawning sites,

Consistent SpatioTemporal Estuarine Habitat Use during Emigration or Immigration of a Western Population of Gulf Sturgeon

“…However, the variability in time spent in the estuary by size-class may be based on the exact size of subadults as the range is large and individuals may move to island habitats if they are larger (see Ross et al 2009) or stay in estuarine areas if they are a smaller subadult. These annual differences in rainfall and subsequent emigration cues can directly affect recruitment and survival within a drainage, remove natural migratory cues, and lead to a reduction in low-salinity coastal water habitat rich in potential prey (Heise et al 2005;Randall and Sulak 2007;Flowers et al 2009). Gulf Sturgeon populations are sensitive to changes in mortality rates (Tate and Allen 2002), and if extreme low-flow events occur with increasing frequency owing to water management choices or climatic events, population recovery could be drastically impaired and a subsequent risk of extirpation may occur (Flowers et al 2009).…”

“…These data illustrate the complexity of abiotic factors affecting the observed large-scale migratory and small-scale activity patterns during sturgeon emigration. Thus, changes in any of these environmental directive cues with natural or maninduced variability in river conditions (Cooke et al 2012;Mims and Olden 2012;Nelson et al 2013) may influence overall life history vital rates (Randall and Sulak 2007;Flowers et al 2009) and seasonal migration cues.…”

“…For example, temporally variable sturgeon movement downriver during fall emigration occurred in drought years in the Pascagoula River compared with fish pulsing quickly from the summer holding area in wet years (Heise et al 2005). This influence of natural variability coupled with the increased urbanization in the coastal zone worldwide (Flowers et al 2009;Peterson and Lowe 2009;Lowe and Peterson 2014) and issues with water withdrawals and climate change (USFWS and Gulf States Marine Fisheries Commission 1995;Flowers et al 2009;USFWS 2009;Mims and Olden 2012;Farrae et al 2014) make it vital that we understand long-term ontogenetic habitat use patterns and how natural riverine variability might influence the initiation of migration of anadromous species. This information will help ensure that we are knowledgeable when promoting any future recovery actions.…”

Spatiotemporal variation in flow-dependent recruitment of long-lived riverine fish: Model development and evaluation

“…The importance of river flow in spawning behavior has been documented for many stream fishes including sturgeon (Flowers et al, 2009;Paragamian and Wakkinen, 2011). In our model, habitat quality based on river flow and drift prey density determines movement and habitat selection probability by sturgeon, and ultimately spawning events.…”

Informing Recovery Goals Based on Historical Population Size and Extant Habitat: A Case Study of the Gulf Sturgeon

“…Some life history information such as age at maturity was based on previous Gulf Sturgeon studies (Huff 1975), while other information such as maximum age or growth rates was updated based on estimates derived from long-term capture-recapture studies (Pine and Martell 2009). Growth curves, age-length, and length-weight relationships were developed by Flowers et al (2009) andFlowers (2008) following standard allometric relationships and von Bertalanffy growth equations. The parameter values and form of We developed a prior for adult natural mortality based on life history characteristics including longevity (Hewitt and Hoenig 2005) and individual metabolic demand (von Bertalanffy k parameter: Jensen 1996).…”