Bioenergetics modeling and assessment of suitable habitat for juvenile Atlantic and shortnose sturgeons (Acipenser oxyrinchus and A. brevirostrum) in the Chesapeake Bay

I evaluated and modeled physiological responses of juvenile shortnose and Atlantic sturgeons to temperature, dissolved oxygen and salinity, within the ranges observed in the Chesapeake Bay during the last decade. All three factors significantly affected physiological energetics, growth and survival in both species. Maximum growth was predicted at 20–22°C, 10–12 ppt and >85% dissolved oxygen saturation in both species. Shortnose sturgeon tended to show higher growth rates than Atlantic sturgeon, especially at the highest tested temperature (28°C). Nonetheless, Atlantic sturgeon grew better than shortnose sturgeon under high salinity conditions (29 ppt). High potential overlap between juvenile sturgeons in the wild was evident from laboratory results, mesocosm experiments suggested interference competition for food would favor shortnose sturgeon. Extrapolation of bioenergetic models to fish >250 g would require further investigation and re-parameterization. In choice experiments, both species tended to identify and select optimal conditions as expected from physiological energetics and survival results, and from field observations in wild populations.; Physiological and survival responses were interpreted following Fry's paradigm. Hence, maximum physiological rates are assumed to be controlled by temperature, but limited by hypoxia (limiting factor) and/or confounded with the osmoregulatory costs demanded by salinity (masking factor). Multivariable spatially explicit bioenergetic models were generated for each species and used to predict recent trends (1990–1999) in potential production, and to index habitat suitability for juvenile sturgeons in the Chesapeake Bay. Predicted effects of persistent hypoxia, high temperature and high salinity indicated severe fragmentation and contraction of nursery habitats during the summer for modeled years. Average suitable summer habitat for juvenile sturgeons in the Chesapeake Bay (1990–1999) was estimated to be circa 1,000 sq-km for both species. However, large inter-annual fluctuations in suitable summer habitat were predicted around that average. Extremely dry years may result in almost no suitable habitat for juvenile sturgeons, especially Atlantic sturgeon.