The Delaware River and Estuary were once home to the largest population of Atlantic sturgeon on the East Coast - today less than 1% of the historic spawning population remains. The Nature Conservancy was approached by regional sturgeon experts to examine the potential impacts of flow, dissolved oxygen (DO) and salt water encroachment on the successful recruitment of Atlantic sturgeon in the Delaware River. In order to examine where and how these factors may be limiting recruitment, we synthesized available literature, data and models on habitat suitability for Atlantic sturgeon. The project was framed by three broad study questions:
- For any given location, at any given time of year, what is the most sensitive life stage present?
- What are suitable habitat conditions to support that life stage?
- What current and future factors influence stability?
We used that information to document current life stage distribution, assess focal hypotheses and to serve as the foundation for a set of recommended habitat conditions suitable for successful recruitment of Atlantic sturgeon in the Delaware River.
Recommendations for estuarine habitats are outside the scope of this report.
Summary of recommended habitat conditions:
To support successful Atlantic sturgeon recruitment in the Delaware River, we recommend*;
- Instantaneous DO ≥ 5.0 mg/L
- Discharge > July Q85 (4,000 cfs @ Ben Franklin), when average daily DO < 5.5 mg/L
*Recommendations represent the minimum values required to support habitat suitable for recruitment based on best available literature, regional data and expert review. To address cumulative stressors present in the Delaware (e.g.dioxins), conservation measures should be more protective.
Study conclusions
- Sturgeon of all life stages occur throughout the freshwater portion of the river, with early life stages occurring year-round.
- Despite improvements in water quality over the last two decades, DO conditions in recent years likely inhibited successful development of early life stages.
- Improved water quality standards are needed to support suitable habitat conditions. Best available technologies could improve DO from lethal to suitable concentrations.
- Current low flow conditions influence salt front encroachment. In 2010, the availability of suitable freshwater habitat was reduced by between 10 and 20 miles throughout the summer, during egg, larval and young-of-year development. Under the drought of record, suitable freshwater habitat was reduced by up to 40 miles.
- Anticipated sea level rise is projected to permanently shift the average salt front upstream. Further, changing precipitation and evapotranspiration patterns may increase the extent