Role of movement and the habitat mosaic in projecting impacts of habitat restoration on juvenile Atlantic Sturgeon in the Delaware River

Hypoxia, or low dissolved oxygen (DO), is a widespread water quality problem affecting coastal habitats worldwide and the control of point and non-point nutrient sources has become the principal method for limiting coastal eutrophication and the resulting biological impacts. Acceptable DO concentration must be established based on their known or predicted biological impacts. Such standards are varied and a common area of contention for decision makers. While it is critical for management decision making to collect empirical data on ambient DO levels and understand the effect of low DO concentration on important species, combining such data into a quantitative predictive model useful for management is a valuable ongoing challenge and currently used standards for applying empirical data to set DO criteria needs review. The Delaware River is under management review because of the extent and severity of hypoxia in summertime caused by nitrification due to ammonia nitrogen entering the river from point sources. The Delaware River is also habitat for native populations of endangered Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and population recovery is a key issue for managing the water quality of the Delaware river south of Philadelphia. We parametrized a spatially explicit individual based model (SEIBM) to describe biological and ecological responses of juvenile Atlantic sturgeon to the habitat mosaic in the Delaware river. This SEIBM was integrated with a hydrodynamic water quality model that projected the habitat mosaic of the river in 2019 under a current scenario and a scenario that reflects simulated responses to pollutant input reductions. Habitat differences between baseline and restored model scenarios were primarily observed in the summer months during the critical period between July 15th and August 30th. Sturgeon response to the spatial mosaic in DO concentration and water temperature were measured as a bioenergetics response in individual growth rates and daily probability of survival. These outcomes were associated with changes in daily movement distance, movement linearity, total individual displacement, and daily DO exposure. Model results indicated a habitat response to restoration that was impacted by daily movement behavior measured as decreases in daily movement distance and path linearity with habitat restoration. The consequences of these differences were observed in an increase in population biomass with time as well as differences in location and DO experience between baseline and restored simulations and between survivors and non-survivors within simulations. Model outcomes suggest movement behavior can impact model predictions of population response to habitat improvements and displays important habitat tradeoffs related to the spatial and temporal change in temperature and dissolved oxygen not considered in non-behavioral models. These outcomes can be important to developing quantitative predictions of biological response to expected habitat improvements.