Resources: York River Water Budget - Fauna as an Indicator of Estuarine Conditions
 The relationship between discharge and finfish/shellfish is often not straightforward and at times not demonstrable, minimizing its effectiveness as a sole determinant in optimum flow. Natural long-period shifting climate regimes, fishing pressures and other anthropogenic stressors (lag responses or nonlinear) may veil links between discharge and the species of interest.
Bay finfish species demonstrably affected by climatic fluctuations can be placed into three reproductive strategy categories:
1) spring-spawning freshwater and anadromous species (e.g. catfishes, American shad, river herring, striped bass);
2) spring/summer spawning year-round residents (bay anchovy, silversides), and
3) fall-winter shelf-spawning species that are transported into the bay as larvae (spot, croaker, menhaden).
All strategies are affected by temperature, with the additional influences of discharge on river spawners, and wind patterns on shelf-spawners. Patterns in temperature, discharge and wind conditions can be depicted as warm-wet or cold-dry regimes that result in varying success for reproductive strategies. Climate conditions favoring bay spawners (warm/dry) are the antithesis of those supporting river spawners (cool/wet springs), thus successful recruitment in one guild could mean recruitment failure for the opposite guild.
Water budget plans should consider underlying climate trends when specifying optimum flows and management goals. For example, during climate regimes that support river spawners, flows should mimic the natural hydrograph closely to achieve successful recruitment during these years which may contribute disproportionately to long-term stock sustainability.
In general, egg dispersal in low flow conditions is more limited than in high discharge conditions, and extreme high flows act to advect eggs and larvae from tidal freshwater nursery environments. The magnitude and variability of flow will fluctuate based on watershed size which may account for disparate relationships. |
