Egg Mortality

Methods to Measure Magnitude and Source of Egg Mortality

We placed fertilized eggs onto pads and placed pads into metal racks that were divided into 4 sections that differed in the size of wire mesh.  Smaller mess sizes would keep out predators.  However, smaller mesh sizes would also reduce water flow.  Thus the experiment evaluated the relative importance of predation (biotic effect) from environmental effects (flow). Data are from Forsythe 2010.

Egg Mortality Experiment

Mortality Experiment Diagram

Mortality Experiment Diagram

 

 

 

 

Egg Mortality Experiment

Egg Mortality Graph

Data collected from locations in the Black River revealed that rates of mortality attributed to developmental failure (embryos dying during incubation) were generally higher than mortality attributed to predation.

Developmental Failure Graph
Predation Graph

 

Experimental studies of lake sturgeon egg predation at the Black River stream-side facility

We conducted additional laboratory experiments to test for the effects of predator density and substrate size on predation using a candidate predator, the rusty crayfish.  Egg mortality was high in this laboratory experiment across treatments (80%). Approximately 17-104 eggs were consumed on average per predator.  In general, the highest levels of mortality were observed in treatments with high predator density and little habitat complexity in the form of small substrate size. Findings suggest that lack of sturgeon recruitment could be attributed to high rates of mortality during the egg stage

Mortality Factors Graph

Crayfish

A large number of predators consume lake sturgeon eggs.  One of the biggest predators may be invasive species such as the rusty crayfish that is very commonin many Great Lakes tributaries