What can we learn by comparing turbines?Some model and speculate about "killer turbines" but I prefer measurements. Some fairly reliable measurements have been made of how fish fare as they pass through the Hydro Green Hydrokinetic system (henceforth, HGH turbine). The basic outcome was that fish were not harmed to any meaningful extent. So it's worth comparing the HGH turbine installation in the Mississippi with an anticipated installation of an OpenHydro turbine in Minas Passage.
The two turbines look similar, except the HGH turbine has only 3 blades and rotates at 21 rpm whereas the OpenHydro turbine has 10 blades and rotates at 6-8 rpm. Thus, a blade passes by every 60/(21*3)=0.95 seconds for the HGH turbine and every 60/(8*10) to 60/(6*10) = 0.75 to 1 seconds for the OpenHydro turbine.
The HGH turbine was installed in currents that ranged from 1.74 to 3 m/s. The currents average about 2 m/s in Minas Passage, where the OpenHydro turbine will be installed, but might peak as high as 5 m/s during a flood, spring tide. (I don't have precise site information --- does CST have a more accurate number?)
The maximum blade speed is 4 m/s for the HGH turbine and it will be a little higher (5.4 m/s) for the OpenHydro turbine.
The diameter (of the area swept by turbine blades) is 3.7 m for the HGH turbine and 12.8 m for the OpenHydro turbine. Having a larger diameter increases the length scale of that part of the blade that moves at high speed. So it is possible that a larger diameter makes life more difficult for a fish --- we don't know.
The species of fish are entirely different in Minas Passage than in the Mississippi. The fish are probably the factor that most differentiates the HGH turbine installation from an OpenHydro in Minas Passage.
From the above comparison, we could fairly say that if the HGH turbine was a "fish killer" then we would have eavery reason to fear that the Open Hydro turbine was a fish killer. But, the HGH turbine is not a fish killer. This is not sufficient evidence to show that the OpenHydro turbine will be safe for fish but it is sufficient evidence to argue that it may be safe and that it would be prudent to make measurements rather than flap around like a hysterical fisherman.