I went looking and found a paper on northern pike gape size. I will email a copy to Bill Cody. Anyone else who wants to see it, send me an email. david.willis@sdstate.edu The authors measured gape of 49 northern pike of varying lengths (5-27 inches)in Sweden. The increasing cross-sectional diameter of a plastic cone (height 215 mm: base diameter 95 mm) was marked along its side at 2-mm increments. The cone was inserted into the mouth of the pike, and the diameter of the gape at the corner of the mouth was registered.

Pike gape size, as measured with the cone, was linearly related to total body length (Gape = (0.098 X total length) - 0.339, r2=0.987, P=0.001). In addition, the maximum prey size consumed at each pike length was quite a bit larger than what the gape size indicated would occur. They have a very nice figure that shows both gape size and maximum prey size as pike length increases. They used common bream Abramis brama L.) and roach (Rutilus rutilus L.) as their prey fishes for maximum size consumed; these are two European cyprinid (minnow) fishes.

The primary limitation is the relatively small size for the largest pike in the study (about 27 inches). Maybe Bill can add to it.

Nilsson, P.A., and C.Bronmark. 2000. Prey vulnerability to a gape-size limited predator: behavioural and morphological impacts on northern pike piscivory. Oikos 88: 539–546.

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From Bob Lusk: Dr. Dave Willis passed away January 13, 2014. He continues to be a key part of our Pond Boss family...and always will be.