Does Barometric Pressure have an effect on fish?

Bill Leuchten

barometer

I usually like to blame the dropping barometer for my poor fishing days. In actuality it’s the change in the weather, not any fluctuation in barometric pressure, that affects both the fish and the fishing. In fact, most underwater species are probably not aware of any barometric changes.

A normal value for barometric pressure is about 30 inches. High pressure is about 31 inches. A hurricane or a strong low can get down to 28 inches. These pressure changes are not significant when compared to the hydrostatic pressure changes that take place underwater when a fish changes depth.

A fish swimming up or down by just 3.28 ft. will result in a decrease or increase in pressure by 1/10 of an atmosphere since water is 700 times denser that air. This pressure change exceeds any change the barometer could produce.

Also, barometric pressure is a slow pressure change, much slower than the pressure changes a fish experiences when is makes normal swimming movements up and down. (Fish have a swim bladder that can adjust to handle quick movements up or down in the water.)

In saltwater, just the tides can exert more pressure changes on fish than barometric pressure changes. A small three-foot rise in tide will increase the hydrostatic pressure by about 0.09 atmospheres. This is about twice the barometric pressure change that accompanies a major hurricane. Waves have the same effect. Just a two foot wave can change the underwater pressure .06 atmospheres, greater than any reasonable change in air pressure.

I will probably continue to blame the barometer for my poor fishing days, and as long as I fish with anglers who never read this article I should be fine.

Credits: Dr. David Ross
 David Ross is a scientist emeritus at the Woods Hole Oceanographic Institution and the author of The Fisherman’s Ocean (Stackpole Books). He is also a regular columnist for Saltwater Fly Fishing Magazine. He can be contacted at DRoss@whoi.edu. The entire article excerpted above first appeared in Saltwater Fly Fishing Magazine. © 2004 Dr. David A. Ross and Saltwater Fly Fishing Magazine.