fallen tree with fungus

Love to fish, don’t have a boat? No worries, go ice fishing!  The Great Bay Estuary and the freshwater lakes and rivers in the New Hampshire Seacoast are alive with delicious fish even in the dead of winter.   When thinking about safety in ice fishing, the most obvious concern is the fishing platform, the ice.  Not only must it be thick enough to support a person, it also has to have a uniform quality to support your weight.  It is not uncommon for ice to vary in thickness.  It may be thick enough in one area, but be unsafe a few yards away.  Currents, springs, salinity level, upwelling, underwater structures and aquatic growth can all affect ice thickness.  A snowfall after first ice can insulate ice from the cold and slow its thickening.

How does this process actually occur?  Water (two molecules of hydrogen and one of oxygen) exists in three forms: liquid, gas and solid.  As winter approaches, the surface of the water cools, packing water molecules more densely together and causing it to become heavier.  The surface water sinks into the less dense, warmer water below.  This cooling and settling process continues until a uniform water temperature of 39.2 degrees Fahrenheit is reached.  Turnover, the name given to this mixing phenomenon, occurs until the whole water column is homogenized, or of equal temperature and density.  An interesting and important event occurs as the water continues to cool.  At 39.2 degrees water has reached its highest density, its molecules tightly packed.  Then as the surface water temperature drops below 39.2 degrees, the water molecules gradually expand, becoming less dense.  Now, they are essentially taking up more room.  At 32 degrees, the water molecules expand even further and begin to form organized ice crystals. Much lighter than the denser, warmer water below, the ice crystals float!

The layers of ice that form on lakes and rivers act as insulators, preventing the water below from freezing.  If it were not for this, a pond or lake would freeze from the bottom up, eliminating a year-round environment for aquatic plants and animals.

How ice forms in the estuary is dependent on a number of factors.  The amount of salinity in the ice drives the temperature point down for freezing.  Tides, currents, salinity levels, and of course temperature in Great Bay all determine if anglers will be able to enjoy smelt fishing in a given year.  Ice that forms will often move in rafts and chunks throughout the winter, contributing to the scouring of the saltmarsh and movement of species throughout the estuary.

For more information on ice safety visit: Stay Safe on the Ice | Outdoor Recreation | New Hampshire Fish and Game Department (state.nh.us)

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fallen tree with large root ball
dead moss covered tree in vernal pool