Hurricanes are major forces of natural destruction.
Pictures in the various news media make it clear that these
immense storms can devastate the landmasses in their path, but it
may be difficult to see how hurricanes and tropical storms could
affect fish. Here are some reasons you may see fish kills following
a major storm event:
Changes in salinities
Freshwater flooding from rain or saline storm surge may trap fish
in an inappropriate salinity. If this happens rapidly and the fish
have no escape, species that are intolerant to changes in salinity
Low dissolved oxygen
Low dissolved oxygen is by far the most common cause of post-storm
fish kills. When oxygen levels get too low, fish are unable to
obtain the required amount of oxygen necessary for metabolism.
Several factors may occur in concert to cause this condition:
- Wind-In small lakes or ponds, wind action may
push surface waters to one side of the lake. Water from the bottom
comes to the surface to fill the space the surface water used to
occupy, bringing with it sediments and organic materials from the
bottom. This water from the bottom is naturally low in oxygen. The
bottom materials may include hydrogen sulfide; in high enough
concentrations, hydrogen sulfide can be lethal to fish and is
responsible for any "rotten egg" or "sewage" odors. Bacteria in the
sediments are also brought to the surface; these bacteria decompose
the organic material from the bottom, using up oxygen in the
process. This whole event is termed a "turnover," since literally,
the bottom comes to the top.
- Long periods of cloudy days-In aquatic
ecosystems, the oxygen manufacturing system consists of microscopic
organisms and aquatic plants that carry out photosynthesis: using
energy from sunlight to create carbon-based nutrition for
themselves with oxygen as a by-product. When there are long periods
of cloudy days, these organisms produce less oxygen. At night,
photosynthesis doesn't occur at all, and these same
oxygen-producers are actually using up oxygen during respiration,
just like fish and other animals. Under these conditions, it does
not take long before there is little oxygen left for fish.
Low-dissolved-oxygen fish kills often occur early in the morning,
when oxygen levels are at their lowest.
Strandings due to flooding
Rising water may flood areas that normally do not contain water.
After water levels recede, fish can become trapped if they are cut
off from the connection to the main body of water. When the small
ponds the fish have been trapped in dry up, the fish die.