|
Summer
Fish Kills
In
2002, 17 fish kills were investigated in Delaware, with more
than 18,000 fish affected. This was lower than past years,
despite the
drought we were experiencing. There was only one major
kill in the Inland Bay area, in the Love Creek which
killed about
10,000 Atlantic Menhaden. The majority of the fish were
killed due to low dissolved oxygen (DO) levels. So far
in 2003 we have had at least
three fish kills in the in the Inland Bay area, two at Torquay
Canal and one at Love Creek. One Torquay Canal event
killed an estimated 50,000 to 100,000 Atlantic Menhaden an 6,000
Menhaden were affected in the other. In the Love Creek
incident, an estimated 2,000 Menhaden died.
Summer is a time of vacations, visits to
the beach, and backyard barbeques. While you are enjoying yourself,
though, summer temperatures can have a negative
impact on fish populations. Large numbers of fish
die suddenly in some areas of the state, particularly the Inland
Bays
region, primarily due to low dissolved oxygen levels.
Like
land animals, fish and aquatic organisms
need
oxygen to live. Oxygen gets into the water by diffusion
from the air, rapid water surface movement, and photosynthesis.
At the
water's surface, gaseous oxygen permeates into the water.
On windy days or during storms more oxygen dissolves into
the water because there is more surface area from waves being
formed.
Most dissolved oxygen, though, comes from photosynthesis in water
plants and algae.
Fish
kills occur as a result of combinations of detrimental environmental
factors.
Common conditions include:
- High
water temperature --- water holds less oxygen when it reaches
80 degrees
- Weather
conditions that include cloudy
skies, high ambient air temperatures, lack of wind
- Impaired
water quality
- Rapid
plant and/or algae growth
- Overabundance
of fish
Lakes,
ponds, and canals located in residential areas are particularly
vulnerable to DO related fish kills. Septic
tanks can create runoff containing increased nutrient loads. This
loading, particularly when combined with high levels of nutrients
from fertilizers applied to lawns, golf courses
and farms help aquatic plants and algae
to thrive. Untreated street
and yard runoff entering water bodies can also impair water quality.
Water
bodies with high
nutrient levels contribute to excessive algae growth, which is
not a problem on sunny days when photosynthesis is at its most
efficient levels.. At night, though, and on heavily cloudy days,
a process known as respiration causes the algae and plants to
consume more oxygen from the water than they produce through
photosynthesis. This uses the oxygen
essential fur the survival of the
fish. When there are excessive amounts of algae in one area,
DO levels can be significantly reduced, resulting in the suffocation
of many of the fish in the area.
Symptoms of low DO include an abnormal number of fish on the
surface that look as if they are gulping air, murky water that
resembles
pea soup, or a rotten-egg smell near the water.
Larger, more active fish tend to be affected first because
they need more oxygen, but other sensitive species can die early
also,
such
as
Atlantic menhaden and inland silversides in tidal creeks and
bays. More tolerant species include catfish,
and carp.
You
can help reduce the numbers and intensity of fish kills by reducing
the amount of fertilizers you use on your lawn and gardens. If
you have a septic tank, keeping up with its maintenance will
also help reduce the nutrient loading in your local water bodies. Sweeping
your driveway and sidewalks instead of washing them will also
help reduce the amount of chemicals that reach Delaware's waterways.
You can also discuss this topic with your neighbors, your local
country clubs, and your local government officials to help encourage
everyone to reduce the amount of excess nutrient loading in the
area where you live.
For
more information on this topic, please
click here.
.
|
