- Pacific
By John Page Williams, CBF Senior Naturalist and avid boater and fisherman. In this two-part series, John Page gives anglers some insight into the images on your sonar fish finders—what they mean and how you can use that information to catch more fish.
Here is what is going on:
This image shows dense schools of bait fish (mostly menhaden) and some larger fish (probably rockfish) suspended high in the water column over 40 feet of water in the Severn River, about a mile above the Route 50 bridge in Annapolis, Maryland, on August 1, 2010. The fish are swimming at depths between 10 feet and 18 feet, where they have water as cool as possible (around 81 degrees instead of 83 degrees at the surface) and enough dissolved oxygen to “breathe.” The dissolved oxygen level in the zone where the fish are holding is 2 to 5 mg/l (milligrams per liter), low enough to cause stress to the menhaden and rockfish but not enough to kill them. Below 18 feet, the dissolved oxygen tails off to lethal levels of just 1.7 mg/l at 20 feet and 0.9 at 35 feet.
In the Chesapeake at this time of year, the water at the surface is generally warmer than the bottom, because it is closer to the sun, and fresher, because it has flowed into the Bay or a river from rainfall. The bottom water, on the other hand, is denser because it is cooler, and saltier because some of it has flowed up the Bay from the Atlantic Ocean. If the weather is stable, without heavy rainfall and strong winds, the lighter surface water sits like a lid on the bottom water.
Meanwhile, trillions of algae cells at the surface die every day and sink into that sealed-off bottom water, where aerobic (oxygen-consuming) bacteria decay them. This process literally sucks the life out of the deep water, causing what we now call “Bad Water” where fish and crabs get stressed (2-5 mg/l) or “dead zones” where they can’t live at all (less than 2 mg/l). The result of this process is a situation like the one you see in the image above.
Sometimes, the boundary line between warmer, fresher, well-oxygenated water and cooler, saltier, poorer water is very sharp:
See the lines going across the screen at 16 feet and 24 feet? Most sonar manufacturers call them thermoclines, a term that refers to sharp temperature changes, but in an estuary like the Chesapeake, those breaks can also be caused by abrupt changes in salinity, or a combination of both factors. In this image, taken in the open Bay off the mouth of the Chester River in May, each of the two breaks is caused by changes in both salinity and temperature. Those density changes are sharp enough to bounce sonar echoes! Notice how fish tend to suspend on or just above them.
How to Fish "Bad Water" - Part II
By John Page Williams, CBF Senior Naturalist and avid boater and fisherman. In Part I of this two-part series, John Page gives anglers some insight into the images on your sonar fish finders. In Part II he looks at how you can use that information to catch more fish.
So what’s an angler to do when bad water shows up on the fish finder?
First, think about what the fish are telling you: they won’t—or
can’t—go any deeper than the levels where you see them. This kind of situation
calls for precise depth control. Can you cast out a jig, count it down to just above the
level where you see them, and swim it back through them? Can you troll a plug or a spoon
through them? If you’re live-lining, can you use a bobber to hang your bait at their
level? Think through your options. You may just find that the way bad water concentrates
fish actually makes it easier to catch them.
In the short run, that is.
In the long run, though, bad water costs our Bay a huge loss in summertime fish habitat.
For one thing, it concentrates fish in thin layers of warm water where diseases like Mycobacteriosis
can spread. On a broader level, over the past 10 summers, more than 80 percent of the Bay
has qualified as "bad water" that does not meet the EPA’s water quality
standards for dissolved oxygen. Between 10 percent and 20 percent of that bad water
qualifies as dead zones that are completely off limits to fish and crabs each summer.
Think of having to give up 20 percent of the space in your boat, or in your house, and
being uncomfortably stressed in most of the rest of it! Think how that loss affects the
“carrying capacity” of the Chesapeake, its ability to serve as home to the fish
species we love! Bad water is costing us the resource we love most in our Bay.
What causes the bad water problem is pollution, nitrogen pollution to be specific. Too much nitrogen (about 600 percent too much, in fact) fertilizes the growth of trillions of algae cells. (See yesterday's post "Hampton Roads Algal Blooms Send Distress Signals")
Over the past twenty-five years, many sewage treatment plants have made good progress reducing nitrogen pollution, and so have some farmers. To really make a difference, though, the Bay needs more farmers to participate fully in reducing nitrogen pollution, more sewer authorities to continue their upgrade progress, and most of all, many states, cities, towns, and private citizens to reduce polluting runoff from roadways, parking lots, and rooftops.
Now there are solutions, and Bay anglers can help, big-time.
Over the next two months, contact your U.S. Senators and ask them to support Senate Bill
1816, the Chesapeake Clean Water Act. It offers the most important legislative opportunity
to reduce runoff pollution to come along in the past thirty-five years. For more
information, visit cbf.org/ccwa.
In addition, the Bay states are putting together Watershed Implementation Plans (“WIPs”) that lay out specific actions they must follow to improve the Chesapeake’s water quality. We anglers can help there by following the WIP development process, participating in the public hearings about them, and urging our state agencies to submit strong plans that really will make a difference in the Bay’s health. CBF’s Anglers for Clean Water Web Site (cbf.org/ccwa-anglers) will keep you informed of those opportunities to help. (8.12.2010) http://cbf.typepad.com/chesapeake_bay_foundation/dead_zone
"To Achieve World
Government it is necessary to remove from the minds of men their individualism,
their loyalty to family traditions and national identification" Brock Chisholm - Director of the World Health Organization
"A society whose citizens refuse to see and investigate the facts, who refuse to
believe that their government and their media will routinely lie to them and fabricate a
reality contrary to verifiable facts, is a society that chooses and deserves the Police
State Dictatorship it's going to
get." Ian Williams Goddard
The fact is that "political correctness" is all about creating uniformity. Individualism is one of the biggest obstacles in the way of the New World Order. They want a public that is predictable and conditioned to do as it's told without asking questions.
"The two enemies of the people are criminals and government, so let us tie the second down with the chains of the Constitution so the second will not become the legalized version of the first." Thomas Jefferson