The bass fishing on Clear Lake has just about all the fishermen completely confused. While the lake is rated as one of the top fisheries in the nation, it is now just about impossible to catch three fish for a day’s effort. Many people are blaming the drought and a falling lake level for the poor fishing. There also could have been a die-off but very few dead fish are being seen.
Has the drought created a situation where there is not enough dissolved oxygen in the water to sustain the fishery? Whereas mammals get their oxygen from the air, fish get their oxygen from the water.
Breathing is something all living creatures do and it’s a requirement to stay alive. When we quit breathing, we die. Mammals have lungs that take in air (oxygen) and distribute it to the blood. Fish also have to inhale oxygen to live, but they don’t have lungs. Instead, their gills serve as lungs.
The gills of a fish are soft membranes containing a lot of blood. When a fish opens its mouth and inhales water, the water passes over the gills. Dissolved oxygen (DO) is the key to a fish breathing. Water in lakes and rivers contains oxygen. The air molecules are called DO and they basically float in the water. Wave action pushes more DO into the water and stagnant water has less DO. A fish heart has only two chambers in contrast to four for a human heart.
The blood in a fish is pumped only in one direction. The blood enters the heart though a vein and then exits the heart and goes to the gills. The gills pick up the oxygen from the water and it is transferred to the blood, which goes back to the heart. It’s a closed-circle circulatory system. The gills are made up of filaments. When the gills are damaged, as when penetrated by a hook, the fish will bleed profusely and often die.
The other factor in a fish getting enough oxygen is the water. DO is measured in milligrams per liter. A bass requires at least 5 milligrams with eight to 10 being optimum. If the DO reading drops to less than 3 the bass normally dies. In other words, the fish will die from a lack of oxygen. A comparison would be if a human climbed a 20,000-foot mountain. When he gets to the summit, the oxygen level would be so low that he would collapse and probably die. The same happens to a fish when it is caught in bad water.
There have been fish die-offs in Clear Lake in the past. Five years ago there was a massive fish die-off along the Clearlake Oaks arm of the lake. The DO readings in that area were below 3. Basically the bass died from a lack of oxygen. A bass can actually live up to about 10 minutes without oxygen but after five minutes it can suffer irreversible brain damage.
The other factor is that when a bass is caught and fights it uses up oxygen rapidly, much like when a human runs fast.
That is why it’s important for tournament fishermen to keep their livewells running constantly when holding fish. Often the DO level in a livewell is under 3. The Department of Fish and Wildlife (DFW) has strict rules governing bass tournaments. Bass must be transported from the contestant’s boat to the weigh-in station in a plastic container with the fish being completely covered in water. Any bass weighing 5 pounds or more most be transported in a separate container. The fish can only be kept in the containers to and from the boat to the weigh-in site no longer than three minutes. Unfortunately, this rule is constantly violated.
Often a fisherman will hold up a bass for photos or he is interviewed by the tournament announcer. The DFW has a rule for tournaments held between June 15 and Sept. 15. These tournaments can be no longer than six hours long.
A few bass also die after a bass tournament, something referred to as delayed mortality. It can occur several days after a fish is released. Studies have shown that up to 10 percent of fished released following a tournament will later die. It all depends on water temperature. Bass often get stressed by being in a fisherman’s livewell too long and without getting sufficient oxygen.
