By George Harvey
Pity the poor brook trout. During the nineteenth century, it was one of the most popular fish with American anglers. In fact, it is the state fish of New York, Vermont, New Hampshire, and six other states. But it has declined rather badly in much of its native habitat. In that respect, it may be taken as emblematic of problems facing many aquatic animals. And the effects of the stresses are matters of vital interest to anglers.
Brook trout are adapted to well-oxygenated, clean, cold water. They become stressed in streams when the water gets sluggish, because it does not have enough oxygen. They do not tolerate pollutants or murky water. And they are not at all happy if the temperature is much over 72° Fahrenheit; at much above that, they die. In addition to these problems, they often have invasive species to contend with.
The effects of these problems have reduced populations of brook trout since the nineteenth century. At that time, fishing expeditions went to sites increasingly distant from urban areas. The Adirondacks became a popular destination for anglers. But as more time passed, those fishing grounds were no longer productive because of acid rain, and the anglers had to move on to new places.
Climate change is already making streams warmer and reducing water flow in streams of the Northeast. With lower oxygen levels and higher temperatures, the brook trout have to head upstream, to higher elevations with cooler temperatures. But this drives them into smaller streams, and climate change is bringing more frequent droughts, reducing streams to the point that they cannot support the fish.
Some of the problems with invasive species are not intuitively obvious. For example invasive insects, such as woolly adelgids, have shown themselves capable of killing large stands of forests. This causes loss of shading over streams and allows soil to wash into them. So invasive insects can kill whole fish populations they have nothing to do with directly.
Of course, it is not just brook trout that are vulnerable. Many species are in trouble, and, without doubt, some will become extinct. Brook trout are likely to be kept alive in carefully selected refugia in northern areas. Other aquatic life will not be so lucky. In most cases, we humans do not seem to care much. After all, whoever has even heard of the dwarf wedgemussel? It is one of many species with no advocate to call attention to its plight.
Invasive species can become important to the changing ecological systems, of course. Brook trout are being replaced by brown trout. Native crayfish are being replaced by rusty crayfish. Some invasive species are edible, and of their own interest. Quagga and zebra mussels are serious problems, for example, but they provide food for perch and sunfish. In some places, numbers of perch have increased five-fold. Unfortunately, they have issues many people are not yet aware of, such as potential for increasing accumulations of toxins and other contaminants in the food chain.
Those who enjoy eating fish they have caught should definitely look at government sites letting them know what waterways and what fish are safe. Mercury in the fish is an especially important issue, because burning coal causes mercury to be vaporized and to come down in rainfall, often hundreds of miles from the plant where the coal was burned. Nature has no ready way to remove it, so the concentration just builds up. In the Northeast, we get mercury from all the coal-burning industries and power plants of the Midwest, so every state in the area has information on fish or other wildlife that are safe to eat, often by species and source. Some of these can be found as follows:
New Hampshire: http://bit.ly/NH-fishing-safety
New York: http://bit.ly/NY-fishing-safety
There is good news. Things we do to address pollution can sometimes be remarkably successful. Many of us remember a time when Lake Erie was considered dead, for example, and some estimates were that it would take two thousand years for it to recover. But that story developed differently than expected.
After the Clean Water Act became law in 1972, the lake bounced back far faster than expected. In 2016, Bassmaster listed Lake Erie as the fourth best bass fishing lake in the country (http://bit.ly/Lake-Erie-bass). Perhaps other problems have more hope than we would imagine, if we just do our work on them.