Status and Distribution of Fish

¶ … Status and Distribution of Fish in an Acid-Impacted

Watershed of the Northeastern United States (Hubbard Brook, NH)"

Warren, Dana; Likens, Gene; Buso, Donald; and Kraft, Clifford

The authors of this study noticed that of at least three species of fish in the water system studied (the Hubbard Brook in New Hampshire specifically), only one was remaining in 2008. The three species known to be found in the water system in 1960 -- and there may have been others -- were the Cottus cognatus, or Slimy Sculpin, the Rhinichthys atratulu, commonly known as the Blacknose Dace, and the Salvelinus fontinalis, better known in the area as the Brook Trout. Of these three known species, only the last, the Brook Trout, remains in the Hubbard Brook today. During the 1970s the river system experienced a period of increased acidification from acid rain. Former studies have shown that both chronic--long-term -- and episodic acidification of water systems can have a huge impact on fish populations. Even when certain individuals in a population survive episodic acidification and repopulate the area, population numbers remain lower than they were before the episode of acidification took place, even when the water returns to normal pH levels.

It is the author's hypothesis that a period of acidification in the 1970s is responsible for destroying the fish population in the Hubbard Brook. Based on earlier studies, they were confident that the surviving species -- the Brook Trout, Salvelinus fontinalis, and the Slimy Sculpin, Cottus cognatus, were some of the most acid-resistant species of fish in the North Temperate Zone water systems. The reason that the authors hypothesize that increased acidification was the main cause of the departure of the Cottus cognatus from Hubbard Brook despite the species known resistance and adaptability to increased acidity is that this species, when the population is taken as a whole, has a more limited range of movement than the Salvelinus fontinalis, which would give the former less access to refuges (where acid levels remained the same or did not climb as drastically). This hypothesis is strengthened by the fact that other studies have shown the Slimy Sculpin (Cottus cognatus) are frequently absent from water systems that have experienced water systems that experience periodic acidification. In addition, the timing of acidification can affect the reproduction process and abilities of the Slimy Sculpin, especially when acidification occurs in the spring.

Because freshwater fish are generally the apex predators of their ecosystems, removing them from an ecosystem can have a huge effect on other parts of the ecosystem. For instance, fish often eat insects. Insects are generally not water dwelling creatures (with some exceptions), so they would not be directly affected by the acidification of the water system, as the fish in the same system are. This means that insect populations will not decline the same way that fish populations do when acidification occurs. Fewer predators (i.e. fish) without simultaneous declines in reproduction would mean an increase in the number of insects in the area of acidification. This can increase the number of pests in the area, affecting crops. It could also lead to an increase in disease carrying insects, such as mosquitoes, leading to higher disease rates among other animals, including humans. This could affect populations of these other animals, affecting populations of other species that prey on or are preyed upon by these species, and so on.

Ecosystems are incredibly complex things; the interconnections between the disparate elements are so intertwined and so complex that it is almost -- perhaps completely -- impossible to know the effects of changing or removing a single element. Even more complex and unknowable are the indirect effects on portions of an ecosystem from other sources. The acidification of the Hubbard Brook is almost certainly a result of human pollution. Carbon dioxide can cause acidity in the atmosphere, which is collected by rainwater as it falls through the levels of the atmosphere and eventually enters the groundwater and, to an even larger degree, surface waterways such as rivers, streams, and lakes. Thus, humans are almost certainly responsible for the acidification of the Hubbard Brook in the 197-s, and the resultant decline in the number of fish species present there. Other effects of this acidification, such as the possible rise in disease vectors like mosquitoes, which has a direct effect on humans, are all related back to human's pollution of the ecosystem. This shows how it is impossible for any constituent of an ecosystem, even (and perhaps especially) humans to escape the effects of their actions upon a given ecosystem.