| Subject: Silurus glanis must adhere to the rules of predation! |
Author:
Paul Scott
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Date Posted: 19:35:22 11/21/04 Sun
Fear and personal opinion of human beings seems to once again lead us down the long dark road of mankind’s continued interference in nature. Humans, both anglers and Ichthyologists alike, are responsible for the presence of Silurus glanis in “so-called” non-native waters. So, we, humans, should not be so quick to condemn Silurus glanis from these same river systems.
In the past, we have found, as scientists, that introducing non-native species across oceans from one continent to another has resulted in the total eradication of other species. Usually this occurs as a result of the invading species occupying the same niche as the indigenous species. On a rare occasion, other factors combined with the presence of this new predator (the invader) may have detrimental consequences for an indigenous prey. Today, naturalist conservationists want to return aqueous ecosystems back to their original states before the introduction of non-native species from both intra-continental and inter-continental origins. In the United States, in the state of Georgia, conservationist introduced flathead catfish (Pylodictis olivaris) into a non-native river system. The predator flourished and quickly populated most of the river systems within the state of Georgia. Other factors combined with the presence of this most capable predator resulted in a population decline of some of Georgia’s native sunfish species. Commercial fisherman and anglers alike were encouraged to eradicate flathead catfish from Georgia’s river systems. Georgia catfish anglers responded with protest and demanded an end to the prejudice being conveyed against their beloved catfish. New research has suggested that flathead catfish are not entirely responsible for the decimation of these sunfish species and that in some cases the presence of flathead catfish actually improved sunfish fisheries. Fishery biologists who are naturalist conservationists in Georgia have been forced into a compromise. They have allowed the continued protection of flathead catfish from eradication while more research is conducted to determine if flathead catfish are as a great of a threat as some scientists and sunfish anglers suggest.
Predators, such as Pylodictis olivaris and Silurus glanis, must adhere to certain predation rules. These rules allow them to change their hunting strategies in order to survive. Predators cannot rely exclusively on one particular type of prey and they usually will not pass up a free meal, even if it means eating another predator’s kill. In other words, they will hunt when they must and scavenge when the opportunity for a free meal presents itself or when live prey is not abundant. Most anglers have found that flathead catfish prefer live bait but can be caught on dead baits from time to time. The same is true for Wels Catfish. Both catfish species are very effective predators that will feed upon multiple prey species. Some prey is probably preferred to other types of prey; however, two factors will always play the greatest role in determining the predator’s diet. The first is the availability of the prey and the second is the vulnerability of the targeted prey. Almost any animal that will fit into the mouth of a hungry Pylodictis olivaris or Silurus glanis and is vulnerable in their presence will be eaten. Prey for these catfish may include any other fish species, mammals, birds, reptiles, amphibians, insects, and even their own kind. Yes, there are even stories of cannibalism, which is common among most fish species. Based on these rules, it is unlikely that Silurus glanis could possibly wipe out every species of fish from an entire river system. It is more likely that they would begin to feed on smaller Silurus glanis or the most abundant prey available to them. The need for complete removal of Silurus glanis from any natural or non-natural intra-continental river system is based more upon fear and prejudice than it is based upon actual scientific data. Before condemning these magnificent creatures from “so called” non-native intra-continental river ecosystems, fishery biologist must first ascertain through multiple studies that the data supports the need for their removal.
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