Creationism in Crisis
How Parasites Alter the Likelihood of Fish Being Caught by Anglers
How Parasites Alter the Likelihood of Fish Being Caught by Anglers
Creationism in Crisis
How Parasites Alter the Likelihood of Fish Being Caught by Anglers
How Parasites Alter the Likelihood of Fish Being Caught by Anglers
Creationism in Crisis
How Parasites Alter the Likelihood of Fish Being Caught by Anglers
How Parasites Alter the Likelihood of Fish Being Caught by Anglers
A whitespotted char caught by angling during the survey
No doubt though, they'll resort to their fall-back strategy of using their own definition of 'evolution' (one 'kind' turning into another, unrelated 'kind', in a single event), rather than the one science uses (change in allele frequency in a population over time).
But this is no so much about the sheer malevolence of any designer that could come up with parasites like this parasitic species of copepod which infects the mouth and gills of fish. Instead, it is about how parasitism, prey and predators are in a complex, dynamic evolutionary relationship which can only be understood and explained by reference to the basics of the Theory of Evolution by Natural Selection.
Fishing has been practiced by humans for about 40,000 years, usually for food but latterly for sport. The functional difference being that fish caught for food are removed from the population as form of predation, whereas fish caught for sport are quickly released back into the wild.
The scientists conducted an elegant experiment consisting of two surveys:
- One of the fish caught by angling with a rod and baited line, which in effect biased the catch in favour of those fish most likely to out-compete other fish for the bait.
- A control group of fish caught by electrofishing, in which fish are temporarily stunned with an electric current, which provided a representative sample of the fish in the stream.
The results were very clear, if somewhat counter-intuitive.
Parasitised fish with a good body condition were more likely to be caught by angling, whereas parasitised fish with a poor body condition were less likely to be caught by angling.
The Hokkaido University news release explains, what appears to be something of a paradox:
Angling, a type of fishing, is a popular pastime across the world, and is known to be 40,000 years old. Angling usually takes place in natural bodies of water, which may have populations of wild fish, or be stocked with cultured fish. Fish caught by angling may either be consumed, or may be immediately released.Creationists might like to ignore the fact that the two scientists are in no doubt that the relationship is an evolutionary one, and that, by releasing parasitised fish because they are difficult to sell commercially in food markets, anglers are acting as natural selectors for fish that are more liable to be parasitised and against those more fitted to resist parasitism.
Parasites are very common in nature, found everywhere that their hosts are found. Parasites are known to alter the susceptibility of fish to predators. Angling can be considered predation of fish; however, there has been almost no in-depth research on how parasites affect the susceptibility of fish to angling.
Associate Professor Itsuro Koizumi at the Faculty of Environmental Earth Science, Hokkaido University, and graduate student Ryota Hasegawa have investigated how a mouth and gill parasite of the whitespotted char, a salmonid fish, affects its vulnerability to angling. Their findings were published in the journal The Science of Nature.
(Left) A whitespotted char caught by angling during the survey; the parasite (yellow circle) attached to the mouth of a whitespotted char (middle); and a light micrograph of the parasite (right)
Photos: Ryota Hasegawa, Itsuro Koizumi.
The study considered two parameters: the body condition of the fish (a relationship between their body mass and body length) and their parasite infection status (whether the fish was infected with parasites or not). Fish were caught by angling and by electrofishing, and the numbers of fish under each category were compared.We performed a field survey in a tributary of the Ito River in Hakodate, Hokkaido. The study area was selected for three reasons: we knew that the parasite was common in the survey area; the char population was geographically confined to the study area; and the study area is part of a year-round protected freshwater area, meaning that the fish had not previously been exposed to angling which could affect their behavior.
Our study shows that both parasites and body condition are important considerations in angling, and studies of behavioral responses of the char induced by human angling activities must take these criteria into account. Additionally, the reaction to parasites in fish angling might result in the increase of both host and parasite survival.
Ryota Hasegawa, first author.
Graduate School of Environmental Science
Hokkaido University, Sapporo, Hokkaido, Japan
Two specific groups of char were most vulnerable to angling: those that had a high body condition and also had parasites, and those that had a low body condition but no parasites. Larger fish were more vulnerable to angling.
When infected by parasites (orange triangles), whitespotted char with high body condition are more likely to be caught by angling (solid orange line). Among uninfected fish (blue circles), those with a lower body condition are more likely to be caught by angling (broken blue line)
Ryota Hasegawa.
A survey of tweets curated from Twitter covering a three-year period was also conducted. Both anglers and customers at fish markets reacted negatively to parasites. The negative reaction to parasites by anglers is important, as they are more likely to release infected fish back into the wild. This increases the likelihood that parasitized fish are more common in areas that experience high amounts of angling.Our findings regarding the vulnerability of the char to angling could be explained by the interaction of behavior and infection status. As parasites negatively affect the body condition of fish in general, those with low body condition and parasites are outcompeted by those with high body condition—and so are less likely to catch the angling bait. Separately, those with high body condition and parasites exhibit a higher vulnerability to angling, as their behavior drives them to consume more sustenance to offset the effects of the parasites.
Associate Professor Itsuro Koizumi, co-author
Graduate School of Environmental Science
And Faculty of Environmental Earth Science
Hokkaido University, Sapporo, Hokkaido, Japan
This situation is a classic example of how evolution consists of a dynamic of competing natural forces. In this case, parasitism is reducing the fishes fitness to survive by placing additional demands on their resources, but, paradoxically, increasing it where humans are discriminatory predators, selectively favouring the survival of those fish more vulnerable to parasitism.
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