The main aim of the ecological research study, “Predation on Zebra by Freshwater Drum and Yellow Perch in Western Lake Erie” by Morrison, Lynch, and Dabrowski, was to identify the fish species that prey in zebra mussels. The zebra mussels population was increasing rapidly and it was thought to cause some ecosystem effects. Thus, methods for controlling their population increase were the key quest of the study (Morrison, Lynch and Dabrowski 177).
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In studying the population of the zebra mussels, diverse objectives were set for achievement. Some of them include determining if the consumption of zebra mussels by freshwater drum and yellow perch was influenced by zebra mussels’ population and determining whether North American fish species selectively consumed zebra mussels.
Additionally, examining how morphological adaptation such as mouth and throat formation of freshwater drum and yellow perch influenced their predation was also a considered objective in the study (Morrison, Lynch and Dabrowski 178).
To augment the studies effectiveness, diverse methods were employed in fish collection. For instance, freshwater drum and yellow perch were collected randomly from selected survey sites by use of grid squares. Semi-balloon bottom trawl that was made up of 10.7mm head rope and mesh of approximately 6.4mm at one end of the cod was also used in the collection of fish study.
The captured fish were enclosed according to their sizes to ensure their survival. SCUBA method was also used in the random collection of zebra mussels. Unlike other methods, SCUBA method collected zebra mussels together with marble and rocks. However, zebra mussels were separated from the marble and rocks manually (Morrison, Lynch and Dabrowski 179).
In order to determine the morphology of the fish species that coexisted in the selected water, diverse laboratory analyses were observed. For instance, the pharyngeal gapes of yellow perch and freshwater drum were measured using the Wainwright method. Wainwright is a process that involves the use of plastic dowels after thawing fish. Dowels of diverse diameters were used in determining the diameters of pharyngeal gapes of fish being studied (Morrison, Lynch and Dabrowski 179).
Diverse parts of zebra mussels were also measured in order to determine their growth and development. For instance, the septa and shell length of zebra mussels of between 3 and 35mm were measured easily with dissecting microscope of 40X magnification power. The length, height and width of the zebra mussels under study were made by use of calipers. To calculate the dimensions of zebra mussels’ fish consumed by yellow perch and freshwater drum fishes, regression equations were employed.
Gastrointestinal tracts of diverse fish that were caught were also examined in order to determine the fish species that predated on zebra mussels. This was made possible by removing gastrointestinal tracts of the caught fish and preserving them in the concentrated alcohol. The stomach contents of the preserved gastrointestinal tracts were removed, observed and isolated under dissecting microscope of 40X magnification power.
To develop the study of zebra mussels, measurements were made by use of ocular micrometer. Additionally, the TL of the prey was also calculated by aid of the provided appendix in order to enhance the calculation of the weight of the each individual species that was consumed by the predators. Wet weight of each fish species was also calculated through the aid of the calculated TL (Morrison, Lynch and Dabrowski 179).
In order to compare the population of zebra mussels in the two selected areas of study, Kolomogorov-Smirnov’s two-sample test was employed. Production of similar frequencies by the method used enhanced the combination of different sites as the predation points. Additionally, the diets of freshwater drum and yellow perch were also used in identifying the size of the zebra mussels that were consumed by the predators in the study area.
Comparison and identification of the consumed zebra mussels was effected by use of Chesson’s alpha method, in which pi is the average size of zebra mussel from the provided sizes of zebra mussels, and ri the average size of zebra mussels in the fish diet.
From the study carried out on freshwater drum, yellow perch and zebra mussels, it is evident that the outcome had significant relationship with the expected values. For instance, the food contents in the gastrointestinal tract of freshwater drum differed with time. In the dry month, May, the estimated dry weight of fish species was greater than that of July.
Additionally, it was observed that freshwater drum fed on zebra mussels in specific months. Thus, from the study it is evident that the predator consumed some zebra mussels. It was also observed that the rate of zebra mussels’ predation increased with the increase in the size of the predator.
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For instance, the gastrointestinal tract of freshwater drum of approximately 250mm TL was found to contain large number of zebra mussels. From the study, it was further evident that freshwater drum alternated its diet with time because of variation in availability of food. For instance, the study showed that its gastrointestinal tract showed some traces of zooplanktons in some months when zebra mussels’ population was inadequate (Morrison, Lynch and Dabrowski 180).
Similarly, zebra mussels were found to have been consumed by yellow perch. Although they were found in all sizes of yellow perch, it is evident that predator size contributed immensely towards an increase in predation.
For instance, yellow perch greater than 200mm TL were found to include lots of zebra mussels in their diet. Additionally, it is evident that yellow perch also consumed zebra mussels as well zooplanktons during specific periods. Thus, from the study it is evident that yellow perch were not fully dependent on zebra mussels as their source of food.
Relationship of size and predation
From the study it is also evident that there was a strong relationship between the size of pharyngeal gape and the predated zebra mussels. In most occasions, the size of the consumed zebra mussels was smaller than the size of the pharyngeal gapes of their predators.
The widths and heights of the zebra mussels were also small compared to the size of the pharyngeal gapes of the respective predators. However, it was also found out that some zebra mussels were larger than the estimated pharyngeal gape. It was also evident that the increase in size of the predators had high relationship with the size of the predators (Morrison, Lynch and Dabrowski 182).
The study also showed that the number of zebra mussels differed with age; their number decreased in the gastrointestinal tract of the predators with increase in age, because very few predators fed on very large zebra mussels.
Morrison, Todd, William Lynch, and Konrad Dabrowski. “Predation of Zebra Mussels by Freshwater Drum and Yellow Perch in Western Lake Erie”. Journal of Great Lakes Research 23.2 (1997): 177-189. Print.