Speciation Differences in the Brazos River and Lake Bryan

¶ … Fish Speciation: Brazos River and Lake Bryan

The sample areas of the Brazos River and Lake Bryan showed clear differences, but also shared a few similarities. The primary difference was the size of the species, which is based on factors including the style of gear used that can tend to skew size of collected populations and the available macroinvertebrates for food. In the Brazos River, there were much smaller diameters of fish recorded, based on the potential for seine and gill net methods do tend to catch smaller species and high presence of the smaller caddis fly. On the other hand, Lake Bryan showed much larger species of fish, possibly based on the increased presence of the mayfly larvae and the environmental conditions of the lake that provide better for larger, predatory fish. Still, since both locations had fewer mosquito larvae, they both showed low levels in mosquito fish. Ultimately, it was the available food source present that tended to define the number of populations seen in the samples collected.

The Brazos River saw larger number of smaller fish species. Reports from the river show a high number of red shiners, or Cyprinella lutrensis, and the Pimpephales vigilax, or the bullhead minnow. These species are relatively small in size compared to other freshwater species. A number of factors can lead to this higher population reading of such small freshwater species. This research used gill nets and seine nets as its primary collection method. Typical designs include a hauled net that swoops through the water. However, the "configuration of nets currently used do not exhibit optimum selectivity, often retaining large numbers of small fish, including juveniles of the targeted species" (Gray, Larsen, & Kennelly, 2000). Prior studies using similar methods generally show a much smaller fish population collected, typically from midsize of the target to juvenile. Moreover, there was a higher recording of the caddisfly present in the river, which was the primary macroinvertebrate. This tends to be a popular food source for smaller species, such as the ones found in the current sample (Wiggins, 2015). As the larvae are smaller, they are a primary food source for smaller fish species throughout the growth cycle. Ultimately, both the primary food source and gear methods used in the collection of species may have resulted in the higher presence of smaller species compared to those seen at Lake Bryan. Still, there were still a high number of mayflies collected as well, suggesting that the conditions of the river itself may be an impact on the smaller species more prevalent compared to Lake Bryan (Wetzel, 2001).

In fact, Lake Bryan saw a much larger number of larger species. The reports from Lake Bryan show a much higher ratio of larger fish. The primary species present in the sample included Lepomis macrochirus, or Bluegill, and Micropterus salmoides, a largemouth bass. These species are much larger in length and diameter compared to the red shiners and bullhead minnows. However, fishing collection methods do present a possible skew, as the study used electrofishing methods. It used both seine nets and electrofishing methods and found a large number of predatory largemouth bass. This may be a result of a higher bluegill population, as the largemouth bass preys on the species. With more bluegill, there was also an increase in predatory fish. Moreover, the drag found that there was plenty of mayfly larvae in the river, which are a great source of sustenance for fish like the bluegill (Gaskell & Gibson, 2003). What the electrofishing and seine nets may have been catching were smaller samples, but still generally larger species compared to the species found in the Brazos River. Environmental conditions differed enough from the river to allow for larger fish to really take prominence in their positions within the ecosystem (Rechlicz & Kolejko, 2012). WIth the lake being so much deeper than the running water habitats of the Brazos River, larger species are more typical. The species differences could thus differ from the given the environmental differences between the larger lake and the running water of the Brazos River.