Fish and Population Growth in the Grand Canyon

¶ … Flannelmouth sucker is quite common within the Colorado River and the surrounding Grand Canyon area. This is particularly true when compared to other popular species within the area such as the Colorado pike minnow, the bony tail, and the Round tail Chub. Many of these species are either no longer found in the area, or endangered. Although these species of fish are quite different from the Flannelmouth sucker, examination of the species is still warranted. Through proper observation and analysis, we are in a better position to properly assess the condition of the Flannelmouth Sucker. In particular, this document will address sample data regarding the Flannelmouth Sucker, the surrounding area, and similarities to other species. We will then relate this analysis to environment conditions such as water discharge and prey availability. Finally, we will conclude with a brief discussion on management issues.

To begin, condition assessment is commonly used to help evaluate fish populations within a particular area. Relative weight is simple and intuitive measure used to better assess the overall flannelmouth population. The mean relative weight of the flannelmouth sucker within the Grand Canyon area has been particularly sporadic. The period examined is the ten-year period from September 1991 to September 2001. It is interesting that from 1991 to 1993 the mean weight of the flannelmouth actually declined from 100 to approximately 95. This may indicate a deterioration of environmental conditions during this period. However, a massive increase in relative weight occurred from 1995 to 1997. During this period, the index improved from 95 to 110. However, the variation in relative weight in 1997 was the highest out of any of the years examined over the decade. In fact, when variation is taken into account, the relative weight of the flannelmouth varied from a low of 103 to a high of 120. Although this increased variation is worrisome, it was still well above the prior years by a large margin. This strong increase and weight and variation could be partially attributed to the increased number of warm water tributaries in the area. In fact, the Paria River, Havasu Creek, and the Littler Colorado River helped to create a much more favorable environment during this period. Subsequently, from 1997 to 2001, the relative weight on the flannelmouth steadily declined to its historical range of 95 to 105.

To be more specific, flannelmouths that were collected in September were vastly different from those collected in the other moths of the year. There are two primary reasons for the disparity. First, migration within tributaries occurs during the spawning season, which generally incorporates the month of September. As noted above, the Flannelmouth sucker has a tendency to mover great distances to find favorable environments in which to flourish. In the above paragraph, these areas tended to consist of tributaries and other smaller environments with fewer predators and enemies. With favorable conditions and less predators, the survival rate of the flannelmouth began to grow. This ultimately what contributed to the explosive growth discussed in the 1995 to 1997 period. Due in part to higher survival rates, the variability between sizes become much more pronounced, as mentioned earlier. The second reason is that the Flannelmouth sucker condition in September was positively correlated with Glen Canyon Dam discharge during the summer months. Experts, within the field believe this result may be due to the larger euphotic zone and greater macro invertebrate abundance observed during higher water flows. Increased dam discharge that stimulates river productivity is believed to provide benefits for this flannelmouth.