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A Survey of Fish Populations in Three Ponds at Calvin College

Student Authors: Eric Kolada, Nathan Lujan, Josh Vander Ark (December 11, 1998)

Introduction | Materials and Methods | Results | Discussion | Figures | Tables


INTRODUCTION

After extensive physical alteration, contamination with urban runoff and exposure to unknown levels of fishery utilization, Ravenswood and President's ponds in the northwest corner of Calvin College's campus are in a substantially unnatural and unhealthy state as was perhaps best illustrated by the die off of several thousand fish on August 31, 1998. These are often contrasted with the third pond in this study, North Pond, a nearby kettle-bog pond which derives from a separate watershed and has remained relatively undisturbed in a preserve during the past 80 - 100 years, influenced only by runoff from a now defunct farm (Cowell and Clearwater, 1998 pers. com.). Approximately 90 acres of commercial/residential runoff from East Grand Rapids and Grand Rapids flows directly into Ravenswood Pond through a storm sewer (Lester and Weemhoff, 1998 pers. com.). This water then enters President's Pond through an underground pipe during low water but in conditions of high water the two ponds, separated only by a thin strip of land, flood together.

We surveyed the ichthyofauna of these three ponds by using minnow traps in conjunction with a 75 foot seine with the goal of obtaining a more complete picture of how distinct the three communities might be and determining to what extent the communities might have been affected by anthropogenic disturbances. We hypothesized that Ravenswood Pond., which experienced the fish kill, would have significantly lower numbers of larger fish due to their greater susceptibility to the anoxic conditions present (Swart 1998, pers. com.). On the other hand, we expected President's Pond and North Pond to have relatively normal trophic taking advantage of the vigorous plankton communities that lend these their deep green eutrophic appearance. Consistent with our hypothesis, we not able to find any of the larger and less hardy Percia flavescens in Ravenswood Pond but traps in this pond held more Lepomis gibbosits than President's. Both Ravenswood and President's Ponds surprised us with populations of very stunted L. gibbosus while North Pond held an altogether unique assemblage of fish.

METHODS

Our study utilized two time-honored methods of catching fish. The first of these involved the fairly even distribution (Figs. 1,2,3) of minnow traps throughout each pond, with each trap left in the water for a standardized time of one hour before being collected. The traps were set and collected from either a canoe or a rowboat and the fish from the traps were immediately counted then returned. Each trap used was a standard wire minnow trap with inverted cones on either side that allowed the fish to enter a hole approximately 2.5 cm (1 inch) in diameter without finding their way out again. This method allowed us to cpmpare the numbers of fish in each pond by averaging the data for each pond and determining average numbers of fish caught in one trap in one hour (#/trap/hr).

Our second method took advantage of a 75 foot by 6 foot seine with 1/4 inch mesh size, tied on each side to 10 foot wooden rods. Due to the soft, sticky and deep sediments in each pond, we had to abandon any hopes of seining in the usual This method allowed us to compare the numbers of fish in manner, requiring several people in waders to trudge through the sediments while dragging the seine around in a semi-circle, then pulling it toward shore. One of us, Josh, stayed close to shore with one end of the seine, while another of us, Nathan, paddled away from shore with the other end of the seine in his boat. The third member, Eric, hauled in a rope that was tied to the bow of the row boat while Josh walked along the shore towards him, thereby effectively sectioning off an area between Eric, Josh and Nathan to be sampled. Fish caught in this manner were also countedand returned except for 100 L. gibbosus and 13 Percia Ravescens from President's Pond which were weighed and measured for length. Three of these perch and two goldfish were brought back to the lab to be preserved.

RESULTS

During eight sampling days we caught a total of 1683 fish. 432 were caught in 42 traps set for an hour and 1251 were caught in three drags of the 75 foot seine. 210 of the trap-caught fish were from 13 traps in Ravenswood pond while 190 were from 18 traps in President's Pond and 32 were from the 10 traps in North pond. Specific locations and numbers of fish caught per trap are available in Figures 1, 2, and 3 and comparisons between ponds and between speices are found in Figure 4 and Table 1 respectively.

1246 of the seine-caught fish were from President's Pond with drag areas makred on Figure 2. 100 of the L. gibbosus from the second seining drag were measured and weighed with data forming the basis for Figure 5. 14 Perch from both seine drags were measured and weighed to provide the data for Figure 6. Five of the seine-caught fish were from Ravenswood Pond and the drag area is marked on Figure 1

As can be seen on the maps, the majority of the fish seem to stay closer toshore in the littoral (if any distinctions between littoral and benthos in these 17 shallow kettle bog ponds can even be made) Particularly striking is the number of L. gibbosus (1152) that were seined and trapped out of the shallow southwestern channel in Presdient's Pond. Shallow water (<5 ft deep) traps prodcued more L. gibbosus (15.5 fish/trap/hr) than deep water (>5 ft) traps (0.9 fish/trap/hour) indicating that the opportunity to maintain close contact with surface dwelling zooplankton prey organisms while remainging close to the secure cover that the substrate provides motivates the giggosus to stay close to shore.

The 2-3 inch size of the majority of the Lapomis (Fig. 5) correlates to a 1-2.5 year age class in these ponds (Van Dragt, 1984). Van Dragt's data from 1984 is supported by our own scale ring counts. The noticeable absence of Lepomis larger than 4 inches in the seines (their absence from the traps could have been due to the small trap hole opening) and the concentration of age groups in smaller size classes indicates that individuals in the Lepomis population are severely stunted, a condition that can arise from too much competition for a limited resource, too few predators thinning out the population and/or generally poor water qualiy.

We were very surprised not only by this, but also by the numbers and sizes of Percia flavescens that came up with the hundreds of L. gibbosus. Two of these were the 8-10 inch range (Fig. 6) and looked very much like the predator they are when out from among hundreds of 2-3 inch fish. As was predicted, none of the P.flavescens were found in Ravenswood Pond however many large specimens were to have been seen floating dead in this pond after the fish kill (Van Dragt, pers. com.). These larger fish, due to their larger body volume/gill surface area are more susceptible to low levels of dissolved oxygen, thus allowing the on August 31 to deal a serious blow to populations of this capstone predator.

Lastly, the second seine in President's Pond produced two large, healthy goldfish. The presence of this non-native species, along with the completely distinct of fish species in Ravenswood and President's Ponds relative to North Pond proves that man has been introducing fish to the first two ponds for some

DISCUSSION

As students, lovers and stewards of nature, our motivation to collect and data on the ichthyofauna of these ponds came first and foremost in the possibility that we might be able to make some educated management recommendations that could improve the overall health of the ponds. Although their role in maintaining the overall health of a pond may not be obvious at first glance, fish affect many water quality parameters through their daily foraging activities, respiration and waste generation.

Gibbosus, as a major constituent of Ravenswood and President's ponds' fish community, have a significant impact on nutrient cycling and general outward appearance in both bodies of water. the fact that they are stunted yet still present in large numbers is an observation that should not be taken lightly. At the predominantly smaller sizes present in these ponds, Lepomis are planktivores with gill rakers suitable for the removal of larger zooplankton (e.g. cladocerans, ostracods) and the affect of the large populations of Lepomis on zooplankton number is obvious upon cursory examination of a plankton net's contents. Only very low numbers of larger zooplankton are present in these ponds yet the overabundance of phytoplankton in these ponds should be obvious even to a passerby. The zooplankton have plenty to feed upon but they themselvees are being over-fed-upon by the legions of Lepomis, thus creating a situation that is generally regarded as unattractive, the unchecked growth of phytoplankton in a nutrient rich pond.

The obvious question then is "why aren't the Lepomis getting any larger?" Lepomis get larger, their foraging patterns change. They increasingly feed and the unchecked growth of phytoplankton in a nutrient rich pond, upon snails and other large macroinvertebrates present in the substrate, creatures that aren't present in any significant numbers in these ponds (Winkelaar and Rylaarsdam, 1996) Limited to feeding on relatively low protein zooplankton, Lepomis themselves stay small and eat as much zooplankton as they can.

Compounding this situation is the removal of large predators, either by a pollution driven fish kill or by fisherman with a rod and reel. Although we have no data to determine the extent of the latter, many people we talked to reported seeing fisherman at the ponds. By thinning the population of Lempomis, a large predator would reduce the grazing pressure on the zooplankton which could then increase in numbers and increase the grazing pressure on the phytoplankton which would then decrease in number, clearing up the pond. A larger population base of zooplankton could even play a role in protecting against another major fish kill by absorbing some of the phytoplankton population explosion that is fueled by urban runoff.

For instance, the August 31 fish kill was preceded by a heavy rain which washed fertilizer and other nutrients into Ravenswood pond. These nutrients were quickly assimilated by the phytoplankton whose population suddenly spiked. Without a healthy population of zooplankton present to take advantage of this situation, the phtoplankton soon died, falling to the bottom to feed bacterial colonies which sucked all of the dissolved oxygen out of the pond, creating the anoxia that killed the fish.

This, then, constitutes our management recommendation, that a large predator such as Amia calva be added to the ponds to control the populations of Lepomis. Although large Percia lavescens are present in the ponds, they are either not present in large enough numbers to place enough pressure on the Lepomis populations or are not targeting the Lepomis as a prey source at all. Further studies are needed to determine with greater accuracy the foraging patterns of Lepomis gibbosus and Percia flavescens and to determine what additional predator might be best suited to the purpose outlined above, to the conditions present in the ponds and to compatibility with other non-target species.

LITERATURE CITED

Van Dragt, R, 1984. Fish Population Study, unpublished report.

Winkelaar, N. and Rylaarsdam, J.N. 1996. Benthic Study of President's and Ravenswood Ponds, unpublished report.

TABLES

Table 1.

Average number of individuals caught in a trap/hr within each species in the ponds at Calvin during 1998.

Species Ravenswood President's North
Lepomis gibbosus 14.4 10.7 0
Notemigonus crysoluecas 0.6 0 0
Percia flavescens 0 0 0
Ictalurus melas melas 0 0 0.2
Carrasus 0 0 0
Pimephales promelas 0 0 3
Umbra limi 0 0 0.2

Table 2.

Total number of individuals within each species caught by seine. President's Pond was sampled twice and North Pond was not sampled with a seine.

Species Ravenswood 1st President's 2nd President's
Lepomis gibbosus 5 26 1152
Notemigonus crysoluecas 0 0 13
Percia flavescens 0 5 13
Ictalurus melas melas 0 0 47
Carrasus aurelius 0 0 2
Pimephales promelas 0 0 0
Umbra limi 0 0 0