Oneida Lake: ever-changing ecosystem

Managing water resources in Oneida Lake, WM Kappel

Oneida Lake watershed: A valuable diverse ecosystem, SM Harrington

Water level management, HM Goebel

Oneida Lake: undergoing ecological change, EL Mills, KT Holeck

Evolution of the Oneida Lake fishery, T VanDeValk, L Rudstam

Regional partnerships for Oneida Lake watershed, AB Saltman

Helping to protect Oneida Lake, J Henke

Trends: technology and management of municipal wastewater, D Interdonato, E McCarthy

Outstanding young researchers

President's message, D. Ellis

Executive director's message, P Cerro-Reehil

People and places

Joint CSO/SSO meeting

Correction

Winter 2001 — Vol. 31, No. 4

by Tony VanDeValk and Lars Rudstam

Oneida Lake is home to a diverse fish community. Over seventy-five species of fish were recorded in the lake during the 20th Century. The species ranged from small minnows that were hard to tell apart, to giants like lake sturgeon and common carp. Some species recorded in the beginning of the century were not seen for many years; others arrived toward the end of the century.

Figure 1. Representatives of Oneida Lake fish community.

Changes in the fish composition are likely to continue because Oneida Lake is connected to both the Great Lakes and the Hudson River systems. New exotic species in either of these systems will likely make it to the lake eventually. Some of these species have little effect on the rest of the fish community; others may have major effects. (We are currently expecting the round goby to arrive from lakes Ontario and Erie where it has become a dominant member of the inshore fish community.)

Most of Oneida Lake's fish species are warm- or cool-water fish. Warm-water fish include sunfish, bass, pickerel, and many of the minnows. Notable examples of cool-water fish are walleye and yellow perch. Fish that prefer cold water, such as salmonids and burbot, are less common although burbot, cisco, and an occasional salmonid are found in the lake.

In contrast to the Finger Lakes, Oneida Lake does not stratify thermally in the summer and, therefore, cannot provide a cold-water refuge for species that require it. Water temperatures in the summer, even in the deeper areas of the lake, can be lethal to fish like burbot and many salmonids. The general trend of warming may be the cause for the decline of cisco, a cold-water relative of the whitefish, and for the increase in gizzard shad, which prefer warmer water. (Oneida Lake has shown a warming trend; mean August water temperatures at 10 m have increased by about 1°C since 1968.) Oneida Lake is at the southern end of the cisco's distribution and the northern end of the gizzard shad's distribution in North America.

Changes in the fish community

Humans use many members of Oneida's fish community. Historical records indicate that Oneida Lake provided Native Americans with a fishery for both eels and salmon. Weirs were used to trap eels entering the lake, and salmon were speared at the mouths of tributaries during their spawning run. By the 19th Century, early settlers had established a commercial salmon fishery, but over-fishing quickly depleted the resource. By 1897, conflicts between anglers and commercial fishermen put an end to all commercial netting.

The most significant change to the fishery, however, came as a result of the completion of the Barge Canal in 1916. The combination of barriers and water level stabilization changed the fish community dramatically. Dams and locks severely restricted movements of migratory species such as eels and salmon, and the draining of wetlands and marshes decreased spawning areas for pike and pickerel.

By the 1940s, a fishery once dominated by pickerel, walleye, and northern pike was transformed to a strictly walleye fishery with smallmouth bass a distant second. Yellow perch also thrived under these conditions and became popular to anglers.

This fishery has persisted to the present, and Oneida Lake has developed a reputation as one of the premier sport fisheries for walleye in the Northeast. The walleye fishery is maintained and enhanced by a combination of natural reproduction and by a continuous stocking program. New York State's Oneida Lake Fish Cultural Station at Constantia has annually stocked over 100 million newly hatched fry since 1893.

Figure 2. Annual abundances of adult walleye and yellow perch in Oneida Lake since 1957.. Click for larger image in new window.

In the 1950s anglers reported substantial year-to-year fluctuations in walleye catches. Their observations raised concern about the sustainability of the fishery. A program was then designed to examine in detail the factors influencing trends in Oneida Lake fish populations (Figure 2).

Early studies by John Forney and colleagues at the Cornell Biological Field Station (CBFS) showed that anglers accounted for most of the adult walleye mortality. They also found that prey abundance had a dramatic effect on walleye recruitment as well as vulnerability to angling. In years with few prey, walleyes were eager to take angler offerings and also cannibalized their young. These circumstances resulted in fewer adults the next two or three years. In years with abundant prey—young yellow perch, white perch, or gizzard shad—fishing was poor, and survival of young walleyes was good, which provided more adults in subsequent years.

Ecosystem shift

This relationship determined the status of the Oneida Lake fish community through the 1980s. Then, the invasion of exotic nonfish species, mainly zebra mussels and double-crested cormorants, changed the fishery dramatically. The proliferation of zebra mussels since 1992 has resulted in much clearer water. Increased water clarity has both direct and indirect effects on the fish community:

• One indirect effect is the expansion of habitat
more suitable for species such as sunfish and bass. This expansion is accommodated by increased plant growth at greater depths, a direct effect of increased water clarity.
• Clearer water may also affect fish populations
directly by increasing the vulnerability of young fish to predation. Increased mortality at young ages may decrease their recruitment to the adult stock which, in turn, will eventually reduce the number of adult fish available to anglers.
• Finally, clear water may affect the behavior of
light-sensitive species like walleye. Low-light habitats, such as deep water or structure (for example vegetation), may then play a more important role in determining their distribution.

Figure 3. Double-crested cormorants nesting on Long Island on Oneida Lake. Photo courtesy of Connie Adams

Double-crested cormorants have also had a dramatic effect on the Oneida Lake fish community. Cormorants were first observed nesting on Oneida Lake in 1988 (Figure 3). Since then, the nesting population has approached 800 individuals, and the addition of migrants in the fall escalates the total to over 2000 birds on any given day.

These birds are opportunistic feeders and consume about 1 lb/day of fish. On Oneida Lake, their diet is dominated by young walleye (ages 1-3) and yellow perch. Recent studies show that they do reduce recruitment of yellow perch and, to a lesser extent, walleye to the adult stock.

The combined effect of increased water clarity and cormorant predation is the likely cause for recent declines in adult walleye and yellow perch populations. (During the 1990s, the adult walleye population decreased from about 600,000 fish to around 250,000. The adult yellow perch population decreased from 3 to 1.5 million fish.)

Continuing investigation

Figure 4. A typical catch in the late 1950s.

Staff at CBFS has continued to study the consequences of these changes on the Oneida Lake sport fishery. Pertinent studies include long-term population assessment of both subadult and adult walleye and yellow perch populations, changes in the species composition of the fish community, and continued monitoring of the effects of cormorants and zebra mussels. Staff have also updated the role anglers play on the fish community. The effects of angling were examined in creel surveys from 1957-59 (Figure 4). In recent years, two studies have been conducted: the Oneida Lake Diary Program (1994-98) and the Oneida Lake Creel Survey (1997).

The Oneida Lake Diary Program was a 5-yr study that enlisted anglers to keep records of their fishing trips to the lake. Data collected by participants indicated the lake continues to provide excellent angling opportunities for its most popular game fish, the walleye, as well as yellow perch, smallmouth bass, and a variety of other species. However, based on reports from anglers and estimates of walleye populations from years before the study, recent catch rates for walleye are probably lower than those experienced before the early 1990s.

Diary programs are effective tools to monitor trends in angling but are not a representative sample of the angling population. These programs tend to include more enthusiastic anglers, and studies say that these individuals are typically more successful. Quantitative assessment of the effect of anglers on a system requires a creel survey.

Anglers' use of the lake

From 1957-59 and again in 1997, creel surveys were conducted on Oneida Lake for both the open water and winter seasons. Methods were consistent for both studies, allowing for direct comparisons between years. Results showed that although walleye were yet the most popular game species and anglers still accounted for most of the walleye deaths in a given year, fewer anglers were using the lake in 1997 than in earlier years. Angler use in 1997 was one-half to one-quarter of the effort observed from 1957-59 and was lower than effort expended on other suburban walleye lakes in North America.

Angler success in 1997 was within the range observed in 1957-59. During earlier years, anglers averaged 0.04, 0.08, and 0.34 walleye/hr. Anglers in 1997 averaged 0.18 walleye/hr. However, the adult walleye population in 1997 was slightly lower than in 1957 and about 70% lower than 1958 and 1959; so, anglers now seem to be more efficient in catching walleye. A possible explanation may be the evolution of technology available to anglers. Fish finders, GPS units, downriggers, and radios certainly continue to make anglers more effective at catching their prey.

Creel survey results also indicate the yellow perch fishery continues to be strong. Anglers caught 0.4 yellow perch/hr during the open water season, and this rate quadrupled during the winter season. Catch rates in 1997 were higher than all three earlier years and also compared favorably to other North American lakes from which similar information was available.

The most dramatic change in terms of angler success from the earlier years came at the expense of smallmouth bass. While annual catch rates never exceeded more than 0.03 smallmouth bass/hr from 1957-59, anglers in 1997 averaged 0.10/hr. Despite this increase in angler success, only about 10% of the angling effort in 1997 targeted smallmouth bass. Estimates of effort targeting smallmouth bass were not available from earlier years, but bass fishing on Oneida Lake is likely more popular now than in the past for two reasons:

• An outstanding bass fishery
• Increased mobility of anglers interested in bass.

There seems to be at least one if not more bass fishing competition on the lake each weekend through the open water season.

Figure 5. Successful anglers in the late 1990s. Photo courtesy of Ray Brown.

Despite the changes of the decades, Oneida Lake continues to provide outstanding angling opportunities. Despite a lower abundance of adult walleye and yellow perch in recent years, angling for these species continues to be as good or better as other popular walleye and perch lakes in North America (Figure 5). The lake also offers outstanding smallmouth bass fishing with an up-and-coming largemouth bass fishery. It offers opportunities to catch other species such as sunfish, white bass and white perch, bullheads and channel catfish, drum, and northern pike, and pickerel. Although recent changes coupled with inevitable future changes to the Oneida Lake ecosystem have and will affect the fishery, continued research and management will strive to maximize opportunities associated with this valuable resource.
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Tony VanDeValk is a fishery biologist at CBFS whose research interests focus on predator-prey interactions; specifically angler-walleye-yellow perch interactions on Oneida Lake as well as other lakes around New York State. He's been a member of the CBFS research team since 1987.

Dr. Lars Rudstam is a fish ecologist with 10 years in Cornell's Department of Natural Resources and is leader of the the Warmwater Fishery Unit at CBFS. Lars' fishery research interests span the globe. He is currently on a sabbatical at the University of Stockholm in Sweden.