Update for Lake Ellwood Association
December 2015
We have monitored Lake Ellwood’s fishery more extensively since 2012 than nearly every other inland lake in WI, so there is a lot of data to share. I have done my best to summarize the information we have collected, but if anyone would like more detailed information just let me know.
Adult Populations:
This year we repeated the entire survey of Lake Ellwood that was conducted in 2012, to see what changes have been made to the fishery over the last 3 years. Here is a shorter summary of what has happened to the adult populations of a few key species.
We have seen a decline in adult LMB and SMB abundance by 58% and 28% in the last 3 years. The decline in largemouth bass abundance was expected, since this species had not had significant natural reproduction since 2006. In 2012, the LMB population was almost entirely comprised of large/old fish. Most of those fish have now moved out of their populations, but the good news is that we are starting to see some new adults entering the population (from natural reproduction that occurred the past few years).
Northern Pike were on the ropes in 2012, due to no natural recruitment since 2004. Like LMB, most of the older fish from the 2012 survey have moved out of the population, but I started a stocking plan after the 2012 survey and we are seeing pretty good survival of stocked fish. This has allowed the adult population to remain relatively stable. In fact, the adult pike population estimate conducted this year shows a slight increase in adult abundance.
The bluegill population declined tremendously from 2002 to 2012, reducing the adult abundance by 65%. However, the bluegill population has rebounded better than I expected over the last three years. The size structure and age structure are now “healthy” and I expect this population to grow much more in the years to come.
Recruitment:
Since the 2012 survey, which showed that recruitment (reproduction) of fish was the major problem in Lake Ellwood, we have spent a lot of time surveying/monitoring fish recruitment. Since 2013 we have conducted a “mini-fyke net” survey in early September and then a few weeks later we conduct a fall electrofishing survey. These two surveys are what we use to monitor/assess fish recruitment in Lake Ellwood. I will summarize some of the results of these surveys.
2013 was the first year in which chemical treatments were not conducted to control EWM. Since the treatments were stopped, recruitment of the major species in Lake Ellwood has increased substantially (Figure 1). The trends in LMB, BG, RKB, SMB and YP recruitment are very encouraging and have me hopeful for a full recovery of these species. However, black crappie and northern have not shown any increase in natural reproduction.
Figure 1. Change in fish recruitment, indexed using age-0 catch rate during fall electrofishing surveys, for Lake Ellwood, Florence County, 2012-15.
To paint a clearer picture of how recruitment has changed in Lake Ellwood we can group the fish species into the typical groups in which we classify fish in Wisconsin; gamefish, pan fish, and non-game fish (Figure 2). This removes some of the effect of competition between similar species. This data shows that recruitment of each species group has increased each year since treatments were stopped.
Figure 2. Change in fish recruitment, indexed using age-0 per mile during fall electrofishing surveys, in Lake Ellwood, Florence County, 2012-15.
Aquatic Vegetation/Water Level:
The last major components of the monitoring that my crew has conducted since 2013 are the changes in aquatic plant abundance and water level. Unfortunately we do not have any pre-treatment or during treatment surveys to compare these surveys to, but what we have seen since 2013 is this, an initial increase in the plant community with the water level being very stable followed by an increase in water level and a decrease in plant abundance and volume in 2015 (Table 1). Since reproduction increased substantially prior to the water level increase we can rule out water level as being the reason for decreased fish recruitment.
Table 1. Water level and aquatic plant population changes in Lake Ellwood, Florence County, 2013-2105.
Greg Matzke
Fisheries Biologist
Wisconsin Department of Natural Resources