Climate Change in the Upper Midwest Affects Management of Sea Lampreys
BY DORANCE BREGE, MARQUETTE BIOLOGICAL STATION
Sea lampreys have had a substantial effect on both native and other desirable fish populations in the upper Great Lakes since the invasion of the exotic species during the 1930’s. Management of the sea lamprey depends primarily upon application of pesticides (treatments) to infested tributaries to kill the larval stage of this parasite. The main pesticide used since 1958, a chlorinated nitro-phenol (TFM), is selectively toxic to larval lampreys when applied at the appropriate dosage. Effectiveness of these treatments is dependent upon having suitable amount of stream discharge to effectively deliver the proper strength of TFM to the larval sea lampreys.
During the past two decades, water levels measured during our treatments in the upper Midwest have notably decreased due to extreme weather patterns with little rainfall. During summer, many streams virtually cease flowing, making effective treatment impossible.
Normally, treatments are expected be highly effective in eradicating larval populations; a small drop in treatment effectiveness results in excessive numbers of residual (surviving) larval lampreys. Treatments at extreme stream discharge require alternate application tactics and are likely to be less effective in eliminating larval sea lampreys.
certified operator using 12 volt pump.
Credit: Karla Bartelt,USFWS
Fifteen streams in the upper Midwest within the Marquette Biological Station’s region of geographic responsibility (Minnesota, Wisconsin and upper Michigan waters) were selected to analyze trends in water levels and dates of treatment. These 15 streams produce large numbers of larval sea lampreys and are regularly treated with TFM. Treatment data were compared for a base time period, 1980 through 1997, and the most recent period from 1998 through 2012.
Analysis of field data of this nature is not without pitfalls; many variables affect treatments. Low water periods also existed in the base years, during the mid-1980’s, making decisions by Service biologists difficult. Average amount of stream discharge during treatments was greater during the base time period in 13 of the 15 selected streams. The average stream discharge in recent treatments, including the two streams with greater average, was also influenced by scheduling to avoid low flow, as discussed below.
Avoidance of TFM treatments during expected low water periods was also examined for each of the 15 selected streams. Biologists avoid scheduling treatments when expected effectiveness is decreased. There are 12 ten-day time periods in our field season when TFM treatments can be scheduled. The time period from July 10th to September 10th includes four of these time periods and is normally the lowest amount of stream discharge. Anticipated low water levels for this time period challenge biologists to schedule the more than 40 TFM treatments normally completed during the field season. A limited number of streams can be scheduled for treatment in each of the 12 time slots. Once prime slots are filled, other streams must go elsewhere in the schedule. This issue has been exasperated during recent years due to the dry weather patterns.
Compared to the base time period (1980-1997), recent treatments of 11 of the 15 streams were less likely to be completed during mid-summer. Of about 50 treatments in each time period, biologists completed 25% of the treatments during the base period at the midsummer flows verses only 10% in the recent time period. Four of the streams were more likely to be treated during the mid-summer due to stable summer flows.
What has this low water phenomenon meant to the Sea Lamprey Control Program? Each field season, biologists at Marquette partake in an exercise in jockeying a full slate of treatments into appropriate time slots. Expected water conditions are only one of the scheduling issues. The dry weather pattern has restricted the options for scheduling. Some treatments are now completed during less effective conditions. Alternate application tactics and special efforts like partial treatments of difficult reaches can be used to successfully complete treatments when stream discharge is very low. These techniques require additional personnel and time; in spite of the extra cost, they may not effectively eradicate larval lampreys. Ultimately, the problem of low stream discharge during treatments has and will continue to impact the success of the Sea Lamprey Control Program.