ABSTRACT This document describes the Common Carp Management Plan for the Rice Creek Watershed District, Minnesota COMMON CARP MANAGEMENT PLAN December 2018 Rice Creek Watershed District Common Carp Management Plan Matt Kocian Lake and Stream Specialist Rice Creek Watershed District 4325 Pheasant Ridge Dr. NE, Suite 611 Blaine, MN 55449‐4539 Voice: 763.398.3075 Fax: 763.398.3088 [email protected] Cover photos Above: Young‐of‐the‐year common carp captured in trap nets in Rice Lake, Anoka County, MN Below: Adult common carp harvested with box nets in Long Lake, Ramsey County, MN 1 December 2018 Contents Executive Summary ....................................................................................................................................... 3 Introduction .................................................................................................................................................. 4 Carp Management Goals .............................................................................................................................. 5 Carp Management Tools ............................................................................................................................... 6 Monitoring and Modelling ........................................................................................................................ 8 Inducing or Increasing Adult Mortality ................................................................................................... 12 Suppressing Recruitment ........................................................................................................................ 15 Adaptive Management Approach ............................................................................................................... 18 System Plans ............................................................................................................................................... 20 Literature Cited ........................................................................................................................................... 21 2 December 2018 Executive Summary This document will describe a plan for common carp management for the Rice Creek Watershed District in Minnesota, USA. The report is organized into two main components: 1) an overview of common carp ecology and available management tools, and 2) specific system management plans. Both components are subject to change as new data and research become available. In this context, “systems” are defined as geographic areas that encompass an individual carp populations, including adult and juvenile seasonal habitats. Specific plans will be updated at individually defined intervals. Common carp are ubiquitous within the Rice Creek Watershed. Although natural resources managers have long known that carp have a negative impact on lake ecology and water quality, recent research has shed light on the magnitude and mechanisms of their impact. Additionally, new management tools have been developed and tested by the University of Minnesota and their many partners. With this information and promising new tools, common carp management has the potential to drastically improve ecological function and water quality in many lakes around the Rice Creek Watershed and Minnesota. 3 December 2018 Introduction Common carp (Cyprinus carpio), indigenous to Eastern Europe and Western Asia, were first introduced in the United States in the late 1800’s. The introduction was purposeful, carried‐out by the U.S. Commission of Fish and Fisheries, and indented to promote a fishery for sport and food sources. Since introduction, common carp spread quickly across the United States; most states now have reproducing populations. In Minnesota, common carp are widespread and often found in high abundance. Several other species of carp have also been introduced to the United States and Minnesota – for example, silver carp (Hypopthalmichthys molitrix), known for their jumping ability, and bighead carp (Hypopthalmichthys nobilis). For the purposes of this report, the term “carp” will be used to describe common carp (Cyprinus carpio) (Figure 1). Figure 1. Common carp (Cyprinus carpio). Image credit: Joseph Tomelleri In North America, common carp negatively impact native ecosystems, fish populations, and water quality by their feeding and spawning behavior (Parkos III, Santucci et al. 2003, Bajer, Sullivan et al. 2009, Weber and Brown 2009). When carp are abundant, the abundance and distribution of native plants declines, nutrients (phosphorus) and chlorophyll‐a (algae) increase, and water clarity decreases. Carp root in lake sediments, destroying native vegetation that would otherwise stabilize lake sediments. Their rooting behavior also disturbs and entrains lake sediments, which carries phosphorus into the water column. Carp ingest invertebrates that live in sediment and excrete dissolved nutrients into the water column. By these mechanisms, carp behavior directly increases phosphorus loading, which fuels algae blooms. Carp also indirectly degrade water quality and are often referred to as “ecosystem engineers”. Ecosystem services that would mitigate phosphorus loading and dampen algae blooms are 4 December 2018 also lost; aquatic plants cannot stabilize sediments or take‐up and store phosphorus, and zooplankton populations decline due to loss of refuge provided by plants. Most research on carp and their negative impacts on lake ecosystems focuses on adult fish. However recent research indicates that juvenile carp have similar negative effects on nutrient concentrations, water clarity, and algae blooms (Weber and Brown 2015). This bolsters that argument for managing common carp on a system‐wide scale – including spawning and juvenile nursery areas ‐ instead of on a lake‐by‐lake basis. The negative effects of carp on lakes are not uniform. Impacts are greater in shallow lakes with more littoral habitat, where ecological mechanisms play a large role in lake nutrient dynamics. Also, the density of carp plays a key role in the magnitude of their impact. The approximate threshold at which the negative effects are observed is 100 kg/ha (Bajer, Sullivan et al. 2009, Bajer, Headrick et al. 2014). When carp density is below this threshold, negative effects may be minor. At higher densities, carp can have a significant negative effect. Although specific details about the impacts of carp on water quality have only recently been identified (e.g. Bajer 2009), lake managers have long understood the general link between carp and poor water quality. Carp management has occurred in Minnesota dating back to the mid‐1900’s. Early management tools included the use of non‐selective fish toxins (rotenone) and winter seining. For example, the Minnesota Department of Natural Resources (MNDNR) has used trap‐nets and seines to remove carp and bullhead in the 1950’s. Based on MNDNR reports, these efforts were met with mixed success, and any positive outcomes were temporary. In recent years, several carp management efforts have found success in reducing carp biomass below the ecological damage threshold and improving water quality (Schrage and Downing 2004). In the Rice Creek Watershed, significant improvements in water clarity have been achieved in Howard (02‐0016) and Silver (62‐0083) Lakes by common carp management. Carp Management Goals Given the currently available management tools, it is not economically feasible to eradicate common carp from the Rice Creek Watershed. Further, it may not generally feasible, regardless of effort. Thus, the management goal for common carp is to attain and maintain a population density below which they 5 December 2018 negatively affect water quality. This threshold is approximately 100 kg/ha (90 lbs/acre) (Bajer, Sullivan et al. 2009, Bajer, Headrick et al. 2014). The actual threshold may vary among systems, and positive outcomes may be achieved at slightly higher or lower carp densities. The variability of density threshold among systems highlights the importance of monitoring and adaptive management. Management of common carp alone will not always fully restore lake water clarity (Weber and Brown 2009, Bajer and Sorensen 2015). For those degraded systems with high carp density, reducing that density below the ecological impact threshold will be a necessary component of lake restoration. However, other phosphorus loading sources must be evaluated and potentially mitigated. Carp Management Tools The Integrated Pest Management (IPM) approach will provide the overall framework for managing common carp in the RCWD. The IPM approach follows a stepwise approach, generally including identification of the problem, prevention and exclusion, monitoring, and multiple‐tactic control methods. In recent years, this approach has been adapted for common carp by Dr. Peter Sorensen and Dr. Prezemek Bajer at the University of Minnesota. The adapted approach focuses on employing an array of methods that target ecological or biological weakness in common carp, implemented in an economically and ecologically sustainable manner. The management tools identified in this plan fit within the IPM framework, and are evaluated for use based on, among other things, overall effectiveness and economic sustainability. As carp management tool are evaluated for individual systems, the Rice Creek Watershed District will consider effectiveness, efficiency, and reliability. Before identifying specific management tools, it is useful to consider the population dynamics