An important aspect of aquatic invasive species (AIS) management is the role humans play in their dispersal. For the spread of AIS among inland lakes, the typical pathway for dispersal is boaters moving from lake to lake. We aim to develop a spatial dynamic model of species invasions within a freshwater lake system in which a set of managing agents is concerned with the inter-seasonal spread of invasive species across lakes (where a season is defined in this case as the annual boating season), and recreational boaters/anglers make a series of intra-seasonal trip decisions to maximize random utility during the course of the season, subject to the actions taken by the manager.
Estimation of the model, and the data required for estimation, focuses on three elements: the Random Utility Model of boater trip decisions (see project 'Boater behavior and specie invasion'), the transmission probability density functions, and the abundance of AIS.
Estimating the probability that a boat leaves with propagules: We will randomly sample boats at landings as they are removed from selected invaded lakes. Each boat will be inspected to determine whether it is carrying any invasive species. Information will be recorded on the absence/presence of invasive species and other species and/or debris on the boat and trailer, the type of boat and trailer, boating activity (fishing, water skiing etc.), time of day, and day of the year. The value of recording the presence/absence of other species and debris on the boat/trailer is that it gives a general indication of the boater’s diligence in cleaning the boat after pulling it from the water. Boaters may be asked several related questions that may be important variables in estimating f, such as whether the boater lives on the lake or is destined for his home lake.
Estimation of the lake-level AIS abundance: We will estimate the abundance function using data from a non-random survey of up to 100 invaded lakes. Depending on the availability of lakes for the particular AIS under investigation, some of the sampling may be conducted on non-NHLD lakes. For each lake, the survey will be repeated three times each summer for three consecutive summers (2010-2012), to allow examination of intra- and inter-seasonal variation in invader intensity. Methods for generating an index of abundance (CPUE) for each of these invaders have generally been developed for the NTL-LTER lakes, and will be used in this survey. We will focus our efforts on lakes for which invasive species, limnological, and habitat data are already available from previous surveys (http://lter.limnology.wisc.edu/). Using this dataset, we will develop statistical models predicting invader abundance using limnological and habitat predictors.
A random survey of lakes in the Northern Highland Lake District (NHLD) indicated high densities of several aquatic invasive species (AIS). 23 of 35 surveyed lakes had at least one population of AIS. Chinese mystery snails (Bellamya chinensis; 17 lakes) were the most common followed by rusty crayfish (Orconectes rusticus; 12 lakes), banded mystery snails (Viviparus georgianus; 9 lakes), and Eurasion watermilfoil (Myriophyllum spicatum; 3 lakes). Curly-leaf pondweed (Potamogeton crispus), spiny waterflea (Bythotrephes longimanus), and zebra mussel (Dreissena polymorpha) were not found at all. Our results indicated that AIS occurrence is much higher in the NHLD than the Wisconsin DNR statewide estimates.