Factors Affecting Population Dynamics of the Invasive Round Goby (Neogobius melanostorrws)

Abstract

<p>The round goby (<em>Neogobius melanostomus</em>) is an invasive fish species that has spread rapidly throughout the Great Lakes. The proliferation of t his invasive species is of interest and concern because of its potentially negative impacts on native species. This thesis focuses on increasing our understanding of the population dynamics of the round goby, exploring causal factors both empirically and theoretically. <br /> We analyzed data collected in Hamilton Harbour (in Lake Ontario) between 2002 and 2008. We found that round gobies have declined over time in both abundance and in body size. We related the observed dynamics to seasonality, to substrate types and to water quality in all locations. Round gobies were found on all substrates sampled including mud, although they were less abundant on mud than on other substrates, and to elate have not extensively colonized Cootes Paradise Marsh , an important breeding ground for native fishes. Our results indicate that muddy and sandy substrates are not resistant to round goby invasion, and may impede but will not prevent round goby colonization. <br /> Recently, two types of phenotypically distinct males have been observed in the population that have different strategies for reproducing. Through mathematical models, we investigate the affects of Male Alternative Reproductive Tactics on population dynamics. We compare two models in which we assume that. tactics are inherited , or not; inherited from the parent. We found in both cases that the presence of sneaker males can result in significantly increased populations, but can also suppress the population. When tactics are not inherited , the model predicts one of three scenarios: extinction, persistence, or persistence above a threshold density (Allee effect). When tactics are inherited we find four possible situations: extinction, a population consisting only of parentals, a coexistence equilibrium, or stable population cycles. Our results suggest t hat it is important to incorporate alternative reproductive tactics into population models, particularly for species of 0nvironmental or commercial concern.</p>