Alternative reproductive tactics (ARTs), occur where members of one sex of a species have two or more strategies of obtaining fertilization. The tactics differ in behavioural approaches to reproduction, but also commonly differ in physiological and morphological traits. The round goby, Neogobius melanostomus, is a globally invasive species with male ARTs. How behaviour may influence invasiveness in round goby has been of recent interest, but researchers have not considered the role or impact that male ARTs may have. I compared guarder and sneaker male round goby, assessing differences in their boldness, activity, exploration, sociality, aggression, startle responses, and dispersal tendencies. Sneaker males were more bold, active, and explorative while guarder males were more aggressive. In addition, I studied whether more guarders or sneakers are caught in a population survey study and how variation in a common round goby trapping method, minnow traps, may create catch biases. Two commonly employed minnow trap models include a black vinyl plastic coated metal trap (black traps) and a galvanized metal steel trap (silver traps). I investigated whether these black and silver traps and baited (corn) and unbaited traps differ in terms of the numbers, ART ratios, and sizes of round goby captured. I found silver traps captured 1.7 times more round goby than black traps, while baited traps captured 3.4 times more round goby than unbaited traps. Baited traps captured larger round goby and tended to capture more guarders than unbaited traps. I also found black traps captured larger males, but there was no difference in the size of females captured. Taken together my results indicate that care needs to be applied when making estimates of round goby populations in terms of the types of individuals present and the trapping method used. / Thesis / Master of Science (MSc)