This paper analyzes the bias in fishermans predicted participation rates in the target fishery associated with ignoring the multi-species aspect of labor supply decisions in spatial bio-economic fishery models. Recent advancements have been made to simultaneously model the biology of a marine species and the strategic behavior of harvesters over both time and space in order to more accurately predict the effect of regulatory policies on harvester effort and resource population. These models assume a nested choice structure in which the harvester first faces a dichotomous decision between shifting for the target species or not on a given day and then chooses a location to finish conditional on participation. This structure implicitly groups all non-target species options together in the first nest forcing participation-specific coefficients to be the same for all outside options, including fishing for an alternative species and staying home, two very different choices. Using a complete 15-year panel of all fishing trips made by fishermen possessing a Florida spiny lobster license, including non-lobster trips, I show that the simplifying assumption of a dichotomous choice structure in the first nest is not innocuous and that the participation probabilities can change substantially with the addition of another species as an outside alternative.