Wildlife populations are negatively impacted in a variety of ways. Humans, in particular, have played a huge part in species declines today as well as species extinctions in the past due to overexploitation. Recent declines of large marine vertebrates that are of little or no commercial value including sea turtles, seabirds, and marine mammals, have drawn attention on the ecological impacts of incidental take or bycatch in global fisheries. The dusky dolphin (Lagenorhynchus obscurus) is a marine mammal that inhabits coastal waters of the Southern Hemisphere which commonly is caught in gillnets. However, the effect of gillnet-related mortality on the population dynamics of this species is unknown. Hence, our objective was to estimate the impacts of gillnet entanglement on population trends of dusky dolphins. We conducted a thorough literature review to obtain the best information available related to gillnet entanglement of dusky dolphins as well as the basic demographic data necessary to develop a stochastic population dynamics model. We then used the model to estimate the potential effect of gillnet-related mortality on the population dynamics of dusky dolphins in view of the parametric uncertainty associated with the model.
When gillnet entanglement was added to the natural survivorships scenarios, the dusky dolphin population was affected either by a fast decline or decrease growth rate in 20 years. Based on the survivorship data and gillnet entanglement effects, the population size had between a 60-85% decrease after 20 years. Our results suggests that the gillnet entanglement could have significantly negative effects on the population size of dusky dolphins and that there needs to be more research to monitor this species.