Harbour Porpoise Presence near Oil Tankers

Harbour porpoises (Phocoena phocoena) are thought to be “shy” animals that are easily disturbed by underwater noises. There is concern that sources of anthropogenic sound, especially those associated with shipping and pile driving, will drive porpoises away from their preferred habitat [1]. A recent study, however, found that harbour porpoises were occasionally present within a few hundred m of a liquefied natural gas (LNG) tanker when it was offloading and departing from the Canaport LNG terminal at Saint John, NB, Canada [2]. The goal of the present study was to obtain more samples of porpoise presence (or absence) when noise levels were high and a tanker was in the immediate vicinity. In addition to measuring the linear (unweighted) noise levels, a weighting function to take the insensitivity of porpoise low frequency hearing into account was used to calculate the likely perceived noise levels [3]. This function is generally analogous to the dB(A) function for humans and is expressed as dB(Pp) where (Pp) represents using the hearing threshold values of Phocoena phocoena to calculate the weighting function.