The Port Jackson shark
One of the most common sight in Sydney's waters is this shark who gets the name from the Port Jackson Harbour (more commonly known as Sydney Harbour). Endemic to East and South Australia, they show a very distinct migration pattern. We know that PJs aggregate in shallow areas for breeding from July to October and then they are virtually absent for the rest of the year, this is what our community of divers at VIZ have been observing for two seasons at the main dive sites such as Cabbage Tree Bay:
Extracts from the research paper:
"It has previously been suggested that female Port Jackson sharks show preference for rocky gutters and crevices on reefs to avoid male harassment, thus allowing them to co-occur at the same sites. Smaller males may avoid rocky gutters and crevices because of the presence of spotted wobbegongs in these habitats, which have previously been found to predate upon Port Jackson sharks"
"Given the lower abundance of males on the reefs because of their earlier departure, females likely delay egg laying to decrease the likelihood of egg mortality by predation by males, thus maximising the survival rates of the eggs laid late in the season."
References: "Long-term migration patterns and bisexual philopatry in a benthic shark species" January 2016, Nathan Charles Bass, Johann Mourier, Nathan A. Knott, Joanna Day, Culum Brown and Tristan Guttridge, CSIRO PUBLISHING
Thanks to Dr Julianna Kadar, Port Jackson shark specialist, for the help in putting together this article and for hosting the excellent presentation on Port Jackson sharks, recording available on Youtube, below