Port Jackson Shark Aggregations

Recent aggregations of Port Jackson sharks at both Port Noarlunga and Aldinga created much interest in this annual event. I was encouraged to review past articles that were published in our newsletters back in 2006.

Our September 2006 newsletter included this article: –

“Port Jackson Shark Congregations” by Steve Reynolds

Large numbers of Port Jackson Sharks, Heterodontus portusjacksoni, will congregate together in shallow waters in summer to mate. According to the book “A Guide To Sharks & Rays” by Leighton Taylor et al, both sexes in the Sydney area do this in August and September each year. Kevin Deacon wrote a section about NSW in the book He particularly mentions Jervis Bay where thousands of Port Jackson Sharks are said to congregate for mating during August and September each year. It seems that they may then hang around the area for a couple of months because Kevin says that most of them disperse during November and December. After reading these details in the book, I was reminded of one of my dives at Port Noarlunga reef in 2005. On 5^th November that year my buddy and I came across about 20 adult Port Jackson Sharks which were congregating in a small area outside the reef. We may well have been very lucky to see them just before they decided to disperse like their Jervis Bay cousins. I then recalled the first time that I had seen a congregation of Port Jackson Sharks. It was at Olivers Reef, Victor Harbor. A quick scan of my old log books revealed that it occurred on 5^th November 1988. By some remarkable coincidence, both dates were the same. I will now be on the lookout for more shark congregations between August and November each year. Don’t expect to find the sharks ‘at it’, however, since mating is said to only occur under cover of darkness. Our 2007 calendar of SA Marine Life features Anne Wilson’s small photo of a Port Jackson Shark at Wool Bay for the month of January (2007).

Picture: Anne Wilson

 Our October 2006 newsletter included this follow-up piece by Scoresby Shepherd: –

“Comment On Pt Jackson Shark Aggregations” by Scoresby Shepherd

In late 1964, Professor Geoff Satchell at Adelaide University was studying the physiology of Pt Jackson sharks, and he asked for a supply of them, so with friends, I undertook searches for several months. In December of that year, on a dive at Pt Noarlunga, inshore of the reef we found a very large number. I had with me a 10m line, so, in the interests of efficiency, I tied a loop round the tail of one, then caught the next and tied it to the same line, about one metre away from the first, and so eventually caught about ten, and tied them to the line, each about a metre apart. By this time the sharks were getting agitated, and one or two became aggressive. Then they all started swimming frantically in different directions. In no time I found myself in a tangled mass of snapping sharks, and line. My mask and mouthpiece were caught up and dragged off, and I desperately made for the surface, along with a seething mass of sharks. Luckily a friend saw my plight and together we got the sharks ashore. They gave their lives for science, but happily I didn’t.

We have since learned that these sharks aggregate annually at about this time of year to lay their eggs, and then migrate to the south, but where they go from Gulf St Vincent is still a mystery. In NSW a large number of the same species were tagged, and it was found that they migrated several hundred km south to eastern Victoria, returning year after year at the same time to the same reefs to lay their eggs. Apparently these sharks have a well-developed spatial memory, enabling them to return to their home sites, and even the same crevices on the same reefs with unerring accuracy. They aren’t so stupid after all!