Seahorses may look a little strange, but they are vital indicators of marine health. Landline's Sean Murphy takes a look at a restocking program at Port Stephens, where the population of the threatened 'White's Seahorse' was decimated by the Hawkesbury River floods of 2021 and 2022.
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00:00Seahorses are among the most unique fish in the sea.
00:14They mate for life and the males give birth.
00:17But besides their fascination value, they're also an important indicator of a healthy marine
00:23environment.
00:25They're like the canary in the coal mine.
00:29If we have really healthy oceans and really good, healthy habitats, we'll have lots of
00:34seahorses.
00:35But if we have an environment where the seahorses don't exist, it means that there's a problem.
00:38It means that there's not enough habitats in the water, it means that there's problems
00:41with the water quality.
00:42So if you see seahorses, we know it's good.
00:44If they're not there, we know we have a problem.
00:53The Port Stephens Estuary is one of the largest in New South Wales and it's a global hotspot
00:58for the threatened white seahorse.
01:03Marine biologist David Harasty has been studying them for 25 years.
01:08His diving partner Merrill Larkin is completing a PhD thesis on the soft corals seahorses
01:14live in.
01:15This expedition will take them just minutes from the safety of the Port Stephens marina.
01:20Yeah, it looks a bit brown out there today, I'm a little bit worried.
01:23We've had a lot of rain over the last couple of weeks, so what will happen is that fresh
01:27water will sit on top and make it really brown and hard for us to see.
01:34Water quality has been a problem in the estuary for a while now.
01:38The Hawkesbury River floods of 2021 and 22 had a devastating impact on the Port Stephens
01:45system.
01:46Seahorses and their habitats virtually disappeared.
01:50There's no sponges left, there's no corals left, the seagrass had all gone.
01:54It just basically became an underwater desert.
01:59The NSW Department of Primary Industries Fisheries Institute is on the Port Stephens estuary.
02:05The DPI team has been able to breed seahorses at scale, but they're still learning about
02:11optimum growing conditions, such as water temperature, light and salinity.
02:16The first 1,000 produced came from wild-caught broodstock.
02:20Ultimately, they hope to use captive breeding stock, but they'll first need to better understand
02:26the genetic diversity of the fish.
02:28So there's lots of challenges because we really are starting from scratch.
02:32And our methodology is to work very rigorously through all those parameters that we can control
02:37in the hatchery to ultimately build that recipe that we'll be able to hopefully produce large
02:42numbers for stock enhancement.
02:44David Harastie has already released hundreds of seahorses into the estuary.
02:55To help them, he installed what he calls seahorse hotels, metal cages to provide habitat and
03:01protection from predators.
03:03Over the last six months, we're actually seeing signs of recovery.
03:06The soft corals are coming back, which is fantastic.
03:09I'm really hopeful in, say, five years' time that Port Stephens has recovered.
03:14I want us to go back here and what it used to be like 30 years ago, when you can dive
03:18through a football field of corals and I can see 20 to 30 seahorses a dive.