Here's something you've probably never heard of... cod hotels. They're breeding boxes which replace lost habitat for the endangered eastern freshwater cod, and researchers were thrilled when the fish used them.
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TVTranscript
00:00 What lies beneath this stretch of the Nimboida River could give nature a helping hand in
00:15 saving an endangered native species.
00:18 We just have a little look in there.
00:20 We're hoping that nesting boxes to help them along to provide them with small bedrooms
00:25 and we've luckily had one really good success.
00:29 It was this vision of baby eastern freshwater cod in one of the boxes that's excited researchers.
00:36 And it means that we're starting to cue in to the biological needs of this fish.
00:40 So being able to supplement a key part of their habitat and know that that design is
00:45 appropriate for its needs is a huge boost to our confidence and moving forward to develop
00:50 and refine nest boxes into the future.
00:53 [Music]
01:00 On the surface the Nimboida and waterways of the Clarence catchment may look beautiful,
01:05 but under the water sediment from historic mining and natural disasters has smothered
01:10 caves and destroyed the cod's breeding habitat.
01:14 One of the most important things with this fish is the fact that it actually has quite
01:18 limited breeding opportunities in the wild.
01:20 That's why we're starting to see the decline of this fish over previous decades.
01:26 Eastern freshwater cod was one of more than 100 species identified as in urgent need of
01:30 help after the 2019 bushfires in the Clarence Valley, attracting a $300,000 federal government
01:37 investment into cod conservation projects.
01:42 In a bid to reduce the cod's decline, local land services has teamed up with the NSW Department
01:48 of Primary Industries to create an alternative breeding space for the species.
01:55 The team tested different breeding box designs at the Grafton Fisheries Centre.
02:00 It's been a really interesting challenge because we've got design constraints around building
02:04 these things and securing them so that they don't get washed away and not fill up with
02:08 too much sediment themselves and then we've got to make them so that it works for the
02:12 fish.
02:14 Training breeding age wild cod, which are usually about five years old, to use the box
02:18 was an additional challenge.
02:21 The male needs to do all the cleaning up of the kitchen, get everything ready to attract
02:24 his lady, then she comes into the room and if she's happy with what he's done then she'll
02:30 lay her eggs, he'll fertilise them, she'll move off and swan off with her life and he's
02:35 left to do the heavy lifting for the next three weeks, which means tending to the little
02:40 ones which are eggs that are glued to the bottom of the nesting box which we got to
02:44 see, which is really neat.
02:50 The final design was put to the test during breeding season last spring when 30 boxes
02:55 were installed along the Nimboida River.
03:00 While breeding was seen in only one out of 30 boxes, Sean Morris says it's a significant
03:05 feat for a population of less than 250 mature fish.
03:10 With just one breeding event in one box we could have produced thousands of fish and
03:15 so it's a huge boost to the population.
03:17 (bubbling)
03:19 [BLANK_AUDIO]