Maturation and sexual ontogeny - Spangled emperor
For any of you interested in Spangled Emperor on the Ningaloo, here's a presentation my old boss did and what I spent a lot of my time working on whilst up here in Exmouth. Theres a lot of scientific terms, but you will be able to grasp the concepts. Effectively spanglies become sexually active at about 360mm, giving them approximately one chance to spawn before becoming legal size. (Around 3 years old and can be caught at 410 or nearly 4 years old)
You can see that the spawning (gonad weight) increases significantly with the age of the fish, as does the fishes length. All juvenile fish we sampled started life as females and approximately 50% of those fish change sex at age 2 (around 250mm)
Having dissected thousands of Spanglies over the last couple of years, you can see the gradual trends in how the fish eat and move when requiring to put on fat stores for growth and sexual reproduction. I've found 3 confirmed aggregations during spawning season that would blow your mind, the sounder is full for a 90m long drift in 25m from top to bottom and you can throw a mulie over board and watch them come in and fight over it. Just glad its windy as all hell around then!! There's a lot more information to come out of the research, I'm sure it will be in the public domain soon.
Here's one of many presentations that you may be interested in.
http://www.ipfc2009asfb.com/pdf/speaker_presentations/Marriott,%20Ross.pdf
Cheers,
Adam
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saltatrix
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Date Joined: 30/03/08
Effectively spanglies become
Effectively spanglies become sexually active at about 360mm, giving them approximately one chance to spawn before becoming legal size. (Around 3 years old)
After reading about additional length benefits to the minimum size on Red Emporer in QLD Adam Im surprised a little additional length isnt added to allow 1 chance in 2 or 3 years of possible spawning.
What's the recruitment success on Spanglies year to year? Are they successful at spawning year to year or are they poor performers like Dhufish?
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Faulkner Family
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and you got paid to do this.
and you got paid to do this
. interesting if you are into this sort of stuff. one thing , the spanglies are very photogenic. i have a couple of pics like those ones .
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Adam Gallash
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summary
I've just summarised what's been said there, the presentation has the actual details.
As for reds Neil, there's been very little research done on them in terms of their spawning habits in WA, just the basics. I've seen some variation in spawning times between Exmouth, Canarvon and Denham. I don't know if this means there is variation in the species between the locations. It would have been nice to find more samples for reds, but again, being at the right place at the right time to get info is a logistical nightmare. Via genetics we were able to prove that spanglies are all the same and don't have any sub-structures or variation between locations.
The journal paper has a lot more in depth info, I'm not sure if it's been released yet for me to make any other comments. Its some pretty serious reading though thats for sure.
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