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Author Topic: Dead Barra - found 100 in the Boyne River  (Read 7535 times)

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Dead Barra - found 100 in the Boyne River
« on: December 26, 2010, 10:42:22 PM »
Joined the multitude of sight seers at Awoonga Dam and the Boyne River, the water was 2m over the spillway at 2pm today and rising (currently 2.47m over at 10:20pm). The stench along the Boyne is unmistakable, counted 100 dead barra in less than 30 minutes and only walked along 1 km of the river.

I know its part of nature, but its a crying shame to lose so many fish. Recent articles quote 10% of fish have died, but after watching the numbers going over the wall per hour and then finding so many dead, I’m guessing the mortality rate is much higher than originally estimated, but I don’t think we will ever know as it a very subjective guessing game.

On the bright side, don’t need to reverse so far at the ramp now days and a couple of local lads were targeting Jacks at Pikes Crossing ;)

At Benaraby Bridge




Down stream from Pikes Crossing







There's a fine line between a hobby and mental illness,
He who dies with the most toys wins - more tackle box jewellery

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Re: Dead Barra - found 100 in the Boyne River
« Reply #1 on: December 26, 2010, 10:47:52 PM »
Dam Wall




Making the best of the wet


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Re: Dead Barra - found 100 in the Boyne River
« Reply #2 on: December 27, 2010, 06:21:54 AM »
G'day Earl,

Thanks for posting up the pictures for those who can't get to see this phenomenon. As I was reading your post in regards to the mortality rate, I was thinking the opposite, more inclined to thinking the other way, being way, way less than 10% at this present time. There would be many more who would have survived than the unfortunate ones floating up on top. Do the math and the numbers to me are a drop in the ocean for Awoonga. It has been an early wet season and as the rain and weather persists the percentage rate will increase slightly.

Kurt would have the figures on how many Barra would have been stocked into Awoonga, say in the past 8 years. At a guess for the exercise, 5 million Barra. Mortality rate of those 5 million fingerlings reaching full size, end of the scale, a 25% loss, maybe a bit more, but for the exercise lets say 25%, which equates to 3,750,000 million fish left in the fishery. A 10% loss over the dam wall would then equate to 375 thousand fish going over the wall, a bit hard to believe in my opinion if those figures are right as not all of them would want to head downstream anyway.

If 3 million fish were stocked into Awoonga in the past 8 years, at 10% going over the dam wall, it would equate to 225,000 fish going over using the same rates I used in the above exercise. Still a lot of fish.

Kurt mentioned in a post when it was first going over the wall, he and two officers were counting and monoriting the fish going over at a rate of 66.4 fish per hour. At that rate, for 30 days, this would equate to 47,808 going over the dam wall. How long has it been spilling? If 3 million fish have been stocked in the past 8 years and Awoonga lost 48 000 fish over the wall for the month, percentage loss is a bit over 2%.

A 10% loss at the moment is BS in my opinion unless my math is totally up the you know what! However it's a shame to see them floating.

Thanks for sharing mate!

Cheers Dave


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Re: Dead Barra - found 100 in the Boyne River
« Reply #3 on: December 27, 2010, 06:55:43 AM »
hey dave
i added to that particular media release of 10% mortalities as it was a little bit of a arse covering figure.  it was unsure of the number that would die due to truama, but i would say the real figure would be in the vacinity of 5%.  the 66 per hour that my team and myself counted was in the peak of the event (over an 8 hour period), so i ran with that figure as it would be the maximum number that exited the dam, but the figure for the total amount was also calculated from 12:45pm on the sunday that it started to spill to present.  the frequency of the fish have slowed right down now, and is highly variable throughout the day.  as a guess and i know im going to get hammered over my estimations, approximately 15,000 have left the building to date, equating to 1,500 deaths.  gawb are assisting in the clean up to the best of their ability.

the reason for the number being so high in the initial stages of the event, is that the densities of the fish were soo great.  as you can see the majority of the fish went over the tower side of the spillway but have a crack at the pressure point created on that side.  many of the fish that have approached the dam wall were fish that resided in close proximity proir to the event, i dont think that the fish are moving too far to exit, at best from the main basin near by. 

for the equation of the fish in the dam at leagal length, i posted a pretty conservative figure of around 510,000 fish in the dam prior to the event (and that is with the maximum attrition and mortality rates).  it is hard in my shoes to push too many figures out as i have been soo busy at the moment with large volumes of fish in the hatchery, and every stocking group experiencing the same as awoonga = low demand at present.  plus for legal reasons.  i guess the guides will be an indication of their catch rates whether it is business as usual.  it will still remain the premier east coast impoundment fishery, and the flushing of these dams will contribute to the health of the waterways both above and below the walls on all trophic levels.  im keen to put that blue skeeter in that a particular guide has in the next couple of days to have a fish and if i can catch one there must be thousands left in there.

have a good break everyone and i hope this cleared a few things up.

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Re: Dead Barra - found 100 in the Boyne River
« Reply #4 on: December 27, 2010, 07:07:33 AM »
Thanks Kurt,

I thought that there were many more fish in there prior to the event, guess I over estimated :o. Over all it's not too bad then.

Have a great time on the water, you deserve the break.

Dave

 

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