Effects of Drought on Bass in Lake Samsonvale.

[rayke1938]

At the PRFMA meeting David Roberts, the Fish Scientist for SEQWater ,gave a very interesting talk on the above subject. I thought that I would share my memories of the talk (with some edits from David).

David has been conducting research on Lake Samsonvale for the past eight odd years and has a wealth of data on which to draw. One interesting fact was the change in the length to weight ratio of Lake Samsonvale fish over the past five years since the drought has really hit hard and water levels dropped to only 15% of full supply. During the 2005 surveys, the average weight of a 44cm bass was 1.9kg. During the follow up surveys in 2007 the average weight of a 44cm bass fish had fallen to 1.4 kg, loosing half a kg in weight. In David’s opinion this is likely due to the low water levels and lack of food for bass. The weed beds in the dam completely dried up in 2005 and as a consequence the food chain diminished with a large reduction in food such as shrimp, redclaw, bony bream etc. With the recent increase of water levels the bass are starting to fatten up again with a 44cm fish weighing around 1.7kg.

The only fish not affected by the drought were tilapia and bony bream. This has something to do with their ability to eat mud and still thrive.

Comparing bass in Lake Samsonvale to other dams, in 2005 Samsonvale bass were approx 25-40% heavier than the next big bass dams like Wivenhoe and Somerset. Compared to some of the other popular bass lakes, bass in Lake Samsonvale are on average 2 and half times bigger than some of these lakes.

The reason ? Probably the quality of the food in the lakes but this will be subject of research in the coming years.

He also spoke on the gradually diminishing size of bass being caught in many other bass impoundments over the last few years and the need for some research into why this is happening and how to prevent it.

Another matters raised were:-

The survival rates of different years of stocking with some years apparently having poor rates.

The possibility of modifying stocking practices to allow better tracking of each stocking event.

Using the bass ‘ear bones’ he showed that the average age of a 50cm impoundment bass was up to 14 years old.

He finished the night with a demo on how to remove the ear bone from bass so that anglers could kept these bones to help in the effort to understand and better manage stocked fish.

He had to defer on speaking on noxious fish and weeds in the dam until another night.

I had this vetted by David and he has made some alterations and given me permission to use his material in this post.

Cheers

Ray

[Do$tylz]

some good info in there Ray.... What would make food quality better in samsonvale?? wouldn't they all eat the same type pf boney bream, bugs, redclaw and shrimp??

I wonder what their average size vs weight will be in 6-12 months time... hopefully they'll just be footballs

[Angus]

Very good info Ray thanks.

Hopefully we get some big ones Monday. To help with the study of course

[rayke1938]

Do$tylz wrote:

some good info in there Ray.... What would make food quality better in samsonvale?? wouldn't they all eat the same type pf boney bream, bugs, redclaw and shrimp??

I wonder what their average size vs weight will be in 6-12 months time... hopefully they'll just be footballs

When there is no weed there is nothing for the plankton,shrimp and redclaw to eat so there is a much reduced foodchain.

Cheers

Ray

[mick fillet]

Very interesting read ray cheers.

I would be interested to know how the ear bone was removed. I would like to see this being done so I could have some insight of what goes on in the world of a researcher.

[Schmuck]

Interesting stuff, I wonder when/if they'll publish anything official?

For once it would have been fun to gather data

[EMP]

Very, very interesting Ray. Thanks for the info.

EMP

[shayned]

One way the guys fishing NPD can help is to keep an eye out for tagged fish recaptures. At a minimum record the tag number, the date and the total fork length of the fish.

The total fork length is the measurement from the "nose" of the fish to the edge of the concave section of the tail, this method gives the most reliable length measure as this section of the tail typically has less chance of having damage on it and you don't end up with the situation where people sometimes bend one tip of the tail to maximise a fishes length.

It's up to you whether you decide to return fish to the water and I would suggest returning tagged fish so they can be recaptured will help generate more helpful data. If you do decide to keep the fish try also to get an accurate weight measure.

[BrisBassMan]

Reckon all the grass that is now decomposing in the water will help the food web along. From the zooplanktons all the way up.

cheers