WLF commission meeting

[redchaserron]

Originally Posted by MathGeek

The weir management plan is reasonable and based on sound science. Since they took over management of the weirs in 2012, CPRA has done a very good job managing the weirs according to the management plan. CPRA has been kind enough to share detailed weir opening data with us that has allowed us to compute correlations between the condition of finfish in the lake (specks, redfish, drum, and gafftops) with the weir openings.

The most consistent and strongest correlations between our data on fish condition and any environmental factor we've considered are the NEGATIVE correlations between weir openings and fish condition. In other words, the more the weirs are opened, the thinner the fish are. The attached graph completely disproves the hypothesis that weir closures somehow negatively impact fish condition. The asterisks denote statistical significance at the p < 0.05 level.

Our working hypothesis to explain the NEGATIVE correlations between weir openings and fish condition is based on an analogy with rotating pastures to maximize the forage available for cattle. If the gates between pastures are open all the time, cattle graze all the pastures continuously which results in less production than limiting the pastures that can be grazed and opening the gates occasionally. As applied to the weirs, the idea is that the marsh behind the weirs produces more forage if more separation is allowed to reduce feeding pressure from the finfish until the crop of forage has achieved a larger biomass.

In any event, there is no scientific basis to complain about CPRA's management of the weirs. The biggest issue relating to Big Lake that is within regulatory control is the overharvesting of oysters.

MG,

Thanks for posting the information from your study. Is it possible, and has consideration been given to the idea that the difference in condition of the fish during open and closed periods may be due to a change in WHAT they are feeding on? If for example open weirs provided easy pickings on shrimp so the fish avail themselve of it, but when the weirs are closed they feed more on menhaden and finfish, it could be a matter of the fish being thinner when the weirs are open becasue they are taking advantage of easy prey that is lower in nutrients verses eating more nutrient dense food.

[MathGeek]

Originally Posted by redchaserron

MG,

Thanks for posting the information from your study. Is it possible, and has consideration been given to the idea that the difference in condition of the fish during open and closed periods may be due to a change in WHAT they are feeding on? If for example open weirs provided easy pickings on shrimp so the fish avail themselve of it, but when the weirs are closed they feed more on menhaden and finfish, it could be a matter of the fish being thinner when the weirs are open becasue they are taking advantage of easy prey that is lower in nutrients verses eating more nutrient dense food.

That could be. But note that our correlations are not between fish condition and whether the weirs were open the day a fish was caught, but rather our correlations are between fish condition and the average weir openings over the 90 day period immediately before each fish was caught.

But thanks for the idea, we need to give more consideration to whether weir closures forces the fish to feed on more nutritional forage.

[redchaserron]

Originally Posted by MathGeek

That could be. But note that our correlations are not between fish condition and whether the weirs were open the day a fish was caught, but rather our correlations are between fish condition and the average weir openings over the 90 day period immediately before each fish was caught.

But thanks for the idea, we need to give more consideration to whether weir closures forces the fish to feed on more nutritional forage.

[QUOTE=MathGeek;780718]That could be. But note that our correlations

How much influence do you think the seasonality of the opening/closing of the weirs have to do with it. For example, the weirs are more likely to be closed in July - August than in April/May. Obviously there are some seasons where fish will weigh more or less Did you compare same season openings/closures?

[MathGeek]

[quote=redchaserron;780724]

Originally Posted by MathGeek

How much influence do you think the seasonality of the opening/closing of the weirs have to do with it. For example, the weirs are more likely to be closed in July - August than in April/May. Obviously there are some seasons where fish will weigh more or less Did you compare same season openings/closures?

All of our studies are in the same period each year (late May/early June). Seasonality can affect fish body weight, but we are comparing with the long term Louisiana average weights from the same time of year for each species.

The weir openings are more governed by salinity than season. For example, the average 30 day weir openings over our study period (same time each year) has varied from a low of the weirs only being open 15% of their maximum possible to a high of about 70%.

Weir openings and closures in July-Aug do not impact our study at all, because all our fish are measured in late May/early June and we only consider the weir openings in 30, 60, and 90 day windows before each fish was weighed and measured.

[redchaserron]

[quote=MathGeek;780737]

Originally Posted by redchaserron

All of our studies are in the same period each year (late May/early June). Seasonality can affect fish body weight, but we are comparing with the long term Louisiana average weights from the same time of year for each species.

The weir openings are more governed by salinity than season. For example, the average 30 day weir openings over our study period (same time each year) has varied from a low of the weirs only being open 15% of their maximum possible to a high of about 70%.

Weir openings and closures in July-Aug do not impact our study at all, because all our fish are measured in late May/early June and we only consider the weir openings in 30, 60, and 90 day windows before each fish was weighed and measured.

Ah, I see now, I thought it was an "all year" study. My saying the weirs are more likely to be open in spring than August July, is simply an observation that we tend to get a lot more rain/lower salinity in spring than mid/late summer.