Why is the conductivity of NaCl, NaBr and NaI decreasing with temperature?

I collected the conductivity of NaCl, NaBr, and NaI from 30 celsius to 80 celsius. I used the solutions mixed in water.
In all instances, the conductivity seemed to reduce as the temperature increased. I am unsure if it was an experimental error, or if my results actually make sense. Please state your reasons for thinking its an error or not.


Experiment Details: 50 ml, 0.1 molar of all solutions. I used vernier sensors for detecting the temperature and the conductivity.


For this experiment, I had a 50ml beaker on a hotplate and had the conductivity and temperature vernier sensors dipped in the liquid.
(I made sure the sensors are only touching the solution and not the bottom of the beaker). Then, I just waited for the hotplate to heat up the liquid to 80 Celsius.


From research, the opposite seems to be accurate, but I have conducted many trials giving the same trend of decreasing conductivity.
Source: <https://link.springer.com/article/10.1007/BF02877571>


(This is my first question, please let me know any other details that would be required to answer this question )


