Here's a usage overview for the -form in Japanese.
Usage 5 is summarised as "Means and Method":
> (I will buy a daikon and then I will make oden.)
>
> **** (I will make oden with daikon.)
> (I will work and then I will buy a new PC.)
>
> **** (I will buy a new PC from my salary.)
With this usage, you're right to interpret the sentence as "He goes out fishing to support his parents."