As you say Paul, laws are for everyone so when they are framed there is not a need to make reference to any particular sector of society.
It may be correct to infer that most fish theft is carried out by immigrants but why as the wording of this petition suggests should only these immigrants be subject to severe penalties?
I may have this wrong but according to the 1968 Theft Act we already have severe penalties in place for those guilty of fish-stealing (in the case of commercial fisheries, club-owned lakes etc.)
According to the Act,
?Wild creatures, tamed or untamed, shall be regarded as property?
and
?A person guilty of theft shall on conviction on indictment be liable to imprisonment for a term not exceeding seven years.?
It seems to me that regardless of the ethnic origin of these thieves, the law is already pretty robust. Perhaps the problem is one of enforcement, eg convincing the police to take these thefts seriously.
With regard to fish ?theft? from rivers, I believe a change in the law is already in the pipeline, but I fear once again that the problem will be convincing the EA and police to enforce it.