At the end of the day, Fisher are different from Miners and Botanist. The latter two may choose between several items, while Fishers are more subject to chance. So a Botanist or a Miner may choose to harvest shards, or stick to the other items if that's what they need. A Fisher might be farming for a certain type of fish, and thus getting shards can turn out as a drawback that slows him down. At the same time, gaining both shards and fish will overpower them.

But since Fishers rely on the kind of bait they use, how about being able to use nets? Where nets will gather shards...? Or something...