Seahorses have never really been my thing, I haven't had time to look at the petition in detail, although from my limited knowledge of this seahorse, it seem common in areas with healthy seagrass populations. I think the CBD might be trying to protect habitats through species listing. There is a strong relationship with habitat loss and endangerment for terrestrial species, and a strong relationship between over exploitation and conservation status in marine species. Perhaps near-shore habitat bound species are more similar to terrestrial species in this case. So really any species that is dependent on healthy seagrasses as their habitat are likely to be under similar endangerment status [if any] as this seahorse. It has nearly direct development so, I don't think they travel very far as pelagic fry. As for the fishery for seahorses in the US, it is small, but CITES increased is value by several orders. The domestic wild aquairum based trade is mostly for the H. erectus and curio (dried used for decoration on lamps and such) is based mostly on H. zosterae. From my memory of management workshops the curio fisherman in Florida were using push nets to catch H zosterae, and almost all of the H. erectus come from bait shrimp trawlers as by-catch.
From a quick read of the report just now, I'm always interested in the data treatments. They suggest there is a lot of trade in the drawf seahorses for aquariums and then list several companies that sell them, many are aquaculture operations, then they list the landings from FWC on there, which are nearly all curio landings, which has nothing to do with the aquarium trade, other than the fact that FWC lumps the curio and aquarium trade together in their database. Worst of all they cite growing demand based on a 2001 paper, then cite other old papers, which are great for historical information but terrible for forecasting anything. We all know that the aquarium trade is a different animal from 10-15 years ago when that data used might have been relevant. It seems lot of these reports I have been reading are stuck in the pre-CITES seahorse trade. This one is just that.
Now the habitat loss issue, that is a real issue, the seagrass is in trouble and has been for a long time, all of that is from all of the over development, runoff and discharges in Florida. The Indian River Lagoon use to be clear and full of seagrass, now its murky and devoid in many areas.