This is certainly some big #news from the #IUCNcongress today, with the release of their latest ratings of tunas, sharks, rays, and other species. @IUCNRedList is hoping to soften the concerning news about sharks and rays with better tuna news but... 1/
Some of the new ratings mask serious concerns with unique populations of yellowfin and Atlantic #bluefin. Concerns that are substantial enough that I (a tuna conservationist - yes that is a thing!) am having trouble celebrating. 2/
To be clear, the tuna team did not really get things wrong. The issue is that the IUCN standard requires experts to examine population trends and status at the species level, meaning a genetically distinct population could be crashing, while the species is doing ok. 3/
Here are two examples: western Atlantic bluefin and Indian Ocean yellowfin. Both *species* were just moved to be species of Least Concern. Not Vulnerable. Not Near Threatened. Least Concern. But these two *populations* are of substantial concern. 4/ 
The western Atlantic bluefin population is naturally about 10% of the size of the eastern pop. The pop is currently only ~15% of its historic size. It is very likely overfished. And it is being overrun by individuals of the eastern pop, which is doing quite well. 5/
In fact the eastern pop is doing so well that the good people over at @IUCNRedList's tuna/billfish specialist group have upgraded the entire species to one that is no longer of concern. Meanwhile, the western pop is at risk of being entirely lost. And that would be really bad. 6/
The western Atlantic bluefin population is likely more resilient to climate change than the eastern pop and if something tragic happened to the population in the east, it would be a shame to look back and realize that we should not have allowed the western pop to be lost. 7/
Ask me about the confusing nature of the western population's scientific assessment, if you want to know more. 8/
Regarding yellowfin, the populations in the Pacific seem to be doing pretty well and the pop in the Atlantic is at least ok. These bits of good news mean the species rated as Least Concern. But the population in the Indian Ocean? Poorly managed and on the brink of collapse. 9/
That does not sound like a Least Concern to me. Again nobody necessarily got anything wrong - it's just not always useful to look at these species-level ratings and conclude that all is well. 10/
This nuance also means that when a species is determined to be in bad shape by these ratings, then that is *really bad* news. It means either all populations are doing poorly or some population is doing so badly as to mask another pop's growth. 11/
So the news that now fully 37% of sharks and rays are either Vulnerable, Endangered, or Critically Endangered is highly concerning. I encourage you to ask more about that as well, and there are lots of great shark experts on twitter to help you out. I can point you to some. 12/
It's not talking out of both sides of my mouth to say that you should dig into positive changes to IUCN ratings to find out the nuance while also taking negative changes to be a sign of really bad news. Hopefully this thread helped to explain why. 13/
One final point. IUCN ratings are meant to examine species' extinction potential. For marine fishes, that may not be the most useful metric. The team upgraded Pacific bluefin to Near Threatened because it has been in its current heavily overfished state for so long. 14/
That is despite the fact that the population is at only 5% of its historic size. The thinking is that if it has been maintained at such a low pop size for so long, its *extinction risk* must be low. But that means there is only 1 adult out there for every 20 there used to be. 15/
Again, I trust that the team followed the @IUCNRedList standard to the letter. It just might not be the best standard for a fish like a tuna. 16/
If you are writing a story about the new ratings and leading with something about the positive shifts in tuna ratings (especially if you are leading with something about Atlantic bluefin now being Least Concern), please reach out. Part of my job is talking about this stuff. 17/17
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