Of Fin-Body Ratios and Smooth Dogfish -UPDATED

As you may have noticed from the previous post, the Atlantic States Marine Fisheries Commission (ASMFC) is proposing draft addendum to the Fishery Management Plan (FMP) for coastal sharks to bring it in line with the current Federal regulations.  These regulations are based on the Shark Conservation Act of 2010, which required all sharks fished in US waters to be landed with fins still attached… with the exception of a familiar yet under-studied species known as Mustelus canis, the smooth dogfish.  These sharks can still be finned in Federal waters as long as the weight of fins does not exceed 12% of the weight of the finless carcasses.  This exception was glaring not just because it singled out one species with a relatively limited range compared to other species in the fishery, but also brought out that seemingly absurd 12% fin-body weight ratio.  The addendum is open for public comment until March 28th at 5 pm.  With any luck, this post will help clarify some of the issues involved.

Why was this exception proposed in the first place?  Because smooth dogfish, like most elasmobranchs, keep high amounts of urea in their tissues (don’t judge, it’s how they osmoregulate) and without being bled out quickly the meat will spoil.  This argument was countered by a short grey literature paper by a Duke University grad student, which I suppose is another reason for the locals to hate Duke.  At least the argument that allowing smooth dogfish finning makes processing at sea easier is based in reality: fishermen are constantly working up the catch at sea, and time quite literally equals money for them.  It may not be the best argument, but at least it’s possible to see where commercial fishermen are coming from.

But what about that 12% fin-body weight ratio?  Where on earth does that come from?

At first glance, it might seem kind of reasonable.  Smooth dogfish tend to be relatively skinny with proportionally large dorsal fins, so it’s possible that the fins are heavier relative to the body than in other species.  Assuming that the 5% ratio that previously informed US fishery management is fairly standard, a 12% ratio might be possible for an especially emaciated smooth dogfish, right?

Skinny little smooth dog. Image by Andy Murch (elasmodiver.com).

The problem is that even the 5% ratio isn’t a great representation for a lot of the species that commonly turn up in shark fisheries.  Actual scientific measurements of fin and body weight don’t even support this as a good average for all commercially-fished sharks.  Biery and Pauly (2012) published an epic review of shark fin-body weight ratios, and found an average ratio of about 3% across most species taken in shark fisheries.  There’s a lot of variation in there, from a 1.06% ratio for the tiger shark to a 10.9% ratio for smalltooth sawfish (which is a listed Endangered Species, so can’t be landed in US waters anyway).  The oceanic whitetip shark comes in second, with a ratio of 7.34% fin weight-body weight.  This makes it the shark with the highest fin-body weight ratio that is likely to be landed at all, and it comes in about 4.7% under the ratio proposed for smooth dogfish.  And oceanic whitetips have huge fins, almost looking like a dorsal fin that happens to have a shark attached.

Look at the size of those fins. That’s what a fin-body weight ratio slightly above 7% looks like. Image by Andy Murch (elasmodiver.com)

What does the smooth dogfish come in at, according to Biery and Pauly (2012)?  About 1.7% fin-to-body weight.

But Biery and Pauly are looking at fin weight vs. whole body weight, which is not how smooth dogfish are likely to be landed (or how sharks are landed in many non-US fisheries).  It might be more useful to measure fin weight vs. dressed weight.  “Dressing” the shark means removing the head, opening the belly, and removing the internal organs.  This is done to a lot of higher-value fish to keep the meat in high quality during the trip back to port, and as mentioned earlier apparently needs to be done to smooth dogfish to keep the meat palatable at all.  Fortunately, Cortés and Neer (2006) are on it, including ratios for dressed weight in their assessment of the 5% ratio standard.  Like Biery and Pauly, Cortés and Neer found that the 5% ratio isn’t great, though their average was a little higher at 3.7-3.8%.  For the smooth dogfish, the fins came in at 3.51% of dressed body weight.  Even accounting for the standard deviation, which shows the ratio varying between 5.35 and 1.67%, isn’t even close to the 12% proposed by the ASMFC.

So where does this 12% ratio come from?  Honestly, I haven’t been able to find out, even after digging through technical papers published by the ASMFC and state agencies.  I keep seeing it come up, but have never seen a cited source.  If any readers have a lead on where, when, and how this 12% ratio was found, please enlighten us in the comments.  As of right now I can’t find a single verifiable source for this number, and yet here it is, informing fisheries policy.

Why does this all matter?  It is just one species, and even I’ve written about how smooth dogfish may be the best candidate for a sustainable shark fishery.  The issue is that it creates a massive loophole in what should otherwise be a landmark measure for shark conservation.  A 12% ratio is based on weight, not actually counting the number of fins vs. carcasses, so it’s possible to land way more sharks’ worth of fins than actual sharks.  This kind of loophole effectively made European shark management measures useless until the EU finally mandated fins-attached landings just five months ago.  Also, once fins and heads have been removed it’s virtually impossible to identify a landed shark without using genetic analysis.  Other, more protectively-manged species such as blacknose and sharpnose sharks can be easily passed off as smooth dogs once they’ve been reduced down to “logs,” and even juveniles of species like sandbar and dusky sharks would be tough to distinguish.

That’s why it’s imperative to make an informed public comment to the ASMFC.  This addendum to the FMP is in its public comment period until tomorrow (March 28th) at 5 p.m., so this is your chance to speak up about these policies.  The ASMFC is attempting to be consistent with the Federal regulations, but it isn’t hard to find fishing regulations in state waters that differ from Federal regulations.  Maintaining a lower fin-body weight ratio or (ideally) including smooth dogfish in the fins-attached requirement would be a brave move by the Commission that would show real leadership in managing this sensitive fishery.  Or they could potentially sell out the whole point of the Shark Conservation Act.  It could be your comment that makes the difference.  Democracy and whatnot.

Making a public comment is as simple as sending an e-mail to comments@asmfc.org.  Be sure to include “Smooth Dogfish Draft Addendum II” in the subject line.  It would also help to read the actual addendum to make sure you’ve got the details right.  And again I stress the “informed” part; just shooting off an e-mail that says “no shark fishing ever!” is not going to be all that helpful.  This is your time to get involved in some real, meaningful conservation.

Update – 03/28/13 11:40 a.m.

I got a response from the ASMFC (kudos to Marin Hawk, who is fielding our questions and comments) that clarifies where the 12% ratio comes from.  The 12% was proposed in the Shark Conservation Act back in 2010 (still not sure where it came from then), prompting the ASMFC to do exactly what a management agency should do and check up on it.  Using smooth dogfish landed in New Jersey, they found a fin-body weight ratio of 7-12%.  However, the sharks landed in New Jersey tended to be smaller than market size and therefore had much heavier fins relative to body weight.  What’s lacking from this analysis is smooth dogfish from North Carolina, which also happens to be the state that lands the most smooth dogfish.  Smooth dogs landed in North Carolina are also well within market size for the species, and would have been ideal for this analysis.  Unfortunately the meeting where this research was presented occurred in February, and smooth dogfish don’t start appearing in North Carolina waters in fishable numbers until late March-early April.  While good to see that, at least on ASMFC’s end, the ratio is based on some science, it’s still very much valid to question whether it’s the best available science.


Biery, L., & Pauly, D. (2012). A global review of species-specific shark-fin-to-body-mass ratios and relevant legislation Journal of Fish Biology, 80 (5), 1643-1677 DOI: 10.1111/j.1095-8649.2011.03215.x

Cortes, E., & Neer, J.A. (2006). Preliminary reassessment of the 5% fin to carcass weight ratio for sharks Collected Volumes of Scientific Papers – ICCAT, 59, 1025-1036


  1. Sonja Fordham · March 28, 2013

    Thanks for this, Chuck. You bring up many great points. Apologies for the lengthy post, but I have a couple of points of clarification that I think are important:

    First: I think in your post you are at times using “finning” (as some do) to refer to the practice of removing the fins at sea during processing . In a policy context, however, “finning” is usually defined as slicing off a shark’s fins and discarding the body at sea. This practice is prohibited in US state and federal waters regardless of species. What is at issue (at least in my post on the ASMFC smoothhound shark proposal) is the method for enforcing finning bans, which usually comes down to keeping fins attached vs. using a fin-to-carcass weight ratio limit. Most find the former much more reliable and also better for data collection purposes.

    Second: NMFS is still working on implementation of the Shark Conservation Act savings clause, which includes rather confusing text on smoothhounds and a 12% ratio. That and related smoothhound management issues are reviewed in this federal register notice: http://www.gpo.gov/fdsys/pkg/FR-2011-11-10/html/2011-29180.htm

    Most important, until NMFS implements a different regulation, the status quo finning rule applies for federal waters (3-200 miles off the US east coast): ALL sharks must be landed with their fins still naturally attached. The exception for smoothhounds is currently only offered under the ASMFC shark plan (in which case a 5% fin-to-dressed-carcass ratio applies, unless individual states have opted for stronger rules).

    The ASMFC is therefore not (as you suggest) attempting to come in line with NMFS rules on fin removal, but rather appears to be trying to get a jump on them by interpreting the federal legislation (or anticipating a particular interpretation) themselves, which could mean a hefty increase in the state waters fin-to-carcass ratio for smoothhounds (from 5% to 12% of dressed weight).

    Because NMFS implemented the federal Atlantic fins-attached regulation in 2008, about the time that the ASMFC was creating a smoothhound exception to their fins-attached rule, I can’t see how (as you suggest) this next addendum is an opportunity for ASMFC to show finning policy leadership (except maybe to Canada). They should, however, in my opinion, reconsider their proposal and follow the rest of the country (and most of Central and South America plus the EU, etc), by embracing the “fins naturally attached” method as the best practice for enforcing finning bans — for all shark species. I am hopeful that hearing from a lot of people who oppose the 12% ratio and support instead a coast-wide ban on at-sea shark fin removal, without exceptions, will be a good start in that direction.

    Thanks for encouraging that voice.

    • Chuck Bangley · March 29, 2013

      Thanks for those clarifications Sonja. Hopefully all these public comments get them to at least re-examine that 12% ratio.

  2. lane · April 18, 2013

    Chuck I am a commercial fisherman and can explain why the smooth dogfish is excluded. It is because the smooth dogfish is the only commercialy caught shark that both of the pectoral finns and both dorsal finns are landed. Smooth dogfish are not at risk of being finned and shoved back over the meat is a large portion of the profit unlike a hammerhead were use to the finns would go for $25 a pound the smoothdog finns are only $2 that is a dramatic differance. Normaly the smoothdog finns run about 9.5% of the carcus wieght landed. Most of the research is only on the dorsal finns thats why the numbers do not look right.

    • Chuck Bangley · April 24, 2013

      Interesting. According to the Biery et al and Cortes et al papers, their fin:body weight ratios come from the “primary fin set,” which includes the first dorsal and pectoral fins and bottom lobe of the tail. However, that isn’t necessarily how some state and regional agencies have been keeping track of it, and those papers do dig into a lot of different sources for their data. Definitely worth looking into. Thanks for the insightful comment.

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