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Discussion Starter · #3 ·
Definitely an eye opener and well-reasoned. At the least, it speaks to the need to better understand cownose ray populations before reflexively trying to cull them.

I found this piece of the article most interesting:
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Fishermen and locals often cite large herds of cownose rays as evidence that their populations are doing just fine. But, of course, that’s what the Brazilians thought when they started shipping their cownose rays to Korea in the 1980s.

Brazilian cownose rays were once plentiful, also appearing in schools that numbered in the thousands. From 1982-1985, these rays filled seine nets off Rio Grande do Sul, with hundreds to thousands caught in each haul. At first they were considered trash fish and tossed, but when the fishing community realized that the rays were considered a Korean delicacy, they began keeping their ray landings, and the Brazilian cownose ray market flourished. Then, the rays disappeared. By the early 2000s, just a couple decades after the fishery began, the animals could no longer be found in their native waters off Rio Grande do Sul. The Brazilian cownose ray is now listed as endangered, but the IUCN notes that the rays may actually be critically endangered . . .
 

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Good enlightening article, but one thing I would like to know is the effect on crabs. The study showed the impact to oysters and clams but did not mention crabs. Why

Chris
 

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I have to do some research on the authors - seems a touch too much tree hugging for me - likely tied into protest group against the bow fishermen.

Funny how Bull sharks were not included. Cownose rays are one of Bull sharks preferred food sources - one reason they come into the bay in summer.
 

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Discussion Starter · #7 ·
Skip, I don't know anything about the authors or their connections/interests. But one thing I've learned in years of analyzing expert reports for my job is that motivation and even bias are not the super-relevant factors that they are made out to be on TV. The reality is that even a biased person can put together a scientifically sound study that leads to factually sound conclusions.

The important thing is that, just as the authors did in the original study, the authors of this study have placed their methods, data sources and reasoning out there for public scrutiny. They clearly articulated the fact-based reasons for why they found the previous study lacking, and its conclusions suspect. By doing this, they have allowed all of us, but especially the scientifically trained, to analyze and critique their methods and conclusions. That's how we improve our understanding of things, not be getting sidetracked by motives.

For my own part, this article underscores what I have previously read and suspected; that at the very least, we ought to learn more about ray populations and ray diet before embarking on a campaign to kill as many as possible. The Chesapeake evolved with rays, so it's likely that the ecosystem would suffer if their numbers became too low.

As for bull sharks and rays, the article did not specifically mention bull sharks, but are you sure the study did not include them in analysis? I'm not aware of a bull shark stomach contents analysis that found rays to be a major component of their diet, but maybe such a study exists.

BTW, here's some recent background on the study's author. I haven't tried to research him, but at first glance, he seems well-respected and not some Sea Shepherd zealot.: http://elasmo.org/pub/Grubbs AES Candidate Statement.pdf
 

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I'm pretty sure this is not correct: Cownose rays are one of Bull sharks preferred food sources - one reason they come into the bay in summer.

bull sharks follow many food sources & are the only shark able to tolerate full fresh water. Lake Zambezi sharks, nicaragua sharks & sharks in the Mississipi are all the same: Bull sharks.

Bull sharks enter the bay following many food sources, and have minimal competition because they are the only shark who can tolerate fresh water. I've had more than 1 shark course taught by the worlds foremost shark expert Eugenie Clark (now deceased), & studied bull sharks, and 99% sure cnr are not a preferred food source.
 

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One thing of interest is that Ransom Myers died in 2007 from a brain tumor, however, this article is dated Feb 24. 7 years is a very long time to wait to publish a deceased authors' work. The aricle is the kind of thing myers would write, as he warned against overfishing of several species.
 

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Dasher: Ransom Myers is quoted from the 2007 press release of the original 2007 paper in Science. The current article is referring to that press release and surrounding response to the paper as evidence of how widely accepted the 2007 paper was at the time. Of course getting published in Science helped a lot.

Skip: this new paper has 8 authors. Lead author and one other are at Florida State Univ Coastal and Marine Laboratory, one is at Virginia Institute of Marine Science, 4 are at various NOAA labs (including the corresponding author...a good hint who likely lead...and perhaps funded...the research), and one is at the USGS. There certainly can be biased folks at all of those places (or anywhere else), but overall I see this as a solid lineup of serious academics and professional experts in their field.
 

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Discussion Starter · #14 ·
I did some more reading on the bus ride into work this morning! Recent studies, that can be easily found by Googling, show the following:

(1) Neither oysters nor crabs are the major diet source for cownose rays in the Chesapeake. They prefer soft-shell clams and mussels, followed by worms and other soft, bottom-dwelling animals.

(2) Like other predators, they are opportunistic and will eat all manner of bottom-dwellers, including oysters and crabs, if they're available and their preferred food source is not.

(3) However, even when rays were captured on commercial oyster grounds, their stomach contents showed a preference for soft clams and mussels -- the rays appear to make an effort to find non-oyster prey among the oyster grounds.

(4) This is likely because the bite force of a ray cannot easily crush a mature oyster, at least not without a lot of expended energy. Even with spat-on-shell, rays appear to prefer other food, perhaps because the energy expended to eat the spat outweighs the energy obtained from it. The most vulnerable oyster population is juvenile, post-spat oysters. It's possible that a herd of rays could decimate an aquaculture reef dominated by oysters at that stage. On the other hand, real-world accounts of rays actually preferring juvenile oysters has yet to bear out.

(5) I found less research on the impact of ray predation on crabs, but this may be because stomach contents from sampling have yet to place a strong link between rays and crabs as a preferred diet. Like with oysters, it's probably true that if rays entered an area where their preferred food was unavailable but crabs were abundant, they'd go to town on the crabs. But that prey-predator scenario is true wherever ecological imbalances occur, and could be said of striped bass, sharks, drum, etc. At least from the study summaries I've read, rays do not appear to be focused on crabs.

Of course, now that more serious research is being focused on cownose rays, we're likely to learn new things.
 

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I compare cownose rays to carp. Both put up a good fight, are not very good to eat, there are too many of them around, and are more or less a nuisance to fishermen.
When I am fishing down in the back bays of Ocean City and a school of cownose rays come by, the fishing immediately shuts down. I've seen schools of probably a thousand rays at times 2 summers ago under and around the Rte 50 bridge. It was unbelievable.
 

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Goose - I wonder how the clam population is ? I know price of razor clams is sky high. This might force the rays to look at other food sources.

Other thing not mentioned is how badly the rays can stir up the shallow waters as they root for food.

I might be way off but I see too many rays as bad news for our bay. I think if you ask anyone with 20 or more years on the bay - they'll tell you how the ray population has exploded.
 

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Goose - I wonder how the clam population is ? I know price of razor clams is sky high. This might force the rays to look at other food sources.

Other thing not mentioned is how badly the rays can stir up the shallow waters as they root for food.

I might be way off but I see too many rays as bad news for our bay. I think if you ask anyone with 20 or more years on the bay - they'll tell you how the ray population has exploded.
I have been fishing the bay far more then 20 years and can remember years (a stretch in the mid sixties) when there was an explosion in the Ray population in the bay.
 
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