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A Tale of Two Cod
This piece was originally published on the New England Ocean Odyssey blog.
The almighty cod – the most legendary fish in our New England waters. Atlantic cod is greyish-green, and a renowned dweller of the Gulf of Maine. It is a staple of our traditional cuisine and a historic driver of our economy. You‘ve seen an Atlantic cod, right? But have you ever seen a red Atlantic cod?
How the red cod got its color is a mysterious tale, and one that even dedicated Gulf of Maine fish researchers don’t fully understand yet. Red cod live throughout the North Atlantic, in discrete populations. The red cod you see in these photos, pictured along with the traditionally colored “olive cod,” live on Cashes Ledge, about 80 miles off the coast of Gloucester, Massachusetts. They are the same species of fish, but they don’t fraternize much. The red cod and olive cod seem to be on different reproductive schedules. They also eat different things and have different ranges. Olive cod like to wander around the North Atlantic, but red cod tend to hang out in one place – “shallow, kelpy habitats,” according to Graham Sherwood, Research Scientist at the Gulf of Maine Research Institute in Portland, Maine. Shallow and kelpy is just where Brian Skerry found these red cod – in fact, in about 40 feet of water. Well, it was shallow for cod, anyway.
Why are they red? The food red cod eat, things like crabs, lobsters, and worms, are high in carotenoids – naturally-occurring chemicals which give the fish the ability to turn red. Not all cod that eat these things DO turn red, though – deeper dwelling olive cod remain traditionally cod-colored even on a high-carotenoid diet. Sherwood speculates that there might be an adaptive advantage to the red coloring for shallow-living cod. Perhaps the shallow water cod need better U/V protection. Or, more likely, it makes it easier to hide in all that red kelp.
There haven’t been any studies yet to indicate whether or not red cod are genetically distinct from olive cod. It’s possible that a red cod and an olive cod could come from the same parents, but be different in appearance and behavior due to having hatched in different habitats. One deeper and darker, one shallower and kelpier. Possible, but unlikely, says Sherwood. He thinks that, while they are the same species of fish, they may be genetically different enough to look and behave distinctly from each other. Maybe different populations of cod began spawning at different times, to take advantage of optimal environmental conditions, and over time they differentiated into the red and olive types. But, nobody knows for sure yet.
The color and habitat preference aren’t the only differences between the cod. Red cod are less streamlined than olive cod – no need to be shaped like a sports car if you’re just going to hang out in the garage. They also have shorter snouts than olive cod. Although, says Sherwood, if it weren’t for the color difference you would have a hard time telling them apart. Maybe because these fish tend to be homebodies, hanging out in remote places like Cashes Ledge, or in shallow inshore waters that are not targeted by fisheries, we’re less likely to run into them. Brian, a 35 year veteran of diving in the Gulf of Maine, says they are unlike anything he has ever seen.
The red cod are just one example of the amazing biological diversity that is found at Cashes Ledge. We can’t wait to show you more as our Ocean Odyssey continues!