First published in Landings, February, 2017

The commotion about cod bycatch has died down since the Marine Stewardship Council wrongly estimated in 2013 that 177,000 cod broke the surface in lobster traps each year. At the time, the New England Fisheries Management Council was preparing for a vote to close new areas sensitive to cod spawning. The Council voted against the measure, 14-1, prompting a sigh of relief from lobstermen and a sigh of discontent from groundfishermen. The problem with the estimate, as Department of Marine Resources Commissioner Patrick Keliher stated at the time, was that it didn’t take into account different parts of the coast, different depths, and different seasons of fishing; instead it more or less just scaled up a small amount of offshore data.

A cod in a University of Maine lobster trap.
Photo by R. Boenish

I came to the University of Maine in 2014, to begin a project looking into the fate of cod bycatch in the Maine lobster fishery. The late Captain Cappy Sargent of Milbridge took me aboard his boat to get a feel for what lobster fishing was like. Before I was a fish scientist, I was a commercial fisherman, having spent nine summers fishing for sockeye salmon in Alaska’s Bristol Bay and one year fishing for Dungeness crab near my hometown on Whidbey Island, Washington.

Soon, other lobstermen took my lab mate Jocelyn Runnebaum and myself aboard their boats and were kind enough to let us run a cod and cusk discard survivability experiment. Some of the highlights for me were working with lobstermen from across the state, including Justin Papkee, Dustin Delano, and Bobby Ingalls and learning “wicked” lobstering strategies. The goal of our ongoing study is to quantify the extent of barotrauma (pressure trauma) cod and cusk undergo when hauled up from the bottom in a trap and to figure out the best handling procedures to return the fish with minimal harm.

Some fish undergo the reverse of what divers call “the bends” when coming from depth rapidly. It works out that for every five fathoms in depth, pressure is one atmosphere greater ( for reference, pressure is roughly one atmosphere unless you are underwater or on top of Mt. Katahdin). We were testing the idea that if we could recompress the cod as a trap sinks back down, we might be able to reverse the barotrauma. We attached a GoPro camera and an LED light inside a trap. When a cod came up in a lobsterman’s trap, we would tag it, take measurements, evaluate its health, then put it in our rigged trap, throw it back, and wait.

We hypothesized that the reason cod swim into the trap either had to do with perceived shelter (lobster traps are nice looking houses to a fish), or food supply. In reality, the truth is likely a bit of both. Many types of bait are fished in different seasons and parts of the coast, but among the most common is herring, which happens to be one of the most energy-rich foods for cod. We saw a wide range of cod sizes in our study, but most were around 18 inches, which is the size at which they shift from eating invertebrates to mainly fish prey.

Overall what we found is that most cod don’t show severe signs of external barotrauma (i.e. stomach sticking out the mouth, bugged out eyes, or skin bubbles). Only about 10% of cod hauled initially were dead, and these were mostly due to hungry lobsters in the trap. Of those remaining, most of the cod looked vibrant and swam around the video trap when recompressed. The GoPro footage suggested cod could be recompressed and swim around inside the trap, but could not find their way out of the trap over the few hours when the GoPro operate

I released some of the cod at the surface, and most could swim down. However, with this method we don’t know a lot about what happens to cod internally after they are surface-released. That being said, our results are encouraging and suggest that if cod are handled properly, a large proportion of them may be able to survive. This will be important if management decisions down the line include cod as a bycatch in the lobster fishery. Often managers make an assumption of 100% mortality, so any reduction in estimated mortality rate would be advantageous. The Maine lobster fishery is one of the cleanest fisheries (in terms of bycatch) around and it is no accident that it has a reputation for marine stewardship.