Friday, November 22, 2013

Thank you, cod!

Aquarium scientists run investigations here on Central Wharf and travel around the world studying marine habitats and helping find solutions to some of our oceans' most challenging problems. Thanks to the recently renovated John H. Prescott Marine Laboratory, Aquarium researchers are engaging in a series of important studies that they will be posting about here on the Global Explorers Blog. This post comes from Lauren Giglio and features work on discard mortality in Gulf of Maine Atlantic cod.

Here in the John H. Prescott Marine Laboratory at the New England Aquarium, we (Dr. John Mandelman and his research team) have been studying key questions that aid the management and conservation of certain vulnerable fish populations. Our chosen species of late? A New England favorite: Atlantic cod (Gadus morhua).

Atlantic cod (Gadus morhua), swim under a shipwreck laden with invertebrates in Stellwagen Bank National Marine Sanctuary | Photo: NOAA via Wikimedia Commons

Unless in relation to a yummy looking recipe on your favorite restaurant menu, this fish may have not crossed your mind much; however, New Englanders have a lot to be thankful for when it comes to cod. For hundreds and perhaps thousands of years, this species has been an important dietary staple of the people native to the region now known as coastal New England. The Native Americans used bone crafted hooks and natural-fiber nets to catch this local fish. When European explorers first began venturing across the Atlantic to the “New World”, arriving exhausted after enduring painfully long journeys, they needed food…badly. When they turned to the ocean as their food source, some described the cod they observed as equal in size to them! As such, this fish, which was plentiful at the time, quickly became a hot commodity. Eventually, this led to the settlement of Europeans on a nearby cape extending from the easternmost point of Massachusetts, mapped and ultimately coined “Cape Cod” by John Smith (Kennedy, 2009).  Indeed, we in New England owe this iconic species its due. Unfortunately, however, the cod populations have not fared very well in recent years, and the once vast fishery has collapsed.

The bold black line on this graph shows the total commercial landings (in metric tons) of Atlantic cod in the Gulf of Maine from 1892 to 2011. In striking contrast, the gray polygon in the upper left indicates the estimated landings from 1861 to 1880 based on analysis of historical data (Alexander et al. 2009). Figure from NEFSC 2013.

If any of you have a love for fishing—whether it be to cash in big at a local fishing tournament; to put a meal on the dinner table; or to just enjoy the environment of the open sea—chances are that while gathering your catch for the day, you’ve probably thrown something back that you either didn’t want, or weren’t allowed to keep, before calling it a day. These things that get thrown back after being caught (e.g. undersized fish) are collectively referred to as discards. The cod fishery has seen its share of discards over the years, including an estimated 2,289 metric tons of it in 2010 alone for recreational fisheries in the Gulf of Maine (NEFSC, 2012)! When you and your friends go out to sea for a fishing trip, you are legally obligated to follow restrictions specific to certain species. With cod caught for recreation (i.e. not in the commercial fishery), for example, you can only keep a certain number of fish per day, and they must all be of a certain size. But what happens to the cod that do not fit those restrictions? Well, they are simply released back into the ocean to go about their day.  …Or do they?

“What Happens to the Rest?” Illustration by Lauren Giglio, 2013

Unfortunately, the experience of being thrown back into the ocean after being caught isn’t necessarily bliss. Being captured and handled by a person can be quite stressful for the fish.  Some of these stressors include physical injury due to hooks, rough handling, air exposure on deck, and temperature changes as they rise to the surface of the sea. The accumulated effects of these stressors also make fish more vulnerable to predation after being thrown back into the sea.  All of these stressors negatively impact the fish’s chance of survival, sometimes resulting in death after the fish is back in ocean (known as “post-release mortality”); but how many succumb to this fate? Because of the nature of fish (“Just keep swimming, just keep swimming…” –Dory, Finding Nemo), it is quite difficult to determine the exact percentage of fish that die after being released back into the open water. At the same time, it is very important to have this estimate to help inform management decisions, future stock assessments, and best fishing practices (to help reduce the number of fish that die in the future). At the present time, the estimated number of cod that die when caught by recreational hook and line fishing is purely guess work, calling the need for a study to address this.

This is where our team, which includes collaborators from the University of New England, Massachusetts Division of Marine Fisheries, and hook fisherman Marc Stettner, step in. Our research studies the health effects and the mortality rates of sub-legally sized cod that are recreationally caught and released. By studying these effects, we gain a better understanding of the fate of these animals after they are released and how to alter fishing methods in order to reduce injury/stress for released animals. Through a variety of modern tracking techniques, we will follow the life of tagged cod in weeks and even months following capture in order to answer the question of how they behave and whether they live or die as a result of these handling/fishing methods. Results of this study will lead to two positive outcomes: first, to better estimate the post-release mortality rate of the species in this fishery, and second, to develop a “best capture and handling practices” guide to be distributed to the recreational fishing community to help promote strategies that reduce post-release mortality rates.
One of the tagged cod who will be working with our team during the study. Where will it swim next?

Not a scientist or interested in recreational fishing in the near future? Not to fret! You have an equally important role in keeping this important species of fish going strong. By having a better understanding of the information on cod in this blog and by visiting the New England Aquarium, you have taken the first step in protecting a very important fish population. You are now able to explain how fishing responsibly is important to keep fish populations stable enough to allow us to keep making memories while fishing with friends out on the open water. If you are interested in further information on sustainable fishing and possible recipes for sustainable seafood.

— Lauren
- Alexander, K. E., W. J. Bolster, A. B. Cooper, J. Cournane, W. B. Leavenworth, A. A. Rosenberg, R. Gee, T. K. Law, R. Dunn, K. Magness, L. Rains, G. Smith, S. Brennan, and S. Claesson. 2009. Gulf of Maine cod in 1861: historical analysis of fishery logbooks, with ecosystem implications. Fish and Fisheries 10,4:428-449.
- Kennedy, Jennifer. 2009. Brief History of Cod Fishing. (Online). About: Marine Life. Accessed October 16, 2013.  
- Northeast Fisheries Science Center (NEFSC). 2012. 53rd Northeast Regional Stock Assessment Workshop (53rd SAW) Assessment Report. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 12-05; 559 p. Available from:  National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online
- Northeast Fisheries Science Center (NEFSC). 2013. 55th Northeast Regional Stock Assessment Workshop (55th SAW) Assessment Report. US Dept Commer, Northeast Fish Sci Cent Ref Doc. 13-01.  Available from:  National Marine Fisheries Service, 166 Water Street, Woods Hole, MA 02543-1026, or online

Facebook Comments


Post a Comment