Tuesday, January 28, 2014

Fishing for Answers

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 intern Lauren Giglio of the Marine Fish Stress and Health Program and features work on discard mortality in Gulf of Maine Atlantic cod.

Thanks to all of you who have been following the progress of the Aquarium’s Atlantic cod discard mortality project; we have really enjoyed blogging about our efforts to help preserve Atlantic cod here in our local waters.

Atlantic cod 

With our cod posts coming to a close (for now), we thought we’d do something a little different for our final entry. We are excited to invite you to explore the infographic below, which recaps our mission to improve the survival rate of discarded undersized cod, provides a visual guide to our field methods, and shares our promising progress and accomplishments thus far.

To see a full-size version of this infographic, visit
our Tumblr page.

We are currently working hard to analyze the huge amount of data that we collected over the summer. Be on the lookout for our results, which we will share with you right here on the Global Explorer’s Blog in the coming months.

Missed any of our previous posts? Catch them all here!

We also invite you to learn about a few of our other fishy research projects here

Until next time, fish enthusiasts!
-Lauren Giglio and the Aquarium’s Mandelman Research Team


  1. Being a Demersal fish, are Atlantic Cod affected at all by the rapid changes in pressure differences when brought up to the surface? Does this affect the mortality rate at all?

  2. Thank you for your interest in our blog. You ask an incredibly astute question. The answer is complicated, so forgive the long response! Cod are indeed affected by pressure changes, and this may increase mortality. Cod, like many species of fish, have an air-filled swim bladder which inflates and deflates to help control buoyancy. Some of these species (including cod) lack a connection between these gas bladders and the gut. As a result, the gas bladder is isolated within the body of the fish, and when the fish is forced to the surface fast, and pressure decreases abruptly, the bladder expands much like a balloon, and may even rupture. The physical damage caused by a rapid decrease in pressure is called barotrauma, and is a big problem for cod, other closely related species like haddock and pollock, and many other demersal fishes. Although a ruptured swim bladder can in itself heal, other organs can be damaged, and importantly, fish may not be able to resubmerge after being thrown back. If stuck floating on the surface of the water like a balloon, they become an easy target for sea birds and predatory fish. Even if not preyed upon, a bottom-dwelling fish at the surface will eventually die for a variety of reasons.

    In our study we kept careful track of the depth at which we caught our cod, how fast we reeled them in, any physical signs of barotrauma (such as a swollen abdomen) and whether fish were able to swim back down after release. We are also evaluating whether the size of the cod had any influence on the extent of the barotraumas in our study. These observations will help us determine whether barotrauma is a large source of mortality for discarded cod and what fishermen can do to help prevent barotrauma. Stay tuned for those. One other tidbit: recent studies across many species have assessed the use of “release devices” for those species most susceptible to barotrauma, so that fish can be manually released back at the depth of preference.