A Better Understanding of Coral Reef Ecosystems

Pelagic predators such as these barracuda, Sphyraena qenie, are part of the coral reef ecosystem in the U.S. Line Islands (NOAA Photo by Kevin Lino).
A team of scientists have embarked from Hawai'i on a three-month survey of coral reef ecosystems at Johnston Atoll, the U.S. Phoenix Islands, the islands of American Samoa, and the U.S. Line Islands in the tropical Pacific Ocean. The overarching objective is to better understand the coral reef ecosystems of these areas, many of which are seldom explored. The research expedition is part of a regular monitoring program, conducted by the Coral Reef Ecosystem Division (CRED), headquartered in Honolulu, Hawai'i. The expedition is supported by NOAA's Coral Reef Conservation Program and involves extensive cooperation among NOAA scientists and research partners, including the University of Hawaii Joint Institute for Marine and Atmospheric Research (JIMAR), the U.S. Fish and Wildlife Service, San Diego State University, and the Papahānaumaokuākea Marine National Monument.

The research expedition will be carried out from February 27 to May 24, 2012 aboard the NOAA ship Hi'ialakai. Under the leadership of Chief Scientists Dr. Jill Zamzow, Dr. Bernardo Vargas-Angél, and Jamison Gove, a diverse team of researchers will be conducting multidisciplinary coral reef ecosystem surveys, assessing the status of fishes, corals, algae, marine invertebrates, and the oceanographic conditions in which these organisms exist. The scientific data collected during the three-month research expedition will enable informed and effective implementation of ecosystem-based management and conservation strategies for coral reef ecosystems, helping to ensure their protection for generations to come.

Tuesday, September 21, 2010

Why do fish school?

By Jamie Gove

The swirling black mass from above was hard to miss, particularly given the flurry of activity of squawking birds dive bombing the ocean surface, only to emerge seconds later with a flopping small fish in their beaks. As an amazing of a spectacle as it was from above the surface, I wasn’t prepared for what was happening below. Jumping in off the side of the boat, it took my eyes a few seconds to focus and my mind even longer to comprehend the scene unfolding before me. A school of thousands of tiny bait fish were swirling in a large tornado-like vortex, while just beneath, a large group of mackerel were rising from below and striking the ball of fish with lightening speed. Also in the mix, albeit on the periphery, were a small group of rainbow runner and few grey reef sharks. Basically, we had just entered nothing short of a total feeding frenzy, with the school of bait fish at the center of it all….
A 3-shot sequence showing mackerel coming from below, striking the school of bait fish.

Fish congregate together in schools for a variety of reasons, ultimately to enhance an individual fish’s chance of survival in a competitive and dangerous fish-eat-fish world.

First and foremost, fish school as a “safety in numbers” strategy; the more fish there are in a group, the less likely a predator will be able to eat any single fish. Generally speaking, it’s much easier for a larger predatory fish to track down and eat a solitary smaller fish, whereas schooling fish can distract and disorient a predator, making it more difficult to snatch a fish from the group.

Danny Merritt goes for an up-close view of the bait ball.

Fish will also school to increase the chances of finding food. Essentially, the more fish there are in a group, the greater an area those fish can cover when searching for prey, or, detecting an area in the ocean which may be more suitable for finding prey. The downside of this strategy is rather obvious; an individual fish must share whatever food they find with the rest of the school. When I write these fish “share”, it’s not as if a fish will offer half of their dinner to another, more that they must compete within the school for the food they do find, making it highly possible for a number of fish to miss out on a meal when the rest have eaten more than their fair share.
A swirling blur of fish.

It is also thought that fish will school for a hydrodynamic advantage. Similar to how professional bicycle riders will draft behind other riders so as to reduce wind resistance and friction, fish swim in schools, following behind one another for the same reasons; to reduce friction in the water thereby conserving energy.

Not all fish school, but many do, particularly those which live in the open ocean which is devoid of hiding places or any form of protection from predators. In general, it is all about trading costs for benefits, and for certain fish, it just makes sense to come together to eat, and to hopefully avoid being eaten.


  1. We used to pick up bait balls on long range fishing trips when bait ran short. NW swells hitting the shore but you knew that yeah.


  2. What species of fish were they? Opelu and nehu?

  3. None of our fish team members were present to observe the bait ball in person, but from the pictures and the description provided by the oceanography team, they are fairly certain that the small bait fish were nehu (Encrasicholina purpurea) and the larger mackerel were opelu (Decapterus macarellus).