Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
Data Buoy Science

Reef Fish Behavior at Gray's Reef

Bait fish feeding

Here, bait fish are pushed to the bottom offering opportunistic feed opportunities for reef-dwelling fish such as groupers.

Imagine you're a gag grouper at Gray's Reef National Marine Sanctuary. You're hungry and are foraging along the bottom on one of the sanctuary's scattered protective ledges. This is your favorite habitat because it offers both food and shelter.

Above you in the water column, pelagic predators such as greater amberjack, Spanish mackerel, and great barracuda are circling a big
mixed school of juvenile tomtate and cigar minnows. As they swim ever tightening circles around the school, the predatory fish drive the small fish to the bottom so they can more readily eat them.

They also happen to drive the tomtate right in front of you. Lunch is served; all you have to do is grab a mouthful. You, the grouper, have benefited from a form of "facilitative" or "optional" behavior. These are behaviors that produce positive outcomes for at least one or a few individuals, with positive or neutral outcome for others. The only losers in this scenario are the bait fish.

Cooperation between animals, both within and between species, is common. Familiar examples include ant or honeybee colonies that cooperate to build shelter and provide food for the group (within species), or the cooperation between sea anemones and clownfish (between species). Forms of cooperation also include forming groups to reduce predation (e.g. schooling of fishes), joint defense of shelter, and finding prey (e.g., group foraging that increases success in food location). No one loses in the facultative cooperation between sea anemone and clownfish, wherein the anemone tolerates the clownfish and the clownfish benefits from the anemone. But for fish like greater amberjack and tomtate, the prey species always loses while the predator wins in a classic predator-prey relationship.

At Gray's Reef, the research staff is working with faculty and students in the Department of Marine Sciences at the University of Connecticut to determine if cooperative hunting and feeding behavior occurs among fishes in the Sanctuary. This research is part of a larger effort to understand the roles of "choices" fishes might make in their behaviors, and how this adds to the high diversity of species found in reef fish communities.

Cooperating scientists conducted 50 dives to describe, classify and enumerate patterns of mixed-species and single species feeding behavior, in relation to the numbers and kinds of species present in Gray's Reef and other reef habitats.; These underwater observations by scuba divers allow comparison of rates of group or cooperative foraging, group sizes, and the strength of such interactions within the Sanctuary and between Gray's Reef and habitats in the Florida Keys National Marine Sanctuary and sites in the Caribbean, where many more species live together and, much like city dwellers in human societies, must determine ways to cooperate and share limited resources like food and space.

Preliminary results from diver observations at Gray's Reef suggest that strong interactions occur between individuals within a fish species, as well as between groups of multiple fish species. For example, groups of greater amberjack, Spanish mackerel, and great barracuda (three fish species that feed on other fishes) interact with coordinated hunting and foraging behaviors, both within a species and among species, when preying upon mixed schools of juvenile tomtate (a small bottom fish) and round scad (locally known as "cigar minnows"). Such behaviors by mid-water predators drive schools of small fish closer to ledge habitats on the bottom and produce opportunities for feeding by bottom-dwelling scamp and gag grouper that forage under and near the seafloor near the ledge.

As a result, foraging by large predatory fish-eaters in the water column actually enhances feeding opportunities for large predatory reef fishes that forage on or near the bottom. Rather than competing for food resources, the behavior of these fishes may result in more feeding opportunities for all. Observations of this behavior in Gray's Reef may also give clues as to what may happen to the reef fish when the free-ranging predators such as Spanish mackerel are removed through fishing.

Bait fish scooling

An example of bait fish, in this case anchovies, found schooling in the waters above Gray's Reef.

Understanding the behavioral relationships of fishes may allow us to identify species whose behavior play important roles in enhancing feeding, growth and survival of others. Further, understanding what might be considered "normal" interactions in such "behavior webs" will allow us to measure change over time with respect to fishing and fishery management practices, and better predict the effects of particular human activities. Such information is not currently available purely from studies of feeding habits of fishes and provides another type of measure of the status of fish populations and communities that can be useful to managers responsible for the conservation and sustainable use of marine biological diversity.

Dr. Peter Auster's team conducted their third year of study on this project in Gray's Reef during June 2010. Click here to view a summary findings.


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