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

Piscivore Ecology at Gray's Reef
Third Year of Study, June 2010

Dr. Peter Auster, University of Connecticut
Dr. Laura Kracker, NOAA

Scamp grouper surrounded by tomtates

Scamp grouper (center) surrounded by a fleeing school of young-of-year tomtates, driven to the seafloor by predatory attacks of Spanish mackerel up in the water column
Photo Credit: Peter Auster, UConn

Cooperation between animals, both within and between species, is common across the animal kingdom. Types of cooperation can, for example, involve forming groups to reduce predation (e.g. schooling), defense of shelter, and finding prey. Such behaviors are forms of an entire class of "facilitative" behaviors that produce positive outcomes for at least one of a pair (or more) of individuals and nothing less than a neutral outcome for others. That is, no one loses from such interactions, in contrast to classic predator-prey relationships, where the predator wins while the prey loses, or in competitive interactions where both species lose access to some resource. This project is focused on quantifying patterns of cooperative foraging by piscivorous fishes (those fish that eat fish) at Gray's Reef National Marine Sanctuary. The primary goal of this work is to determine the importance that these types of behavioral interactions have in local food webs. Beyond basic ecological interests, the results of this work have important implications for managing marine protected areas in regards to maintaining and enhancing such interactions.

Dr. Laura Kracker, overseeing Didson operations

Dr. Laura Kracker, overseeing Didson operations
Photo Credit: Eric Heupel, UConn

In June 2010, the third year of this study, we conducted 50 nitrox dives (for a total of about 24 hours of bottom time) and two Didson sonar deployments to quantify patterns of mixed-species and single species foraging as well as local species composition. We have demonstrated that when pelagic predators drive their prey (small schooling fishes) towards the seafloor, such high densities of fish produce feeding opportunities for the piscivores that live on and in reefs. For example, groups of greater amberjack, Spanish mackerel, and barracuda interact with coordinated behaviors both separately and together when preying upon mixed schools of juvenile tomtate and mackerel scad. Such behaviors by mid-water predators "drive" small fish closer to reef habitats and produce opportunities for enhanced predation by scamp and gag grouper that forage under and near the seafloor over the ledge.

Dr. Peter Auster's team conducting underwater surveys

Dr. Peter Auster's team conducting underwater surveys
Photo Credit: Peter Auster, UConn

The data collected in 2010 confirms that these behavioral patterns are consistent properties of these reef fish communities. A detailed behavior web has been constructed using survey data from 2008-2010 and we are currently scaling survey data to attribute interactions strengths to the linkages in the web. A model to predict the effects of a range of facilitated feeding rates will be developed in order to better understand how such behaviors link to the population processes of different fish species. These results will allow us to match model prediction to outcomes in the real world. If such interactions have significant consequences for growth and reproduction of reef fishes, then alternatives to manage for such interactions may be desired.


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