Abstract

Gray triggerfish is an important sport and commercial fish species in the northern Gulf of Mexico, yet, there is little information on the reproductive biology and behavior of gray triggerfish Balistes capriscus. There are also important gaps in the early life history stages of gray triggerfish, e.g., there are no published descriptions of gray triggerfish early development and metamorphosis to juvenile stages. Also needed is information on the ecology and biology of these early stages. For example, at what size and season do gray triggerfish go through metamorphosis and leave the pelagic environment for a benthic existence? Equally important, yet lacking, is information on competitive interactions that might be occurring between gray triggerfish and red snapper, Lutjanus campechanus, because they are dominant co-occurring species on artificial reef structures in the northeastern Gulf with overlapping diets. To our knowledge, no studies have examined the interactions between these two species.

Therefore, both field manipulations and controlled laboratory experiments will be completed to examine gray triggerfish reproductive behavior, early life history stages, juvenile settlement, and interspecific interactions. Our objectives are to:

1. Quantify the reproductive behavior of gray triggerfish;
2. Describe egg, larval, and juvenile stages of gray triggerfish, from laboratory reared fish;
3. Describe size distribution, seasonality, and growth rate of settled juvenile gray triggerfish;
4. Complete field removal experiments on gray triggerfish versus control reefs;
5. Complete lab experiment on growth of juvenile red snapper and gray triggerfish, together versus apart.

This study will describe the reproductive behavior of gray triggerfish in the northern Gulf of Mexico. In the laboratory, we will determine egg size and describe development and growth rates for larval and juvenile gray triggerfish. The juvenile recruitment study will determine the size, seasonality, abundance, and growth of newly settled gray triggerfish. This project will provide information about competitive interactions that could be affecting the distribution, size, and density of red snapper and gray triggerfish on artificial reefs and will broaden our understanding of reef fish communities, their interactions and potential limitations of artificial reef structures.

Objectives

Our objectives are to:

1. Describe and quantify the reproductive behavior of gray triggerfish. 
2. Describe egg, larval, and juvenile stages of gray triggerfish, from laboratory reared fish. 
3. Describe size distribution, seasonality, and growth rate of newly settled gray triggerfish. 
4. Compare species interactions of gray triggerfish and red snapper by field removal experiments. 
5. Examine species interaction effects by comparing growth rates of juvenile red snapper and gray 
6. triggerfish, in controlled laboratory conditions. 

Methodology

We will use artificial reefs that are proven attractants for gray triggerfish and red snapper. Our preliminary SCUBA surveys of similar reefs have observed gray triggerfish spawning behavior and nest building. We will use a state-of-the-art image analysis system for documentation of larval and juvenile morphology and development. In the field, we will use 1.2 m3 wire mesh/ concrete block nursery habitats for juvenile gray triggerfish recruitment and growth studies; and gray triggerfish removals from artificial reefs (steel cages 2.5 x 1.3 x 1.2 m) to compare interspecific effects on other reef fish species especially red snapper. In the laboratory, we will compare inter and intraspecific competitive effects on growth rate by comparisons of mixed (gray triggerfish and red snapper) to single species treatments (gray triggerfish or red snapper).

Rationale

In the northern Gulf of Mexico there has been extensive building of artificial reefs along with the construction of oil/gas platforms and related structures (Minton and Heath 1998). Some consider these structures beneficial to important fishery resources; in contrast, others feel that hese structures may only act as fish attractants making fish stocks easier to locate and harvest and thus driving them toward faster depletion. One aspect that will help in understanding the question of benefit or detriment of these structures would be documentation of habitat limitations. If in fact habitat is limited then we would expect evidence of competitive interactions both among and between species that are associated with these structures. Gray triggerfish and red snapper are co-occurring species that are dominant components of 
artificial structures, and information on their interactions may reveal ecological functioning mechanisms of these made structures. This project will examine competitive interactions that could be affecting the distribution, size, and density of red snapper and gray triggerfish on artificial reefs. The determination of gray triggerfish and red snapper behavior and habitat requirements will greatly affect a large and economically important recreational, charter boat, and commercial fishery that is almost totally dependent on reef fish harvest. In addition, in the northern Gulf of Mexico, most of these fishers are dependent on harvest from such artificial reef structures rather than natural rock or coral reef habitats.