What kind of fish live at Oculina Bank and how do you count them?
About thirty years ago, the Oculina Banks were dominated by large, predatory fish such as snapper and grouper, however due to overfishing and the destruction of essential fish habitat (i.e. Oculina coral heads), the abundance of these reef fish has substantially diminished and been replaced by smaller, non-exploited species such as small sea bass, butterflyfish, damselfish, and wrasses.
Groupers are of particular importance to us because they are an exploited species and their life history characteristics make them even more vulnerable to overfishing. Many are protogynous hermaphrodites meaning that they all start out as females and have the ability to become males, which a small portion of them will do given the appropriate environmental cues. This leads to highly female-skewed ratios. Some groupers spawn in large groups and display strong site fidelity, offering knowledgeable fishermen the possibility to harvest large numbers of reproductively active fish in a short period of time. Dominant males aggressively defend these spawning aggregation sites and are more easily caught than during non-spawning periods, leading to further skewing of the sex ratios. Some of the grouper species found in the OHAPC include scamp, gag, warsaw grouper, speckled hind, red grouper, rock hind, and snowy grouper. Currently, the most abundant species is scamp. Oculina coral heads also serve as nursery habitat for several juvenile reef fish species including speckled hind and snowy grouper.
Since 2001, we have been conducting remotely operated vehicle (ROV) surveys of the Oculina Habitat Area of Particular Concern (OHAPC) and the surrounding areas outside the reserve to monitor the fish populations and how they interact with various habitat types. Back at the lab, videotapes from the ROV dives are analyzed. This involves identifying and counting all fish observed and describing what habitat type they were found on. To estimate fish abundances, we calculate densities (number of fish per unit area) by estimating the area of view of the video camera. This standardizes the data and allows us to compare numbers of fish among habitat types and management areas (inside vs. outside the reserve). Given enough time, we hope to see grouper densities begin to return to levels they were at prior to overfishing.