Ochavillo, D.

Coral reef fishery assessment in American Samoa

2012

Department of Marine and Wildlife Resources

30

"Factors that affect coral reef fishery ecosystems can be grouped into two categories: man-made and natural disturbances. Presumably these factors interact as well and their interactions probably compound their impacts. Jackson (1997) has made to date the most compelling historical analyses of various factors affecting a coral reef fishery ecosystem with the Caribbean as a case study. He pointed out that overfishing especially of mega-vertebrates and coral reef degradation through sedimentation had completely altered the processes on Caribbean coral reefs long before scientific research started. Overharvesting of mega-vertebrates (turtles, manatees, monk seals) were keystone species and their decimation dramatically reduced and qualitatively changed grazing and predation on seagrasses and sponges. These significant changes led to the loss of production in adjacent ecosystems and changed the structure of food chains. Large herbivores and carnivores are now ecologically extinct on Caribbean coral reefs and seagrasses, where food chains are presently dominated by small fishes and invertebrates that specialize on chemically-defended prey. Sedimentation due to deforestation and poor agricultural practices also contributed to the massive decline of Caribbean coral reefs (Cortes and Risk 1985, Rogers 1985, 1990, Tomascik and Sander 1985, 1987, Bak 1987, Jackson et al. 1989, Guzman et al. 1991). The vegetation of the island was also completely destroyed thrice by hurricanes (references in Lewis 1984) which perhaps led to significant runoff of sediments degrading coral reefs and seagrass beds and probably led to the decline of Acropora palmata. Recent historical events such as the loss and/or decline in the abundance of herbivores have also contributed to the reef decline. Corals had catastrophic mortality due to overgrowth by macroalgae. Macroalgae overgrew corals after the heavy mortality of the algal grazer Diadema sea urchin and this was exacerbated by the large decline of large herbivorous fishes by the 20th century. The damage on coral reefs due to the physical force of strong waves (by hurricanes and tsunamis) includes sand-blasting and abrasion of coral tissues, dislodging of fragments and/or whole colonies and smothering and/or burial with sand. Tsunami waves together with earthquakes can crack large massive coral colonies and coral limestone (personal observation in Tutuila Island). The physical impact of strong waves can alter benthos characteristics and sometimes lead to abundance of macroalgae (Rogers et al. 1991). The impacts of cyclones have been similarly speculated to cause decline of coral reef fisheries catch in American Samoa (Zeller et al. 2000). The decline in fish catch can be attributed to the loss of habitat (e.g. live branching coral). However, reef fish species vary in their habitat preference so the possibility of increase in abundance of some other species cannot be ruled out. The main objectives of this report were: (1) to establish historical trends in catch-per-unit effort and fish catch composition in American Samoa, and; (2) to correlate these trends with known events as a very general way of inferring their impacts of these historical events on the coral reef fisheries. In this study, we analyzed the catch-per-unit effort (CPUE) data for various fish families for each fishing gear (shore-based and boat-based). In addition, we analyzed species group catch composition among the fishing years. We correlated the historical patterns in catch-per-unit effort and catch composition with known severe natural disturbances and the timing of changes in the fishing technology in American Samoa. We hypothesize that there would be changes in CPUE after banning scuba spearfishing and decline in CPUE after the cyclone and tsunami occurrence. In addition, we also hypothesize that there will be significant changes in fish group catch composition around the occurrence of these severe natural disturbances."

NOAA grant NA10NMF4410061

NA10NMF4410061