of aquarium collectors on coral reef fishes in Kona, Hawai’i
Global trade in ornamental fishes is a large industry involving highly selective harvesting with a high potential for overexploitation. There are no conclusive studies, however, which have documented the magnitude of these impacts on natural populations, despite repeated calls for such studies to help develop sustainability in the aquarium trade industry. In addition to the direct effects of harvesting fish for the aquarium trade, there have been additional concerns on the effects on the coral reef community due to destructive harvesting practices and reductions in the abundance of herbivorous fishes.
In Hawai’i, concern over the effects of aquarium collecting on reef fish populations began in the early 1970s, primarily in response to multiple-use conflicts between aquarium fish collectors and recreational dive tour operators over apparent declines in nearshore reef fishes. Based on collection reports, the annual harvest of aquarium fishes rose from 90,000 in 1973 to 422,823 in 1995, with the majority of the current industry centered on the Kona and Milolii areas of the island of Hawai’i. Accordingly, the goals of this study were to: 1) obtain quantitative estimates of the impact of aquarium collectors on reef fishes in Kona, Hawai’i; and 2) evaluate evidence for destructive harvesting methods and changes in the reef community associated with reductions in herbivory.
We used a paired control-impact design to estimate the impact of aquarium collectors on fish abundance by comparing the differences in abundance at "impact (I)" sites, where aquarium fish collecting was known to occur, relative to "control (C)" sites where collecting was prohibited. We established two geographically adjacent pairs of control and impact study sites at Honoköhau (C) - Papawai (I) and at Red Hill South (C) - Red Hill North (I). At each study site four permanent 50m transects were established at 10-15 m depths where the abundances of 21 species were estimated using a visual strip-transect search method. We surveyed a combination of species harvested by aquarium collectors and those not harvested to provide data to support assumptions of the experimental design. Data were also collected at the beginning and end of the study on the abundance of corals, macro-algae, and the general substratum of each transect using photographs taken with an underwater camera. We also estimated the percent cover of bleached and broken coral.
Overall, there were numerous significant differences in the abundance of aquarium fishes between control and impacts sites but few differences in the abundance of non-aquarium species. All of the ten aquarium species displayed significant impact, location, or location-impact interaction effects in the two-way repeated-measure analysis of variance. In contrast, only one of the non-aquarium species displayed a significant impact effect, five exhibited a significant location or location-impact interaction, and three had no significant differences. The magnitude of the overall percent decline at impact sites ranged between 57% percent in Acanthurus achilles to 38% in Chaetodon multicinctus. Although some changes were noted in the extent of bleaching, broken coral, and coral cover among study areas, there were no consistent, nor significant, differences between control and impact sites that would indicate the presence of destructive fishing practices. In addition, there were no increases in the abundance of macro-algae in collected areas where the abundance of herbivores were reduced by aquarium collecting.
The results of this study indicate that aquarium collectors are having significant impacts on eight of the ten species examined. However, in order to assess whether these abundance patterns are clearly due to aquarium fish collecting requires better knowledge about the intensity and location of collecting activities. Several lines of evidence suggest that the current system of reporting is underestimating the harvest, perhaps by a large margin. It is strongly suggested that additional conservation measures be applied to this fishery and current efforts to establish a marine reserve network in Hawai’i are supported by numerous studies as a successful method to manage reef fisheries.