Project Report PR-95-06
An Analysis of the Fish and Macrobenthos Along the Sand Island Ocean Outfall, Oahu, Hawaii, Using Remote Video: V. 1994 Data
Richard E. Brock
Because the diffuser of the Sand Island Ocean Outfall lies below safe diving depths, a remotely controlled video camera system was used to determine the status of the fish and diurnally exposed macrobenthos resident to the diffuser. The use of a remotely operated vehicle is stipulated in the National Pollutant Discharge Elimination System 301(h) waiver permit for the Sand Island Wastewater Treatment Plant. Video reconnaissance was completed over the entire 1036 m length of the outfall diffuser. Five visual “transects,” which “sampled” approximately 41% of the total diffuser length, were established on the diffuser pipe. Video sampling of the diffuser marine communities was carried out in 1990, 1991, 1992, 1993, and 1994. Only a few species of diurnally exposed macroinvertebrates are evident on the videotapes of the diffuser; the numbers are insufficient for any meaningful analysis. In 1994, 33 fish species (1,473 individuals) having an estimated biomass ranging from 16 to 46 g/m2 (mean 35 g/m2) were censused; in 1993, 22 species (279 individuals) having a standing crop ranging from 6 to 39 g/m2 (mean 21 g/m2) were encountered; in 1992, 30 fish species (2,936 individual fish) having an estimated standing crop ranging from 39 to 77 g/m2 (mean 53 g/m2) were censused, and in 1991, 27 species (1,785 individuals) having a biomass ranging from 8 to 106 g/m2 (mean 42 g/m2) were counted. Because the 1990 video census covered only the terminal 183 m of the diffuser, whereas the later surveys were spread out along the entire diffuser length, a direct comparison cannot be made between the 1990 Data and the Data for subsequent years. In 1990, one “new” fish species was encountered for every 22.9 m2 of substratum sampled and one fish was seen for every 5.6 m2; in 1991, it was one new species for every 13.1 m2 sampled and one fish for every 0.7 m2; in 1992, it was one new species for every 7.4 m2 and one fish for every 0.4 m2; and in 1993, it was one new species for every 38.5 m2 and one fish for every 3.0 m2. The 1994 census noted one new fish species for every 10.2 m2 of substratum sampled and one fish for every 0.7 m2. In the 1991 – 94 period, measures of the fish community (number of species, number of individuals, and biomass) increased from 1991 to 1992, decreased in 1993, and increased again in 1994. From a statistical perspective, changes in the mean number of species per transect and the mean number of individual fishes per transect are significant (Kruskal – Wallis ANOVA); changes in the biomass of fishes over the same period are not significant. These changes in the fish community are attributed to changes in the general viewplane in 1994 from earlier years as well as to a change in the resolution of the videotape from which the Data are derived. Poorer camera resolution results in lower counts; camera resolution is affected by local wind and currents interacting with the camera, tether, and support vessel as well as by water visibility. Controlling these sources of variation inherent with the use of the remotely operated video system is difficult if not impossible. Until an alternative can be found, the remotely controlled video system is the only low-cost means available to view the marine communities on the diffuser. Until a more accurate means of visual assessment is available, the biological Data generated by the remotely operated video camera should be viewed as qualitative, with little statistical rigor.