Project Report PR-98-06
An Analysis of the Fish and Macrobenthos Along the Sand Island Ocean Outfall Using Remote Video: VIII.1997 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 1,036 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 annually from 1990 through 1997. 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 1997, 30 fish species (3,111 individuals) having an estimated biomass ranging from 15 to 90 g/m2 (mean 34 g/m2) were censused. In the 1991 through 1996 period the number of fish species encountered during a survey ranged from 22 species (in 1993) to 31 species (in 1992), the total number of individuals from 279 (in 1993) to 2,936 (in 1992), and the mean biomass from 21 g/m2 (in 1993) to 92 g/m2 (in 1996). 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. The 1997 census noted one new fish species for every 11.6 m2 of substratum sampled and one fish for every 0.7 m2. In the 1991 through 1997 period, measures of the fish community (number of species, number of individuals, and biomass) after an initial increase from 1991 to 1992 and a decrease in 1993 oscillated annually. 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 of the videotapes recorded in 1994 and later years from that recorded in 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.