Analysis of towed camera images to determine the effects of disposed mustard-filled bombs on the deep water benthic community off south Oahu

Still images from a towed camera sled were used to evaluate the potential ecological effects of M47A2 mustard-filled (1,1′-thiobis[2-chloroethane]) bombs disposed of in over 500 m of water off the south coast of Oahu in 1944. The types of munitions and munitions debris in the images were identified by an ordnance and explosives safety specialist. To the extent feasible, non-munitions related debris were also identified. Biologists then examined the images and identified the types and numbers of animals: (1) on or near (<1 m) the M47A2 bombs; (2) on other manmade debris, including other munitions; and (3) on the natural substrate that was predominantly sediment with little, if any, topographic relief. Multivariate statistical techniques were used to analyze these data to identify differences between the biota inhabiting the three substrates. The analysis indicated that the types and numbers of animals associated with the M47A2 bombs were not significantly different from those observed on other types of munitions and other manmade debris; however they were significantly different from the animals found only on the natural sediment. Based on these results, it appears that the mustard-filled bombs are providing hard substrate similar to other disposed objects, attracting “hard substrate species” that would not have otherwise colonized the area. Even though it is apparent that many of the mustard-filled bombs have breached and their contents exposed, the analysis did not find any evidence of animals avoiding the mustard-filled bombs.