242 • Marine Minerals: Exploring Our New Ocean Frontier 



ment on the bottom and, in an emergency, from 

 release of materials in the lift pipe. Ten hours af- 

 ter suspension, most material will be redeposited 

 within 65 feet of the miner track, but only 1 per- 

 cent of the smallest particles will be redeposited after 

 100 hours. From the test mining data, the research- 

 ers calculated that about 90 percent of the resus- 

 pended material would be redeposited within 230 

 feet of the miner track, and the maximum redepo- 

 sition thickness would be a little more than half an 

 inch thick near the centerline of the track. '^ 



The crust scenario envisions recovery of about 

 two-thirds of the ore volume of the nodule scenario 

 but assumes a much thinner range of overburden. 

 Peak base-case crust miner redeposition thicknesses 

 were about one-thousandth of an inch.'' There is 

 a highly significant difference between the two min- 

 ing scenarios. The "worst case" scenario for crust 

 mining,'* would result in less than 1 percent of the 

 maximum deposition in the nodule mining scenario. 



From the DOMES baseline data (average of 16 

 macrofaunal individuals/ft^) and an assumed nod- 

 ule mining scenario, Jumars'^ calculated that a nod- 

 ule miner would directly destroy 100 billion indi- 

 viduals. In comparison, data from a case study done 

 at Cross Seamount (see box 6-G) indicate that pas- 

 sage of the crust miner over 1 1 mi^ per year would 

 directly destroy from 100,000 to 10,000 macro- 

 faunal organisms at 2,600 and 7,800 feet respec- 

 tively. The DOMES and Cross Seamount data- 

 bases differ in that infaunal organisms (those 

 actually living within the sediments) were not sam- 

 pled in the Cross Seamount reconnaissance. How- 

 ever, the crusts provide little sediment for organ- 

 isms to inhabit. Nevertheless, it appears that the 

 number of macrofaunal organisms destroyed in the 

 crust mining scenario is orders of magnitude less 

 (one-millionth to one ten-millionth) than in the nod- 

 ule scenario.'® 



"J.W. Lavelle et al. "Dispersal and Resedimentation of the Ben- 

 thic Plume from Deep-Sea Mining Operations: A Model with Calibra- 

 tions," Marine Mining, vol. 3 (1982). No. 1/2, pp. 185-212. 



"U.S. Department of the Interior, Minerals Management Serv- 

 ice, p. 197. 



'^Mining at the shallowest depth and superimposition of surface 

 and bottom plume footprints. 



"Jumars, "Limits in Predicting and Detecting Benthic Commu- 

 nity Responses." 



"U.S. Department of the Interior, Minerals Management Serv- 

 ice, p. 240. 



The severity of the impacts on populations in 

 areas adjacent to the miner track would be deter- 

 mined by the intensity of the disturbance, i.e., 

 proximity to the track, and the type of feeding be- 

 havior characteristic of the population. As in the 

 case with shallow water mining, highly motile or- 

 ganisms such as fish, amphipods, and shrimp would 

 be most able to avoid localized areas of high redepo- 

 sition and turbidity. Once conditions become toler- 

 able, these organisms could venture into the mined 

 area to feed on the dead and damaged organisms. 



The area mined may be invaded by opportunis- 

 tic species with dispersal capabilities greater than 

 those of the original resident species. Reestablish- 

 ment of the original community has been postu- 

 lated to take a very long time, perhaps decades or 

 longer. 



Temperature 



Comparing the ambient surface water tempera- 

 ture in the lease areas with a temperature of 4 to 

 10 degrees C for the bottom water released at the 

 surface, there is reason to believe that eggs and lar- 

 vae coming into direct contact with the cold dis- 

 charge water could be affected adversely; such ef- 

 fects should be limited to the area immediately 

 beneath the ship's outfall." 



To estimate the annual loss of tuna larvae and 

 the impact of this loss on adult fish biomass, it was 

 assumed that all tuna eggs and larvae coming into 

 direct contact with the cold water discharge could 

 die. At least 46,000 skipjack tuna and 15,000 yel- 

 lowfin tuna could be lost annually due to thermal 

 mortality. These values would be about four times 

 larger if the mining ship acts as a fish aggregating 

 device by concentrating tuna schools in the imme- 

 diate vicinity. 



The loss of adult fish biomass due to death of 

 larvae would be a very small fraction (less than 1 

 percent) of the total annual harvest of these spe- 

 cies in the central and eastern North Pacific. The 

 crust mining scenario assumes a surface plume vol- 

 ume about 60 percent that of the nodule mining 

 scenario, and the effects of thermal mortality of lar- 

 val fish would be reduced proportionately. 



"Matsumoto, "Potential Impact of Deep Seabed Mining." Con- 

 tact of larvae with cold water could cause the development of deformed 

 larvae. 



