. Commercial fisheries review. Fisheries; Fish trade. Fig, 9 - Suction dredging system mounted on barge is used to harvest shells to be used as cultch and to remove oyster drills from oyster Fig. 10 - Spreading quicklime to kill starfish which invaded oys- ter bed. Tank on boat holds 15 tons of quicklime. used exclusively to control starfish, and 2 boats and a barge are equipped with suction dredges. The boats are 55 to 85 feet long. The barge (Fig. 9) can dredge up 10,000 bush- els of buried shells from the botttom,or re- move oyster drills from 1 to 2 acres of bot- tom a day. Causes o
. Commercial fisheries review. Fisheries; Fish trade. Fig, 9 - Suction dredging system mounted on barge is used to harvest shells to be used as cultch and to remove oyster drills from oyster Fig. 10 - Spreading quicklime to kill starfish which invaded oys- ter bed. Tank on boat holds 15 tons of quicklime. used exclusively to control starfish, and 2 boats and a barge are equipped with suction dredges. The boats are 55 to 85 feet long. The barge (Fig. 9) can dredge up 10,000 bush- els of buried shells from the botttom,or re- move oyster drills from 1 to 2 acres of bot- tom a day. Causes of Oyster Mortality, 1966-69 The most important cause of mortality of oysters was starfish, Asterias forbesi. A single starfish can consume several oyster spat simultaneously. On beds where star- fish were numerous, more than 1 per square yard, they reduced good sets of oysters to non-commercial levels within a few weeks; even on beds where good starfish control was practiced, up to 94 percent of spat were killed in bands 15 to 20 feet wide along borders of beds (MacKenzie). The rate of feeding on 1- year-olds has not been determined, but Mac- Kenzie (196 9) observed that a starfish can consume as many as five 2-year-old oysters per 28 days. Silt The secondmost important cause of mor- tality was silt. This settled over beds during winter, and suffocated seed oysters in late April and May when water temperatures rose above 43° F. (Fig. 4). Silt may accumulate to 2 inches by late March in areas where cur- rents are low and wave action is slight. In open waters, where currents are strong or wave action generated by storms disturbs the bottom, silt deposit is usually negligible. In the Housatonic River, a protected area, 75 percent of about 65,000 bushels of 1- and 2- year-old oysters were suffocated by silt in spring 1969. In calm sections of harbors, such as New Haven, the mortality of 1-year- olds due to suffocation was 50 percent. In a more open area of that harbor, it was abou
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