Discard mortality played a major role in the loss of 10 billion juvenile scallops in the Mid-Atlantic Bight: Reply to Hart & Shank (2011)

Abstract

An exceptionally large year class (1.31 × 1010 sea scallops) was observed in 2003 in the Mid-Atlantic Bight. Over half of these scallops vanished by 2004. At this time the majority of fishing effort was focused in the Mid-Atlantic due to large closures on Georges Bank. We concluded that this mass mortality was likely the result of incidental fishing mortality. During harvest, scallops were exposed to lethal surface water and air temperatures. Fishermen reported large bycatches of small scallops which were discarded in the 2003−2004 fishing year. Hart & Shank (2011; MEPS 443:293–297) argue that this hypothesis was not likely, as the mortality patterns observed were not consistent with those expected from high discard mortality, and suggested the alternative hypothesis that the mortality was caused by crab predation. After examining estimated retention rates of juvenile scallops collected in scallop dredges with 89 mm rings, prey size preference of crabs, and the limited observer data (5% of 2003 fishing trips), we maintain that discard mortality, due to exposure to lethal water and air temperatures, played a major role in the decrease of juvenile scallop abundance in the Mid-Atlantic Bight.