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High speed hauling of traps is being looked at as the possible cause of increased die-off among lobsters. The percent of the die-off, or shrinkage as it is known, has been rising over the last 20 years. The Maine Department of Marine Resources has received a grant to study the effects of stress on lobster.
Dr. David Basti, a marine biology researcher at the University of Maine at Orono studied the effects on lobster of being hauled quickly from the bottom. He said, “Anything that stresses the lobster may predispose them to mortality” He noted that being exposed to air, being handled, held on deck, and thrown back can all cause stress. But the most pronounced negative effect on lobster is from being hauled up rapidly from 400 feet or more. The effects of being brought to the surface were monitored with blood studies. Physiological changes in the blood such as lactate and ammonia accumulation were very elevated in lobster hauled rapidly from deep water. Modern haulers used for the last 20 years, bring up a trap at 300 to 500 feet per minute. That is 14 atmospheres of change in fewer than 2 minutes. To avoid the crippling effects from rising too fast human divers are required to rest after each atmosphere of assent, or every 33 feet. Basti said deep water is very different from shallow water, 35 feet or less. In some cases offshore lobster may be coming up from hundreds of feet. Humans are not biologically like lobster, and the necrosis (the bends) that humans suffer when rising through a water column too quickly is not what is impacting lobster. However, there are changes in the blood in both cases. For humans, a rapid rise forces nitrogen into the blood and muscle tissue causing intense pain and muscle contraction. This apparently does not happen with lobster, but the accumulation of lactate and ammonia can have negative consequences. Conse- quences that may be fatal. Lobsters live in a very stable environment and any change causes them to stress over returning to stability. Being hauled up from deep water, or hauled rapidly, or both, are major stressors. Basti said, “Throw-backs often don’t make it back to the bottom. It is not known if throw-backs are being caught by predators on the way down, or succumbing to so much atmospheric change, or something else.” The study Basti did used special cages in deep and shallow water. The cages were hauled at two speeds, at two depths, and the lobsters were held in different conditions. The results of blood tests were compared with a group of lobsters tested to establish a baseline. Basti said that in time, about four weeks, many of the lobsters with physiological changes in their blood went back to normal. Also, 17 percent did not survive, their blood never returned to normal, and they died of bacterial infections. Stress reduces the effectiveness of the immune system to fight infections. Basti pointed out that this study was just the “tip of the iceberg” on what needs to be done in order to better understand the effects of rapid changes in depth on lobster health. |
