SMITH and HOWELL: BOTTOM TRAWLING EFFECTS ON AMERICAN LOBSTERS 



changes were defined by water temperature vari- 

 ation whereas molt condition (newshell vs. hard- 

 shell) was based on the bimodal distribution of 

 lobster molting (June-July and October- 

 November) observed in Long Island Sound (Lund 

 et al. 1973). The relationship between tempera- 

 ture and shell condition was evaluated by com- 

 paring data derived from postmolt periods follow- 

 ing the summer (warming seawater temperature) 

 vs. fall (cooling seawater temperature) molts. 

 Postmolt lobsters recovered from the capture 

 process in flowing seawater of 20°C in the July 

 test and 15°-16°C in the November test. Intermolt 

 lobsters in May recovered in 12°C seawater and, 

 in August-September, at 22°C. In all cases, sea- 

 water temperatures reported here were elevated 

 approximately 1°-2°C from passage through the 

 circulation system. 



The trawl-caught sample included 74 lobsters 

 taken from research vessel catches. Comparison 

 of delayed mortality rates between research and 

 commercial samples revealed no significant dif- 

 ference (x^ = 0.305) so the samples were pooled. 

 Delayed mortality rates from samples taken from 

 small (12 m) and large (20 m) trawl vessels in 

 November 1983 and August 1984 were not signif- 

 icantly different (x^ = 0.05), therefore, large and 

 small vessel data were also pooled. All damage 

 observations were recorded in the same manner 

 as reported above. 



Mortality Due to Freezing 



Seventy hardshell, undamaged, trawl-caught 

 American lobsters <81 mm CL were held in an 

 open circulating seawater system at 8°C. On 15 

 January 1985, three groups of 20 lobsters were 

 exposed in a wooden box (2 m x 1 m x 0.3 m) to 

 ambient air temperature of -9.5°C for periods of 

 30, 60, and 120 minutes. The remaining 10 lob- 

 sters were held without exposure as a control. 

 After the prescribed time had elapsed, the test 

 lobsters were returned to the holding system and 

 observed several times during the following 48-h 

 period for incidence of mortality. 



RESULTS 



Incidence of Damage Due to 

 Trawling 



Damage to American lobsters of all sizes caused 

 by commercial trawling throughout the 19-mo 

 sampling period is summarized in Table 1. The 



monthly incidence of major damage (including 

 immediate mortality) varied seasonally, from to 

 14.0% in the trawl fishery and from to 3.5% in 

 the pot fishery. Minor damage ranged from 0.9 to 

 8.1% in the trawl fishery and from to 10.7% in 

 the pot fishery. Differences between pot and trawl 

 damage rates were compared only for months in 

 which both gears were sampled. The incidence of 

 major damage was significantly greater for trawl 

 samples in July and October-November, but not 

 in August or September (Table 2). 

 The incidence of damage due to the two gears 



Table 1. — Incidence of damage to American lobsters taken by 

 commercial otter trawl from July 1983 through January 1985.1 



'Data from months in successive years are pooled. 



Table 2. — Incidence of damage to American lobsters taken by 

 commercial pot and otter trav^^l gears, 1983-84. 



■"significantly different (P < 0.001). 



'1983 data only (no pot fishery samples taken in 1984). 



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