SMITH and HOWELL: BOTTOM TRAWLING EFFECTS ON AMERICAN LOBSTERS 



present study, minor damage (which included im- 

 mediate claw loss) ranged from 0.9 to 8.1% per 

 month in the trawl fishery and from to 10.7% in 

 the pot fishery. 



While the mortality of trawled newshell Amer- 

 ican lobsters was high during the two molting 

 periods, they represented such a small percentage 

 of the total trawl catch (1-8%) that the estimated 

 total mortality to the entire catch was little 

 changed by their presence. Similarly, while dam- 

 aged lobsters sustain a high rate of mortality, it is 

 their proportion in the catch which determines 

 the rate of additional mortality experienced by 

 the population. 



No truly soft American lobsters (stage A, after 

 Passano 1960) were observed in the pot catches 

 sampled for delayed mortality estimates, and 

 they occurred rarely in other commercial pot sam- 

 ples (up to 3% in July 1984). They were observed 

 infrequently in trawl catches as well (up to 7.8% 

 in November 1984). The low incidence of soft lob- 

 sters in commercial catches is probably due to 

 reduced mobility during the shell hardening proc- 

 ess (Herrick 1909) when American lobsters are 

 most vulnerable to damage and predation. 



No significant difference was observed in dam- 

 age rates or delayed mortality based on sampling 

 of vessels <15 m or >15 m. There was no differ- 

 ence in delayed mortality rate between 13 m re- 

 search vessel samples and either 12 m commer- 

 cial or 15-26 m commercial trawlers. Finally, 

 there was no difference between damage rates to 

 American lobsters >81 mm CL taken by research 

 and commercial vessels in October-November 

 1984, the only period for which comparable data 

 (tows of 2-h duration) were available for both ves- 

 sel categories. The former results suggest that 

 trawl-induced damage and mortality is indepen- 

 dent of vessel size; the latter suggests that obser- 

 vations of fishery-induced damage made by biolo- 

 gists were representative of actual fishing 

 conditions. 



While American lobsters may succumb to sub- 

 freezing air temperatures, consideration of this 

 source of mortality is a function of both tempera- 

 ture and exposure time and must be judged on the 

 behavior of the fishery in question. Edwards and 

 Bennett (1980) reported a survival rate of 42-85% 

 for Nephrops norvegicus after 1-h exposure to air, 

 noting that favorable weather conditions and the 

 type of vessel used were factors contributing to 

 higher survival. In the present study, American 

 lobsters exposed to -9.5°C air temperatures for 

 30 minutes all survived. Those exposed for 120 



minutes all succumbed. Intermediate exposure 

 (60 minutes) produced intermediate results (30% 

 survival). In Long Island Sound, field observa- 

 tions during a 19-mo period suggested that opera- 

 tors in the trawl fishery commonly sorted the 

 catch within 15-45 minutes. 



Our design tended to maximize the debilitating 

 effect of freezing temperatures. Trawl net con- 

 tents are commonly released onto the vessel deck 

 in a pile. Consequently, organisms on the inside 

 of the pile are protected from cold air tempera- 

 tures. In our test, all American lobsters were 

 placed on a flat table with 0.3 m high sides; thus, 

 all lobsters were equally exposed to freezing tem- 

 peratures and none were able to benefit from the 

 "piling" of a normal catch. As a consequence, this 

 experiment very likely overstated the impact of 

 subfreezing air temperatures on commercially 

 taken American lobsters. 



An additional consideration beyond the di- 

 rected fishery is the mortality to "sublegal" 

 American lobsters (those <81 mm CL) and the 

 damage to lobsters during molting periods which 

 may result from a mixed species trawl fishery 

 which includes a so-called incidental catch or 

 "bycatch" of lobsters. As with freeze-induced mor- 

 tality, this factor must be judged based on the 

 performance of the fishery in question. 



In Connecticut, trawlers reported <10% of the 

 commercial American lobster landings reported 

 by all fishermen during the period 1982-86 (CT 

 DEP fn. 2). However, given the controversy sur- 

 rounding trawling during this investigation and 

 the weaknesses inherent in catch reporting sys- 

 tems during periods of controversy (Matlock 

 1986; Ferguson 1986), a number of independent 

 methods of observation were used to determine 

 the actual impact to the resource associated with 

 trawling. Unannounced boardings by Connecti- 

 cut Conservation Officers were utilized to esti- 

 mate the true magnitude of lobster catches. Biol- 

 ogists made sampling trips on the vessels of 

 commercial trawl fishermen fishing in Long Is- 

 land Sound to document the fishery-induced inci- 

 dence of damage. Research vessel sampling was 

 used to estimate a fishery-independent rate of 

 trawl-induced damage. The results of these obser- 

 vations suggested that the magnitude of Ameri- 

 can lobster catches per trip was about the same as 

 those reported in mandatory logbooks and, except 

 during molting periods, trawl-induced damage 

 was minimal. 



Observations in controlled laboratory condi- 

 tions were utilized to estimate the delayed 



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