FISHERY BULLETIN: VOL. 85, NO. 4 



obstructions to trawling, lobsters can be taken 

 simultaneously with both gears, raising concerns 

 that trawl gear is detrimental to the resource. 



In Narragansett Bay, RI, using a 13 m stern 

 trawl-rigged research vessel, Ganz (1980) found 

 low immediate mortality to trawl-caught Ameri- 

 can lobsters and low damage rates during inter- 

 molt periods, and higher damage rates immedi- 

 ately following molting. He observed that 

 hardshell lobsters were not likely to sustain criti- 

 cal injuries but postulated that commercial-scale 

 operations might produce higher damage rates 

 than the research vessel because of net com- 

 paction. We found that major damage (including 

 immediate mortality) was greatest during molt- 

 ing periods, ranging from 12.6% in July to 14.0% 

 in November. Hardshell (intermolt) lobsters suf- 

 fered little damage by commercial trawling, with 

 the monthly incidence of major damage and im- 

 mediate mortality <3% from January through 

 June and in August. Minor damage, including 

 autotomy of claws, ranged from 0.9 to 8.1% and 

 was greatest in October-November. Minor dam- 

 age was <2% from March through June. 



The incidence of immediate mortality by month 

 never exceeded 0.5% in the pot fishery or 2.2% in 

 the trawl fishery. Moreover, we found that dam- 

 age rates were independent of vessel size, 

 whether in the commercial fishery or between 12 

 m commercial and 13 m research vessels (see 

 below). Newly molted American lobsters were 

 damaged by both trawl and pot gears but trawl- 

 ing caused greater damage. 



Spurr (1978) found experimental otter trawl- 

 induced injury in summer to be greater in July 

 than in September; however, since he aggregated 

 minor damage with major damage and did not 

 provide sample sizes, quantitative comparison of 

 major damage between the two studies is not pos- 

 sible. Spurr concluded that lobster damage due to 

 trawling in winter would be minor, a conclusion 

 supported by our data. 



Ganz (1980) suggested that damaged, sublegal 

 American lobsters might suffer mortality upon 

 release, although he did not investigate this pos- 

 sibility. We found that delayed mortality ap- 

 peared to be influenced by the condition (inci- 

 dence of damage) of American lobsters. Only 2 of 

 309 undamaged, hardshell lobsters experienced 

 delayed mortality after trawling, compared to 26 

 of 47 (55.3%) damaged, hardshell, trawl-caught 

 lobsters. Delayed mortality never occurred to lob- 

 sters with minor damage or autotomized claws. 

 Although the sample size was small in = 18), 



only one-third of all trawled newshell American 

 lobsters experienced delayed mortality. 



While both trawl and pot gear damage lobsters, 

 trawl-caught lobsters alone sustained delayed 

 mortality. One of the initial concerns about trawl- 

 ing was that visibly undamaged American lob- 

 sters less than the minimum length, returned to 

 the water after trawling, would suffer a high level 

 of unobserved mortality. Our results indicate that 

 such mortality rarely occurs to undamaged Amer- 

 ican lobsters; consequently, potential delayed 

 mortality may be ascertained simply by inspec- 

 tion of the incidence of major damage in the catch. 



Of the two molting periods in Long Island 

 Sound, a higher rate of mortality was observed in 

 July than in November, possibly related to the 

 warmer postmolt water temperatures which 

 occur in summer compared with late fall. Damage 

 rates during postmolt periods were similar (12.6% 

 July vs. 14.0% November) notwithstanding the 

 difference in water temperature. These results 

 suggest that the resistance of trawled postmolt 

 American lobsters may be lowered by warm sea- 

 water temperatures and that such temperatures 

 may increase the occurrence of delayed mortality 

 independent of the incidence of damage. Mean 

 values of immediate and delayed mortality for all 

 samples taken during intermolt periods were neg- 

 ligible (<1.0% and <2.0%, respectively). 



There appeared to be some variability in mor- 

 tality depending on the type of damage sustained. 

 Damage to the abdomen and carapace was almost 

 always lethal (100% and 92%, respectively), while 

 broken parts such as claws or rostrum resulted in 

 25% and 50%' mortality, respectively. However, 

 small sample sizes precluded definitive analysis. 



Ganz (1980) speculated that the most signifi- 

 cant impact of trawling might be related to the 

 cumulative effect of trawling and damaging sub- 

 legal American lobsters, and subsequently re- 

 leasing them to be taken again. In discussing this 

 possibility, he reported an immediate claw loss 

 (cull) rate of 3.5% and a prior cull rate of 8.8%. 

 This is a valid concern, and one which should be 

 considered in both trawl and pot fisheries. For 

 example, Smith (1977) reported a cull rate of 26% 

 in an area of Long Island Sound which had not 

 been trawled during recent years and a rate of 

 23% in an area lightly fished with trawls, sug- 

 gesting that a high cull rate can occur in the ab- 

 sence of trawling (both areas were heavily fished 

 with pots). These observations, while higher than 

 Ganz's, included both new and old claw loss as 

 well as lobsters with regenerated claws. In the 



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