Chen et al Population structure of Homaius ameiicanus in tlie Gulf of Maine 



251 



of tows with zero lobsters in the NMFS survey, a delta 

 transformation was used to estimate the stratified mean 

 of lobsters per tow. Because the DMR inshore survey 

 program began in fall 2000, we used data from the 

 NMFS survey program for the same time period only 

 for our comparison of data. Currently the stock assess- 

 ment uses only female data because females and males 

 exhibit similar pattern; therefore we report results for 

 females only in the present study. 



Results 



The average weight per lobster tended to be low and rela- 

 tively constant for lobsters caught in the tows conducted 

 in waters shallower than 73 m but increased greatly 

 with increased depths (Fig. 2). The average carapace 

 length for the first two depth strata, which were shal- 

 lower than 72 m, were similar for each year and sam- 



pling season, but were much smaller than the average 

 carapace length of lobsters in the third depth stratum 

 which was deeper than 73 m (Table 1). For example, for 

 the 2000 fall survey, the average lobster size for depth 

 strata I and II were 61.9 and 64.4 mm — much smaller 

 than 80 mm for stratum III. These distributional pat- 

 terns in the lobster average weight and average size 

 were consistent among years and seasons, indicating 

 that lobsters inhabiting waters shallower than 73 m 

 were mainly small individuals, whereas lobsters in 

 waters deeper than 73 m were much larger than those 

 in the shallow waters. A fourth depth stratum was used 

 in the 2003 spring survey, where the average towing 

 depth was 125 m. The average size of lobsters sampled 

 in this stratum was 99.5 mm, which was similar to the 

 stratified mean size of lobsters estimated in the NMFS 

 survey program (Fig. 3). 



There were no significant differences in size distri- 

 butions among years in a given sampling season (i.e., 



