FISHERY BULLETIN: VOL. 84, NO. 2 



tense during spring, followed in descending order 

 by summer, fall, and winter. Table 2 summarizes the 

 sighting effort by season and for the entire year. 

 The BPUE data are summarized in Table 3. The 

 distributions of BPUE values for all categories and 

 seasons were very similar. Each distribution was 

 highly skewed toward lower values. This can be seen 

 from the table; mean values ranged between 33 and 

 423 kg/km, but maximum values were as high as 

 33,747 kg/km. In 20 of the 25 cases, the median value 

 was 0, and in 9 of these the 75th percentile value 

 was also 0, indicating that no cetaceans of that par- 

 ticular category were seen in one-half or three- 

 quarters, respectively, of the blocks surveyed. In fact, 

 in two cases (endangered species and planktivores 

 sighted in winter) even the 90th percentile value was 



0; no endangered or plankton-feeding cetaceans 

 were observed in 9 out of 10 blocks surveyed in the 

 winter. 



The overall pattern of high habitat use by ceta- 

 ceans is depicted in Figure 1, which shows those 

 10-minute blocks with the top 10% of the whole-year 

 BPUE values (all species combined). The figure also 

 identifies locations to be used for geographic refer- 

 ence Three principle high-use areas can be de- 

 lineated: 1) the western margin of the Gulf of 

 Maine, from the Great South Channel northward to 

 Jeffreys Ledge, 2) the eastern portions of Georges 

 Bank, along with the Northeast Channel and rela- 

 tively deep basin north of the bank, and 3) the con- 

 tinental shelf edge There are also scattered high- 

 use blocks in other areas. 



Table 2.— Summary of sighting effort in 10-minute blocks, expressed as kilometers 

 of track line surveyed within acceptable criteria, for CETAP dedicated and POP surveys. 



Season 



Table 3.— Mean, median, and maximum values of biomass sighted 

 per unit of sighting effort, by season and for the entire year, for all 

 cetacean species combined, endangered species only, and fish-, 

 squid-, and plankton-feeding cetaceans. 



Biomass per unit effort 

 (kg/km) 



Cetacean category Season Mean Median Maximum 



All cetaceans All 368 67 15,170 



All cetaceans Winter 234 1 23,049 



All cetaceans Spring 423 2 20,928 



All cetaceans Summer 386 28,447 



All cetaceans Fall 270 33,747 



Endangered species All 296 15,170 



Endangered species Winter 198 12 22,048 



Endangered species Spring 350 20,268 



Endangered species Summer 323 1 27,478 



Endangered species Fall 190 1 33,072 



Piscivores All 205 21 6,920 



Piscivores Winter 139 '0 16,266 



Piscivores Spring 256 1 15,446 



Piscivores Summer 235 22,483 



Piscivores Fall 158 23,995 



Teuthivores All 83 1 4,249 



Teuthivores Winter 62 1 11,879 



Teuthivores Spring 80 3,582 



Teuthivores Summer 83 5,380 



Teuthivores Fall 79 5,625 



Planktivores All 80 12,323 



Planktivores Winter 33 12 8,190 



Planktivores Spring 87 5,874 



Planktivores Summer 68 '0 12,910 



Planktivores Fall 33 '0 5,805 



1 75th percentile value was also 0. 

 2 90th percentile value was also 0. 



Figure 2 shows the patterns of high habitat use, 

 again as the upper 10% of BPUE values, for the en- 

 tire cetacean community in each of the four seasons. 

 The seasonal patterns do not show any major dif- 

 ferences; however, a slight north-south shift in the 

 pattern is evident. The number of high-use blocks 

 is higher in the northern portion of the area and 

 lower in the southern portion during spring and sum- 

 mer than during fall and winter. It should be em- 

 phasized that the plots in Figure 2 do not indicate 

 differences in magnitude of utilization intensity 

 between seasons, but only pattern differences. Since 

 the blocks which are plotted are the upper 10% of 

 the BPUE values for each seasonal distribution, the 

 numbers of blocks plotted for each season are fair- 

 ly equivalent. For example, it appears from the plots 

 that the shelf edge may be more intensely used in 

 the winter than during the other seasons, but ac- 

 tually the reverse is true It is simply that the blocks 

 with highest winter utilization tend to be on the shelf 

 edge, but the intensity of use in these blocks is still 

 lower. Seasonal differences in intensity of habitat use 

 can be seen by referring back to Table 3. The inten- 

 sity of habitat use is highest in the spring and se- 

 cond highest in the summer for all categories except 

 the teuthivores, where the summer utilization is most 

 intense and spring and fall very close behind. There 



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