FISHERY BULLETIN: VOL. 83, NO. 3 



Changes in Relative Abundance 

 Between 1970 and 1978 



Table 1 gives sightings of individuals per hour by 

 month for each year from 1970 to 1978. As some 

 observation periods were eliminated (see above) the 

 results sometimes differ slightly from values given 

 by Gaskin (1977) for the earlier years. Results sug- 

 gest a decline in relative abundance from 1972 on- 

 wards in Fish Harbour and from 1974 onwards in 

 Simpson's Passage. Because the 1970 values were 

 based on a relatively short series of observations, the 

 apparent rise from 1970 to 1971 may be spurious. 

 The slight increase in 1978 is also suspect as most 

 observers were less experienced than the teams used 

 in 1970-77. The overall trend however, seems unmis- 



takable. Furthermore, a decline in each month of the 

 July-September period is evident when data for the 

 whole study area are pooled (Fig. 2). 



Results of the categorical data procedure tests for 

 relative abundance of porpoises against the set of en- 

 vironmental parameters are presented in Table 2 

 (Fish Harbour) and 3 (Simpson's Passage). As might 

 be expected, large x^ and significant P values were 

 generated from the sharp drop in overall numbers 

 sighted per observation period (regardless of its 

 length) from 1972 to 1975, and from the great in- 

 crease occurring each year between July and 

 September. Time of day appeared to exert no in- 

 fluence on relative abundance in either section (P = 

 0.45, 0.20), nor was any statistically significant rela- 

 tionship noted between relative abundance and 



0) 



c 





i 



1 



^ \ 



, » 





Aug. \ 



i ! 



.■n 



July 



Oct. 



Figure 2. -Comparison of sightings per hour of 

 porpoises in good condition in the Fish Harbour 

 study area (Fish Harbour + Simpson's Passage), 

 1970-78 by month, from July to September. Octo- 

 ber and November values available for 1978 only. 

 Vertical dots and bars represent standard error 

 about the means. 







- Nov. 2 

 -. » 



1970 1971 1972 1973 1974 1975 1976 1977 1978 



Year 



432 



