Payne et a\ Abundance fluctuations of baleen whales in the southern Gulf of Maine 



689 



70°00' W 



ATLANTIC 

 OCEAN 



Figure 1 



Baleen whale study area in southern Gulf of 

 Maine (outlined) and geographical regions 

 referred to throughout the text. 



Whale sighting data Data for this study on the oc- 

 currence and distribution of humpback, fin, right, and 

 sei whales were collected by naturalists working aboard 

 commercial whalewatching vessels during the study 

 period 1982-88. Data recorded from these vessels for 

 all cetacean sightings include species, group size, time, 

 location (using LORAN-C), behavior, and the photo- 

 graphically confirmed identity of individual animals. 

 Vessels ran 4-hour cruises to the Stellwagen Bank and 

 Massachusetts Bay areas from two ports: Province- 

 town and Plymouth, Massachusetts. The cruise track 

 of the whalewatching vessels was decided by the cap- 

 tain based upon the greatest number of whale sightings 

 recorded on the previous trip or day; consequently, 

 sampling was neither random nor systematic. None- 

 theless, the intensity of the coverage resulted in ex- 

 tremely comprehensive surveys of the region during 

 most of the study period. The information collected 

 aboard these vessels in this region represents one of 

 the most detailed databases available anywhere on a 

 multispecies group of whales. 



Data used in this study were taken from the first 

 cruise of each day from each of the two ports and con- 



sidered a reliable index of relative abundance of whales 

 in the area. The total number of whales observed dur- 

 ing each morning whalewatching trip from each port 

 was summed by species and month, June-September 

 (the period when coverage from whalewatching vessels 

 was effectively continuous). These totals were then 

 divided by the number of trips each month (each trip 

 was considered a unit of effort), resulting in an index 

 of whale abundance, expressed as number of whales/ 

 effort/month for each species between 1982 and 1988. 

 While there are undoubtedly biases associated with the 

 collection of these data, the intensity of coverage is 

 such that this index can be used to accurately monitor 

 relative changes in the local abundance and distribu- 

 tion of whales. 



Using these sighting data, the temporal co-occur- 

 rence between the four whale species within the 

 study area was tested by ranking the mean number of 

 whales/effort/month (by species), then calculating 

 Spearman's coefficient of rank correlation (rj (Zar 

 1984) between species for all paired data, 1982-88 

 (A^ = 28 for each possible pairing). 



