PAYNE ET AL.: DISTRIBUTION OF HUMPBACK WHALE 



topography are also critical factors in the foraging 

 strategy of humpbacks, hence the present distribu- 

 tion of these whales. We base this hypothesis on 

 observed sightings of humpbacks throughout the 

 shelf waters of the northeastern United States in 

 relation to sand eel abundance, and on an apparent 

 shift in the center of feeding areas used by hump- 

 backs in the Gulf of Maine since the mid-1970's. 



METHODS 



The collection of fisheries data used in these 

 analyses was carried out by National Marine Fish- 

 eries Service/Northeast Fisheries Center (NMFS/ 

 NEFC) scientists and technicians on domestic 

 research vessels during standardized spring bottom- 

 trawl surveys. These surveys measure trends in fin- 

 fish population abundance and have been used to 

 monitor changes in the size and composition of fin- 

 fish biomass (Clark and Brown 1977; Grosslein et 

 al. 1980). 



Meyer et al. (1979) found that spring (March-May) 

 bottom-trawl surveys accurately reflect trends in 

 sand eel abundance. Therefore, the fisheries data 

 we examined were from these surveys, 1978-82. The 

 stratified mean catch per tow of sand eel was 

 calculated for each region and considered propor- 

 tional to the population size within each region. We 

 transformed the mean catch into logarithmic values; 

 then, using a two-way analysis of variance (F- 

 statistic), we compared sand eel population size by 

 region and year. 



The survey area includes shelf waters from Cape 

 Hatteras north to Nova Scotia and has been spatially 

 stratified by the NMFS/NEFC, based principally on 

 depth and latitude (Grosslein 1969). Sampling sta- 

 tions are randomly assigned within a stratum and 

 the number of stations allocated to strata approx- 

 imately in proportion to the area of each stratum 

 (Grosslein 1969). In this study, individual stratum 

 have been combined into regions (Fig. 1), in a man- 

 ner consistent with NMFS/NEFC management 

 units. The two important regions emphasized are 

 the Gulf of Maine and Georges Bank. 



Sightings of humpback whales were recorded by 

 observers from the Manomet Bird Observatory 

 (MBO) on NMFS/NEFC research vessels conducting 

 standardized surveys. Observations were recorded 

 continuously along the predetermined cruise path 

 between the sampling stations (following Payne et 

 al. (1984)) in 15-min periods where each period 

 represents a transect. Thus, the duration of each 

 observation period was constant, but the linear km 

 surveyed within each 15-min period depended upon 



vessel speed. The location (latitude-longitude) of 

 each 15-min observation and the location and num- 

 ber of humpback whales observed were recorded 

 and assigned to appropriate regions to facilitate 

 direct comparisons between the observed number 

 of humpbacks per linear km (humpbacks/effort) and 

 potential prey densities. 



Humpback whales are generally present in the 

 study area from spring through fall (March-Novem- 

 ber) and absent during the winter (CETAP 1982). 

 Therefore, sighting data and effort for winter 

 months were excluded from the analyses. We also 

 examined sighting data collected only during op- 

 timum sea conditions less than Beaufort (Kenney 

 et al. 1981) (<16 nmi/h). Difference between the 

 number of humpbacks/effort sighted by region and 

 year were also compared by a two-way analysis of 

 variance (F-statistic). 



A coefficient of correlation (r) from the linear 

 regression between the stratified mean catch of sand 

 eel (log) and the number of humpbacks/effort was 

 used to determine whether concentrations of hump- 

 back whales co-occurred with patches of sand eel 

 within regions of the Gulf of Maine and Georges 

 Bank. 



A P < 0.05 was considered statistically significant. 



RESULTS 



Distribution of Sand Eel 



The stratified mean number of sand eel varied sig- 

 nificantly between regions on Georges Bank (F = 

 14.14, df = 3, 12) and in the Gulf of Maine (F = 

 16.90, df = 2, 8). On Georges Bank, sand eel were 

 very abundant on the shoals with catches ranging 

 from 1.117 sand eel/tow (log value) in 1978 to 2.846 

 (log value) in 1982 (Table 1). Sand eel were absent 

 from most tows along the northern and shelf edges. 

 Sand eel were also abundant in the southwest Gulf 

 of Maine ranging from 0.670 sand eel/tow (log value) 

 in 1978 to 2.422 in 1981 (Table 1). Sand eel were not 

 abundant in the deeper, central Gulf of Maine This 

 patchy distribution reflects a known preference of 

 the sand eel for sand-bottom substrates (Bigelow and 

 Schroeder 1953) characteristic of submarine banks 

 and shoals. No significant differences were found 

 between the stratified mean catch per tow (log value) 

 by year. 



Distribution of Humpback Whales 



Since 1978, the observed number of humpbacks/ 

 effort in the Gulf of Maine has steadily increased 



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