For mapping purposes, the SPUE values were ranked into levels.
Calculations of effort and SPUE were performed with custom SAS programs developed at the University of Rhode Island.
Sightings of 203 whales occurred during unacceptable survey conditions (mostly due to high sea state), and eight whales were documented for cells with acceptable conditions but during which there was less than 2 km of effort during a particular 2-week period; therefore sightings of 1342 whales were included in the SPUE analysis.
The overall 5-year mean SPUE value for all 101 sampled cells was 11.
Annual mean SPUE was highest in 2000 and lowest in 2002 (Table 2), and the difference was almost an order of magnitude.
When separated into two-week periods pooled across all years, mean SPUE values varied considerably.
The timing of the SPUE maximum varied markedly between years: late February-early March in 1998, early to mid-April in 1999, late March--early April in 2000, early March to mid-April in 2001, and late February--early March in 2002.
The majority of cells within which right whales were sighted were inside the critical habitat, but 17 cells with SPUE >0 fell partially or entirely outside the critical habitat (Fig.
The SPUE analysis provided a more refined interpretation of raw sighting data than have earlier analyses by reducing bias caused by uneven allocation of effort.
The boundaries of the Cape Cod Bay critical habitat encompassed the areas of highest SPUE values when pooled across all years and periods, and therefore the existing boundaries appear to service as a good management unit.
The significant interannual variations in mean SPUE and timing of annual SPUE maxima were likely due to physically forced changes in available food resources.
The results of the aerial surveys and SPUE analysis confirmed earlier findings of Hamilton and Mayo (1990) in that peak occurrence of right whales in the study area occurred from February through April.