HOLT: DENSITY OF DOLPHIN SCHOOLS 



Table 1 . — Estimates of school density made during all conditions and during calm and 

 rough seas using aerial and ship data: estimates made during good and poor sun condition 

 using aerial data. Estimates are made for data in the Inshore, offshore and total areas. 

 Estimates for all conditions were calculated using 1977 through 1983 data and estimates 

 for sun and sea state conditions were calculated using 1979 through 1983 data. Estimates 

 are also presented for data collected during an aerial experiment testing effects of sea state 

 and sun glare. 



schools ( 18 trackline schools in the coastal and 10 

 schools in the offshore band were detected). Lower 

 offshore estimates for data recorded under the 

 same Beaufort state were consistent with a de- 

 creasing onshore-offshore density gradient. 



Within each band, sea state conditions were 

 also spatially stratified because the lower Beau- 

 fort conditions occurred mostly in the nearshore 

 and northern regions of each band (Fig. 3). Pre- 

 dictably, detection rates for all schools within 

 each band declined as the Beaufort condition in- 

 creased. Because of the large variability inherent 

 in small sample sizes and spatial stratification of 

 searching effort at the various Beaufort condi- 



tions, comparisons of rates of detecting trackline 

 schools did not yield consistent trends. For exam- 

 ple, within both bands, the trackline detection 

 rate for Beaufort 2 conditions was larger than for 

 Beaufort 1 conditions. In the coastal band Beau- 

 fort 5 conditions had higher trackline detection 

 rates than Beaufort 4 conditions and rates for 

 Beaufort 4 were higher than rates for Beaufort 3 

 (Fig. 5). 



Searching effort for aerial data during good and 

 poor sun conditions was also confounded with dis- 

 tance from shore (Fig. 4) and thus with sea condi- 

 tions. Most good sun conditions (78%) occurred in 

 the coastal band, whereas 59% of all poor sun 



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