Similarly, the larger geographic area and ability to sample intervening areas will 

 facilitate identification of movement patterns and their relative significance in local and 

 overall populations. 



SEA SURFACE TEMPERATURES 



The sea surface temperatures recorded during the Pilot Study are comparable to 

 winter and summer patterns previously known for the Gulf of Mexico (Leipper 1954). 

 During August sea surface temperatures were warmer nearshore, decreasing in a seaward 

 direction, but overall they remained quite uniform. For example, the mean temperatures 

 recorded for each species observed in STEX ranged from 28.0" to 29.2° C. The mean 

 temperatures observed in NTEX were slightly lower (27.5° to 28.6° C), as would be 

 expected moving from south to north in the western Gulf of Mexico. In both Texas 

 subunits during August, certain birds only seasonally present (i.e., absent in November) 

 were concentrated in the areas of lowest sea surface temperatures. These species 

 included sooty terns and masked boobies. The latter species, a diving bird poorly known 

 in Texas waters, was reported to be one of the most conspicuously effected bird species 

 during the Ixtoc oil spill (NOAA news briefing 1979). 



During November temperatures were not only lower, but the temperature gradient 

 from shore to seaward was reversed in relation to August. Temperature gradients were 

 steepest off NTEX and NFLA, which may explain the absence or low numbers of marine 

 mammals during November surveys in these subunits. Whether the scarcity of bottlenose 

 dolphins in STEX during August and in NTEX during November represents seasonal 

 movements in response to temperatures remains to be confirmed, but temperatures 

 where these dolphins were observed in Florida during both seasons were comparable to 

 those in Texas waters. Movements into and out of coastal lagoons also may account for 

 the intermittent absence of bottlenose dolphins in Texas survey subunits (Schmidly and 

 Shane 1978). 



OBSERVER BIAS 



The quantification of observations by independent observers on opposite sides of 

 the aircraft depends upon the comparability of sighting frequencies. Visual scan 

 patterns, observer confidence, and individual reaction times are all important factors, 

 but their effects can be minimized by appropriate training. A matched pair of observers 

 simultaneously flying over the same geographic area would be expected to record 

 approximately equal numbers of sightings and similar faunal compositions. Some 

 deviation from a 50% frequency would be explained by sampling error and random 

 deviations. Figure 5 charts the deviation of the observer pairs from the expected 50% 

 sighting frequency. Only in two sampling periods does the deviation reach 15%. The 

 samples in Figure 5 are arranged in chronological order from left to right and a trend 

 toward reduction of the deviation is apparent as the observer team gained experience and 

 methods were improved. 



This trend is probably explained by added observer experience and the 

 improvement of observer methods during the Pilot Study. No discernible differences 



63 



