FISHERY BULLETIN: VOL. 78, NO. 3 



area. Poff ^ reported that Thick Fin remained pre- 

 dominantly a spring and summer resident and 

 Bent Fin primarily a fall and winter resident in 

 the study area through midsummer 1979. 



Daily Movements 



Field observations indicated that tide and time 

 of day influenced the movement patterns of dol- 

 phins in some sections of the study area. Most 

 apparent was the tendency of dolphins in the lower 

 sections of the study area ( 1, 3, and 6 on Figure 1) to 

 move up against an ebb tide. The most apparent 

 time of day effect occurred in Morris and Cum- 

 mings Cut (section 5) where dolphins moved 

 northward early in the day, all directions at mid- 

 day, and southward late in the day. 



The chi-square test showed that tide and direc- 

 tion of movement were significantly related 

 (P<0.0001) in the lower section of the study area 

 (sections 1, 3, and 6 combined) at three separate 

 periods of the day (early, midday, late) and at all 

 times of day combined. At all time periods most 

 dolphins moved up during ebb tide. During flood 

 tide most dolphins moved down, although many 



moved across the channel or randomly. The associ- 

 ation between tide and direction of movement was 

 strongest early (V - 0.513) and weakest at midday 

 (V — 0.297) with intermediate values late (V = 

 0.410) and at all times combined (V = 0.407). Di- 

 rection of movement and tide were significantly 

 related in four of the six sections of the study area 

 considered (Table 2). 



The relationship between direction of move- 

 ment and time of day also proved significant in 

 four out of six sections under some conditions (Ta- 

 ble 3). The observations on dolphin movements in 

 Morris and Cummings Cut were quantitatively 

 confirmed, and the association between direction 

 of movement and time of day was stronger in that 

 section than in any other section (see Cramer's V 

 values in Table 3). 



The frequency of sightings of groups of dolphins 

 was calculated for all of the conditions presented 

 in Tables 2 and 3. In all cases where the relation- 

 ship between the variables was significant (chi- 

 square P<0.01), the group sighting data con- 

 formed with the individual sighting data. 



Individual Distribution Patterns 



*M. Poff, Research Assistant, University of Texas, Marine Sci- 

 ence Institute, Port Aransas, TX 78373, pers. commun. July 

 1979. (Deceased.) 



Sightings of each recognizable individual were 

 confined to a specific portion of the study area 

 rather than distributed randomly throughout the 



Table 2. — Relationship between direction of movement and tide proved significant (chi-square P<0.01) in 

 four sections of the Port Aransas, Texas, study area at certain times of day. Numbers in the table represent 

 frequency of individual dolphin sightings. Cramer's V indicates strength of the relationship between the 

 two variables, and each V is comparable with every other V. 



' Insufficient data in a given case made the chi-square test potentially invalid. 



596 



