known that seven taxa of mammals and nine taxa of birds occurred in the subunit. For 

 some species the seasonal data set includes three daily estimates of abundance; for 

 others only one or two daily estimates exist. 



Clearly, replicates add information and robustness to the sampling strategy. The 

 number of replicates necessary to monitor the entire fauna is unknown. However, the 

 need for replicates and information over a broad geographic area must be balanced with 

 cost, time, and logistical considerations. As seasonal and annual replicates are compared 

 with daily replicates in future studies, an approximation of the relative effectiveness of 

 the sampling strategy will be able to be evaluated. 



The seasonal variation seen during the Pilot Study appears to be largely a result of 

 seasonality and not a product of increased sampling as might be expected if three 

 replicates were inadequate to approximate occurrence and frequency. 



BATHYMETRY AND DISTANCE FROM SHORE 



Marine animals vary in their distribution offshore and in the depths of the waters 

 in which or over which they occur. Both of these variables were analyzed quantitatively 

 as well as graphically. In general, maps were used to illustrate the distribution of animal 

 groups in relation to bathymetric contours and the shoreline, and within the individual 

 survey subunit. These maps also show the position of a species in relation to other 

 species. 



In most areas the depth of the ocean increases with the distance offshore. 

 However, the width of the continental shelf affects the relationship of these 

 environmental factors. In the STEX survey subunit the continental shelf is narrow and 

 the 200-m contour is approximately 90 km from the coastline (Map 2). Maximal depths in 

 STEX approach 2,400 m. The bathymetric contours of the NTEX subunit are more 

 complex (Map 3). In the northeastern extreme of this survey subunit, maximal depths are 

 409 m at a distance approximately 170 m from the nearest point on the Texas coast and 

 over 200 km from the landward extreme of the actual survey subunit. The 200-m contour 

 is within 90 km of shore. The southeastern extreme of the NTEX subunit is near the 

 1,500-m contour at a distance of 222 km from the shoreline of Texas. The NFLA subunit 

 has a more regular and gradual bathymetric profile with depths of approximately 200 and 

 280 m, 222 km offshore at the southwestern and southeastern extremes respectively (Map 

 4). In SFLA the shelf is wider and the 200-m contour is approximately 260 km from the 

 west coast of Florida (Map 5). 



The diversity in bathymetric profiles in relation to offshore distance potentially 

 offers an opportunity to separate the relative effects of distance and depth on the 

 distribution of animals in the Gulf of Mexico. If a species was consistently further 

 offshore in areas of greater continental shelf width, depth was considered to be 

 potentially more important than distance in delimiting the movements and occurrence of 

 that species. Identification of such relationships is important for predicting distributions 

 in areas studied less intensively, and for estimating abundance in a variety of geographic 

 and environmental situations. 



Waters of moderate to shallow depths are known to support a greater species 

 diversity and abundance than waters further offshore. This relationship between animal 



42 



