partially due to the fact that the selected ELMR species 

 are primarily estuarine, not freshwater species. Also, 

 there may be fewer published studies of the tidal fresh 

 zones of many estuaries. 



• Estuarine utilization by adults, juveniles, and larvae 

 is highest in the summer, and lowest in the winter 

 (Figure 6). 



• The number of species present as larvae in the mixing 

 and seawater zones is highest in June and July (Figure 

 6). 



Data Content and Quality 



An important aspect of the ELMR program, especially 

 since it is based primarily on published and unpub- 

 lished literature and consultations, is to determine the 

 quality of available data. For many species, gear 

 selectivity, difficulty in identifying larvae, and difficulty 

 in sampling various habitats has limited the amount of 

 reliable information. Therefore, a deliberate effort was 

 made to assess data reliability so that the data base 

 could be used appropriately. 



Estimates of the reliability of the distribution and abun- 

 dance information organized by species, life stage, 

 and estuary are presented ui Table 6 (pp. 157-190) of 

 the Data Summary Tab/es section. Data reliability was 

 classified using the following categories: 



• Highly certain: considerable sampling data available. 

 Distribution, behavior, and preferred habitats well docu- 

 mented within an estuary. 



• Moderately certain: some sampling data availablefor 

 an estuary. Distribution, preferred habitat, and behav- 

 ior well documented in similar estuaries. 



• Reasonable inference: little or no sampling data 

 available. Information on distributions, ecology, and 

 preferred habitats documented in similar estuaries. 



The quality and quantity of available data vary by 

 species, life stage, and estuary. For example, a large 

 amount of information is available on blue crab be- 

 cause they are highly valued both commercially and 

 recreationally. For most species, the least amount of 

 information and poorest quality of data occur for the 

 spawning, egg, and larval life stages. Except for a few 

 species (e.g., blue crab), little data has been generated 

 on particular habitat preferences and environmental 

 tolerances. This is particularty true for the smaller 

 forage and/or non-commercial fishes and invertebrates. 

 Gear selectivity, inability to correctly identify larval 

 stages, and difficulty in sampling various habitats limits 

 the development and reliability of this information. In 



addition, life history data are lacking on some of the 

 commercially important sciaenid and pelagic species. 



Data reliability was also based on experimental design 

 and whether the studies were relatively recent. In the 

 case of limited studies, information was occasionally 

 inferred. An opportunity exists to refine the data 

 presented based on additional reviews. 



Given that the amount and quality of available informa- 

 tion varies by species, by life stage, between estuaries, 

 and even within an estuary, considerable scientific 

 judgment is required to derive or infer spatial and 

 temporal distributions from existing data and available 

 literature. Unfortunately, even the most informed judg- 

 ment is far from perfect due to the complexity of 

 estuarine systems. Consequently, information on the 

 level of certainty associated with each data element 

 must be presented when synthesizing multiple data 

 sets (Table 6). Appendices 2, 3, and 4 provide a 

 complete summary of the personal communications 

 and primary references used so that readers can track 

 and obtain additional information efficiently. 



Variability in Space and Time. Species data were 

 organized according to the salinity zone boundaries 

 developed for each estuary in the NEI data atlas- 

 Volume 1 (NOAA 1985). However, division of an 

 estuary on the basis of salinity is highly variable due to 

 the many interacting factors that affect salinity, such as 

 variations in freshwater inflow, wind, and tides. To 

 compile information on species distribution according 

 to these zones, it is assumed that if a particular salinity 

 zone expands or contracts, the distribution of a mobile 

 species in that zone will correspond to the shift. For 

 example, if increased freshwater inflow shifts the tidal 

 fresh zone further down the estuary, the distribution of 

 a species confined to that zone increases to include the 

 new area. If a species exhibits a wide range of salinity 

 tolerance, a shift may or may not occur. The placement 

 of species in a salinity zone was ultimately determined 

 by where they have been observed or captured. 



Species temporal distributions are often dependent on 

 annual climatic conditions and water currents. Monthly 

 distributional patterns were derived based on the con- 

 sistent presence of a life stage within a particular 

 month. If a species is only present in an estuary in 

 unusual years (e.g., drought), it was not portrayed as 

 part of that species' spatial or temporal distribution. 

 However, if a species is usually there, even during a 

 restricted time period, it was considered present forthe 

 specific month(s). Greater temporal resolution, such 

 as on a biweekly rather than on a monthly basis, was 

 not feasible. 



