interacting factors that affect salinity such as freshwa- 

 ter 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 enlarges the tidal fresh 

 zone, the distribution of a species confined to that zone 

 increases to include the new area. If a species tolerates 

 a wide range of salinity, a shift may or may not occur. 

 The assignment of a species in a salinity zone was 

 ultimately determined by where they have been regu- 

 larly observed or captured. 



Species temporal distributions are often dependent on 

 annual climatic conditions and water currents. Monthly 

 distribution patterns were derived based on the consis- 

 tent presence of a life stage within a particular month. 

 If a species was only present during unusual events 

 (e.g., drought), it was not included in the description of 

 that species' distribution. However, if a species regu- 

 larly occurs, even during a restricted time period, it was 

 considered to be present for the specific month(s). 

 Greater temporal resolution, such as on a biweekly 

 rather than on a monthly basis, was not feasible. 



Data reliability analysis. Mean data reliability by 

 estuary was highest for the Sheepscot River and 

 lowest for Narraguagus Bay (Figure 7). The reliability 

 estimates seem to reflect the amount of fisheries 

 research that has been conducted within an estuary. 

 These data reveal that some estuaries have been the 

 focus of numerous studies (e.g., Passamaquoddy Bay, 

 Sheepscot River, Great Bay, Cape Cod Bay), particu- 

 larly those that have academic/state research facilities 

 or industries requiring environmental monitoring (e.g., 

 nuclear power plants). These estimates also suggest 

 that many smaller bays and estuaries have not been 

 extensively researched (e.g., Englishman/Machias 

 bays, Narraguagus Bay, Saco River, Wells Harbor, 

 Merrimack River). 



• When averaged across estuaries and analyzed by 

 salinity zone, data reliability was lower in the tidal fresh 

 than in the mixing and seawater zones. This may be 

 because the selected species are primarily estuarine, 

 not freshwater. In addition, relatively few systematic 

 faunal surveys have been conducted in tidal freshwa- 

 ters. 



• Data for juveniles and adults were most reliable, while 

 data for spawning adults, larvae, and eggs (particularly 

 demersal eggs) were less certain. This reflects that 

 most biological surveys have focused on adult and 

 juvenile life stages. Species-specific studies of spawn- 

 ing adults, larvae, and eggs have not been conducted 

 in most estuaries. Thus, some of the information for 



these life stages was inferred from general life history 

 studies and data from similar estuaries. 



• When averaged across salinity zones and life stages, 

 and analyzed by species (Figure 8), data reliability was 

 relatively high for most of the highly exploited commer- 

 cial and recreational species (e.g., bivalves, Atlantic 

 salmon, striped bass), and for endangered species 

 (shortnose sturgeon). This reflects the comparatively 

 greater number of studies conducted to monitor and 

 manage species that are economically important . Data 

 reliability was relatively low for several species that: 1 ) 

 were at the edge of their environmental ranges (e.g., 

 daggerblade grass shrimp, tautog); 2) were of little 

 commercial importance (e.g., sticklebacks, smooth 

 flounder); 3) had relatively unclear present distribu- 

 tions compared to past estimates (e.g., haddock, At- 

 lantic sturgeon); and/or 4) had certain life stages that 

 were unavailable to conventional gear types (e.g. , rock 

 gunnel, American sand lance). 



Figure 7. Mean data reliability by estuary. 



Less 

 certain 



Data reliability 



Estuary 

 Cape Cod Bay 

 Boston Harbor 

 Massachusetts Bay 

 Merrimack River 

 Great Bay 

 Wells Harbor 

 Saco Bay 



Casco Bay 

 Kennebec/ 

 Androscoggin Rivers 

 Sheepscot River 



Damariscotta River 



Muscongus Bay 



Penobscot Bay 



Blue Hill Bay 



Narraguagus Bay 



Englishman/ 

 Machias Bays 

 Passamaquoddy Bay 



Less 

 certain 



Data reliability 



13 



