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Abstract -
We report the extirpation of Notropis bifrenatus (Bridle Shiner) from Maryland. This once widespread species has not been observed in this state since 1984 despite recent and extensive collection efforts in areas of historical occurrence. Based on these results, the status of the Bridle Shiner in Maryland was changed from endangered to endangered/extirpated in 2010.
Notropis bifrenatus (Cope) (Bridle Shiner) is a small cyprinid fish (Fig. 1) that prefers clear and slow-flowing streams, rivers, and lakes with abundant aquatic vegetation and a fine substrate (Harrington 1947, Jenkins and Burkhead 1994). It is known from the Lake Ontario-St. Lawrence River basin in Canada to the Santee River basin in South Carolina (Jenkins and Burkhead 1994, Rohde et al. 2009, Starnes 2002). Although it seems to prefer lakes and non-tidal rivers throughout most of its range (Jenkins and Zorach 1970, Rohde et al. 2009), 33 of 55 (60%) Maryland records are from tidal portions of tributaries to the Chesapeake Bay. The majority of these tidal records are from the Potomac River and tributaries from Bryan Point south to Liverpool Point, and from the northern portion of the Chesapeake Bay from Northeast River to Spesutie Island. Although these areas are predominately oligohaline (<5 ppt salinity), this Shiner has been reported in salinities as high as 11.8 ppt (Hildebrand and Schroeder 1928, Murdy et al. 1997). The Shiner was also historically collected in non-tidal, freshwater portions of the Bush, Gunpowder, Patapsco, Severn, South, and Patuxent river basins on the western shore of the Chesapeake Bay, and in the Chester, Choptank, Nanticoke, and Atlantic Coast basins on the Delmarva Peninsula (Franz and Lee 1976; Schwartz 1963, 1964). The majority of historical records (80%) date from prior to 1960, and there are only 1 1 records of the species from the past 50 years (Table 1). It was last collected in Maryland in 1984 in the northern Chesapeake Bay near Havre de Grace (Maryland Department of Natural Resources [MDNR] Fisheries Service, Annapolis, MD, unpubl. data).
Much sampling effort has been focused on this fish within its historical range in Maryland over the past 26 years (Fig. 2). MDNR Fisheries Service has routinely sampled 86 sites in the tidal, freshwater to mesohaline (5-18 ppt salinity) portions of the Potomac...