Results of a Preliminary
Survey of Fishes of the Patuxent River on the
Purpose and Background
To update our knowledge of the fish fauna of the Patuxent River, we collected fishes by seining and electrofishing at three localities on PWRC property in September 1997. Historically, at least 45 fishes occurred in the Patuxent River at PWRC (1979 reprint and revision of N. Hotchkiss and R. E. Stewart, 1947, Vegetation and vertebrates of the Patuxent Wildlife Research Center: outline of ecology and annotated lists). As of 1979, 15 of the listed fish species were noted as perhaps gone. Collections during the 1960's indicated replacement of native riverine species by fishes more common in organically enriched lentic habitats (Tsai 1968, Chesapeake Science 9: 83-93). More recent data on extant fishes at PWRC appeared limited, and included a seining effort in the Little Patuxent River in 1992 by students from the University of Maryland (H. Obrecht, personal communication).
We sampled fishes by seining (10 ft seine) and by backpack electrofishing at three localities within a 3 km reach of the Patuxent River, on 09-10 September 1997 (Table 1). Discharge in the river was low, allowing us to sample most habitats in the stream, to a depth of about 1 m. All collected fishes were preserved and returned to a laboratory for identification and measurement.
We collected a total of 19 species (Table 2). These included five fishes previously listed as perhaps gone from the river at PWRC: cutlips minnow (Exoglossum maxillingua), redbreast sunfish (Lepomis auritus), shield darter (Percina peltata), tessellated darter (Etheostoma olmstedi, listed as E. nigrum in Vegetation and vertebrates of the PWRC), and glassy darter (Etheostoma vitreum). We also collected one species, yellow bullhead (Ameiurus natalis) not listed in Vegetation and vertebrates of the PWRC. The yellow bullhead natively occurs across a wide portion of the eastern and central United States, and its occurrence in the Patuxent River is not unexpected.
Two species numerically dominated our collections, the swallowtail shiner (Notropis procne, 43% of all individuals) and the tessellated darter (28% of all individuals). Both fishes were collected in the vicinity of Duvall Bridge in 1945 but not in 1966 (Tsai 1968, Chesapeake Science 9: 83-93). The glassy darter, cutlips minnow, fallfish (Semotilus corporalis) and redbreast sunfish also occurred in 1945 collections, were not found by Tsai in 1966, but were present in 1997 collections. The fallfish and glassy darter were relatively abundant in our samples, whereas we caught only one cutlips minnow (Table 2). In all, eight of the 19 species collected in 1997 were represented by only one or two individuals. The four most abundant fishes (swallowtail shiner, tessellated darter, fallfish and glassy darter) had wide size ranges present, representing at least two age classes for each species.
The occurrence of a suite of fishes not found in 1966 could indicate partial recovery of the native fauna in the Patuxent River since reportedly severe pollution in the 1960's. We failed, however, to find a number of fishes known from earlier collections and for which there appears to be suitable physical habitat available. These include the stripeback darter Percina notogramma, the rosyside dace Clinostomus funduloides and at least five other riverine cyprinids, any catostomid (sucker) species other than the relatively tolerant white sucker Catostomus commersoni (at least 3 other species possible), and either of the possible species of madtom catfishes (genus Noturus). One of the cyprinids that we expected but did not find, the satinfin shiner Cyprinella analostana, was collected by University of Maryland students seining in the Little Patuxent River in 1992, along with the same three darter species that we found and eight other more common fishes (H. Obrecht, personal communication).
Our effort was limited to a relatively small portion of the Patuxent River. A more extensive survey of the river habitat at PWRC would likely discover additional fishes. It would also be interesting to investigate the relationship of riverine populations on PWRC property to fauna occurring in upstream and downstream portions of the drainage. To what extent, for example, does PWRC property function as a refuge for river fauna? We conceptualize rivers as primarily unidirectional systems in which upstream processes and events (e.g., contaminant inputs or flow alteration) may strongly influence communities for some distance downstream. Recovery from upstream disturbances is expected to occur along a downstream gradient, so that a physically protected but relatively short reach might be overwhelmed by upstream degradation and might lack downstream refuge populations. However, the reoccurrence of a number of previously rare fishes in the reach of the Patuxent River that crosses PWRC suggests that other refuges exist in the drainage and (or) that the physically protected conditions at PWRC allow local recovery of system function sufficient to support a portion of the native community. The absence of other expected fish species may (or may not) indicate that habitat degradation is too extensive throughout the drainage for these species to persist. If more extensive surveys failed to find these species, analyzing their ecological characteristics could provide information on what types of fishes are most vulnerable to extirpation in urbanizing rivers. Investigation of invertebrate diversity, composition and productivity in the Patuxent River at PWRC and elsewhere in the drainage could also elucidate longitudinal changes in river function that result from local changes in land-use. Understanding how forested (or otherwise protected) patches along a river corridor may contribute to preserving the native fauna and system function could significantly contribute to river management strategies in urbanizing landscapes.
Table 1. Localities of PWRC-Patuxent River fish collections, September 1997.
|Field #||Date||Locality and Habitat Description|
|MCF 97-13||970909||Patuxent River, 2.5 air km upstream from Duvall Bridge, 2.2 air km downstream from Baltimore-Washington Parkway crossing. Seined an approximate 30 m reach of the river containing pool habitat to 1 m in depth, with abundant woody debris. Very low flow; current imperceptible in pools. Mary Freeman and John Seginak.|
|MCF 97-14||970909||Patuxent River, 1.8 air km upstream from Duvall Bridge, 2.8 air km downstream from Baltimore-Washington Parkway crossing. Seined an approximate 30 m reach of the river containing shallow riffle habitat with interspersed pools, gravel substrata and large woody debris, and one patch of emergent vegetation. Mary Freeman and John Seginak.|
|MCF 97-15||970910||Patuxent River at and up to 0.5 km downstream from Duvall Bridge, 4.5 - 5 air km downstream from Baltimore-Washington Parkway crossing. Backpack electrofished and seined; habitat comprised riffle and pool sequences with abundant woody debris. Mary Freeman, John Seginak and Donald White.|
Table 2. Fishes collected from the Patuxent River at the Patuxent Wildlife Research Center, 09-10 September 1997. Numbers of individuals are separately listed by collection field number.
|Petromyzon marinus||sea lamprey||1|
|Anguilla rostrata||American eel||1||5|
|Esox niger||chain pickerel||2|
|Exoglossum maxillingua||cutlips minnow||1|
|Notropis procne||swallowtail shiner||116||53||88|
|Notropis hudsonius||spottail shiner||2|
|Catostomus commersoni||white sucker||1|
|Ameiurus natalis||yellow bullhead||1||1|
|Gambusia holbrooki||eastern mosquitofish||3||4|
|Enneacanthus gloriosus||bluespotted sunfish||7|
|Micropterus salmoides||largemouth bass||2|
|Lepomis auritus||redbreast sunfish||2||4|
|Percina peltata||shield darter||10|
|Etheostoma olmstedi||tessellated darter||18||35||110|
|Etheostoma vitreum||glassy darter||1||35|
24 November 1997