In addition to the species mentioned above, we have encountered other fishes in Hudson River tributary mouths. Our observations of these species range from seeing certain life stages consistently but temporarily in tributary mouths to seeing an occasional individual.
We have already mentioned that some fishes maybe feeding on alewife eggs during their spring spawning runs (e.g., white perch). We often see adult predatory fishes in tributary mouths in the spring and our hypothesis is that they are following anadromous and potamodromous species upstream to feed on them or their eggs. These species include striped bass (Morone saxatilis), catfishes (Ameiurus catus, A. natalis, A. nebulosus, Ictalurus punctatus), chain pickerel (Esox niger), largemouth bass (Micropterus salmoides), and walleye (Sander vitreus). We have no information that would provide a test for this hypothesis. If we accept that we are observing a feeding migration, the concentration of forage fishes and eggs in a small area in the early season could be a significant nutritional supplement for these opportunistic predators.
After the spring concentration of migratory fishes subsides in Hudson River tributaries, there is a summer and fall occurrence of immature fishes. We have only examined one tributary thoroughly through this time period (Quassaic Creek - RKM 96.5, Lake and Schmidt, 1997) but incidental observations elsewhere suggest that our observations on Quassaic Creek are applicable to other tributaries.
These small herrings (Alosa aestivalis, A. pseu-doharengus, A. sapidissima), white perch, striped bass, and spottail shiner are found throughout the Hudson estuary in large numbers and, although it is tempting to suggest that tributary mouths provide some valuable habitat for these fishes, they may be seen in tidal tributary mouths simply because they are widespread in tidal waters. Young-of-year bluefish (Pomatomus saltatrix), and crevalle jack (Caranx hippos) are regularly found in the vicinity of tributaries in Haverstraw Bay and southward (Juanes et al., 1993; McBride and Able, 1995) and have been observed at least in the Croton River (Wallhauser and Tashiro, 1989). Bay anchovy are similarly very abundant in the southern end of the estuary (Schmidt, 1992) and are often observed in tributary mouths.
We must mention that we have observed yoy and yearling blue crab (Callinectes sapidus) in tributary streams. RES collected them as far north as the Poesten Kill (RKM 241.5) and as far as 4 km (approximately) from the tidal Hudson River in Minisceongo Creek (RKM 64.5; Schmidt and Cooper, 1996). The presence of these animals in certain tributaries varies interannually. We have no information on what significance this behavior may have for blue crab or for the tributary mouth habitat.
Finally, there are a number of fishes that we have encountered occasionally in tributary mouths. The mainhabitats for these species are elsewhere in the watershed, either upland in lentic or lotic environments, or in the tidal Hudson River. The presence of these species enhances the diversity of the tributary mouth habitat, but our observations indicate that they are occasional wanderers and probably do not interact significantly with the other species mentioned above. Theoretically, any species in the watershed would probably show up in a tributary mouth and one could consider our observations as a small sample of that possibility. It is possible that some of these species might be more accurately classified in some other category of tributary use, but our sampling efforts were inadequate to document seasonal or interannual use of the tributaries.
There is a bias in our efforts to sample tributaries. The vast majority of our effort has been in tributaries in the freshwater portion of the Hudson River (roughly north of RKM 75). We expect that a number of euryhaline (for example, Menidia spp., Microgadus tomcod) and marine species (for example, Pseudopleuronectes americanus, Cynoscion regalis) would appear in tributary mouths in the vicinity of the higher salinity areas of the Hudson River, but we feel our sampling has been inadequate to document the presence of these species.
Summary. The young-of-year individuals and their predators that appear in Hudson River tributaries are an indicator of the dynamic nature of the fauna in tributary mouths and of the nursery function of the Hudson River in general. We have no information about whether tributaries are playing a significant role as nursery areas.
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