spring, 2000-2001

stages taken in ichthyoplankton surveys in the tidal Hudson River compared to their abundance in the tributaries. From 1988-95, onlyfifty-sixwhite suckers were collected in the ichthyoplankton surveys out of 107 individuals identified (J. Young, ASA Analysis & Communication, State College, PA, personal communication).

Concluding that tributaries are significant to white sucker is a relatively simple deduction from our observations, but determining whether white sucker are significant to the tidal Hudson River is considerably more difficult. Carlson (1986) reported that white sucker were as abundant as striped bass in the tidal Hudson north of RKM 169. White sucker are relatively large (47.6 cm TL individual from Coxsackie Creek, RKM 204.5), ben-thic carnivores feeding on small organisms (Yozzo, 1990; Schmidt, Chandler, and Strayer, 1995). An abundant large benthic carnivore could play a significant role in the tidal Hudson River, but white sucker is not the only species that would fit that description.

Smallmouth bass (Micropterus dolomieu). Some populations of smallmouth bass are known to be potamodromous (e.g., Robbins andMacCrimmon, 1977; Gerber and Haynes, 1988). Schmidt and Stillman (1998) provided evidence from their capture of drifting young that Hudson River small-mouth bass may be potamodromous, at least in Stockport Creek (RKM 194.5). Recent tracking of radio-tagged smallmouth bass adults showed a spring migration from the tidal Hudson River into Stockport Creek above the first barrier (J. Hecht, Lawler, Matusky, and Skelly Engineers, Pearl River, NY, personal communication). This observation substantiates the Schmidt and Stillman (1998) hypothesis.

We think that the Hudson River smallmouth bass population is entirely supported by potamod-romy. There are three pieces of evidence for this supposition. First, we have never seen a small-mouth bass nesting in the tidal Hudson River, nor have we heard any reports of smallmouth bass nesting there. Researchers have looked in the Hudson for nesting bass and have documented largemouth bass (M. salmoides) nesting in tidal water (Nack and Cook, 1987).

Smallmouth bass spend the early stages of larval development in the nest and become free-swimming at about 8 mm TL (Meyer, 1970). These free-swimming individuals are called "black fry" because they are heavily pigmented with discrete black spots (Auer, 1982). Although we have collected yoy smallmouth bass in the tidal Hudson River, especially in recent years, we have never seen a black fry in the main Hudson River. The smallest smallmouth bass we have measured was 3.1 cm TL from Tivoli North Bay (RKM 159).

Our observations of Hudson River tributaries indicate that smallmouth bass are widespread and that potamodromous migrations occur throughout the Hudson River. We base this statement on observations of nesting adults in areas where they are not resident, presence of black fry in areas with easy access to the tidal Hudson River, and the presence of smallmouth bass in the spring in tributaries where they are not resident. Some Hudson River tributaries do have resident smallmouth bass populations that can complicate our interpretations as is true for white sucker.

Smallmouth bass are a valuable resource in the tidal Hudson River. Largemouth and smallmouth bass are heavily fishedfor sport andin tournaments (Green et al., 1993). Our observations suggest that adequate spawning habitat in the tributaries and potamodromy are critical phenomena for maintaining this population.

White perch (Morone americana). The biology of white perch in the Hudson River is well documented (Klauda et al., 1988) and they spawn throughout the tidal Hudson River from the Troy Dam to Yonkers. Some portion of the population is potamodromous (Waldman, 1981) and eggs and yolk-sac larvae are common in tributaries.

White perch appear in Hudson River tributaries early in the season (late March; Lake and Schmidt, 1997) and are one of the three (white sucker and yellow perch) early spring potamodromous species. We collected adults in the spring in all tributaries where we sampled for adult fishes, but we did not necessarily confirm spawning in all Hudson River tributaries. We did not collect early life stages in the drift in Pocantico River (RKM 45), Sing Sing Brook (RKM 53), Peekskill Hollow Brook (RKM 71), and Lattintown Creek (RKM 111) although we collected adults in the latter tributary (Schmidt and Lake, 2000) and in Annsville and Sprout Creeks whose mouths are adjacent to Peekskill Hollow Brook (Schmidt and Cooper, 1996). Very few white perch early life stages were observed in Stockport Creek (RKM 194.5 - Schmidt and Stillman, 1994), but here adults may be barred from ascending the first rapids.

White perch eggs and larvae are the most to third most abundant fishes in the drift in Hudson River tributaries, median of second most abundant. Yolk-sac larvae are more abundant than eggs since the eggs are adhesive until hatching (Wang and Kernehan, 1979). White perch early life stages are present in the drift from mid-April through early June, which correlates well with their reported presence in the tidal Hudson River (Klauda et al., 1988). Spawning may continue until the end of June (Klauda et al., 1988) but we have usually stopped sampling larval drift before then.

No one has yet been able to estimate the relative contribution of tributary-spawned white perch to the egg and larval standing crop in the tidal Hudson River. This would be a Herculaean task given that white perch are spawning in most Hudson River tributaries for a rather extended period of time. We suspect, from our subjective observations, that this contribution is significant.

In addition to spawning in tributaries, TRL has observed white perch actively feeding on alewife eggs and glass eels in several Hudson River tributaries. Although many are potamodromous, there may be alternative reasons for a given individual white perch to be in a Hudson River tributary in the spring.

Yellow perch (Perca flavescens). As mentioned above, yellow perch is one of the three early spawning fishes to appear in Hudson River tributaries. Their spawning runs in tributaries are spatially erratic, being abundant in some tributaries and absent from others. Of the five tributaries we intensively sampled for adults, none were seen in Canterbury Brook (RKM 91.5) or the Moordener Kill (RKM 221), nine were collected in Quassaic Creek (RKM 96.5) andfive in Lattintown Creek (RKM 111), and substantial numbers were seen in Coxsackie Creek (RKM 204.5). TRL observed many egg strands ofyellow perch in Fishkill Creek (RKM 95.5) in 1998 and has collected many ripe females in Popolopen Brook (RKM 75.5) over the past ten years. We have collected adults in other tributaries but our spot samples, unless taken early in the season, would not necessarily detect their presence.

Drifting larvae were seen in eight of twenty-one rivers sampled (Schmidt and Limburg, 1989; Schmidt and Stillman, 1994; Lake and Schmidt, 1997; Schmidt and Lake, 2000). Larvae were collected usually in May except in two of the southern tributaries (Peekskill Hollow Brook, RKM 71 -April 15 and Pocantico River, RKM 45 - April 22) suggesting that spawning is earlier for this species along the southern tidal Hudson.

The most substantial yellow perch run that we observed occurred in Coxsackie Creek (RKM 204.5) in 1999. Adults were collected when we first began sampling on April 6 and were last seen on May 18. Most of the individuals were females (94.6 percent) and were rather small (average 22.0 cm TL, range 20.0-24.0). The males were smaller, however (average 16.7 cm TL, range 14.0-19.4). Yolk-sac and post-yolk-sac larvae were collected from April 17 through May 18, 1999, and yellow perch was the fourth most abundant species in the drift.

It is not possible for us to assess the value of tributary spawning for this species since we have no understanding of the population size in the tidal Hudson River nor do we know the magnitude of spawning that may occur in the tidal areas. The mature adults that we observed were all quite small compared to the yellow perch that support a small sport fishery (for instance in the mouth of Rondout Creek in the late fall and winter). We do not know where these larger individuals may be spawning.

Spottail shiner (Notropis hudsonius). Spottail shiner is one of the most abundant fishes in the tidal Hudson River. Some fraction of the spottail shiner population is potamodromous and we have observed spring and early summer spawning runs (Lake and Schmidt, 1997) in several tributaries. Spottail shiner larvae were the third most abundant species (after alewife and white perch) in the drift in tributaries in 1988 taking into account that many of the "unidentified minnow" specimens reportedby Schmidt andLimburg(1989)were spot-tail shiner in hindsight. Lake and Schmidt (1997) collected substantial numbers of adult spottail shiner in small mesh gill nets in Quassaic Creek (RKM 96.5) and estimated a run of 2,850 adults, almost twice as many as the potamodromous white perch.

Subsequent to the above studies, the picture of potamodromy in this species changed. We sampled Quassaic Creek in 1997 (Lake and Schmidt, 1998) using the same gill nets as in 1996 (Lake and Schmidt, 1997) and caught no spottail shiners. In fact, we have not seen a spottail shiner adult in small mesh gill nets in any tributary since (except a small catch in the mouth of the Roeliff Jansen Kill, RKM 178 - Coote, 2001). We still collect spot-tail shiner larvae in the drift (Lake and Schmidt, 1998; Schmidt and Lake, 2000) but in considerably smaller numbers than in the past. It may be that the large spottail shiners (average 11.2 cm TL; Lake and Schmidt, 1997) which would probably be 2+ years old (Schmidt, 1986) are no longer spawning in the tributaries. Spottail shiners aged 1+ (6-9 cm TL; Schmidt, 1986) which would not be taken in our gear could be the source of the drifting larvae.

Given that spottail shiner are abundant and ubiquitous in the tidal Hudson River, we doubt that tributary spawning makes a significant difference to the population. We do remain curious about the changes we observed in this species' behavior.

Golden shiner (Notemigonus crysoleucas). Golden shiner is a common ubiquitous species in the tidal Hudson River. Spawning occurs in association with submerged vascular plants and larvae are frequently seen around water chestnut (Trapa natans) beds (Anderson and Schmidt, 1989). We have collected mature golden shiner moving upstream into tributaries throughout the Hudson River, butnever inlarge numbers. TRLhas observed a robust annual spring run of golden shiner into Wappingers Creek (RKM 108.5), however. Golden shiner larvae are taken in drift nets, but again in lownumbers.Althoughpotamodromy is occurring in this species, compared to the numbers that we see in the tidal Hudson River, tributary spawning is probably not significant to the Hudson River population.

Carp (Cyprinus carpio). Carp is an abundant very large minnow in the tidal Hudson River. Most of the spawning of this species occurs in beds of vascular plants, particularly noticeable in water chestnut stands. Comparativelyfewindividuals migrate into tributaries, but we have seen large carp moving upstream through rapids (Schmidt and Stillman, 1994) and we have collected carp larvae in the drift. The numbers of adults and larvae that we have seen in tributaries are very small compared to the population in the tidal Hudson River.

Gizzard shad (Dorosoma cepedianum). This large herring is a comparatively recent immigrant into the Hudson River and is still expanding its range in the Northeast. Gizzard shad is now becoming abundant in the tidal Hudson River and large individuals are often observed. Gizzard shad larvae have been reported from the tidal Hudson since at least 1989 (J. Young, ASA Analysis and Communication, personal communication) and their abundance in ichthyoplankton samples has been increasing since then.

In the last five years, we have encountered gizzard shad in several tributaries. We suspect they are spawning in those tributaries but we have not been in the right place with drift nets to collect early life stages. TRL has observed and anglers have reported large numbers of gizzard shad adults accumulating at the base of the Eddyville Dam on Rondout Creek (RKM 146.5). The gizzard shad population is still increasing in the Hudson River and we suspect that tributary spawning will become significant to this species in the future.

Northern pike (Esox lucius). This large piscivore is one of the targets for an early spring and late fall sport fishery in the northern end of the tidal Hudson River (also "tiger muskellunge," E. luciusX E. masquinongy and other fishes). Pike spawn over beds of submersed macrophytes in the early spring (Smith, 1985), a habitat that is unavailable in the tidal Hudson River.

RES collected two spawning pike (66 and 76 cm TL) in Coxsackie Creek (RKM 204.5) on April 16, 1999. The habitat was inappropriate for pike spawning, tidal with a rocky and silty bottom. This observation plus reports (G. Stevens, Hudsonia

Ltd., Annandale, New York, personal communication) of anglers catching post spawning pike in the mouth of Mill Creek (RKM 206.5), suggests that pike are spawning in Hudson River tributaries. A fewyoy pike are collected in the tidal Hudson River every year (K. Hattala, NYS DEC, New Paltz, New York, personal communication).

Walleye (Sander vitreus). Walleye has been stocked in Hudson River tributaries for quite a few years, and therefore it is not surprising to see individuals in the tidal Hudson River. Observations of adult walleye have become more frequent in the past five years. RES collected three in Murderers Creek (RKM 190), TRL collected one in Rondout Creek (RKM 146), and J. Hecht (LMS Engineers, personal communication) saw several in Stockport Creek (RKM 194.5). Also, ayoy walleye was reported from Norrie Point (W. Gilchrest, Norrie Point Environmental Laboratory, Staatsburg, New York, personal communication). We have a recent (2003) report of several hundred walleye in the Poesten Kill (RKM 241.5) in April.

We do not know if walleye are spawning in the Hudson River, but the most appropriate habitat (Smith, 1985) occurs mainly in the tributaries. Walleye larvae are difficult to distinguish from yellow perch larvae and they may have been collected but not noticed.

Shorthead redhorse (Moxostoma macrolepidotum).

A small group (12-15) of shorthead redhorse was observed in the Poesten Kill (RKM 241.5) in early June, 2000. An individual was collected (R. Morse and D. Peterson, NYSM) and the identification confirmed. These fish were in breeding color with bright red pectorals, pelvics, and the lower caudal lobe. This is the first record of this species for the tidal Hudson River but their presence in the Poesten Kill and their life history (Smith, 1985) suggests that potamodromy is reasonable for this species. We were unable to confirm successful spawning. RES observed these fish in the Poesten Kill in 2001 and 2003.

Summary. Potamodromous use of tributaries in the Hudson River may be the most significant aspect of the relationship between fishes and tributary streams in this ecosystem. We suggest this because the number of potamodromous species is large (and may be increasing) and the number of individuals seen in tributaries is often large. Several of these species are acknowledged as having significant value for sport fishing as a major component of the ecosystem.

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