Greg C. Garman

Urbanization of a Watershed and Historical Changes in a Stream Fish Assemblage

Abstract During recent decades, the Tuckahoe Creek (Virginia) watershed has been altered by human activities, including road and bridge construction, commercial and residential development, and riparian losses. We used historical (1958) and recent (1990) data to evaluate the hypothesis that long-term, low-intensity urbanization affects a warmwater stream fish assemblage in ways usually attributed to acute, high-intensity perturbations. In 1990, fish species diversity of Tuckahoe Creek was significantly lower (P < 0.05) than it had been in 1958, and abundance was substantially lower for all species and trophic guilds. Four cyprinids, one ictalurid, and one percid present in 1958 were not collected in 1990. Jaccards community similarity coefficient (species composition by site between 1958 and 1990) was negatively correlated with near-stream development of the watershed at six study sites (r = –0.84; P < 0.05). Some characteristics of the feeding ecology of selected fish species, including consumption of t...

Marine nutrient contributions to freshwater apex predators

Abstract Recent investigations into the nutrient cycling of coastal ecosystems have suggested that migratory or anadromous fish could be important vectors of marine nutrients. Anadromous fish have assimilated marine nutrients that would contribute to the nutrient budgets of freshwater systems by excretion, gamete release, or the decay of post-reproductive carcasses. However, the extent to which freshwater predators utilize marine material is not well understood. In systems where anadromous fish temporarily constitute a major portion of the fish community, they may contribute substantially to the diet of piscivorous fish and other predators. Here we show the contribution of anadromous blueback herring, shad, and alewife (Alosa) to diets of large, non-indigenous piscivorous catfish (Ictalurus furcatus) using δ34S and δ13C. The spawning anadromous Alosa, captured in tidal freshwater, had enriched δ34S and δ13C values compared to resident, native freshwater species. As a result of consuming the anadromous Alosa, the I. furcatus isotope signature shifted towards the marine signal. The isotope analysis revealed that anadromous fish contribute substantially to the diet of most captured I. furcatus. The percentage of anadromous Alosa carbon and sulfur that was incorporated into I. furcatus (≥38 cm total length) ranged from 0 to 84% and 10 to 69%, and had means (±SD) of 42 (±24) and 43 (±16)%, respectively. Although the δ15N signal of marine-derived biomass is enriched by approximately 3‰ relative to terrestrial or freshwater biomass, it was not as useful as δ34S and δ13C for nutrient source owing to trophic fractionation. This study demonstrates that anadromous fish may be a significant source of nutrients to tidal freshwater apex predators.

Contribution of marine-derived organic matter to an Atlantic coast, freshwater, tidal stream by anadromous clupeid fishes

This study used stable isotope analysis to evaluate the hypothesis that upstream migrations by anadromous clupeid (Alosa spp.) fishes represent an ecologically important seasonal subsidy to annual energy and nutrient budgets for coastal waters of the Atlantic slope. Dual stable isotope ratio analyses (δ 13C and δ 15N, ‰) were conducted on >200 samples representing major ecological components of Wards Creek, Virginia, and temporal trends in the stable isotope signatures of these components were related to the timing of Alosa-derived allochthonous inputs. Carbon ratios (δ 13C) for migratory (oceanic) Alosa spp. arriving in Wards Creek were enriched by 10.2‰ compared to ratios for resident fishes. The timing and magnitude of shifts in the δ 13C values of documented Alosa predators suggest that predators in Wards Creek derive a substantial proportion of their biomass carbon from marine sources during the Alosa spawning run. The unique trophic structure of Wards Creek may be related to ecological linkages between tidal fresh waters and coastal marine systems and the greater taxonomic complexity of tidal freshwater faunal assemblages compared to other aquatic systems.

Use of terrestrial arthropod prey by a stream-dwelling cyprinid fish

SynopsisThe spatio-temporal availability to, and use of terrestrial (allochthonous) prey by, a subset of the fish assemblage of a Virginia piedmont stream were investigated during spring and summer. Terrestrial invertebrates were most abundant in drift nets, but least common in fish stomachs, during April. In contrast, during August, terrestrial prey dominated the diet of the major cyprinid fish,Notropis ardens, even though terrestrial prey availability in the stream declined by an order of magnitude. Several other co-occurring fishes only rarely consumed prey of terrestrial origin. Drifting terrestrial invertebrates, were concentrated at the surface near the thalweg, compared to stream margin or substrate locations. This study suggests that morphologial and behavioral constraints of individual fish taxa, including predator avoidance responses, regulate the use of terrestrial prey within a given fish assemblage.

Interannual Variation in Diet and Condition in Juvenile Bluefish during Estuarine Residency

Abstract We examined the diets and weight–length relationships of juvenile bluefish Pomatomus saltatrix from Sandy Hook Bay, New Jersey, during 1981, 1983, and 1984. Diets consisted of a variety of polychaete, crustacean, and fish prey. Opossum shrimp Neomysis americana, sand shrimp Crangon septemspinosa, grass shrimp Palaemonetes vulgaris, bay anchovy Anchoa mitchilli, striped killifish Fundulus majalis, and Atlantic silverside Menidia menidia dominated the diet in terms of biomass and frequency of occurrence. Consumption of invertebrate and fish prey varied between years. Bluefish condition factor was highest in 1981, when fish were the predominant prey, and lower in 1983 and 1984, when the diets consisted mostly of invertebrate prey. The diets of juvenile bluefish in Sandy Hook Bay contained more invertebrate prey than has been described previously.

Fate and Potential Significance of Postspawning Anadromous Fish Carcasses in an Atlantic Coastal River

Abstract Large numbers of spawning, anadromous clupeid fish (Alosa spp.) ascend North American coastal rivers and streams annually. In many regions, post-spawning mortality is high, resulting in potentially significant inputs of marine-derived animal detritus to tidal and nontidal freshwater systems. I estimated retention of carcasses and assessed the mechanism(s) of biological processing for carcasses of migratory blueback herring Alosa aestivalis in the James River, Virginia. In a first experiment, 418 tagged and weighed carcasses placed in the river were transported downstream at an average rate of 986 m/h. In a second experiment, 72 carcasses were fixed in the river as artificial substrates and recovered over the next 192 h. Instantaneous decomposition rates averaged 0.015/h, and the predicted mean time to complete decay was more than 240 h. An aquatic saprolegniale fungus (Saprolegnia sp.) heavily colonized most carcasses after 48 h. No aquatic macroinvertebrates were associated with any recovered ca...

Diet and annual production of two boreal river fishes following clearcut logging

SynopsisDiet and annual production of two cyprinid fishes in the Piscataquis River, Maine, were investigated before and after extensive deforestation of the surrounding watershed. Observed patterns were evaluated relative to post-logging changes in the benthic macroinvertebrate community, and to differences in ecomorphology between the two fishes. Prey selection was generally density-dependent for both predator species throughout the study, but significant exceptions to density-dependence were observed for several aquatic insect lifemode groups (e.g., swimmers, climbers, burrowers). This apparent preference/avoidance for certain prey taxa by fish predators could be adequately explained by differential availability (vulnerability) among prey taxa. Compared to the year before logging, significant post-logging changes in diet composition and gut fullness were observed for both blacknose dace,Rhinichthys atratulus, and creek chub,Semotilus atromaculatus, concomitant with post-logging changes in the availability of benthic prey. Annual production of blacknose dace was significantly lower (52.7 vs. 37.7 kg ha−1 y−1) in the year following logging. In contrast, annual production of creek chub increased significantly after logging, from 8.6 to 17.4 kg ha−1 y−1. Because post-logging changes in the physical environment were probably not sufficient to directly affect fish populations, we hypothesize that blacknose dace were morphologically constrained to feed on a declining aquatic prey resource, with a resultant decline in production. In contrast, the generalist creek chub switched to a non-aquatic prey resource (terrestrial arthropods) and no decline in production was observed for that species.

Initial effects of deforestation on physical characteristics of a boreal river

Physical characteristics of the Piscataquis River, a fourth-order river in Maine, USA, were studied for one year prior to and one year following clearcut deforestation of the spruce-fir watershed. Results suggest that even the most careful, and apparently innocuous, timber harvest operation may alter the physical character of a river system. Significant changes in several factors, including thermal regime, benthic organic matter, substrate composition and suspended particulate matter were observed after logging. Changes were largely consistent with results of studies of smaller streams in deciduous forests, and with predictions of the River Continuum Concept. Post-logging conditions should favor a shift from heterotrophy to autotrophy in the trophic structure of the river community.

Exposure to the Cyanotoxin Microcystin Arising from Interspecific Differences in Feeding Habits among Fish and Shellfish in the James River Estuary, Virginia.

The cyanotoxin, microcystin (MC), is known to accumulate in the tissues of diverse aquatic biota although factors influencing exposure, such as feeding habits and seasonal patterns in toxin production, are poorly known. We analyzed seasonal variation in the MC content of primary and secondary consumers, and used dietary analysis (gut contents and stable isotopes) to improve understanding of cyanotoxin transport in food webs. Periods of elevated toxin concentration were associated with peaks in the abundance of genes specific to Microcystis and MC toxin production (mcyD). Peak toxin levels in consumer tissues coincided with peak MC concentrations in seston. However, toxins in tissues persisted in overwintering populations suggesting that potential health impacts may not be limited to bloom periods. Interspecific differences in tissue MC concentrations were related to feeding habits and organic matter sources as pelagic fishes ingested a greater proportion of algae in their diet, which resulted in greater MC content in liver and muscle tissues. Sediments contained a greater proportion of allochthonous (terrestrial) organic matter and lower concentrations of MC, resulting in lower toxin concentrations among benthic detritivores. Among shellfish, the benthic suspension feeder Rangia cuneata (wedge clam) showed seasonal avoidance of toxin ingestion due to low feeding rates during periods of elevated MC. Among predators, adult Blue Catfish had low MC concentrations, whereas Blue Crabs exhibited high levels of MC in both muscle and viscera.

Changes in age composition and growth characteristics of Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) over 400 years.

Populations of sturgeon (Acipenseridae) have experienced global declines, and in some cases extirpation, during the past century. In the current era of climate change and over-harvesting of fishery resources, climate models, based on uncertain boundary conditions, are being used to predict future effects on the Earths biota. A collection of approximately 400-year-old Atlantic sturgeon spines from a midden in colonial Jamestown, VA, USA, allowed us to compare the age structure and growth rate for a pre-industrial population during a ‘mini-ice age’ with samples collected from the modern population in the same reach of the James River. Compared with modern fish, the colonial population was characterized by larger and older individuals and exhibited significantly slower growth rates, which were comparable with modern populations at higher latitudes of North America. These results may relate to higher population densities and/or colder water temperatures during colonial times.