Fisheries ecololgy and management of the Jaraqui (Semaprochilodus Taeniurus,S. Insignis) in central Amazonia

The decline of heavily exploited stocks of large, high quality, food fishes in central Amazonia has led to increasing fishing pressure on smaller taxa, especially the jaraqui (Semiprochilodus spp.). The Prochilodontids, now the most important species to the fisheries, are seined by commercial fishermen during three distinct peridos. At the beginning of the annual floods, schools of mature jaraquis in poor-water tributaries migrate downstream to spawn in the nutrient rich white-water rivers. During these rapid spawning runs, fishing effort is concentrated in the lowermost reaches of the tributaries. After spawning, they return in small groups to feed intensively in the flooded forest of the same tributaries from which they had migrated. This period, of approximately three months, may be considered as a natural closed season to the fisheries. The dispersal migration is most complex and requires distinct fishing strategies. In the middle of the floods large schools of fat jaraqui descend from the tributaries to the white-water rivers again. From there, they move upstream to different poor-water tributaries. As downstream movements are more diffcult to observe, fishermen remain at fixed fishing grounds. This contrasts with the dynamic strategies of the subsequent upstream fishing period which contributes 60 per cent of the annual catches. Fluctuations in catch are shown to reflect year to year variations in abundance, which are linked to the hydrological cycle. Considering that fishing over the stocks of jaraqui has already more than compensated for the deficit in catch of larger species, a combination of increased effort and environmental problems could lead, in a short period to a depletion of one of the most profitable fisheries of central Amazonia. Regulation of the fisheries could benefit from a more reasonable distribution of effort among other migratory illiophagous species which remain unexploited, if the goal of sustainable yield and conservation of these stocks is to be achieved. Reserved waters in large strategic units of at least 300 km along white-water rivers (which is equivalent to the maximum upstream displacement of jaraqui during their dispersal migrations) could also be useful to compensate for the loss of floodplain areas due to deforestaion, river regulation, use of pesticides, and mining. River impoundments in tributaries in central Amazonia may have little effect on jaraqui stocks, as spwning movements are unlikely to be directly interrupted by dams. However, alterations of the hydrological regime may also benefit from simulation of the flood cycle to mitigate potential negative impacts.     

Tracking the Surface Flow in Lake Champlain

Understanding the hydrodynamics of Lake Champlain is a basic requirement for developing forecasting tools to address the lake‘s environmental issues. In 2003 through 2005, surface drifting buoys were used to help characterize the circulation of the main body and northeast region (Inland Sea) of the lake. Progressive vector diagrams of over-lake winds when compared to drifter trajectories suggest the presence of gyre-like circulation patterns. Drifter statistics suggest average current speeds of 10 cm s⁻¹ and were predominantly northward (+ V) due to northerly-directed winds and lake geometry. Singleparticle eddy diffusivities on the order of 10⁶ cm² s⁻¹ were calculated which is consistent with results from the Great Lakes and in some oceanic regions. However, the Lagrangian length and time scales, a measure of flow decorrelation scales, were in general smaller than seen in the Great Lakes, which is a natural consequence of the smaller basin size of Lake Champlain relative to the Great Lakes.     

Spatial and temporal variation in sedimentary phosphorus species in Lake Champlain (Vermont,New York,Québec)

We tested the hypothesis that the analysis of operationally defined sedimentary phosphorus species gives a finer resolution of historical land-use changes in lake watersheds than does total phosphorus alone. We measured loosely sorbed/interstitial, reductant soluble, aluminum-bound, apatite, organic and total phosphorus in eleven cores taken from heterogeneous regions of Lake Champlain using sequential extraction. During the pre-settlement period (before 1770 C.E.) concentrations of all P species were low, stable, and dominated by apatite P. With the exception of apatite P, sediment concentrations of all P species increased from pre-settlement times to the present. When accumulation rates were examined, the three P species least susceptible to post-depositional migration (apatite, aluminum-bound, and organic P) were unaffected by deforestation and the development of small, family-scale farms in the 19th century. Increases in accumulation rates were only detected in the early 20th century coincident with afforestation of the watershed as marginal farms were abandoned. By mid-20th century, the accumulation rate of apatite P decreased in all but the lake regions most affected by the industrialization of agriculture and urban development. Aluminum-bound and organic P rates continued to increase in all regions.     

Exotic species in Lake Champlain

The Lake Champlain basin contains substantially fewer exotic species (N = 48) than the Great Lakes (N > 180), in part due to its isolation from commercial traffic. Exotic species have been introduced by authorized and unauthorized stocking, bait buckets, use of ornamental plants, and through the Champlain and Chambly canals that link the lake to the Hudson River, Mohawk River, Erie Canal, and the Great Lakes. Several species, such as water chestnut and zebra mussels, have had severe ecological, economic, and nuisance effects. The rate of appearance of new species increased in the 1990s, potentially as a result of increasing activity in the basin, improved water quality in the Champlain Canal, and increased sampling. Efforts to slow the introduction of new species have focused on public education and legislation to reduce bait bucket introductions and quarantine undesirable plants; however, the major remaining vector for introductions is the Champlain Canal. An estimated 20 species have entered the lake via canals, of which at least 12 used the Champlain Canal, and numerous species in the connected drainage systems could still enter via this route; some are already in the Erie Canal. Most recently (2008), the Asian clam was discovered two locks below Lake Champlain. The Lake Champlain canals also function as a conduit for exotic species exchange between the Hudson River, St. Lawrence River, and Great Lakes. The potential for future introductions could be reduced by a biological barrier on the Champlain Canal, and additional emphasis on public education.     

The relative roles of point and nonpoint phosphorus sources in the eutrophication of Lake Champlain as recorded in sediment cores

Thirteen sediment cores from Lake Champlain (Vermont-New York- Quebec) were analyzed for sediment accumulation rate and eleven indicators of trophic status to reconstruct eutrophication history and relate it to phosphorus inputs from soil erosion, urban point sources, and agricultural runoff including P extracted from phosphate ore and brought to the catchment in fertilizer and livestock feed. Although the catchment was severely deforested and grazed by sheep and cattle in the 19th century, ten of thirteen sites accumulated excess sediment only in the 20th century, a consequence of slow sediment transport through the catchment. Of the three sites that received extra sediment, one remained oligotrophic, while two exhibited mild eutrophication. All sites underwent eutrophication in the 20th century. Three reached their current trophic status before agriculture's intensification, while point-source P input was maximal (1950–1980), four stayed in the reference state until agriculture intensified in the 1970s, and six responded incrementally first to point and then to agricultural P input. Pigment accumulation rates diminished at the surface of seven cores, evidence that the 1990s expansion of P removal from point sources reduced phytoplankton biomass. Additional water quality improvement depends on P management at the catchment border to balance inputs and outputs, and thus avoid P accumulation in soil that saturates phosphate sorption capacity, increasing the proportion of runoff P that is highly-bioavailable orthophosphate. Erosion control is of lower priority because the P native to the catchment's soil is of relatively low bioavailability, and retention structures do not retain dissolved P.     

On the Assessment of Atmospheric Deposition of Sulfur and Nitrogen Species to the Surface of Large Inland Lakes—Lake Champlain

Early work indicated that wet deposition of radioactive fallout to the water surface of a lake greatly exceeded dry, when calculated as annual averages. To test whether this result also applies to the deposition rates of soluble trace gases from the lower atmosphere, data collected at land sites near Lake Champlain have been used to estimate deposition rates to the lake itself, using an analysis of the wind speed-up factor as an intermediate step. The contribution of dry deposition of the major nitrogen and sulfur chemical species is estimated to have been less than 20% of the total atmospheric deposition. However, this result must not be extrapolated to the watershed in which Lake Champlain resides, since evidence obtained elsewhere indicates that the dry deposition contribution over the entire watershed will likely be similar to the wet. The analysis indicates that for the period from 1992 to 1997 the annual total deposition rates of oxidized nitrogen and sulfur ranged from 300 to 500 tonnes per year and 600 to 1,100 tonnes per year, respectively.     

Optical characterization of Lake Champlain: Spatial heterogeneity and closure

A robust optical characterization of the underwater and emergent light fields of Lake Champlain was conducted for sites (n = 11) throughout the lake in August 2011, based on in situ measurements with modern instrumentation and laboratory measurements of optically active constituents (OACs) and components (a_x) of the absorption coefficient (a). Inherent optical property (IOP) measurements included a, a_x, and the particulate scattering and backscattering coefficients. Metrics of apparent optical properties (AOPs) included Secchi depth, the diffuse attenuation coefficients for downwelling [K_d(λ)] and scalar (K₀) irradiance and remote sensing reflectance [R_rs(λ)]. The credibility of the measurements is demonstrated through: (1) consistency of relationships between OACs and IOPs and AOPs, (2) the approach toward equivalence of laboratory and field measurements, and (3) the extent of closure of predictions of K_d(λ) and R_rs(λ), based on IOP measurements and radiative transfer expressions, with paired observations of these AOPs (average differences of 9.4 and 19.3%). Wide spatial differences in OACs, and the resulting IOPs and AOPs, are documented throughout the bounds of the lake and are the result of its morphologic complexity and differing external loading. The lake is a complex case 2 system, with uncoupled variations in OACs and a_x over the bounds of the lake. Both empirical and radiative transfer expressions are used to predict changes in AOPs in response to hypothetical changes in OACs.     

The Effects of Zebra Mussels on the Lower Planktonic Foodweb in Lake Champlain

Selective grazing by zebra mussels has altered phytoplankton communities in many North American lakes, but the specific changes are not the same in each ecosystem. Because of this variation in response, we investigated the impacts of zebra mussels on the plankton community of Lake Champlain with two objectives: first to determine whether zebra mussels increased the dominance of potentially toxic cyanobacteria in the phytoplankton, and second to explore the impact of zebra mussels on protozoans, rotifers, copepod nauplii, and other microzooplankton in the lower food web. Experiments were conducted in 200-L mesocosms filled with Lake Champlain water filtered through a 150-μm sieve to remove macrozooplankton. Zebra mussels were added to half of the mesocosms while the others were maintained as controls. Over a 96-hour experimental period, we tracked nitrogen and phosphorus concentration, chlorophyll a, microcystin concentration, and both phytoplankton and microzooplankton composition and abundance. We found an increase in SRP and total nitrogen concentration and a decrease in the ratio of TN:TP in the zebra mussel treatments over time. Microcystin was undetectable throughout the experiment using the ELISA assay. Phytoplankton biovolume, including cyanobacteria biovolume, declined significantly in the zebra mussel treatments, as did rotifer, protozoan and nauplii abundance. By both direct (consumption) and indirect (altered nutrient availabilities and increased competition) means, zebra mussels clearly seem capable of strongly influencing the lower planktonic foodweb in the many shallow water habitats of Lake Champlain.     

Rapid water level rise drives unprecedented coastal habitat loss along the Great Lakes of North America

Lake Michigan rose to record high water levels in the 2010s; during this time, some coastal sites experienced habitat loss rates an order of magnitude higher than during previous high water periods throughout the 20th century. The high magnitude and rapid rate of rise observed during the 2012–2020 period in combination with a slight increase in the percentage of storm waves likely accelerated habitat loss rates beyond levels that were observed over the past century. Our data suggest that rapid and relatively large changes from low water levels to high water levels are the main driver of large erosional losses, as the coastal system shifts abruptly from one water-level regime to another. One likely impact of climate change on Great Lakes’ water level is an increase in the variability of fluctuations, thus more scenarios of abrupt and rapid water-level rise and associated habitat loss are expected in the future. We propose that the unprecedented habitat loss observed during the 2012–2020 timeframe will become the new normal in the coming century as enhanced variability in water levels facilitates sustained coastal land loss.     

Evaluation of harassment of migrating double-crested cormorants to limit depredation on selected sport fisheries in Michigan

Diverse management techniques have been used to mitigate conflicts between humans and double-crested cormorants (Phalacrocorax auritus) including harassment methods supplemented by lethal take. In this study we evaluated impacts of programs to harass spring migrating cormorants on the walleye (Sander vitreus) fishery in Brevoort Lake and the yellow perch (Perca flavescens) and walleye fisheries at Drummond Island. Cormorant foraging declined significantly (p < 0.05) at both locations subsequent to initiation of harassment programs. Overall harassment deterred 90% of cormorant foraging attempts while taking less than 6% lethally on average at each site. Yellow perch were a predominate prey item in number and biomass at both locations. Walleye made up a small proportion of the diet at both locations. However, both walleye and yellow perch abundance increased significantly (p < 0.05) at Drummond Island. Walleye abundance at age 3 increased to record levels in 2008 following 3 years of cormorant management at Brevoort Lake. The estimated cormorant consumption of age-1 walleye in the absence of management at Brevoort Lake during 2005 would account for 55% of the record 2006 age-1 walleye population. These results support the hypothesis that cormorant predation on spawning aggregations of sportfish was a significant mortality factor and cormorant management reduced sportfish mortality and increased abundance at both locations. Continuation of harassment programs and fishery assessments will determine whether improvement of targeted sport fisheries through control of spring migrating cormorants is sustainable.     

Discriminating natal origin of spawning adult sea lamprey (Petromyzon marinus) in Lake Champlain using statolith elemental signatures

Sea lamprey (Petromyzon marinus) is a nuisance species in the Great Lakes and Lake Champlain. Information about tributary contributions to the spawning adult phase is critical for appropriate allocation of efforts to control this species. We examined the accuracy of statolith elemental composition to identify the natal origin (i.e., individual rivers or clusters of rivers) of 33 known-origin adults from the Lake Champlain basin. To do so, we first established natal origin chemical signatures using the statoliths of 238 larvae from the same basin. Using laser-ablation inductively coupled plasma mass spectrometry, the 238 larvae originating from 12 streams and one delta were discriminated with a classification accuracy of 57% (range: 25–80%) and 70% (range: 29–80%) when individual streams and groups of streams were considered respectively, highlighting the potential of statolith microchemistry to identify natal origins. However, the assignment of natal origin for adults was overwhelmingly incorrect. Using a maximum likelihood procedure, 88% of the adults were assigned to a cluster of three streams and one delta, while only 3% of these individuals were known to originate from this particular cluster. More research is required to understand the low classification accuracy of sea lamprey adults and validate the use of statolith microchemistry to identify sea lamprey natal origin.     

Habitat use by subyearling Chinook and coho salmon in Lake Ontario tributaries

The habitat use of subyearling Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) was examined in three tributaries of Lake Ontario. A total of 1781 habitat observations were made on Chinook salmon (698) and coho salmon (1083). During both spring and fall, subyearling coho salmon used pool habitat with abundant cover. During spring, principal component analysis revealed that water depth was the most important variable governing subyearling Chinook salmon habitat use. Substrate materials used by Chinook salmon in the spring and coho salmon in the fall were significantly smaller than were present on average within the study reaches. When the two species occurred sympatrically during spring they exhibited similar habitat selection. Although the habitat used by coho salmon in Lake Ontario tributaries was consistent with observations of habitat use in their native range, higher water velocities were less important to Chinook salmon than has previously been reported.