Joel C. Hoffman

Global Trophic Position Comparison of Two Dominant Mesopelagic Fish Families (Myctophidae, Stomiidae) Using Amino Acid Nitrogen Isotopic Analyses

The δ15N values of organisms are commonly used across diverse ecosystems to estimate trophic position and infer trophic connectivity. We undertook a novel cross-basin comparison of trophic position in two ecologically well-characterized and different groups of dominant mid-water fish consumers using amino acid nitrogen isotope compositions. We found that trophic positions estimated from the δ15N values of individual amino acids are nearly uniform within both families of these fishes across five global regions despite great variability in bulk tissue δ15N values. Regional differences in the δ15N values of phenylalanine confirmed that bulk tissue δ15N values reflect region-specific water mass biogeochemistry controlling δ15N values at the base of the food web. Trophic positions calculated from amino acid isotopic analyses (AA-TP) for lanternfishes (family Myctophidae) (AA-TP ∼2.9) largely align with expectations from stomach content studies (TP ∼3.2), while AA-TPs for dragonfishes (family Stomiidae) (AA-TP ∼3.2) were lower than TPs derived from stomach content studies (TP∼4.1). We demonstrate that amino acid nitrogen isotope analysis can overcome shortcomings of bulk tissue isotope analysis across biogeochemically distinct systems to provide globally comparative information regarding marine food web structure.

A review of selected ecosystem services provided by coastal wetlands of the Laurentian Great Lakes

Significant ecosystem services derive from the coastal wetlands of the Laurentian Great Lakes even though two-thirds of the original coastal wetlands have been lost since European settlement, and the remaining 126,000 ha of U.S. coastal wetlands and ≥70,000 ha of Canadian wetlands are affected by anthropogenic stressors. Published information indicates that wildlife habitat, fisheries support, and water quality improvement are significant ecosystem services provided by Great Lakes coastal wetlands that should be strongly considered during management decision making. 30 species of waterfowl, 155 breeding bird species, and 55 species of reptiles and amphibians are supported by coastal wetland habitats across the Basin. Nearly all sport and commercial Great Lakes fish species use coastal wetlands for life-cycle functions, and Great Lakes food webs are supported by wetland export of young sport and forage fish. Biological responses indicate declines in the wildlife and fishery services with increasing levels of anthropogenic disturbance. Extrapolation from a single well-studied system suggests that, Basin-wide, coastal wetlands may retain nearly 4000 tonnes P and 53,000 tonnes N per year, but additional studies are needed to support these estimates and determine stressor effects. Coastal wetlands appear to retain sediments over long time scales, but may either retain or release sediments during storm events. Extrapolation of carbon sequestration from other wetland types suggests that less than 90 g C yr−1 might be retained across the Basin. Wild rice production provides a culturally important ecosystem service, and coastal protection may be locally significant where fringing wetland remain. To support management decisions, quantitative relationships between specific stressors or land use practices and the delivery of ecosystem services are needed, as are ecosystem service indicators to measure those responses.

Tracking Nursery Habitat Use in the York River Estuary, Virginia, by Young American Shad Using Stable Isotopes

Abstract We developed and applied a stable isotope turnover model to estimate how long age-0 American shad Alosa sapidissima reside within tidal freshwater and brackish-water habitats in the York River estuary, Virginia. The residence time was estimated by modeling the changing stable isotope ratio (either the carbon [δ13C] or sulfur [δ34S] stable isotope ratio) of an age-0 American shad as it migrates seaward from its present habitat to a new habitat and determining the minimum time required to acquire the isotopic signature of its new habitat. A sensitivity analysis of our turnover model indicates that the results are robust at relatively fast turnover rates, such as those experienced by young fish, but that at slow turnover rates the model can yield biologically meaningful differences with relatively small changes in variables. The average ± SE isotopic ratios for the dorsal muscle tissue of age-0 fish increased along the estuary, from −31.8 ± 0.3‰ for δ13C and −5.2 ± 0.7‰ for δ34S at the farthest upri...

Contribution of allochthonous carbon to American shad production in the Mattaponi River, Virginia, using stable isotopes

Our objective was to quantify the contribution of autochthonous, locally-produced phytoplankton, and allochthonous, terrestrial-derived organic matter (OM) to the production of young-of-year (YOY) American shad(Alosa sapidissima) using stable isotopes. We measured the carbon and nitrogen stable isotope composition of YOY American shad in the tidal fresh water of the Mattaponi River, a tributary in the York River estuary, during three consecutive years. The isotopic ratios of larval American shad varied among years, indicating a switch from reliance on a primarily autochthonous food web pathway during low and moderate discharge years (50–90%; 2002, 2004) to a primarily allochthonous pathway during a high discharge year (< 35% phytoplankton; 2003). Reliance on phytoplankton by larval fish declined exponentially with increasing Mattaponi River discharge. In 2003, juvenile production was also supported by allochthonous OM, though autochthonous phytoplankton accounted for an increasingly large fraction during June through August, up to 40–55%. We also found a long-term, positive relationship between the duration of above average flow during April through June in the Mattaponi River and a corresponding index of juvenile American shad abundance. The largest American shad cohort recorded since 1967 was observed in 2003, a high discharge year. The production of this cohort was largely supported by allochthonous OM. The results suggest an important link between river discharge, energy flow, and recruitment, wherein high discharge favors reliance on terrestrial carbon by YOY American shad, owing to changes in zooplankton diet, macroinvertebrate abundance, or both, and also favors high American shad abundance.

Potential for DNA-based identification of Great Lakes fauna: match and mismatch between taxa inventories and DNA barcode libraries

DNA-based identification of mixed-organism samples offers the potential to greatly reduce the need for resource-intensive morphological identification, which would be of value both to bioassessment and non-native species monitoring. The ability to assign species identities to DNA sequences found depends on the availability of comprehensive DNA reference libraries. Here, we compile inventories for aquatic metazoans extant in or threatening to invade the Laurentian Great Lakes and examine the availability of reference mitochondrial COI DNA sequences (barcodes) in the Barcode of Life Data System for them. We found barcode libraries largely complete for extant and threatening-to-invade vertebrates (100% of reptile, 99% of fish, and 92% of amphibian species had barcodes). In contrast, barcode libraries remain poorly developed for precisely those organisms where morphological identification is most challenging; 46% of extant invertebrates lacked reference barcodes with rates especially high among rotifers, oligochaetes, and mites. Lack of species-level identification for many aquatic invertebrates also is a barrier to matching DNA sequences with physical specimens. Attaining the potential for DNA-based identification of mixed-organism samples covering the breadth of aquatic fauna requires a concerted effort to build supporting barcode libraries and voucher collections.

Estimation of Bottom Trawl Catch Efficiency for Two Demersal Fishes, the Atlantic Croaker and White Perch, in Chesapeake Bay

Abstract The use of fisheries-independent trawl survey data to estimate fish abundance in shallow coastal systems can present challenges for producing reliable population estimates. We used hydroacoustic and trawl data to estimate the catch efficiency of a demersal trawl that is presently used in surveys to support stock assessments in Chesapeake Bay, USA. Specifically, we determined the efficiency of catching Atlantic croakers Micropogonias undulatus and white perch Morone americana, two of the most common species captured in the trawl survey. Monotypic hauls (>90% by abundance) from 2003 to 2004 were used to estimate catch efficiency, defined as the ratio of the observed catch to the number of fish encountered by the trawl, which we estimated by deploying a scientific echosounder directly in front of the trawl net. The catch efficiency estimates ranged from 0.18 to 1.26 for Atlantic croakers (n = 29 tows) and from 0.11 to 0.60 for white perch (n = 7 tows). For Atlantic croakers, Spearmans rank correlation between the total and predicted catch was 0.53. A post hoc analysis of the Atlantic croaker efficiency estimates based on general linear modeling suggests that trawl efficiency is a function of fish behavior, gear geometry, and habitat. Efficiency declined with increasing fish density and increasing trawl width; to lesser extent, an increasing proportion of fines in the sea bed and decreasing depth were also associated with declines in efficiency. We conclude that because catch efficiency is variable, the trawl should be integrated with hydroacoustics to obtain improved population data.

Status of Non-Indigenous Benthic Invertebrates in the Duluth-Superior Harbor and the Role of Sampling Methods in Their Detection

ABSTRACT As part of a study to develop recommendations for non-indigenous species (NIS) monitoring in Great Lakes areas at risk of invasion, we conducted intensive sampling in the Duluth-Superior Harbor and lower St. Louis River in 2005 and 2006. Of the ∼240 benthic invertebrate taxa identified, 19 were non-indigenous, including 8 first detection records for this system: New Zealand mud snail Potamopyrgus antipodarum; African/Asianorigin cladoceran Daphnia lumholtzi; Eurasian-origin amphipod Echinogammarus ischnus; Eurasian-origin bivalves Dreissena bugensis, Pisidium henslowanum and Pisidium supinum; and possibly range expanding oligochaetes Paranais frici and Pristina acuminata. Dreissenids were by far the most abundant NIS. Several other NIS were also common, but others were detected in only a few of the >200 samples taken. Non-indigenous amphipods and Dreissena were most frequently detected in sweep net and colonization plate samples of littoral vegetation, while NIS oligochaetes, gastropods, and non-dreissenid bivalves were most frequently detected in ponar and bottom sled samples of sediments. Our findings confirm that this major shipping port remains a NIS “hotspot” and emphasize that regular surveys covering a range of habitats with multiple sampling gears and thorough taxonomic effort are needed to detect and monitor non-indigenous species.

Cohort-Specific Growth and Mortality of Juvenile American Shad in the Pamunkey River, Virginia

Abstract We estimated the variation in instantaneous rates of growth (G) and mortality (M) between intraannual cohorts of juvenile American shad Alosa sapidissima in the Pamunkey River, Virginia. The ages of juveniles captured by push net during the juvenile abundance index surveys in 1998 and 1999 were estimated by counting daily rings on the sagittal otoliths. Weight-at-age and abundance-at-age data were used to generate instantaneous daily rates of growth and mortality for 5-d cohorts. In 1998, the peak hatch date lagged behind the peak spawning periods that had been inferred from collections of American shad broodstock and occurred after peak spring flow events. In 1999, the correspondence between the hatch date distribution and the peak spawning periods was greater than in 1998. The instantaneous daily growth rate was relatively constant between cohorts, ranging from 0.037 to 0.064 in 1998 and from 0.046 to 0.066 in 1999. The instantaneous daily mortality rate was more variable between cohorts, rangi...

Rapid stable isotope turnover of larval fish in a Lake Superior coastal wetland: Implications for diet and life history studies

Trophic linkages of larval fish in Lake Superior coastal habitats can be identified using naturally occurring differences in the stable isotope ratios of nitrogen (15N:14N, δ15N) and carbon (13C:12C, δ13C). We measured 13C and 15N values in common fish larvae weekly during spring run-off (late-April to mid-July) in the hydrologically complex drowned river mouth of the St. Louis River, the second largest tributary to Lake Superior. For all species, δ13C was increasingly negative with increasing weight as the fish developed from the yolk-sac stage, during which they possess a maternally-derived isotopic signature, to an exogenously feeding larvae. Trends in δ15N with increasing weight varied among species; an increase, decrease, and no change in δ15N were observed. A weight-based stable isotope turnover function modeled well the observed changes in δ13C and δ15N. In general, fish obtained a constant signature after a 10-fold gain in body mass, implying their tissue was at isotopic equilibrium with their diet. Difference between yolk-sac and larvae δ13C and δ15N revealed distinct patterns in larval origin and settlement. Based on the species analyzed, we identify two specific Lake Superior coastal wetland-dependent fish early life histories that incorporate habitat use, movement, and trophic dynamics. This study thus provides a methodological approach that can potentially help resolve interactions between watershed character, coastal productivity, and Lake Superior that are of significance to the lakes fisheries.

Coastal wetland support of Great Lakes fisheries: progress from concept to quantification.

AbstractFishery support is recognized as a valuable ecosystem service provided by aquatic systems, but it is harder to quantify than to describe conceptually. In this paper, we combine data on fish inhabiting Great Lakes coastal wetlands (GLCWs) with information on commercial and recreational harvest and the piscivore forage base to develop quantitative understanding of the multiple species involved in direct and indirect fishery support of this complex fishery. We then examine patterns of species co-occurrence and life history and relationships to GLCW conditions in order to identify fishery support metrics useful in aggregating species patterns and evaluating management outcomes. Our criteria for wetland prevalence (≥10% occurrence) and fishery importance (≥1% of recreational or commercial harvest in one or more of the Great Lakes or having a major forage fish role) yielded 21 wetland-using, fishery-relevant species representing multiple taxonomic groups and life history attributes. Wetland-using specie...