Final Report to the VMRC and RFAB
Project Title: Establishment of a Chesapeake Bay Trophic Interaction Laboratory Services Program Report Number: 5 Principal Investigators: Christopher F. Bonzek, Dr. Robert J. Latour Period of Performance: 1 June 2003 to 1 June 2004 Award Number: RF 03-16 Funding Total: $102,118 ($89,475 VMRC, $12,643 VIMS) Introduction: Fisheries researchers and managers in the Chesapeake Bay region are developing multispecies management plans for commercially, recreationally, and ecologically important species. Both the Chesapeake 2000 (C2K) agreement and the recently completed regional Fisheries Ecosystem Plan (FEP) commit the states of Maryland and Virginia to incorporating an ecosystem-based approach into fisheries management. A principal requirement of multispecies fisheries assessment models is well-quantified estimates of predator-prey relationships (Latour et al. 2003). Trophic interactions among populations are typically elucidated through the analysis of stomach contents. It must be recognized, however, that such interactions vary according to temporal and spatial scales. Therefore, to adequately characterize these interactions within an ecosystem, an extensive database of fish diet composition information is needed. Further, given that increased survival in the early life history stages may ultimately improve the year-class strength of a fish population (Boynton et al., 1981), consideration of young-of-the year (YOY) and juvenile fish diets is particularly important. The goal of this project is to provide fisheries researchers and managers with an integrated trophic interations database that can be used to support the development of ecosystem-based fisheries assessment models. To meet that goal, the following objectives are established: ď‚§
Continue development of a network of collaborating researchers in the Chesapeake Bay region to collect fish stomach samples and associated environmental data.
Construct a thorough fish diet composition database encompassing an array of species, locations/habitats, seasons, and age-classes throughout the Chesapeake Bay region.
To ensure that our database reflects adequate temporal and spatial scales, samples and associated environmental data will be acquired from a client network of research projects across the bay and near-coastal region. Participation by Virginia Institute of Marine Science (VIMS) surveys will include that of the juvenile fish and blue crab trawl survey, the juvenile striped bass and bluefish seine surveys, and the newly established seagrass trammel net survey. Maryland Department of Natural Resources (MDNR) participation will include that of the juvenile striped bass seine survey, the adult striped bass creel survey, and adult spawning stock survey. Participation by the United States Fish and Wildlife Service (USFWS) near-coastal winter striped bass tagging survey (SEAMAP) is also anticipated.
Accomplishments and Benefits: Goals for the CTILS program were established and successfully achieved in each quarter for the 2003/2004 funding year. In the first quarter, the position for CTILS coordinator was filled, a laboratory balance was purchased and initial contacts were established with various fish monitoring surveys from both VIMS and MDNR. In the second quarter, effort was placed heavily on publicizing the CTILS program as a laboratory service and communication continued with both potential and established partners. A website was developed to demonstrate the programâ€™s services and can be accessed at www.vims.fisheries.edu/ctils. In addition, a dissecting scope was purchased as well as other laboratory supplies needed for fish stomach content processing. In the third quarter, the CTILS program presented a poster at the Chesapeake Bay Fisheries Research Program Symposium in Laurel, Maryland. Field and laboratory protocols for the collection and processing of stomach samples by participating surveys were implemented. Juvenile and adult striped bass (Morone saxatilis) specimens were supplied to CTILS by MDNR, and an analysis of the adult striped bass diet was performed. A digital camera with microscope adapter rings was purchased to create an image library of prey organisms. In the fourth quarter, the CTILS laboratory presented an exhibit at the 2nd annual Marine Science Day, an event allowing free admission to people of all ages to explore and learn about research taking place at VIMS. An analysis of the juvenile striped bass diet was performed with the samples provided in the previous quarter by MDNR. Regular participation by VIMS juvenile trawl and trammel net surveys was initiated. After 1 June 2004, the VIMS juvenile seine surveys commenced sampling for the season and actively participated with the CTILS program. Currently, CTILS receives and processes samples from two surveys from MDNR and four VIMS surveys (Figure 1). The CTILS database now contains 632 samples from VIMS (620 from trawling, 12 from seining) and 589 from MDNR (352 from seining, 178 from hook and line trolling, 46 from gillnetting, 12 from electrofishing, and one from a poundnet). Approximately 600 stomachs await processing in the laboratory.
Figure 1. Potential locations sampled by various VIMS and MDNR monitoring surveys. Exact locations, chosen at random, may change each month. The Chesapeake Bay main stem is surveyed by the MDNR adult striped bass creel survey as well as the Chesapeake Bay Multispecies Monitoring and Assessment Program (ChesMMAP) at VIMS.
Chesapeake Bay, USA
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VIMS Juvenile Bluefish Seine Survey VIMS Juvenile Trawl Survey VIMS Juvenile Striped Bass Seine Survey MDNR Juvenile Striped Bass Seine Survey
To quantify prey types in fish diets, four common indices were used, including frequency of occurrence (%F, the percentage of stomachs in which one or more individuals of a particular prey type was found), percent number (%N, the percentage of the total number of prey items accounted for by a particular prey type), percent weight (%W, the percentage of the total weight of all prey accounted for by a particular prey type), and percent index of relative importance (%IRI, an indication of the relative importance of each prey item taking into account %F, %N, and %W). Striped bass specimens collected by MDNR were analyzed by CTILS (Figures 2, 3) and compared to striped bass diet data collected and analyzed by the Chesapeake Bay Multispecies Monitoring and Assessment Program (ChesMMAP, Figure 4). The disparity and diversity in diet composition shown here emphasize the importance of collecting diet data from a variety of surveys, which expands the spatial and temporal coverage as well as the size range of fish sampled. Combining data from a variety of surveys provides a comprehensive diet composition database, and therefore, a more reliable parameterization of multispecies fisheries assessment models.
A stomach fullness index (SFI) (Walter and Austin, 2003) can also be calculated to indicate a ratio of stomach content weight to individual fish weight, which can offer evidence of foraging success by a specific age class or during a specific time of year. The SFI of the MDNR adult striped bass specimens was calculated by month (Figure 5). The figure shows the highest mean standard fullness of the adult Maryland striped bass in 2003 occurred in May. Error bars indicate standard deviation. The sample size for each month is displayed above the bars.
Variations in diet of age-0 striped bass are most often attributable to salinity (Markle and Grant, 1970; Boynton et al., 1981) and spatial variations where salinity was significantly different among sites (Jordan et al., 2003). For the 2004 Maryland age-0 striped bass samples, salinity appeared to explain the diversity in diet between the five river systems studied (Figure 6). The dominant prey types encountered in the stomachs of the fish from each river are displayed with %IRI above each salinity bar. This correlation is an important factor when developing and implementing an integrated fish diet database for the Chesapeake Bay system as a whole, and further validates the need for thorough spatial and seasonal representation.
Figure 6. Dominant prey types (by %IRI) found in the stomachs of age-0 striped bass from Maryland river systems of Chesapeake Bay with varying salinity sampled by the MDNR juvenile striped bass survey, August 2003.
Barnacle cirri 58% Chironomids 31%
Horseshoe crabs 22%
Corophium spp. (amphipods) 26%
Aorid amphipods 38%
Corophium spp. (amphipods) 13%
Corophium spp. (amphipods) 25%
Corophium spp. (amphipods) 43%
Chironomids 54% 4.00
Copepods 30% 3.00
Head of Bay
Individual analyses of these data and results are detailed in formal reports to the participating surveys and are available upon request. The database created by CTILS will be incorporated into the Chesapeake Bay Ecopath with Ecosim (EwE) model as well as several multispecies bioenergtics models (Latour et al. 2003) currently under development by our research group. From these models, sound management decisions can be made based upon a more complete understanding of the population dynamics and interactions of commercially and recreationally exploited fish stocks. All diet and related field data will become a part of a regional library and will be identifiable as to survey and/or investigator. Any publications that result from shared samples will either be joint publications with those who provide samples, or the partners will be given appropriate acknowledgement according to the level of participation. In addition, these publications will formally acknowledge Virginia Marine Resources Commissionâ€™s Recreational Fishing Advisory Board.
Literature Cited Boynton, W.R., T.T. Polgar, and H.H. Zion. 1981. Importance of juvenile striped bass food habits in the Potomac estuary. Transactions of the American Fisheries Society. 110:56-63. Jordan, R.C., D.V. Howe, T.P. Hurst, and F. Juanes. 2003. Feeding habits of age-0 striped bass, Morone saxatilis, in the mid-Hudson River estuary: Temporal, spatial, and ontogenetic variation. Estuaries. 26(6):1486-1493. Latour, R.J., M.J. Brush, and C.F. Bonzek. 2003. Toward ecosystem-based fisheries management; strategies for multispecies modeling and associated data requirements. Fisheries 28:10-22. Markle, D.F. and G.C. Grant. 1970. The summer food habits of young-of-the year striped bass in three Virginia rivers. Chesapeake Science. 11(1):50-54. Walter, J.F. III and H.M. Austin. 2003. Diet composition of large striped bass (Morone saxitilis) in Chesapeake Bay. Fish. Bull. 101:414-423.