Ecosystem-Based Approach To Assess Black Drum In Baffin Bay
Ecosystem-Based Approach to AssessBlack Drum in Baffin BayPublication CBBEP – 98Project Number – 1421January 2015Prepared byGreg Stunz, Ph.D., Principal InvestigatorMatthew Ajemian, Ph.D., Co-principal InvestigatorJennifer Pollack, Ph.D., Co-principal InvestigatorTexas A&M University-Corpus ChristiHarte Research Institute for Gulf of Mexico Studies6300 Ocean Drive, UNIT 5869Corpus Christi, TX 78412-5869Submitted to:Coastal Bend Bays & Estuaries Program1305 N. Shoreline Blvd., Suite 205Corpus Christi, TX 78401The views expressed herein are those of the authors and do not necessarily reflect the views of CBBEP or otherorganizations that may have provided funding for this project.
Ecosystem-based Approach to Assess Black Drum in Baffin BayInterim Technical Reportby:Greg Stunz, Ph.D., Principal InvestigatorMatthew Ajemian, Ph.D., Co-principal InvestigatorJennifer Pollack, Ph.D., Co-principal InvestigatorTexas A&M University-Corpus ChristiHarte Research Institute for Gulf of Mexico Studies6300 Ocean Drive, UNIT 5869Corpus Christi, TX 78412-5869Final Report to:Coastal Bend Bays& Estuaries ProgramJanuary 19, 2015
Table of ContentsTable of Contents .ixList of Tables . xList of Figures .xiExecutive Summary . 1Introduction . 2Methods . 4Benthic Sampling . 4Gut Content and Stable Isotope Analysis . 5Acoustic Telemetry . 6Results . 9Water Quality Monitoring . 9Benthic Sampling . 10Gut Content Analysis . 15Stable Isotope Analysis . 19Acoustic Telemetry . 19Conclusions and recommendations . 23Literature Cited . 25ix
List of TablesTable 1. Location and capture information for 25 Black Drum fitted with acoustictransmitters . 7Table 2. Summary of environmental conditions by site over the project period . 9Table 3. Presence and absence of different taxonomic groups found in benthic cores 15Table 4. Dietary data of Black Drum from Gut Content Analysis . 17Table 5. Acoustic detection record data from the 15 receiver array . 20x
List of FiguresFigure 1. Map of the Baffin Bay Complex . 2Figure 2. Black Drum catch per unit effort from TPWD gillnet surveys . 3Figure 3. Shell remnants of dwarf surf clams along the Baffin Bay shoreline 2012 . 3Figure 4. Map of the Baffin Bay Complex with benthic coring stations. . 5Figure 5. Map of the Baffin Bay Complex acoustic array. 8Figure 6. Time-series scatter plots of environmental data . 10Figure 7. Map of macrofaunal abundance by station. 12Figure 8. Map of macrofauna biomass by station . 13Figure 9. Map of Mulinia lateralis abundance by station. 14Figure 10. Pie chart of overall benthic taxa composition in cores. 18Figure 11. Pie chart of overall prey taxa composition (by weight) in Black Drum guts . 18Figure 12. Acoustic detection pie charts by receiver station. 21Figure 13. Abacus plot of detection history for 25 transmitters released in Baffin Bay. 22xi
AcknowledgementsWe would like to thank the Coastal Bend Bays & Estuaries Program (CBBEP) forfunding this research. We would also like to thank the staff of CBBEP, particularly JaceTunnell and Rosario Martinez, for their help and support throughout this study. Mr.Scott Murray was instrumental in getting this project off the ground and we are indebtedto his efforts to link our group with his various contacts around the Baffin Bay system.This project would not have been possible without the assistance of numerousmembers (students and staff) of the Fisheries and Ocean Health Lab at Harte ResearchInstitute and the Restoration and Coastal Conservation Lab at TAMU-CC. In particular,we would like to acknowledge Terry Palmer for his guidance on the benthic samplingcomponent of this project as well as his efforts on data processing and analysis. Thisproject heavily involved contributions from Kat Mendenhall.xii
Ecosystem-based Approach to Assess Black Drum in Baffin BayGreg Stunz, Ph.D., Principal InvestigatorMatthew Ajemian, Ph.D., Co-principal InvestigatorJennifer Pollack, Ph.D., Co-principal InvestigatorExecutive SummaryThe Black Drum, Pogonias cromis, is a large-bodied sciaenid fish species of bothrecreational and commercial importance to the Texas coastal-bend. In 2012, a largeproportion of Black Drum landed by both recreational and commercial fisheries in theBaffin Bay estuary exhibited abnormal physical characteristics. These included belowaverage weights, transparent tissue morphology, and empty guts. Following the designof previous studies in the Baffin Bay estuary, we reinstituted a standardized benthicsampling program to understand the spatial and temporal patterns in the abundance ofpotential Black Drum prey (i.e., benthic invertebrates) (Objective 1). To examine BlackDrum reliance on these potential resources and spatial variability in trophic role, theresearch group conducted comparative diet analyses from specimens collected fromBaffin Bay and adjacent areas (Objective 2). The final component of this projectexamined movement patterns of Black Drum (e.g., fidelity to Baffin Bay) and how theyrelate to the environmental regime. Twenty-five Black Drum were fitted with codedacoustic transmitters and tracked across receiver arrays deployed in Baffin Bay andadjacent water bodies (Objective 3). Coupled with a concurrent, spatially explicit waterquality study in Baffin Bay, the project attempted to integrate fine-scale environmentalmonitoring with tracking data and build a comprehensive picture of ecosystem dynamicsin the Baffin Bay system. Benthic sampling efforts revealed spatial density and biomassgradients in potential Black Drum prey, with both parameters apparently increasingtowards the extremities of all three “arms” that empty into this system. Stomach contentanalysis revealed heavy reliance of Black Drum on many of these food sources, withparticularly strong affinity for bivalve species such as the pointed venus clam,Anomalocardia auberiana, and the dwarf surf clam, Mulinia lateralis. Acoustic telemetrymonitoring data showed that Black Drum exhibit relatively high mobility and do notappear constrained to a single sub-embayment or arm within this ecosystem. However,we also observed potential egress in at least three individuals, which indicates that theresidency and fidelity to this water body may be variable in this species. Additionalacoustic downloads this spring (2015) should shed further light on the importance of theBaffin Bay complex to Black Drum. In summary, our ecosystem-based approach hasallowed us to develop a more comprehensive understanding of trophic linkagesbetween benthic communities and an important regional fishery. Our continuedmonitoring efforts will allow us to examine further temporal impacts on these dynamicsin the upcoming year.1
IntroductionThe Black Drum, Pogonias cromis, is a large-bodied sciaenid fish species that occursthroughout warm-temperate to subtropical estuaries in the northwest Atlantic Ocean,including the Gulf of Mexico (Leard et al. 1993). In Texas, Black Drum are an importantcommercial and recreational fish species. In 2010 alone, 1.7 million pounds of BlackDrum were landed in Texas, valued (ex-vessel) at 1.6 M, second only to RedSnapper (TPWD 2012). Despite this species’ wide distribution and important fisherystatus, the ecology of Black Drum remains poorly characterized in the vast majority ofits range, particularly along the Texas coast.Black Drum are known to be primarily benthic, aggregating around a variety of bottomhabitats such as seagrass, oyster reef, sand and mud bottoms (Leard et al. 1993). Inthese habitats, Black Drum diet varies ontogenetically, with smaller individualspreferring crustaceans and worms and larger individuals consuming large, hard-shelledmollusks such as eastern oyster, Crassostrea virginica (Leard et al. 1993). Due to theirability to impact oyster communities via predation, a considerable amount of researchhas been devoted to methods of deterring Black Drum from oyster lease areas offLouisiana (Brown et al. 2003, Brown et al. 2006) including studies of Black Drumfeeding effects and fine-scale habitat use (George 2007, Brown et al. 2008).Unfortunately, despite the rather ubiquitous nature of this species, there have been nostudies of Black Drum movement behavior in other habitats (sand and mud bottoms) orover large spatial scales ( 10 km2). As such, the factors explaining Black Drum spatialdistributions (aside from oyster density) remain unknown, though studies of this type aresorely needed (Brown et al. 2008).The Baffin Bay Complex (BBC, Fig. 1; comprising Baffin Bay, Alazan Bay, Cayo DeGrullo, and Laguna Salada) and Upper Laguna Madre (ULM) appear to support some ofthe highest catches of Black Drum throughout Texas bay systems, with abundancessteadily increasing since the 1980’s and saturating over the last decade (TPWD,unpublished data; Fig. 2). However, in 2012, a large proportion of Black Drum landedby both recreational and commercial fisheries have exhibited abnormal physicalcharacteristics. These include below average weights, transparent tissue morphology,and empty guts (Grubbs et al. 2013).The factors explaining the current condition ofBlack Drum in the BBC is an area of activedebate. However, many researchers agreethat these abnormal characteristics are due tosome degree of resource limitation. Forexample, the saturating trend in abundancepatterns in the nearby ULM may be indicativeof the population reaching its carryingcapacity. With few predators to control BlackFigure 1. Map of the Baffin Bay Complex2
Drum populations in the hypersaline waters of theULM and demonstrated fidelity of Black Drum tospecific embayments elsewhere (Osburn & Matlock1984), this species may have reached maximumabundance in this protected water body.Alternatively, or perhaps coincidentally, alteredwater quality mayhave played a largerole in reducingFigure 2. Black Drum catch per unitpopulations of Blackeffort (fish/net/hr) from TPWD gillnetDrum food resourcessurveys (1983-present).or accessibility tothese resources. For example, intermittent hypoxia, whichhas been noted in Baffin Bay in recent years, canconcentrate demersal sciaenid fish in suboptimal (preydeficient) habitats, thus reducing overall carrying capacity(Eby et al. 2005). In the BBC, populations of dwarf surfclam (Mulinia lateralis), a potentially major prey item ofBlack Drum (Breuer 1962, Simmons & Breuer 1962, Martin1979), have not been assessed in nearly a decade.Figure 3. Shell remnants ofdwarf surf clams along theHowever, anecdotal evidence suggests major unpredictedBaffin Bay shoreline 2012.die-offs of surf clams in recent years (Fig. 3) that may be(photo: S. Murray)related to deteriorating water quality conditions, and whichmay have led to sub-lethal effects on Black Drum. These findings clearly indicated aneed for a comprehensive multi-trophic level study in the BBC as there are potentiallystrong linkages between water quality of this system and Black Drum condition. Thisneed was supported by the Texas Parks and Wildlife Department (TPWD), who in theirreport on the “Emaciated Black Drum Event” made the following recommendation:“Additional information on the current status of the benthic community, including M.lateralis, in Baffin Bay as well as gut content or tissue analysis (elemental or stableisotope) of P. cromis could be beneficial in further tracking the impact of a potentialdecline in food sources or an ecosystem-wide trophic shift in its feeding mode of thespecies” (Grubbs et al. 2013). Initial seed funding for very limited preliminaryassessment work (via Coastal Bend and Bays Estuaries Program) allowed us to test thefeasibility of conducting benthic sampling and acoustic telemetry in this region and itsapplicability to Black Drum. Funding from Sea Grant will allow us to expand our initialwork that is temporally/spatially restricted to a more comprehensive ecosystem-basedapproach over multiple seasons and years. This support will allow us to develop aconcrete understanding of the linkages between water quality, benthic invertebrates,and Black Drum ecology in the BBC. Our working hypothesis was that Black Drumexhibit strong fidelity to the BBC and prefer feeding on M. lateralis, which in turn exhibitdistribution patterns related to the local environmental regime and water qualityconditions.3
MethodsFollowing the design of previous work by Dr. Paul Montagna and guidance from theTexas Parks and Wildlife Department, we reinstituted a standardized benthic samplingprogram to understand the spatial and temporal patterns in the abundance of potentialBlack Drum prey (i.e., benthic invertebrates) across Baffin Bay (Objective 1). Toexamine Black Drum reliance on these potential resources and spatial variability introphic role, the research group conducted comparative diet analyses from specimenscollected from Baffin Bay and adjacent areas (Objective 2). The final component of thisproject examined movement patterns of Black Drum (e.g., fidelity to Baffin Bay) andhow they relate to the environmental regime. Twenty-five Black Drum were fitted withcoded acoustic transmitters and tracked across receiver arrays deployed in Baffin Bayand adjacent water bodies (Objective 3). To do this, an existing acoustic array deployedthroughout the coastal bend was modified to examine Black Drum fidelity to Baffin Bayand potential connectivity with other embayments. Coupled with a concurrent, spatiallyexplicit water quality study by Dr. Mike Wetz in Baffin Bay, the project attempted tointegrate fine-scale environmental monitoring with tracking data and build acomprehensive picture of ecosystem dynamics in the Baffin Bay system.Benthic SamplingSeasonal benthic surveys of bio-indicating benthic communities were conducted todetermine the distribution and abundance of potential infaunal prey items for BlackDrum in Baffin Bay. Currently the TPWD conducts seasonal trawl surveys in this region,but buried infauna (e.g., M. lateralis) are generally not susceptible to this gear type. Theplan was therefore to use cores to assess populations of these benthic species acrossthe Baffin Bay complex (BBC).Ten uniformly spatially distributed sampling stations were sampled from March December of 2014 (Fig. 4). Actual dates included 3/20/2014 (this trip was conductedusing Harvey Weil funds), 6/11/2014, 7/16/2014, 9/10/2014, and 12/10/2014. Stationswere distributed along this gradient to allow for spatial interpolation of invertebrateabundance and spatial distribution patterns in ArcGIS (ESRI, Inc.). Six of these siteswere surveyed previously from 1989 to 1993 by Montagna et al. (1993) and Street et al.(1997) and are currently being surveyed by Texas A&M University-Center for CoastalStudies with the resumption of the Regional Coastal Assessment Program (RCAP)sampling plan across multiple water bodies of the coastal-bend area. The goal was tosupplement this coverage with more focused sampling within the BBC to answer moresystem-specific questions on finer spatial and temporal scales. On each benthicsampling date, hydrographic measurements (salinity, temperature, dissolved oxygen,and pH) were taken at the water surface and 10 cm from the bay floor at each stationand benthic macrofauna were collected for assessments of abundance and diversity. Inthe laboratory, organisms were extracted on a 0.5 mm sieve, sorted using a stereomicroscope, identified to the lowest practical identifiable level (usually species), andenumerated. Biomass measurements were obtained after combining individual4
macrofauna into higher taxa levels (Crustacea, Mollusca, Polychaeta, and others), driedat 55 C for 24 h, and then weighed. Mollusk shells were removed with 1 N HCl prior todrying and weighing.BayFigure 4. Map of the Baffin Bay Complex with benthic coring stations. Stations arecolor-coded by arm.Gut Content and Stable Isotope AnalysisWe collected 138 Black Drum carcasses opportunistically from the TPWD andcommercial and recreational fishermen during spring 2014 for trophic analyses. Wholedigestive tracts were removed beginning with the esophagus ending with the anal vent.Excised digestive tracts were fixed in solutions of 10% formalin. After a 48 hr fixationperiod, tracts were transferred to jars with 70% ethanol until further processing.Categories of prey items were determined for presence, classified to the lowest possibletaxonomic level, enumerated (if possible), weighed, and recorded on the appropriateform.5
Epaxial muscle tissue samples for carbon and nitrogen stable isotope analysis wereremoved from the anterior portion of the fish fillet using a clean stainless steel scalpeland rinsed with deionized water between each sample. Tissue samples were placed inindividual WhirlPak bags and stored at -80 C until further analysis. A subset of thesemuscle tissue samples were selected to represent the size class of the main fish cohortcollected. Individual samples were homogenized with a ball-mill grinder or mortar andpestle and stored in clean glass scintillation vials in preparation for chemical analysis inan external laboratory.Acoustic TelemetryIn 2014, 25 Black Drum were surgically implanted with Vemco V13 coded acoustic tagsbetween 23-April and 20-May. All individuals were tagged and released at the capturelocation. While we successfully released tagged individuals from all major arms of theBBC, we had the greatest success in Alazan Bay (n 17). Additional tagged animalswere released from Cayo De Grullo (n 3), Baffin Bay (n 3), and Laguna Salada (n 2).No animals died during surgery, and all swam off without any major struggle.An array of 15 moored acoustic receivers (Vemco VR2W) was deployed throughout the
Ecosystem-based Approach to Assess Black Drum in Baffin Bay . Interim Technical Report . by: Greg Stunz, Ph.D., Principal Investigator . Matthew Ajemian, Ph.D., Co-principal Investigator . Jennifer Pollack, Ph.D., Co-principal Investigator . Texas A&M University-Corpus Christi . Harte Research
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