Bay scallop, Argopecten irradians irradians, restoration efforts in the northeastern United States

Ronald Goldberg
NOAA/NMFS/NEFSC, 212 Rogers Ave., Milford, CT 06460-6499

Over the last several decades, there has been a marked decline in population abundance of bay scallops, Argopecten irradians irradians (Lamarck, 1819), in nearshore waters and estuaries of the northeastern United States.  Losses of habitats, deterioration of water quality, and harmful algal blooms have probably contributed to this decreased abundance.  Bay scallops generally spawn only once in their short 18-22 month lifespan and this characteristic increases the possibility of recruitment limitation when year-class survival is poor. In northeastern coastal states, local shellfish commissions, community groups, and shellfishers have explored many ways to restore or enhance the bay scallop resource.  Establishment of spawner sanctuaries, direct transplantation of hatchery seed, and collection of native spat have all been attempted, but results have been highly variable.  In most cases, no genetic analysis relating parent stock to progeny is available.  Additionally, unpredictable and relatively abrupt changes in habitat (eelgrass decline), environmental quality (harmful microalgal blooms), or low levels of natural spatfall available for collection can negate enhancement efforts.  Unfortunately, many projects have been curtailed after one or two seasons, when sustained and adaptive efforts are required.  Some of the bay scallop stock enhancement projects in this region have, however, documented increased production or have resulted in improved methodology.  Specific projects in Massachusetts, Rhode Island, Connecticut, and New York are reviewed in an attempt to determine promising strategies to pursue in the future.

Keywords: bay scallops, Argopecten, stock enhancement

Condition of young-of-the-year bluefish (Pomatomus saltatrix) from two different estuaries along the Mid-Atlantic Bight

Estuaries along the Mid-Atlantic Bight (MAB) have been identified by the National Marine Fisheries Service as essential fish habitat for young-of-the-year (YOY) bluefish, Pomatomus saltatrix.  Several MAB estuaries are contaminated with PCBs, PAHs, and heavy metals.  YOY bluefish utilizing polluted MAB estuaries during periods of rapid growth and development are conceivably chronically exposed to contaminants in the water column, sediments and food.  The objective of the study was to compare the condition of YOY bluefish from two different MAB estuaries (Great Bay, New Jersey-pristine and Hackensack River, New Jersey-contaminated) using biomarkers that target different levels of biological organization.  Fish were collected upon immigration into estuaries in summer and just prior to emigration in fall.  Summer collections were analyzed for baseline PCB contamination in whole fish.  From the fall collection, fish have been analyzed for gross pathologies, class and concentration of lipids in tissues, and DNA adducts.  Analyses in progress include concentration of PCBs in tissues and vitellogenin and cytochrome P-450 induction in the liver.  Analysis of biliary FACs is planned.  Significant differences were detected between bluefish from the two different estuaries including higher total lipid content and an increase in hepatic DNA adducts in fish from the contaminated estuary.  Analyses of field-collected fish from two different estuaries are expected to provide much needed information on the impact of habitat quality on the condition of YOY bluefish condition. Understanding the impact of habitat qualities on fish health is an important aspect of essential fish habitat designation, management and protection.

We used multi-panel gill nets and 100-foot haul seines to study the distribution, diet, and growth of young-of-the-year bluefish.  Bluefish were collected from June to October 2003 in the Navesink River/ Sandy Hook Bay estuary.  Gill nets were fished biweekly for 2h at stratified random sites at depths less than 3m.  Haul seines were fished biweekly at 6 fixed stations.  A total of 2966 fish was captured, (seine: N=1986, 30-248 mm FL, mean FL=108 mm); (gill net: N=980, 72-385 mm FL, mean FL=164 mm). Bluefish were first collected in June and reached peak abundance in July (bay=1745, river=185).  Overall, more fish were caught in the bay than the river.  Length frequencies derived from catch data were used to estimate daily growth rates.  Preliminary analysis showed that bluefish grew at an average of 1.34mm/day.  A total of 372 individuals was analyzed for stomach contents.  Four indices:  percent weight (%W), percent number (%N), percent occurrence (%O), and percent index of relative importance (%IRI) were calculated for all prey items consumed.  Mysids were the most important prey (%W=37, %IRI=91) followed by silversides Menidia menidia (%W=22, %IRI=3) and sand shrimp Crangon septemspinosa (%W=9, %IRI=4).  The presence of a large amount of invertebrate prey may suggest that they are more important diet items than previously expected.

The Milford Mass Culture Room (MCR), houses a unique system for the cultivation of research-grade microalgae.  The research of Dr. Ravenna Ukeles, of the Milford Laboratory, on techniques for the mass culture of microalgae led to the design and construction of the MCR that was completed in 1970.  A 1973 publication describes the carboy system that, with only minor modifications, is in current use.  This system allows for production of large quantities of contaminant-free algal biomass.  Semi-continuous culture management under consistent conditions of light, temperature, and media composition provides a product of repeatable and reliable quality.  Large (500-l) open tanks, also in the MCR, serve as models for commercial aquaculture applications and provide large volumes of algae to other Milford research initiatives. 

Despite a long history, the MCR is not static.  Recent challenges, new research directions and applications, and technological developments have taught us not to rest on past success.  For example, research on bivalve and rotifer nutrition led to the replacement of some algal strains traditionally used in aquaculture with others (e.g., high-lipid Tetraslemis, and Pavlova).  In the past, open cultures mixed with bubbled air were very susceptible to bacterial degradation and limited to short-term (5-7 days) batch harvesting.  Replacing bubbling with mechanical mixing (initially a wooden paddle and currently a mechanized foil) significantly increased production and permitted long-term (2-3 years), semi-continuous production.  We also found that open cultures with higher air-surface area-to-volume ratio were more productive and sustainable.  Ciliate contamination in open cultures became an issue in rotifer-feeding applications. This problem was addressed first by using fresh water and artificial salt to eliminate the seawater source – effective, but too expensive.  More recently, we are using sub-micrometer, capillary tangential-flow filtration of seawater.  The importance of supplemental carbon dioxide, as both carbon source and pH regulator, in bacteria-free carboy cultures was re-enforced through chance observations and subsequent adjustments.  And most recently, we discovered that the pH buffer in our carboy and tank media degrades to ammonia (and much faster in bacterized cultures).  This ammonia stresses grazers in closed systems, and degradation of the buffer reduces its effectiveness; the buffer problem is a top MCR priority.  Current MCR work is a combination of refining existing procedures and applying them to new initiatives, including:  studying harmful algal effects upon native and aquacultured grazers, using flow-cytometry to evaluate algal culture dynamics and grazer physiology, gaining a better understanding of the chemical processes within the algal media, and developing new and more effective methods of algal production.