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2001

Life History Attributes of Mid-Atlantic Menidia menidia (Pisces: Atherinidae) and a Comparison with Northern (Massachusetts) and Southern (South Carolina) Populations

Richard K. Holmquist College of William and Mary - Virginia Institute of Marine Science

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Recommended Citation Holmquist, Richard K., "Life History Attributes of Mid-Atlantic Menidia menidia (Pisces: Atherinidae) and a Comparison with Northern (Massachusetts) and Southern (South Carolina) Populations" (2001). Dissertations, Theses, and Masters Projects. Paper 1539617782. https://dx.doi.org/doi:10.25773/v5-exa9-3976

This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. LIFE HISTORY ATTRIBUTES OF MID-ATLANTIC MENIDIA MENIDIA

(PISCES: ATHERINIDAE) AND A COMPARISON WITH NORTHERN

(MASSACHUSETTS) AND SOUTHERN (SOUTH CAROLINA) POPULATIONS

A Thesis

Presented to

The Faculty of the School of Marine Science

The College of William and Mary in Virginia

In Partial Fulfillment

Of the Requirements for the Degree of

Master of Science

by

Richard K. Holmquist

2001 APPROVAL SHEET

This thesis is submitted in partial fulfillment of

the requirements for the degree of

Master of Science

Richard K.

Approved, April 2001

Herbert M. Austin, Ph.D. Committee Chairman / Advisor

Mark E. Chittenden, Jr., Ph.D.

JbftrrAT Musick, Ph,

David O. Conover, Ph.D. State University of New York, Stony Brook Stony Brook, New York TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS...... iv

LIST OF TABLES...... v

LIST OF FIGURES...... vi

ABSTRACT...... viii

INTRODUCTION...... 2

MATERIALS AND METHODS...... 10

Sampling Sites...... 10

Sampling Methodology...... 16

Data Analysis...... 18

RESULTS...... 22

DISCUSSION...... 59

SUMMARY...... 75

APPENDIX...... 77

LITERATURE CITED...... 83

VITA...... 88

iii ACKNOWLEDGMENTS

I wish to thank Dr. Herbert Austin for his academic assistance in this research and for his financial support via grants from the Virginia Marine Resources

Commission (VMRC) and the VMRC Virginia Recreational Fishing Development

Fund. I also wish to thank my other committee members, Drs. David Conover, Jack

Musick, Mark Chittenden, and David Evans for their assistance with the analysis of the data and for their critical review of the manuscript. Additionally, I received invaluable field assistance from Donald Seaver, Michael Wagner, Albert Curry, Geoff

White, and others. Chris Bonzek offered critical technical assistance with data management. Susanna Musick was a great help counting silverside eggs. Finally, I wish to thank my numerous friends, especially my wife, Julie. Her support for the completion of this work was unfaltering despite our being apart for most of the last three years.

iv LIST OF TABLES

Table Page

1. Silverside total length (mm) and somatic weight (g) at the end 36 of the first season of growth and at the end of life. 1994 and 1995 cohorts. Silver Beach and Wachapreague.

V LIST OF FIGURES

Map of the six Virginia sampling sites at Bloxom, 12 Silver Beach, Kiptopeke, Fisherman’s Island, Oyster, and Wachapreague.

Graph of the mean surf-zone water temperatures during 27 sampling at the six sites between 1994 and 1996. Also included is a graph of daily water temperatures recorded at the VIMS pier, York River, Gloucester Point, VA during the same period.

Graph of mean total length at the Wachapreague and Silver 29 Beach stations for the 1994 silverside cohort.

Graph of mean total length at the Wachapreague and Silver 31 Beach stations for the 1995 silverside cohort.

Graph of somatic weight at the Wachapreague and Silver Beach 33 stations for the 1994 silverside cohort.

Graph of somatic weight at the Wachapreague and Silver Beach 35 stations for the 1995 silverside cohort.

Graph of condition at the Wachapreague and Silver Beach 38 Stations for the 1994 silverside cohort.

Graph of condition at the Wachapreague and Silver Beach 40 Stations for the 1995 cohort.

Histogram of silverside abundance versus water temperature, 42 using data collected from the VIMS trawl survey, 1987-1996.

Graph of gonadosomatic index for silverside males from both 44 the 1994 and 1995 cohorts.

Graph of gonadosomatic index for silverside females from both 46 the 1994 and 1995 cohorts.

vi Graphs of total number of eggs (mature & recruitment) versus ovary-free body weight near the start of spawning for individual females from the 1994 and 1995 cohorts.

Graphs of batch fecundity versus ovary-free body weight for the 1994 cohort during four sampling dates.

Graphs of batch fecundity versus ovary-free body weight for the 1995 cohort during four sampling dates.

Three graphs that depict the mean numbers of recruitment eggs, mature eggs, and total eggs (mature plus recruitment) per gram ovary-free body weight for the 1994 cohort.

Three graphs that depict the mean numbers of recruitment eggs, mature eggs, and total eggs (mature plus recruitment) per gram body weight for the 1995 cohort. Curves of relative batch fecundity by sampling period for the 1994 and 1995 cohorts.

Comparison of silverside gonadosomatic index curves between males from Virginia (1995, 1996) and previous studies from a 1977 Massachusetts population (Conover 1985) and a 1984 South Carolina population (Sosebee 1991).

Comparison of silverside gonadosomatic index curves between females from Virginia (1995, 1996) and previous studies from a 1977 Massachusetts population (Conover 1985) and a 1984 South Carolina population (Sosebee 1991).

Comparison of silverside relative batch fecundity between females from Virginia (1995, 1996) and previous studies from a 1977 Massachusetts population (Conover 1985) and a 1984 South Carolina population (Sosebee 1991).

A diagram of silverside life history in Virginia. ABSTRACT

The Atlantic silverside,Menidia menidia, is one of the most abundant and frequently-occurring fish in seine sampling along the mid-Atlantic coast, yet a comprehensive life-history for this fish has not been written for the region. This study was designed to measure growth, the dynamics of the winter silverside migration to deep water, the potential for size-specific mortality in Virginia, fecundity, and additional gonadal analysis. Additionally, the data were compared with previous studies from Massachusetts and South Carolina. Atlantic silverside collections were made by beach seine at six stations along both the eastern and western coasts of the Virginia segment of the Delmarva Peninsula. Data from the VIMS juvenile finfish trawl survey were used for analysis of the winter migration. Temperatures within the surf zone were found to warm earlier in the Chespaeake Bay than the Atlantic Ocean, suggesting the possibility for enhanced growth within the Chesapeake Bay during the regular growing season. Mean total length was found to reach approximately 80mm by the end of the first season of growth. Evidence was inconclusive regarding winter growth rates and size-specific mortality over the winter months. Predation was tested as a potential cause for size specific mortality, but the analysis did not support this hypothesis. The minimum and maximum dates of silverside spawning were measured in this study as March 27 and July 5, containing six possible semi-lunar spawning dates. Individual silversides were estimated to spawn four times during a spawning season and evidence suggests that they do not survive to reproduce during a second year of spawning. The average number of eggs produced per female was calculated as 4343 eggs/female produced by the 1994 cohort and 4434 eggs/female by the 1995 cohort. Gonadosomatic index and batch fecundity were demonstrated to vary with respect to latitude. Peak GSI and fecundity occurred approximately one month later in Virginia than was previously determined for a South Carolina population. Similarly, these events occurred in Massachusetts a month later than Virginia. Maximum total length, GSI, and fecundity were all found to increase with latitude. Finally, five silverside recipes are included for the adventurous soul. LIFE HISTORY ATTRIBUTES OF MID-ATLANTIC MENIDIA MENIDIA

(PISCES: ATHERINIDAE) AND A COMPARISON WITH NORTHERN

(MASSACHUSETTS) AND SOUTHERN (SOUTH CAROLINA) POPULATIONS INTRODUCTION

The Atlantic silverside,Menidia menidia, is one of the most common forage fish in the marine surf-zone of the North American, mid-Atlantic coast, yet there has been little comprehensive study of the species within Virginia’s share of the

Chesapeake Bay and mid-Atlantic coastline. This thesis addresses regional life history aspects of this ecologically-important species that include growth rate, seasonal migration, size-specific mortality, and fecundity. It investigates whether variations inMenidia menidia growth exist between the Chesapeake Bay and the coastal Atlantic Ocean. Furthermore, the data are compared to previous studies of

Northern (Massachusetts) and Southern (South Carolina) populations.

Local life history information for this species is necessary because of its ecological importance. The Atlantic silverside is a significant contributor to the biomass of the North American, Atlantic coast surf-zone. Its range extends from

Quebec, Canada to the northeast coast of Florida (Robbins 1969). Beach seine studies from Georgia (Dahlberg 1972) to Maine (Ayvazian,et al. 1992, Lazaari, et al.

1999) list M. menidia as one of the most frequently occurring and abundant fish in shallow coastal water. Studies in the mid-Atlantic states of North Carolina (Pearse,et al 1942), Virginia (Richards and Castagna 1970), and New Jersey (Sogard and Able

1991) show similar results.

2 The silverside is an important forage species for many of the commercially- and recreationally-valuable piscivorous fish that frequent Virginia waters. The species is a major component in the diet of juvenile bluefish,Pomatomus saltatrix (Friedland, et al. 1988, Juanes,et al. 1994). It is also consumed by striped bass,Morone saxatilis

(Smith and Wells 1977, Walter 1999), sandbar sharks,Carcharhinus plumbeus

(Medved,et al. 1985), summer flounder,Paralichthys dentatus (Poole 1964), weakfish, Cynoscion regalis (Wilk 1979), spotted seatrout, Cynoscion nebulosus

(Middaugh 1981), and black sea bass,Centropristis striata (Bayliff 1950). Avian predators in Virginia include black skimmers,Rynchops niger, and common terns,

Sterna hirundo, which at times utilize silversides for over 75% of their respective diets (Erwin 1977). Furthermore, silverside embryos have been observed as a food source for mummichogs,Fundulus heteroclitus (Conover and Kynard 1984), and blue crabs, Callinectes sapidus (Middaugh 1981).

In addition to its value as a forage fish, the silverside is also an important predator. Because of the high biomass of the species and its concentration within the surf-zone, silversides can have a locally-substantial impact on their primary food sources. Silversides are omnivorous, opportunistic feeders. The animal prey of

30mm+ silversides primarily include harpacticoid copepods, calanoid copepods, and

Balanus nauplii. Secondary contributions to their diet include amphipods, isopods,

Hymenoptera, and variable amounts of plant material (Mulkana 1966). Results of a study in the York River of Virginia found that barnacle cyprids Limulusand

* Reference to “silverside” in this document will refer to the Atlantic silverside,Menidia menidia.

3 hatchlings were also important food sources during the full moon (Spraker and Austin

1997).

From the spring to the fall, silversides occupy estuarine and coastal unvegetated surf-zone areas, as well as the vegetated banks of coastal bays, lagoons, and marsh creeks. As a habitat, the sandy-beach surf-zone is believed to be a productive nursery area for many species (McDermott 1983, Lasiak 1986). This habitat can be found to varying degrees along the unprotected shores of the main stem of the Chesapeake Bay and the Atlantic coast. Numerous species of juvenile fish seek refuge in the surf. Shallow water protects them from large piscivorous fish (Ruiz,et al. 1993), and the high-energy environment may protect them from both avian and marine predators, as well as maintain forage in a constant suspension.

Since the Atlantic silverside is such an important element of the Virginia coastal ecosystem, an analysis of its life history in the region is crucial. Both interspecific interactions and the transport of carbon and nutrients from shallow to deep water are effected by silverside growth, seasonal migration patterns, population size, and survival.

Growth:

This intent of this study was to address several aspects of silverside growth.

Growth rate of the Atlantic silverside is determined for several locations along the

Virginia portion of the Delmarva Peninsula, also known as “Virginia’s Eastern

Shore,” and it was investigated whether there was a difference between the stations on

4 the Bay and those along the ocean side of the Peninsula. Skeletal growth was evaluated over the winter months to determine whether it ceases during this period as it does in northern populations. Finally, growth rates were compared between northern and southern populations.

The Chesapeake Bay is considered to be a particularly productive estuary.

One of the goals of this study was to determine whether silversides show enhanced growth at Chesapeake Bay locations relative to the sandy-beach surf-zone of the

Atlantic Ocean. Presumably, food for the opportunistic silversides is more plentiful in the nutrient-rich Bay than in the coastal Atlantic. Phytoplankton production, which is higher in estuaries than at coastal shelf stations (Smayda 1957, Nesius,et al. 1983), spurs the growth of numerous planktonic Crustacea and small grazers on which the silversides feed. Further, Bay production is enhanced by the seaward input of detritus from the rich emergent grasses, like Spartina species. This disparity in production between the two water bodies, coupled with different temperature dynamics, could lead to enhanced silverside growth within the Bay.

The alternate hypothesis is that no difference in silverside growth exists between the two water bodies. Phytoplankton production in the tidal creeks and lagoons along the ocean-side of the Delmarva Peninsula is often comparable to other eastern United States estuaries (Nesius,et al. 1983). Since silverside feeding occurs in and around these coastal creeks and lagoons, differences in growth due to food availability might be negligible. If the Bay surf-zone is substantially more productive for silversides than the

Atlantic, it could show some discontinuity with the countergradient growth that the species demonstrates with respect to latitude. Silverside populations along the

Atlantic coast have been shown to attain a similar mean total length at the end of their first year of growth, but the growing season is shorter in higher latitudes (Conover and Present 1990). Northern populations, therefore, grow significantly faster than their southern counterparts. The difference in growth rates is genetic; caused by increased consumption and enhanced growth efficiency in high-latitude populations

(Present and Conover 1992), that Billerbeck,et al. (2000) suggest “result from trade­ offs with other energetic components, namely sustained and burst swimming.”

Skeletal growth in northern populations has been shown to cease during the late autumn and winter, and silversides stop feeding at temperatures less than 6-8°C

(Conover and Ross 1982). Cessation of growth in the winter has also been reported for Chesapeake Bay silversides (Bayliff 1950). In contrast, Sosebee (1991) found that growth in a South Carolina population continued at a constant rate throughout the winter.

Seasonal migration & size-specific mortality:

One portion of this study describes the dynamics of the silverside local migration in Virginia. Winter migration from the near-shore to deeper shelf water has been documented forM. menidia between Cape Cod and Cape Hatteras (Conover and

6 Murawski 1982). Richards and Castagna (1970) noted thatM. menidia numbers declined during the winter in the near-shore and increased in the deeper mid-marsh channels on the seaside of Virginia’s Eastern Shore. Hildebrand and Schroeder

(1928) documented a similar experience within the Chesapeake Bay, but no large- scale analysis of the migration was undertaken. Southern populations seem to show a weaker, but observable, winter migration (Sosebee 1991).

It seems that low water temperature is responsible for the silverside migration.

Migration in fishes has evolved as a means to spatially separate life-history stages, move to a particularly favorable spawning location, follow the movement or abundance of prey, or respond to physical or chemical environmental conditions

(Moyle and Cech 1988). With the silverside, a response to environmental conditions is the most likely cause. As temperatures fall, the fish likely obtain an energetic benefit by migrating away from the surf zone to deeper water. Since silversides require water warmer than ~1.5 °C for survival (Hoff and Westman 1966), they may seek deep water to avoid the extreme and rapid cooling of the shallows. Deep water is far more resistant to rapid thermal changes and rarely declines to less than 1.5 °C in this region.

The Atlantic silverside exhibits over-winter mortality that can approach 99%

(Conover and Ross 1982). In higher-latitude populations, this mortality is size- specific (Conover 1992, Schultz,et al. 1998). Over-winter mortality is highest among smaller fish. This is represented in length-frequency curves by an increase in the minimum and mean lengths over the duration of the winter months, without a corresponding increase in maximum size.

Migration and temperature stresses causing depletion of lipid reserves are immediately implicated because size-specific mortality is not seen in southern populations where migration is limited and temperature stress less severe (Sosebee

1991). Small individuals show relatively low levels of lipid reserves compared with larger members of their local population, and there is a dramatic decrease in lipids over the winter months (Schultz and Conover 1997, Schultz and Conover 1999).

During the winter, silversides exhibit reduced feeding due to cold water temperatures

(Warkentine and Rachlin 1989). Northern populations appear to be better adapted to the cold than southern populations (Schultz,et al. 1998), but southern populations are less frequently tested.

Lack of adequate lipid reserves during the migration is the most likely cause of size-specific mortality, but additional mechanisms are possible. Significant relationships between fish size and water depth during the migration may be important in the understanding of size-specific mortality in this species. If small silversides make a less extensive migration, then mortality would likely be higher in the smaller, near-shore fish that are more exposed to environmental extremes.

Evidence also suggests that in shallow water during the summer, smaller silversides are more susceptible to predation (Ruiz,et al. 1993). Juaneset al. (1993) found that in the summer, juvenile bluefish preyed on smaller members of silverside populations. If water temperatures force these small fish into deep water, predation could also help drive size-specific mortality.

Fecundity and Gonadal Analysis:

The silversides is a serial, intertidal spawner. Seasonal spawning is triggered when water temperatures reach a minimum threshold of approximately 16-17°C

(Middaugh and Lempesis 1976, Middaugh 1981), and then occurs with a semilunar periodicity. Spawning events coincide with daylight high tides near the full and new moons (Middaugh 1981, Middaugh and Takita 1983, Conover and Kynard 1984).

The fish deposit their semi-demersal, adhesive eggs among vegetation on tidal creek banks, where the eggs adhere to the vegetation with threads. The number of times that the silverside spawns during the year varies with latitude. Conover (1985) found that in Salem Harbor, MA, the majority of spawning occurred on a single day, and that individual females spawn, at most, once per semilunar cycle. Five semilunar spawning periods were observed in his study. In South Carolina, up to seven spawning periods were commonly observed (Middaugh 1981). An accurate assessment of fecundity is important for a reliable understanding of silverside population dynamics.

9 MATERIALS AND METHODS

Sampling Sites

Silverside specimens were collected at six sites on the Virginia segment of the

Delmarva Peninsula (Figure 1). These sites were chosen primarily on the basis of their accessibility, geographical distribution, and sandy, unvegetated sediment. Three sites were selected on the Atlantic Ocean-side of the Penninsula and three on the

Chesapeake Bay-side. The Bay locations included Bloxom (BX), Silver Beach (SB), and Kiptopeke State Park (KP), all of which were accessible by vehicle. The ocean locations were reached by boat at Wachapreague (WA), Oyster (OY), and

Fisherman’s Island (FI).

Bloxom:

The Bloxom site, located on a sandy spit at the southeast comer of the

Pocomoke Sound, was the most northerly of the six stations. The unprotected side of the spit faced the open Chesapeake Bay but it was impossible to sample because it was littered with stone rip rap and other debris. Sampling was performed on the protected side of the spit, facing a small embayment. The embayment was primarily connected to the Bay but also received water from at least one canal that drained a sizable marsh, as well as agricultural and residential areas.

The sampling area was particularly shallow with little slope. The seine was always fully-deployed during sampling, and the maximum sampling depth never

10 Figure 1. The locations of the three Chesapeake Bay (Bloxom , Silver Beach,

Kiptopeke) and three coastal Atlantic Ocean (Wachapreague, Oyster, Fisherman’s

Island) sampling sites.

11 76 ° 2 0 ' 76 ° 10' 76 ° 0 0 ' 75 ° 5 0 ' 75 ° 4 0 ' 75 ° 3 0 '

Bloxom (BX) 37°50'-

37°40-

Wachapreague (WA) Silver Beach 37°30'- (SB)

37°20'- y Oyster (OY)

. < 3 ? „ n (

37° 10'- Kiptopeke (KP)

Fisherman's Island (FI) _

37°00L

36°50'-

Atlantic Ocean

36°40'-

76° 10'

12 exceeded one meter. The sampling area was unvegetated, with a muddy-sand sediment.

Silver Beach:

The Silver Beach station was located at a relatively undeveloped camping area, 1.25 km north of Nassawadox Creek. A single outflow pipe for stormwater drainage was located approximately 100 meters south of the sampling location, and the beach was separated from the camping area by small grass-, shrub-, and tree- covered dunes. The beach was open to the Chesapeake Bay, but shallow sandbars approximately two hundred meters offshore reduced the wave action along the beach.

The sampling area exhibited a large initial slope in the first five meters from the beach, but this flattened out at approximately one-meter depth for the remaining extension of the sampling gear. The sediment within the sampling area was course sand and there was no aquatic vegetation.

Conditions at this sampling site may have been modified since the study was conducted, since it is now occupied by a large YMCA camp development.

Kiptopeke:

Kiptopeke State Park is a campground, boat launch, wildlife refuge, fishing area, and public beach. Sampling was performed on a relatively undisturbed beach that was not used for swimming. The sampling location was approximately one hundred meters south of a large fishing pier, formerly the Chesapeake Bay ferry

13 terminal. The beach was somewhat protected from wave exposure by two sunken concrete ships, used as breakwaters and reefs, approximately three hundred meters offshore.

The sediment in the sampling area was sandy and unvegetated. The sampling area showed a moderate to severe slope. Seining was only possible within ten meters of shore. At approximately ten meters from shore the slope accelerated and the depth quickly exceeded three meters.

Fisherman’s Island:

Fisherman’s Island is a restricted-access wildlife refuge at the mouth of the

Chesapeake Bay. The sampling location was approximately three hundred yards north of the pilings that support the Chesapeake Bay Bridge-Tunnel. The steep, vegetated sand-dunes drop to the beach, which was clearly carved out of ancient marsh beds by the waves. I considered the site to be one of my three “ocean” stations because the physical dynamics were more related to ocean conditions than estuarine, Chesapeake

Bay conditions. Wave energy was often high due to ocean swells, and salinity at the site was also high; little effected by fresh water run-off from land.

The sampling area showed a gradual slope from the beach. Water depth at full extention of the sampling gear slightly exceeded one meter on most occasions. The sediment was sandy and unvegetated, and sparsely littered with shells. Wave energy was high at times, dependent on wind direction and the height of ocean swells. In the time since the sampling was performed for this study, the dynamics of this beach have changed significantly, due to the construction of another Bridge-

Tunnel lane.

Oyster:

Sampling for the Oyster site was actually performed on Wreck Island, one of the barrier islands east of Oyster, Virginia. The sampling location was on the ocean- side of Wreck Island, approximately three hundred meters south of an inlet to the lagoon system. The island was undeveloped, with limited access to the public. The depressed center of the island and the small dunes were covered in marsh grasses, but the island showed signs of occasional overwash.

The beach and shallow-water bottom was unvegetated and extremely hard.

Anchoring a boat in the shallows was almost impossible because of compact sediment and a shell-covered bottom. Tidal currents were quite strong at times this close to the inlet mouth. There was substantial wave action on the beach since it faced the open ocean, but a series of offshore shallows reduced some of the energy. The beach had a steep, steady slope, reaching a depth of approximately 1.5 meters at a distance of fifteen meters from the waterline.

Wachapreague:

Sampling for the Wachapreague station was actually performed on Dawson

Shoal, a small, sandy island on the ocean side of Wachapreague inlet. The sparsely-

15 vegetated island showed enormous change during the three years of sampling. Storms caused significant changes to the island’s margins, and other features like tidal ponds on the interior of the island formed and disappeared over time. As such, the island is dynamic and undeveloped, with little human disturbance.

The beach and shallows were unvegetated and sandy. The morphology of the bottom in the sampling area was not consistent between years or even between some sampling dates. In most cases the seine could be fully deployed, meaning the depth did not exeed 1.5 meters in the first 30.5 meters from shore. Tidal currents were strong at times due to the proximity to the inlet.

Sampling methodology

The primary sampling gear used for this study was a 30.5m x 1.8m seine with

6mm bar mesh. The net was set from the beach, with one pole stationed on the beach and the other drawn perpendicular from shore until it was extended to its full length or a depth of approximately 1.2 m was reached. The net was swept in an arc toward the down-current side and pulled onto the beach where all fish were collected.

The procedure was repeated one-half hour after the first tow. At each of the six Eastern Shore stations, during each sampling period at least twenty-five silversides were preserved in a solution of 10% formalin for future length, weight, gonadal analysis, sex identification, and condition measurements. If fewer than twenty-five fish were collected, all were measured and preserved. Seine sampling was conducted monthly in 1994 and biweekly in 1995 and

1996, between the months of April and October. Additional collections were made monthly during the winter of 1995-96.

Data from the VIMS juvenile flnfish trawl survey were also used in this study, from the period 1988 to 1996. Sampling was performed monthly in the Chesapeake

Bay, with the exception of the winter months of January through March, when only a single cruise was made yearly from 1991-1996 (Geer 1994). The collections were made with a 9.12-m semi-balloon otter trawl (38.1-mm stretch mesh, 6.35-mm codend liner) with a tickler chain. The net was towed parallel to isobaths during daylight hours at approximately 1.1 m/s for a period of five minutes. All catches were sorted to species, counted, and individual lengths recorded. Hydrographic parameters were measured, including depth, salinity, temperature, and dissolved oxygen for every tow.

Stations were selected using a stratified random sampling design for depths greater than twelve feet in the Virginia portion of the Chesapeake Bay. This area was divided into three longitudinally-equal regions. The regions were subsequently divided into four cross-Bay depth strata — western littoral (3.7 - 9.2 m), eastern littoral

(3.7 - 9.2 m), central plain (9.21 - 12.8 m), and deep channel (>12.8 m). Stations were equally allocated to each of the twelve strata. Two to four trawl tows were made in each stratum, each month. Further detail in regard to the sampling design can be found in Geer,et al. (1994) and Colvocoresses and Geer (1991). Data Analysis

Growth:

Silverside growth rate was determined by following the mean length of three year-classes from recruitment until they disappeared from the overall population.

An index of condition (K) was also established from the preserved specimens. The condition index was based on the following formula (Ricker 1975): K = (Total

Weight - Gonad Weight) x 100 / Total Length3. All growth and condition data were collected from specimens from the seine project that had been preserved in 10% formalin.

Yearly cohorts were separated by inspection of the length-frequency distributions. In most cases, the recruiting cohort was clearly distinguishable in size from the parent cohort. In a few cases where overlap occurred, the adults could be distinguished by the clear disparity in gonad development. Juveniles showed a marked difference in gonad development from the one-year-old fish. The scales from fish greater than 100mm FL were examined for an annulus to determine if any two- year-old fish were present, and to separate them from the one-year-old cohort

(Conover and Ross 1982).

A complicating aspect of length-frequency relationships with this species is that females are often larger than males in the population as a whole. During larval development, sex is significantly influenced by temperature (Conover and Kynard

1981). Development in cooler water produces more females, and warmer water more males. Growth occurs at the same rate between the sexes, but because their growth

18 begins earlier, females enjoy a longer growing season. This accounts for their larger size in the overall population. Every effort was made in this study to evaluate life history characteristics on a sex-specific basis.

Size-Specific Mortality and Migration:

I assessed the presence of size-specific mortality of silversides in Virginia by comparing length-frequency distributions in the late autumn with those of early spring at each of the seining locations. Size-specific mortality is indicated by an increase in mean length without a corresponding increase in maximum length. In this process, smaller fish suffer a disproportionately large mortality (Conover 1992, Schultz,et al.

1998). The magnitude of the migration in Virginia was estimated by comparing the abundance of adults in the winter with that of the autumn. Winter sampling was conducted at the Silver Beach and Wachapreague stations monthly through the 1995-

96 winter.

The dynamics of the migration within the Chesapeake Bay were analyzed using data collected from the VIMS trawl survey. The geographical distribution of silversides during the migration was plotted by year, based on these data.

Additionally, the relationship of silverside length with depth was investigated. An analysis of covariance was used to test whether there was a significant relationship of length with depth across all years of the study. For the test, individual lengths were the dependent variable, year was a factor, and depth was a covariate. It was assumed that the length of one fish in a trawl sample was independent from others in the same

19 trawl. Conover and Murawski (1982) found that silversides dispersed across the inner continental shelf waters during the winter. This suggests that the strong schooling behavior that occurs during the summer months is less pronounced during the winter.

Without as strong schooling, there is less chance that the presence of an individual of a certain size will influence the sizes of the individuals around it.

Fecundity and Gonadal Analysis:

Fecundity and gonadal analysis for the 1994-95 and the 1995-96 cohorts were conducted in accordance with the procedures described by Conover

(1985). A gonadosomatic index (GSI) was expressed as a percentage of total weight

(Snyder 1983) for each sex between the months of February and June in the first cohort, and between October and June for the second. After June, very few adults were found in the surf zone. The total body weight of each preserved fish (up to a maximum of 53 fish per station) was measured, and the gonads were excised from the fish and weighed. GSI was determined based upon the following equation: GSI =

[Gonad Weight / (Gonad Weight + Somatic Weight)] x 100. GSI data were pooled among all stations by sampling date.

The ovaries that were removed and weighed in the GSI analysis were used to determine total and batch fecundity. The analysis was performed on up to ten fish per sampling location and sampling date between the months of February and June for both cohorts. A randomly-chosen portion of each ovary, comprising approximately

20% of the total ovarian weight, was dissected, weighed, and placed in modified

20 Gilson’s fluid (Begenal and Braum 1978) for at least a month. The eggs were counted and classified as belonging to either the “recruitment” or “mature” egg pool, based on size and color. Conover (1985) defined three distinct egg classifications for the silverside. Batch fecundity was calculated by multiplying the number of eggs in the most mature egg class by an expansion factor (total ovarian weight/subsample weight). Relative batch fecundity was also assessed, and was determined by dividing the batch fecundity by the somatic weight of the female to normalize the results relative to somatic weight.

21 RESULTS

Growth:

In the spring, the shallow waters of the Bay were found to warm more rapidly than water of similar depth on the ocean side of the peninsula. Mean surf-zone temperature data collected from the bay and ocean stations from May 1994 to January

1997 show that in the spring, the Chesapeake Bay reached 17°C one to four weeks before the coastal Atlantic Ocean (Fig. 2). The Bay remained warmer throughout the summer, and in the fall, temperatures in both bodies of water declined, dropping below 17°C at approximately the same time.

A one way analysis of variance performed by sampling period determined that the mean total lengths of both males and females were significantly different between the six sampling sites over the course of this study (p<0.001). Tukey tests found that fish from the Silver Beach sampling site were frequently significantly larger than those at other stations on a given date during their first summer of growth. No consistent relationship was observed within the three Bay or three Ocean stations.

Because of this result, data were not pooled among stations, and valid comparisons were not possible between the bay and ocean stations. Figures 3-8 describe the

Wachapreague and Silver Beach stations as examples of total length, somatic weight, and condition because sampling was performed most frequently at these two locations and silverside abundance was highest at these two sites. Table 1 lists the lengths and somatic weights for the two cohorts at the end of the first year of growth and the end of life.

Size-Specific Mortality and Migration:

Over ten years (1987-1996), the VIMS trawl survey captured 2594 silversides in the Virginia segment of the Bay in depths greater than 12 m. Of those individuals,

95.2% were captured in water temperatures of <= 9 °C (Figure 9). An analysis of covariance of the VIMS trawl survey data showed no significant relationship (p<0.05) between water depth and silverside length by year, and no apparent geographical concentrations were observed in yearly plots of geographical distribution.

Silverside abundance was quite variable in the surf-zone during the course of the study, and abundance was low during the winter months. Because of this, errors around the mean for male and female total length in most cases were too high to draw any conclusions about size-specific mortality or winter growth. The best results were obtained from the 1995 cohort at the Silver Beach station.

Collections at this station had the largest sample sizes immediately before and just after the winter migration (Figure 4). Sampling performed in September and early

February at this site found no significant change in mean total length over that period.

Fecundity and Gonadal Analysis:

The first clearly maturing ova of the 1994 cohort were observed during the

April 4 sampling period and during the March 27 sampling date for the 1995-96

23 cohort. Measurements of fecundity and gonadosomatic index (GSI) for these two cohorts demonstrated no significant differences between sampling sites. Fecundity and GSI data for these factors were therefore pooled among the six sampling sites in subsequent calculations.

GSI peaked for males in late April and for females in early May during both years of this study (Figures 10-11). Male GSI peaked at 15.24% ± 0.91% (95% Cl) for the 1995-96 cohort and 14.67% ±0.71% for the 1996-97 cohort. Female GSI peaked at 13.13% ± 1.05% for the 1995-96 cohort and 13.57% ± 1.28% for the 1996-

97 cohort. In both cohorts, GSI increased substantially for both males and females beginning in February, from a late-January GSI of approximately 1.3% for males and

1.9% for females. After peaking, GSI declined for both sexes and cohorts until the cohorts disappeared from the population in mid to late summer.

Linear regression indicated a significant relationship between the total number of eggs (recruitment plus mature) and ovary-free body weight during the sampling period shortly after the start of spawning in 1995 (R-sq 0.21) and 1996 (R-sq 0.78).

During spawning, linear relationships were also observed between ovary-free body weight and the number of mature eggs (Figs. 13-14).

Mean batch fecundity per female peaked at 1178 eggs/female on May 24,

1995 for the 1994 cohort and at 1419 eggs/female on May 6, 1996 for the 1995 cohort. The mean ovary-free body weight of a female during the 1995 spawning

24 season was 6.09 g. During the 1996 spawning season, the mean ovary-free body weight was 6.17 g.

As a function of ovary-free body weight, the total number of eggs and the number of recruitment eggs declined throughout the spawning season for both the

1994 and 1995 cohorts (Figs. 15-16). The 1994 cohort showed a decline in total fecundity (recruitment plus mature egg classes) from 1305 ± 402 (95% Cl) on April 4,

1995 to 746 ± 81 on June 17. The 1995 cohort declined from 1202 ± 147 on March

27, 1996 to 607 ± 208 on July 1.

A similar decline was observed in recruitment eggs. Recruitment eggs declined from 1154 ± 390 to 592 ± 123 in the 1994 cohort. The decline in the 1995 cohort was from 1128 ± 185 to 484 ± 202.

Relative batch fecundity peaked on May 6, 1996 at 222 ± 20.6 for the 1995 cohort (Fig. 17) before declining to 123 ± 33.8 on July 1. The 1994 cohort, however, showed a fairly constant relative batch fecundity throughout the spawning season, with values ranging from 151 to 189. The largest value (189 ± 20.8) occurred on

April 18, 1995.

There was little evidence that any adults were able to survive through a second winter. All adults over 100 mm were checked for annuli on their scales. Three fish were observed to have annuli, although all three were captured in August. I suspect that the annuli were checkmarks produced 4-5 months earlier during spawning. Figure 2. Mean surf-zone temperatures for the Chesapeake Bay (Red) and Coastal

Atlantic Ocean (Green) stations taken when sampling was performed at these sites.

Since daily monitoring of these sites was not possible, the blue line indicates the daily mean water temperatures recorded at the Virginia Institute of Marine Science,

Gloucester Point pier, on the York River. The three horizontal, dashed lines identity the temperatures above whichM. menidia spawning begins (17 °C), and below which feeding ceases (6 °C), and mortality occurs (1.5 °C).

26 Temp 20 30 10 0 a Ar u Ot a Ar u Ot a Ar u OctJan Jul Apr Jan Oct Jul Apr Jan Oct Jul Apr Jan VIMS,YorkRver 9 4 95 1996 1995 1994 Date Bay Bay Surf Ocean Surf Ocean 27 Figure 3. Mean total lengths (95% Cl) of the 1994 Mmenidia cohort at the Silver

Beach and Wachapreague sites. Values for males are indicated by filled circles, females by open circles, and unidentified sex by filled triangles.

2 8 Total Length (mm) Total Length (mm) 100 120 100 120 20 - 40 0 - 60 0 - 80 - 40 20 0 - 60 0 - 80 - - - • ▼ o Sex Unidentified Sex Female Male AUG OCT EJ NJUN DECJUN FEB Wachapreague 94-95 Wachapreague ivrBah 94-95 Beach Silver APR AUG 29 Figure 4. Mean total lengths (95% Cl) of the 1995M. menidia cohort at the Silver

Beach and Wachapreague sites. Values for males are indicated by filled circles, females by open circles, and unidentified sex by filled triangles.

30 Total Length (mm) Total Length (mm) 100 120 100 120 20 - 40 0 - 60 80 - - T o • U AG C DC E AR U AUG JUN APR FEB DEC OCT AUG JUN U AG C DEC OCT AUG JUN Sex UnidentifiedSex Female Male i n ------r E AR U AUG JUN APR FEB Wachapreague 95-96 Wachapreague ivrBah 95-96 Beach Silver 31 Figure 5. Mean somatic weight (±1 SE) of the 1994M. menidia cohort at the Silver

Beach and Wachapreague sites. Values for males are indicated by filled circles and females by open circles.

32 Somatic Weight (grams) Somatic Weight (grams) 10 10 2 4 6 3 5 7 o 8 9 1 o • i — U AG C DC E AR U AUG JUN APR FEB DEC OCT AUG JUN JUN Females Males ------1 ------1 ------DECAUG OCT 1 ------E APR FEB Wachapreague 94-95 Wachapreague 1------1 ivrBah 94-95 Beach Silver ------JUN 1 ------AUG 1— 33 Figure 6. Mean somatic weight (±1 SE) of the 1995 M menidia cohort at the Silver

Beach and Wachapreague sites. Values for males are indicated by filled circles and females by open circles.

34 Somatic Weight (grams) Somatic Weight (grams) 10 10 4 2 6 o 3 5 7 8 9 1 4 2 o 6 3 5 7 8 9 1 o • JUN JUN Males Females U C DEC OCT AUG CA GDEC OCTAUG FEB FEB Wachapreague 95-96 Wachapreague ivrBah 95-96 Beach Silver APR APR JUN JUN AUG AUG 35 Table 1: Silverside total length (mm) and somatic weight (g) at the end of the first growing season and at the end of the second summer, just prior to the cohort disappearing from the population. The data are from the Silver Beach and Wachapreague sites and include the 1994 and 1995 cohorts.

Total Length

Autumn Final Silver Beach N TL 1 SE N TL 1 SE

1994 Cohort Males 15 73.2 1.81 10 77.4 5.12 Females 21 84.4 2.15 38 104.8 1.66 1995 Cohort Males 5 73.6 2.94 11 88.2 2.70 Females 39 85.0 1.26 19 100.7 2.67

Wachapreague N TL 1 SE N TL 1 SE

1994 Cohort Males 13 69.2 2.25 6 101.0 5.70 Females 12 74.3 2.76 8 115.5 2.38 1995 Cohort Males 7 75.9 6.03 7 77.1 2.82 Females 49 80.3 1.25 37 99.0 1.57

Somatic Weight

Autumn Final Silver Beach N Wt (e) 1 SE N Wt (e) 1 SE

1994 Cohort Males 15 2.310 0.172 10 2.681 0.596 Females 21 3.460 0.303 38 7.769 0.370 1995 Cohort Males 5 2.945 0.381 12 3.976 0.337 Females 39 4.462 0.192 19 6.284 0.459

Wachapreague N Wt fg) 1 SE N Wt (e) 1 SE

1994 Cohort Males 13 1.901 0.152 6 7.05 1.160 Females 12 2.364 0.304 8 9.236 0.523 1995 Cohort Males 7 3.091 0.630 7 2.729 0.256 Females 49 3.513 0.166 37 6.084 0.258

36 Figure 7. Mean condition (K) (xlOOO) (±1 SE) for the 1994M. menidia cohort at the

Silver Beach and Wachapreague sites. Values for males are indicated by filled circles and females by open circles.

37 0.9

o o o I*

£Z o

Silver Beach 94-95

o . o JUN AUG OCT DEC FEB APR JUN AUG

0.9

o o o X

a o TJ C o O

Wachapreague 94-95 o.o E JNAUG OCT DECJUN FEB APR JUN AUG

• Male o Female Figure 8. Mean condition (K) (xlOOO) (±1 SE) for the 1995M. menidia cohort at the

Silver Beach and Wachapreague sites. Values for males are indicated by filled circles and females by open circles.

39 Condition (K) (x1000) Condition (K) (x1000) o . o 0.9 o . o 0.9 2 4 3 6 5 7 8 1 o • U OCT JUN JUN Male Female AUG AUG OCT DEC E JUN DEC FEB FEB Wachapreague 95-96 Wachapreague ivrBah 95-96 Beach Silver APR APR JUN AUG AUG 40 Figure 9. Histogram ofM. menida abundance by water temperature from the Virginia

Institute of Marine Science juvenile finfish trawl survey (1987-1996)(n = 2594).

41 Frequency 400 200 300 100 0 0 Temperature (Celsius) Temperature 5 10 15 20 42 Figure 10. Gonadosomatic Index (GSI) curves (±95% Cl) M.for menidia males from the 1994 (closed circles) and 1995 (open circles) cohorts.

43 44 Aug SepApr May Aug SepApr Jun Jul Feb Mar 1994-1995 Males 1995-1996 Males Jan - - 18 16 - 14 - 12 10

ISO Figure 11. Gonadosomatic Index (GSI) curves (±95% Cl) M.for menidia females from the 1994 (closed circles) and 1995 (open circles) cohorts.

45 46 1— ------Aug Sep — i JulJan ~ r Apr May “T i Mar r ~ Feb 1995-1996 Females 1994-1995 Females - - 16 16 - 14 - 12 10

ISO Figure 12. Regression of total number of eggs per (mature plus recruitment) on ovary-free body weight for individual females from April 18, 1995 (1994 cohort) and

April 22, 1996 (1995 cohort), shortly after the start of their respective spawning seasons.

47 Total Number of Eggs Total Number of Eggs 10000 12000 - 14000 16000 10000 12000 - 14000 16000 2000 - 4000 00 - 6000 00 - 8000 00 - 4000 2000 - 6000 00 - 8000 ------0 0 1995-96 Cohort 1995-96 1994-95 Cohort 1994-95 2 2 4 4 Ovary-Free Female Weight (g) Weight Female Ovary-Free Ovary-Free Fem ale Weight (g) Weight ale Fem Ovary-Free 6 8 6 8 2.()+3884.5 + 322.1(X) = Y -q 024 n=25 0.214 = R-Sq Y = 1128.2(X) + 220.3 + 1128.2(X) = Y -q 074 n=32 0.784 = R-Sq 10 10 12 12 14 416 14

16 48 Figure 13. Regression of batch fecundity on ovary-free female weight for four collection dates (1994 cohort)

49 3000 April 4 2500 Y = 94(X) + 220 R-Sq = 0.48 n = 10

2000

1500

1000

500 0 2 4 6 8 10 12 14 16 3000 April 18 2500 y i

2000 •• / / 1500 • A f y / 1000 • - >fi• X • • 500 V . • Y = 169(X) + 95 • R-Sq = 0.72 n = 25 0 2 4 6 8 10 12 14 16 3000 May 9 2500 • • • / 2000 •• • _^

1500 • •• # 1000

500 • •• • Y = 137(X) + 276 R-Sq = 0.54 n= 59 0 2 4 6 8 10 12 14 16 3000

May 24 Y = 97(X) + 406 2500 R-Sq = 0.27 n= 24

2000 • • • t 1500

1000 •

500 • . • 0 2 4 6 8 10 12 14 16 Ovary-free Female Weight (g)

50 Figure 14. Regression of batch fecundity on ovary-free female weight for four collection dates (1995 cohort)

51 3000 April 22

2500

2000

1500

1000

500 Y = 260(X) - 248 < R-Sq = 0.686 n = 32 0 2 4 6 10 12 14 16 3000 May 6 2500

2000

1500

1000

500 Y= 194(X) + 150 R-Sq = 0.759 n = 22 0 10 12 14 16 3000 May 22 2500

2000

1500

1000

500 Y = 125(X) +446 R-Sq = 0.461 n = 18 0 8 10 12 14 16 3000 June 3 2500

2000

1500

1000

500 Y = 156(X) + 87 R-Sq = 0.489 n = 17 0 4 6 8 10 12 14 16 Ovary-free Female Weight (g)

52 Figure 15. Graphs of mature, recruitment, and total numbers of eggs per gram body weight by sampling date (± 95% Cl) for the 1994 cohort. The numbers in parentheses indicate the number of individuals sampled on each date.

53 1750

1500

1250

1000

750

500

250

0

1250

1000

750

500

250

0

250

200

150 (25) (59) (25) (24) 100 (10) (20 )

50

0 APR MAY JUN JUL

54 Figure 16. Graphs of mature, recruitment, and total numbers of eggs per gram body weight by sampling date (± 95% Cl) for the 1995 cohort. The numbers in parentheses indicate the number of individuals sampled on each date.

55 Number of mature eggs (per g body wt) Number <* recruitment eggs (per g body wt) Total number of eggs (per g body wt) 56 Figure 17. Curves of relative batch fecundity by sampling period for the 1994 (closed circles) and 1995 (open circles) cohorts.

57 Relative Batch Fecundity (eggs/g body weight) 250 300 200 100 150 50 0 Apr May 1995-1996 1994-1995 JulJun 58 DISCUSSION

Growth, Size-Specific Mortality, and the Winter Migration:

Previous studies found that in general, warmer temperatures substantially enhance silverside growth (Bengtson and Barkman 1981) and survival is poor among eggs that develop at temperatures below 17 °C (Austin,et al. 1975). The results of my study confirm that the Chesapeake Bay side of the Delmarva Peninsula warms earlier that the coastal Atlantic Ocean and remains warmer throughout the summer. This pattern provides a longer and warmer potential growing season for Chesapeake Bay silversides in comparison to their coastal-Atlantic counterparts.

Although the thermal regime in the Bay surf zone suggests more favorable toward growth and survival than the coastal Atlantic Ocean, the results were inconclusive as to whether the thermal environment translates into significant variations in growth between these two habitats. The high variation in growth between the sampling sites on similar dates suggests that local conditions may play a larger role in growth and survival than the broader environmental differences between water bodies.

No conclusions about size-specific mortality were possible from this study, but temperature measurements suggest some possibilities that might be tested in future studies. In South Carolina, Sosebee (1991) found that silverside growth continued linearly throughout the winter months. In contrast, Conover and Present

(1990) found silverside growth to cease during the winter, with mortality highest among smaller individuals. A possible explanation for the continued, linear growth observed by Sosebee is that temperatures in South Carolina tended to stay above 6 °C, so silverside feeding was possible throughout the winter months.

Virginia’s coastal waters, in contrast, dropped below the 6 °C threshold for three months in the winter of 1995 and for a brief period during the previous winter.

Winter temperatures in the Chesapeake Bay and Coastal Atlantic normally fall very close to the 6 °C threshold in Virginia and often do not remain there for extended periods of time. It follows that silverside growth might be evident in mild winters, but size-specific mortality might occur when the winter is particularly cold. One would also expect to observe a reduced effect along the Atlantic coast because of the moderating influence of the Atlantic Ocean.

This suggests a very strong relationship between temperature and the silverside winter migration in Virginia. Although the most recent research strongly indicates that depletion of lipid reserves during stretches of cold winter temperatures is the predominant reason for size-specific mortality in northern populations (Schultz, et al. 1998, Schultz and Conover 1999), other mechanisms are possible. The strong relationship between the winter migration and cold temperatures, combined with research that shows a relationship between silverside mortality and depth (Ruiz,et al.

1993), suggests the possibility of a size-specific predatory mechanism for the observed pattern of winter mortality in northern populations.

Size-specific mortality could be driven by predation in one of two ways. The first would be if smaller silversides were more easily driven into deeper waters than

60 larger individuals when temperatures cooled. If shallow water is a refuge from larger predators as Ruiz,et al. suggest, then mortality would be higher among the smaller individuals. The second mechanism is if silverside predators were size-selective in their predation for some other reason. In this case, one would assume that the longer the silversides were away from their shallow water refuge, the more skewed the length-frequency curves would become toward larger individuals.

If either of these two mechanisms were active in the Chesapeake Bay, one would expect to find a length-frequency change with respect to depth. In the case of the second mechanism, depth is a proxy for distance, and thus time, away from shore.

An analysis of covariance identified no such relationship between fish length and depth across ten years of survey data. This result suggests that the two predation mechanisms for size-selective mortality are unlikely. This study fails to support an alternative to the prevailing theory.

Fecundity and Gonad Analysis:

The silverside spawning period in Virginia is bracketed by the sampling date when clearly maturing ova were observed and the date of senescence of the adult population. In this study, the earliest date when maturing ova were observed was

March 27. The latest date when adults were observed in any substantial frequency was harder to establish. Variations were substantial between the three cohorts that were studied, and even between sampling sites. The 1994 cohort disappeared from collections at four of six stations by July 5,

1995. In 1997, there were no adults from the 1996-1997 cohort captured after June

17. The 1995 cohort was the most persistent, with adults captured on August 6 at five of the six stations, and one adult captured in Wachapreague as late as October 1.

Despite the yearly variation, July 5 seems to be the best estimate for the end of the silverside life span in Virginia. Except for the Wachapreague station, few adult silversides were captured after July 5, even during 1996 when some fish lingered on for several months. Wachapreague was an anomaly. Silversides continued to be captured at this site well after July 5 in both 1995 and 1996. The extended life span may be due to cooler water temperatures at this northern, ocean-influenced location, reducing the metabolic demand on these fish.

The minimum and maximum dates of silverside spawning are measured in this study as March 27 and July 5. This three month period normally contains six semi- lunar spawning periods that would be favorable for spawning, and mature eggs were observed during all six periods. The earliest that spent silverside ovaries were observed in this study was June 7 for the 1994 cohort and June 19 for the 1995 cohort.

Therefore, at least some individuals spawned no more than four times during the spawning season.

Conover (1985) estimated the number of eggs produced annually by subtracting the number of the recruitment eggs remaining at the end of the spawning season from the number of eggs present just prior to the start of the spawning season.

The calculation assumes that the pool of recruitment eggs is fully formed prior to the

62 start of spawning. Conover found this to be a reasonable assumption since he “noted few eggs which appeared to be atretic or in the process of resorption” until near the end of the season. I had similar results in this study, and found nothing to contradict this assumption.

Results from the 1994 and 1995 Virginia cohorts were quite consistent. The annual egg production for the 1994 cohort was calculated to be (1305 ± 402) - (592 ±

123) = 713 ± 364 eggs/g ovary-free body wt. The results from the 1995 cohort were

(1202 ± 147) - (484 ± 202) = 7181214. Multiplying these values by the mean ovary free body weights of adult females during the 1995 and 1996 spawning seasons,

6.09 lg and 6.175g respectively, gives the average number of eggs produced per female during each spawning season. These values were 4343 eggs/female produced by the 1994 cohort and 4434 eggs/female by the 1995 cohort.

One can estimate the number of spawning events per season by dividing the total number of eggs produced per female by the average number of eggs per batch.

Batch fecundity was 174.2 eggs/g x 6.09lg =1061 eggs for the 1994 cohort and 180.6 eggs/g x 6.175g =1115 eggs for the 1995 cohort. Dividing the total number of eggs per female by the average batch size produced values of approximately four spawning events for each cohort.

Four spawning events corresponds well with the number of semi-lunar periods between the beginning of the spawning season (March 27) and the date when spent ovaries were first detected in Virginia samples (June 7).

63 Comparisons with northern and southern populations:

The results regarding growth, GSI, and fecundity from this study are intermediate to results obtained by Conover (1985) in Massachusetts and Sosebee

(1991) in South Carolina. There is a gradient with respect to latitude, not only in the timing but in the magnitude of these aspects of silverside life history.

The countergradient variation in growth rate described by Conover and

Present (1990) was evident, as the growth rate and maximum total lengths were higher in northern populations than Virginia. Correspondingly, Virginia growth rates and maximum total lengths were larger than South Carolina.

The gonadosomatic index for both males and females demonstrated a similar variation with respect to latitude (Figs. 19-20). GSI in Virginia peaked in May for both males and females. This is approximately one month later than South Carolina and a month earlier than Massachusetts. Peak GSI in Virginia was roughly one third larger than found in the South Carolina study, and a third smaller than was found in the Massachusetts population.

Batch fecundity in Virginia as a function of ovary-free body weight was similarly greater than South Carolina and less than Massachusetts (Fig. 21). As with

GSI, relative batch fecundity peaked in early May, and this peak was offset by one month with respect to South Carolina and Massachusetts populations. Again, mean batch fecundity was largest in Massachusetts and smallest in South Carolina, with

Virginia falling between the two. The annual egg production in this study was found

64 to be less than the Massachusetts result of 5001 eggs/female. The difference was 567 eggs/female in 1995 and 658 eggs/female in 1996.

Sosebee did not calculate a value for annual egg production per female in

South Carolina, but estimated that annual fecundity for an average female was 840 eggs/g body weight, calculated by multiplying the peak batch fecundity in her study by the estimated number of seasonal spawning events (6). This estimate of six events was based on visual observations by Middaugh (1981) of spawning events in the field. This is in contrast to 1040 eggs/g in Massachusetts and values of 888 and 756 eggs/g for the two Virginia cohorts, assuming four spawning periods. A maximum of six spawning events are possible in Virginia, based on the number of semi-lunar spawning events from the time that temperatures became favorable for spawning (and mature eggs were observed) to the time that the adult population disappeared. This assumption would lead to annual fecundity estimates of 1332 and 1134 for the two cohorts. These are the maximum fecundity estimates for Virginia silversides.

Evolutionarily, one would expect the results regarding GSI and batch fecundity. This study found that an individual silverside spawns four times during the reproductive season - the same number of batch spawnings determined by Conover

(1985). Spawning in Massachusetts, however, occurred later in the year.

Development was therefore more likely to be subject to hostile (i.e. colder) environmental conditions. One would expect that to obtain similar levels of reproductive success, northern silverside populations must be more fecund throughout the season to maintain similar population levels. Although an individual silverside in

65 Virginia spawned four times, there were six potentially-favorable dates to spawn.

Thus, Virginia silversides had more opportunities to spawn on a date when environmental conditions were appropriate, suggesting less evolutionary pressure toward high batch fecundity.

The difference in fecundity and GSI come at a cost, however. Northern populations must allocate proportionally more energy to reproduction than more southerly populations. The toll in the north appears to be heaviest during the winter among smaller individuals that can not meet the combined metabolic and reproductive demands when feeding capability is reduced due to thermal stress.

Continued, linear growth in southern populations provides little evidence to demonstrate a similar demand.

6 6 Figure 18. Gonadosomatic Index - Males - Virginia vs. Massachusetts and South

Carolina

67 6 8 Aug Sep Jun Jul SC Males (Sosebee, 1991) MA Males (Conover, 1985) VA Males 1994-95 VA Males 1995-96 Jan Feb Mar Apr May - - - 18 18 - 16 - 10 14 14 - 12 22 20 ISO Figure 19. Gonadosomatic Index - Females - Virginia vs. Massachusetts and South

Carolina.

69 70 Jul Aug Sep i i i i Apr May Jun r— ------1 SC Females (Sosebee, 1991) MA Females (Conover, 1985) VA Females 1994-95 VA Females 1995-96 ------Jan Feb Mar “ i ------8 6 4 - 2 0 18 18 - 16 - 14 - 12 10 22 20 ISO Figure 20. Relative Batch Fecundity - Virginia vs. Massachusetts and South Carolina

71 Relative Batch Fecundity (eggs/g ovary-free body weight) 200 - 250 0 - 300 350 100 0 5 1 0 - 50 - - S 1984 SC - a Apr Mar VA1995 VA1996 a u Jul Jun May 72 Figure 21. Life history diagram ofM. menidia in the coastal waters of Virginia.

73 Spawning Shallow marsh April-June Larvae April - July

Surf zone Adults Juveniles April-August May - October * Shallow Coastal Water Adults Juveniles June-September October-December

Deep Bay or 7* Atlantic Ocean Adults Decern ber-February

74 SUMMARY

Silverside life history begins in Virginia during the first daylight spring tide in

April. The first of four spawning events occurs at this time within the flooded

Spartina stalks of the Chesapeake Bay and tributaries, as well as within the coastal lagoons and marshes on the Atlantic Ocean side of the Delmarva Peninsula (Fig. 22).

On the following spring tide, the silverside larvae hatch and begin to develop in the shallow waters. Average total length reaches approximately 80 mm by the end of the first season of growth, and females are larger than males, on average.

A migration to deeper water occurs when temperatures cool in the autumn.

The silverside migration reaches the deeper portions of the Bay once water temperatures drop below about 9 °C, but there is some movement away from the shallower waters before then. The study did not find evidence of size-specific mortality among Virginia silverside populations, but there is some evidence that particularly cold winters may reduce winter growth, possibly leading to this condition.

In March, silverside populations begin to move back to shallow waters.

Spawning occurs from late March to early July, although most of the spawning probably occurs between March 27 and June 7.

Most adult silversides disappeared from collections by July 5 and were assumed to die. Some silversides survived as late as October, particularly in the northerly, Atlantic coast Wachapreague location, although there was little evidence to suggest that any adults survive another winter to spawn again. Growth, gonadosomotac index, and fecundity all demonstrated gradients with respect to latitude in both their timing and magnitude. Peak GSI and fecundity occurred approximately a month later in Virginia than was previously determined for a South Carolina population (Sosebee 1991). Similarly, these events occurred in

Massachusetts (Conover 1985) a month later than Virginia. Maximum total length,

GSI, and fecundity were all found to increase with latitude.

76 APPENDIX

Atlantic Silverside Recipes

For the adventurous reader, following are five recipes for the Atlantic silverside (Menidia menidia). These recipes were modified by the author from smelt recipes found on the web site, http://chef2chef.com. Any responsibility for the failure of a recipe to meet the reader’s palate lies with the cook, the diner, or the author, not with the reader’s committee member for whom the recipe pays tribute.

One additional warning. This appendix was produced very close to the publication date of the thesis. The author has not actually tested these recipes (yet).

The preferred collection method for Atlantic silversides is by beach seine. In Virginia, the best time of the year for collecting is late May when silversides are large and adults abundant. Abundance decreases rapidly in June as the adults reach the ends of their lives. Refrigerate fish immediately after capture and prepare within the day. Silversides can also be frozen. Immediately freeze silversides in freezer bags after capture. Thaw quickly in warm water prior to preparation.

Atlantic silversides, like smelt, have small bones that are quite flexible, especially when cooked. The fish can be eaten whole. If desired for larger specimens, it is possible to make a slit along the dorsum, lift the flesh, and remove the spine. Cleaning the fish normally includes removing the head, making an incision along the ventral edge of the fish, removing the internal organs, and washing well with fresh water.

77 Austin’s [I’d prefer to just pop them in my mouth raw, but if I have to cook them I’ll eat them] Fried Silversides 5 Servings

Ingredients'.

24 silversides 1 cup flour 1/2 tsp. salt 1/2 tsp. pepper 2 medium lemons 4 tbsp. butter

Instructions:

Clean the silversides and remove the heads. Mix the flour, salt and pepper in a bowl and coat the fish in this. In a hot frying pan, add the butter and fry the silversides until golden brown. Serve with a wedge of lemon.

78 Conover’s Long Island Cheese Silversides 6-8 Servings

Ingredients:

3 lbs. silversides 1/2 cup milk 1/2 tsp. salt 11/2 cups flavored bread crumbs 1/4 cup freshly grated parmesan or romano cheese 1/3 cup melted butter paprika

Instructions:

Wash and dry fish. Combine milk and salt. Combine breadcrumbs and cheese. Dip fish in milk and roll in crumbs. Place fish in a single layer in a well-greased 15x10x1" baking dish. Pour butter over fish and sprinkle liberally with paprika. Bake in 500 °F oven 8-10 minutes.

79 Musick’s [Don’t fall in front of the electroshocker or you’ll be] Fried Silversides 4 Servings

Ingredients:

1 lb. silversides 1/4 cup all-purpose flour 1/4 tsp. salt 1 tsp. dry mustard 1/4 tsp. cayenne pepper 1/2 tsp. paprika 1 finely grated lemon peel vegetable oil for frying 2 tbsp. chopped fresh parsley 1 lemon wedge 1 lemon peel strip (opt) 1 fresh dill sprig (opt)

Instructions:

Rinse silversides under cold running water. Pat dry on paper towels.

In a plastic bag, combine flour, salt, mustard, cayenne pepper, paprika and lemon peel. Add silversides and shake well until fish are evenly coated. Half fill a deep-fat fryer or saucepan with oil; heat to 375 °F or until a 1/2" cube of day-old bread browns in 40 seconds.

Place 1/2 of silversides in a frying basket. Lower basket gradually into hot oil and fry 1 minute, shaking basket frequently. Drain on paper towels. Reheat oil to 375 °F. Repeat with remaining silversides. Place all of the silversides into basket and fry 1 -2 minutes more or until lightly golden and crisp. Drain on paper towels. Turn into a warm serving dish, sprinkle with chopped parsley and serve hot with lemon wedges. Garnish with lemon peel strips and dill sprigs, if desired.

80 Chittenden’s Silverside and Onions [but shad tastes better] 4-6 Servings

Ingredients’.

20 to 24 silversides 3 eggs 1/4 cup water 1/2 cup flour 1 cup matzo meal 2 tsp. salt 1/4 tsp. white pepper 1/2 cup com or safflower oil 2 medium onions, sliced

Instructions:

Wash silversides and pat dry with paper towels.

In a bowl, mix together eggs and water. In another bowl mix together flour, matzo meal, salt, and pepper. Dip silversides first in beaten egg mixture and then dredge in flour-matzo mixture.

In a heavy skillet, heat oil and saute onion slices for a few minutes. Push onions to the side and fry silversides for a few minutes on each side. Continue cooking onions on the side of the pan until all silversides are fried. The fried silversides should be golden and crisp and onions should be a dark golden brown. Serve with boiled, parsleyed potatoes and green vegetable.

81 Evans’ Silverside [is a cut of beef!] Stew 4 Servings

Ingredients:

8 (or more) large silversides 1/2 Korean white radish 3 1/2 oz hot green peppers 4 red peppers 2 green onions 2 cloves garlic 1/3 oz fresh ginger root 1/3 lb. beef

Beef Seasonings: 1 tbsp. soy sauce 2 tsp. minced green onion 1 tsp. minced garlic 1 tsp. sesame seed powder 1 tsp. sesame oil 1/4 tsp. pepper 4 tbsp. red pepper paste 1 tbsp. vinegar 2 tsp. molasses

Instructions:

Remove scales by holding the silverside’s tail and scraping toward the head. Remove the internal organs. Wash well, and cut off the tail.

Shred beef finely. Add soy sauce, minced green onion, minced garlic, sesame seed powder, sesame oil and pepper, and mix well.

Place seasoned beef into cavity of silverside. Cut radish into 1 l/2"-long pieces and slice intol/4”-thick rectangles. Wash hot green and red peppers, remove stems, and cut diagonally. Shred green onions, garlic and ginger finely. Place radish slices on bottom of pan. Place stuffed silversides in pan and sprinkle with shredded green onions, garlic, ginger and peppers. Mix 1/2-cup water, red pepper paste, vinegar and molasses together and pour into pan. After it boils reduce heat and simmer over low heat, basting with liquid. Cook until most of the liquid is absorbed.

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87 VITA

Richard Kimball Holmquist

Bom in Boston, Massachusetts on May 11,1969. Graduated from South Lakes High

School, Reston, Virginia, in June 1987. Earned a B.S. in biology and history from the

College of William and Mary, Williamsburg, Virginia in May 1991. Employed as an

Alaska Domestic Groundfish Observer for Saltwater, Inc., Anchorage, Alaska from

April to November 1992. Hired in January 1993 as a Laboratory Aide by the

Crustaceology Department, Virginia Institute of Marine Science (VIMS). Entered the

Masters program in Marine Science at the College of William and Mary, School of

Marine Science, VIMS in August 1994. Deployed to Sarajevo, Bosnia-Herzegovina as commander of the 129th Field Artillery Detachment, Virginia Army National Guard in August 1997. Employed in December 1998 as an Environmental Specialist,

Division of State Lands, Florida Department of Environmental Protection,

Tallahassee, Florida. Hired in August 1999 as an Oceanographer with Orbital

Imaging Corp., Dulles, Virginia.

8 8