TECHNICAL SUMMARY 

STUDY TITLE: Environmental Investigation of the Use of Shoals Offshore Delaware 

and Maryland by Mobile Benthos and Finfish Species 

REPORT TITLE: Comparisons Between Marine Communities Residing on Sand Shoals 

and Uniform-Bottom Substrate in the Mid-Atlantic Bight 

CONTRACT NUMBER: MMS 1435-01-02-CT-85060 

SPONSORING OCS REGION: Headquarters-Leasing Division, Marine Minerals Branch 

APPLICABLE PLANNING AREA: East and Gulf of Mexico Coasts 

FISCAL YEARS OF PROJECT FUNDING: 2003, 2004, and 2005 

COMPLETION DATE OF REPORT: March 2006 

COSTS: FY 2003: $250,528.00, FY 2004: $165,496.00, FY 2005: $83,219.00 

Cumulative Cost: $499,216.00 

PROJECT MANAGER(S): William H. Burton and H. Ward Slacum Jr. 

AFFILIATION: Versar, Inc 

ADDRESS: 9200 Rumsey Rd., Columbia, MD. 21045 

PRINCIPAL INVESTIGATOR: William H. Burton 

KEY WORDS: Mid-Atlantic Bight, inner-continental shelf, sand mining, beach 

nourishment, Habitat, fisheries, shoals, guilds 

BACKGROUND: Many of the beaches along the Mid Atlantic Bight (MAB) are 

undergoing long-term erosion due to sea level rise, human activities, and from severe 

coastal storms. In efforts to try to restore beaches lost to erosion various state and federal 

governmental agencies have ongoing or proposed beach stabilization projects that require 

significant sand resources to complete. As the need to replenish beaches increases new 

sand resources will be required and those will likely be taken from federal waters. The 

Minerals Management Service (MMS) has jurisdiction over all mineral resources 

occurring in federal waters. The MMS along with both Maryland and Delaware 

Geological Survey have identified four specific sand shoals off of their coasts as potential 

resources for long-term sand mining. The specific shoals are, Shoal B, Shoal D, Fenwick 

Island Shoal, and Weaver Shoal. If shoals provide important habitat to specific marine 

communities, then mining activities could have negative impacts to those communities, 
and before mining can occur, information must be gathered pertaining to what species of 

fish and mobile benthos may be affected by mining. 

OBJECTIVES: The main objectives of this study were to 1) determine what species of 

fish and mobile benthos reside at offshore sand shoals, and 2) evaluate if the shoals 

represent important habitat for those species. The focus of this study was to compare the 

four sand shoals to four reference habitats located in the same region that exhibited 

similar macro and microhabitat features, but did not exhibit vertical relief like the shoals. 

To evaluate if shoals are important habitat, we compared species abundances and 

diversity between the four shoals and four reference habitats. Species abundance and 

diversity were used as determinants of habitat quality and we defined an area to be 

“preferred” if total species or communities occur at greater abundances and higher 

diversities within that area. 

DESCRIPTION: The study was located on the inner continental shelf of the MAB 

region off the coast of Maryland and Delaware. The primary focus was four sand shoals; 

shoal B, D, Fenwick, and Weaver, and four flat-bottom reference sites. The shoal and 

reference areas were located between 16 and 25-km off the coast and encompass 

approximately 800 square km of the inner shelf. 

A randomized paired site design was used to compare the distribution, total relative 

abundance, and diversity of finfish and mobile benthos species residing on the shoals and 

nearby uniform-bottom habitat. Four pairs of sites were established by pairing each of 

the four shoals to a specific uniform-bottom reference site. To identify comparable 

reference sites and to quantify species and community abundance three specific methods 

were used. Initially, underwater video technology was used to identify and characterize 

reference locations in proximity to the shoals. Then four reference sites were chosen 

based on similarities of physical and biological micro and macrohabitat features that were 

present at those sites and the shoals. Once the sites were identified, then a multi-year 

comprehensive fisheries study consisting of daytime trawling, gillnetting and nighttime 

bioacoustics was employed to compare and contrast the relative abundance, diversities 

and distribution of fish and mobile benthos communities between the shoals and flatbottom reference sites. 

A total of 41,893 individuals were collected from a combination of 384 small trawl 

(n=128), commercial trawls (n=128) and gillnet sets (n=128) that were conducted for two 

consecutive years. In the collections there were 57 species of fish including 15 species of 

sharks, skates, and rays. In addition, there were 17 invertebrate species represented by 7 

decapod crustations and 10 other invertebrate species. Comparisons between catch per 

unit effort (CPUE; relative abundance), species richness, and diversity were performed 

between shoals and reference sites for each season and gear using the Analysis of 

Variance tests (ANOVA). There were mixed results with generally higher numbers of 

total species abundance, total species richness, and total species diversity at the reference 

sites in trawls and no clear patterns in gillnet data. There were significant seasonal 

differences in species densities throughout the study at all the sampling sites and between 

all gears. There were also differences in catch between all gears within a season. 
Comparisons of specific species guilds using ANOVA were also done on site pairs. The 

analysis was performed for each combination of gear and guild except pelagic 

invertebrates in gillnets. For this study we defined a guild based on feeding strategies 

found in the literature, such as primarily benthic oriented feeding or pelagic feeding 

strategies. Four functional groups or guilds were defined from the fisheries data: benthic 

finfish, benthic invertebrates, pelagic finfish, and pelagic invertebrate. Analysis of 

specific species guilds show that more benthic finfish, pelagic finfish, and pelagic 

invertebrates (squid) were captured in the commercial and small trawls at reference sites 

than at shoals. The difference was statistically significant at α = 0.05 for all of these 

comparisons except benthic finfish in the commercial trawl, which had α = 0.058 level of 

significance. Each of the trawl gears captured benthic invertebrates in nearly equal 

numbers at shoal and reference sites. Capture rates in gillnets differed from those in 

trawls. In gillnets, all assemblages except pelagic invertebrates were captured in about 

equal numbers, and no significant differences were detected. No pelagic invertebrates 

were captured in gillnets. 

Meta-analysis of the trawl gears confirmed that benthic finfish, pelagic finfish, and 

pelagic invertebrates occurred in greater densities at reference sites than at shoals. The 

standardized difference in mean transformed densities was about 0.5 standard deviations 

for all three assemblages, and 95% confidence intervals indicated the difference was 

probably at least 0.2 standard deviations for all three guilds. There was little evidence 

that benthic invertebrate density differed between shoal and reference sites, as indicated 

by the small standardized difference between mean densities (0.01 standard errors) and 

associated 95% confidence interval that intersected zero by a large amount. 

For all three gears, there was strong separation of sites according to season in cluster 

analysis. Shoal and reference samples collected with the small trawl showed a tendency 

to form groups in spring and summer, but not in fall or winter. For the commercial trawl 

samples, there was a tendency for shoal and reference samples to group in summer, a 

clearer pattern of separation in fall and winter, and no pattern in spring. No structure 

existed for the gillnet samples that would suggest differences between the shoal and the 

reference sites. Two-way crossed ANOSIM tests detected a significant difference 

between sites for the commercial trawl data, a difference at the 10.9% level for the small 

trawl, and no difference for the gillnet data. For the commercial trawl, an observed value 

of R of 0.18 is a very unlikely event and leads to the rejection of the null hypothesis at the 

0.1% level. For the small trawl, a significant difference can be inferred given that only a 

relatively small number (10.9%) of the simulated R values is larger than the observed R 

of 0.06. Season was highly significant for all tests. 

The results of the two-way crossed ANOSIM tests suggest that despite the strong effects 

of season, differences in species composition between the shoal and the reference sites 

could be interpreted for the small trawl and commercial trawls. SIMPER was then used 

for these two gears to determine which species typified the shoal and the reference sites. 

For the commercial trawls, striped bass and several other species more equally 

contributed to the separation between shoal and reference sites in the fall; winter skate, 

windowpane, and little skate contributed most in winter; scup, butterfish, and squids in 

the spring; northern searobin, scup, and squid in the summer. Many species contributed 
to the discrimination between the shoal and the reference sites, but none better than scup 

in the fall, winter skate in winter, and northern searobin in summer. All three fish species 

were more abundant in the reference than in the shoal sites. 

Six seasonal bioacoustic surveys in all seasons but winter were conducted at each pair of 

sites over the two year study. Analysis of bioacoustic data was conducted using ANOVA 

with mean Sv (relative fish biomass in decibels) and fish density (number/10,000 m3) and 

variables. In general, fish densities and biomass fluctuated between sites throughout the 

seasonal surveys. Differences between individual shoals and their reference sites were 

found in many seasons and some patterns are evident within site pairs. 

In summary, comparisons between shoals and reference sites for each season and gear 

showed mixed results with generally higher numbers of total species abundance, species 

richness, and species diversity at the reference sites in the trawl data and no clear patterns 

in gillnet data. There were significant seasonal differences in species densities 

throughout the study at all the sampling sites and between all gears. There were also 

differences in catch between all gears within a season. Analysis of specific species guilds 

showed that more benthic finfish, pelagic finfish, and pelagic invertebrates (squid) were 

captured in the commercial and small trawls at the reference sites compared to the shoals. 

In gillnets, all guilds except pelagic invertebrates were captured in about equal numbers, 

and no significant differences were detected. No pelagic invertebrates were captured in 

gillnets. In general, fish densities and biomass quantified using bioacoustics fluctuated 

between sites throughout the seasonal surveys. However, differences between individual 

shoals and their reference sites were found in many seasons and some patterns were 

evident within site pairs. In particular, Fenwick Island Shoal and Weaver Shoal exhibited 

higher nighttime densities and biomass when compared to their reference pairs, and when 

tests were significant they favored higher estimates at these shoals the majority of the 

time. Shoal B and D and their reference sites did not exhibit any consistent nighttime 

pattern of higher estimates throughout the study. 

Two consecutive years of fisheries monitoring in Federal waters off the coast of 

Maryland and Delaware documented that there are significant seasonal variations in 

species richness and abundances at the shoals and reference sites in this region of the 

MAB. There were also yearly variations in abundance, but overall the seasonal patterns 

of species assemblages are consistent and the majority of the species inhabiting the shoals 

and reference site habitats are seasonal residents. Comparisons between the net and 

bioacoustic data suggest that pelagic fish are using habitats differently between day and 

night. Multiple analyses were conducted on the data collected over the two years and 

from those analyses we conclude that 1) fish and squid occurring in the MAB either have 

no preference or prefer substrates at uniform-bottom types to sandy shoals during the day, 

2) benthic invertebrates have no preferences for shoals over uniform-bottom types during 

the day, and 3) there are diel (Day/Night) differences in the abundance of pelagic fish 

using the shoals and reference sites. Theses data suggest fish could be using the adjacent 

uniform-bottom habitats during the day and move onto the shoals at night to exploit new 

habitat, in which case shoals could represent an important resource for fish at night. 
STUDY PRODUCTS: Slacum, H.W. JR., W.H. Burton, J.H. Volstad, J. Dew, E. 

Weber, R. Llanso, D.Wong. 2006. Comparisons Between Marine Communities 

Residing on Sand Shoals and Uniform-Bottom Substrate in the Mid-Atlantic Bight. Final 

Report to the U.S. Department of the Interior, Minerals Management Service, 

International Activities and Marine Minerals Division, Herndon, VA. Contract No. 1435-

01-02-CT-85060. 

H. Ward Slacum Jr. and William H. Burton. Environmental Investigation of the Use of 

Shoals Offshore Delaware and Maryland by Mobile Benthos and Finfish Species. 

Presentation given at the Minerals Management Service Offshore Sand Workshop 

Thursday, Oct. 23, 2003, University of Delaware. 

H. Ward Slacum Jr. and William H. Burton. Environmental Investigation of the Use of 

Shoals Offshore Delaware and Maryland by Mobile Benthos and Finfish Species. 

Presentation given at the Tidewater Chapter of the American Fisheries Society Meeting 

January 2, 2004, Salisbury University. 

 

H. Ward Slacum Jr., William H. Burton, Jon Volstad, Jodi Dew, and Ed Weber. 2005. 

Differences in Relative Abundance of Marine Guilds Residing on Offshore Sand Shoals 

and Flat-Bottom Substrates in the Mid-Atlantic Bight. Presentation given at the 2005 

Annual Estuarine Research Federation (ERF) Meeting. Norfolk VA.