OCS Study 

MMS 2005-042 

FINAL REPORT 

COMPARISONS BETWEEN MARINE COMMUNITIES RESIDING 

ON SAND SHOALS AND UNIFORM-BOTTOM SUBSTRATES IN 

THE MID-ATLANTIC BIGHT 

PREPARED FOR: 

U. S. DEPARTMENT OF THE INTERIOR 

MINERALS MANAGEMENT SERVICE 

LEASING DIVISION 

MARINE MINERALS BRANCH 

March 2006 
OCS Study 

MMS 2005-042 

COMPARISONS BETWEEN MARINE COMMUNITIES 

RESIDING ON SANDSHOALS 

AND UNIFORM-BOTTOM SUBSTRATES 

IN THE MID-ATLANTIC BIGHT 

Contract No. MMS 1435-01-02-CT-85060 

Prepared for 

Department of the Interior 

Minerals Management Service 

381 Elden Street, MS-2500 

Herndon, Virginia 20170-4817 

Prepared by 

H. Ward Slacum Jr. 

William H. Burton 

Jon Vølstad 

Jodi Dew 

Ed Weber 

Roberto Llansó 

David Wong

Versar, Inc. 

9200 Rumsey Road 

Columbia, MD 21045 

March 2006 
DISCLAIMER 

This report has been reviewed by the Minerals Management Service (MMS) and approved for 

publication. The opinions, findings, conclusions, or recommendations expressed are those of the 

authors and do not necessarily reflect the views or policies of the MMS. Mention of trade names 

or commercial products does not constitute endorsement for use. This report has been technically 

reviewed according to contractual specifications; however, it is exempt from further review by 

MMS technical editors. 

Suggested Citation 

Slacum, H.W. Jr., W.H. Burton, J.H. Vølstad, J. Dew, E. Weber, R. Llansó, 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. OCS Report MMS 2005-042, 149 pp. + app. 
Acknowledgments 

iii 

ACKNOWLEDGMENTS 

There were many people who were essential throughout this project. Special thanks are 

extended to Jeff Eustler, the captain of the commercial trawler “Tony and Jan”, and to Harold 

Martin, the captain of the gillnetter “Leanna”, for their hard work and dedication to this project. 

Also we are indebted to “Timmie” and Phil, the two crew members of those vessels who both 

contributed their expertise and dedication toward this project. We thank Dr. Kyle Hartman of 

UWV for conducting the bioacoustic survey and to John Howell for being flexible and sticking it 

out even when the going got rough at midnight. Lastly, we would like to thank Dr. Bob Diaz and 

Dr. Janet Nestlerode of VIMS for conducting the video survey and collaboration in choosing the 

reference sites. This report was improved by the comments of several reviewers, whose 

constructive comments were greatly appreciated. 
Acknowledgments 

iv 
Executive Summary 

v 

EXECUTIVE SUMMARY 

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 or “mined” 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. 

The study was located on the inner continental shelf of the MAB region off the coast of 

Maryland and Delaware. The primary focus was the four sand shoals and four 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. 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. In this 

region of the MAB, shoals and uniform-bottom (lacking extreme vertical relief) habitats are the 

dominant megafeature. For comparison, four uniform-bottom habitats were chosen as the 

reference sites. 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. 

To identify comparable reference sites, underwater video technology was used to 

characterize the shoal and reference habitats. 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 reference sites were identified, a multi-year comprehensive fisheries study 

consisting of daytime trawling, gillnetting and nighttime bioacoustics was employed to compare 

and contrast the abundance, diversities and distribution of fish and mobile benthos communities 

between the shoals and reference habitats. 

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 
Executive Summary 

vi 

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. 
Table of Contents 

vii 

TABLE OF CONTENTS 

Page 

ACKNOWLEDGMENTS........................................................................................................... iii

EXECUTIVE SUMMARY ..........................................................................................................V 

1.0 INTRODUCTION ......................................................................................................... 1-1 

1.1 PROJECT OVERVIEW AND OBJECTIVES ....................................................... 1-3 

1.2 ENVIRONMENT SETTING.................................................................................. 1-7 

1.2.1 Climate........................................................................................................1-7

1.2.2 Biological Resources ..................................................................................1-7 

1.2.3 Geology....................................................................................................... 1-9 

1.2.4 Linear Shoals ..............................................................................................1-9 

2.0 FIELD METHODS........................................................................................................ 2-1 

2.1 STUDY AREA ....................................................................................................... 2-1 

2.2 SAMPLING DESIGN ............................................................................................ 2-1 

2.2.1 Reference Site Selection .............................................................................2-2 

2.2.2 Fisheries sampling ...................................................................................... 2-3 

2.2.2.1 Net Survey ...................................................................................2-3 

2.2.2.2 Bioacoustics .................................................................................2-4 

3.0 STATISTICAL ANALYSIS OF NET SURVEY DATA............................................ 3-1 

3.1 TOTAL CATCH ANALYSIS ................................................................................ 3-1 

3.1.1 Total Catch Analysis Methods....................................................................3-1 

3.1.2 Total Catch Analysis Results......................................................................3-1 

3.1.2.1 Small Trawls ................................................................................3-5 

3.1.2.2 Commercial Trawls....................................................................3-17 

3.1.2.3 Gillnets....................................................................................... 3-30 

3.2 SPECIES GUILD AND META ANALYSIS....................................................... 3-42 

3.2.1 Species Guild and Meta-Analysis Methods.............................................. 3-42 

3.2.1.1 Species Guild and Meta-Analysis Results .................................3-44 

3.3 MULTIVARIATE ANALYSIS............................................................................ 3-47 

3.3.1 Multivariate Analysis Methods.................................................................3-47 

3.3.1.1 Multivariate Analysis Results....................................................3-48

4.0 STATISTICAL ANALYSIS OF BIOACOUSTIC SURVEY DATA........................ 4-1 

4.1 BIOACOUSTIC SURVEY ANALYSIS................................................................ 4-1 

4.1.1 Bioacoustic Survey Analysis Methods ....................................................... 4-1 

4.1.2 Bioacoustic Survey Analysis Results..........................................................4-3

5.0 MANAGED SPECIES................................................................................................... 5-1
Table of Contents 

viii 

TABLE OF CONTENTS (CONTINUED) 

Page 

6.0 DISCUSSION................................................................................................................. 6-1

7.0 CONCLUSIONS AND RECOMMENDATIONS....................................................... 7-1 

8.0 REFERENCES............................................................................................................... 8-1

 

APPENDICES 

A Bottom Imaging and Habitat Characterization of Potential Sand 

Borrow Areas in the Fenwick Shoal Region Offshore Maryland................. A-1 

 B Small Trawls...................................................................................................... B-1 

 C Commercial Trawls .......................................................................................... C-1 

 D Gillnet................................................................................................................. D-1

22\mms\13754-r.doc 
List of Tables 

 ix 

LIST OF TABLES 

Table Page 

2-1 Latitude and longitude locations of four shoals and four reference sites 

sampled of the coast of Maryland and Delaware using trawls, gillnets and 

bioacoustics from November 2002 until September 2004............................................2-6

2-2 Physical and biological micro and macrohabitat features measured at four 

shoals and five uniform-bottom sites off the coast of Maryland and Delaware 

using underwater video images.....................................................................................2-6 

2-3 Beginning and ending dates from all seasonal net surveys conducted at four 

shoals and four reference sites off the coast of Maryland and Delaware from 

November 2002 until September 2004 .........................................................................2-7 

2-4 Total number of bioacoustic transects performed at four shoals and four reference 

sites off the coast of Maryland and Delaware from six seasonal surveys conducted 

from November 2002 to September 2004.....................................................................2-7 

3-1 Species list of fish and mobile benthos and associated guild collected at four 

shoal and four reference sites in the Atlantic Ocean off the coast of Maryland and 

Delaware from November 2002 to September 2004. ...................................................3-3 

3-2 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in small trawls at four shoal and four reference 

sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004 .............................................................................3-9 

3-3 Seasonal mean total species CPUE, number of species, and species diversity 

collected in small trawls at four shoal and four reference sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004...............................................................................................................................3-9 

3-4 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in small trawls at eight sites in the Atlantic Ocean 

off the coast of Maryland and Delaware from November 2002 to September 2004..3-10 

3-5 Seasonal mean total species CPUE, number of species, and species diversity 

collected in small trawls at eight sites in the Atlantic Ocean off the coast of 

Maryland and Delaware from November 2002 to September 2004...........................3-11 

3-6 Combined two-year seasonal mean of total species CPUE, number of species, and 

species diversity collected in commercial trawls at four shoal and four reference 

sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004 ...........................................................................3-22 
List of Tables 

 x 

LIST OF TABLES (Continued) 

Table Page 

3-7 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in commercial trawls at four shoal and four reference sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 

to September 2004. .....................................................................................................3-22 

3-8 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in commercial trawls at eight sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004 ..........................................................................................................3-23 

3-9 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in commercial trawls at eight sites in the Atlantic Ocean off the coast of 

Maryland and Delaware from November 2002 to September 2004...........................3-24 

3-10 Combined two-year seasonal mean of total species CPUE, number of species, and 

species diversity collected in gillnets at four shoal and four reference 

sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004 ...........................................................................3-34 

3-11 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in gillnets at four shoal and four reference sites in the Atlantic Ocean 

off the coast of Maryland and Delaware from November 2002 to September 2004..3-34 

3-12 Combined two-year seasonal mean of total species CPUE, number of species, and 

species diversity collected in gillnets at eight sites in the Atlantic Ocean off the 

coast of Maryland and Delaware from November 2002 to September 2004 .............3-35 

3-13 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in gillnets at eight sites in the Atlantic Ocean off the coast of Maryland 

and Delaware from November 2002 to September 2004............................................3-36 

3-14 Results of analyses of variance for treatment effects on the model, loge = 

treatment + site + season, by gear and species guild ..................................................3-45 

3-15 Standardized mean differences in loge captured at shoals versus reference sites 

from meta-analysis of commercial and small trawl surveys, for each species guild..3-45 

3-16 Average dissimilarity and percent contribution of species to the separation of 

shoal and reference sites, by season, for the small trawl ............................................3-50 

3-17 Average dissimilarity and percent contribution of species to the separation of 

shoal and reference sites, by season, for the commercial trawl..................................3-52 

4-1 Mean biomass and confidence limits for all acoustic transects conducted during 

sampling at four shoals and four reference sites in the Atlantic Ocean off the 

coast of Maryland and Delaware from November 2002 to September 2004 ...............4-6 
List of Tables 

 xi 

LIST OF TABLES (Continued) 

Table Page 

4-2 Mean fish density per 10,000 m3

 and confidence limits and confidence limits 

for all acoustic transects conducted during sampling at four shoals and four 

reference sites in the Atlantic Ocean off the coast of Maryland and Delaware 

from November 2002 to September 2004.....................................................................4-7 

5-1 List of fish and invertebrate species by life-stage for which the study area in the 

Atlantic Ocean off the coast of Maryland and Delaware has been designated as 

Essential Fish Habitat by the National Marine Fisheries Service.................................5-1 

5-2 List of fish species with management plans collected at four shoals and four 

reference sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004. ............................................................................5-4
List of Figures 

 xii 

LIST OF FIGURES 

Figure Page 

1-1 Project organization chart and responsibilities. ............................................................... 1-6 

2-1 Map of four shoals and four reference sites sampled for marine biota off the coast of 

Maryland and Delaware using trawls, gillnets and bioacoustics from November 2002 

until September 2004. ......................................................................................................2-8 

2-2 Locations of five potential reference sites and four shoals with video transect lines 

followed in the September 2002 underwater video survey off the coast of Maryland 

and Delaware ...................................................................................................................2-9 

2-3 Video sled used to characterize benthic habitats ........................................................... 2-10 

2-4 Map of Fenwick Island Shoal with eight transect lines completed in the spring 2004 

bioacoustic survey off the coast of Maryland and Delaware as one part of a fisheries 

study conducted between November 2002 and September 2004 ..................................2-11 

3-1 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in small trawls at four shoal and four reference sites 

in the Atlantic Ocean off the coast of Maryland and Delaware from November 2002 

to September 2004. ........................................................................................................3-13 

3-2 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in commercial trawls at four shoal and four reference sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004................................................................................................................................3-14 

3-3 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in small trawls at eight sites in the Atlantic Ocean 

off the coast of Maryland and Delaware from November 2002 to September 2004.....3-15 

3-4 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in small trawls at eight sites in the Atlantic Ocean off the coast of 

Maryland and Delaware from November 2002 to September 2004..............................3-16 

3-5 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in commercial trawls at four shoal and four reference 

sites in the Atlantic Ocean off the coast of Maryland and Delaware from November 

2002 to September 2004 ................................................................................................3-26 

3-6 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in commercial trawls at four shoal and four reference sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004................................................................................................................................3-27
List of Figures 

 xiii 

LIST OF FIGURES (Continued) 

Figure Page 

3-7 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in commercial trawls at eight sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004 .............................................................................................................3-28

3-8 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in commercial trawls at eight sites in the Atlantic Ocean off the coast of 

Maryland and Delaware from November 2002 to September 2004..............................3-29 

3-9 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in gillnets at four shoal and four reference sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004 .............................................................................................................3-38

3-10 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in gillnets at four shoal and four reference sites in the Atlantic Ocean off the 

coast of Maryland and Delaware from November 2002 to September 2004 ................3-39 

3-11 Combined two-year seasonal mean of total species CPUE, number of species, 

and species diversity collected in gillnets at eight sites in the Atlantic Ocean off 

the coast of Maryland and Delaware from November 2002 to September 2004...........3-40 

3-12 Seasonal mean of total species CPUE, number of species, and species diversity 

collected in gillnets at eight sites in the Atlantic Ocean off the coast of Maryland 

and Delaware from November 2002 to September 2004...............................................3-41 

3-13 Least-squares means for loge at shoals and reference sites from the model loge = 

treatment + site + season, by gear and species guild. ....................................................3-46 

3-14 Cluster analysis of sites based on species composition and abundance for the three 

gears used in this study. Dendrograms show strong separation of sites by season ......3-54 

3-15 MDS ordinations of shoal and reference sites for the small trawl in each of four 

seasons ...........................................................................................................................3-56 

3-16 MDS ordinations of shoal and reference sites for the commercial trawl and in each 

of four seasons ............................................................................................................... 3-57 

3-17 MDS ordinations of shoal and reference sites for gillnets in each of four seasons. ......3-58 

3-18 Simulated distributions of the test statistic R under the null hypothesis of no differences 

between shoals and reference sites ................................................................................3-59 

3-19 MDS ordinations of shoal and reference sites for the small trawl with superimposed 

circles representing mean CPUE of, respectively, Spotted hake (Urophycis regia) 

and Northern searobin (Prionotus carolinus) ................................................................ 3-60
List of Figures 

 xiv 

LIST OF FIGURES (Continued) 

Figure Page 

3-20 MDS ordinations of shoal and reference sites for the commercial trawl with 

superimposed circles representing mean CPUE of, respectively from top to 

bottom, Northern searobin (Prionotus carolinus), Scup (Stenotomus chrysops), 

and Winter skate (Raja ocellata) ................................................................................... 3-61 

4-1 The relationship of individual target strength of acoustic targets to fish length 

for fishes with swim bladders as described by Love (1977) for many species of 

fish at 120 kHz frequency................................................................................................ 4-8 

4-2 Relative biomass of fish detected with a 120 kHz hydroacoustic split beam system 

at Shoal B and its reference site for each of 6 seasonal surveys......................................4-9 

4-3 Fish density of fish detected with a 120 kHz hydroacoustic split beam system at 

Shoal B and its reference site (diagonal striped bars) for each of 6 seasonal surveys...4-10 

4-4 Relative biomass of fish detected with a 120 kHz hydroacoustic split beam system 

at Shoal D and its reference site for each of 6 seasonal surveys....................................4-11 

4-5 Fish density of fish detected with a 120 kHz hydroacoustic split beam system at 

Shoal D and its reference site for each of 6 seasonal surveys .......................................4-12 

4-6 Relative biomass of fish detected with a 120 kHz hydroacoustic split beam system 

at Fenwick Shoal and its reference site for each of 6 seasonal surveys.........................4-13 

4-7 Fish density of fish detected with a 120 kHz hydroacoustic split beam system at 

Fenwick Shoal and its reference site for each of 6 seasonal surveys.............................4-14 

4-8 Relative biomass of fish detected with a 120 kHz hydroacoustic split beam system 

at Weaver Shoal and its reference site for each of 6 seasonal surveys..........................4-15 

4-9 Fish density of fish detected with a 120 kHz hydroacoustic split beam system at 

Weaver Shoal and its reference site for each of 6 seasonal surveys..............................4-16 

4-10 Seasonal size frequency distribution of fish satisfying individual target criteria 

from hydroacoustic transects during spring 03 and spring 04 sampling at Shoal B 

site and its reference area............................................................................................... 4-17 

4-11 Seasonal size frequency distribution of fish satisfying individual target criteria 

from hydroacoustic transects during summer 03 and summer 04 sampling Shoal 

B site and its reference area ...........................................................................................4-18 

4-12 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during fall 02 and fall 03 sampling at Shoal B site and its 

reference area.................................................................................................................4-19 

4-13 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during spring 03and spring 04 sampling at Shoal D site and 

its reference area. ........................................................................................................... 4-20
List of Figures 

 xv 

LIST OF FIGURES (Continued) 

Figure Page 

4-14 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during summer 03and summer 04 sampling at Shoal D site 

and its reference area .....................................................................................................4-21

4-15 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during fall 02 and fall 03 sampling at Shoal D site and its 

reference area.................................................................................................................4-22 

4-16 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during spring 03 and spring 04 sampling at Fenwick Shoal 

site and its reference area............................................................................................... 4-23 

4-17 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during summer 03 and summer 04 sampling at Fenwick 

Shoal site and its reference area.....................................................................................4-24 

4-18 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during fall 02 and fall 03 sampling at Fenwick site and its 

reference area.................................................................................................................4-25 

4-19 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during spring 03 and spring 04 sampling at Weaver Shoal 

site and its reference area............................................................................................... 4-26 

4-20 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during summer 02 and summer03 sampling at Weaver site 

and its reference area .....................................................................................................4-27

4-21 Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects during fall 02 and fall 03 sampling at Weaver site and its 

reference area.................................................................................................................4-28 
List of Figures 

 xvi 
Introduction 

1-1 

1.0 INTRODUCTION 

Coastal and marine tourism is one of the largest industries in the world, and is the largest 

growing industry in America (Miller 1993). In particular, beaches represent the biggest 

attraction for coastal tourists with an estimated 180 million Americans making 2 billion trips to 

the beach annually (Houston 1996). Beaches have an intrinsic value that is appreciated by all 

citizens, yet they also generate economic wealth from year to year for local and national 

governments, households and businesses. For example, in Monroe County Florida, yearly 

visitors spend about $1.12 billion dollars accounting for nearly 50% of all income and 

employment in the county (English et al. 1996). In addition to providing public recreation, 

beaches also function as protection from storm winds and waves, thereby reducing losses of 

infrastructure and private property to coastal communities in extreme weather. Thus, a great deal 

of effort has been spent trying to stabilize and maintain beaches along our coasts. 

Galgano (1998) estimates that between 85 and 90% of the beaches along the East Coast 

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 several management strategies have 

been employed with minimal success (Green 2002). One common and effective management 

strategy has been beach nourishment. This process involves the placement of sand fill, with or 

without supporting structures, along the shoreline to widen a beach. Sand is usually dredged 

from offshore sand deposits or “borrow” sites and pumped or taken directly to a beach by a 

dredge. Beach nourishment is the only management tool that serves a dual purpose of protecting 

coastal lands and preserving beach resources. 

Beach nourishment projects have been conducted since the 1950’s and currently several 

states along the Middle Atlantic Bight (MAB) have either ongoing or anticipated beach 

nourishment projects. To guarantee the sustainability of nourished beaches, several states have 

developed long-term beach maintenance plans that include routine beach nourishment projects. 

For long-term management to be successful, access to beach quality sand is imperative, and 

therefore, as near-shore sand resources are depleted, efforts to identify new long-term sand 

resources are moving farther offshore onto the continental shelf region of the Exclusive 

Economic Zone (EEZ) (3 to 200 nautical miles from shore; see Drucker et al. 2004 for a more 

detailed description). 

Under the federal Outer Continental Shelf Lands Act (P.L. 103-426), all mineral 

resources within the EEZ, including sand, gravel, and shell, falls under the jurisdiction of the 

Minerals Management Service (MMS). To ensure the availability of suitable sand for future 

beach nourishment projects, the MMS in collaboration with several coastal state agencies have 

been conducting detailed geologic investigations of continental shelf mineral resources (Drucker 

et al. 2004; Michel 2004). Investigations off the coast of Maryland and Delaware by the State 

Geological Survey have identified numerous shoal fields as potential sites with suitable sand for 

beach nourishment (Conkwright and Williams 1996; Conkwright et al. 2000). Within these 
Introduction 

1-2 

shoal fields several individual shoals have been designated as potential resources for long-term 

erosion and emergency damage control on local beaches. 

The MMS is obligated to comply with all relevant federal, state and local policies and 

regulations in planning and implementing any sand mining in federal waters under their 

jurisdiction. As stewards of these resources the MMS must ensure any use of sand resources 

does not adversely affect marine biological resources. MMS’s “Environmental Report: Use of 

Federal Offshore Sand Resources for Beach and Coastal Restoration in New Jersey, Maryland, 

Delaware, and Virginia” (MMS 1999) was prepared to assist MMS in meeting those regulatory 

obligations, in particular the requirements of the National Environmental Policy Act (NEPA). In 

addition to meeting NEPA requirements, MMS must also coordinate with the National Marine 

Fisheries Service (NMFS) in order to comply with requirements of the Magnuson-Stevens Act 

with regard to protection of Essential Fish Habitat (EFH). 

A review of the Environmental Report suggests that while extensive geological 

investigations have been performed to assess the quantity and suitability of the shoal sands as 

beach nourishment material (e.g., Conkwright and Gast 1994), the ecological value of the shoals 

and their importance to the marine biota have been subject to only limited study. In particular, 

the value of individual shoals as EFH has not been specifically addressed, and little information 

is available relative to the use of specific shoal areas by fish and various mobile species. 

Unlike tropical and Pacific marine habitats adjacent to the continental United States, the 

inner continental shelf of the MAB is relatively flat and devoid of hard natural structures, such as 

reefs (Stiemle and Zetlin 2000). Most of the shelf is composed of soft sediments, mostly sands, 

but grading to silt-clay in deeper areas. Sand shoals are considered the dominant structure 

providing vertical relief in an otherwise flat environment (MMS 1999; Stiemle and Zetlin 2000). 

Vertical relief in the bottom profile can be of enhanced value as forage and refuge areas 

for marine fish and benthos species (Kohn 1967; Gilinsky 1984; Diaz et al. 2003). The majority 

of information pertaining to marine communities and vertical relief comes from studies of 

natural and artificial reef fish communities (Brock 1954; Sale 1991; Williams 1990; Rilov and 

Benayahu 2000). Combined with diverse spatial heterogeneity, it has been shown that vertical 

relief directly influences reef fish community structure, fish density, and dictates the presence or 

absence of certain species (Sale et al. 1994). On the west coast, high relief associated with rocky 

reefs increases densities of rockfish and is likely to be one of the most significant environmental 

determinants of distribution, abundance, and species richness (Larson 1980; Richards 1986; 

Williams 1990; Yoklavich et. al. 2000). In their assessment of the Gulf of Mexico ancient reefs, 

“the pinnacles”, Snyder (2001) found a higher abundance of fish species at high relief areas 

when compared to low relief, but noted that habitat complexity was more of a factor influencing 

distribution than was relief alone. 

Most of the work along the east coast regarding marine species communities has focused 

on the mesoscale distribution (Grosslein and Azarovitz 1982; Colvocoresses and Musick 1984, 

Musick et al. 1986; Murawski 1993) and environmental preferences of fishes (Stiemle and Zetlin 
Introduction 

1-3 

2000; Colvocoresses and Musick 1984). Some information exists describing fish assemblage in 

relation to habitat, however, these studies either focus on deep continental shelf communities 

(Auster et al. 1995; Langton et al. 1996; Auster et al. 2001), or are directed toward the 

understanding of species-specific life stages (Bologna 2002; Diaz et al. 2003; Miller et al. 2003). 

Rarely have studies addressed the relevance of specific habitats to communities as a whole 

within the inner continental shelf of the MAB, and little information exists relative to the use of 

offshore shoals by fish or mobile benthos. 

EFH is defined broadly under the Magnuson-Stevens Act as “those waters and substrate 

necessary to fish for spawning, breeding, feeding and growth to maturity.” Current EFH for fish 

species in New England and the Middle Atlantic Bight is derived using abundance data from 

broad fishery-independent trawl surveys (Reid et al. 1999) rather than specific habitat criteria. 

Because most managed species are widely distributed, this approach designates EFH for most 

species at the megahabitat scale (i.e., the continental shelf). While assigning large areas as EFH 

is protective of a species, it does not contribute to the identification and conservation of specific 

habitats, such as shoals, which may be important to a species at the meso or macrohabitat level 

(Slacum et al. 2005). 

Further, provisions of the act require a more holistic approach in managing marine fish 

stocks (Benaka 1999). This requirement necessitates evaluating the effects of potential 

disturbances at the community scale and not just for single species under management. To 

thoroughly evaluate impacts to marine communities, an attempt to identify and describe the biota 

of an area both spatially and temporally must be done. In addition, because there are 

considerable similarities in community structure defined by ecological associations, classifying 

communities into functional groups or guilds can also be used to gain better insight into the 

function of a specific habitat (Joern and Lawlor 1990; Auster 2001; Aguilar-Ibarra 2003). 

Subsequently, the number and abundance of ecologically functional guilds present in particular 

habitat can be used in determining if that habitat is unique as compared to other surrounding 

habitats. If the habitat is determined to be unique, then decisions can be made regarding the 

influence that particular habitat may have on the ecosystem as a whole. Knowledge of such 

information is critical when there is potential for negative impacts; however, under the current 

state of knowledge the ecological value of shoals and their importance to specific marine biota 

cannot be effectively determined. 

1.1 PROJECT OVERVIEW AND OBJECTIVES 

The MMS in collaboration with both the 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. Therefore, the MMS funded the current study to 

design and implement a field program to address the following two objectives: 1) determine what 
Introduction 

1-4 

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

represent important habitat for those species. 

In the ocean, habitats occur at many scales and are generally defined by their geology, 

biology, and physical climate. Four generally accepted categories of marine habitat are mega, 

meso, macro, and microhabitats (Greene 1999). Shoals are a megahabitat features (< kilometer) 

comprised of macro and microhabitats. Mesohabitats are those features having a size of tens of 

meters to a kilometer. Macrohabitats are features such as sand waves, boulders, and bars, and 

microhabitats are fine scale features like biogenic structures, sand, or other seafloor material 

(Greene 1999). 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. In this region of the MAB, shoals and uniformbottom (lacking extreme vertical relief) habitats are the dominant megafeature (MMS 1999). For 

comparison, four uniform-bottom habitats were chosen as the reference sites. Because species 

abundance and diversity have long been recognized as indicators of community structure, with 

higher abundance and diversities indicating more complex and stable ecosystems (May 1975), in 

this study, we use those measures as determinants of habitat quality and define a habitat to be 

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

within that habitat. In order to identify comparable reference sites and to quantify species and 

community abundance three specific methods were used. 

Those methods were: 

1. Use remote video technology to identify and characterize reference locations in 

proximity to the shoals that exhibited uniform bathymetry (i.e., non-shoal), but that 

are otherwise nearly identical to the shoals in terms of micro and macrohabitat 

features; 

2. Conduct a multi-year comprehensive fisheries study to compare and contrast the 

abundance, diversities and distribution of fish and mobile benthos communities 

between the shoals and reference habitats; and 

3. Use bioacoustics to map fish relative biomass, densities and distributions at the shoals 

and at reference habitats. 

To accomplish the project objectives, Versar, Inc. compiled a multidisciplinary team of 

experts, including several University scientists as sub-contractors. Figure 1-1 shows the project 

team and responsibilities of each team member. The project organization included oversight of 

all project tasks by Versar, Inc. with specific tasks managed by appropriate experts. The 

qualifications and responsibilities of all primary team members are listed below. 

William Burton - Versar, Inc.: Program Manager/Senior Scientist 

• Over 20 years of experience designing and implementing fisheries and benthic ecological 

monitoring programs and impact assessments 
Introduction 

1-5 

• Authored or co-authored more than 150 reports and peer-reviewed publications 

• Single point of contact with MMS project management staff, and final editor and 

contributing author to final project report and manuscript 

H. Ward Slacum Jr. - Versar, Inc.: Project Manager/Fisheries Ecologist 

• 15 years of professional experience designing, managing, and conducting aquatic surveys 

and biological assessments in the Mid-Atlantic Bight Region 

• Extensive experience defining and evaluating aquatic habitats as they relate to aquatic 

natural resources 

• Project manager responsible for supervision of all staff, including subcontractors, 

directed data analysis and was primary author of the final report 

Bob Diaz - VIMS: Lead Benthic Habitat Characterization/Benthic Ecologist 

• Senior Benthic ecologist with over three decades of research experience 

• Extensive experience conducting remote sensing sediment and benthic community 

characterizations along the east coast using underwater videography 

• Technical lead for habitat characterization, responsible for video sled data acquisition and 

analysis, and reference site selection 

Kyle Hartman - WVU: Lead Bioacoustics Survey/Fisheries Biologist 

• Extensive publication record in the use of bioacoustics in fisheries surveys, with many 

projects having been conducted in support of the U.S. Corps of Engineers 

• Technical lead for the bioacoustics survey, responsible for collecting and analysis of 

bioacoustic survey data 

Roberto Llans\ - Versar, Inc.: Multivariate Statistics/Benthic Ecologist 

• Over 10 years experience in conducting ecological and sediment quality assessments, and 

developing metrics for benthic indices 

• Contributing author for the Multivariate Analysis Section 

Ed Weber - Versar, Inc.: Multivariate Statistics/Senior Statistician 

• Nine years of research experience in fisheries ecology and management, statistical 

analysis, population-dynamics modeling, and technical writing 

• Contributing author for the Multivariate Analysis Section 
Introduction 

1-6 

Figure 1-1. Project organization chart and responsibilities. 

William Burton 

Senior Project Manager 

Versar, Inc. 

•Program Manager 

•Senior Reviewer 

Quality Assurance Officer’s 

Bill Richkus, 

Oceanographer 

Versar, Inc. 

•Senior Reviewer 

Jon Vølstad, 

Principle Statistician 

Versar, Inc. 

•Senior Reviewer 

H. Ward Slacum Jr., 

Fish Ecologist 

Versar, Inc. 

•Project Manger 

•Principle Author 

Bob Diaz, 

Benthic Ecologist 

Virginia Institute of Marine 

Science (VIMS) 

•Technical Lead Benthic 

Habitat Characterization 

Kyle Hartman, 

Fisheries Biologist 

West Virginia University 

(WVU) 

•Bioacoustics Technical Lead 

Roberto Llans\, 

Benthic Ecologist 

Versar, Inc. 

•Contributing Author for 

Multivariate Analysis 

Ed Weber, 

Senior Statistician 

Versar, Inc. 

•Contributing Author for 

Multivariate Analysis 

Jodi Dew, 

Statistician 

Versar, Inc. 

•Contributing Author 
Introduction 

1-7 

1.2 ENVIRONMENTAL SETTING 

1.2.1 Climate 

The weather in the study area is characterized by extreme climate variability. Weather 

conditions in the fall and winter consistently produce strong storms with extreme winds and high 

seas. Summer conditions are much more stable with the prevailing southerly winds rarely 

reaching 20 knots during the day. Prevailing winds in the fall and winter tend to be out of the 

northwest, but occasional nor’easters occur. These storms can last for several days and generate 

high winds, cold rain, and heavy seas (MMS 1999). 

The dominant water mass in the study area is from coastal inputs and adjacent shelf 

waters. Other water masses occurring over the continental shelf are the slope, and the Gulf 

Stream water masses. Water over the shelf originates from the coastal waters of Canada where is 

moves southward down the coast over the shelf. Currents over the shelf generally move in a 

southerly direction, however, patterns can change depending on wind conditions, local tides, and 

influences from other water masses. Shelf water is continually modified from coastal influences 

and air-sea interactions, and because of this, the shelf water mass can experience large 

temperature and salinity fluctuations. Temperatures range from a low of 3.0oC in winter to 

nearly 26oC at its maximum from late summer into fall. Salinities are generally highest around 

the coast in the winter when coastal riverine influence is less, and lower salinities occur in late 

spring to early summer (MMS 1999; Hardaway 2000). 

Waves over the inner continental shelf are primarily derived from air-sea interactions 

generated from far offshore. Although local wind conditions can influence wave action within 

the study area, air-sea interactions created by two semi-permanent pressure systems are what 

influence the dominant wave patterns in the area. Southwesterly winds with average winds of 

three m/sec are generated in mid-summer by the Bermuda High, and in the winter months three 

to five m/sec west to northwesterly winds are generated by the Icelandic Low pressure system 

(MMS 1999). Subsequently, there are strong seasonal fluctuations in wave heights over the 

inner shelf. Waves approach the study area from the northeast to southeast directions, but waves 

from the east and southeast are more common (Hardaway 2000). Average waves in the area 

were recorded with heights 0.8 m and periods of 8.2 seconds. Waves generated by storms can be 

2.7 m in height with a period of 11 seconds on average (MMS 1999). 

 

1.2.2 Biological Resources 

The biological resources that occur in the study area along the inner continental shelf 

region of the MAB are unique. This region of the inner shelf is comprised of a large variety of 

species with varying temporal and spatial patterns. Nowhere else in the Atlantic do such a wide 

variety of cold-temperature, warm-temperature, and estuarine species co-exist. Seasonal changes 

in water temperature are primarily responsible for species composition and distribution, but 

sediment type, water depth, and hydrodynamics are also important (MMS 1999). 
Introduction 

1-8 

Phytoplankton, zooplankton, and ichthyoplankton resources in the study area are very 

abundant. Phytoplankton has been estimated to have the highest productivity along the east 

coast (Sherman et al. 1996). Coccolithophores and silicoflagellates dominate production, but 

species of dinoflagellates and single celled diatoms are also abundant in the study area 

(Raymond 1963). There are approximately 400 taxa of zooplankton species in this area 

including copepods, cheatognaths, barnacles, cladocerans, appendicularia, brachyuran, 

echinoderm, and thaliaceans (Sherman 1996). Zooplankton biomass is at its peak in late summer 

after rising from low abundance in the winter months. Ichthyoplankton diversity and abundance 

is highly seasonal in the study area. However, Grosslein and Azarovitz (1982) noted large 

amounts of fish larvae can be found throughout the year. 

Benthic resources in the study area consist of moderate densities of Arthropoda, 

Annelida, Mollusca, and Echinodermata (Wigley and Theroux 1981). Many of the benthic 

organisms located in the study area have wide ranging distributions within the entire MAB 

region. Benthic community found in the study area are similar to those off New Jersey, but 

biomass and species densities are lower than what is common in northern areas (Wigley and 

Theroux 1981). Common macro invertebrates include lobed moon snail, whelks, sea stars, 

surfclams, and horse shoe crabs (USACE 1998). Recent work done by Cutter and Diaz (2000) in 

the study area reported over 160 taxa benthic organisms from 72 samples. The most abundant 

species in that study were Annelid worms, followed by mollusks and crustaceans. Species 

densities ranged from 90 to 70,000 organisms/m2 and biomass was from 0.03 to 2,000 g wet/m2. 

These results are similar to those reported by Scott and Burton (2005) who surveyed several sites 

inshore from those reported by Cutter and Diaz (2000). 

Nekton resources in the study area consist of fish, sea turtles, marine mammals, and large 

mobile invertebrates (squid). Most of the fish and squid, and all the sea turtles and marine 

mammals are seasonal migrants through the area (Musick et al. 1986). Resident species include 

few fish but several macrobenthos invertebrates are common throughout the year. Over 300 

species of fish are known in the MAB and many of them occur within the study area on a 

seasonal basis (Sherman et al. 1996). Several recent inshore studies conducted in the area by 

Slacum et al. (2005) and Scott and Burton (2005) list over 60 fish, 16 invertebrate, and several 

squid species in the area. The highest diversity was found in the summer and the lowest 

diversities were found in the winter (Scott and Burton 2005). 

Five species of sea turtles occur in the study area, of which the loggerhead and Kemp’s 

ridley are the most abundant. The leatherback, green, and hawksbill turtles also occur, but are 

far less abundant. Most turtles overwinter south of Cape Hatteras and migrate into or through 

the area in early spring or summer. Loggerhead turtles reach peak abundance in the study area 

during the summer (Keinath et al. 1987), and Kemp ridley are at peak abundance during fall 

migrations (Musick 2000). 

Upward of 20 marine mammals, including pinnipeds and cetaceans, may occur in the 

study area on a seasonal basis (Waring et al. 2002). The study area is adjacent to areas on the 

mid-shelf, where marine mammals that prefer fish and squids are known to concentrate (Kenney 
Introduction 

1-9 

and Winn 1986). In the summer, bottlenose dolphin occurs in high concentrations in the study 

area, and the boreal harbor porpoise dominates in winter (Waring et al. 2002). Harbor seals are 

also common in the study are during winter. Several whales are transient seasonally through the 

area. Juvenile humpback whales are known to overwinter in the area. Right whales are common 

in the area during migrations to and from calving grounds in the South Atlantic. Short-finned 

pilot whales are also common in the study area during summer months (Waring et al. 2002). See 

MMS (1999) for a detailed review of specific species occurring in the study area. 

1.2.3 Geology 

This part of the continental shelf is characterized by gentle slopes of 0.1°or less. 

Topographic and subsurface features on the shelf consist of paleoshorelines; shoals; filled 

channels; and retreat paths of estuary mouths (MMS 1999). Toscano et al. 1989 identified the 

stratigraphy of the inner shelf of Maryland and based on seismic records and sedimentological 

analyses, a late Quaternary stratigraphic model was developed. Five distinct stratigraphic units 

were identified and described on the Maryland inner shelf (Kerhrin et al. 1999). These units 

represent late Pleistocene interglacial deposits of transgressive shelf sands. Subsurface sediments 

are characterized by a Tertiary unit with steep internal reflectance and extensive channeling near 

its top. Overlying the Q1 unit, the Q2 unit is a 6-meter thick mud sequence of oxygen-isotope 

stage 5 (128-75 ka) age. Units Q3 and Q4 representing fluvial and leading edge estuarine 

deposits (oxygen-isotope stages 4, 3 and 2) filled numerous paleochannels that were incised into 

units Q2 and Q1. Modern trailing-edge transgressive shelf shoals (Unit Q5) discontinuously cap 

the sequence (Kerhrin et al. 1999). 

Surface sediments off the Maryland and Delaware coasts within the study region are 

mostly terrigenous sand and silt with locally abundant clays. Muddy sands are located close to 

shore and in the troughs between linear shoals. Estuarine deposits consist of channel fill 

sequences with a prevalence of mud and peat with channel fill sand. Paleochannels fills that 

underlie linear shoals contain silty fine sands. Nearshore tidal fills consist of fine sands, dark 

grey mud, and interbedded sand and mud. Detailed geological descriptions of the Maryland 

inner shelf can be found in Toscano et al. (1989), Wells (1994), and MMS (1999). 

1.2.4 Linear Shoals 

The study shoals are part of a network of linear shoal fields, also referred to as ridge and 

swales, which constitute the majority of prominent natural features on the Delmarva inner shelf 

(Wells 1994). Linear shoals are scattered along the continental shelves, and have been observed 

in the central Dutch coast (Van de Meene 1994), along the German coast (Antia 1996), the 

middle Atlantic shelf of South America (Swift et al. 1978; Parker et al. 1982), and the east coast 

of Australia. Linear shoals are just one of several types of sand bodies present on the continental 

shelf of the USA, and the best examples occur in the MAB, northeastern Gulf of Mexico, and 

Sable Island Bank, eastern Canada (Michel et al. 2001). 
Introduction 

1-10 

Since Uchupi’s (1968) description of their occurrence, numerous investigations have 

been conducted along the Atlantic inner continental shelf looking into the origins and 

morphological characteristics of linear sand shoals (e.g., Duane et al. 1972; Swift et al. 1972; 

Swift and Field 1981; Figueiredo et al. 1981; McBride and Moslow 1991), but still their origin is 

in question. Several researchers suggest the shoals were formed in response to nearshore storm 

generated currents and eventually become detached as a result of sea level rise (Duane et al. 

1972; Field 1979; Swift and Field 1981). McBride and Moslow (1991) correlated the shore 

attached and detached shoals with historical and active tidal inlets. Still others suggest that they 

are maintained by the confluence of wave, tide, and oceanic currents (Hayes and Nairn 2004). 

Once formed, shoals become detached from the adjacent shoreface as sea level rises and 

continue to evolve in form and size. As water depth increases, sand ridges increase in height, 

width and area, become more asymmetric, and exhibit lower contrast in grain size between up 

and down-current flanks with respect to the primary coastal flow distribution (e.g., Stubblefield 

and Swift 1976; Swift and Field 1981; Figueiredo et al. 1981; Snedden et al. 1999). Although 

there are numerous theories to what exact mechanisms are behind the formation and maintenance 

of these shoal features (Hayes and Nairn 2004), it is generally accepted that maintenance and 

evolution of shoal features changes from nearshore to offshore. 

Several authors attribute the maintenance and evolution of shoal features by way of the 

dune-forming processes, where erosion from the up-current flank is deposited on the downcurrent flank (Stubblefield and Swift 1976; Rine et al. 1991; Snedden et al. 1999). Subsequent 

enlargement of the shoal in deeper water may be accomplished through the merging of smaller 

shoals and the addition of excavated underlying sands. In deep water, however, the processes of 

dune forming may not be as dramatic and shoals formation may become inactive due the 

armoring of the sediment surface, inhibiting erosion (Goeff et al. 1999). The evolution and 

maintenance of shoal features may be dependent upon the local sediment budget and associated 

sediment transport processes (Byrnes et al. 2004). However, because these processes are 

complex and difficult to study few attempts have been made to quantify the relationship between 

sediment transport and shoal maintenance (Hayes and Nairn 2004). Most of the work regarding 

shoal maintenance in deep water is related to effects of shoal manipulation on local wave 

processes and or borrow pit evolution (Byrnes et al. 1999; Byrnes et al. 2000). 

Recently, Hayes and Nairn (2004) proposed a way of investigating shoal maintenance in 

wave dominated environments. Using a Boussinesq wave model (phase revolving) developed by 

the Danish Hydraulic Institute (Madsen et al. 1991), Hayes and Nairn (2004) evaluated the 

influence of waves on a two of the study shoals offshore of Maryland and Delaware. This model 

simulates irregular multi-directional waves including full and partial reflection, and current 

interactions. To evaluate waves influencing Fenwick shoal, a northeasterly storm wave was 

simulated that represented the dominant storm wave direction within the region. Results of that 

simulation indicated that waves would wrap around Fenwick shoal from the seaward end and 

converge at the crest near the landward side. In addition, this would be the active area of net 

sediment transport. These results indicate a mechanism for extending the shoal in the direction 

of the steep edge of the shoal, a phenomenon documented by other researchers. 
Introduction 

1-11 

Linear shoals are generally found in clusters with long axes that trend obliquely relative 

to the coastline and are oriented into the predominant storm wave direction (McBride and 

Moslow 1991). Along the MAB, linear shoals are located within the inner, mid, and outer 

continental shelf, and are generally similar in morphology and size. Shoals off the coasts of 

Maryland and Delaware range from 3 – 12-m in relief, 0.9 – 2.8-km in width, and are spaced 1.5 

– 11.1-km from one another (Swift and Duane 1981). Vibracore records taken through the crest 

of some of these shoals show a large portion of the sands represent modern transgressive shoal 

sands, with sediment characteristics ranging from homogenous sands to stratified, alternating 

layers of sand, silt and clay (Wells 1994; Conkwright 2000). 
Introduction 

1-12 

 
Field Methods 

2-1 

2.0 FIELD METHODS 

2.1 STUDY AREA 

The study was conducted on the inner continental shelf of the Middle Atlantic Bight 

region off the coast of Maryland and Delaware, known as the Delmarva shelf. The primary 

focus was four sand shoals; Shoal B, D, Fenwick, and Weaver, and reference sites located in the 

same region. The shoal and reference areas were within and adjacent to several shoal fields that 

are located between 16 and 25-km off the coast and encompass approximately 800 square km of 

the inner shelf (Figure 2-1). The approximate latitude and longitude location of each shoal and 

the minimum and maximum sampling depths are presented in Table 2-1. 

The four specific shoals identified as sand resources off the Maryland and Delaware 

coasts are located within 20-km of the shore, between the 10 and 20-m contour. Each of the 

study shoals share similar morphological characteristics associated with linear shoals, but all of 

them possess a unique shape and differ in their relief. The average base depth for all the shoals 

is 18.3-m deep, but Fenwick and Weaver exhibit shallower areas with minimum depths of 3.8 

and 7.3-m compared to 8 and 11-m minimum depths found at shoal B and D, respectively. The 

shoals differ in their grade of relief with Fenwick Island Shoal and Weaver Shoal exhibiting 

slopes with over 30% grades and shoal B and D with less grading (Conkwright and Williams 

1996; Conkwright et al. 2000). 

The reference sites were of similar sizes as the study shoals and as indicated from 

underwater video footage (Nestlerode and Diaz 2003; Appendix A) the reference sites exhibited 

similar habitat characteristics to the shoals, but were generally much deeper than shoals. These 

sites were deeper and of uniform bathymetry and did not exhibit any significant relief like the 

shoals. Average sampling depths with approximate latitude and longitudes of the reference areas 

is presented in Table 2-1. 

2.2 SAMPLING DESIGN 

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 

reference sites. Four pairs of sites were established by pairing each of the four shoals to a 

specific reference site. Reference sites were chosen from video data collected from an under 

water video sled used to map the physical and biological micro and macrohabitat characteristics 

of the shoals and habitats with uniform depths in the proximity of the shoals (Appendix A). 

Based on the habitat characteristics shoals were paired with a specific reference site that 

exhibited similar characteristics (discussed in section 2.2.1 below), but differed only in vertical 

relief. 
Field Methods 

2-2 

2.2.1 Reference Site Selection 

Prior to initiating the video survey, we reviewed several sets of bottom habitat 

information available from other surveys conducted in the study area. This information included 

underwater vide and profile camera imagery (Cutter and Diaz 2000), fisheries data (Musick 

2000; Olney 2000), and bathymetry data (National Geophysical Data Center 2002) from the 

shoals and nearby deep uniform bottom areas. This information was used to refine our search for 

potential reference sites close to the study shoals. From this information we identified five 

potential reference areas to be mapped along with the shoals during the video survey (Figure 2-

2). The potential reference sites were chosen in the same general area as the shoals to alleviate 

any other outside factors such as proximity to shore or separate water masses that could 

influence species distributions and therefore be misinterpreted as a preference for the shoals or 

reference sites. In addition, potential reference sites were chosen that exhibited uniform 

bathymetry (i.e., non-shoal). In the region of the shoals the only areas of uniform bathymetry 

were deeper areas away from the shoals, and because of this the potential reference sites were 

generally located in water depths similar to the depths of the shoal bases (Figure 2-1). 

Using a transect survey design, we conducted a video survey between the 16th and 19th of 

September 2002. The video sled was towed off the stern of a 12-m vessel moving at speed of 1.5 

to 2.8 knots. Approximately 90-km of bottom habitat was covered during the survey (Figure 

2-2). The video sled was equipped with three video cameras mounted in three different 

configurations to provide a broad overview of the bottom, a near bottom horizontal view to see 

fish over the bottom and bed form types, and a direct vertical high-resolution view for sediment 

type and biogenic features (Figure 2-3). All the bottom video footage was recorded on Sony 8-

mm video cassettes and Differential Global Positioning System (DGPS) data was collected 

simultaneously so each video frame could be georeferenced. 

When the survey was complete benthic habitats were classified by analyzing videotapes 

recorded from the horizontal and vertical cameras. Physical and biological micro and 

macrohabitat features were documented from the recorded videotape at 2.5-minute intervals. 

Analysis of the videotape was conducted using a Sony editing deck and high-resolution video 

monitor. Bottom habitats were then classified based on both physical and biological 

characteristics. Physical characteristics included variables for bedforms type and size, and 

sediment grain size. Biological characteristics included variables for shell fragment cover, 

mobile fauna, sedentary fauna, and other biogenic structures (Table 2-1). 

Based on a combination of the physical and biological micro and macrohabitat features 

analyzed from the video footage, four reference sites were chosen, for a total of eight sampling 

sites (Figure 2-1; Nestlerode and Diaz 2003). Each individual shoal was paired with a reference 

site that exhibited similar habitat characteristics, but did not exhibit high relief like the shoals 

(Table A-3). Based on the micro and macrohabitat similarities, reference area two was chosen as 

Weavers shoals reference, reference area three was designated as Fenwick Island Shoals 

reference, reference area four was chosen for shoal D, and reference five was selected for Shoal 

B reference. Reference area one was dropped because it exhibited the least similar habitat 
Field Methods 

2-3 

characteristics between the shoals (Table A-3). Most of the shoals and their reference sites were 

between 4.5 and 6.5-km apart, but the site most similar to Weaver shoal was 19-km away from 

Weaver shoal. The distance between a specific shoal and its reference site does not influence 

this study, because it is only the habitat similarities that were important when choosing the 

reference sites, and in general all the reference sites were within 5-km of a shoal (Figure 2-1). 

For a more thorough description of all the sites and the habitats associated with them see 

Appendix A; Nestlerode and Diaz 2003. 

2.2.2 Fisheries sampling 

2.2.2.1 Net Survey 

The fisheries sampling began in the fall of 2002 and was conducted seasonally for two 

years. To maximize the probability of capturing all species that might use the shoals and 

reference locations during any one season, we reviewed available literature to identify specific 

times when species densities would be at their highest during any one season. Several 

documents including, Musick (2000), Olney (2000), Wirth (2001), and the NMFS (2002) web 

page were synthesized during this review. Information from that review was then used as a 

guide for planning seasonal sampling events throughout the year. 

Fish sampling was conducted using multiple gears with different species and size 

selectivity to ensure that all fish and mobile benthic species could be sampled. Two different 

trawls were used to sample fish during the survey. To capture larger mobile species, a 30.5-m 

“round net” commercial trawl with a with 15-cm stretch mesh body tapering to 5-cm stretch 

mesh codend was used. Large net sampling was conducted from a 16.5-m wooden stern 

commercial trawling vessel, the “Tony and Jan” based in Ocean City, MD. Smaller individuals 

were sampled using a 7.6-m semi-balloon research otter trawl with a with 4-cm stretch mesh 

body fitted with a 3-mm stretch mesh liner in the codend. Small net trawling was conducted 

from Versar’s 7.6-m research vessel, the “R/V Integrity.” Commercial trawling speeds were 

from 3.0 to 3.5 knots, and the small net was trawled at between 1.5 and 2.0 knots. Trawls were 

deployed for a duration of 10-minutes. 

 

Gillnets were also used to sample large mobile fish species. These nets were deployed 

from the commercial fishing vessel “Leanna”, based in Ocean City, MD. Gillnets were 30.5-m 

in length and 3-m deep, consisting of six 30-m panels of varying mesh sizes. By dividing the net 

into two panels of 7-cm stretch mesh, two panels of 9-cm, and two panels of 15-cm for a total of 

six panels of three mesh sizes, each net represented one sample with replication. Nets were set 

on the bottom and were deployed parallel to the current, and were generally fished for an average 

of four hours. 

All organisms were identified to the lowest practical taxon, counted, and a sub-set of 25 

specimens of each species were measured to the nearest mm standard length. During each 

collection, nets were typically deployed in the same general area at each site with replication. 
Field Methods 

2-4 

Attempts were made to conduct all net sampling as close together in time as possible during each 

seasonal sampling event. However, on occasion, unfavorable weather conditions and vessel 

availability restricted consistent sampling and some time gaps were unavoidable within each 

seasonal sampling event (Table 2-2). 

2.2.2.2 Bioacoustics 

In addition to traditional fisheries sampling, we used bioacoustics to compare fish 

densities and relative biomass between the four study shoals and the four reference sites. 

Seasonal bioacoustics surveys were conducted in every season except the two winter seasons, 

when fish densities would be the lowest. Bioacoustics was collected with a Simrad ® EY500, 

120-kHz split-beam system. Prior to each seasonal survey the bioacoustic system was calibrated 

using information from a standard (-40.4 dB) copper sphere and the methods outlined by Brandt 

(1996). Acoustic data were corrected for signal loss and absorption using standard techniques. 

 

Each seasonal survey included a targeted bioacoustic survey aimed at directly comparing 

the shoals to reference sites. Surveys consisted of a series of transects across each of the eight 

study areas, plotted so as to ensure representative coverage of all portions of each area (Table 

2-3). An example of eight bioacoustic transects conducted at Fenwick shoal in the spring 2004 

survey is presented in Figure 2-4. During each seasonal survey the system transducer was 

deployed near the water surface (about 1.0 m depth depending upon sea conditions) in a downlooking orientation. The transducer was housed in a tow body that was towed alongside the 

research vessel during survey tracks at a speed of about 2.5 knots. To insure that cumulative 

densities and biomass values could be standardized by transect length and referenced 

geographically, beginning and ending latitude and longitude coordinates were documented for 

each transect. 

During the fall 2002 survey, all acoustic transects were conducted off of either the large 

fishing vessel during large net trawling, or from the small research vessel provided by Versar, 

Inc. Trawling operations were conducted entirely during daytime so all acoustic transects were 

conducted during daytime as well. Due to a relatively low number of acoustic targets satisfying 

individual target criterion, acoustic data collection during all subsequent seasonal surveys were 

conducted at night. Night acoustic surveys have typically produced higher numbers of individual 

targets due to fish dispersal from schools and the tendency for fish to move off of the bottom at 

night. A total of 45, 64, and 62 transects were completed during fall 2002, spring 2003 and 

summer 2003 surveys. During fall 2003, spring 2004 and summer 2004, 64 transects were 

completed in each seasonal survey (Table 2-4). At each site, transects were replicated from 4-8 

times during fall-02 and 7-8 times for all other seasonal sampling. Depths over which 

bioacoustic transects were performed varied throughout the sampling sites with average depths 

of 7, 10, 6, and 7 meters at Shoal B, D, Fenwick Island, and Weaver respectively and an average 

depth of 12-m at the reference sites. 
Field Methods 

2-5 

Bioacoustic data were processed on a microcomputer using EchoView ® 3.00.81 

software (SonarData, Pty Ltd, Hobart, Australia). A minimum threshold value of –50 dB was 

used in processing of acoustic data to eliminate very small targets from contributing to densities 

that might be finfish species. A threshold value of –50 dB would be similar to the backscatter 

received from a small (e.g. 35-mm) fish. 
Field Methods 

2-6 

Table 2-1. Latitude and longitude locations of four shoals and four reference sites 

sampled of the coast of Maryland and Delaware using trawls, gillnets and 

bioacoustics from November 2002 until September 2004. The minimum 

and maximum sampling depths for net sampling are also presented. 

Location 

(Degrees Decimal Minutes) 

Sampling Depths 

Site (m) 

Latitude Longitude Minimum Maximum 

Fenwick Shoal 38 0 27.21 74 0 56.07 5 9 

Fenwick Reference 38 0 26.23 74 0 52.34 14 19 

Weaver Shoal 38 0 25.38 74 0 55.22 7 10 

Weaver Reference 38 0 14.50 74 0 57.25 12 18 

Shoal B 38 0 17.41 74 0 53.24 8 11 

Shoal B Reference 38 0 20.41 74 0 54.09 13 22 

Shoal D 38 0 15.43 74 0 51.52 10 16 

Shoal D Reference 38 0 19.56 74 0 50.49 12 22 

Table 2-2. Physical and biological micro and macrohabitat features measured at four shoals and 

five uniform-bottom sites off the coast of Maryland and Delaware using underwater 

video images. All variables are classified as present or absent, except burrows and 

tubes, which were counted. 

Physical Characteristics 

Bedform size and shape: 

 Large bedforms, wavelength 30 cm or more 

 Small bedforms, wavelength less than 30 cm 

 None, no bedforms, flat relatively even bottom. 

Bedform shape: 

 Smooth crested, with top of bedform rounded 

 Sharp crested, with top of bedform peaked 

Sediment type: 

 Fine to medium sand 

 Medium to coarse sand 

 Coarse sand to small granules 

Biological Characteristics 

Shell cover: 

 <10% of the bottom covered by shell and shell fragments. 

 >10% of the bottom covered by shell and shell fragments. 

Biogenic structure: 

 No biology obvious 

Burrow opening, tubes, or sessile fauna present 
Field Methods 

2-7 

Table 2-3. Beginning and ending dates from all seasonal net surveys conducted at four shoals 

and four reference sites off the coast of Maryland and Delaware from November 

2002 until September 2004 

Dates Gear 

Season 

Begin End Commercial 

Trawl 

Research 

Trawl Gillnet 

Fall 02 11/19/02 12/19/02 16 16 16 

Winter 03 03/10/03 03/25/03 16 16 16 

Spring 03 05/29/03 06/10/03 16 16 16 

Summer 03 08/10/04 10/03/03 16 16 16 

Fall 03 11/11/03 11/18/03 16 16 16 

Winter 04 02/04/04 02/24/04 16 16 16 

Spring 04 05/25/04 06/02/04 16 16 16 

Summer 04 08/09/04 08/19/04 16 16 16 

Total Samples 128 128 128 

Table 2-4. Total number of bioacoustic transects performed at four shoals and four reference 

sites off the coast of Maryland and Delaware from six seasonal surveys conducted 

from November 2002 to September 2004. 

Season 

Site Fall 

2002 

Spring 

2003 

Summer 

2003 

Fall 

2003 

Spring 

2004 

Summer 

2004 

Fenwick 6 8 8 8 8 8 

Weaver 4 8 8 8 8 8 

Shoal B 8 8 8 8 8 8 

Shoal 

Shoal D 6 8 8 8 8 8 

Fenwick 5 8 7 8 8 8 

Weaver 6 8 7 8 8 8 

Shoal B 5 8 8 8 8 8 Reference 

Shoal D 5 8 8 8 8 8 

Total 45 64 62 64 64 64 
Field Methods 

2-8 

Figure 2-1. Map of four shoals and four reference sites sampled for marine biota off the coast of 

Maryland and Delaware using trawls, gillnets and bioacoustics from November 

2002 until September 2004. 

New Jersey

Delaware

Atlantic 

Ocean

Maryland

VA.

Fenwick 

Shoal

Weaver Reference

Shoal D Reference

Shoal B

Shoal D

Fenwick Reference

Weaver Shoal

Shoal B Reference

Fenwick 

Shoal

Weaver Reference

Shoal D Reference

Shoal B

Shoal D

Fenwick Reference

Weaver Shoal

Shoal B Reference
Field Methods 

2-9 

Figure 2-2. Locations of five potential reference sites and four shoals with video transect lines 

followed in the September 2002 underwater video survey off the coast of Maryland 

and Delaware. All sites are labeled with potential reference sites circled and shoals 

not circled. 

Reference Area 3

Reference Area 1

Reference Area 5

Reference 

Area 4

Reference Area 2

Fenwick Island Shoal

Shoal B

Weaver Shoal

Shoal D

Reference Area 3

Reference Area 1

Reference Area 5

Reference 

Area 4

Reference Area 2

Fenwick Island Shoal

Shoal B

Weaver Shoal

Shoal D
Field Methods 

2-10 

Figure 2-3. Video sled used to characterize benthic habitats. Overview camera is at the top 

right corner of the sled, horizontal camera is in the front center and flanked by two 

electronic video strobes, close-up vertical camera is in the center of the sled, behind 

the horizontal camera. Sled runners are 0.8 m apart. 
Field Methods 

2-11 

Figure 2-4. Map of Fenwick Island Shoal with eight transect lines completed in the spring 2004 

bioacoustic survey off the coast of Maryland and Delaware as one part of a fisheries 

study conducted between November 2002 and September 2004. Depths are in feet. 
Field Methods 

2-12 

 
Statistical Analysis of Net Survey Data 

3-1 

3.0 STATISTICAL ANALYSIS OF NET SURVEY DATA 

3.1 TOTAL CATCH ANALYSIS 

3.1.1 Total Catch Analysis Methods 

All catch data were summarized by season and site. We tested for differences in total 

species relative abundance (CPUE), total species richness, and total species diversity between 

shoals and reference site habitats, individual shoals and reference sites, for all years combined 

and for individual seasons. Since differences in catch efficiencies were present between all 

gears, all tests were gear specific. Catch data were standardized to catch per unit of effort 

(CPUE) before analysis, where units were the number of animals captured per 500 m (1640 ft) 

trawled in small trawls, 1000m (3280 ft) per commercial trawl, and number captured per hour of 

soak time in gillnets. These estimates were transformed to loge (CPUE + 1) before analysis to 

meet the assumption of equal variance among treatments for ANOVA. We conducted ANOVA 

with loge (CPUE +1) as the response variable, site and season as blocks, and treatment (shoal or 

reference) as a factor, using the SAS GLM procedure (SAS Institute 2004). Community 

diversity was tested on the transformed CPUE data and was calculated using the Shannon index. 

The formula for the calculation of the Shannon-Wiener Index is: 

( )( ) i i

s

i

H p 2 p

1

∑ log =

= −

where 

H = index of species diversity 

S = number of species 

pi = proportion of total sample belonging to ith species 

Because three separate gears were used to target specific portions of the species populations 

residing on the shoal and reference site habitat a qualitative description of the catch is given for 

each gear type. 

3.1.2 Total Catch Analysis Results 

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

(n=128), commercial trawls (n=128) and gillnet sets (n=128). In the collections there were a 

total of 57 species of fish including 15 species of sharks, skates, and rays (Table 3-1). In 

addition, there were 17 invertebrate species represented by 7 decapod crustations and 10 other 

invertebrate species. Seasonal gear comparisons between the reference sites revealed few 

significant differences in measured values between individual seasons or combined seasons, and 
Statistical Analysis of Net Survey Data 

3-2 

no overall patterns of higher values at one site or another Between shoal comparisons were 

similar with few significant differences between the shoals seasonally or when all years were 

combined. Like the reference sites, no patterns of higher or lower measured values at a 

particular shoal were evident. 

 

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 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. 

Therefore an overall description of total species abundance, species richness, and species 

diversity by gear is presented below. 

 

The information from the net survey data described here and in Appendices B, C, and D 

presents our study in several different configurations designed to assist the reader in the fullest 

interpretation. Specific configurations are 1) all the shoals and reference site data combined with 

both yearly seasonal samples combined, 2) all the shoals and reference site data combined for 

every season sampled, 3) all sampling sites presented with both yearly seasonal samples 

combined, and 4) all sampling sites presented for every season sampled. We believe the latter 

format is the most germane for this study and therefore the seasonal descriptions by gear is 

presented with an emphasis on all sites with both years of data combined. 

 
Statistical Analysis of Net Survey Data 

3-3 

Table 3-1. Species list of fish and mobile benthos and associated 

guild collected at four shoal and four reference sites in 

the Atlantic Ocean off the coast of Maryland and 

Delaware from November 2002 to September 2004.

Taxonomic Name Common Name 

Benthic Finfish 

Ammodytes americanus American sand lance 

Astroscopus guttatus Northern stargazer 

Centropristis striata Black sea bass 

Cynoscion regalis Weakfish 

Dasyatis centroura Roughtail stingray 

Etropus microstomus Smallmouth flounder 

Gadus morhua Atlantic cod 

Gymnura micrura Smooth butterfly ray 

Hippocampus erectus Lined seahorse 

Leiostomus xanthurus Spot 

Lophius americanus Goosefish 

Menticirrhus saxatilis Northern kingfish 

Micropogonias undulatus Atlantic croaker 

Morone saxatilis Striped bass 

Mustelus canis Smooth dogfish 

Myliobatis freminvillei Bullnose ray 

Ophidion marginatum Striped cusk-eel 

Paralichthys dentatus Summer flounder 

Pleuronectes americanus Winter flounder 

Prionotus carolinus Northern searobin 

Prionotus evolans Striped searobin 

Raja eglanteria Clearnose skate 

Raja erinacea Little skate 

Raja laevis Barndoor skate 

Raja ocellata Winter skate 

Rhinoptera bonasus Cownose ray 

Rhizoprionodon terraenovae Atlantic sharpnose shark 

Scophthalmus aquosus Windowpane 

Sphoeroides maculatus Northern puffer 

Squalus acanthias Spiny dogfish 

Squatina dumeril Atlantic angel shark 

Stenotomus chrysops Scup 

Syngnathus fuscus Northern pipefish 

Synodus foetens Inshore lizardfish 

Urophycis chuss Red hake 

Urophycis regia Spotted hake 
Statistical Analysis of Net Survey Data 

3-4 

Table 3-1. (Continued)

Taxonomic Name Common Name 

Pelagic Finfish 

Alopias vulpinus Thresher shark 

Alosa aestivalis Blueback herring 

Alosa mediocris Hickory shad 

Alosa pseudoharengus Alewife 

Alosa sapidissima American shad 

Anchoa hepsetus Striped anchovy 

Anchoa mitchilli Bay anchovy 

Brevoortia tyrannus Atlantic menhaden 

Caranx crysos Blue runner 

Carcharhinus obscurus Dusky shark 

Carcharhinus plumbeus Sandbar shark 

Clupea harengus harengus Atlantic herring 

Menidia menidia Atlantic silverside 

Merluccius bilinearis Silver hake 

Peprilus alepidotus Harvestfish 

Peprilus triacanthus Butterfish 

Pomatomus saltatrix Bluefish 

Rachycentron canadum Cobia 

Sarda sarda Atlantic bonito 

Scomber scombrus Atlantic mackerel 

Scomberomorus maculatus Spanish mackerel 

Benthic Invertebrate 

Asteroidea Starfishes 

Busycon carica Knobbed whelk 

Busycotypus canaliculatus Channeled whelk 

Callinectes sapidus Blue crab 

Cancer irroratus Atlantic rock crab 

Crangon septemspinosa Sand shrimp 

Echinoidea Heart urchins 

Gastropoda Gastropods 

Libinia emarginata Portly spider crab 

Limulus polyphemus Horseshoe crab 

Nudibranchia Nudibranchs 

Octopus vulgaris Common octopus 

Ovalipes ocellatus Lady crab 

Ovalipes stephensoni Coarsehand lady crab 

Paguridae Right-handed hermit crabs 

Polinices Moon snails 

Pelagic Invertebrate 

Cephalopoda Squids 
Statistical Analysis of Net Survey Data 

3-5 

3.1.2.1 Small Trawls 

Small trawling was conducted at all the sites and in every season throughout the entire 

study. However, because of problems associated with the gear (a double cable instead of a single 

bridal was used which did not effectively sample deep stations) during the first sampling season 

(fall 2002), data from that season and year is excluded from any analysis regarding small trawls. 

Small trawls were used to characterize smaller individual species and the early life stages 

of species present at the shoals and reference sites. On average, total abundance was consistently 

higher at the reference sites when compared to the shoals (Table 3-2 and 3-3; Figures 3-1 and 3-

2). However, on some occasions throughout the study, some of the shoals exhibited higher total 

abundance than their paired reference site (Table 3-4 and 3-5; Figures 3-3 and 3-4). 

A total of 41 different species of fish and invertebrates were collected in the small trawls 

at the shoals and reference sites during the course of the study (Table B-1). Total species 

richness was generally highest at the reference sites during each season (Table 3-2 and 3-3; 

Figure 3-1 and 3-2). Twenty-four fish and 15 invertebrate species were collected at the reference 

sites as opposed to 19 fish and 14 invertebrates collected at the shoals. Among those species, six 

fish and two invertebrate species collected at the reference sites were never collected on the 

shoals, and only two species, the blue crab and inshore lizard fish were found only on the shoals. 

Right-handed hermit crabs and starfish were the most abundant organisms over the twoyear study (Table B-1). These two species were also the most frequently collected species, with 

right-handed hermit crabs present at all stations in every season and starfish present at most of 

the stations in every season (Table B-7). Among the fish species collected, spotted hake was the 

most common, and spotted hake and northern searobin were the most abundant over all the sites 

during the two years of sampling (Table B-7 and B-9). 

Fall

In the fall (2003) collection, catch per unit of effort was mixed between shoal and the 

reference sites (Table 3-4; Figure 3-3). Both Fenwick Island (33±10.49 SE) and Weaver 

(98.38±18.5 SE) shoal were higher in total abundance when compared to their paired reference 

sites (16.7±0.82 SE and 69.81±10.25 SE, respectively). Conversely, Shoal D and B exhibited 

lower abundances than their reference sites, with Shoal B having significantly less abundance 

than its reference site (Table 3-4). 

Total species richness was similar between paired sites in the fall, with Shoal B 

Reference exhibiting the highest average species number (Table 3-4). A total of 15 fish and 9 

invertebrates were collected at all sites in the fall, with 14 fish species and 8 invertebrates at the 

reference sites compared to 11 fish and 7 invertebrates at the shoals (Table B-1). The mean 

Sannon-Weaver index of diversity was similar between all sites with the highest diversity at 

Shoal B Reference (2.73±0.12 SE) and the lowest at Shoal D Reference (1.43±0.22 SE). 
Statistical Analysis of Net Survey Data 

3-6 

Starfish were collected at all but one of the sites (Table B-7), and accounted for 36% of 

the entire combined catch. Right-handed hermit crab was the second most abundant species 

comprising 19% of the catch and was present at every site (Table B-7). Starfish was also the 

most abundant invertebrate collected on the shoals, but was not as abundant as squid at the 

reference sites (Figure B-1). Spotted hake and smallmouth flounder were the most frequently 

occurring fish species, collected at nearly every site (Table B-7). Atlantic croaker was the most 

abundant fish species overall with higher abundance at the reference sites than at the shoals 

(Table B-3). The second most abundant fish overall and the most abundant at the shoals was the 

spotted hake (Table B-2). Of the 22 total species collected at the reference sites in the fall, six of 

them were not present on the shoals and only two species, the little skate and moon snails, were 

found on shoals and not in a reference site. 

Winter

Overall, total abundance on shoals and reference sites in the winter sampling was lower 

than that of any other season (Table 3-4; Figure 3-3). Total abundance was higher at the 

reference sites for all paired sites but Weaver Shoal, and the difference between Weaver and its 

reference was minimal (Table 3-4; Figure 3-3). No significant differences in abundance were 

detected between shoals and their reference sites (Table 3-4). The reference site for Shoal D 

exhibited the highest abundance (33.1±18.37 SE) in winter and Shoal B had the lowest 

(11.27±4.98 SE). 

 Total species richness was also lowest compared to all other seasons (Table 3-4), and 

invertebrates were more common than fish accounting for 83% of the entire collection (Table B8). A total of 8 fish and 10 invertebrate species were collected overall. Shoals always had less 

species than the paired reference sites (Table 3-4). A total of 6 fish and 6 invertebrates were 

collected at the shoals, and 8 fish and 9 invertebrates were collected at the reference sites. Four 

invertebrate and two fish species were found only on the reference sites and only the portly 

spider crab was collected on the shoals. In addition, species diversity was also lower on the 

shoals than on the reference sites (Table 3-4). 

 

Sand shrimp and right-handed hermit crabs were the most abundant species and most 

prevalent species collected throughout the study sites in the winter (Table B-7; Figure B-1). 

Sand shrimp occurred at every site and accounted for 36% of the catch at shoals and 28% of the 

catch at the reference sites. Although right-handed hermit crabs had higher abundance overall, 

the second most abundant invertebrate species collected at the reference sites was moon snails 

(17%). Gastropods (21%) were the second most abundant invertebrate collected on shoals. 

Very few fish were collected during winter sampling (Table B-8 and B-9). In general, 

fish were not as abundant as invertebrate species accounting for only 17% of the entire winter 

collection. Spotted hake was the most abundant fish at both shoals and reference sites, 

representing over half of all fish collected (Table B-3). The next most common fish was the little 

skate, which made up 13% of the fish species and was evenly distributed across shoals and 

reference sites (Table B-7). 
Statistical Analysis of Net Survey Data 

3-7 

Spring 

 

In the spring, total abundance was mixed between shoal and reference sites (Table 3-4; 

Figure 3-3). Both Shoal D (35.31±20.33 SE) and Weaver Shoal (46.12±26.05 SE) were higher 

in total abundance when compared to their paired reference sites (29.59±20.89 SE and 

19.09±8.42 SE, respectively). Conversely, Shoal B Reference had significantly higher total 

abundance than did Shoal B (Table 3-4), and Fenwick reference (38.29±14.76 SE) had slightly 

higher abundance than Fenwick Shoal (33.75±22.21 SE). 

The total number of species collected throughout the sites in the spring was the third 

highest for all the seasons (Table 3-4; Figure 3-1), with a total of 14 fish and 12 invertebrates 

collected. Overall, invertebrates were more abundant than fish accounting for 77% of the entire 

collection. Total species richness varied between shoals and reference sites, with the sites that 

exhibited high total abundance also showing higher total species richness (Table 3-4). For 

example, abundance was higher at Shoal B Reference site with an average of 9 species compared 

to Shoal B which averaged only 4 species and had lower total abundance. A total of 11 fish and 

9 invertebrates were collected on shoals compared to 12 fish and 11 invertebrates on the 

reference sites. Because sites with higher abundance also exhibited higher total species richness, 

diversity values followed the same trend, with the highest species diversity at Shoal B Reference 

(2.38±0.54 SE) and the lowest at Fenwick Shoal (1.32±0.55 SE). Of the 26 species collected at 

the reference sites in the spring, five of them were not present at the shoals and only two species, 

the clearnose skate and horseshoe crab, were found on shoals and not in a reference site. 

 

Squids and right-handed hermit crabs were the most abundant and most prevalent species 

throughout the spring collections (Table B-7; Figure B-2). Both squids and right-handed hermit 

crabs were also the most abundant invertebrates on the shoals (Table B-1). These two species 

accounted for more than half of all species collected at the shoals. Squid accounted for 35% and 

right-handed hermit crabs accounted for 26% of all invertebrates at shoals. Squid and starfish 

were the most abundant invertebrates at the reference sites accounting for over 30% of all 

collected species and 53% of all invertebrates collected at reference sites combined. 

Fish species accounted for only 12% of the total catch on the shoals and 36% of the catch 

at the reference sites. Spotted hake was the most abundant fish species overall (Table B-8), but 

was more common at the reference sites than on the shoals, accounting for 48% of all fish 

collected at the reference sites. Northern sea robin was the second most abundant fish overall, 

exhibiting higher abundance at the reference sites than at the shoals (Table B-8 and B-9). 

Northern sea robin accounted for 24% of all fish species collected at the reference sites and for 

15% of fish at the shoals. 

Summer

Total abundance in the summer sampling at shoals and reference sites was slightly higher 

than the fall season (Table 3-4; Figure 3-3). Overall no significant differences in abundance 

were detected between shoals or reference sites, but total abundance was generally higher at the 
Statistical Analysis of Net Survey Data 

3-8 

reference sites than at shoals for all paired sites (Table 3-4). Shoal B Reference site exhibited the 

highest abundance (126.26±75.81 SE) in summer and Shoal B had the lowest (23.89±3.27 SE). 

Even though the total number of species collected throughout all the sites was higher than 

any other season, the average total species richness at individual sites was slightly lower than the 

fall sampling (Table 3-4; Figure 3-3). A total of 19 fish and 12 invertebrate species were 

collected throughout the sites, with invertebrates being more abundant than fish (Table B-1). 

The total number of invertebrate species were similar between references (n=9) and shoal (n=10) 

collections, and more fish species were collected at the reference sites than at the shoals, with 19 

species at the reference sites compared to only 9 species collected at the shoals. Species 

diversity was found to be significantly different between Fenwick Shoal reference (2.19±0.19 

SE) and Fenwick Island Shoal (0.75±0.26), but all other paired sites exhibited similar diversities 

(Table 3-4). Shoal B was found to have the highest diversity in the summer, and Fenwick Shoal 

had the lowest (Table 3-4; Figure 3-3). Of the 31 species collected in the summer, 12 occurred 

only at reference sites and 5 species were found only at the shoals. 

Right-handed hermit crabs and squid were the most abundant species and most prevalent 

species collected throughout the study sites in the summer (Table B-7; Figure B-2). Righthanded hermit crabs were found in greater abundance at the shoals (52%) compared to reference 

sites (8%). Squid was more abundant at the reference sites accounting for 41% of the total catch 

at reference sites and 66% of the total invertebrates collected. 

In the summer collections, fish accounted for 28% of the entire catch over all the sites 

(Table B-2). Even though it was not present at any of the shoal sites, overall bay anchovy was 

the most abundant fish species collected, accounting for 27% of the fish collected and 41% of all 

the fish collected at the reference sites. The second most abundant fish was northern sea robin 

(Table B-8 and B-9). This species was collected at every site, but was more abundant at the 

reference sites than at the shoals (Table B-7). Conversely, scup was also collected at every site, 

but was more abundant at shoals than at the reference sites. 

 
Statistical Analysis of Net Survey Data 

3-9 

Table 3-2. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in small trawls at four shoal and four 

reference sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004. Significant differences between shoal and 

reference sites from ANOVA tests are highlighted. 

Mean Mean Mean Season Site 

Total CPUE Number of Spp Shannon 

Ref 85.32 +/- 23.2 9.13 +/- 1.38 2.07 +/- 0.28 Fall 03 

Shoal 40.69 +/- 13.61 7.75 +/- 0.75 2.2 +/- 0.17 

Ref 27.37 +/- 5.8 5.31 +/- 0.44 1.88 +/- 0.11 Winter 

Shoal 14.98 +/- 2.96 4 +/- 0.45 1.6 +/- 0.16 

Ref 30.38 +/- 6.45 6.63 +/- 0.96 1.83 +/- 0.21 Spring Shoal 31.76 +/- 9.58 5.75 +/- 1.04 1.61 +/- 0.25 

Ref 96.76 +/- 26.41 7.94 +/- 0.95 1.86 +/- 0.23 Summer 

Shoal 43.2 +/- 11.49 6.25 +/- 0.79 1.59 +/- 0.18 

* Highlighted denotes significant difference (alpha = 0.05) 

Table 3-3. Seasonal mean (and SE) total species CPUE, number of species, and species 

diversity collected in small trawls at four shoal and four reference sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. Significant differences between shoal and reference sites from 

ANOVA tests are highlighted. 

Season Site Mean 

Total CPUE 

Mean 

Number of Spp 

Mean 

Shannon 

Ref 31.13 +/- 7.2 6.25 +/- 0.65 2.17 +/- 0.08 Winter 03 

Shoal 12.37 +/- 4.75 4.13 +/- 0.85 1.6 +/- 0.3 

Ref 15.57 +/- 2.75 4.63 +/- 0.96 1.47 +/- 0.24 Spring 03 Shoal 5.26 +/- 2.25 2.63 +/- 0.92 0.92 +/- 0.32 

Ref 56.79 +/- 23.3 7.5 +/- 1 2.01 +/- 0.19 Summer 03 

Shoal 14.77 +/- 4.04 4.13 +/- 0.91 1.36 +/- 0.27 

Ref 85.32 +/- 23.2 9.13 +/- 1.38 2.07 +/- 0.28 Fall 03 

Shoal 40.69 +/- 13.61 7.75 +/- 0.75 2.2 +/- 0.17 

Ref 23.61 +/- 9.4 4.38 +/- 0.38 1.59 +/- 0.14 Winter 04 

Shoal 17.59 +/- 3.61 3.88 +/- 0.35 1.6 +/- 0.15 

Ref 45.18 +/- 10.4 8.63 +/- 1.36 2.2 +/- 0.3 Spring 04 Shoal 58.27 +/- 13.7 8.88 +/- 1.01 2.3 +/- 0.16 

Ref 136.72 +/- 44.6 8.38 +/- 1.67 1.71 +/- 0.44 Summer 04 

Shoal 71.63 +/- 17.86 8.38 +/- 0.75 1.83 +/- 0.21 
Statistical Analysis of Net Survey Data 

3-10 

Table 3-4. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in small trawls at eight sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004. Significant differences between paired sites from ANOVA tests are 

highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Spp 

Mean 

Shannon 

Fenwick Island Shoal 33 +/- 10.49 8 +/- 0 2.47 +/- 0.03 

Fenwick Reference 16.7 +/- 0.82 6.5 +/- 2.5 2.27 +/- 0.48 

Shoal B 9.17 +/- 2.66 4.5 +/- 0.5 2.06 +/- 0.17 

Shoal B Reference 136.51 +/- 61.54 13 +/- 2 2.73 +/- 0.12 

Shoal D 22.19 +/- 0.74 9 +/- 0 2.71 +/- 0.09 

Shoal D Reference 118.25 +/- 50.23 8 +/- 2 1.43 +/- 0.22 

Weaver Shoal 98.39 +/- 18.5 9.5 +/- 0.5 1.54 +/- 0.16 

Fall 03 

Weaver Reference 69.81 +/- 10.25 9 +/- 4 1.86 +/- 1.01 

Fenwick Island Shoal 17.59 +/- 7.46 4.75 +/- 1.11 1.83 +/- 0.28 

Fenwick Reference 28.59 +/- 12.85 5.25 +/- 1.44 1.8 +/- 0.23 

Shoal B 11.27 +/- 4.98 3.75 +/- 0.85 1.61 +/- 0.34 

Shoal B Reference 29.91 +/- 11.16 5.75 +/- 1.11 1.93 +/- 0.16 

Shoal D 12.5 +/- 7.99 3.5 +/- 1.26 1.35 +/- 0.54 

Shoal D Reference 33.1 +/- 18.37 5.25 +/- 0.48 2.05 +/- 0.15 

Weaver Shoal 18.55 +/- 4.23 4 +/- 0.41 1.6 +/- 0.1 

Winter 

Weaver Reference 17.89 +/- 1.56 5 +/- 0.41 1.76 +/- 0.33 

Fenwick Island Shoal 33.75 +/- 22.21 5.5 +/- 2.4 1.32 +/- 0.55 

Fenwick Reference 38.29 +/- 14.76 7.5 +/- 1.76 2.15 +/- 0.38 

Shoal B 11.87 +/- 6.74 4.25 +/- 0.63 1.8 +/- 0.1 

Shoal B Reference 34.54 +/- 6.14 9 +/- 2.04 2.38 +/- 0.54 

Shoal D 35.31 +/- 20.33 6.25 +/- 3.35 1.41 +/- 0.82 

Shoal D Reference 29.59 +/- 20.89 4.75 +/- 1.8 1.39 +/- 0.27 

Weaver Shoal 46.12 +/- 26.05 7 +/- 1.73 1.89 +/- 0.39 

Spring 

Weaver Reference 19.09 +/- 8.42 5.25 +/- 1.97 1.42 +/- 0.35 

Fenwick Island Shoal 42.73 +/- 27.73 4.5 +/- 2.1 0.75 +/- 0.26 

Fenwick Reference 112.67 +/- 38.88 9.5 +/- 1.32 2.19 +/- 0.19 

Shoal B 23.89 +/- 3.27 7 +/- 1.08 2.22 +/- 0.33 

Shoal B Reference 126.26 +/- 75.81 9.25 +/- 2.02 2.17 +/- 0.6 

Shoal D 37.51 +/- 14.57 6.25 +/- 0.85 1.73 +/- 0.25 

Shoal D Reference 81.19 +/- 60.96 7 +/- 1.47 2 +/- 0.34 

Weaver Shoal 68.68 +/- 36.03 7.25 +/- 2.17 1.67 +/- 0.13 

Summer 

Weaver Reference 66.91 +/- 47.11 6 +/- 2.65 1.07 +/- 0.54 
Statistical Analysis of Net Survey Data 

3-11 

Table 3-5. Seasonal mean (and SE) total species CPUE, number of species, and species 

diversity collected in small trawls at eight sites in the Atlantic Ocean off the coast 

of Maryland and Delaware from November 2002 to September 2004. Significant 

differences between paired sites from ANOVA tests are highlighted. 

Season Site Mean 

Total CPUE 

Mean Number of 

Species 

Mean 

Shannon 

Fenwick Island Shoal 22.24 +/- 16.92 5.5 +/- 2.5 1.99 +/- 0.62 

Fenwick Reference 50.78 +/- 1.65 7.5 +/- 1.5 2.19 +/- 0.11 

Shoal B 4.52 +/- 0.68 3 +/- 1 1.46 +/- 0.46 

Shoal B Reference 43.72 +/- 18.95 6.5 +/- 2.5 2.06 +/- 0.35 

Shoal D 5.88 +/- 4.78 4 +/- 3 1.31 +/- 1.31 

Shoal D Reference 12.74 +/- 0.38 5.5 +/- 0.5 2.25 +/- 0.21 

Weaver Shoal 16.84 +/- 10.03 4 +/- 1 1.62 +/- 0.07 

Winter 03 

Weaver Reference 17.29 +/- 3.68 5.5 +/- 0.5 2.18 +/- 0.05 

Fenwick Island Shoal 3.84 +/- 3.84 1.5 +/- 1.5 0.49 +/- 0.49 

Fenwick Reference 13.95 +/- 1.37 4.5 +/- 0.5 1.52 +/- 0.27 

Shoal B 4.86 +/- 1.45 3.5 +/- 0.5 1.67 +/- 0.17 

Shoal B Reference 24.72 +/- 5.6 6.5 +/- 3.5 1.74 +/- 0.96 

Shoal D 0.52 +/- 0.52 0.5 +/- 0.5 0 +/- 0 

Shoal D Reference 8.8 +/- 5.04 3 +/- 1 1.29 +/- 0.29 

Weaver Shoal 11.79 +/- 7.56 5 +/- 3 1.5 +/- 0.78 

Spring 03 

Weaver Reference 14.82 +/- 4.51 4.5 +/- 2.5 1.33 +/- 0.68 

Fenwick Island Shoal 2.16 +/- 2.16 1 +/- 1 0.49 +/- 0.49 

Fenwick Reference 68.13 +/- 7.15 7.5 +/- 0.5 1.92 +/- 0.07 

Shoal B 20.1 +/- 1.73 6 +/- 2 1.92 +/- 0.66 

Shoal B Reference 29.05 +/- 18.76 7.5 +/- 1.5 2.47 +/- 0.18 

Shoal D 28.9 +/- 3.62 5.5 +/- 1.5 1.42 +/- 0.43 

Shoal D Reference 12.45 +/- 7.62 5 +/- 2 1.74 +/- 0.6 

Weaver Shoal 7.91 +/- 1.37 4 +/- 1 1.6 +/- 0.3 

Summer 03 

Weaver Reference 117.53 +/- 90.46 10 +/- 3 1.89 +/- 0.56 

Fenwick Island Shoal 33 +/- 10.49 8 +/- 0 2.47 +/- 0.03 

Fenwick Reference 16.7 +/- 0.82 6.5 +/- 2.5 2.27 +/- 0.48 

Shoal B 9.17 +/- 2.66 4.5 +/- 0.5 2.06 +/- 0.17 

Shoal B Reference 136.51 +/- 61.54 13 +/- 2 2.73 +/- 0.12 

Shoal D 22.19 +/- 0.74 9 +/- 0 2.71 +/- 0.09 

Shoal D Reference 118.25 +/- 50.23 8 +/- 2 1.43 +/- 0.22 

Weaver Shoal 98.39 +/- 18.5 9.5 +/- 0.5 1.54 +/- 0.16 

Fall 03 

Weaver Reference 69.81 +/- 10.25 9 +/- 4 1.86 +/- 1.01 

Fenwick Island Shoal 12.94 +/- 1.98 4 +/- 0 1.68 +/- 0.18 

Fenwick Reference 6.4 +/- 1.87 3 +/- 0 1.4 +/- 0.03 

Shoal B 18.01 +/- 7.57 4.5 +/- 1.5 1.76 +/- 0.65 

Shoal B Reference 16.1 +/- 2.74 5 +/- 0 1.8 +/- 0.07 

Shoal D 19.13 +/- 16.5 3 +/- 0 1.39 +/- 0.19 

Shoal D Reference 53.46 +/- 34.57 5 +/- 1 1.84 +/- 0.09 

Weaver Shoal 20.26 +/- 0.92 4 +/- 0 1.57 +/- 0.23 

Winter 04 

Weaver Reference 18.49 +/- 0.54 4.5 +/- 0.5 1.33 +/- 0.54 
Statistical Analysis of Net Survey Data 

3-12 

Table 3-5. (Continued) 

Season Site Mean 

Total CPUE 

Mean 

Number of Species 

Mean 

Shannon 

Fenwick Island Shoal 63.65 +/- 34.01 9.5 +/- 0.5 2.15 +/- 0.46 

Fenwick Reference 62.63 +/- 10.94 10.5 +/- 0.5 2.77 +/- 0.04 

Shoal B 18.89 +/- 13.13 5 +/- 1 1.93 +/- 0.01 

Shoal B Reference 44.35 +/- 1.51 11.5 +/- 0.5 3.01 +/- 0.2 

Shoal D 70.1 +/- 7.69 12 +/- 1 2.83 +/- 0.16 

Shoal D Reference 50.39 +/- 41.56 6.5 +/- 3.5 1.5 +/- 0.58 

Weaver Shoal 80.44 +/- 40.71 9 +/- 1 2.29 +/- 0.15 

Spring 04 

Weaver Reference 23.36 +/- 19.21 6 +/- 4 1.52 +/- 0.52 

Fenwick Island Shoal 83.29 +/- 36.33 8 +/- 1 1.02 +/- 0.19 

Fenwick Reference 157.2 +/- 71.07 11.5 +/- 1.5 2.46 +/- 0.26 

Shoal B 27.67 +/- 5.71 8 +/- 1 2.52 +/- 0.2 

Shoal B Reference 223.46 +/- 123.42 11 +/- 4 1.86 +/- 1.39 

Shoal D 46.11 +/- 33.37 7 +/- 1 2.05 +/- 0.02 

Shoal D Reference 149.93 +/- 113.08 9 +/- 1 2.26 +/- 0.45 

Weaver Shoal 129.45 +/- 20.01 10.5 +/- 2.5 1.74 +/- 0.04 

Summer 04 

Weaver Reference 16.29 +/- 2.79 2 +/- 1 0.25 +/- 0.25 
Statistical Analysis of Net Survey Data 

 3-13 

Figure 3-1. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in small trawls at four shoal and four 

reference sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004. 

25ft Trawl - Mean Total CPUE

0

20

40

60

80

100

120

140

Fall 03 Winter Spring Summer

Catch Per Unit Effort 

Reference

Shoal

25ft Trawl - Mean Number of Species

0

2

4

6

8

10

12

Fall 03 Winter Spring Summer

Num ber of S pecies .

Reference

Shoal

25ft Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

Fall 03 Winter Spring Summer

Shannon

Reference

Shoal
Statistical Analysis of Net Survey Data 

 3-14 

Figure 3-2. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in commercial trawls at four shoal and four reference sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. 

25 ft Trawl - Mean Total CPUE

0

20

40

60

80

100

120

140

160

180

200

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

C atch p er Un it E ffo rt 

Ref

Shoal

25 ft Trawl - Mean Number of Species

0

2

4

6

8

10

12

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

N u m b er o f S p ecies

Ref

Shoal

25 ft Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Shannon

Ref

Shoal
Statistical Analysis of Net Survey Data 

 3-15 

Figure 3-3. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in small trawls at eight sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004. 

25ft Trawl - Mean Total Catch per Unit Effort

0

50

100

150

200

250

Fall 03 Winter Spring Summer

Catch per Unit Effort 

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference

25ft Trawl - Mean Number of Species

0

2

4

6

8

10

12

14

16

Fall 03 Winter Spring Summer

Num ber of S pecies .

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference

25ft Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

3.5

Fall 03 Winter Spring Summer

Shannon

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference
Statistical Analysis of Net Survey Data 

 3-16 

Figure 3-4. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in small trawls at eight sites in the Atlantic Ocean off the coast 

of Maryland and Delaware from November 2002 to September 2004. 

25 ft Trawl - Mean Total Catch per Unit Effort

0

50

100

150

200

250

300

350

400

Fenwick

Island Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver

Shoal

Weaver

Reference

Catch per Unit Effort 

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

25 ft Trawl - Mean Number of Species

0

2

4

6

8

10

12

14

16

Fenwick

Island Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver

Shoal

Weaver

Reference

Num ber of Species

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

25 ft Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

3.5

Fenwick

Island Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver

Shoal

Weaver

Reference

Shannon

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04
Statistical Analysis of Net Survey Data 

 3-17 

3.1.2.2 Commercial Trawls 

Commercial trawls were used to characterize the community of larger epibenthic and 

pelagic individuals present at the shoals and reference sites. Overall, total abundance from commercial trawl collections was mixed between shoals and reference sites, but mean total species 

richness and species diversity were higher at the reference sites when compared to the shoals 

(Table 3-6 and 3-7; Figure 3-5 and 3-6). When significant differences in abundance, richness, or 

diversity were detected, it generally favored higher measured values at the reference sites; 

however, occasionally the study some of the shoals exhibited higher abundance, richness, and 

diversity when compared to their paired reference site (Tables 3-8 and 3-9; Figure 3-7 and 3-8). 

A total of 56 different species of fish and invertebrates were collected in the commercial 

trawls on shoals and reference sites (Table C-1). Overall total species richness was highest at the 

reference sites during each season (Table 3-6 and 3-7). The total number of species collected in 

the commercial trawls was much higher at the reference sites as opposed to the shoals (Table C1). Forty-one fish and 12 invertebrates were collected at the reference sites and 31 fish and 11 

invertebrates were collected at the shoals. Twelve fish and one invertebrate species collected at 

the reference sites were not collected at the shoals, and only three species, the blue crab, 

harvestfish, and Spanish mackerel were found only on the shoals. 

Scup and winter skate were the most abundant organisms over the two-year study, 

comprising 19% and 13% of the total collection, respectively. Windowpane flounder and winter 

skate were the most prevalent species, collected in every season at nearly every site (Table C-7). 

Among the invertebrate species collected, squid and lady crabs were the most abundant over all 

the sites during the two-years (Table C-1; Figure C-1). In addition, squid were also the most 

commonly collected invertebrate species present throughout the sites in every season, but winter 

(Table C-7). 

Fall

In the fall season, catch per unit of effort was mixed between shoal and the reference sites 

(Table 3-8; Figure 3-6). Both Fenwick Island (437.25±280.08 SE) and Weaver (271.74±68.51 

SE) shoal were higher in abundance when compared to their paired reference sites 

(240.93±43.02 SE and 220.71±10.25 SE respectively). Conversely, Shoal D and B exhibited 

lower abundance than their reference sites and differences between Shoal B and its reference 

were significant (Table 3-8). 

Total species richness and species diversity followed a similar pattern in the fall with 

higher richness and diversities at all reference sites but Shoal D Reference (Table 3-8). Shoal B 

exhibited the lowest total species richness overall, and the differences between Shoal B (9±2.12 

SE) and its paired reference site (16.75±1.89 SE) were significant. Species diversity was highest 

on Weaver Shoal Reference and lowest on Shoal D Reference. Significant differences in species 

diversity were also detected between Weaver Shoal and Weaver Shoal Reference (Table 3-8). 
Statistical Analysis of Net Survey Data 

 3-18 

A total of 24 fish and 13 invertebrate species were collected throughout the sites in the 

fall. Fish were more abundant than invertebrates accounting for 89% of the total catch in the fall 

collections and invertebrates accounted for 11% (Figure C-1). More fish species were found at 

the reference sites than at the shoals, with 23 fish at the reference sites compared to only 14 at 

the shoals. Invertebrate numbers were equal between references and shoal with eleven species of 

invertebrate on shoals and reference sites. Of the 37 species collected in the fall by the 

commercial trawl, 10 fish and 2 invertebrates occurred only at reference sites and only three 

species, the blue crab, moon snails, and Spanish mackerel were found only at the shoals (Table 

C-1). 

Spiny dogfish and winter skate were the most abundant fish species and most common 

fish collected throughout the fall (Table C-7 and C-8; Figure C-1). Both species were collected 

at every site and accounted for over 50% of the total catch combined and 57% of total fish 

abundance in the fall. Spiny dogfish comprised 21% of the total catch on shoals, and 38% of the 

reference sites catch. Winter skate was less abundant than spiny dogfish, but represented 25% of 

the shoal catch and 18% of the reference catches. Striped bass were collected in limited numbers 

in the fall, however that species accounted for 31% of the total shoal catch due to one large 

collection at Fenwick Shoal (1,225 in one tow in fall of 2003). Other fish species collected in the 

fall were little skate, clearnose skate, summer flounder, and windowpane flounder. 

Starfish and lady crabs were the most abundant invertebrate species in the fall collections 

accounting for 7% of the total abundance combined (Table C-7 and C-8; Figure C-1). Starfish 

comprised 56% of the total invertebrate abundance on the shoals and 27% at the reference sites. 

Lady crabs accounted for 25% of invertebrates found on the shoals and 31% of invertebrates at 

the reference sites. Other invertebrate species collected in the fall were squid, horseshoe crab, 

channeled whelk, and Atlantic rock crab. 

Winter

Overall, total abundance in the winter sampling was lower than that of any other season 

(Table 3-6 and 3-8). Total abundance was higher at all reference sites for all paired sites with 

significant differences detected between Fenwick Shoal, shoal D, and their reference sites (Table 

3-8; Figure 3-6). The reference site for Shoal B exhibited the highest abundance (31.86±11.96 

SE) and Weaver Shoal had the lowest (8.33±4.33 SE). 

Similar to total abundance, overall total species richness was also the lowest compared to 

all other seasons (Table 3-6 and 3-8). Total species richness was highest at all the reference sites 

except Shoal D Reference, which had equal numbers of species as Shoal D in the winter. When 

compared to the reference sites species diversity followed the same pattern as total species 

richness with lower diversity on all shoals except Shoal D (Table 3-8). The highest diversity was 

found on Shoal B Reference and the lowest was found on Shoal B. 

A total of 17 fish and 4 invertebrate species were collected throughout the sites in the 

winter sampling (Table C-1). Altogether fish were much more abundant than invertebrates 
Statistical Analysis of Net Survey Data 

 3-19 

accounting for 93% of the total catch in the winter collections (Table C-2; Figure C-1). A total 

of 13 fish species were collected at the reference sites compared to 14 collected at the shoals. 

Invertebrate numbers were similar between references and shoal with only two species present at 

the reference sites and 4 on the shoals. Of the 21 species collected in the winter, 4 fish and 

2 invertebrates occurred only at the shoals and just four fish, the Atlantic menhaden, clearnose 

skate, hickory shad, and spotted hake were found only at reference sites (Table C-1). 

Three fish species, the winter skate, windowpane flounder, and little skate dominated the 

winter collections (Figure C-1). Together these three species accounted for 60% of the entire 

total abundance in the winter. Little skate and windowpane flounder were collected at every site 

and winter skate was collected at every site but Weaver Shoal (Table C-7). Between them, 

winter skate exhibited the highest abundance and was more abundant at the reference sites than 

at the shoals (Table C-2; Figure C-1). Winter skate accounted for 25% of the total catch and 

27% of total fish abundance. The little skate was more abundant at the shoals accounting for 

19% of total catch and 22% of the total fish catch at the shoals. Windowpane was found to be 

equally abundant on shoals and reference sites (Table C-2 and C-8). Other fish species collected 

in the winter were little skate, clearnose skate, summer flounder, and windowpane flounder. 

Invertebrates accounted for only 7% of the entire collection over all the sites in the 

winter. Starfish and horseshoe crabs were the most abundant invertebrate species in the winter 

collections accounting for just 7% of the total species abundance combined (Table C-2; Figure 

C-1). Starfish were collected at every site but Shoal B and accounted for 60% of the total 

invertebrate abundance on the shoals and 44% at the reference sites. Horseshoe crabs were 

collected at every site but Shoal D Reference and Weaver Shoal, and accounted for 22% of 

invertebrates found on the shoals and 56% of invertebrates at the reference sites. Two other 

invertebrates were also collected in winter, moon snails and Atlantic rock crab. These species 

were in very low abundance and were collected only at shoal sites (Table C-1 and C-2). 

Spring

In the spring, total abundances were higher overall compared to any other season with 

catch per unit of effort generally higher on the shoals than at reference sites (Table 3-8; Figure 

3-6). Fenwick Island Shoal (1807.44±1106.40 SE) exhibited the highest abundance for shoals 

and Weaver Shoal Reference (1328.73±719.38 SE) had the highest total abundance for paired 

reference sites. Shoal B and Shoal B Reference had the lowest abundances in the spring. No 

significant differences in abundance were detected between shoals and the paired reference sites 

in the spring (Table 3-8). 

Total species richness and species diversity were much higher in the spring compared to 

winter (Table 3 -6). Total species richness was highest at all the reference sites except Shoal D 

Reference, which had an average total species richness of 9 species compared to Shoal D where 

12 species were collected in the spring (Table 3-8). Significant differences in total species 

richness were detected between Fenwick Island Shoal (8.5±0.29 SE) and Fenwick Island 
Statistical Analysis of Net Survey Data 

 3-20 

Reference (14±1.22 SE). Species diversity was highest at Shoal B Reference (2.49±0.12 SE) and 

the lowest was found on Shoal D Reference (1.04±0.34 SE). 

A total of 23 fish and 8 invertebrate species collected in the spring catch (Table C-1). 

Altogether fish were more abundant than invertebrates accounting for 90% of the total catch in 

the winter collections (Table C-2; Figure C-2). More fish species were collected at the reference 

sites than at the shoals, with 21 species at the reference sites compared to 17 species collected at 

the shoals. Total invertebrate species was also higher at reference sites (8) than at shoals (5). Of 

the 31 species collected in the spring, 6 fish and 2 invertebrates occurred only at reference sites 

and only two fish species, bluefish and Spanish mackerel were found only at the shoals (Table 

C-1). 

Scup and butterfish were the most abundant fishes and the two most common species 

collected in the spring (Table C-7 and C-8; Figure C-2). Altogether these two species accounted 

for over 75% of the total catch in the spring. Both scup and butterfish were collected at every 

site and accounted for 87% of the total fish abundance (Table C-7 and C-8; Figure C-2). Scup 

was more abundant at shoals than at reference sites accounting for over 65% of the total catch 

and 73% of the total fish catch at shoal sites. Conversely, butterfish were more abundant at 

reference sites accounting for 61% of the catch and 68% of the total fish abundance at the 

reference sites. Other fish species collected in the spring were smooth dogfish, little skate, 

northern searobin, and winter skate (Table C-1). 

In the spring, invertebrates were more abundant than in winter, accounted for 10% of the 

entire collection. Squid was the most dominate invertebrate collected and was present at all sites 

in the spring (Table C-7 and C-8; Figure C-2). This species accounted for 9% of the total catch 

and 92% of all invertebrates on shoals and reference sites. Starfish were also collected in the 

spring and were found on both shoals and reference sites (Table C-7 and C-8). Six other 

invertebrate species were collected in the spring; among them were portly spider crab, knobbed 

and channeled whelk, and horseshoe crabs (Table C-1). 

Summer

In the summer, catch per unit of effort was mixed between shoal and the reference sites. 

Both Shoal D (163.83±78.31 SE) and Weaver (808.14±694.09 SE) shoal were higher in total 

abundance when compared to their paired reference sites (128.25±24.40 SE and 169.54±48.25 

SE respectively). Conversely, Fenwick Island Shoal and Shoal B exhibited lower abundances 

than their reference sites (Table C-1). Weaver Shoal had the highest abundance overall and 

Shoal B had the lowest. No significant differences in total abundance were detected between 

shoal and paired reference sites (Table 3-8). 

Total species richness was higher at all reference sites when compared to the shoals 

(Table 3-8). Fenwick Island Shoal reference (12±0.71 SE) exhibited significantly higher 

abundance when compared to Fenwick Island Shoal (6.75±0.75). Species diversity was also 
Statistical Analysis of Net Survey Data 

 3-21 

higher at the reference sites compared to the shoals (Table 3-8). The highest diversity was found 

on Fenwick Island Shoal Reference and the lowest was found on Shoal B. 

The total number of species collected in the summer was second only to the fall 

collections, with a total of 26 fish and 10 invertebrate species collected throughout the sites. 

Like all other seasons in the commercial catch, fish were more abundant than invertebrates 

accounting for 84% of the total catch in the summer collections (Table C-2; Figure C-2). More 

fish species were collected at the reference sites than at the shoals, with 25 species at the 

reference sites compared to only 18 species collected at the shoals. Total numbers of 

invertebrate species at shoals and at the reference sites also differed, with a total of 

9 invertebrates at the reference sites and 7 at the shoals. Of the 36 species collected in the 

summer, 8 fish and 3 invertebrates occurred only at reference sites and only harvest fish and 

portly spider crab were found only at the shoals (Table C-1). 

Scup and northern searobin were the two most abundant fish species collected in the 

summer (Table C-8; Figure C-2). Although present at only four sites, scup still dominated the 

summer collection accounting for 32% of the total catch. Scup was more abundant at shoals than 

at reference sites accounting for over 56% of the total catch and 68% of the total fish catch at 

shoal sites. Conversely northern searobin was more abundant at reference sites accounting for 

36% of the total catch and 42% of the total fish catch at the reference sites. Other fish species 

collected in the summer were clearnose skate, summer flounder, windowpane flounder, and a 

thresher shark (Table C-1). 

In the commercial trawls, invertebrates accounted for 16% of the entire collection over all 

the sites in the summer. Invertebrates were more abundant and more common in the summer 

than any other season (Table C-1 and C-2). Lady crabs and squid were the most abundant 

invertebrate species in the summer collections accounting for 20% of the total species abundance 

combined (Table C-2 and C-3). Lady crabs comprised 65% of the total invertebrate abundance 

on the shoals and 26% at the reference sites (Figure C-3). Squid accounted for 12% of 

invertebrates found on the shoals and 66% of invertebrates at the reference sites. Other 

invertebrate species collected in the fall were starfish, coarse hand lady crabs, horseshoe crab, 

and Atlantic rock crab (Table C-1). 
Statistical Analysis of Net Survey Data 

 3-22 

Table 3-6. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in commercial trawls at four shoal and 

four reference sites in the Atlantic Ocean off the coast of Maryland and Delaware 

from November 2002 to September 2004. Significant differences between shoal 

and reference sites from ANOVA tests are highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Spp 

Mean 

Shannon 

Ref 248.32 +/- 30.36 14.81 +/- 1.07 2.47 +/- 0.16 Fall Shoal 258.28 +/- 72.03 11.44 +/- 0.82 2.04 +/- 0.13 

Ref 25.98 +/- 3.42 5.5 +/- 0.52 1.93 +/- 0.12 Winter Shoal 11.73 +/- 2.29 3.81 +/- 0.47 1.49 +/- 0.2 

Ref 612.08 +/- 202.12 11.38 +/- 0.9 1.75 +/- 0.26 Spring Shoal 735.7 +/- 311.31 10 +/- 0.55 1.9 +/- 0.24 

Ref 253.9 +/- 62.11 9.88 +/- 0.71 1.85 +/- 0.15 Summer Shoal 306.2 +/- 174.49 6.5 +/- 0.52 1.41 +/- 0.13 

* Highlighted denotes significant difference (alpha = 0.05) 

Table 3-7. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in commercial trawls at four shoal and four reference sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. Significant differences between shoal and reference sites from 

ANOVA tests are highlighted. 

Season Site Mean 

Total CPUE 

Mean 

Number of Species 

Mean 

Shannon 

Ref 166.02 +/- 22.57 14.75 +/- 1.86 2.76 +/- 0.23 Fall 02 

Shoal 135.28 +/- 17.64 11 +/- 1.55 2.14 +/- 0.18 

Ref 30.33 +/- 6.1 6.63 +/- 0.8 2.32 +/- 0.08 Winter 03 

Shoal 17.53 +/- 3.15 4.75 +/- 0.45 1.79 +/- 0.13 

Ref 263.27 +/- 75.68 12.38 +/- 1.41 2.07 +/- 0.43 Spring 03 Shoal 110.46 +/- 17.3 11.25 +/- 0.75 2.7 +/- 0.1 

Ref 171.84 +/- 67.75 10.25 +/- 0.88 2.21 +/- 0.22 Summer 03 

Shoal 571.55 +/- 332.12 7.88 +/- 0.44 1.29 +/- 0.21 

Ref 330.61 +/- 38.8 14.88 +/- 1.2 2.18 +/- 0.2 Fall 03 

Shoal 381.28 +/- 132.66 11.88 +/- 0.64 1.93 +/- 0.2 

Ref 21.62 +/- 2.76 4.38 +/- 0.42 1.55 +/- 0.11 Winter 04 

Shoal 5.94 +/- 1.72 2.88 +/- 0.69 1.19 +/- 0.35 

Ref 960.89 +/- 366.87 10.38 +/- 1.08 1.44 +/- 0.26 Spring 04 Shoal 1360.94 +/- 550.78 8.75 +/- 0.53 1.11 +/- 0.24 

Ref 335.96 +/- 100.08 9.5 +/- 1.15 1.49 +/- 0.12 Summer 04 

Shoal 40.86 +/- 8.15 5.13 +/- 0.64 1.53 +/- 0.15 
Statistical Analysis of Net Survey Data 

 3-23 

Table 3-8. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in commercial trawls at eight sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. Significant differences between paired sites from ANOVA tests 

are highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Spp 

Mean 

Shannon 

Fenwick Island Shoal 437.25 +/- 280.08 11.75 +/- 1.38 1.98 +/- 0.42 

Fenwick Reference 240.93 +/- 43.02 15.5 +/- 0.87 2.44 +/- 0.23 

Shoal B 119.16 +/- 39.6 9 +/- 2.12 1.82 +/- 0.21 

Shoal B Reference 308.75 +/- 75.53 16.75 +/- 1.89 2.72 +/- 0.45 

Shoal D 204.96 +/- 30.24 10.5 +/- 0.87 1.84 +/- 0.1 

Shoal D Reference 222.87 +/- 90.3 9.5 +/- 2.06 1.79 +/- 0.1 

Weaver Shoal 271.74 +/- 68.51 14.5 +/- 0.87 2.51 +/- 0.07 

Fall 

Weaver Reference 220.71 +/- 31.91 17.5 +/- 1.04 2.93 +/- 0.14 

Fenwick Island Shoal 10.5 +/- 3.06 4.25 +/- 0.63 1.86 +/- 0.19 

Fenwick Reference 29.99 +/- 6.11 6.25 +/- 1.31 1.94 +/- 0.26 

Shoal B 16.25 +/- 7.94 3.25 +/- 1.31 0.78 +/- 0.45 

Shoal B Reference 31.86 +/- 11.96 6.25 +/- 1.31 2.06 +/- 0.25 

Shoal D 11.85 +/- 1.59 4.75 +/- 0.63 1.98 +/- 0.21 

Shoal D Reference 24.37 +/- 1.44 4.75 +/- 0.25 1.9 +/- 0.11 

Weaver Shoal 8.33 +/- 4.33 3 +/- 1.08 1.35 +/- 0.46 

Winter 

Weaver Reference 17.69 +/- 3.37 4.75 +/- 1.11 1.85 +/- 0.37 

Fenwick Island Shoal 1807.44 +/- 1106.4 8.5 +/- 0.29 1.46 +/- 0.59 

Fenwick Reference 563.94 +/- 166.06 14 +/- 1.22 1.55 +/- 0.08 

Shoal B 138.68 +/- 41.73 9 +/- 0.82 2 +/- 0.42 

Shoal B Reference 113.08 +/- 30.29 10.25 +/- 0.25 2.49 +/- 0.12 

Shoal D 594.3 +/- 338.6 12.25 +/- 1.18 2.01 +/- 0.62 

Shoal D Reference 442.56 +/- 80.67 9.25 +/- 1.25 1.04 +/- 0.34 

Weaver Shoal 402.38 +/- 229 10.25 +/- 1.03 2.14 +/- 0.39 

Spring 

Weaver Reference 1328.73 +/- 719.38 12 +/- 2.94 1.94 +/- 0.9 

Fenwick Island Shoal 152.15 +/- 72.69 6.75 +/- 0.75 1.71 +/- 0.13 

Fenwick Reference 412.44 +/- 196.82 12 +/- 0.71 1.99 +/- 0.38 

Shoal B 100.68 +/- 54.99 5.5 +/- 1.76 1.1 +/- 0.1 

Shoal B Reference 305.36 +/- 136.32 11 +/- 1.68 1.91 +/- 0.44 

Shoal D 163.83 +/- 78.31 6 +/- 0.41 1.21 +/- 0.22 

Shoal D Reference 128.25 +/- 24.4 6.75 +/- 0.48 1.7 +/- 0.19 

Weaver Shoal 808.14 +/- 694.09 7.75 +/- 0.75 1.6 +/- 0.42 

Summer 

Weaver Reference 169.54 +/- 48.25 9.75 +/- 1.11 1.82 +/- 0.28 
Statistical Analysis of Net Survey Data 

 3-24 

Table 3-9. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in commercial trawls at eight sites in the Atlantic Ocean off 

the coast of Maryland and Delaware from November 2002 to September 2004. 

Significant differences between paired sites from ANOVA tests are highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Species Mean Shannon 

Fenwick Island Shoal 169.32 +/- 13.17 14 +/- 1 2.5 +/- 0.02 

Fenwick Reference 188.09 +/- 40.98 16.5 +/- 1.5 2.76 +/- 0.29 

Shoal B 62.35 +/- 5.55 5.5 +/- 1.5 1.56 +/- 0.28 

Shoal B Reference 221.15 +/- 30.74 19.5 +/- 1.5 3.46 +/- 0.09 

Shoal D 153.14 +/- 10.68 9.5 +/- 1.5 1.88 +/- 0.16 

Shoal D Reference 83.67 +/- 14.8 7 +/- 2 1.89 +/- 0.1 

Weaver Shoal 156.3 +/- 34.04 15 +/- 2 2.62 +/- 0.04 

Fall 02 

Weaver Reference 171.18 +/- 33.04 16 +/- 1 2.94 +/- 0.19 

Fenwick Island Shoal 86.46 +/- 12.09 9 +/- 0 2.48 +/- 0.05 

Fenwick Reference 298.82 +/- 42.46 13.5 +/- 2.5 1.64 +/- 0.08 

Shoal B 79.83 +/- 5.08 10 +/- 1 2.64 +/- 0.13 

Shoal B Reference 61.09 +/- 7.94 10 +/- 0 2.66 +/- 0.11 

Shoal D 117.72 +/- 14.68 14 +/- 0 3.08 +/- 0.1 

Shoal D Reference 557.38 +/- 112.58 9 +/- 3 0.48 +/- 0.22 

Weaver Shoal 157.84 +/- 64.67 12 +/- 0 2.61 +/- 0.17 

Spring 03 

Weaver Reference 135.79 +/- 30.27 17 +/- 1 3.49 +/- 0.03 

Fenwick Island Shoal 266.76 +/- 73.16 8 +/- 0 1.9 +/- 0.03 

Fenwick Reference 79.94 +/- 21.8 11 +/- 1 2.63 +/- 0.18 

Shoal B 186.79 +/- 57.55 8.5 +/- 0.5 1.02 +/- 0.13 

Shoal B Reference 358.67 +/- 274.86 13 +/- 0 2.51 +/- 0.49 

Shoal D 255.63 +/- 140.82 6 +/- 0 1.14 +/- 0.53 

Shoal D Reference 109.93 +/- 3.69 7 +/- 1 1.61 +/- 0.44 

Weaver Shoal 1577 +/- 1307.01 9 +/- 0 1.07 +/- 0.67 

Summer 03 

Weaver Reference 138.82 +/- 65.02 10 +/- 1 2.1 +/- 0.53 

Fenwick Island Shoal 14.08 +/- 5.54 4.5 +/- 1.5 1.86 +/- 0.45 

Fenwick Reference 30.94 +/- 14.65 7.5 +/- 2.5 2.34 +/- 0.26 

Shoal B 29.92 +/- 1.7 5.5 +/- 0.5 1.57 +/- 0.09 

Shoal B Reference 46.12 +/- 20.99 8 +/- 2 2.46 +/- 0.05 

Shoal D 10.97 +/- 3.57 4.5 +/- 1.5 1.83 +/- 0.45 

Shoal D Reference 22.47 +/- 1.34 4.5 +/- 0.5 2.08 +/- 0.09 

Weaver Shoal 15.14 +/- 4.15 4.5 +/- 0.5 1.9 +/- 0.07 

Winter 03 

Weaver Reference 21.8 +/- 0.27 6.5 +/- 0.5 2.4 +/- 0.18 

Fenwick Island Shoal 705.18 +/- 571.78 9.5 +/- 0.5 1.46 +/- 0.72 

Fenwick Reference 293.77 +/- 61.97 14.5 +/- 0.5 2.12 +/- 0.2 

Shoal B 175.97 +/- 54.05 12.5 +/- 0.5 2.08 +/- 0.25 

Shoal B Reference 396.36 +/- 133.92 14 +/- 2 1.98 +/- 0.3 

Shoal D 256.78 +/- 0.54 11.5 +/- 0.5 1.8 +/- 0.17 

Shoal D Reference 362.07 +/- 99.79 12 +/- 3 1.7 +/- 0.17 

Weaver Shoal 387.17 +/- 18.71 14 +/- 0 2.39 +/- 0.04 

Fall 03 

Weaver Reference 270.25 +/- 10.56 19 +/- 1 2.92 +/- 0.28 
Statistical Analysis of Net Survey Data 

 3-25 

Table 3-9. (Continued) 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Species Mean Shannon 

Fenwick Island Shoal 3528.43 +/- 1192.02 8 +/- 0 0.44 +/- 0.13 

Fenwick Reference 829.06 +/- 151.89 14.5 +/- 1.5 1.46 +/- 0.13 

Shoal B 197.54 +/- 59.13 8 +/- 1 1.36 +/- 0.45 

Shoal B Reference 165.07 +/- 6.03 10.5 +/- 0.5 2.32 +/- 0.14 

Shoal D 1070.88 +/- 483.12 10.5 +/- 1.5 0.95 +/- 0.26 

Shoal D Reference 327.74 +/- 1.87 9.5 +/- 0.5 1.6 +/- 0.13 

Weaver Shoal 646.92 +/- 436.88 8.5 +/- 0.5 1.67 +/- 0.65 

Spring 04 

Weaver Reference 2521.67 +/- 507.84 7 +/- 1 0.39 +/- 0.01 

Fenwick Island Shoal 37.54 +/- 8.74 5.5 +/- 0.5 1.51 +/- 0.16 

Fenwick Reference 744.95 +/- 104.04 13 +/- 0 1.34 +/- 0.1 

Shoal B 14.58 +/- 1.87 2.5 +/- 0.5 1.17 +/- 0.18 

Shoal B Reference 252.05 +/- 173.99 9 +/- 3 1.3 +/- 0.43 

Shoal D 72.03 +/- 10.24 6 +/- 1 1.29 +/- 0.08 

Shoal D Reference 146.56 +/- 53.73 6.5 +/- 0.5 1.78 +/- 0.11 

Weaver Shoal 39.28 +/- 0.86 6.5 +/- 0.5 2.13 +/- 0.19 

Summer 04 

Weaver Reference 200.26 +/- 88.61 9.5 +/- 2.5 1.53 +/- 0.18 

Fenwick Island Shoal 6.92 +/- 0.03 4 +/- 0 1.86 +/- 0.06 

Fenwick Reference 29.04 +/- 2.72 5 +/- 1 1.54 +/- 0.12 

Shoal B 2.58 +/- 1.36 1 +/- 0 0 +/- 0 

Shoal B Reference 17.59 +/- 3.32 4.5 +/- 0.5 1.65 +/- 0.23 

Shoal D 12.73 +/- 0.97 5 +/- 0 2.12 +/- 0.08 

Shoal D Reference 26.27 +/- 1.87 5 +/- 0 1.72 +/- 0.06 

Weaver Shoal 1.51 +/- 1.51 1.5 +/- 1.5 0.79 +/- 0.79 

Winter 04 

Weaver Reference 13.58 +/- 5.87 3 +/- 1 1.3 +/- 0.44 
Statistical Analysis of Net Survey Data 

 3-26 

Figure 3-5. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in commercial trawls at four shoal and four 

reference sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004. 

Commerical Trawl - Mean Total Catch per Unit Effort

0

200

400

600

800

1000

1200

Fall Winter Spring Summer

Catch per Unit Effort 

Reference

Shoal

Commerical Trawl - Mean Number of Species

0

2

4

6

8

10

12

14

16

18

Fall Winter Spring Summer

Number of Species.

Reference

Shoal

Commerical Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

Fall Winter Spring Summer

Shannon

Reference

Shoal
Statistical Analysis of Net Survey Data 

 3-27 

Figure 3-6. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in commercial trawls at four shoal and four reference sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. 

Commerical Trawl - Mean Total Catch per Unit Effort

0

500

1000

1500

2000

2500

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Catch per Unit E ffort 

Reference

Shoal

Commerical Trawl - Mean Number of Species

0

2

4

6

8

10

12

14

16

18

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Num ber of Species

Reference

Shoal

Commerical Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

3.5

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Shannon

Reference

Shoal
Statistical Analysis of Net Survey Data 

 3-28 

Figure 3-7. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in commercial trawls at eight sites in the 

Atlantic Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. 

Commerical Trawl - Mean Total Catch per Unit Effort

0

500

1000

1500

2000

2500

3000

3500

Fall Winter Spring Summer

Catch per Unit Effort 

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference

Commerical Trawl - Mean Number of Species

0

2

4

6

8

10

12

14

16

18

20

Fall Winter Spring Summer

Num ber of S pecies

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference

Commerical Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

3.5

Fall Winter Spring Summer

Shannon

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference
Statistical Analysis of Net Survey Data 

 3-29 

Figure 3-8. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in commercial trawls at eight sites in the Atlantic Ocean off the 

coast of Maryland and Delaware from November 2002 to September 2004. 

Commerical Trawl - Mean Total Catch per Unit Effort

0

500

1000

1500

2000

2500

Fenwick

Island Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver

Shoal

Weaver

Reference

Catch per Unit E ffort 

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Commerical Trawl - Mean Number of Species

0

5

10

15

20

25

Fenwick Island

Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver Shoal Weaver

Reference

N u m b er o f S p ecies

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Commerical Trawl - Mean Shannon

0

0.5

1

1.5

2

2.5

3

3.5

4

Fenwick Island

Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver Shoal Weaver

Reference

Shannon

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04
Statistical Analysis of Net Survey Data 

 3-30 

3.1.2.3 Gillnets 

Gill nets were used to characterize highly mobile benthic and pelagic species that were 

otherwise not susceptible to capture by the trawling gears. Overall, mean total abundance, mean 

total species richness, and species diversity did not differ greatly between reference sites and 

shoals with no obvious patterns (Table 3-10 and 3-11; Figure 3-9 and 3-10). There were two 

occasions where significant differences in abundance were detected between individual shoals 

and reference sites with split results, and very few significant differences were detected between 

individual shoals or reference sites for total species richness or species diversity (Table 3-12 and 

3-13; Figure 3-11 and 3-12). 

 

A total of 36 different species of fish and invertebrates were collected in the gill nets on 

shoals and reference sites (Table D-1). Overall total species richness was slightly higher at the 

reference sites with a total of 22 fish and 5 invertebrates as opposed to 21 fish and 5 invertebrates 

collected on the shoals. Nine fish and one invertebrate species collected at the reference sites 

were not collected at the shoals, and eight fish and one invertebrate were found only on the 

shoals (Table D-1). 

Spiny and smooth dogfish were the most abundant organisms over the two-year study, 

comprising 40% and 21% of the total collection, respectively. These two species exhibited a 

seasonal transition where spiny dogfish dominated the fall and winter collections followed by 

smooth dogfish making up the bulk of the catch in the spring and summer collections (Table 

D-1; Figure D-1 and D-2). Throughout the study, only three species were present in every 

season, those were bluefish, winter skate, and smooth dogfish. Due to the nature of the sampling 

gear, invertebrate species were collected in low numbers throughout the survey (mostly tangled 

in the nets or attracted by the fish caught in the nets). Among the invertebrate species collected, 

starfish and portly spider crab were the most frequently caught and exhibited the highest 

abundance (Table D-1 and D-2). 

Fall

In the fall, catch per unit of effort was mixed between shoal and the reference sites (Table 

3-12; Figure 3-10). Shoal D Reference (30.28±16.7 SE) and Shoal B (25.04±13.11 SE) 

exhibited the highest total abundance, and Shoal D (4.97±1.99 SE) and Shoal B Reference 

(6.75±1.85 SE) had the lowest. Significant differences were detected between Fenwick Shoal 

and it’s reference with an average number of 8 individuals on the shoal and 16 at the reference 

(Table 3-12). 

Total species richness was similar between shoals and reference (Table 3-12; Figure 

3-10). Weaver Shoal had the highest mean number of species and Shoal B Reference had the 

lowest. Species diversity was also similar between shoals and reference sites (Table 3-12; Figure 

3-10). The highest diversity was found on Weaver Shoal and the lowest was found on Fenwick 

Shoal reference site. 
Statistical Analysis of Net Survey Data 

 3-31 

A total of 9 fish and 2 invertebrate species were collected throughout the sites in the fall 

(Table D-1). Altogether fish were more abundant than invertebrates accounting for 96% of the 

total catch in the fall collections (Table D-1; Figure D-1). More fish species were collected at 

the reference sites than at the shoals, with 9 species at the reference sites compared to 5 at the 

shoals. There were two invertebrate species collected in the fall in low abundance. The Atlantic 

rock crab was collected at Fenwick Island Reference and starfish were collected at Fenwick 

Island Shoal and Shoal B. Of the 11 species collected in the fall, four fish and Atlantic rock crab 

occurred only at reference sites and only starfish were found only at the shoals (Table D-1). 

Spiny dogfish was the most abundant species in the fall and dominated the collection 

accounting for 87% of the total catch (Table D-8; Figure D-1). Bluefish and striped bass were 

also present in limited numbers both accounting for just over 7% of the total abundance in the 

fall (Table D-8). Spiny dogfish was the only species present at every site and accounted for 90% 

of all fish collected at both the shoal and reference sites (Table D-7 and D-8). Striped bass were 

more prevalent on shoals than at the reference sites, and bluefish exhibited similar composition 

throughout all the sites (Table D-7 and D-8). Other fish species collected in the fall were winter 

skate, smooth dogfish, weakfish, and blueback herring. 

Winter

Gillnet net catches in the winter sampling were lower than that of any other season (Table 

3-12; Figure 3-10). Very few individuals in low abundances were collected throughout the sites. 

Just as the fall collection, the total abundance was mixed between shoal and the reference sites in 

the winter (Table 3-12; Figure 3-10). For the majority of the sites the average abundance was 

less than one in the winter due to many collections where no organisms were taken. No 

differences were detected for total abundance (Table 3-12). 

 

Total species richness was similar between sites (Table 3-12). Weaver Shoal Reference 

exhibited the highest number of species and Fenwick Island Shoal and its reference site both had 

the lowest species richness values. As a consequence of low abundance and low species 

richness, species diversities were also lower in the winter compared to all other seasons (Table 

3-12). 

A total of 7 fish and 2 invertebrate species were collected throughout the sites in the 

winter (Table D-1). Greater numbers of fish species were collected at the reference sites than at 

the shoals, with 7 species at the reference sites compared to only 2 at the shoals. Two different 

species of invertebrate were collected in low numbers during the winter, portly spider crab and 

Atlantic rock crab. Of the 9 species collected in the winter, five fish and the portly spider crab 

occurred only at the reference (Table D-1). 

Spiny dogfish was the most abundant species in the winter and dominated the collection 

accounting for 74% of the entire collection (Table D-8; Figure D-1). Spiny dogfish was again 

the only species present at every site and accounted for 95% of all fish collected at the shoals and 

64% of the fish caught at the reference sites. Smooth dogfish were also collected in limited 
Statistical Analysis of Net Survey Data 

 3-32 

abundance at the reference sites accounting for 8% of fish in the total catch and for 16% of the 

fish catch at the reference sites (Table D-8; Figure D-1). Other fish species collected in the 

winter were alewife, striped searobin, and windowpane flounder. 

Spring

In the spring, catch per unit of effort was higher on the shoals than at the reference sites 

(Table 3-12; Figure 3-10). Weaver Shoal (7.97±1.46 SE) and Fenwick Island Shoal (6.66±0.91 

SE) exhibited the highest total abundance in the spring. Shoal B Reference (1.17± SE) had the 

lowest abundance and was significantly lower than its paired reference, which exhibited a mean 

abundance of 4 individuals (Table 3-12). 

Total species richness was also greater at the shoals than at the reference sites in the 

spring (Table 3-12; Figure 3-10). Weaver and Fenwick Island Shoal had the highest mean total 

species and Shoal B Reference had the lowest. Species diversity was higher at all shoal sites 

except Weaver Shoal which had slightly lower diversity that its reference site. Fenwick Island 

Shoal exhibited the highest diversity and Shoal B Reference had the lowest (Table 3-12). 

A total of 15 fish and 2 invertebrate species were collected throughout the sites in the 

spring. Altogether fish were more abundant than invertebrates accounting for 96% of the total 

catch in the spring collections. More fish species were collected at the shoals sites than at 

reference sites, with 12 species of fish collected at the shoals compared to only 7 species at the 

reference sites. Total numbers of invertebrate species at the shoals and reference sites were 

similar with the moon snail and portly spider crab collected at the reference sites and only the 

portly spider crab collected at the shoals. Of the 17 species collected in the spring, 8 fish 

occurred only at shoal sites and three fish and one invertebrate were found only at the reference 

sites. 

Smooth dogfish was the most abundant species in the spring and dominated the collection 

accounting for 59% of the total catch (Table D-7 and D-8; Figure D-2). Atlantic menhaden and 

striped sea robin were also abundant in the spring, accounting for 27% of total abundance 

combined (Table D-1; Figure D-2). Smooth dogfish was the only species present at every site 

and accounted for 57% of all fish abundance on shoals and 61% of the abundance at reference 

sites (Table D-7). Both Atlantic menhaden and striped sea robin exhibited similar abundance on 

shoals and reference sites (Table D-8; Figure D-2). Several other fish species were collected in 

the spring; among them were winter skate, American shad, and three sharks species, the dusky, 

sandbar, and thresher shark. 

Summer

In the summer, catch per unit of effort was generally higher at the reference sites than at 

the shoals sites (Table 3-12; Figure 3-10). Weaver Shoal (5.1±2.01 SE) was the only shoal with 

higher total abundance compared to its reference site (2.18±1.1 SE). Shoal B (0.99± 0.43 SE) 
Statistical Analysis of Net Survey Data 

 3-33 

had the lowest average total abundance and Fenwick Island Shoal reference had the highest 

(22.46±12.44 SE). 

Total species richness followed the same pattern of abundance with higher species 

numbers at every reference site except Weaver Shoal Reference where it was slightly lower than 

that of Weaver Shoal (Table 3-12; Figure 3-10). Fenwick Island Shoal reference had the highest 

mean total species and Shoal B and D had the lowest. Species diversity was mixed between 

shoals and references, with Weaver Shoal and Fenwick Island Reference exhibiting the highest 

diversity, and Shoal D and its reference exhibiting the lowest (Table 3-12; Figure 3-10). 

A total of 17 fish and 3 invertebrate species were collected throughout the sites in the 

summer (Table D-1). Altogether fish were more abundant than invertebrates accounting for 92% 

of the total catch in the summer collections. More fish species were collected at the reference 

sites than at shoals, with 14 species of fish collected at the reference sites compared to 10 species 

at the shoals. Total numbers of invertebrate species at the shoals and reference sites were similar 

with four at the shoals and three at reference sites. Of the 21 species collected in the spring, 

7 fish occurred only at reference sites and three fish and one invertebrate were found only at the 

shoals (Table D-1). 

Similar to the commercial trawl collections, summer gill net collections generally had 

more species in greater abundance, therefore more species contributed to total abundance. 

Smooth dogfish was collected at all the sites and was the most abundant species in the summer 

accounting for 21% of the entire collection (Table D-7; Figure D-2). Two species of sharks, the 

Atlantic sharpnose and dusky shark were abundant in the summer and accounted for 18% of total 

abundance. Atlantic menhaden was not collected on the shoals, but accounted for 15% of the 

total abundance and 31% of total fish abundance at the reference sites. Other fish species 

collected in the summer were Atlantic croaker, butterfish, northern searobin, and striped 

searobin. 

Invertebrates were the most abundant in the summer than any other season in gill nets. 

Starfish accounted for 6% of the total abundance and 69% of the total invertebrate abundance. 

Portly spider crabs were collected at more sites than starfish and accounted for 17% of the total 

invertebrate abundance in the summer (Table D-7 and D-8). The Atlantic rock crab, lady crab, 

moon snails and coarsehand lady crab were the other invertebrates collected in summer. 
Statistical Analysis of Net Survey Data 

 3-34 

Table 3-10. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in gillnets at four shoal and four reference 

sites in the Atlantic Ocean off the coast of Maryland and Delaware from 

November 2002 to September 2004. Significant differences between shoal and 

reference sites from ANOVA tests are highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Spp 

Mean 

Shannon 

Ref 15.57 +/- 4.56 1.94 +/- 0.17 0.48 +/- 0.1 Fall Shoal 13.18 +/- 3.68 2.13 +/- 0.27 0.57 +/- 0.12 

Ref 0.38 +/- 0.12 0.94 +/- 0.27 0.2 +/- 0.11 Winter Shoal 0.46 +/- 0.18 0.69 +/- 0.18 0.11 +/- 0.07 

Ref 2.49 +/- 0.55 2.13 +/- 0.38 0.71 +/- 0.19 Spring Shoal 5.22 +/- 0.77 2.88 +/- 0.3 0.97 +/- 0.13 

Ref 8.41 +/- 3.69 3.5 +/- 0.87 1.01 +/- 0.23 Summer Shoal 2.57 +/- 0.67 2.5 +/- 0.32 1.04 +/- 0.18 

* Highlighted denotes significant difference (alpha = 0.05) 

Table 3-11. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in gillnets at four shoal and four reference sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004. Significant differences between shoal and reference sites from ANOVA 

tests are highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Species 

Mean 

Shannon 

Ref 5.97 +/- 1.94 1.75 +/- 0.16 0.46 +/- 0.14 Fall 02 

Shoal 6.08 +/- 1.9 1.75 +/- 0.37 0.56 +/- 0.19 

Ref 0.24 +/- 0.16 1 +/- 0.46 0.16 +/- 0.16 Winter 03 

Shoal 0.02 +/- 0.02 0.25 +/- 0.16 0 +/- 0 

Ref 2.94 +/- 0.76 2.38 +/- 0.5 0.83 +/- 0.23 Spring 03 Shoal 6.11 +/- 0.95 3.13 +/- 0.23 1.05 +/- 0.12 

Ref 16.31 +/- 6.38 5.88 +/- 1.23 1.69 +/- 0.27 Summer 03 

Shoal 4.15 +/- 1.05 2.88 +/- 0.3 1.22 +/- 0.14 

Ref 25.17 +/- 7.68 2.13 +/- 0.3 0.5 +/- 0.15 Fall 03 

Shoal 20.28 +/- 6.33 2.5 +/- 0.38 0.58 +/- 0.16 

Ref 0.52 +/- 0.17 0.88 +/- 0.3 0.24 +/- 0.16 Winter 04 

Shoal 0.89 +/- 0.28 1.13 +/- 0.23 0.22 +/- 0.14 

Ref 2.04 +/- 0.81 1.88 +/- 0.58 0.59 +/- 0.31 Spring 04 Shoal 4.33 +/- 1.2 2.63 +/- 0.56 0.89 +/- 0.24 

Ref 0.52 +/- 0.16 1.13 +/- 0.3 0.33 +/- 0.16 Summer 04 

Shoal 0.99 +/- 0.35 2.13 +/- 0.55 0.86 +/- 0.33 
Statistical Analysis of Net Survey Data 

 3-35 

Table 3-12. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in gillnets at eight sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to September 

2004. Significant differences between paired sites from ANOVA tests are 

highlighted. 

Season Site 

Mean 

Total CPUE 

Mean 

Number of Spp 

Mean 

Shannon 

Fenwick Island Shoal 7.93 +/- 2.35 2 +/- 0.41 0.51 +/- 0.22 

Fenwick Reference 16.38 +/- 1.75 2 +/- 0.41 0.34 +/- 0.19 

Shoal B 25.04 +/- 13.11 2.25 +/- 0.85 0.51 +/- 0.3 

Shoal B Reference 6.75 +/- 1.85 1.5 +/- 0.29 0.36 +/- 0.22 

Shoal D 4.97 +/- 1.99 1.75 +/- 0.25 0.5 +/- 0.2 

Shoal D Reference 30.28 +/- 16.7 2.25 +/- 0.25 0.6 +/- 0.23 

Weaver Shoal 14.8 +/- 3.17 2.5 +/- 0.65 0.77 +/- 0.31 

Fall 

Weaver Reference 8.88 +/- 4.1 2 +/- 0.41 0.62 +/- 0.22 

Fenwick Island Shoal 0.25 +/- 0.16 0.5 +/- 0.29 0 +/- 0 

Fenwick Reference 0.3 +/- 0.19 0.5 +/- 0.29 0 +/- 0 

Shoal B 1.01 +/- 0.6 0.75 +/- 0.48 0.2 +/- 0.2 

Shoal B Reference 0.39 +/- 0.27 1 +/- 0.41 0.23 +/- 0.23 

Shoal D 0.29 +/- 0.11 1 +/- 0 0 +/- 0 

Shoal D Reference 0.31 +/- 0.23 0.75 +/- 0.25 0 +/- 0 

Weaver Shoal 0.28 +/- 0.28 0.5 +/- 0.5 0.23 +/- 0.23 

Winter 

Weaver Reference 0.53 +/- 0.32 1.5 +/- 0.96 0.57 +/- 0.34 

Fenwick Island Shoal 6.66 +/- 0.91 3.5 +/- 0.65 1.13 +/- 0.22 

Fenwick Reference 3.21 +/- 0.93 2.75 +/- 0.63 1.05 +/- 0.36 

Shoal B 3.69 +/- 0.65 2.5 +/- 0.5 0.85 +/- 0.29 

Shoal B Reference 1.17 +/- 0.34 1.25 +/- 0.25 0.18 +/- 0.18 

Shoal D 2.55 +/- 1.49 2 +/- 0.41 0.73 +/- 0.27 

Shoal D Reference 1.65 +/- 0.84 1.5 +/- 0.65 0.39 +/- 0.25 

Weaver Shoal 7.97 +/- 1.46 3.5 +/- 0.65 1.19 +/- 0.3 

Spring 

Weaver Reference 3.93 +/- 1.63 3 +/- 1.08 1.23 +/- 0.46 

Fenwick Island Shoal 3.07 +/- 0.83 3.5 +/- 0.29 1.58 +/- 0.21 

Fenwick Reference 22.46 +/- 12.44 6 +/- 2.35 1.73 +/- 0.47 

Shoal B 0.99 +/- 0.43 1.5 +/- 0.29 0.36 +/- 0.21 

Shoal B Reference 7.47 +/- 4.67 3.75 +/- 2.06 0.98 +/- 0.57 

Shoal D 1.12 +/- 0.61 1.5 +/- 0.65 0.61 +/- 0.37 

Shoal D Reference 1.55 +/- 0.66 1.75 +/- 0.25 0.53 +/- 0.18 

Weaver Shoal 5.1 +/- 2.01 3.5 +/- 0.29 1.6 +/- 0.07 

Summer 

Weaver Reference 2.18 +/- 1.1 2.5 +/- 1.32 0.81 +/- 0.5 
Statistical Analysis of Net Survey Data 

 3-36 

Table 3-13. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in gillnets at eight sites in the Atlantic Ocean off the coast of 

Maryland and Delaware from November 2002 to September 2004. Significant 

differences between paired sites from ANOVA tests are highlighted. 

Season Site Mean 

Total CPUE 

Mean 

Number of Species 

Mean 

Shannon 

Fenwick Island Shoal 8.64 +/- 5.59 2.5 +/- 0.5 0.83 +/- 0.18 

Fenwick Reference 14.02 +/- 1.68 2 +/- 0 0.24 +/- 0.02 

Shoal B 3.33 +/- 3.33 1.5 +/- 1.5 0.68 +/- 0.68 

Shoal B Reference 6.33 +/- 0.33 1.5 +/- 0.5 0.25 +/- 0.25 

Shoal D 1.56 +/- 0.34 1.5 +/- 0.5 0.46 +/- 0.46 

Shoal D Reference 1.43 +/- 0 2 +/- 0 1 +/- 0 

Weaver Shoal 10.8 +/- 1.2 1.5 +/- 0.5 0.27 +/- 0.27 

Fall 02 

Weaver Reference 2.1 +/- 1.5 1.5 +/- 0.5 0.33 +/- 0.33 

Fenwick Island Shoal 0 +/- 0 0 +/- 0 0 +/- 0 

Fenwick Reference 0 +/- 0 0 +/- 0 0 +/- 0 

Shoal B 0 +/- 0 0 +/- 0 0 +/- 0 

Shoal B Reference 0.18 +/- 0 1 +/- 0 0 +/- 0 

Shoal D 0.1 +/- 0.03 1 +/- 0 0 +/- 0 

Shoal D Reference 0.12 +/- 0.06 1 +/- 0 0 +/- 0 

Weaver Shoal 0 +/- 0 0 +/- 0 0 +/- 0 

Winter 03 

Weaver Reference 0.66 +/- 0.66 2 +/- 2 0.65 +/- 0.65 

Fenwick Island Shoal 7.09 +/- 0.55 3.5 +/- 0.5 1.01 +/- 0.21 

Fenwick Reference 3.23 +/- 0.57 3.5 +/- 0.5 1.36 +/- 0.21 

Shoal B 4.74 +/- 0.63 3 +/- 0 1.06 +/- 0.08 

Shoal B Reference 1.74 +/- 0.19 1.5 +/- 0.5 0.36 +/- 0.36 

Shoal D 4.6 +/- 2.2 2.5 +/- 0.5 0.96 +/- 0.31 

Shoal D Reference 3.09 +/- 0.18 2.5 +/- 0.5 0.78 +/- 0.28 

Weaver Shoal 8 +/- 3.33 3.5 +/- 0.5 1.19 +/- 0.45 

Spring 03 

Weaver Reference 3.69 +/- 3.69 2 +/- 2 0.84 +/- 0.84 

Fenwick Island Shoal 4.16 +/- 1.09 3 +/- 0 1.21 +/- 0.07 

Fenwick Reference 43.83 +/- 3.95 10 +/- 1 2.53 +/- 0.18 

Shoal B 1.74 +/- 0 2 +/- 0 0.72 +/- 0 

Shoal B Reference 14.77 +/- 4.92 7 +/- 2 1.95 +/- 0.12 

Shoal D 2.13 +/- 0.43 2.5 +/- 0.5 1.23 +/- 0.23 

Shoal D Reference 2.63 +/- 0.44 2 +/- 0 0.66 +/- 0.07 

Weaver Shoal 8.57 +/- 0 4 +/- 0 1.72 +/- 0.03 

Summer 03 

Weaver Reference 4 +/- 0.73 4.5 +/- 1.5 1.63 +/- 0.41 

Fenwick Island Shoal 7.21 +/- 0.87 1.5 +/- 0.5 0.19 +/- 0.19 

Fenwick Reference 18.75 +/- 2.08 2 +/- 1 0.44 +/- 0.44 

Shoal B 46.74 +/- 8.84 3 +/- 1 0.34 +/- 0.05 

Shoal B Reference 7.16 +/- 4.48 1.5 +/- 0.5 0.46 +/- 0.46 

Shoal D 8.37 +/- 0.7 2 +/- 0 0.54 +/- 0.15 

Shoal D Reference 59.13 +/- 3.04 2.5 +/- 0.5 0.2 +/- 0.04 

Weaver Shoal 18.8 +/- 5.2 3.5 +/- 0.5 1.26 +/- 0.12 

Fall 03 

Weaver Reference 15.65 +/- 2.61 2.5 +/- 0.5 0.91 +/- 0.03 
Statistical Analysis of Net Survey Data 

 3-37 

Table 3-13. (Continued) 

Season Site Mean 

Total CPUE 

Mean 

Number of Species 

Mean 

Shannon 

Fenwick Island Shoal 0.51 +/- 0.17 1 +/- 0 0 +/- 0 

Fenwick Reference 0.6 +/- 0.2 1 +/- 0 0 +/- 0 

Shoal B 2.01 +/- 0.4 1.5 +/- 0.5 0.41 +/- 0.41 

Shoal B Reference 0.6 +/- 0.6 1 +/- 1 0.46 +/- 0.46 

Shoal D 0.47 +/- 0 1 +/- 0 0 +/- 0 

Shoal D Reference 0.5 +/- 0.5 0.5 +/- 0.5 0 +/- 0 

Weaver Shoal 0.56 +/- 0.56 1 +/- 1 0.46 +/- 0.46 

Winter 04 

Weaver Reference 0.39 +/- 0.39 1 +/- 1 0.5 +/- 0.5 

Fenwick Island Shoal 6.23 +/- 2.08 3.5 +/- 1.5 1.24 +/- 0.48 

Fenwick Reference 3.2 +/- 2.21 2 +/- 1 0.75 +/- 0.75 

Shoal B 2.65 +/- 0 2 +/- 1 0.65 +/- 0.65 

Shoal B Reference 0.59 +/- 0 1 +/- 0 0 +/- 0 

Shoal D 0.5 +/- 0.17 1.5 +/- 0.5 0.5 +/- 0.5 

Shoal D Reference 0.2 +/- 0.2 0.5 +/- 0.5 0 +/- 0 

Weaver Shoal 7.94 +/- 1.32 3.5 +/- 1.5 1.18 +/- 0.59 

Spring 04 

Weaver Reference 4.17 +/- 1.5 4 +/- 1 1.62 +/- 0.53 

Fenwick Island Shoal 1.97 +/- 0.76 4 +/- 0 1.95 +/- 0.05 

Fenwick Reference 1.09 +/- 0.1 2 +/- 0 0.92 +/- 0 

Shoal B 0.24 +/- 0 1 +/- 0 0 +/- 0 

Shoal B Reference 0.17 +/- 0.17 0.5 +/- 0.5 0 +/- 0 

Shoal D 0.12 +/- 0.12 0.5 +/- 0.5 0 +/- 0 

Shoal D Reference 0.47 +/- 0.28 1.5 +/- 0.5 0.41 +/- 0.41 

Weaver Shoal 1.62 +/- 0.32 3 +/- 0 1.48 +/- 0.02 

Summer 04 

Weaver Reference 0.35 +/- 0.35 0.5 +/- 0.5 0 +/- 0 
Statistical Analysis of Net Survey Data 

 3-38 

Figure 3-9. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in gillnets at four shoal and four reference 

sites in the Atlantic Ocean off the coast of Maryland and Delaware from November 

2002 to September 2004. 

Gillnet - Mean Total Catch per Unit Effort

0

5

10

15

20

25

Fall Winter Spring Summer

Catch per Unit Effort 

Reference

Shoal

Gillnet - Mean Number of Species

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Fall Winter Spring Summer

N u m b er o f S p ecies

Reference

Shoal

Gillnet - Mean Shannon

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Fall Winter Spring Summer

Shannon

Reference

Shoal
Statistical Analysis of Net Survey Data 

 3-39 

Figure 3-10. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in gillnets at four shoal and four reference sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. 

Gillnet - Mean Total Catch per Unit Effort

0

5

10

15

20

25

30

35

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Catch per Unit Effort 

Reference

Shoal

Gillnet - Mean Number of Species

0

1

2

3

4

5

6

7

8

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Number of Species .

Reference

Shoal

Gillnet - Mean Shannon

0

0.5

1

1.5

2

2.5

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Shannon

Reference

Shoal
Statistical Analysis of Net Survey Data 

 3-40 

Figure 3-11. Combined two-year seasonal mean (and SE) of total species CPUE, number of 

species, and species diversity collected in gillnets at eight sites in the Atlantic 

Ocean off the coast of Maryland and Delaware from November 2002 to 

September 2004. 

Gillnet - Mean Total Catch per Unit Effort

0

5

10

15

20

25

30

35

40

45

50

Fall Winter Spring Summer

Catch per Unit Effort 

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference

Gillnet - Mean Number of Species

0

1

2

3

4

5

6

7

8

9

Fall Winter Spring Summer

Num ber of S pecies .

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference

Gillnet - Mean Shannon

0

0.5

1

1.5

2

2.5

Fall Winter Spring Summer

Shannon

Fenwick Island Shoal

Fenwick Reference

Shoal B

Shoal B Reference

Shoal D

Shoal D Reference

Weaver Shoal

Weaver Reference
Statistical Analysis of Net Survey Data 

 3-41 

Figure 3-12. Seasonal mean (and SE) of total species CPUE, number of species, and species 

diversity collected in gillnets at eight sites in the Atlantic Ocean off the coast of 

Maryland and Delaware from November 2002 to September 2004. 

Gillnet - Mean Total Catch per Unit Effort

0

10

20

30

40

50

60

70

Fenwick Island

Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver Shoal Weaver

Reference

Catch per Unit Effort 

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Gillnet - Mean Number of Species

0

2

4

6

8

10

12

Fenwick Island

Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver Shoal Weaver

Reference

Number of Species

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04

Gillnet - Mean Shannon

0

0.5

1

1.5

2

2.5

3

Fenwick

Island Shoal

Fenwick

Reference

Shoal B Shoal B

Reference

Shoal D Shoal D

Reference

Weaver

Shoal

Weaver

Reference

Shannon

Fall 02 Winter 03 Spring 03 Summer 03 Fall 03 Winter 04 Spring 04 Summer 04
Statistical Analysis of Net Survey Data 

 3-42 

3.2 SPECIES GUILD AND META ANALYSIS 

3.2.1 Species Guild and Meta-Analysis Methods 

Data were standardized to catch per unit of effort (CPUE) before analysis, where units 

were the number of animals captured per 10,000 m2

 of area swept by the trawls, and number 

captured per hour of soak time in gillnets. These estimates were transformed to loge (CPUE + 1) 

before analysis to meet the assumption of equal variance among treatments for ANOVA. We 

conducted ANOVA with loge (CPUE +1) as the response variable, site and season as blocks, and 

treatment (shoal or reference) as a factor, using the SAS GLM procedure (SAS Institute 2004). 

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

invertebrates in gillnets, because no invertebrates were captured in them. Guilds were defined 

using life history information. 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 (Table 3-1). Essentially squid was the 

pelagic invertebrate guild, because no other pelagic invertebrates were collected. 

Individual cell means were plotted for each gear and visually inspected for interactions 

between the effects of treatment, site, and season. Because interactions did not follow any 

consistent pattern among gears and did not appear to be biologically plausible, they were not 

included in the analyses of variance. For each ANOVA, the least-squares mean difference in 

transformed CPUE between shoals and reference sites was calculated for use in a meta-analysis. 

Meta-analysis was conducted for each guild to judge the overall pattern in abundance 

across sampling gears. In this analysis, sampling with each gear was viewed as an independent 

field experiment that measured the effect of shoals on abundance of fish and invertebrates. 

Estimates of effect sizes (differences in abundance between shoals and reference sites) differed 

among gears not only because they included sampling variation, but also because each gear 

captured fish and invertebrates with different efficiency. However, the differences in efficiency 

likely affected only the mean and standard deviation of the estimate for each experiment, not the 

size of the effect on abundance of fish and invertebrates. That is, effects estimated for each 

experiment were hypothesized to be linearly equitable because all three gears were deployed to 

sample the same true differences in fish and invertebrate abundance. The result of the metaanalysis was an estimate of the difference in abundance between shoal and reference areas for 

each guild scaled to the standard normal curve (i.e., mean 0 and SD 1), and pooled across 

multiple sampling gears. 
Statistical Analysis of Net Survey Data 

 3-43 

The meta-analysis was conducted following Hedges and Olkin (1985). First, 

standardized mean differences in transformed CPUE between shoal and reference sites (di) were 

calculated for each ANOVA using the unbiased estimator: 

s

Y Y J N

N

di

E C

( 2) 4 9

3 1 − ⎟ − ⎠

⎞ ⎜

⎝

⎛

− = − 

Where: 

N = the total number of samples, 

E Y = the mean abundance for shoals, 

C Y = the mean abundance for reference areas, 

s = the standard deviation of the treatment effect, 

and the function 

4 1

3 ( ) 1 − = − m

J m . 

Standardized estimates within each guild were then tested for homogeneity using the Q

statistic: 

∑=

− + =

k

i i

i

d

d d Q

1

2

2

( ) ˆ

( )

δ 

Where: 

k = the number of experiments, 

∑ ∑ = =

+ =

k

i i

k

i i

i

d d

d d

1

2

1

2 ( ) ˆ

1

( ) ˆδ δ , 

N

d

n n

N i

E C 2

ˆ 2

2 δ = + , 

E

n = number of shoal samples, 

and C n = number of reference samples. 

The Q statistic has an asymptotic chi-square distribution with k – 1 degrees of freedom. 

A significant chi-square result indicates that the pooled experiments can not be described as 

sharing a common effect size. Gillnet data were excluded from the meta-analysis because the 

test of homogeneity indicated that the three experiments probably did not measure the same 

effect sizes for two of the four guilds (Benthic finfish, Q = 7.01, P = 0.97, and Pelagic Finfish, Q

= 7.25, P = 0.97). When the data were combined for both trawl experiments, the homogeneity 

test was not significant at the 10% level for any group, indicating that the trawl data could 

reasonably be pooled to estimate the relative magnitude of effects. 
Statistical Analysis of Net Survey Data 

 3-44 

Estimates of effect sizes pooled over the two trawl gears were calculated for each guild as 

d+ above, with variance: 

( ) ( )

1

1

2

2 1 −

=

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = ∑

k

i di

d

δ

δ

Where: 

( ) di

2 δ = the variance of di 

3.2.1.1 Species Guild and Meta-Analysis Results 

Results from these analysis 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 (Figure 3-13; Table 3-14). 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. 

However, 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 guilds 

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 (Table 3-15). 

The standardized difference in mean transformed densities was about 0.5 standard deviations for 

all three guilds, 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. 
Statistical Analysis of Net Survey Data 

 3-45 

Table 3-14. Results of analyses of variance for treatment effects (shoal versus reference 

sites) on the model, loge (CPUE + 1) = treatment + site + season, by gear and 

species guild. Effect sizes are shown in Figure 3-13. The habitat with the higher 

treatment values for a specific test is indicated by an S (shoal) or R (reference). 

An asterisk indicates a test was significant at the α = 0.05 level. 

Gear Guild F P 

Benthic finfish 3.66 0.058 (R) 

Pelagic finfish 8.29 0.005* (R) 

Benthic Invertebrates 0.38 0.538 (S) Commercial trawl 

Pelagic Invertebrates 6.25 0.014* (R) 

Benthic finfish 11.07 0.001* (R) 

Pelagic finfish 12.62 <0.001* (R) 

Benthic Invertebrates 0.27 0.605 (R) Small trawl 

Pelagic Invertebrates 5.53 0.021* (R) 

Benthic finfish 0.02 0.893 (S) 

Pelagic finfish <0.01 0.950 (R) 

Benthic Invertebrates 0.55 0.458 (S) Gillnet 

Pelagic Invertebrates NA NA 

Table 3-15. Standardized mean differences in loge (CPUE + 1) captured at shoals versus 

reference sites from meta-analysis of commercial and small trawl surveys, for 

each species guild. Negative numbers indicate more animals were captured in 

reference areas. 

95% Confidence limits Group Standardized effect Lower Upper 

Benthic finfish -0.47 -0.22 -0.73 

Benthic invertebrates 0.01 0.27 -0.24 

Pelagic finfish -0.58 -0.32 -0.84 

Pelagic invertebrates -0.44 -0.18 -0.70 
Statistical Analysis of Net Survey Data 

 3-46 

Figure 3-13. Least-squares means (± 95% CI) for loge (CPUE + 1) at shoals and reference sites 

from the model loge (CPUE + 1) = treatment + site + season, by gear and species 

guild. 

Commercial

Trawl

Small

Trawl

Gillnet Commercial

Trawl

Small

Trawl

Gillnet

Gear

1

2

3

1

2

3

Log(CPUE + 1)

Benthic Finfish Benthic Invertebrates

Pelagic Finfish Pelagic Invertebrates

Shoal

Reference

NA
Statistical Analysis of Net Survey Data 

 3-47 

3.3 MULTIVARIATE ANALYSIS 

3.3.1 Multivariate Analysis Methods 

Multivariate analyses were used to elucidate whether differences between shoal and 

reference sites were attributed to differences in faunal composition as quantified by the three net 

gears used in this study. Specifically, the objectives of these analyses were (1) to assess whether 

there were differences in species composition between the shoal and the reference sites, and (2) 

examine whether these differences were maintained in all seasons and different years. 

Multivariate analyses were carried out using the routines in the PRIMER (Plymouth 

Routines in Multivariate Ecological Research) v.5 statistical package (Clarke and Gorley 2001). 

Species abundance data were log-transformed as described in the Total Catch Analysis section, 

and subjected to cluster analysis and non-metric multidimensional scaling (MDS) ordination on a 

Bray-Curtis similarity matrix (Clarke and Warwick 2001). The group average method was used 

to link sites in cluster analysis. Transformation was used prior to calculating similarities in order 

to balance the contribution of abundant species with high CPUE against those of less common 

species. Analyses of small trawl data excluded bay anchovies (Anchoa mitchilli) because this is 

a pelagic species that is only occasionally collected in high numbers in trawls. This species 

exhibits a strong tendency to form schools and thus introduces large variability in the analyses. 

Such species tend to obscure the pattern and interpretation of the multivariate analyses. 

Non-metric MDS is one of many ordination techniques. It was chosen here for its 

simplicity of concept. Non-metric MDS constructs a plot in which samples are arranged in rank 

order according to their relative similarity. Main advantages of non-metric MDS over other 

ordination methods (e.g., Principal Component Analysis) are the lack of assumptions about 

species distributions, and a greater ability to represent accurately the complex relations among 

the samples. The algorithm involves non-parametric regression, and the success of the 

ordination is measured by the level of scatter in the regression, or “stress”. 

Two-way crossed ANOSIM tests (Analysis of Similarities) were used to test for 

differences in species composition between the shoals and the reference sites after blocking for 

the effects of season. Significant differences produced by the ANOSIM test are determined by 

the R-statistic value. The R statistic reflects the observed differences between groups (in this 

case shoal versus reference sites) contrasted with differences among replicates within groups. 

Within each shoal and reference group, sites (i.e., Shoal B, and Shoal D, Fenwick Island Shoal, 

and Weaver Shoal) and years were treated as replicates. R is based on the rank similarities 

between samples and usually ranges from +1, when all samples within groups are more similar to 

each other than to any sample from other groups, to 0, when average similarities within and 

between groups are the same (i.e., the null hypothesis). The observed value of R is then 

compared to the spread of all the R values possible from the random re-labeling of samples, or to 

a subset of these values if the number of permutations is high (> 1,000). The null hypothesis of 

no difference between groups is rejected if the observed value of R looks unlikely to have come 

from the distribution of R values given by the random rearrangements. For the two-way crossed 
Statistical Analysis of Net Survey Data 

 3-48 

design, the observed R is calculated for each separate block (in this case season), and the 

resulting values averaged. Its permutation distribution under the null hypothesis was generated 

by examining the random re-labeling of sites (shoal and reference) within each season. 

For ANOSIM tests that were significant, the SIMPER procedure (Similarity Percentages) 

was used to identify which species were responsible for the separation of samples in the MDS 

ordination, and to characterize shoal and reference sites. The analysis identifies which species 

contribute most to the average dissimilarity between groups of sites (e.g., shoal vs. reference 

sites) and which species contribute more consistently (by examining the ratio of the average 

dissimilarity contribution of each species to its standard deviation). Differences in mean CPUE 

of species contributing most to the separation between the shoal and the reference sites were 

examined graphically by overlaying on the ordination plot circles of size proportional to the 

magnitude of the abundance. Total CPUE and total species richness among sites was also 

examined in this way. 

For the purposes of the multivariate analysis the samples were coded to indicate area, 

treatment, season, and year. For example Weaver Shoal winter 2003 was coded WS-1-03, where 

WS=Weaver Shoal, 1= winter, and 03 = year 2003. 

The various seasons were coded: 

Winter=1, spring = 2, summer = 3, and fall = 4 

The sampling sites were coded: 

Weaver Shoal =WS, Weaver Reference =WR, Fenwick Shoal = FS, Fenwick 

Reference = FR, Shoal B = BS, Shoal B Reference = BR, Shoal D = DS, Shoal D 

Reference =DR. 

3.3.1.1 Multivariate Analysis Results 

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

analysis (Figure 3-14). Individual samples linking at very low similarity values (DS-2-03, FS-3-

03, WS-1-04, and BR-1-03) had low abundance and 1-3 species, generally invertebrates. A few 

other samples had no catch in gillnets (BS-1-03, FR-1-03, FS-1-03, and WS-1-03) or in small 

trawls (BR-4-02, DR-4-02, and FR-4-02). Samples with no catch were excluded from the 

analyses. Year was also a factor contributing to the separation of sites, but its effect was less 

distinct than season. 

Given the strong effect of seasonality, data were examined within each season and 

ordination plots constructed to examine site configuration and whether there was any tendency 

for sites to form groups according to location (shoal vs. reference). 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 (Figure 3-15). 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 
Statistical Analysis of Net Survey Data 

 3-49 

no pattern in spring (Figure 3-16). No structure existed for the gillnet samples that would 

suggest differences between the shoal and the reference sites (Figure 3-17). There was also clear 

segregation of samples according to year in the MDS plots (not shown) for all seasons and gears. 

Two-way crossed ANOSIM tests with location (shoal vs. reference) as the main factor, 

and seasons as blocks, 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. The 

simulated distributions of the R statistic under the null hypothesis of no differences between 

shoal and reference sites can be examined in Figure 3-18. 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. 

For this last analysis, the 2002 fall samples were excluded because of the gear problems 

discussed elsewhere in this report. For gillnets, the observed R is negative and below 72% of the 

simulated R values. For this last gear, shoal and reference sites were undistinguishable. Season 

was highly significant for all tests. 

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

of season (and the further differences in year identified in the MDS plots), 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. 

Many species played at least some part in determining the dissimilarity between the shoal 

and the reference sites. Those that contributed to 90% of the dissimilarity are listed in Tables 

3-16 and 3-17. However, about 40% of the dissimilarity was accounted for by three species in 

the small trawl and by 3-5 species in the commercial trawl. Species contributing most to the 

separation between the shoal and the reference sites varied across seasons. For the small trawl, 

sand shrimp, spotted hake, and moon snails contributed most in the winter; spotted hake, squids, 

and right-handed hermit crabs in spring; and squids, right-handed hermit crabs, and starfishes in 

summer and fall (Table 3-16). No one species was “best” discriminator (high dissimilarity to 

standard deviation ratio), except perhaps the northern searobin in summer commercial trawls. 

The influence of spotted hake in the spring and of northern searobin in the summer small trawls 

can be observed in Figure 3-19. Both fish species were on average more abundant in the 

reference than in the shoal sites. 

For the commercial trawl the 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 (Table 3-17). Again, 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 (Figure 3-20). All three 

fish species were more abundant in the reference than in the shoal sites. 
Statistical Analysis of Net Survey Data 

 3-50 

Table 3-16. Average dissimilarity (Av.Diss) and percent contribution of species (Contrib%) to 

the separation of shoal and reference sites, by season, for the small trawl. The 

average abundance in shoal (S) and reference sites (R). The dissimilarity to 

standard deviation ratio (Diss/SD), a measure of how well a species discriminates 

between the groups of sites (the larger the better), is also indicated in the table. 

Group S Group R Species Av.Abund Av.Abund Av.Diss Diss/SD Contrib% Cum.%

Fall 

(Average dissimilarity = 61.10) 

Squids 16.92 20.21 9.24 1.29 15.12 15.12 

Starfishes 11.22 12.84 7.9 1.66 12.92 28.04 

Right handed hermit crabs 4.01 13.15 6.78 1.41 11.09 39.14 

Atlantic croaker 0.46 9.87 6.7 1.08 10.96 50.1 

Spotted hake 3.69 3.53 3.91 1.2 6.4 56.5 

Smallmouth flounder 0.76 1.64 3.24 1.36 5.31 61.81 

Windowpane 0.44 1.39 3.01 1.11 4.92 66.73 

Winter skate 1.03 1.04 2.93 1.32 4.79 71.52 

Moon snails 0.91 0 2.6 0.88 4.25 75.77 

Silver hake 0.49 0.53 1.91 0.67 3.12 78.89 

Scup 0 0.99 1.88 1.04 3.08 81.97 

Northern searobin 0.39 0.44 1.74 0.97 2.85 84.83 

Lady crab 0.26 0.53 1.66 1.1 2.72 87.55 

Clearnose skate 0.32 0.35 1.54 0.93 2.51 90.06 

Winter 

(Average dissimilarity = 48.54) 

Sand shrimp 4.2 9.81 6.86 1.41 14.14 14.14 

Spotted hake 0.87 3.69 6.75 1.37 13.91 28.05 

Moon snails 2.3 3.68 6.58 1.51 13.56 41.61 

Gastropods 2.7 1.47 5.47 0.69 11.27 52.88 

Starfishes 0.68 3.3 5.38 1.06 11.08 63.97 

Right handed hermit crabs 2.98 2.9 3.24 1.39 6.67 70.63 

Atlantic silverside 0.17 0.63 2.88 0.88 5.92 76.56 

Little skate 0.35 0.58 2.86 1.12 5.88 82.44 

Smallmouth flounder 0.26 0.48 2.3 0.93 4.74 87.18 

Windowpane 0.17 0.28 1.42 1.06 2.93 90.11 

Spring 

(Average dissimilarity = 65.48) 

Spotted hake 0.39 5.24 10.11 1.13 15.44 15.44 

Squids 9.84 5.42 8.29 1.42 12.66 28.09 

Right handed hermit crabs 7.27 4.53 6.94 1.27 10.59 38.69 

Starfishes 3.74 4.89 5.98 1.26 9.14 47.82 

Gastropods 3.58 1.8 4.88 1.01 7.45 55.28 

Sand shrimp 1.67 1.27 4.14 1.16 6.32 61.6 

Northern searobin 0.5 2.63 3.91 0.81 5.97 67.57 

Smallmouth flounder 0.73 1.25 3.57 1.11 5.46 73.03 

Moon snails 1.17 1.1 3.52 1.4 5.38 78.41 

Windowpane 0.61 0.16 1.79 0.97 2.74 81.14 
Statistical Analysis of Net Survey Data 

 3-51 

Table 3-16. (Continued) 

Group S Group R Species Av.Abund Av.Abund Av.Diss Diss/SD Contrib% Cum.%

Spring (cont’d) 

(Average dissimilarity = 65.48) 

Winter skate 0.56 0.16 1.75 1.05 2.68 83.82 

Atlantic rock crab 0.71 0.1 1.25 0.63 1.91 85.73 

Striped searobin 0.17 0.15 1.13 0.58 1.73 87.46 

Black sea bass 0 0.44 1.12 0.35 1.72 89.18 

Butterfish 0 0.22 0.99 0.48 1.52 90.69 

Summer 

(Average dissimilarity = 64.08) 

Squids 4.11 39.69 9.22 1.01 14.39 14.39 

Right handed hermit crabs 22.27 7.57 7.59 1.34 11.85 26.23 

Starfishes 3.31 10.35 6.97 1.29 10.88 37.12 

Northern searobin 0.98 11.99 5.88 1.46 9.18 46.3 

Scup 3.48 1.82 5.06 1.09 7.9 54.2 

Butterfish 1.28 1.9 3.6 1.09 5.62 59.82 

Lady crab 1.71 1.72 3.31 1.05 5.16 64.98 

Clearnose skate 1.16 1.64 3.19 1.24 4.98 69.96 

Gastropods 2.66 0 2.64 0.54 4.12 74.08 

Smallmouth flounder 0.46 1.29 2.21 1.27 3.45 77.53 

Striped anchovy 0 0.99 1.97 0.55 3.07 80.6 

Heart urchins 0.44 0.11 1.86 0.64 2.91 83.51 

Spotted hake 0.05 0.38 1.18 0.77 1.85 85.35 

Striped cusk eel 0 0.6 1.18 0.55 1.84 87.2 

Atlantic rock crab 0 0.51 1.04 0.72 1.62 88.81 

Portly spider crab 0.12 0.38 0.98 0.79 1.52 90.34 
Statistical Analysis of Net Survey Data 

 3-52 

Table 3-17. Average dissimilarity (Av.Diss) and percent contribution of species (Contrib%) 

to the separation of shoal and reference sites, by season, for the commercial 

trawl. The average abundance in shoal (S) and reference sites (R). The 

dissimilarity to standard deviation ratio (Diss/SD), a measure of how well a 

species discriminates between the groups of sites (the larger the better), is also 

indicated in the table. 

Group S Group R Species Av.Abund Av.Abund Av.Diss Diss/SD Contrib% Cum.%

Fall

(Average dissimilarity = 42.05) 

Striped bass 80.57 0.6 3.23 0.88 7.67 7.67 

Windowpane 4.03 31.48 3.21 1.38 7.64 15.31 

Scup 0.26 5.2 3.11 2.31 7.38 22.7 

Starfishes 14.56 7.67 2.92 1.16 6.94 29.63 

Little skate 11.41 7.69 2.83 1.24 6.72 36.36 

Spiny dogfish 55.49 94.38 2.59 1.44 6.15 42.51 

Squids 2.28 7.14 2.12 1.27 5.04 47.55 

Striped searobin 0.65 5.49 1.82 0.99 4.32 51.87 

Clearnose skate 4.68 3.35 1.72 1.23 4.09 55.96 

Bluefish 1.37 4.23 1.7 1.39 4.04 60 

Summer flounder 7.89 4.59 1.62 1.17 3.84 63.85 

Butterfish 0.21 2.58 1.62 1.36 3.84 67.69 

Horseshoe crab 0.54 2.53 1.42 1.2 3.37 71.05 

Lady crab 6.64 8.79 1.21 0.92 2.87 73.92 

Weakfish 0 2.4 1.19 0.74 2.84 76.76 

Bay anchovy 0 8.37 1.17 0.55 2.79 79.55 

Winter skate 64.86 44.94 1.16 1.26 2.77 82.32 

Smooth dogfish 0.5 0.79 0.97 1.02 2.31 84.63 

Northern searobin 0.19 1.85 0.93 0.76 2.22 86.86 

Coarsehand lady crab 0.48 0.72 0.84 0.81 2 88.85 

Channeled whelk 0.63 0.62 0.81 1.22 1.94 90.79 

Winter

(Average dissimilarity = 58.78) 

Winter skate 1.54 9.48 11.82 1.69 20.1 20.1

Windowpane 1.86 5.26 7.39 1.22 12.58 32.68

Little skate 2.27 4.02 6.66 1.19 11.32 44

Atlantic herring 1.53 2.17 4.61 0.89 7.85 51.85

Spiny dogfish 0.93 1.04 4.36 0.9 7.42 59.27

Barndoor skate 0.49 1.04 3.64 0.91 6.19 65.45

Starfishes 0.65 0.49 2.81 1.17 4.79 70.24

Horseshoe crab 0.36 0.71 2.72 0.96 4.63 74.87

Atlantic menhaden 0 0.45 2.38 0.7 4.05 78.91

American sand lance 1.29 0 2.28 0.55 3.88 82.8

Blueback herring 0.15 0.41 2.04 0.97 3.47 86.26

Summer flounder 0.07 0.42 1.77 0.8 3.01 89.27

Atlantic silverside 0.07 0.14 1.13 0.64 1.93 91.2
Statistical Analysis of Net Survey Data 

 3-53 

Table 3-17. (Continued) 

Group S Group R Species Av.Abund Av.Abund Av.Diss Diss/SD Contrib% Cum.%

Spring 

(Average dissimilarity = 41.23) 

Scup 483.61 103.56 5.55 1.44 13.46 13.46

Butterfish 101.66 373.11 5.42 1.12 13.15 26.62

Squids 66.06 55.92 4.53 1.4 10.97 37.59

Northern searobin 10.95 26.94 3.27 1.06 7.92 45.51

Starfishes 4.65 2.58 2.36 1.07 5.71 51.22

Striped searobin 4.29 2.14 2.29 1.32 5.55 56.77

Clearnose skate 3.66 0.15 2.18 1.04 5.28 62.05

Smooth dogfish 19.51 12.29 1.92 1.4 4.66 66.71

Little skate 10.93 5.65 1.85 1.38 4.48 71.19

Summer flounder 0.76 1.5 1.43 1.52 3.46 74.65

Winter skate 22.4 19.74 1.33 1.38 3.23 77.88

Spotted hake 0.48 1.99 1.3 1.17 3.15 81.03

Northern kingfish 0.72 0.59 1.03 1.06 2.49 83.52

Windowpane 3.15 2.44 0.92 1.26 2.23 85.75

American sand lance 0.74 0.08 0.77 0.59 1.87 87.62

Channeled whelk 0.2 0.81 0.77 0.75 1.86 89.48

Horseshoe crab 0.21 0.42 0.75 1.01 1.82 91.31

Summer 

(Average dissimilarity = 53.20) 

Northern searobin 25.95 90.94 5.39 1.31 10.13 10.13

Scup 171.46 18.93 4.52 0.94 8.49 18.63

Squids 12.93 24.43 4.45 1.15 8.37 27

American sand lance 42.46 0.89 3.82 0.68 7.18 34.18

Butterfish 0.4 5.43 3.53 1.13 6.63 40.81

Atlantic croaker 0 79.62 3.44 0.6 6.47 47.28

Clearnose skate 11.16 5.23 3.32 1.35 6.24 53.52

Coarsehand lady crab 9.01 2 3.07 1.18 5.78 59.3

Lady crab 28.3 10.79 2.58 1.19 4.85 64.15

Starfishes 2.09 1.86 2.35 1.11 4.41 68.56

Spotted hake 0.13 2.33 2.3 0.96 4.33 72.89

Winter skate 0.28 2.64 1.99 0.6 3.74 76.63

Windowpane 0.39 1.03 1.37 1.73 2.58 79.22

Spot 0 2.27 1.26 0.55 2.37 81.58

Bullnose ray 0.15 0.99 1.2 0.85 2.25 83.83

Summer flounder 0.21 0.8 1.14 1.14 2.14 85.98

Weakfish 0 1.07 1.01 0.56 1.89 87.87

Striped searobin 0.07 0.37 0.62 0.53 1.17 89.04

Atlantic rock crab 0 0.27 0.59 0.94 1.11 90.15
Statistical Analysis of Net Survey Data 

 3-54 

Small Trawls 

DS-2-03

FS-3-03FS-2-03FS-4-02

WR-3-04

DS-4-02

WR-4-02

BS-4-02

WS-4-02

BS-2-03BS-1-03

DS-1-03

FR-1-04

FS-1-04

WS-1-04

DR-1-03

WS-1-03

WR-1-03

FS-1-03

FR-1-03

BR-1-03

DR-1-04

BS-1-04

DS-1-04BR-1-04

WR-1-04

FR-2-03

WR-2-03

BR-2-03

DR-2-03

WS-2-03

BS-4-03

WS-3-03

DR-3-03

DS-3-03

WR-3-03

DS-2-04

FR-2-04

BR-2-04

DR-4-03

FS-2-04

WS-2-04

WR-4-03

BR-4-03

FS-4-03

WS-4-03

BS-3-03

DS-4-03BR-3-04

FR-3-04

DR-3-04

FS-3-04

WS-3-04

FR-3-03

BR-3-03

BS-3-04

WR-2-04

BS-2-04

DS-3-04

FR-4-03

DR-2-04

100

80

60

40

20

0

Similarity

WS-1-04

BS-1-03

FS-1-04

BS-1-04

DS-1-04

FR-1-04

WR-1-04

BR-1-04

DR-1-04

FS-1-03

WS-1-03

WR-1-03

FR-1-03

BR-1-03

DR-1-03

DS-1-03

FR-2-04

DS-2-04

WR-2-04

BS-2-03

DS-2-03BR-2-03

BS-2-04

DR-2-04

FS-2-03FS-2-04

FR-2-03

DR-2-03

BR-2-04

WR-2-03

WS-2-03WS-2-04

BS-4-02

DR-4-02

FS-4-03

WS-4-03

FR-4-03

DR-4-03

BR-4-03

BS-4-03

DS-4-02DS-4-03

WR-4-03

FS-4-02

WS-4-02

FR-4-02

BR-4-02

WR-4-02

BS-3-04

FR-3-04

BR-3-04

DR-3-03

BS-3-03

DS-3-03

WR-3-04

DR-3-04

WR-3-03

WS-3-03

FR-3-03

BR-3-03

FS-3-04

WS-3-04

FS-3-03

DS-3-04

100

80

60

40

20

0

Similarity

Figure 3-14. Cluster analysis of sites based on species composition and abundance for the three 

gears used in this study. Dendrograms show strong separation of sites by season. 

Labels: first letter indicates site (F = Fenwick, W = Weaver, B = Shoal B, D = Shoal 

D); second letter, location (R = reference, S = shoal); first digit, season (1 = Winter, 

2 = Spring, 3 = Summer, 4 = Winter); last two digits, year (2002 through 2004). 

Fall ‘02 Winter Spring/ Summer Fall ‘03 Spring/ Summer 

Small Trawl Data

Winter Spring Fall Summer 

Commercial Trawl Data
Statistical Analysis of Net Survey Data 

 3-55 BR-1-03 FR-4-02 WS-4-02 FS-4-03 BR-4-02 BR-4-03 DS-4-03 WR-4-03 WS-4-03 DR-4-03 FR-4-03 BS-4-03 FS-3-03 FS-4-02 BS-4-02 WS-1-04 BR-1-04 FR-1-04 DS-1-04 FS-1-04 DR-1-04 BS-1-04 WR-4-02

DR-4-02

DS-4-02

WR-1-04

DR-1-03

DS-1-03

WS-3-03

FR-3-03

BR-3-03DS-2-04BR-2-04

WR-1-03WR-2-04

WS-2-04

FS-2-03

WS-2-03

BS-2-03

WR-2-03

FR-2-03

DS-2-03

FS-2-04

FR-2-04

BS-2-04

DS-3-03BR-2-03

BS-3-03

WR-3-03

DR-2-03DR-3-03

WR-3-04

BS-3-04

BR-3-04DS-3-04

FS-3-04

WS-3-04

DR-3-04

FR-3-04

DR-2-04

100

80

60

40

20

0

Similarity

Figure 3-14. (Continued) 

Fall Winter Spring/ Summer 

Gillnet Data
Statistical Analysis of Net Survey Data 

 3-56 

Figure 3-15. MDS ordinations of shoal (S) and reference (R) sites for the small trawl in each of 

four seasons. 

Stress: 0.12

Small Trawl Spring

Stress: 0.11

Small Trawl Summer

S R

Stress: 0.08

Small Trawl Fall

Stress: 0.1

Small Trawl Winter
Statistical Analysis of Net Survey Data 

 3-57 

Figure 3-16. MDS ordinations of shoal (S) and reference (R) sites for the commercial trawl and 

in each of four seasons. 

Stress: 0.18

Stress: 0.12

Commercial Trawl Fall

S R

Stress: 0.09

Commercial Trawl Winter

Stress: 0.15

Commercial Trawl Spring Commercial Trawl Summer
Statistical Analysis of Net Survey Data 

 3-58 

Figure 3-17. MDS ordinations of shoal (S) and reference (R) sites for gillnets in each of four 

seasons. 

Stress: 0.06

Gillnet Summer

Stress: 0.11

Gillnet Spring

Gillnet Fall

Stress: 0.07

S R

Stress: 0.01

Gillnet Winter
Statistical Analysis of Net Survey Data 

 3-59 

Figure 3-18. Simulated distributions of the test statistic R under the null hypothesis of no 

differences between shoals and reference sites. The observed value of R (averaged 

over the four seasons) is 0.18, 0.06, and –0.027 for each of the 25-foot trawl, 

100-foot trawl, and gillnet samples, respectively. 

Small Trawl Data

Commercial Trawl Data 

Gillnet Data 

Frequency

R

2

12

49

112

162

202

154

126

74

53

31

13

5

3

1

-0.12 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 -0.10-0.08-0.06-0.04-0.02

0.06

Frequency

R

4

7

42

95

192

201

165

135

77

45

21

12

2

0

1

-0.12 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 -0.10-0.08-0.06-0.04-0.02

0.18

Frequency

R

3

10

50

115

166

205

168

106

73

49

25

11

6

55

1

0

1

-0.12 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 -0.10 -0.08 -0.06 -0.04 -0.02

-0.027
Statistical Analysis of Net Survey Data 

 3-60 

Small Trawl, Spring + Urophycis regia 

Small Trawl, Summer + Prionotus carolinus 

Figure 3-19. MDS ordinations of shoal (S) and reference (R) sites for the small trawl with 

superimposed circles representing mean CPUE of, respectively, Spotted hake 

(Urophycis regia) and Northern searobin (Prionotus carolinus). Differences in the 

size of the circles reflect differences in the magnitude of the abundance. 

S

R

R

S

R

S

R

S

Stress: 0.05

R

R

S

R

S

R S

Stress: 0.03
Statistical Analysis of Net Survey Data 

 3-61 

Figure 3-20. MDS ordinations of shoal (S) and reference (R) sites for the commercial trawl with 

superimposed circles representing mean CPUE of, respectively from top to bottom, 

Northern searobin (Prionotus carolinus), Scup (Stenotomus chrysops), and Winter 

skate (Raja ocellata). Differences in the size of the circles reflect differences in 

the magnitude of the abundance. 

S S

R

R

R

R

S

S

R

R

S

S

R

R

S S

Stress: 0.15

Summer + Prionotus carolinus

S S

R

R

R

R

S S

R

R

S

S

R

R

S

S

Stress: 0.12

Fall + Stenotomus chrysops

Commercial Trawl

S

S

R

R

R

R

S

S R

R

S

S

R

R

S

S

Stress: 0.09

Winter + Raja ocellata
Statistical Analysis of Net Survey Data 

 3-62 
Statistical Analysis of Bioacoustic Survey Data 

 4-1 

4.0 STATISTICAL ANALYSIS OF BIOACOUSTIC 

SURVEY DATA 

4.1 BIOACOUSTIC SURVEY ANALYSIS 

4.1.1 Bioacoustic Survey Analysis Methods 

Analysis of bioacoustic data was completed using ANOVA techniques in SAS (SAS 

Institute 2004). Analysis variables were mean Sv (relative fish biomass in decibels) and fish 

density (number/10,000 m3

). The mean biomass (Sv) is calculated first by calculating the linear 

mean sv using the equation: 

S

s V

V

v

s s vs s

s

s s

s

N D

N D

= =

=

−

−

∑

∑

( )

( )

ε τ

ε

0

0

1

1

where: 

sv = The linear mean Sv for all samples in the transect D (m2/m3), 

ND = Number of samples in the transect D (-), 

svs = The linear Sv value for sample s (m2

/m3), and 

Vs = Volume of sample s (m3). 

The mean Sv value is calculated as follows: 

S s v v = 10log( )

where: 

sv = The linear mean Sv as calculated above (m2

/m3), and

Sv = The mean Sv, Sv mean (dB re m2/m3)

Fish density measures are reported in units of fish/10,000 m3

. Density is calculated by: 

Density = 10 (Sv / 10) / 10 (TS / 10)
Statistical Analysis of Bioacoustic Survey Data 

 4-2 

where, Sv is the mean relative biomass (dB) and TS is the mean individual target strength (dB) 

within the same transect (MacLennan and Simmonds 1991). In cases where transects lacked 

sufficient individual targets to calculate a density estimate (fewer than 3 individuals), the mean 

TS for all transects at that site and survey were used to calculate density. 

As noted by Foote (1980), the echo returned from a fish comes from its swim bladder, so 

this means that all invertebrates or fish lacking swim bladders in the survey area will not be 

detected acoustically. Thus, our acoustic biomass and density estimates do not include echoes 

associated with fish lacking a swim bladder which constitute a good portion of the catch 

composition from the net survey. 

Attempts were made to quantify differences in fish size classes between sites using 

DEVIS software (Jech and Luo 2000), which is designed to partition fish densities obtained from 

the hydroacoustics into discrete size classes. However, too few individual targets were detected 

throughout the study to justify doing so. Therefore, size frequency distributions of targets 

satisfying the individual target criteria (individual targets) were qualitatively compared between 

shoals and their reference sites to gain an understanding of whether larger finfish targets were 

more frequently using shoals or deeper reference areas. Sizes of individual targets are measured 

by the hydroacoustics system in units of decibels (dB). These units are converted to approximate 

fish length (mm) through the use of Love’s (1977) equation as applied to a 120 kHz system. 

Figure 4-1 presents Love’s relationship and shows the approximate size of fish with swim 

bladders for a given individual target strength. Note that as fish increase in size the target 

strength (in dB) becomes less negative. 

Analysis of acoustic data consisted of comparison of mean fish density and relative 

biomass across sites and seasons. As a first step, response variables (Sv, fish density) were 

evaluated for the effects of site, seasonal sample date, and treatment (shoal or reference site) and 

their interaction terms. Next, response variables were modeled as functions of site, treatment, 

and the interaction term (site * treatment) to evaluate whether within a site pair (e.g. Fenwick 

Shoal versus Fenwick Reference) there were any influences of treatment. Finally, for each site 

pair we evaluated the effect of treatment (shoal or reference) for each seasonal sample. This 

latter analysis provides the evidence of whether fish biomass or fish density, as measured with 

hydroacoustics, differed between each of the four shoal sites and its reference sites during the six 

seasonal samples. We considered a site to have higher fish use when the following occurred: 

(1) overall Sv or density showed a significant treatment effect for a pair of sites, or (2) where Sv 

or density was significantly higher in a shoal than in the reference for two or more seasonal 

surveys. 
Statistical Analysis of Bioacoustic Survey Data 

 4-3 

4.1.2 Bioacoustic Survey Analysis Results 

Six seasonal surveys covering each pair of sites were completed within the study time 

frame. With the exception of fall 2002, all surveys were conducted at night. Overall, fish 

densities and mean biomass collected using hydroacoustics did not differ significantly between 

all shoals and reference sites combined. However, in concurrence with the net survey results, the 

hydroacoustic data indicated significant seasonal differences, thus demonstrating the general 

seasonality and transitory nature of species within the entire study area. 

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

surveys with no discernable patterns overall (Table 4-1 to 4-2). The highest densities of fish 

were found on Shoal B in the second summer survey, but when compared to all other sites, 

Fenwick Island Shoal had highest densities of fish throughout the survey (Table 4-2). Shoal D 

had the lowest densities of fish overall and the lowest biomass overall (Table 4-2). For all the 

sites, the highest mean densities and biomass were measured in the summer surveys, and the 

lowest densities and biomass were measured in the spring surveys. Differences between 

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

evident within site pairs (Figure 4-2 to 4-9). In particular, Fenwick Island Shoal and Weaver 

Shoal exhibited higher 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. The 

other two shoals and reference sites did not exhibit any consistent pattern of higher estimates 

throughout the study. Seasonal descriptions of all measures for each shoal as it compares to its 

reference site is presented here. 

Shoal B

Differences between fish densities and biomass at Shoal B when compared to its 

reference were mixed and no consistent patterns were evident. During fall 2002 and summer 

2004 surveys the reference had significantly higher relative biomass than Shoal B (Figure 4-2). 

Only in fall 2003 was fish biomass higher at the shoal when compared to its reference site. The 

only significant difference in density also occurred during fall 2003 when Shoal B fish density 

exceeded Shoal B Reference (Figure 4-3). 

Despite few targets at Shoal B, the size ranges and distributions of sizes appeared similar 

between the shoal and its reference area (Figures 4-10 to 4-12). In spring surveys, targets ranged 

from -50 to -33 dB (Figure 4-10). During the summer surveys, size distributions were skewed 

towards small sizes, but were slightly larger in summer 03 at the reference than the shoal (Figure 

4-11). Fall distributions differed between years with generally smaller targets in fall 03 than fall 

02 (Figure 4-12). Fall 02 distributions at the reference site were widely distributed with multiple 

modes at -48 dB (~ 50 mm), -43 dB (~80 mm), -39 dB (~125 mm), -37 dB (~175 mm), -33 dB 

(~290 mm ), and -27 dB (~500 mm ). This multimodal distribution suggests a diverse size 

and/or species assemblage at the reference site during fall 2002. 
Statistical Analysis of Bioacoustic Survey Data 

 4-4 

Shoal D

The Shoal D and its reference site showed significant differences in Sv and density 

between one another, with a split result. For relative biomass Shoal D was significantly higher in 

spring 03 and fall 03, but was significantly lower than the reference during both summer surveys 

(Figure 4-4). Fish density was significantly higher on the shoal during fall 03, but was lower 

during summer 03 (Figure 4-5). 

There were only very minor differences in target strength distributions between Shoal D 

and its reference in any surveys within a season (Figures 4-13 to 4-15). Shoal D and its 

reference site had very few targets during spring sampling (Figure 4-13). All targets were small 

(< 120 mm or -39 dB). In summer the distributions between the shoal and reference site were 

very similar (Figure 3-14). Fish up to -29 dB (> 390 mm) were found on both sites with the 

majority of fish under -44 dB or about 70 mm. In fall, larger targets comprised more of the 

frequency at Shoal D and its reference (Figure 4-15). Ranges in target strength were similar 

between the shoal and reference, although the fall 03 survey was very limited in numbers of 

targets. 

Fenwick Island Shoal

Relative fish biomass showed a seasonal pattern and indicated greater fish use of 

Fenwick Shoal than the reference (Figure 4-6). Fish biomass was lowest in spring and generally 

highest in summer surveys. In fall 02 the reference had significantly higher biomass than the 

shoal. However, in summer 03, fall 03, and spring 04, Fenwick Shoal had significantly higher 

fish biomass than the reference. Fish densities tended to be low in both spring surveys at 

Fenwick Shoal and its reference with higher values in summer and fall. However, fish density 

was only significantly different in two surveys (Figure 4-7). In fall 02 fish density was higher in 

the reference and in summer 03 fish density was higher at Fenwick Shoal. 

Size ranges and distributions between Fenwick Shoal and the reference were generally 

similar except during fall (Figures 4-16 to 4-18). In spring most fish were less than -42 dB (~80 

mm) although targets up to -32 dB was detected (Figure 4-16). Distributions showed two peaks 

in summer 03 at -48 and -42 dB. Summer 04 distributions ranged from -49 to -31 dB (Figure 4-

17). In fall 02 few targets were detected at Fenwick Shoal (Figure 4-18). The reference site 

showed a multimodal distribution ranging to -27 dB in fall 02, but was mostly smaller fish (< -43 

dB) in fall 03. The shoal had a greater number of larger targets in fall 03 than the reference 

suggesting greater use of the shoal by larger fish in fall 03. The opposite was observed at the 

Fenwick Reference where larger fish were recorded at the site in fall 02. 

Weaver Shoal

The relative biomass between Weaver Shoal and the reference site was significantly 

different during three surveys (Figure 4-8). On two occasions, spring 03 and summer 03, the 

relative biomass was higher on the shoal than on the reference and once (summer 04) the 
Statistical Analysis of Bioacoustic Survey Data 

 4-5 

reference was significantly higher than the shoal. Fish density was significantly higher at 

Weaver Shoal than the reference during the fall 02 and summer 03 surveys (Figure 4-9). 

During spring, the mode of target strengths at Weaver Shoal and reference were similar 

and dominated by smaller (-45 dB) targets, approximately 60-65 mm in length (Figure 4-19). 

Larger targets up to 350 mm (-31 dB) were detected at both sites. However, there does not 

appear to be anything in the length data that would suggest differences in size classes or species 

using the two sites. 

During summer, size distributions were similar between the two sites and the two surveys 

(Figure 4-20). Most fish were small (< 117 mm or -40 dB), with peaks in modes at -49 to -48 dB 

in both years. However, at the shoal a secondary modal peak at -42 to -41 dB was apparent in 

both years suggesting some differences in abundance of species in the 100-125 mm size range 

that may favor the shoal over the reference site. 

The fall surveys appear to show a higher use of larger targets at both sites (Figure 4-21). 

Targets extended from -50 to -25 dB on the shoal and -50 to -21 dB on the reference site. Most 

targets fell below -44 dB (75 mm) on both sites in fall 03. However, in fall 02 the reference site 

had very few targets in this smaller size group. Large targets were more common in fall02 than 

fall 03 at Weaver Shoal, a pattern similar to the reference site. 
4-6 

Table 4-1. Mean biomass (expressed as backscattering coefficient Sv in dB) and confidence limits for 

transects conducted during sampling at four shoals and four reference sites in the Atlantic O

coast of Maryland and Delaware from November 2002 to September 2004. 

Date/ Mean 95%CL Mean 95%CL Mean 95%CL Me

Survey Weaver Shoal Reference 

Date/ 

Survey Shoal D 

 Fall 2002 -57.8 3.4 -62.7 4.7 Fall 2002 -72.9 7.7 -67 Spring 2003 -74.3 7.5 -91.3 1.4 Spring 2003 -85.7 3.4 -91 Summer 2003 -59.2 1.5 -64.4 1.2 Summer 2003 -76.6 2.3 -61 Fall 2003 -69.1 5.7 -73.6 2.0 Fall 2003 -75.9 4.4 -81 Spring 2004 -77.7 4.6 -78.3 3.6 Spring 2004 -86.6 3.7 -88 Summer 2004 -62.4 0.8 -59.8 2.2 Summer 2004 -62.6 1.2 -59 Sum -400.5 -430.0 Sum -460.2 -450

Shoal B Reference Fenwick Shoal 

 Fall 2002 -72.9 5.9 -58.3 9.0 Fall 2002 -69.3 10.4 -54 Spring 2003 -79.8 2.9 -83.6 5.1 Spring 2003 -78.5 6.2 -78 Summer 2003 -63.9 5.3 -63.8 1.5 Summer 2003 -57.8 0.6 -63 Fall 2003 -70.6 4.0 -78.1 1.9 Fall 2003 -64.4 6.1 -73 Spring 2004 -92.8 5.8 -91.0 2.1 Spring 2004 -70.9 5.6 -87 Summer 2004 -59.6 0.7 -58.4 0.8 Summer 2004 -60.7 3.9 -59 Sum -439.5 -433.2 Sum -401.6 -416
4-7 

Table 4-2. Mean fish density per 10,000 m3 and confidence limits and confidence limits for all acousti

 conducted during sampling at four shoals and four reference sites in the Atlantic Ocean off 

 the coast of Maryland and Delaware from November 2002 to September 2004 

Date/ Mean 95%CL Mean 95%CL Mean 95%CL Me

Survey Weaver Shoal Reference 

Date/ 

Survey Shoal D R

 Fall 2002 208.2 143.4 35.6 49.3 Fall 2002 1.6 3.1 76. Spring 2003 19.6 34.3 0.8 0.3 Spring 2003 3.2 2.6 1. Summer 2003 382.6 89.8 169.2 33.3 Summer 2003 6.2 2.9 241. Fall 2003 198.5 252.3 28.8 14.9 Fall 2003 11.7 9.8 0. Spring 2004 4.3 2.4 7.2 4.6 Spring 2004 0.7 0.6 0. Summer 2004 206.1 53.2 370.5 178.0 Summer 2004 230.5 88.1 205. Sum 1019.2 612.1 Sum 253.9 524.

Shoal B Reference Fenwick Shoal R

 Fall 2002 14.7 21.3 515.3 544.7 Fall 2002 89.4 148.9 359. Spring 2003 2.1 2.2 0.6 0.6 Spring 2003 41.3 85.6 2. Summer 2003 226.7 244.1 108.8 42.3 Summer 2003 544.9 77.6 227. Fall 2003 63.5 53.9 9.6 6.0 Fall 2003 509.4 648.3 28. Spring 2004 0.3 0.4 0.3 0.4 Spring 2004 50.9 61.9 4. Summer 2004 598.2 130.6 533.9 171.8 Summer 2004 194.3 77.4 220. Sum 905.6 1168.5 Sum 1430.1 842.
Statistical Analysis of Bioacoustic Survey Data 

4-8 

Figure 4-1. The relationship of individual target strength of acoustic targets (dB) to fish 

length (mm) for fishes with swim bladders as described by Love (1977) for many 

species of fish at 120 kHz frequency. 

0

200

400

600

800

1000

1200

1400

-55 -50 -45 -40 -35 -30 -25 -20 -15

Target Strength (dB)

Fish Length (mm)
Statistical Analysis of Bioacoustic Survey Data 

4-9 

Figure 4-2. Relative biomass (Sv in dB) of fish detected with a 120 kHz hydroacoustic split 

beam system at Shoal B (open bars) and its reference site (diagonal striped bars) 

for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-120.000

-100.000

-80.000

-60.000

-40.000

-20.000

0.000

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Relative biomass (Sv, dB)

Shoal B

Reference

* *

*
Statistical Analysis of Bioacoustic Survey Data 

4-10 

Figure 4-3. Fish density (N per 10,000 m3

) of fish detected with a 120 kHz hydroacoustic split 

beam system at Shoal B (open bars) and its reference site (diagonal striped bars) 

for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-200

0

200

400

600

800

1000

1200

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Fish density (N per 10,000 m3

Shoal B

Reference

*
Statistical Analysis of Bioacoustic Survey Data 

4-11 

Figure 4-4. Relative biomass (Sv in dB) of fish detected with a 120 kHz hydroacoustic split 

beam system at Shoal D (open bars) and its reference site (diagonal striped bars) 

for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-120.000

-100.000

-80.000

-60.000

-40.000

-20.000

0.000

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Relative biomass (Sv, dB)

Shoal D *

Reference

*

*

*
Statistical Analysis of Bioacoustic Survey Data 

4-12 

Figure 4-5. Fish density (N per 10,000 m3

) of fish detected with a 120 kHz hydroacoustic split 

beam system at Shoal D (open bars) and its reference site (diagonal striped bars) 

for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-150

-100

-50

0

50

100

150

200

250

300

350

400

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Fish density (N per 10,000 m3)

Shoal D

Reference

*

*
Statistical Analysis of Bioacoustic Survey Data 

4-13 

Figure 4-6. Relative biomass (Sv in dB) of fish detected with a 120 kHz hydroacoustic split 

beam system at Fenwick Shoal (open bars) and its reference site (diagonal striped 

bars) for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-120.000

-100.000

-80.000

-60.000

-40.000

-20.000

0.000

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Relative biomass (Sv, dB) .. 

Fenwick Shoal

Reference

*

*

*

*
Statistical Analysis of Bioacoustic Survey Data 

4-14 

Figure 4-7. Fish density (N per 10,000 m3) of fish detected with a 120 kHz hydroacoustic split 

beam system at Fenwick Shoal (open bars) and its reference site (diagonal striped 

bars) for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-400

-200

0

200

400

600

800

1000

1200

1400

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Fish density (N per 10,000 m3) .

Fenwick Shoal

Reference

* *
Statistical Analysis of Bioacoustic Survey Data 

4-15 

Figure 4-8. Relative biomass (Sv in dB) of fish detected with a 120 kHz hydroacoustic split 

beam system at Weaver Shoal (open bars) and its reference site (diagonal striped 

bars) for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-100.000

-90.000

-80.000

-70.000

-60.000

-50.000

-40.000

-30.000

-20.000

-10.000

0.000

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Relative biomass (Sv, d

B

Weaver shoal

Reference

*

* *
Statistical Analysis of Bioacoustic Survey Data 

4-16 

Figure 4-9. Fish density (N per 10,000 m3

) of fish detected with a 120 kHz hydroacoustic split 

beam system at Weaver Shoal (open bars) and its reference site (diagonal striped 

bars) for each of 6 seasonal surveys. Error bars represent 95% confidence intervals 

about the mean. An asterisk (*) denotes a significant difference between the shoal 

and its reference in a given survey. 

-100

0

100

200

300

400

500

600

Fall 02 Spring 03 Summer 03 Fall 03 Spring 04 Summer 04

Survey

Fish density (N per 10,000 m3)

Weaver Shoal

Reference

*

*
Statistical Analysis of Bioacoustic Survey Data 

4-17 

Shoal B

0

0.2

0.4

0.6

0.8

1

1.2

-50.00-48.00-46.00-44.00-42.00-40.00

-38.00-36.00-34.00-32.00

-30.00-28.00

-26.00

-24.00-22.00

-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03

Shoal B Reference

0

1

2

3

4

5

6

7

8

-50.00-48.00-46.00

-44.00-42.00-40.00

-38.00

-36.00-34.00

-32.00

-30.00-28.00

-26.00

-24.00

-22.00

-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03

Figure 4-10. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during spring 03 and spring 04 sampling at 

Shoal B site and its reference area. Fish sizes are in decibels as measured with the 

acoustics. Using Love’s (1977) equation, these target strengths equate roughly to 

the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB 

is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 
Statistical Analysis of Bioacoustic Survey Data 

4-18 

Figure 4-11. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during summer 03 and summer 04 sampling 

Shoal B site and its reference area. Fish sizes are in decibels as measured with the 

acoustics. Using Love’s (1977) equation, these target strengths equate roughly to 

the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB 

is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Shoal B

0

20

40

60

80

100

120

140

160

-49.00-46.00-43.00-40.00-37.00

-34.00-31.00-28.00-25.00-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03

Shoal B Reference

0

50

100

150

200

250

-49.00

-46.00

-43.00-40.00

-37.00

-34.00

-31.00-28.00

-25.00

-22.00

-19.00

Target Strength (dB)

Frequency

Summer 04

Summer 03
Statistical Analysis of Bioacoustic Survey Data 

4-19 

Figure 4-12. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during fall 02 and fall 03 sampling at Shoal B 

site and its reference area. Fish sizes are in decibels as measured with the acoustics. 

Using Love’s (1977) equation, these target strengths equate roughly to the 

following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB is 

213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Shoal B

0

10

20

30

40

50

-50.00-47.00-44.00-41.00-38.00-35.00-32.00

29.00

-26.00-23.00-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02

Shoal B Reference

0

10

20

30

40

50

60

70

80

90

-50.00

-47.00-44.00-41.00

-38.00

-35.00

-32.00

29.00

-26.00

-23.00

-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02
Statistical Analysis of Bioacoustic Survey Data 

4-20 

Figure 4-13. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during spring 03and spring 04 sampling at 

Shoal D site and its reference area. Fish sizes are in decibels as measured with the 

acoustics. Using Love’s (1977) equation, these target strengths equate roughly to 

the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB 

is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Shoal D

0

0.5

1

1.5

2

2.5

-50.00

-47.00-44.00

-41.00-38.00

-35.00

-32.00-29.00

-26.00

-23.00-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03

Shoal D Reference

0

0.5

1

1.5

2

2.5

-50.00-47.00-44.00

-41.00-38.00

-35.00

-32.00

-29.00

-26.00

-23.00-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03
Statistical Analysis of Bioacoustic Survey Data 

4-21 

Figure 4-14. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during summer 03 and summer 04 sampling at 

Shoal D site and its reference area. Fish sizes are in decibels as measured with the 

acoustics. Using Love’s (1977) equation, these target strengths equate roughly to 

the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB 

is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Shoal D

0

10

20

30

40

50

60

70

-49.00-46.00

-43.00-40.00

-37.00

-34.00-31.00

-28.00

-25.00-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03

Shoal D Reference

0

50

100

150

200

250

300

350

400

-49.00

-46.00

-43.00

-40.00-37.00

-34.00

-31.00-28.00

-25.00-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03
Statistical Analysis of Bioacoustic Survey Data 

4-22 

Figure 4-15. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during fall 02 and fall 03 sampling at Shoal D 

site and its reference area. Fish sizes are in decibels as measured with the acoustics. 

Using Love’s (1977) equation, these target strengths equate roughly to the 

following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB is 

213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Shoal D Reference

0

2

4

6

8

10

-50.00

-47.00-44.00

-41.00

-38.00-35.00

-32.00

29.00

-26.00

-23.00-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02

Shoal D 

0

10

20

30

40

50

-50.00-47.00

-44.00-41.00-38.00-35.00-32.00

29.00

-26.00

-23.00-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02
Statistical Analysis of Bioacoustic Survey Data 

4-23 

Figure 4-16. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during spring 03 and spring 04 sampling at 

Fenwick Shoal site and its reference area. Fish sizes are in decibels as measured 

with the acoustics. Using Love’s (1977) equation, these target strengths equate 

roughly to the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 

mm; -35 dB is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 

1301.7 mm. 

Fenwick Reference

0

10

20

30

40

50

60

-47.00-44.00-41.00

-38.00-35.00-32.00

-29.00

-26.00-23.00

-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03

Fenwick Shoal

0

2

4

6

8

10

12

-47.00-44.00-41.00-38.00-35.00-32.00-29.00

-26.00-23.00-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03
Statistical Analysis of Bioacoustic Survey Data 

4-24 

Figure 4-17. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during summer 03 and summer 04 sampling at 

Fenwick Shoal site and its reference area. Fish sizes are in decibels as measured 

with the acoustics. Using Love’s (1977) equation, these target strengths equate 

roughly to the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 

mm; -35 dB is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 

1301.7 mm. 

Fenwick Shoal

0

50

100

150

200

250

300

-49.00-46.00

-43.00

-40.00-37.00

-34.00-31.00-28.00

-25.00-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03

Fenwick Reference

0

200

400

600

800

1000

1200

1400

-49.00-46.00

-43.00-40.00-37.00

-34.00-31.00-28.00

-25.00-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03
Statistical Analysis of Bioacoustic Survey Data 

4-25 

Figure 4-18. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during fall 02 and fall 03 sampling at Fenwick 

site and its reference area. Fish sizes are in decibels as measured with the acoustics. 

Using Love’s (1977) equation, these target strengths equate roughly to the 

following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB is 

213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Fenwick Shoal

0

10

20

30

40

50

60

70

-50.00-47.00

-44.00-41.00-38.00-35.00

-32.00

29.00

-26.00

-23.00-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02

Fenwick Reference

0

5

10

15

20

25

30

-50.00

-47.00-44.00

-41.00

-38.00

-35.00-32.00

29.00

-26.00

-23.00

-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02
Statistical Analysis of Bioacoustic Survey Data 

4-26 

Figure 4-19. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during spring 03 and spring 04 sampling at 

Weaver Shoal site and its reference area. Fish sizes are in decibels as measured 

with the acoustics. Using Love’s (1977) equation, these target strengths equate 

roughly to the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 

mm; -35 dB is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 

1301.7 mm. 

Weaver Reference

0

10

20

30

40

50

60

70

80

-50.00-47.00

-44.00

-41.00

-38.00

-35.00

-32.00

-29.00

-26.00

-23.00

-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03

Weaver Shoal

0

1

2

3

4

5

6

-50.00-47.00-44.00

-41.00-38.00

-35.00

-32.00

-29.00

-26.00

-23.00-20.00

Target Strength (dB)

Frequency

Spring 04

Spring 03
Statistical Analysis of Bioacoustic Survey Data 

4-27 

Figure 4-20. Seasonal size frequency distribution of fish satisfying individual target criteria from 

hydroacoustic transects (combined) during summer 02 and summer03 sampling at 

Weaver site and its reference area. Fish sizes are in decibels as measured with the 

acoustics. Using Love’s (1977) equation, these target strengths equate roughly to 

the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB 

is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm. 

Weaver Shoal

0

50

100

150

200

250

300

-49.00-46.00-43.00-40.00-37.00-34.00-31.00-28.00

-25.00-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03

Weaver Reference

0

200

400

600

800

1000

-49.00

-46.00

-43.00

-40.00

-37.00-34.00

-31.00

-28.00-25.00

-22.00

Target Strength (dB)

Frequency

Summer 04

Summer 03
Statistical Analysis of Bioacoustic Survey Data 

4-28 

Figure 4-21. Seasonal size frequency distribution of fish satisfying individual target criteria 

from hydroacoustic transects (combined) during fall 02 and fall 03 sampling at 

Weaver site and its reference area. Fish sizes are in decibels as measured with the 

acoustics. Using Love’s (1977) equation, these target strengths equate roughly to 

the following: -50 dB is 35.0 mm; -45 dB is 63.9 mm; -40 dB is 116.8 mm; -35 dB 

is 213.4 mm; -30 dB is 389.9 mm; -25 dB is 712.4 mm; and –20 dB is 1301.7 mm.

Weaver Shoal

0

5

10

15

20

25

30

-50.00-47.00

-44.00-41.00-38.00-35.00-32.00

29.00

-26.00-23.00

-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02

Weaver Reference

0

20

40

60

80

100

120

140

160

-50.00-47.00-44.00-41.00

-38.00-35.00-32.00

29.00

-26.00-23.00

-20.00

Target Strength (dB)

Frequency

Fall 03

Fall 02
Managed Species 

5-1 

5.0 MANAGED SPECIES 

Under the 1996 amendments to the Magnuson-Stevens Fishery Conservation and 

Management Act (MSFCMA) all federal agencies that fund, permit, or undertake activities that 

may adversely affect EFH are required to consult with the National Marine Fisheries Service 

(NMFS). The EFH guidelines encourage using existing interagency consultation procedures or 

environmental reviews that notify NMFS with an assessment of the effects of proposed actions 

on EFH, and no appropriate procedures exist, then the consultation process outlined in 50 CFR 

600.920 should be used. The lead Federal agency determines the effects of the proposed action 

on EFH, and if the action may have an adverse effect, then an EFH Assessment must be provided 

to the NMFS. Under the guidelines an adverse effect is “any impact that reduces quality and/or 

quantity of EFH, including direct (e.g. contamination and physical disruption), indirect (e.g. loss 

of prey, reduction in species’ fecundity), site-specific or habitat wide impacts, including 

individual, cumulative, or synergistic consequences of actions”. The length of the EFH 

Assessment can vary depending on the magnitude of the potential impacts to EFH (NMFS 2004). 

EFH has been identified for a total of 59 species covered by 14 fishery management plans 

(FMPs), under the jurisdiction of the New England Fishery Management Council, Mid-Atlantic 

Fishery Management Council, or the NMFS. EFH designated for federally managed species is 

primarily based on the geographic distribution of species densities inferred from survey data 

gathered over the last 40 years (Reid 1999). If the data is available, separate EFH designations 

are given for the four life-history stages of each species (i.e., eggs, larvae, juveniles, and adults). 

For juvenile and adult life stages of fish and mobile invertebrate species (squid), EFH 

designations are developed from trawl data averaged within 10-minute squares (of latitude and 

longitude) and mapped over the continental shelf. In general, four alternative EFH designations 

are calculated from the species distribution defined by these squares. They are the 100, 90, 75, 

and 50% of the total abundance over all years of the trawl surveys. For most species the 75% or 

90% distribution alternative is used as the definition of EFH (Reid 1999). 

The NMFS has designated the area where this study occurred as EFH for a total of 25 

fish and two invertebrate species (Table 5-1, NMFS web site 2006). From that group, a total of 

eleven fish and squid species were collected in this study. Several other fish species under 

management were also collected during the study and a comprehensive list of all the species 

under management collected in this study is presented in Table 5-2. Species with EFH 

designations collected in this study are highlighted. In addition, because we sampled with 

several nets of varying mesh sizes and species selectivity, Table 5-2 also indicates if juveniles or 

adult life stages were collected for species susceptible to multiple gears during those life stages. 

Most of the species under management were collected infrequently and in limited 

abundance. Except for possibly scup, winter skate, and squids, a limited review of the data does 

not indicate consistently higher or lower numbers of species under management at the shoals or 

reference sites. Most of the managed species were migratory species collected during seasonal 

migrations through the study area. Migratory species included six alosids, Atlantic and Spanish 
Managed Species 

5-2 

mackerel, three Sciaenid species, butterfish, striped bass, bluefish, cobia, and six shark species. 

Among the sharks, spiny dogfish was the only species collected in high numbers throughout the 

duration of the study. 

Several bottom dwelling demersal species, including red and silver hake, monkfish, black 

sea bass, scup and Atlantic cod were also collected in limited numbers during the study. Three 

flounder species were collected during the study, from which the windowpane was the most 

abundant. Some of the most abundant species collected in the study were skates. Overall, four 

skates were collected and from those the winter and little skate exhibited the highest abundance. 

In addition to fish, the horseshoe crab and squid were collected at the sites. Horseshoe 

crabs were collected throughout the study in limited number. Although squid were not identified 

to species level while in the field, most of the squid collected in the study were likely short and 

long-finned squid, of which both have management plans. 
5-3 

Table 5-1. List of fish and invertebrate species by life-stage for which the study area in the Atlantic 

the coast of Maryland and Delaware has been designated as Essential Fish Habitat by the 

Marine Fisheries Service. 

Taxonomic Name Common Name Eggs Larvae Juvenil

Clupea harengus harengus Atlantic herring X Centropristus striata Black sea bass X X Thunnus thynnus Bluefin tuna X Pomatomus saltatrix Bluefish X X Rachycentron canadum Cobia X X X Scomberomorus cavalla King mackerel X X X Lophius americanus Monkfish X X Urophycis chuss Red hake X X X Stenotomus chrysops Scup X Katsuwonus pelamis Skipjack tuna Scomberomorus maculatus Spanish mackerel X X X Paralicthys dentatus Summer flounder X X X Xiphias gladius Swordfish X Scopthalmus aquosus Windowpane flounder X X X Glyptocephalus cynoglossus Witch flounder X X Pleuronectes ferruginea Yellowtail flounder X Squatina dumerili Atlantic angel shark X X Rhizopriondon terraenovae Atlantic sharpnose shark Prionace glauca Blue shark Charcharinus obscurus Dusky shark X Odontaspis taurus Sand tiger shark X Charcharinus plumbeus Sandbar shark X X Sphyrna lewini Scalloped hammerhead shark X Isurus oxyrhyncus Shortfin mako shark X X Galeocerdo cuvieri Tiger shark X X Loligo pealei Long finned squid X Spisula solidissima Surf clam X 
Managed Species 

5-4 

Table 5-2. A list of fish species with management plans collected at four shoals and 

four reference sites in the Atlantic Ocean off the coast of Maryland and 

Delaware from November 2002 to September 2004. The study area is 

designated as EFH for highlighted species. 

Taxonomic Name Common Name Juvenile Adult

Alosa pseudoharengus Alewife X 

Alosa sapidissima American shad X 

Squatina dumeril Atlantic angel shark X 

Gadus morhua Atlantic cod X 

Micropogonias undulatus Atlantic croaker X X 

Clupea harengus harengus Atlantic herring X 

Scomber scombrus Atlantic mackerel X 

Brevoortia tyrannus Atlantic menhaden X 

Rhizoprionodon terraenovae Atlantic sharpnose shark X 

Raja laevis Barndoor skate X 

Centropristis striata Black sea bass X X 

Alosa aestivalis Blueback herring X 

Pomatomus saltatrix Bluefish X 

Peprilus triacanthus Butterfish X X 

Raja eglanteria Clearnose skate X 

Rachycentron canadum Cobia X 

Carcharhinus obscurus Dusky shark X 

Lophius americanus Monkfish X 

Alosa mediocris Hickory shad X 

Limulus polyphemus Horseshoe crab X 

Raja erinacea Little skate X 

Urophycis chuss Red hake X 

Carcharhinus plumbeus Sandbar shark X 

Stenotomus chrysops Scup X X 

Merluccius bilinearis Silver hake X 

Scomberomorus maculatus Spanish mackerel X 

Squalus acanthias Spiny dogfish X 

Leiostomus xanthurus Spot X 

Cephalopoda Squids X X 

Morone saxatilis Striped bass X 

Paralichthys dentatus Summer flounder X 

Alopias vulpinus Thresher shark X X 

Cynoscion regalis Weakfish X X 

Scophthalmus aquosus Windowpane X 

Pleuronectes americanus Winter flounder X 

Raja ocellata Winter skate X 
Discussion 

6-1 

6.0 DISCUSSION 

Previous studies of habitat relationships have focused on macro and micro-scale habitat 

features (Diaz et al. 2003) or species-specific life stages within a particular habitat of the MAB 

(Able and Fahay 1998; Slacum 2005), but studies linking marine biota to large natural physical 

features, such as sand shoals, are rare. In the present study, we compared differences in species 

abundance, species richness, species diversity and community guild abundances between sand 

shoals and nearby uniform-bottom habitats on the inner-continental shelf of the MAB. 

In general, the species collected at both habitats were comparable to those reported in 

other studies within the MAB (Musick et al. 1986; Diaz et al. 2003; Wirth 2001; Slacum 2005). 

There were extreme seasonal fluctuations in species distributions and abundance similar to those 

described in previous work (Colvocoresses and Musick 1984), with the highest diversity in the 

late summer and fall and the lowest in the winter. The multivariate cluster analysis conducted on 

the CPUE of all species shows a distinct difference in community composition between seasons, 

regardless of habitat (Figure 3-14). This is primarily due to the fact that the study area has one of 

the most extreme seasonal temperature ranges in the world, and the majority of the species 

collected in this study were highly migratory boreal or warm-temperate/subtropical species 

(Musick et al. 1986). Because of this, only a small percentage of the species encountered, 5 fish 

out of 57 and 2 invertebrates out of 17, were present or resident throughout all the seasonal 

surveys. 

In addition to seasonal differences, there were also differences in all catches between 

years. These differences were not site specific and occurred throughout the sites in every season. 

More than likely these differences were due to annual changes in recruitment (population 

fluctuations) of certain species and the timing when seasonal surveys occurred between years. In 

general, the species collected in a particular season during year one were similar to those present 

in the same seasonal samples of the following year, and it was only the abundances of those 

species that varied. For example, the first fall commercial trawl sample had similar species 

composition as the second year fall sample (Table C-15). For the most part the species 

composition did not vary between years. 

Based upon the net and bioacoustic surveys we determined there were distinct patterns in 

species abundances, species richness, species diversity and community guild abundance between 

the shoals and the reference sites. However, because each gear sampled a different portion of the 

species assemblages within each habitat (i.e., bioacoustics sampled fish with swim bladders at 

night), the patterns associated with each gear are somewhat different. The species distributions 

collected in the trawls indicates that the reference habitat is preferred over shoal habitat in the 

MAB. In fact, total species richness and total diversity values collected from commercial trawls 

were higher during every season at almost all the reference sites. Those same data also show no 

differences in mobile benthos between either habitat. In addition, gillnet data shows equal 

numbers of fish invertebrates at both habitats, suggesting that shoal habitat is not preferred over 

the reference site habitat for those species. 
Discussion 

6-2 

The analysis of the four faunal marine guilds found a similar trend in that shoals are not 

preferred over the reference site habitat. Both commercial and small trawls collected 

significantly higher abundances of benthic and pelagic fish species guilds at the reference sites, 

and there were no differences found between habitats in the gillnet data. These patterns were 

also shown in the multivariate analysis, which indicates differences in species composition 

between shoals and reference sites. These differences were due to several species in high 

abundance during seasonal samples. Species such a windowpane, butterfish, squid, and spotted 

hake were caught throughout seasonal samples and were consistently higher in abundance at the 

reference sites adding significantly to the abundance of both the benthic and pelagic finfish 

groupings. The abundance of benthic invertebrate (epi-benthic) groups between the two habitats 

showed no differences, also suggesting that shoals are not preferred by benthic invertebrate 

species when compared to the reference site habitat. 

The data from the net survey indicate that more species in higher abundances used the 

reference sites more so than the shoals. If this is the case and higher diversity and species richness are determinants of preferred habitat, then we would determine that fish, squid and mobile 

epi-benthos in the MAB, either have no preference or prefer the reference site habitat over the 

high relief sand shoals. Presumably fish would be using the reference habitats more than the 

shoals because there are more food resources available. The availability of food resources has 

been shown to influence fish distribution in many marine species (Rooker and Holt 1997). 

Jenkins and Hamer (2001) found that the distribution of King George whiting was influenced 

more by prey availability than the density of seagrasses. Prey abundance was also a significant 

component of age-0 winter flounder distribution models from studies conducted in a New Jersey 

estuary (Stoner 2001). A recent survey by Cutter and Diaz (2000) found uniform-bottom areas 

in the troughs next to Fenwick Island and Weaver shoal to be more biologically productive than 

areas on the crest of those shoals. Although the reference sites in our study were not as close to 

shoals as the deep areas sampled in the Cutter and Diaz (2000), the reference sites exhibited 

similar features and likely similar biological productivity. In this study, no diet or forage base 

information was collected, but if the uniform-bottom sites in this study were similar to those 

sampled in the Cutter and Diaz (2000) survey, then this could be why fish and squid prefer the 

reference sites over the shoals. However, information collected in the bioacoustic survey does 

not suggest that pelagic fish prefer the reference site habitats more that the shoals at night. 

The bioacoustic survey showed the majority of the time there were generally higher 

biomass and fish densities at shoals, but when tests were performed the analysis was split. 

Significantly higher biomass and fish densities were found at Fenwick Island and Weaver Shoal, 

and biomass and density values were equal or significantly lower the majority of the time at 

shoal D and B when compared to their reference pairs. An overview of the net and bioacoustic 

data presents no evidence indicating that more species susceptible to bioacoustics (i.e., fish with 

swim bladders) were present at Fenwick or Weaver shoal. In addition, because trawls and 

bioacoustics were not collected concurrently there is no way of knowing what species were 

present during the night, and it is conceivable that there could be a different species assemblage 

at night. Therefore, the fact that there is a somewhat conflicting pattern between night and day 

suggests that fish may be exhibiting a diel pattern of use at the shoals. That is, species numbers 

and species densities are different at the shoals in the day compared to the night. 
Discussion 

6-3 

There is a wealth of information pertaining to fish behavior or movements between habitats throughout the diel cycle (Helfman 1993; Wootton 1990). Most species are only active during limited periods in the diel cycle and within certain fish assemblages there are groups that 

exhibit different diel activity patterns (Helfman 1978). Many fish are only active at night, 

because of prey availability or because of predator avoidance during the day (Helfman 1993). In 

their study of juvenile fishes present on Fenwick Island Shoal, Diaz et al. (2003) showed through 

cluster analysis that different species assemblages were present on the shoal between day and 

night. In fact, the presence of fish in some habitats on the shoal was four times higher at night 

than in the day. Diaz et al. (2003) concluded that the fish are indeed exhibiting a diel behavior, 

by balancing the proximity of complex habitat found nearer to the troughs to the simpler habitats 

on the majority of the shoal. By doing this, fish are allowed greater refuge from predation during 

the day and can exploit shoal habitats with increased resources at night with less of a risk of 

predation (Diaz et al. 2003). Although the research conducted by Diaz et al. (2003) focused on 

juveniles (which would likely not be detected by the bioacoustic gear), it is plausible that larger 

predatory fish preying upon those smaller individuals would exhibit the same behavioral pattern 

of using the shoals to feed at night. In this case the data suggest that during the diurnal period 

fish prefer the reference sites, and at night the pattern was somewhat changed, with less variation 

in abundance between the habitats, and higher overall fish abundance on Fenwick Island and 

Weaver Shoal. 

The net survey data shows that fish preferred all four reference sites over the shoals, but 

the bioacoustics indicates only two shoals, Fenwick Island and Weaver, were preferred to the 

reference site habitat. One explanation for higher use at these two shoals could be the amount of 

relief exhibited by the shoals, because each of the four study shoals exhibits varying degrees of 

relief (Conkwright and Williams 1996; Conkwright et al. 2000). Weaver Shoal, which is the 

smallest shoal, also has one of the steepest slopes, and Shoal D is the deepest shoal and has the 

least extreme relief. Fenwick Island is more similar to Weaver in relief and has the steepest 

shoreward slope in the region (Swift and Field 1981). Shoal B is closer to shoal D with no 

extreme grading. The fact that Fenwick Island and Weaver Shoal exhibit some of the most 

extreme relief (i.e., large depth variation) between the study shoals could be why there are more 

fish at these shoals compared to shoal B and D. 

Although no studies could be found comparing the use of high relief habitat between 

night and day, there is a wealth of information regarding vertical relief and fish distribution 

(Brock 1954; Sale 1991; Williams 1990; Rilov and Benayahu 2000), however, depending on the 

species, not all the information suggests that relief alone is a determinant of higher fish use 

within a habitat (Frank and Shackell 2001; Snyder 2001; Anderson et al. 2005; Gratwicke and 

Speight 2005). Many other variables in addition to high relief have been shown to influence 

species distributions. For example, in a study of large offshore banks on the continental shelf of 

eastern Canada, Frank and Shackell (2001) showed that when using just the top of the banks, 

which exhibited little depth variation, there was no correlation with species richness, but when 

the slopes of the banks were figured into their analysis, thereby increasing the heterogeneity of 

depths within a bank, the high variation associated with depth was an important determinant of 

species richness. Another study by Anderson et al. (2005) using long-term trawl and detailed 
Discussion 

6-4 

bathymetric data found that juvenile haddock on the Eastern Scotian Shelf prefer habitats with 

more rugged surfaces at finer scales, indicating that preferred habitats may be more complex 

than areas that are not preferred. Both studies concluded that megascale relief associated with a 

shelf or bank is not as important as the variety of relief available at differing scales within those 

habitats. (Frank and Shackell 2001; Anderson et al. 2005). 

As a priori, the reference sites in this study were chosen based on macro and 

microhabitat similarities exhibited between them and the shoals. This was done to account for as 

much habitat variation as possible between the shoals and the paired reference sites so that if 

differences were detected, those differences would likely be due to the megascale relief and not 

differences associated with other habitat variables. This did not take into account the varying 

degree on habitat complexities within the shoals, but only similarities between the shoals and 

their chosen reference sites. In their benthic characterization of the study area habitats, 

Nestlerode and Diaz (2003) point out that many of the shoals and reference site habitats were 

patchy over multiple scales. Although, that characterization only documented the frequency and 

type of habitats at the shoals and not the proportion of habitats, if Fenwick Island or Weaver 

Shoal exhibit more complex habitats, it is likely that fish would prefer them to shoal D or B, 

although this cannot be determined from the current analysis. 

If fish are reacting to the larger megascale habitat complexity over the entire shoal, then 

the diversity of adjacent habitat may also be influencing the distribution of species as well. A 

recent study by Slacum (2005) conducted at several shoals and troughs within Maryland State 

waters, found that micro and macrohabitat features collected using underwater video techniques 

did not influence the distribution of adult summer flounder, rather, mesohabitat features such as 

shoals and trough bathymetry were possibly influencing distribution. That study concluded that 

mesohabitat features may be proxies for other features such as appropriate currents or the 

availability of prey items. 

 

The availability and proximity of food resources to Fenwick Island and Weaver shoal 

could also be influencing the distribution of fish in this study. The comprehensive survey 

conducted by Cutter and Diaz (2000) characterized the benthic communities on Fenwick Island 

and Weaver shoal and deeper adjacent areas. That characterization indicated that the deeper 

uniform-bottom areas surrounding the two shoals, especially the trough between the two shoals, 

were more biologically active and productive than were the tops of the shoals. Cutter and Diaz 

(2000) indicate that the area of greatest bathymetric change between the shoals is also the area 

with the most habitat diversity. Those areas surrounding the shoals might hold significant fish 

resources during the day, and as suggested by Diaz et al. (2003), if fish are using the more 

protected deeper trough areas during the day, and exploiting the resources on the shoals at night, 

the proximity of this habitat to the shoals might be influencing the higher biomass and densities 

at these two shoals compared to shoals B and D. However, again, because no similar 

information on benthic productivity is known from shoal B or D this cannot be determined from 

the current analysis. Therefore, the pattern of higher fish use of the Fenwick Island and Weaver 

shoals at night is clear, but the exact mechanism behind the higher use remains unclear. 
Conclusions and Recommendations 

7-1 

7.0 CONCLUSIONS AND RECOMMENDATIONS 

The primary objective of this study was to determine what species resided on shoals in 

the MAB, and to evaluate if the shoals represent important habitat for those species. To 

accomplish those objectives we sampled the shoals and reference sites using several nets and 

bioacoustics sampling techniques. 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: 

• Fish and squid occurring in the MAB either have no preference or prefer substrates at 

uniform-bottom types to sandy shoals during the day. 

• Benthic invertebrates have no preferences for shoals over uniform-bottom types. 

• There are diel (Day/Night) differences in the abundance of pelagic fish using the 

shoals and reference sites. 

In addition, we found that only two of the shoals, Fenwick Island and Weaver Shoal, 

exhibited higher fish use at night. Although the pattern of higher fish use is clear, the 

mechanism behind this pattern is not. As pointed out in our discussion, fish could be using the 

adjacent uniform-bottom habitats areas during the day and move onto the shoals at night to 

exploit new habitat, in which case shoals would represent an important resource for fish at night. 

However, it is clear that not all the shoals are preferred by pelagic fish at night, which suggests 

that all shoals are not alike or there are other factors influencing higher fish use of Fenwick 

Island and Weaver shoals. Therefore, if these shoals are to be used as sand resources for future 

beach nourishment activities, we recommend using the precautionary approach as outlined by 

Auster (2001), which advocates minimizing impacts until more information can be gathered as to 

why Fenwick Island and Weaver shoal were preferred over shoal B and D at night. 

 

There are several data gaps that need to be filled before a full evaluation of the shoal 

habitat can be completed. This would involve more data collection and the use of existing data 

sets to further refine comparisons between the shoals. To aid in the interpretation of the 

bioacoustic data, nighttime commercial trawling should be conducted over the same sites for one 

year (i.e., four seasons). Because trawl data was not collected concurrent with the bioacoustic 

data there is no way of knowing what species were actually using the shoals at night. It is 

reasonable to assume that there were fish present on the shoals and reference sites that were not 

ensonified by the acoustics either because they have no swim bladder or they do not move up 

into the water column at night. In this study only daytime net surveys were conducted, therefore 
Conclusions and Recommendations 

7-2 

we do not know whether significant day night differences in abundance and species composition 

occurs with fish or other bottom dwelling species that could not be quantified by the 

hydroacoustic equipment. 

In addition, using existing data in conjunction with data from this study and other new 

data would enhance the further interpretation of the ecological value of the shoals. For example, 

benthic community data collected by Cutter and Diaz (2001) at Fenwick Island and Weaver 

shoals could be used to establish a trophic linkage between the shoals and the communities 

associated with them. However, this data is not available for shoal B and D and must be 

collected for a thorough evaluation to be completed. Food habits data from fish would also help 

with establishing trophic linkages between the shoals and associated species, but that data is 

currently missing as well. Data from the habitat characterization in this study and other relevant 

habitat data from Cutter and Diaz (2001) survey and Maryland Geologic Survey (2004) could be 

used to determine the overall habitat complexity associated with the shoals. This information 

would help to determine if differences in habitat complexity associated with individual shoals 

might be influencing species distributions. 

Until a more thorough evaluation of the shoals can be done, the best way to minimize 

impacts to biological resources dependent on the shoals would be to conduct sandmining 

activities in a way that insures that the habitat diversity associated with the shoals remains intact 

to some extent. We agree with Diaz et al. (2004), who suggest avoiding total removal of 

surficial substrates in such a way that habitat patches are left behind. This is beneficial not only 

because it preserves habitat diversity on the shoals, but will also leave representative patches of 

established benthic species and facilitate recolonization by providing a local source of potential 

recruits. Facilitating rapid recolonization of a mined site by established community members 

would minimize alteration of community structure and function and reduce potential effects upon 

trophically dependent fishes (Diaz et al. 2004). 
References 

8-1 

8.0 REFERENCES 

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Atlantic Bight. Rutgers University Press New Brunswick, New Jersey, U.S.A. 

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influence fish guilds composition using a back-propagation network: Assessment of 

metrics for indices of biotic integrity. Ecological Modelling 160:281-290. 

Anderson, J.T., J. E. Simon, D.C. Gordon, and P.C. Hurley. 2005. Linking Fisheries to Benthic 

Habitats at Multiple Scales: Eastern Scotian Shelf Haddock. In: P.W. Barnes and J. P. 

Thomas (eds.), Benthic habitats and the effects of fishing. AFS Symposium 41:251-264.

Antia, E.E. 1996. Shoreface-connected ridges in German and US Mid-Atlantic bights: 

similarities and contrasts. J. Coastal Res. 12, 141–146. 

Auster, P.J. 2001. Defining Thresholds for Precautionary Habitat Management Actions in a 

Fisheries Context. North American Journal of Fisheries Management 21: 1-9. 

 

Auster, P.J., K. Joy, and P.C. Valentine. 2001. Fish species and community distributions as 

proxies for seafloor habitat distributions: the Stellwagen Bank National Marine Sanctuary 

example (Northwest Atlantic, Gulf of Maine). Environmental Biology of Fishes. 60:331-

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Auster, P.J., R.J. Malatesta, and S.C. LaRosa. 1995. Patterns of microhabitat utilization by 

mobile megafauna on the southern New England (USA) continental shelf and slope. 

Marine Ecology Progress Series. 127:77-85. 

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