Northeast Fisheries Science Center Reference Document 09-11

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Northeast Fisheries Science Center

Woods Hole, Massachusetts

July 2009

Ecosystem Status Report

For the Northeast U.S. Continental Shelf Large Marine Ecosystem

by the Ecosystem Assessment Program

Northeast Fisheries Science Center

166 Water Street

Woods Hole, MA 02543
Northeast Fisheries Science Center Reference Documents

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Ecosystem Assessment Program. 2009. Ecosystem Assessment Report for the Northeast 

U.S. Continental Shelf Large Marine Ecosystem. US Dept Commer, Northeast Fish 

Sci Cent Ref Doc. 09-11; 61 p. Available from: National Marine Fisheries Service, 

166 Water Street, Woods Hole, MA 02543-1026, or online at http://www.nefsc.noaa.

gov/nefsc/publications/
Ecosystem Status Report 

For the Northeast U.S. Continental Shelf Large Marine Ecosystem 

Ecosystem Assessment Program, Northeast Fisheries Science Center July 2009

Main Findings 

The Northeast U.S. Continental Shelf Large Marine Ecosystem (NES LME) has undergone 

sustained perturbations due to environmental and anthropogenic impacts over the last 

four decades, resulting in fundamental changes in system structure. 

Thermal conditions in the NES LME are changing due to warming of coastal and shelf waters 

and cooling in the northern end of the range. As a consequence, there has been a 

constriction of thermal habitats in the ecosystem, a northward shift in the distributions of 

some fish species and a shift to a warmer-water fish community. 

Zooplankton community structure has also changed in concert with climate and physical 

processes acting over the North Atlantic Basin indicating the importance of remote 

forcing to the function and structure of this ecosystem 

Important changes in some components of benthic communities, notably increased 

abundance of sea scallops and lobster are evident, reflecting changes in fishery 

management and/or ecological conditions. 

The direct and indirect effects of species-selective harvesting patterns have also contributed to 

shifts fish community composition which is now dominated by small pelagic fishes and 

elasmobranch species (skates and small sharks) of low relative economic value. 

The trajectory of regional human population size suggests that anthropogenic pressure in the 

ecosystem will continue to increase. 

The Northeast U.S. Continental Shelf is classified as experiencing ecosystem overfishing 

according to published criteria for this designation, although improvement in the 

condition of several resource species has occurred and exploitation effects have been 

reduced for some system components over the last decade. 

Contents 

1 Introduction............................................1 

2 Climate Forcing ......................................2 

3 Physical Pressures ..................................4 

4 Primary and Secondary Production ... 11 

5 Benthos ................................................ 17 

6 Upper Trophic Levels ......................... 19 

7 Anthropogenic Factors....................... 22 

8 Integrative Ecosystem Measures ....... 25 

Summary ................................................. 29 

Literature Cited ...................................... 30 

Further Information............................... 33 

Acknowledgments ................................. 33 

Glossary................................................... 33 

1 Introduction 

The Northeast U.S. Continental Shelf Large 

Marine Ecosystem (NES LME) is a dynamic, highly 

productive, and intensively studied system providing 

a broad spectrum of ecosystem goods and services [1, 

2]. This region, encompassing the continental shelf 

area between Cape Hatteras and the Gulf of Maine 

(Figure 1.1), spans approximately 250,000 km2 and 

supports some of the highest revenue fisheries in the 

nation. The system has historically undergone 

profound changes due to very heavy exploitation by 

distant-water and domestic fishing fleets [3]. Further, 

the region has experienced changes in climate and 

physical forcing that have contributed to large-scale 

alteration in ecosystem structure and function. 

Projections of future climate change highlight the 

need to understand the effects of natural and 

anthropogenically driven perturbations to this system 

and to devise effective management and mitigation 

strategies in response to these changes. 

In this report, we track changes in key 

indicators of climate, physical forcing, ecosystem 

dynamics, and the role of humans in this system. 

These indicators can be broadly classified into natural 

and anthropogenic drivers, resulting pressures, and 

ecosystem states (see Glossary). Drivers are 

identified as forcing factors such as climate and 

 1 
Figure 1.1 Map of study region on the Northeast continental shelf of 

the United States. 

Driver Pressure 

State 

Impact 

Response 

Identify major 

human and 

natural 

factors affecting 

Ecosystem. 

Organize 

relevant 

data. Select key 

Indicators of 

Ecosystem 

t t

Link ecosystem 

status 

indicators 

 to drivers 

Evaluate ecological, 

social & economic 

impacts 

of management 

Adaptive 

management 

Ecosystem 

Indicators 

Ecological 

Forecasts & Models 

Risk 

Management 

Evaluation 

Figure 1.2 Driver-Pressure-State-Impact-Response sequence. 

human population size underlying a constellation of 

pressures exerted on the system. These pressures 

include human-related impacts such as removal or 

degradation of living marine resources through 

harvesting, shipping, pollution, and impacts on the 

coastal zone such as habitat loss. Climate-related 

pressures include changes in atmospheric and 

oceanographic processes directly or indirectly 

affecting marine life. We distinguish external 

physical pressures representing large-scale oceanatmospheric processes affecting this system from 

internal physical pressures as representing local or 

regional physical manifestations of these broader 

pressures. We then identify indicators of ecosystem 

state potentially affected by these drivers and 

associated pressures with a focus on holistic or 

integrative metrics of ecosystem condition. State 

variables include metrics such as the abundance of 

different species groups and measures of 

productivity. 

Changes in ecological state variables can 

result in impacts on ecosystem services which in turn 

may require a management response (Figure 1.2). 

For example a driver such as changes in seafood 

demand, might result in increased fishing pressure to 

meet this demand, leading to a change in the 

abundance (state) of exploited species with an impact

on the economic value of the catch. This would then 

be followed by a specified management response. 

Our objective is to characterize changes in the 

system state variables in relation to these forcing 

mechanisms and to identify change points in system 

dynamics. An understanding of the inter-relationships 

between drivers, pressures and states is an essential 

prerequisite to moving toward an ecosystem 

approach to management. 

2 Climate Forcing 

Climate patterns over the North Atlantic are 

important drivers of oceanographic conditions and 

ecosystem states. Steadily increasing atmospheric 

carbon dioxide levels can not only affect climate on 

global and regional scales but alter critical aspects of 

ocean chemistry. Here, we describe the atmospheric 

forcing mechanisms related to climate in this region 

including large-scale atmospheric pressure systems, 

natural ocean temperature cycles in the North 

Atlantic, components of the large-scale circulation of 

the Atlantic Ocean, and issues related to ocean 

acidification. 

North Atlantic Oscillation Index 

Climate and weather over the North Atlantic 

are strongly influenced by the relative strengths of 

two large-scale atmospheric pressure cells -- the 

Icelandic Low and the Azores High [4]. As the 

relative strengths of these two pressure systems vary, 

characteristic patterns of temperature, precipitation, 

and wind fields are observed. An index of this dipole 

pattern has been developed based on the standardized 

difference in sea level pressure between Lisbon, 

Portugal and Reykjavík, Iceland in the winter 

(December-February; see Glossary for a description 

of methods used to create standardized indicators). 

This North Atlantic Oscillation (NAO) index has 

 2 
Figure 2.1 Trends in the winter North Atlantic Oscillation Index over 

the last century expressed as standardized anomalies. 

 

Figure 2.2 Trends in the Atlantic Multidecadal Oscillation Index 

expressed as standardized anomalies. 

been related to key oceanographic and ecological 

processes in the North Atlantic basin [5]. 

When the NAO index is high (positive NAO 

state), the westerly winds shift northward and 

increase in strength. Additionally, there is an 

increase in precipitation over southeastern Canada, 

the eastern seaboard of the United States, and 

northwestern Europe. Water temperatures are cool 

off Labrador and northern Newfoundland, 

influencing the formation of Deep Labrador Slope 

water, but warm off the United States. Conversely, 

when the NAO index is low (negative NAO state), 

there is a southward shift and decrease in westerly 

winds, decreased storminess, and drier conditions 

over southeastern Canada, the eastern United States, 

and northwestern Europe. Water temperatures are 

warmer off Labrador and Newfoundland, but cooler 

off the eastern United States. Since 1972, the NAO 

has primarily been in a positive state (Figure 2.1), 

although notable short-term reversals to a negative 

state have been observed during this period. Changes 

in the NAO have been linked to changes in plankton 

community composition in the North Atlantic, 

reflecting changes in both the distribution and 

abundance of warm and cold-temperate species. 

Atlantic Multidecadal Oscillation 

Multidecadal patterns in sea surface 

temperature (SST) in the North Atlantic are 

represented by the Atlantic Multidecadal Oscillation 

(AMO) index. The AMO signal is based on spatial 

patterns in SST variability after removing the effects 

of anthropogenic forcing on temperature, revealing 

natural long term cycles in SST. The AMO is 

characterized by warm and cool phases [6] with 

periods of approximately 20-40 years. The AMO 

index is related to air temperatures and rainfall over 

North America and Europe and is associated with 

changes in the frequency of droughts in North 

America and the frequency of severe hurricane 

events. The AMO is thought to be related to the 

North Atlantic branch of the deep thermohaline 

circulation (for more see The Gulf Stream below) 

which is in turn directly related to dynamics of the 

Gulf Stream. 

The AMO index shows a relatively cool 

period starting in the early 1960s, extending through 

the mid 1990s. Since 1997, the AMO has been in a 

warm phase (Figure 2.2). If past patterns continue to 

hold, the warm phase will potentially continue for the 

next several decades. 

Carbon Dioxide Levels 

Carbon dioxide (CO2 ) emissions have 

increased rapidly from the inception of the industrial 

age as a result of burning of fossil fuels and other 

human activities (Fig. 2.3). The rate of addition of 

this greenhouse gas is an order of magnitude greater 

than any observed over the last million years [7]. 

This increase in emissions has led to increases in 

atmospheric CO2, which holds important implications 

for oceans chemistry and the ecology of marine 

systems. Approximately 40% of emitted CO2 has 

been absorbed by the ocean, buffering the effect on 

atmospheric levels but resulting in increases in 

 3 
Figure 2.3 Trends in estimated North American CO2 emission and 

globally averaged marine surface atmospheric CO2 concentrations 

(annual mean; parts per million). 

dissolved CO2 and a concomitant decrease in pH of 

ocean waters. Dissolved CO2 is critical in 

photosynthesis and primary production, fueling the 

base of marine food webs. Further, dissolved CO2 is 

used to form tests, shells and otoliths of some marine 

phytoplankton and animals ranging from mollusks to 

fish. 

Uptake of CO2 has resulted in ocean 

acidification, potentially disrupting the ability of 

organisms to form calcium carbonate structures as 

noted above and affecting the biogeochemical cycles 

of many compounds. Chemical speciation of 

phosphorus, nitrogen, and other elements that are 

essential to ocean productivity is also affected by 

increasing acidification (see Glossary for further 

information on biogeochemical cycles and chemical 

speciation). Ocean acidification may also affect 

oxygen saturation levels, resulting in hypoxia in 

coastal systems. The full consequences of ocean 

acidification for living marine resources are not fully 

understood, but the ecological and economic impacts 

of decreasing pH levels are potentially very high. 

Broad-scale time series of ocean pH 

measurements are not currently available to assess 

the effects of ocean acidification in this region. 

However, agreement between atmospheric CO2 and 

dissolved CO2 in ocean waters is good in regions 

where estimates of both are available. Globally 

averaged marine surface atmospheric CO2 has 

increased 13.2% since 1981 (Figure 2.3). 

3 Physical Pressures 

The physical environment of the NES LME is 

impacted by climatic drivers in two ways. First, as 

noted above, climate oscillations (e.g., NAO, AMO) 

and long-term trends (e.g., warming, acidification) 

affect the larger North Atlantic environment. These 

large-scale environmental pressures affect the 

internal physical environment of the NES LME, but 

also external pressures at its boundaries. The external 

pressures include the Gulf Stream at the southern and 

offshore boundary, the Labrador Coastal current at 

the northern boundary, riverine discharges at the land 

boundary and winds at the atmospheric boundary. In 

addition to these external pressures, climate processes 

also affect the internal physical environment directly, 

including temperature, salinity, and stratification. 

These physical pressures in turn cause various 

ecosystem changes, which are discussed in sections 

4-6. 

The Gulf Stream 

The Gulf Stream system is an important 

component of global climate and an important 

physical pressure on ecosystems in the North 

Atlantic. The Gulf Stream carries much of the heat 

from the tropics to higher latitudes and results in 

milder climates in Europe compared to similar 

latitudes in North America (for example Ireland vs. 

Labrador). This warm water then cools at high 

latitudes and sinks, forming a deep southward cold 

current that balances the northward warm surface 

current. This process of deep thermohaline 

circulation known as the Meridional Overturning 

Circulation and plays an important role in regulating 

the earth’s climate. 

Measuring the Meridional Overturning 

Circulation is difficult owing to the large-scale nature 

of the circulation system and the variability in the 

system at short-time scales. One long-term index is 

the volume transport of the Florida Current which has 

been measured from the early 1980s to the present 

[8]. The Florida Current is part of the southern 

portion of the Gulf Stream system and previous 

analyses of this data series found a negative 

relationship between the NAO and Florida Current 

transport. The suggested mechanism is that a positive

 4 
Figure 3.1 Trends in the Florida Current transport and Latitude of the 

Gulf Stream Index expressed as standardized anomalies. 

Figure 3.2 Trends in volume transport of the Labrador Current along 

southwest Newfoundland and the percent of Labrador Subarctic 

Slope Water in the Northeast Channel of the Gulf of Maine (as 

anomalies). 

NAO results in wind patterns that reduce the volume 

transport of the Gulf Stream system one year later 

[9]. During the mid 1990s when the NAO was 

strongly positive, Florida Current transport was low 

(Figure 3.1). The link between Florida Current 

transport and the NAO has reduced in recent years 

indicating that the relationship is not simple and 

involves, other, yet to be defined factors. 

Changes in NAO are also related to shifts in 

the position of the north wall of the Gulf Stream 

which in turn affects plankton community 

composition (see Climate Drivers, Physical 

Pressures, and Zooplankton Community Structure 

below). The latitude of the Gulf Stream north wall is 

positively related to the NAO index with a lag of 

approximately two years. Further examination of this 

relationship reveals that the correlation is dominated 

by the influence of the Icelandic low pressure system 

with the Azores High playing a relatively minor role 

[10]. Taylor et al. [11] subsequently showed that 

consideration of El Niňo-Southern Oscillation 

(ENSO) events further increases the predictability of 

the Gulf Stream position. An index of the position of 

the North Wall of the Gulf Stream available since 

1966 reveals a shift in the early 1980s from low to 

high index values (Figure 3.1), reaching a peak in the 

mid-1990s, but characterized by subsequent 

multiyear reversals related to changes in the NAO 

index. 

Labrador Slope Water 

The Labrador Current flows southward from 

the Labrador Sea around Newfoundland and down 

the Nova Scotian shelf into the NES LME. This 

inflow is an important physical pressure and 

contributes to the volume of shelf water, the addition 

of nutrients, and the transport of plankton in the 

ecosystem. When the NAO is in a positive state, the 

volume transport of Labrador-Subarctic Slope Water 

(LSSW) is relatively low and does not penetrate 

much beyond the Gulf of St. Lawrence basin. When 

the NAO is in a negative state, volume transport of 

the Labrador Current is high and the LSSW 

penetrates to the Mid-Atlantic Bight, displacing 

Atlantic Temperate Slope Water (ATSW) further 

offshore [12]. During these low NAO conditions, the 

amount of LSSW entering the Gulf of Maine through 

the Northeast Channel is high. 

The NAO index was low during the mid1950s to early 1970s and was high during the late1980s and 1990s. Over the last decade, there have 

been two major drops in the NAO index (late-1990s, 

mid-2000s). These drops in the NAO are associated 

with increases in the volume transport of the 

Labrador Current [13] and in the influx of LSSW into 

the Gulf of Maine at lags of approximately 12-18 

months - the time it takes for the LSSW to reach the 

northeast shelf from northern Canadian waters 

(Figure 3.2). These changes hold important 

implications for the ecology of the region because the 

LSSW is colder and lower in critical nutrients than 

the ATSW. 

 5 
River Flow 

The amount of freshwater entering the ocean 

is another important pressure that responds to 

climatic drivers. Freshwater transports pollutants and 

nutrients to the continental shelf, which can affect 

coastal ecosystems. Nutrient over-enrichment – 

termed eutrophication – is a major problem in many 

coastal systems and has been linked to increased 

algal biomass, including harmful algae species, 

hypoxia/anoxia, and increased water turbidity. 

Increased freshwater run off can also affect coastal 

circulation through the influx of less dense water on 

the continental shelves. Most freshwater enters 

marine systems through rivers, rather than direct 

precipitation or runoff. River flow is tightly 

correlated across the northeastern region, resulting in 

coherent freshwater forcing along the entire coastal 

boundary (Figure 3.3). Complex long-term patterns 

have been identified. Tootle et al. [14] found 

interactions among different climate drivers affecting 

river flow; for example, the AMO and ENSO (El 

Niňo Southern Oscillation) signals combine to affect 

river flow in the southern part of the region. Earlier 

work by Visbeck et al. [15] found links between river 

flow in the northeast and NAO. A time series of river 

flow suggests the effect of multiple factors (Figure 

3.3). Earlier in the time series (1950-1970) there 

appears to be one long cycle of 18-20 years. 

However, after the late-1970s, the period and 

magnitude of oscillations appeared to decrease. 

Recent years, 2005 and 2006 have had high stream 

flows. 

Winds 

Winds are an important pressure on shelf 

ecosystems. They act to mix the water column and 

drive horizontal currents. In the NES LME, winds are 

responsible for breaking down seasonal stratification 

in the fall and for causing reversals in the general 

southwestward surface currents during summer. The 

NOAA Pacific Fisheries Environmental Group 

maintains records of wind stress over the global 

ocean: wind stress is the force of the wind on the 

surface of the ocean. The greater the wind stress, the 

more horizontal mixing and the more force for 

driving currents. These long-term records indicate 

substantial inter-annual variability in wind stress 

(Figure 3.4). Over the past 10 years wind stress has 

been higher, but has recently decreased. Similarly, 

Figure 3.3 Trends in river flow from 25 rivers in the Mid-Atlantic, 

Southern New England and Gulf of Maine regions. Data presented 

as annual anomalies. 

Figure 3.4 Annual averages of monthly mean wind stress. Top panel 

shows the magnitude of wind stress; middle panel shows the eastwest component of wind stress, and bottom panel shows north-south 

component of wind stress. 

the amount of eastward wind stress (wind force from 

west to east) is also variable. In the northern part of 

the system, wind stress has been primarily from the 

west, but has switched from the west to the east in the 

southern part of the system. Southward wind stress is 

 6 
Figure 3.5 Annual mean sea surface temperature anomaly for the 

northeast U.S. continental shelf and adjacent waters from the 

ERSST v3 dataset. 

Figure 3.6 Mean surface (red) and bottom (blue) temperatures from 

the NEFSC survey programs. Anomalies show the mean value for 

1977-1987 as 0, above the mean as positive and below the mean as 

negative (see Mountain [3]) 

also variable, but has increased in the south and 

decreased in the north. These changes in wind stress 

may be linked to the NAO, as well as a northward 

shift in the location of the jet stream [16]. Despite the 

uncertainty as to the cause of the inter-annual 

variability, these changes in wind will have impacts 

on local physical conditions and local marine 

resources. 

Temperature 

Temperature is one of the most important 

governing environmental factors for marine 

organisms. Marine organisms have minimum and 

maximum temperatures beyond which they cannot 

survive. Additionally, they have preferred 

temperature ranges. Within the bounds of these 

thermal limits, temperature influences many 

processes including metabolism, growth, 

consumption, and maturity. Thus, changes in 

temperature will have far-reaching impacts on 

species in the ecosystem and on the ecosystem itself. 

Temperature in the NES LME has varied 

substantially over the past 150 years (Figure 3.5). 

The late 1800s and early 1900s were the coolest in 

the 150 year record. This relatively cool period was 

followed by the warmest period in the record: 1945-

1955. There was a rapid drop in temperatures through 

the 1960s followed by a steady increase to the 

present. Current temperatures are not as warm as 

experienced during the early 1950s, but they are 

within half-a-degree. Temperatures from specific 

coastal sites along the U.S. northeast coast follow this 

same pattern [17]. 

Temperatures measured on the continental 

shelf by the Northeast Fisheries Science Center 

(NEFSC) tell a slightly different story (Figure 3.6). 

These measurements have been made since the late 

1970s, so the time series are shorter. Measurements 

from within 5 m of the surface exhibit an increase 

from the early 1980s to the present and mirror the 

temperature patterns described above. Temperatures 

from within 10 m of the bottom appear similar to 

surface temperatures, but there is no long-term trend. 

Rather, there is multi-decadal variation on the order 

of 2°C. 

Satellite-derived maps of annual mean SST 

available since 1985 reveal interesting spatial 

patterns of annual differences in temperature. We’ve 

selected three years to illustrate different conditions 

on the shelf (expressed as deviations from the 

average for 1998-2008). Sea surface temperature 

was uniformly warm on the shelf in 1999 (Figure 3.7 

upper). In contrast, cool shelfwide temperatures 

prevailed in 2004 relative to the average conditions 

during 1998-2008 (Figure 3.7 middle). In 2007, most 

of the shelf system was close to the average 

temperature except for southern Georges Bank and 

the Scotian Shelf which were colder than average 

(Figure 3.7 bottom). Other years also reveal regional 

 7 
differences in temperature conditions that reflect 

more localized variation. 

Temperature trends on the shelf and in coastal 

waters are resulting in changes in the availability of 

thermal habitat for marine life. There has been an 

overall increase in the area occupied by warm waters 

(≥16°C) by about 10% over the period 1982-2008 

(Figure 3.8). Similarly, the area occupied by colder 

water (≤4°C) has increased by approximately 20%; 

this increase was most pronounced from the early 

1980s to mid-1990s. The increase in the areas of the 

warmest and coldest thermal habitat has squeezed the 

area of intermediate thermal habitat (5-15°C). The 

decrease in intermediate thermal habitat has been 

consistent throughout the time series and has totaled 

a 15-20% reduction. Thus, cold temperate species are 

experiencing a general reduction in available habitat 

and warm-temperate species are experiencing and 

general increase. In addition, strictly cold water 

species may be experiencing an increase in habitat. 

Average Temperature Preference of Finfish 

 

As water temperatures increase, we expect 

fish species that prefer cool waters (cold-temperate 

species) in the ecosystem to respond by shifting their 

distribution northward to avoid warm waters. We 

would also expect that their abundances will 

decrease. However, species that prefer warm water 

(warm-temperate species) will also shift their 

distribution northward, but will likely increase in 

abundance. An indicator of this multifaceted biotic 

response to warming temperature is the mean 

preferred temperature of the fish community (Figure 

3.9). The preferred temperature of the community 

was calculated by weighting the mean preferred 

temperature of each species by its biomass for both 

the spring and fall surveys. The mean preferred 

temperature of the community can be seen as an 

indicator of three processes; a change in water 

temperature, a change in community assemblage, and 

a change in the spatial distribution of fish stocks. 

 S i m i l a r t o d i r e c t m e a s u r e m e n t s o f 

temperature, mean preferred temperature of the fish 

community has increased over both the fall and 

spring bottom trawl time series. While the preferred 

temperature of the spring fish community has shifted 

by approximately 0.5°C over the 40-year spring time Figure 3.7 Sea surface temperature patterns for the northeast 

continental shelf for selected years (1999 upper; 2004 middle; and 

2007 lower). Temperatures expressed as deviations from average 

conditions during 1998-2008). 

 8 
Figure 3.8 Amount of thermal habitat expressed as a proportion of 

the maximum amount of thermal habitat observed over the time 

series. Original data were in 1°C bins and were grouped here based 

on a preliminary analysis of common time trends. 

Figure 3.9 Mean preferred temperature of the finfish community (°C) 

for the Fall (red) and Spring (blue) NEFSC multispecies bottom trawl 

surveys. 

series, the preferred temperature of the fall 

community has increased by almost 2°C over the 45-

year fall time series. This indicates that the fish 

community of the NES LME has shifted such that 

warm-water species are more abundant than coldtemperate species. Because the southern boundary of 

many cold-temperate species and the northern 

boundary of many warm-water species occurs within 

the ecosystem, this indicator suggests that the 

boundary between these two assemblages has shifted 

northward such that the area occupied by warm-water 

species is greater than the area occupied by coldtemperate species. 

Distribution Shifts 

To illustrate shifts in northward distribution 

patterns of some fish species, we show the spatial 

distribution of red hake in the NES LME for three 

time periods; 1968-1980 (Figure 3.10 upper) 1981-

1994 (Figure 3.10 middle) and 1995-2008 (Figure 

3.10 lower). Red hake is a cold-temperature species 

whose center of biomass has shifted poleward over 

time as temperatures have increased. Abundance of 

red hake steadily diminished on the outer shelf region 

of the Middle-Atlantic Bight and now is principally 

concentrated in the western Gulf of Maine. 

Salinity 

Most aquatic organisms also are affected by salinity – 

the amount of salt in the water. Organisms in 

nearshore environments are adapted to wide ranging 

salinities owing to the interaction between freshwater 

(salinities of 0) and ocean-water (salinities in the 

30s). However, many organisms found on the 

continental shelf, slope and deep-sea are sensitive to 

small changes in salinity because they are adapted to 

more constant conditions. The NEFSC has also been 

measuring salinities on the continental shelf since the 

mid-1970s (Figure 3.11). Surface and bottom 

salinities track similarly with general decreases in 

salinity from the mid-1970s to the late-1990s. From 

the late 1990s into the early 2000s there were slight 

increases in salinity, followed again by decreasing 

salinity in recent years. 

Stratification 

During much of the year, portions of the NES 

LME are stratified. Stratification is a term for layers 

 9 
Figure 3.10 Distribution of red hake on the northeast continental 

shelf for three time periods; 1968-1980 (upper), 1981-1994 (middle), 

and 1995-2008 (lower) based on NEFSC spring bottom trawl 

surveys. 

Figure 3.11 Mean anomaly of surface (red) and bottom (blue) 

salinities from the NEFSC survey programs. Anomalies show the 

mean value for 1977-1987 as 0, above the mean as positive and 

below the mean as negative (see Mountain [3]). 

Figure 3.12 Mean annual stratification over the northeast U.S. 

continental shelf measured as the density different between the 

surface and 50 m (NEFSC). Anomalies show the mean value for 

1977-1987 as 0, above the mean as positive and below the mean as 

negative. 

of water of different densities stacked on top of one 

another. If there is no stratification, density is 

uniform throughout the water column and mixing is 

uninhibited. If denser water overlays less dense 

waters, the denser waters sink thereby mixing the 

water column (this occurs as the surface ocean cools 

in the fall). If less dense waters overlays more dense 

water, the water column is stable and it takes some 

kind of force to mix the water column. The greater 

the stratification, the greater the difference in density 

 10 
from the surface to depth, and the more force 

required to mix the water column. The issue of 

stratification is important, because deeper waters are 

often nutrient rich, thus increased stratification makes 

it harder for these nutrient rich waters to make it to 

the surface where they can be used by primary 

producers. The major components of water density 

are salinity and temperature. Thus, the NEFSC 

measurements of temperature and salinity (Figures 

3.6 and 3.11) can be used to measure stratification. 

Stratification decreased from the mid-1970s to mid1980s and then increased again (Figure 3.12). The 

temporal pattern in stratification is similar to that of 

surface temperatures and thus, the ecosystem-wide 

patterns in stratification seem to be linked to the 

warming of surface layers (e.g., less dense) and the 

relatively constant temperatures at depth (e.g., 

constant density). However, low salinity pulses move 

through the system from north to south over 1-2 year 

periods, and thus the effect of salinity is blurred in 

this ecosystem-wide stratification measure. In 

regional representations (e.g., in the Gulf of Maine), 

the effects of both temperature and salinity on 

stratification would be clearer. 

4 Primary and Secondary Production 

. 

Trends in Primary Production 

Primary production of the NES LME is 

governed by the photosynthetic activity of a wide 

range of phytoplankton species. Phytoplankton is the 

base of the aquatic food web and globally accounts 

for nearly half of the total photosynthesis on the 

planet with the balance of global production coming 

from terrestrial sources [18, 19]. Though some of the 

photosynthetically-derived organic matter within the 

NES LME originates from outside the ecosystem, 

these inputs are minor. For example, some organic 

materials derived from estuarine phytoplankton, 

terrestrial plants, and submerged aquatic vegetation 

enters the ecosystem with river discharges. 

One proxy measure of phytoplankton biomass 

is the concentration of chlorophyll in the water 

column. Shipboard sampling for phytoplankton in 

the NES LME is not sufficient to provide a 

comprehensive depiction of phytoplankton biomass 

in the entire ecosystem, nor is it representative of the 

complete annual production cycle. However, we can 

characterize these parameters using ocean color 

Figure 4.1 Annual mean chlorophyll concentration (red symbols) and 

primary production (blue symbols) for the Northeast Shelf Large 

Marine Ecosystem. 

remote sensing data, which provides much greater 

spatial and temporal coverage compared with shipbased sampling. In 2008, the mean chlorophyll 

concentration in the NES LME was approximately 

1.6 mg m-3 which is the highest annual concentration 

of the satellite data time series (Figure 4.1). 

Chlorophyll concentration has varied over the last 

decade; chlorophyll increased in the late 1990s, 

declined between 2000 and 2004, and subsequently 

increased to the maximum observed in 2008. 

A key limitation with the use of satellite data 

is that it only represents the concentration of 

chlorophyll in the upper part of the water column. In 

some seasons, parts of the ecosystem can develop 

subsurface chlorophyll maxima due to the limited 

availability of nutrients in the upper part of the water 

column. As a result, surface chlorophyll 

measurements may underestimate the total water 

column biomass. There are, however, specific 

phytoplankton models that use surface chlorophyll 

measurements to estimate chlorophyll concentrations 

throughout the water column. 

Measures of chlorophyll concentration have a 

number of ecological applications. The biomass 

represents the standing crop available for grazing by 

zooplankton and other primary consumers. The 

amount of phytoplankton biomass in the water 

column, particularly during seasonal bloom events, is 

a useful predictor of the rate of energy flow from the 

pelagic zone to the benthos. Many of the resource 

species of the NES LME are benthic organisms and 

are dependent on mechanisms to transfer energy from 

the pelagic zone to the benthos [20]. Additionally, 

 11 
satellite derived chlorophyll can be incorporated into 

models that relate the standing stock of 

phytoplankton biomass to the rate of carbon fixation. 

Marine primary production is the rate at 

which dissolved inorganic carbon (CO2) is 

photosynthetically fixed by phytoplankton into 

organic carbon such as carbohydrates and sugars. 

Primary production is a fundamental biological 

parameter that affects global carbon cycling, trophic 

food-web dynamics, and ecosystem health [18, 19]. 

In addition to chlorophyll concentration, production 

models use other satellite derived parameters such as 

the amount of photosynthetically available solar 

radiation and sea surface temperature. The average 

primary production of the NES LME is 

approximately 0.85 grams carbon m-1 day-1 (Figure 

4.1). Trends in annual primary production mirror 

those of the chlorophyll concentration, including the 

peak production rate in 2008. 

Spatial Distribution of Chlorophyll 

Strong spatial and interannual differences in 

annual chlorophyll concentration are evident in 

satellite-derived maps of the NES LME. For 

example, Figure 4.2 shows chlorophyll concentration 

patterns for the three years corresponding to those 

selected for temperature change on the shelf (Figure 

3.7). In 1999, chlorophyll levels were higher than the 

1998-2008 average in the Gulf of Maine and on 

Georges Bank, but below average in the southern 

Middle Atlantic Bight (Figure 4.2 upper). By 

comparison, chlorophyll concentrations were 

uniformly below average on the shelf in 2004 with 

the exception of the Nantucket Shoals-Northwestern 

Georges Bank region (Figure 4.2 middle). In 2007, 

chlorophyll concentrations were lower in the western 

Gulf of Maine and Bay of Fundy but above average 

in the central-Middle-Atlantic Bight and 

southwestern Georges Bank (Figure 4.2 lower). 

Annual Phytoplankton Cycle 

The abundance of phytoplankton changes 

seasonally, alternating between bloom and interbloom periods (Figure 4.3). The seasonal biomass 

cycle for the NES LME shows the highest 

abundances associated with the spring bloom period. 

The winter period has a minor peak in January 

followed by relatively low levels of chlorophyll 

through early March. The spring bloom on the shelf 

Figure 4.2 Chlorophyll concentration patterns for the northeast 

continental shelf for selected years (1999 upper; 2004 middle; and 

2007 lower). Chlorophyll expressed as deviations from average 

conditions during 1998-2008).

 12 
Figure 4.3 Annual chlorophyll biomass (green symbols) and primary 

production (blue symbols) seasonal cycles for the Northeast Shelf 

Large Marine Ecosystem. 

Figure 4.4 Seasonal bloom intensity and magnitude for the 

Northeast Shelf Large Marine Ecosystem. 

usually begins in April and lasts for 4-6 weeks. The 

summer inter-bloom period is typically a period of 

low chlorophyll concentrations primarily due to 

nutrient limitation. The fall period can be highly 

variable year to year and can be represented by a 

period of gradually increasing chlorophyll 

concentrations or marked by distinct bloom events in 

some parts of the ecosystem. 

The annual cycle of primary production 

differs from that of chlorophyll in that it reflects 

changes in phytoplankton photosynthesis rather than 

changes in phytoplankton biomass. The spring 

bloom appears as a secondary peak to the summer 

maximum that dominates the production cycle 

(Figure 4.3). The summer maximum in primary 

production is the result of greater available solar 

radiation that limits production in other times of the 

year. Thus higher rates of primary production can be 

maintained with relatively low levels of 

phytoplankton biomass. An active area of research is 

attempting to quantify the fraction of the summer 

production that is available to higher trophic levels. 

Plankton blooms can be quite variable which 

affects the way pelagic and benthic resources use the 

primary production associated with the bloom. To 

quantify these characteristics, two measures of bloom 

size are used; chlorophyll intensity and chlorophyll 

magnitude, which respectively reflect the 

concentration and duration of the bloom. Bloom 

intensity is the mean chlorophyll concentration for 

the seasonal time period in a region. Bloom 

magnitude is the mean chlorophyll concentration for 

a seasonal time period multiplied by the duration of 

the time period. In some years, the time period start 

or stop dates were not obvious from the annual data, 

in these cases the climatological time period was 

used instead. 

The intensity and magnitude of the 

phytoplankton component of the food web for the 

winter period were relatively low for 2008 despite the 

high annual levels of chlorophyll shown for the entire 

year (Figure 4.4). The winter period bloom intensity 

was approximately 1.6 mg m-3, with lowest values in 

the time series at approximately 1.3 mg m-3 in 2008. 

Bloom magnitude follows that same trend as bloom 

intensity for the winter bloom period. Winter bloom 

activity may hold importance to a number of species 

that have young that feed early during the spring. 

The spring bloom period is a dominant feature 

of the phytoplankton cycle over most of the 

Northeast Shelf. Though the duration is short, the 

timing of the bloom is considered critical to many 

species. The spring period is a time of high 

phytoplankton concentration, which provides the 

food resource for zooplankton grazers. However, the 

bloom often produces phytoplankton concentrations 

in excess of what can be used in the water column, 

thus providing material for the benthos. Compared to 

other bloom periods, the spring bloom has a greater 

 13 
intensity but lower magnitude due to the short 

duration of the bloom (Figure 4.4). Bloom intensity 

and magnitude are not well correlated during the 

spring bloom period, reflecting the highly variable 

nature of the spring bloom. In 2008, the spring 

bloom was about average, with respect to the 11-year 

time series. 

The summer interbloom period is the longest 

period, but is characterized by relative low 

chlorophyll concentrations. The summer has the 

greatest amount available sunlight, so despite lower 

chlorophyll intensity levels, it is the period of highest 

primary production. The data for the summer bloom 

(Figure 4.4) largely mirror the time series trends seen 

in the annual mean chlorophyll concentration and 

primary production for the entire ecosystem (Figure 

4.1). The summer 2008 interbloom intensity level 

was the second highest in the time series, while the 

bloom magnitude was close to the mean. 

The fall bloom period is an important and 

sometimes overlooked part of the production cycle 

that is affected by many factors, including weather 

events, that mix nutrients into the euphotic zone. In 

some parts of the ecosystem, such as the Gulf of 

Maine and Georges Bank, the fall bloom is a distinct 

event of equal or greater size than the spring bloom. 

In some years, however, the fall bloom does not fully 

develop and thus there is no temporal or spatial 

phytoplankton event that can be considered a fall 

bloom. In some parts of the ecosystem, such as the 

Middle Atlantic Bight, the fall production period is a 

continuous part of the winter production cycle; 

though a period of higher production it is not really a 

distinct bloom event. As with the spring bloom, the 

enhanced chlorophyll concentration results in periods 

of enhanced benthic flux, delivering energy to the 

benthic portion of the ecosystem. The 2008 fall 

bloom intensity was the highest in the time series 

(Figure 4.4), while the fall bloom magnitude was 

about average. The fall magnitudes tend to be second 

only to the summer magnitude values. 

Mean daily primary production rates were 

computed for the same bloom periods as determined 

from the chlorophyll biomass seasonal cycle (Figure 

4.5). The annual primary production seasonal cycle 

is dominated by the peak in production associated 

with the summer and the high amount of solar 

radiation that occurs during that time of the year. 

There is often a second peak in production associated 

Figure 4.5 Primary production rates associated with the partitioned 

production cycle for the Northeast Shelf Large Marine Ecosystem. 

with the spring bloom, but the seasonal cycle of 

primary production is not as structured as the 

chlorophyll cycle. The seasonal trends in mean 

primary production reflect the mean annual trend, 

especially the spring and summer production periods. 

The primary production rates are lowest during 

winter. The 2008 winter primary production rate was 

close to the seasonal mean for the time series, thus 

winter production was not a major contributor to the 

overall system production. 

In summary, phytoplankton productivity has 

been increasing in recent years and by a number of 

production indices it appears 2008 is among the most 

productive years the ecosystem has experienced over 

the past decade. This increase represents on the order 

of a 20% increase in energy input into the ecosystem 

since the localized minimum in production that 

occurred in 2004. 

Color Index 

Another measure of phytoplankton abundance 

is the Continuous Plankton Recorder (CPR) Color 

Index. The CPR is a mechanical instrument that is 

towed behind merchant vessels. Water enters the 

 14 
Figure 4.6 Standardized color index from three Continuous Plankton 

Recorder routes on the northeast U.S. shelf ecosystem: across the 

Gulf of Maine (1961-present), from New York to Bermuda (1977-

present), and across Georges Bank (1992-present). 

Figure 4.7 Time series of annual zooplankton biovolume from the 

northeast U.S. continental shelf ecosystem. Approximately 600-800 

samples are included annually. Biovolume is log-transformed and 

then averaged across all samples. 

CPR and is filtered through a piece of silk. The silk 

slowly advances as the CPR moves through the water 

and thus a continuous record of plankton 10 m below 

the surface is recorded. The color of the silk is 

assessed relative to standard color charts to estimate 

the quantity and density of phytoplankton, thereby 

providing an indicator of overall abundance of 

phytoplankton. This method is very selective 

because the mesh of the silk is large relative to the 

size of most phytoplankton, thus the index is best 

viewed as a measure of the abundance of larger 

phytoplankton (e.g., diatoms and large 

dinoflagellates). 

Although this index is crude compared with 

satellite measures of chlorophyll concentration, the 

CPR color index has been used since the early 1960s 

providing a longer time series. Three CPR routes are 

operated in the NES LME. Combining the color 

index data from these three routes shows an overall 

decline in color (and by proxy larger phytoplankton) 

over the series (Figure 4.6). This decline in larger 

phytoplankton has important implications for food 

webs in the ecosystem and may indicate a shift to 

smaller phytoplankton in recent decades (e.g., smaller 

dinoflagellates). 

Zooplankton Abundance 

The energy produced by phytoplankton is 

transferred via three main pathways. Some energy is 

transported directly from the water column to the 

bottom fueling benthic production. A recent study 

hypothesizes that this route is responsible for high 

recruitment of the 2003 year-class of haddock [21]. 

Unfortunately, there is little long-term data to 

evaluate the direct contribution of primary production 

to benthic habitats nor to overall benthic productivity. 

Future research and observations are needed owing to 

the potential importance of this route to fisheries 

production in the ecosystem. 

A second pathway of energy from primary 

production is remineralization by bacteria and 

microzooplankton – the so called microbial loop. 

Some of this energy remains in the microbial loop, 

some sinks to the benthos, and some is consumed by 

zooplankton. Although very little data exists on 

bacteria and microzooplankton in the NES LME, the 

microbial foodweb is believed to be extremely 

important in the energy flow on Georges Bank [22]. 

The third route of energy produced by 

phytoplankton is consumption by zooplankton. 

Traditionally, this energy route has been the most 

studied and NEFSC has been monitoring zooplankton 

abundance and species composition since the 1970s. 

These monitoring efforts involve deploying a small 

(61 cm diameter), fine meshed (333 μm) net at 

numerous locations throughout the ecosystem. The 

net is deployed from the surface to near the bottom, 

providing an integrated sample through the entire 

water column. Currently, the NEFSC’s sampling 

includes six surveys with ~120 stations over the 

whole ecosystem; these surveys are designed to 

 15 
capture seasonal and annual trends, but not smallerscale variability. 

One measure of zooplankton abundance is the 

volume of material collected in the net, termed 

zooplankton biovolume (Figure 4.7). This relatively 

simple indicator is related to the amount of 

zooplankton biomass. Levels of zooplankton 

biovolume have been remarkably consistent over the 

past 20 years with some inter-annual variability. In 

the early years of the time series, there was a marked 

drop and recovery in zooplankton abundance, with 

variable but near constant values since the late 1980s. 

The pattern of a decrease in the early 1980s, recovery 

in the late-1980s and fluctuating but near constant 

values through to the present is also seen through 

much of the seasonal cycle (Figure 4.8). This pattern 

is not as obvious in July-August, in part because of 

missing data in the late-1980s and early 1990s. This 

pattern also is not found in the winter months (JanFeb). Zooplankton biovolume and thus secondary 

production is at its lowest in winter, and highest 

winter biovolumes were observed in the early 1990s. 

Another measure related to secondary 

production is the absolute number of copepods 

(Figures 4.9). Copepods, microscopic animals 

related to lobsters and crabs, are the primary grazers 

on phytoplankton and microzooplankton, and are the 

primary food source for forage fishes (e.g. herring 

and mackerel) and for young groundfishes (e.g., cod, 

haddock). Copepods are also an important food 

source for many baleen whales and the endangered 

right whale feeds primarily on a species of copepod – 

Calanus finmarchicus – which is very rich in lipids. 

The total number of copepods in the spring was 

relatively low and decreased from the late 1970s to 

early 1990s. Abundance then increased and has been 

fairly constant since. The decrease and recovery 

early in the time series is more evident in copepod 

abundance in the fall, than the spring. Interestingly, 

fall abundance has also been declining since about 

2000, diverging from the nearly constant levels in 

spring copepod number. 

Recent work has found that the composition 

of the zooplankton community has changed over time 

[23]. Specifically, several species of small copepods 

increased in abundance in the 1990s resulting in an 

increase in total zooplankton abundance. The 

community composition changed again around 2000 

consistent with the drop in zooplankton abundance in 

Figure 4.8 Time series of seasonal zooplankton biovolume from the 

northeast U.S. continental shelf ecosystem. Approximately 100-150 

samples are included in each two month period in each season. 

Biovolume is log-transformed and then averaged across all samples. 

Figure 4.9 The abundance of copepods per 100 m3 on the northeast 

U.S. continental shelf ecosystem in spring and fall based on 

approximately 100-150 samples each season. Time series for the 

spring and fall are shown because sampling coverage through time 

was best during these seasons.

 16 
Figure 4.10 The abundance of five species of copepods per 100 m3

on the northeast U.S. continental shelf ecosystem in spring based on 

approximately 100-150 samples each season. 

Figure 4.11 Trends in zooplankton size index, salinity, percent 

Labrador Slope Water, Gulf Stream location, and NAO. All data are 

presented as anomalies to standardize the y-axis scale and a 10 

year smoother was applied to emphasize decadal trends. NAO was 

adjusted 2 years forward and shelf salinity was adjusted 3 years 

back based on a cross-correlation analysis. Zooplankton size index 

is an indicator of the abundance of small copepods (C. typicus, C. 

hamatus, T. longicornis, and Psuedocalanus spp.) compared to 

large copepods (C. finmarchicus). 

the fall. Individual copepod species can serve as 

indicators of these broader changes in overall species 

composition (Figure 4.10). During the spring, 

Pseudocalanus spp., Temora longicornis, 

Centropages typicus, and Centropages hamatus were 

all more abundant in the 1990s compared to the 

1980s and the 2000s. Calanus finmarchicus was 

more abundant during the 1990s and 2000s compared 

to the 1980s. 

Climate Drivers, Physical Pressures, and 

Zooplankton Community Structure 

 Zooplankton community structure is linked to 

both climate drivers and physical pressures. At the 

decadal scale, increase in the NAO, northward 

movement of the Gulf Stream, decreases in Labrador 

Slope Water and decreases in salinity are linked to 

changes in zooplankton community structure (Figure 

4.11). This chain of drivers, pressures, and state 

responses indicates that the northeast U.S. shelf 

ecosystem is affected significantly by remote climate 

forcing [12]. That said, the specific processes that 

result in changes in zooplankton community structure 

remain unresolved and the implications for the 

remainder of the ecosystem are unclear. 

5.1 Benthos 

The organisms that live on the bottom or 

directly in the sediments are referred to as benthos. 

As noted earlier, benthic animals play an important 

role in energy transfer in marine systems. Benthic 

species such as mollusks filter phytoplankton and 

suspended detritus from the water column while other 

groups depend on the organic content of sediments or 

detritus that has reached the seafloor for their 

energetic needs (e.g. certain species of marine 

worms). Other benthic organisms, such as sea stars, 

are predators on mollusks and other benthic species. 

The benthos also comprises important prey items of 

fish and larger crustaceans. Over two thousand 

species of benthic invertebrates have been identified 

on the Northeast Continental shelf although most are 

relatively rare. Benthic species of the NES LME 

(including lobsters, crabs, scallops, clams, and sea 

urchins) support major commercial and recreational 

fisheries, including some of the highest revenue 

fisheries in the region. 

 17 
Temporal Trends of Selected Species 

Information on longer term trends in 

abundance is available only for selected 

commercially and recreationally important benthic 

species based on directed research vessel surveys and 

related stock assessments. The sea scallop, 

Placopectin magellanicus, the highest value fishery 

in the NES LME, has increased dramatically in 

abundance over the last decade (Figure 5.1). This 

dramatic overall increase is related to the 

implementation of effective management measures 

including reductions in fishing effort, constraints on 

crew size, gear restrictions, and the establishment of 

long-term closed areas in late 1994. Population 

estimates of the ocean quahog, Arctica islandica, 

indicate a sharply declining population trend over the 

last decade and a half (Figure 5.1) following a more 

modest decline since 1980. In contrast, estimates of 

population size of the surf clam Spisula solidissima 

show a general increase until the mid to late 1990s 

followed by a sharp decline. The relative abundance 

of the American lobster Homarus americanus on the 

NES LME has increased markedly over the last two 

decades (Figure 5.1) until 2004 after which there has 

been an overall decline in NEFSC bottom trawl 

survey indices for this species. An aggregate 

assemblage of crab species, including the 

commercially harvested red crab (Geryon 

quinquidens), the jonah crab (Cancer borealis) and 

the rock crab (Cancer irroratus) exhibit high 

variability and no clear trend in NEFSC trawl 

surveys. 

Fish Diets as Indicators of Change in the Benthos 

Some species are known or suspected to be 

important in the dynamics of the food web [24] but 

are not routinely surveyed to assess changes in their 

abundance. One way to compensate for this is to use 

fish as ‘samplers’ [25, 26] for groups that are 

understudied, under-sampled or otherwise underdetermined. We can calculate an index of relative 

abundance from the percent frequency of occurrence 

of these organisms in the stomachs of major 

predators in the food web. Many fish species 

consume food items in proportion to the abundance 

of the prey although other factors such as the 

availability of alternative prey can sometimes also be 

important. Examples of the representation of some 

Figure 5.1 Trends in abundance of sea scallops based on NEFSC 

scallop surveys, American lobster and crab species based on 

NEFSC bottom trawl surveys, and surf clam and ocean quahog 

stock assessment models. 

Figure 5.2 Index of relative abundance for macrobenthos species 

groups (3 yr blocks). Indices are based on using fish predators as 

samplers, representing how often one of these organism groups 

occurs in stomachs of fish sampled in this ecosystem.

 18 
important macrobenthic groups in the diets of 

selected fish ‘samplers’ are provided in Figure 5.2. 

The estimates derived in this way exhibit substantial 

variability but also demonstrate a broad coherence 

among the fish species used as samplers. Among the 

echinoderms, sea cucumbers show a decline followed 

by a recent increase in the diets of several predators. 

Starfish generally varied without trend at low levels, 

except for showing a decline in ocean pout, Brittle 

stars, sea urchins and sand dollars similarly varied 

without trend at relatively low levels, except for 

urchins showing a decline in haddock and sand 

dollars showing an increase in ocean pout. Finally, 

we note a general decline in hermit crabs in the diet 

of a number of predators over time (Figure 5.2). The 

importance of monitoring change in benthic 

communities is well recognized [27] and the direct 

and indirect sampling methods described here for 

benthos of the NES LME meet a critical need. 

6 Upper Trophic Levels 

This section provides a community-level 

perspective on changes in fish populations over time 

to complement more traditional species-based 

approaches (c.f. http://www.nefsc.noaa.gov/sos/). We 

focus on species groups for which consistent time 

series information (i.e., extending a decade or more) 

are available. We note that continuous time series 

data are not generally available for major species 

groups such as marine mammals, sea birds, and sea 

turtles in this region and these groups are not further 

analyzed here. Because of their ecological 

importance, however, we do provide information on 

projected consumption of fish and other prey items 

by marine mammals as one indicator of their role in 

ecosystem structure and function. 

Integrative measures can provide further 

insights into how an ecosystem responds to a wide 

range of pressures and drivers. This “big picture” 

view of the biotic components of the food web 

provides a better sense of relationships among its 

component species and processes of energy flow 

within this ecosystem. 

 The species comprising a community and 

those targeted by a fishery can be characterized by 

how they are partitioned into different habitats. For 

example, demersal fish (species such cod, haddock, 

and flounders) are found in near-bottom waters or 

associated with the seabed. In contrast, pelagic fish 

Figure 6.1 Ratio of pelagic to demersal fish species caught in 

NEFSC autumn bottom trawl surveys. 

Figure 6.2 Ratio of lower tropic level feeding guilds, Planktivores and 

Benthivores, to upper trophic level feeding guilds, Piscivores and 

Shrimp-Fish feeders, biomass caught in NEFSC bottom trawl surveys. 

Figure 6.3 Mean length (cm) of all finfish species caught in NEFSC 

bottom trawl surveys. 

 19 
(species such as herring and mackerel) are typically 

found higher in the water column. An index of the 

ratio of pelagic to demersal fish provides important 

insights into relative changes in these two major 

groups of fish and pathways of energy flow (Figure 

6.1;[28, 29]). At a coarse level, this ratio indicates 

where energy is processed in the ecosystem. In the 

1960s, the demersals were dominant in the 

ecosystem. This was followed by a more even ratio 

in the 1970s to early 1980s (reflective of declines in 

demersals and increases in pelagics; c.f. Fig. 6.7). 

Then, in the 1990s, the pelagics dominated fish 

biomass before declining in the early 2000s. Pelagics 

are now beginning to increase to a ratio double that 

of demersals. 

An alternative way to explore pathways of 

energy flow is by partitioning the fish community 

into various feeding guilds. The ratio of planktivores 

and benthivores to piscivores and shrimp-fish feeders 

(Figure 6.2) shows changes in the relative importance 

of lower and upper trophic level fish groups 

(planktivores and benthivores are generally lower 

trophic level feeders, implying that there is less 

energy needed to make their food; c.f. Figure 6.3). 

The groups are also distinguished by relative size 

(usually piscivores—fish that eat other fish—tend to 

be larger species). During the earlier part of the time 

series, the ratio was below 1.0 with less feeding at 

lower trophic levels, implying an imbalanced food 

web [28]. Since the mid 1990s, the ratio has been 

higher than 1.0 indicating that there are relatively 

fewer fish feeding on other fish, and by implication, a 

shift towards lower trophic levels, more prominence 

of invertebrate prey, and likely smaller fish in the 

ecosystem. 

We can also characterize the fish community 

and species of commercial and ecological 

significance with respect to their size distribution [28, 

29]. An indicator of overall mean length, taken from 

the lengths of all finfish species caught in fisheries 

independent surveys, shows the size composition of 

the entire fish community (Figure 6.3). There was a 

decline of almost one half from the 1960s to mid 

1970s from an average fish size of approximately 30 

cm (~12 inches) to 17 cm (~6 1⁄2 inches). There has 

been some change thereafter, but effectively the 

mean size of fish has been between 15 and 20 cm for 

the past 30 years, with only recent signs of an 

increasing trend. This would indicate that the 

average size of fish in this entire ecosystem has 

Figure 6.4 Average trophic level of all finfish species caught in 

NEFSC bottom trawl surveys. 

Figure 6.5 Estimated total consumption of selected marine mammal 

species (million mt). 

declined. It appears that fishing pressure on larger 

organisms has resulted in declines in their average 

size while there has also been an increase in smaller 

bodied fish (particularly small pelagic fish such as 

herring and mackerel; see Figure 6.1). 

The ‘trophic level’ of a species (its place in 

the food web) is an important aspect of understanding 

not only the (implied) size of species in an 

ecosystem, but also the transfer of energy in the 

system [27]. We can determine the trophic level of a 

species by examining its diet. It is then possible to 

determine the mean trophic level in the sampled 

community by weighting the trophic levels of 

individual species by their abundance (biomass) and 

averaging over all species. 

 20 
Figure 6.6 Estimates of biomass for highly migratory species (top) and 

indices of abundance for two major sharks (bottom, CPUE) for the 

northwest Atlantic. 

The mean trophic level is an indicator of how 

much energy is transferred to species feeding higher 

in the food web. The mean trophic level of species 

captured in the NEFSC bottom trawl surveys has 

remained relatively stable over time (average TL= 

4.05) but has varied from lower values in the late 

1960s to mid 1980s and a slightly increasing trend in 

recent years (Figure 6.4). 

Consideration of feeding by selected marine 

mammal species provides important insights into 

upper trophic level processes. Consumption was 

calculated based on survey estimates of marine 

mammal biomass, food habits, and modeled 

estimates of metabolism [30]. Marine mammal 

consumption indicates how much energy is flowing 

through the system to upper trophic levels that have a 

special status (Figure 6.5). Many mammal species 

are protected or managed and monitored distinctly 

from targeted fish species. The index also shows how 

much food was removed by these organisms and 

indicates an increase in marine mammal consumption 

over time, largely reflective of increasing populations 

of some toothed whales and seals. It is interesting to 

contrast this to the amount of food eaten to total 

fisheries landings in the region (c.f., Figure 6.1), 

Figure 6.7 Mean catch (kg) per tow caught in NEFSC bottom trawl 

surveys by species group. 

particularly of forage species such as herring and 

mackerel, to get a sense of the relative magnitude of 

the different sources of removal experienced by these 

fish and invertebrates. 

Biomass trends of selected highly migratory 

species found in the North Atlantic are shown in 

Figure 6.6. These indices are for the entire north 

Atlantic, but are indicative of trends for these species 

in the NES LME. Species such as tunas, swordfish, 

and sharks all feed at or near the top of a food web. 

Declines in these species have served as proxies for 

ecosystem and stock overfishing. The biomasses of 

these highly migratory species have declined since 

the 1970s and 1980s to currently lower values. 

Certainly yellowfin tuna and the two species of 

sharks exhibited a notable peak in the mid to late 

1980s, but their biomasses have mostly declined 

since then. Only swordfish and shortfin mako have 

shown a slightly increasing trend in recent years. 

Changes in biomass of taxonomically-related 

fish species are provided in Figure 6.7. These 

indicators show the relative biomass of major fish 

groups that are often commercially targeted in the 

 21 
Figure 6.8 Total biomass of all species caught in NEFSC bottom 

trawl surveys (million mt) based on areal expansion of catch per tow 

data without adjustment for survey catchability. 

NES LME. Note the obvious and sustained increases 

in small pelagics and elasmobranchs over time. The 

groundfish and other finfish show a general decline 

through the end of the 1980s, followed by recovery in 

recent years due to various management measures. 

The index values for these groups however have 

declined again in recent years. 

Trends in total biomass based on all species 

captured in the trawl surveys indicate a steady 

increase over time (Figure 6.8), reflecting the 

increases in major species groups such as the 

elasmobranchs and small pelagics with other groups 

contributing during different time periods. 

Implications of this increase, as well as potential 

underlying causes (related to various abiotic and 

human drivers) are discussed in the next section. 

7 Anthropogenic Factors 

Landing by Major Species Group 1960-2007 

Total landings for major groups of fishes and 

invertebrates from the NES LME have generally 

declined during the last four decades (Figure 7.1). 

Landings of groundfish (Atlantic cod, haddock, silver 

hake, yellowtail flounder etc.) and small pelagic 

fishes (primarily Atlantic mackerel, herring, and 

menhaden) peaked in the mid 1960s to the mid 1970s 

during a period of heavy fishing by foreign distant 

water fleets. 

Groundfish landings peaked at 703,000 t in 

1965 with the appearance of a very strong year class 

of haddock (Figure 7.1). However, serial depletion of 

groundfish occurred very rapidly and landings 

declined to about 30% of the peak by 1978. 

Groundfish landings have continued to decline since 

the mid 1970s due to severe overfishing and, more 

recently, to regulatory intervention to rebuild 

depleted stocks; currently they are a minor 

component of total system removals. 

Landings of small pelagic fishes reached 

988,000 t in 1973 but declined to about 31% of this 

peak value by 1984 due to the collapse of the 

Georges Bank herring stock and a severe decline in 

Atlantic mackerel. Recovery of the Atlantic herring 

and mackerel stocks during the late 1980s and 

sustainable landings of Atlantic menhaden are 

responsible for relatively robust landings, averaging 

about 360,000 t from 1977-2007. 

Landings of other finfish (redfish, Atlantic 

croaker, black sea bass etc.) and crustaceans 

(primarily American lobster) have been relatively 

stable during 1960-2007. 

Landings of molluscs increased during the 

early 1980s due to a rapid expansion of the surf clam 

and ocean quahog fishery by the U.S. industry 

(Figure 7.1). With the recovery of the scallop 

resource in the mid to late 1990s, this category of 

landings (molluscs) now comprises the largest 

proportion of current landings (Figure 7.1). 

Trophic Level of the Landings 

It has been recognized for some time that a 

substantial level of depletion of large picivorous fish 

has occurred on a global basis during the last 40-50 

years of fishery exploitation [27, 31, 32]. In some 

cases this has resulted in the loss of important 

predators, the shortening of food chains, and 

simplification of marine ecosystems, depending on 

the region. Measuring this effect is not easy, but 

several metrics have been proposed for assessing 

these impacts, including trophic level of catch [27] 

and catch-per-unit-effort of community biomass [31]. 

These metrics are designed to measure the overall 

impact of fishing on large regions of the global 

oceans. 

The mean trophic level of landings (TLL) was 

calculated for the NES LME during 1960-2007 to 

monitor possible changes in the trophic structure in 

the region. This method accounts for the trophic 

level of each species in the landings weighted by the 

total landings of each species in a given year. The 

 22 
Figure 7.1 Landings by species group (million mt) landings for the 

Northeast continentals shelf LME. 

Figure 7.2 Mean trophic level of landings for the Northeast 

continental shelf LME.

Figure 7.3 Total primary production required to support landings.

TLL for the system has declined steadily since 1960. 

This reflects the changes that have been observed in 

large piscivorous fish in the region during the 1960s 

and as recently as in the 1990s, as well as a major 

change in the composition of the landings. More 

recently, landings have been dominated by molluscs 

and small pelagic fishes. The higher TLL in the 

1960s reflects the representation of cod, haddock, and 

silver hake in the ICNAF fishery, while the decline in 

the 1970s reflects a high proportion of small pelagic 

fishes in catches by the distant water fleets of that era 

(Figure 7.2). Further declines in the 1980s reflect the 

dominance of surf clams, ocean quahogs, Atlantic 

menhaden, and continued declines in groundfish in 

the landings by the U.S. industry, after the imposition 

of extended jurisdiction (the 200 mile limit) in 1977. 

The continued decline in TLL in the 1990s and 

through 2007 resulted from directed fishing on large 

spiny dogfish, white hake, and cod, coupled with 

increased landings of Atlantic mackerel, Atlantic 

herring, sea scallops, and steady landings of Atlantic 

menhaden (Figure 7.2). Note that these results differ 

from those based on research vessel surveys (Figure 

6.4) in that the survey estimates do not include 

shellfish and that the small pelagic fishes at lower 

trophic levels are less catchable in the bottom trawl 

surveys than demersal fish. Over the almost 50 year 

period, the TLL in the region declined by more than a 

full trophic level, perhaps suggesting a much more 

simplified ecosystem at present, and a focus on 

landing species that are at a much lower trophic level. 

Primary Production Required 

Other approaches have been developed to measure 

the impact of fishing on large regions of the global 

oceans [33]. Thorough either direct consumption or 

transfer of energy, every trophic component of a 

marine ecosystem is connected to the primary 

production in that particular region. A metric known 

and PPR (primary production required) can be used 

to measure the impact of fishery removals in a 

particular region. This quantity measures the impact 

of fishing on the base of the food web and is sensitive 

to the amount of landings. By accounting for 

landings and trophic efficiencies, the percentage of 

primary production being utilized in a region can 

used to judge whether the amount removed is 

sustainable or excessive in relation to ecosystem 

overfishing. 

 23 
PPR was calculated for the NES LME to 

monitor historic and recent fishery requirements 

during 1960-2007. The percentage of primary 

production required to support landings during the 

mid 1960s to 1970s was very high, averaging about 

33% (Figure 7.3). This trend reflected the large scale 

removal of accumulated cod, haddock, and silver 

hake biomass that occurred over a short time horizon, 

an indication that this level of energy removal was 

unsustainable. PPR declined rapidly in the mid to 

late 1970s to about 10% in 1978, reflecting an overall 

decline in landings and a dominance of small pelagic 

fishes that function at a lower trophic level. PPR has 

slowly declined from about 10% in 1980 to less than 

5% in 2007 (Figure 7.3). 

PPR to Support Herring and Mackerel Landings 

Atlantic mackerel and herring not only 

support important fisheries in the NES LME, but are 

also key prey items in the diets of many of the 

regions predators. The PPR metric was calculated 

separately for Atlantic herring and Atlantic mackerel 

to track PPR required to sustain the fisheries on these 

important prey species. PPR for Atlantic herring 

peaked at 9.4% in 1968 and at 8.6% for Atlantic 

mackerel in 1972 (Figure 7.4). Both of these stocks 

collapsed shortly thereafter, following several years 

of intense fishing. The percentage of these two 

species in the diets of predators also declined 

following this period of overexploitation [30]. 

During the early 1980s, PPR for herring dropped to 

below 1%, gradually increasing to about 2% in 2006-

2007 (Figure 7.4). This is related to a recovery in the 

Gulf of Maine-Georges Bank herring complex and a 

gradual improvement in the herring fishery. PPR for 

Atlantic mackerel declined to very low levels in 

1979, increased to about 1.4% in 1990, declined to 

very low levels for a decade, and more recently 

increased to about 1% (Figure 7.4). The current level 

of mackerel landings from the NES LME represents a 

small proportion of the regional primary production. 

The occurrence of Atlantic herring and mackerel in 

predator diets increased during the 1990s and 2000s 

following the recovery of both stocks. 

The Northeast Otter Trawl Fishery 

Performance in the Northeast otter trawl 

fishery (large mesh nets targeting groundfish, 

dogfish, monkfish, and skates) is a general barometer 

Figure 7.4 Primary production required to support mackerel and 

herring landings. 

for how well the finfish industry in the Northeast has 

fared during the last 40-50 years. Three variables, 

total pounds landed, total value (in 2000 dollars) and 

total number of fishing vessels, were monitored 

during 1964-2007. Total landings have greatly 

declined during the period. Landings declined from a 

series high of 386 million lbs in 1964 to 176 million 

lbs in 1976, increased to 348 million lbs in 1982 and 

declined steadily to about 50 million lbs in 2006 

(Figure 7.5). Total value averaged about 110 million 

dollars during 1964-1975, doubled to over 200 

million dollars in 1982, and plunged to about 57 

million dollars in 2006 (Figure 7.5). On a per vessel 

basis, average revenue actually increased during 

2001-2006. The number of otter trawl vessels 

averaged about 300 during 1964-1976, increased to 

over 600 in 1984, and declined to 189 in 2006 

(Figure 7.5). The general decline in these measures 

can be attributed to overall declines in the groundfish 

biomass during 1964-2007 and management 

restrictions implemented during the last decade. The 

increase in number of vessels during the late 1970s 

and early 1980s occurred in part because of 

government subsidies and short-term increases in 

groundfish biomass, subsequent short term increases 

in landings and revenue followed. 

Population Trends and Per Capita Income 

Trends in the population and per capita 

income for 5 coastal counties in or adjacent to large 

metropolitan areas in the Northeast and Mid-Atlantic 

 24 
Figure 7.5 Total groundfish landings and value in the upper panel. 

Number of vessels in the lower. 

Figure 7.6 Population index and state incomes. 

regions were used in this analysis of human drivers of 

ecosystem change. Near shore population and 

disposable income are proposed as indicators of 

seafood demand in the region. They also may be 

useful predictors of human impacts on near shore 

environments indicative of increased nitrogen loading 

and stress on estuarine habitats. After declining 

slightly in the 1970s, the northeast coastal population 

index increased steadily during 1981-2006 (Figure 

7.6). Per capita income (measured in 2000 dollars) 

increased steadily from 1969-2006 particularly in the 

New York and Boston metropolitan areas (Figure 

7.6).

8 Integrative Ecosystem Measures 

The NES LME has undergone sustained 

perturbations directly related to human activities 

(particularly harvesting) and climate and 

environmental forcing over the last four decades. In 

this section, we provide an integrated evaluation of 

changes in anthropogenic and physical drivers, 

associated pressures, and ecological states for this 

system. We focus on information from 1977 to the 

present, reflecting the period for which observations 

were consistently available for most of the assembled 

indicators of drivers, pressures and states. The 

analysis uses 18 indicators of anthropogenic drivers 

and pressures, 25 metrics of climate and physical 

change and 26 indicators of biotic state to 

characterize change in ecological state on the 

northeast shelf (see appendix for variable names used 

in Figure 8.1). 

We transformed each of the indicator series to 

standard normal deviates (where the mean is 

subtracted from each observation and this difference 

is divided by the standard deviation of the series – 

see Glossary) to place all variables on a common 

scale. We have color coded the standardized 

variables according to five levels (quintiles) for each 

series and constructed graphical arrays representing 

time trends for each series in each of the three major 

categories identified above (i.e., anthropogenic 

drivers and pressures; climate/physical changes; 

biotic state). 

The time trajectory of anthropogenic drivers 

and related pressures indicates steady increases in 

human population growth in coastal counties and in 

disposable income. Both of these factors potentially 

exert pressures through increased demand for 

seafood, and impacts on coastal environments 

(through pollution, habitat loss and coastal zone 

alteration). In contrast, indicators related to 

groundfish landings, revenues and fishing effort, and 

 25 
mean trophic level of the catch show overall declines 

over time (Figure 8.1 top panel). Declines in mean 

trophic level of the landings reflect, in part, the 

transformation from a groundfish dominated fishery 

to one increasingly exploiting other ecosystem 

components, notably invertebrates and small pelagic 

fishes. Overall declines in the primary production 

required to support the observed catch for all species 

are related to changes in the mean trophic level of 

harvest and declines in the fishery removals; similar 

recent declines for the small pelagics are related to 

sharply reduced exploitation rates. The overall 

pattern is one of decadal-scale shifts with major 

declines in groundfish-related metrics in the first 

decade of the series as human population size and 

income increased. The transformation was complete 

by the last decade in the series. 

The array of climate and physical indicators 

reveals a diffuse transition beginning in the mid-tolate 1990s, reflecting an increase in the climate 

drivers (NAO and AMO) and the suite of associated 

physical pressures including the temperature-related 

metrics, river flow, and wind stress in the more 

northern locations (Figure 8.1 middle panel). In 

contrast, the first decade showed higher salinity 

values and higher wind stress in the more southern 

locations. 

Consideration of the ecosystem state variables 

again reveals a transformation in system state that 

appears to be related to both anthropogenic change 

and climate/physical factors. Changes in key 

indicators related to fishery resource status show a 

transition in the early 1990s (Figure 8.1 bottom 

panel). In particular we observed increases in total 

fish biomass, elasmobranchs, small pelagics, 

crustaceans, and the ratio of pelagic to demersal fish 

(which did decline at the end of the series). We 

attribute these increases to the direct and indirect 

effects of exploitation on the system. Consumption 

by marine mammals also increased steadily during 

this period. 

The other major class of metrics included in the array 

biotic ecosystem indicators is the abundance of five 

major copepod species on Georges Bank in both 

spring and fall. These show an increase in abundance 

of smaller-bodied species starting in the early 1990s 

and extending to the early years of this decade. The 

period of high abundance of smaller copepod species 

on Georges Bank (see Figure 4.10) coincides with 

strong negative salinity anomalies on Georges Bank. 

Figure 8.1 Human-related (top panel), climate and physical forcing 

(middle panel) and biotic ecosystem (bottom panel) indicators of 

change. The series have been ordered using a Principal 

Components Analysis to group variables showing similar patterns. 

Shaded box indicates transition period. 

We can provide an alternative view of the 

changes in the driver, pressure, and state variables by 

first constructing a new set of indices that reduces the 

original large number of variables to a smaller group 

that combines information from the entire suite. We 

have used a Principal Components Analysis for this 

 26 
Figure 8.2 Time trajectories of change in canonical phase space for 

anthropogenic, physical, and biotic indicator variables. 

purpose. This technique involves the construction of 

a set of mutually independent linear combinations of 

the original variables (see Glossary for a more 

detailed description). 

Taking this approach, we find that the original 

set of 18 anthropogenic variables can be reduced to 

two ‘combined’ indicators that explain over 75% of 

the variance in the full set of indicators. The first 

principal component (PC) in fact accounts for 66% of 

the variance in the suite of indicators. The 

contributions of the original variables to the first PC 

are remarkably even, with the relative contributions 

of the variables reflecting strong inverse relationships 

between the human population and income variables 

and the fishery-related variables. Only the landings of 

crustaceans, molluscs and the primary production 

required for the small pelagics had low loadings (and 

these were strong in the second principal component 

as expected). A plot of the time trajectory for the 

first PC against the second PC provides a view of 

relative changes in each (Figure 8.2; top panel). The 

trajectory indicates a strong directional change in this 

set of variables as would be inferred from Figure 

8.1). 

For the array of 25 climate and physical 

variables considered, we find that the first six 

principal components explain 75% of the variance in 

the full set. The first PC, which explains 20% of the 

variance is dominated by salinity (surface and 

bottom) and wind stress variables with a strong 

opposite contribution by the Atlantic Multidecadal 

Oscillation. The second PC, explaining an additional 

16% of the variance, reflects strong contributions by 

water temperature at coastal locations, sea surface 

temperature on the shelf, and Gulf Stream position 

with opposite contributions by river flow indicators 

and wind stress in southern locations. Unlike the 

clear directional change in anthropogenic variables, a 

more complex and variable pattern emerges for the 

physical variables with no discernable trend when 

only the first two principal components are 

considered (Figure 8.2 middle panel). 

Finally, a more clearly defined directional 

change is evident for the biotic indicator set (Figure 

8.2 bottom panel). The first six principal components 

explain 77% of the variance of the original 26 

variables. The first PC strongly reflects the relative 

abundance of all species groups represented in the 

trawl surveys, marine mammal consumption, and 

spring abundance indices of Georges Bank copepod 

species. The second component is dominated by 

autumn abundance of Georges Bank copepod species, 

the pelagic to demersal fish ration and negative 

loadings of marine mammal consumption, relative 

abundance of survey species groups. 

If we plot the time course of the first principal 

component for each of the three major groups, we see 

a strongly increasing trend in the anthropogenic 

indicators (Figure 8.3 top panel). The trajectory of 

the first PC for the physical metrics is decreasing, 

reflecting the influence of salinity and other variables 

(Figure 8.3 middle panel). The PC indicator for 

biotic factors is again increasing as a result of the 

dominant influence of factors such as increasing 

abundance of major species groups represented in the 

trawl survey (Figure 8.3 bottom panel). 

 27 
Ecosystem Overfishing 

The need for the adoption of an ecosystem 

approach to management of marine ecosystems is 

now broadly accepted. A necessary corollary for its 

implementation is the specification of targets and 

limits to exploitation in an ecosystem context. Link 

[28] discusses this issue in the context of a suite of 

ecosystem indicators. Murawski [34] suggested that 

an ecosystem could be considered overfished if one 

or more of the following criteria were met: 

• Biomasses of one or more important species 

assemblages or components fall below minimum 

biologically acceptable limits, such that: 

1) recruitment prospects are significantly 

impaired, 

2) rebuilding times to levels allowing catches 

near MSY are extended, 

3) prospects for recovery are jeopardized 

because of species interactions, 

4) any species is threatened with local or 

biological extinction; 

• Diversity of communities or populations declines 

significantly as a result of sequential ‘‘fishingdown’’ of stocks, selective harvesting of ecosystem 

components, or other factors associated with 

harvest rates or species selection; 

• The pattern of species selection and harvest rates 

leads to greater year-to-year variation in 

populations or catches than would result from 

lower cumulative harvest rates; 

• Changes in species composition or population 

demographics as a result of fishing significantly 

decrease the resilience or resistance of the 

ecosystem to perturbations arising from nonbiological factors; 

• The pattern of harvest rates among interacting 

species results in lower cumulative net economic or 

social benefits than would result from a less intense 

overall fishing pattern or alternative species 

selection; 

• Harvests of prey species or direct mortalities 

resulting from fishing operations impair the longterm viability of ecologically important, nonresource species (e.g., marine mammals, turtles, 

seabirds). 

According to these criteria, Murawski [34] 

determined that the NES LME was subject to 

ecosystem overfishing. 

Figure 8.3 Time trends for the first principal components for 

anthropogenic, climate/physical, and biotic indicators. 

Figure 8.4 Time trajectory of primary production required and mean 

trophic level of the catch for the Northeast continental shelf large 

marine ecosystem. All points above the smooth curve are 

classified as overfished from an ecosystem perspective according to 

the criteria of Tudela et al. [1]. 

Tudela et al. [2] provided a meta-analysis of 

49 ecosystems (including parts of the NES LME) to 

which these criteria could be applied and for which 

estimates of PPR and mean trophic level (TL) were 

available. The demarcation point between overfishing 

 28 
and sustainably fishing in the context of changes in 

primary production required and mean trophic level 

was identified using these a priori overfishing 

classifications. In this representation, losses incurred 

by fishing at low trophic levels affect the energy 

available to higher trophic levels and the interplay 

between the mean TL (Figure 7.2) and the primary 

production required to support the observed fishery 

yield (see Figure 7.3) determines the ecosystem 

classification. 

Classification of ecosystem status for the NES 

LME for the period 1960-2007 is provided in Figure 

8.4. Only at the start the series (1960-61) does the 

system meet the criteria of sustainable fishing at the 

ecosystem level according to the Tudela et al. 

criterion. At the height of distant water fleet 

activities, characterized by both high mean trophic 

level of the catch and high appropriation of available 

primary production, a steadily increasing level of 

ecosystem overfishing occurred. Despite the drop in 

PPR over the last two decades and the improvement 

in condition of some components of the system, the 

concomitant drop in mean trophic level still results in 

an a classification of ecosystem overfishing in 2007 

(Figure 8.4). 

Summary 

The U.S. Northeast continental shelf has 

experienced large-scale perturbations over the last 

four decades due to human activities (notably 

harvesting) and environmental change (including 

climate-related impacts). The need for holistic 

assessments of ecosystem status in relation to natural 

and anthropogenic forcing is now widely recognized 

as a critical element in support of the development of 

an ecosystem approach to management. In particular, 

linking the pressures related to anthropogenic and 

natural drivers of ecosystem change to alteration in 

system status is an essential first step in developing 

effective management strategies. We have compiled 

key indicators of climate, physical dynamics, 

ecosystem state, and human activities and conditions 

to evaluate the status of this large marine ecosystem. 

Decadal and multidecadal scale changes in 

climate and physical forcing factors affecting the 

ecosystem are evident at a number of different levels. 

Water temperatures have increased in coastal 

locations and on the continental shelf from a low in 

the late 1960s to the present. There has been 

corresponding increase in high temperature (>16°C) 

and a relative decline in intermediate (5-15°C) 

thermal habitat available for marine organisms. 

Increases in temperature and decreases in salinity 

have led to increases in water column stratification 

from a low in 1984 to the present that has had a 

profound effect on primary and secondary 

productivity. 

The changes observed in some of the physical 

variables have been accompanied by clear changes in 

some of the biotic variables. The decreases in salinity 

have been accompanied by concomitant changes in 

an index of larger-bodied phytoplankton species 

(principally diatoms) in the ecosystem. A related 

index of water column stratification is closely related 

to the time series change in the total biomass of 

zooplankton and changes in the species composition 

copepod communities. There has been a pronounced 

shift from a demersal fish-dominated community to 

one dominated by elasmobranchs and pelagic fish. 

The fish community has also been affected by a 

persistent change in conditions that favor temperatecold water fish community to one favoring warmer 

water species. 

The overall biomass of the entire fish 

community as indexed by trawl surveys has increased 

over the last four decades as elasmobranchs and 

small pelagic fishes have increased in abundance 

even as other groups such as groundfish have 

undergone decreases. Some of these changes reflect 

apparent species replacements as heavily exploited 

species declined. The mean trophic level of fish in 

trawl surveys has fluctuated without trend. In 

contrast, the mean trophic level of the catch 

(invertebrates and vertebrates) has declined steadily 

since 1960, reflecting changes in the abundance of 

economically important species. 

Estimates of the primary production required 

to support observed catch levels indicate that recent 

fisheries are probably more sustainable than those in 

the 1960s and 1980s for all species and for small 

pelagic species specifically. 

The human component has been a critically 

important agent of change in this large marine 

ecosystem. Economic indicators for the groundfish 

fishery suggest that this resource has been in a longterm state of decline. Trends in human population 

and disposable income in the region suggest that 

human induced pressures on marine resources will 

remain high and perhaps continue to increase in the 

future. 

 29 
Although marked improvement in the 

condition of some components of the NES LME is 

now evident under more effective management, the 

system remains classified as experiencing overfishing 

from an ecosystem perspective according to criteria 

of Murawski [33] and Tudela et al.[2] . 

Future Directions and Research Needs 

This is the first of a planned series of 

Ecosystem Status Reports to document change in the 

NES LME. We have focused on metrics of 

ecosystem change in response to drivers and 

pressures on this system. The anthropogenic drivers 

highlighted in this report and the associated pressures 

exerted have been centered on harvesting activities 

and their impacts on the NES LME. Although fishing 

is recognized as a dominant agent of ecosystem 

change in marine systems in general, in future 

editions of this status report, we will strive to 

incorporate additional measures of human impacts on 

the NES LME. Coastal development, point and nonpoint source pollution, and other anthropogenic 

factors all have important effects in nearshore waters 

in particular [35]. We will also seek to represent 

how natural and anthropogenic changes affect human 

communities dependent on this system for vital goods 

and services. The economic component of this report 

has focused on the iconic groundfish fishery. Future 

updates will include additional fishery sectors. We 

will also attempt to include consideration of 

aquaculture production, an additional important use 

of the marine environment. 

Important local studies of the role of humans 

as part of this large marine ecosystem are available 

[36]. However, studies on the broad spatial and 

temporal scales represented in this report have not yet 

been conducted for these human-related metrics. 

To date, we have applied one measure of 

ecosystem overfishing to characterize the state of this 

system. We are currently exploring other indicators 

of ecosystem condition in response to exploitation for 

consideration in future editions of this report. 

We have identified strong trends in human 

drivers of change in this system, including population 

growth in coastal counties and in disposable income, 

both of which will result in an escalation of 

anthropogenic pressures. Projections of future 

climate change for the northeast, if realized, also will 

result in changes in ecosystem pressures [37]. 

Increases in water temperatures and changes in other 

hydrographic properties (salinity, stratification) are 

anticipated and these will affect the provision of 

ecosystem goods and services. Some of the changes 

documented in this report presage future change if 

current trends in temperature and other factors 

continue or accelerate under some climate change 

scenarios. The documented changes already 

experienced may serve as early warning indicators of 

future change. For example, if the current trend in 

water mass stratification continues, we anticipate 

important changes in nutrient regeneration in the 

system, affecting the flow of energy and overall 

levels of productivity. Observed changes in the 

amount of thermal habitat and in the relative species 

composition of fish communities with respect to 

temperature preferences indicate the potential for 

strong changes in fish community structure in the 

NES LME. 

In this report, we have focused on 

documenting change in a suite of physical, 

ecological, and human variables and have made 

initial attempts to relate changes in ecosystem state 

variables to proximal pressures. These pressures are 

in turn related to underlying drivers of change. The 

observed changes in the system indicate a clear need 

to explore their underlying mechanistic basis and to 

determine causal pathways. Tracing important 

changes in this system has been made possible by the 

strong commitment to sustained monitoring by many 

agencies and institutions in this region. It is no less 

important to frame hypotheses concerning the 

mechanisms of change and to test these hypotheses 

using an appropriate combination of process-oriented 

research, comparative analysis, and integrative 

modeling. 

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management on the basis of a two-dimensional 

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Science, 2005. 62(3): p. 585-591. 

3. Fogarty, M.J. and S.A. Murawski, Large-scale 

disturbance and the structure of marine system: 

Fishery impacts on Georges Bank. Ecological 

Applications, 1998. 8(1): p. S6-S22. 

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 32 
Further Information 

For further information contact: 

Dr. Michael Fogarty 

National Marine Fisheries Service 

Ecosystem Assessment Program 

166 Water Street 

Woods Hole, MA 02543 

e-mail: michael.fogarty@noaa.gov 

Tel: (508)495-2386 

This report is a product of the Ecosystem Assessment 

Program of the Northeast Fisheries Science Center with 

contributions by: Michael Fogarty, Kevin Friedland, 

Laurel Col , Robert Gamble, Jon Hare, Kimberly Hyde, 

Jason Link, Sean Lucey, Janet Nye and William 

Overholtz. 

Acknowledgments 

We thank the following people for their help in 

developing this report: S. Doney, C. Meinen, G. Han, J. 

Manning, M. Taylor, L. Dewitt , C. Natunewicz, J. Kane, 

J. Jossi. D. Kitts, E. Thunberg, P. Rago, C. Legault, R. 

Mayo, L. Jacobson, M. Traver, M. Palmer, S. Wigley, A. 

Seaver, J. O’Reilly, B. Smith and T. Ducas. We are 

grateful for the helpful reviews of this report provided by 

Christopher Brown, Jim Manning, Tom Noji, Fred 

Serchuk, Ken Sherman, Maureen Taylor, and three 

anonymous reviewers. 

Glossary 

Biogeochemical Cycle: The path which a chemical takes as 

it moves through biological organisms and abiotic areas 

which the organisms live in. Chemical compounds are 

transferred from organism to organism and to different 

parts of the ocean through numerous biogeochemical 

cycles. 

Chemical Speciation: The processes by which different 

types (species) of chemicals are formed. 

Driver: In the Driver-Pressure-State-Impact-Response 

sequence, a driver is generally a broad forcing factor that 

creates specific pressures on the ecosystem being studied. 

Impact: In the Driver-Pressure-State-Impact-Response 

sequence, an impact is the effect on humans of a changed 

state in the ecosystem being studied. 

Indicator: In environmental or ecological terms, an indicator 

is a statistic that has been shown to be representative of a 

particular aspect of the environment. Indicators in an 

ecosystem can show overall trends, can point to potential 

areas needing management, or can help show the effects 

of current management. Examples we use are 

temperature, salinity, biomass of species and aggregated 

groups, etc. One analogy is the stock quote for a 

company which shows the ‘health’ of that company in 

general terms. Similarly the NASDAQ is an aggregate 

indicator of a number of stocks, which is often used as 

one of the indicators to determine the economic health of 

the United States. 

Pressure: In the Driver-Pressure-State-Impact-Response 

sequence, specific pressures are created by the drivers. 

The pressures cause changes in state of one or more 

elements of the ecosystem being studied. 

Principal Components Analysis (PCA): A commonly used 

statistical technique designed to take possibly correlated 

sets of variables and reduces it to a smaller set of 

uncorrelated variables, the principal components. Each 

principal component (PC) is a combination of all the 

initial variables into one number. In each principal 

component, some of the original variables are typically 

more important than others. The first principal component 

can be considered the most important as it explains most 

of the variance. The second PC explains the next most of 

the variance, etc. 

Response: In the Driver-Pressure-State-Impact-Response 

sequence, a response is a change in management strategy 

based on changes in state of the ecosystem and impacts 

on humans. 

Standardized Anomalies: In statistics, an anomaly is a 

measure of how far from the mean a given observation is. 

So, if the mean temperature over 10 years in a given 

oceanic region is 18.2°C, and the temperature during one 

of the years was 16.2°C, the anomaly would be -2.0. To 

make comparisons more meaningful, we use standardized 

anomalies which effectively convert all indicators to the 

same scale. A standardized anomaly is each anomaly 

divided by the standard deviation for a set of data. So a 

standardized anomaly of -2 in a temperature time series is 

as likely (or unlikely) to occur as a standardized anomaly 

of -2 in a salinity time series. 

States: In the Driver-Pressure-State-Impact-Response 

sequence, a state is the current status or value of a given 

facet of the ecosystem being studied. 

Thermohaline circulation: Also referred to as the ‘ocean 

conveyer belt’, (or more formally, the Meriodonal 

Overturning Circulation), the thermohaline circulation is 

that part of the global ocean circulation which is driven 

by density gradients, which are in turn caused by 

temperature and salinity differences in the ocean. In 

general, water flowing to the north through wind driven 

currents, such as the Gulf Stream, sinks near the North 

Pole due to the creation of ice, which increases the 

salinity in the underlying water while also making it cold. 

This water flows into the ocean basins, with the bulk of it 

rising (upwelling) in the Southern Ocean and North 

Pacific. This circulation permits mixing between the 

ocean basins, decreasing the differences between them.

 33 
Appendix Variables for Figure 8.1 

NAO North Atlantic oscillation 

AMO Atlantic multidecadal oscillation

GSL Gulf Stream Location

PLSSWGOM Percent Labrador-Subarctic Slope Water in the Gulf of Maine

RFGOM River Flow-Gulf of Maine

RFMAB River Flow-Middle Atlantic Bight

RFSNE River Flow-Southern New England

WSCH Wind Stress, Cap Hatteras

WSNY Wind Stress, New York

WSGB Wind Stress, Georges Bank

WSEWCH Wind Stress East-West, Cap Hatteras

WSEWNY Wind Stress East-West, New York

WSEWGB Wind Stress East-West, Georges Bank

WSNSCH Wind Stress North-South, Cap Hatteras

WSNSNY Wind Stress North-South, New York

WSNSGB Wind Stress North-South, Georges Bank

ERSST Extended Reconstructed SST

CTVA Coastal Temperature, Virginia

CTWH Coastal Temperature, Woods Hole

CTBH Coastal Temperature, Boothbay

SSST Survey sea surface temperature

SBST Survey bottom sea temperature

SSS Survey surface salinity

SBS Survey bottom salinity

STRAT Stratification

CPRCI Continuous Plankton Recorder Color Index.

ZOOECOBV Zooplankton Ecosystem Biovolume 

GBCOPESP Georges Bank Copepods, Spring

GBCOPEFA Georges Bank Copepods, Fall

GBCALFINNSP Georges Bank C. finmarchicus, Spring

GBPSEUDOSP Georges Bank Pseudocalanus spp. , Spring

GBTEMORASP Georges Bank T. longicornis, Spring

GBCTYPSP Georges Bank C. typicus, Spring

GBCHAMSP Georges Bank C. hamatus, Spring

GBCALFINNFL Georges Bank C. finmarchicus, Fall

GBPSEUDOFL Georges Bank Pseudocalanus spp. , Fall

GBTEMORAFL Georges Bank T. longicornis, Fall

GBCTYPFL Georges Bank C. typicus, Fall

GBCHAMFL Georges Bank C. hamatus, Fall

SVLZOO Small v Large Zooplankton

PDRATIO Pelagic to Demersal Ratio 

MEANL Mean Length

TLSUR Total Length Surveyed Species

MMCONS Marine Mammal Consumption

RACRUS Relative Abundance, Crustaceans

RAELAS Relative Abundance, Elasmobranch

RAGF Relative Abundance, Ground Fish

RAMOL Relative Abundance, Mollusc

RAOF Relative Abundance, Other Fish

RASP Relative Abundance, Small Pelagics

RAALL Relative Abundance, All Species

LANDPG Landings, Principal Groundfish

LANDOF Landings, Other Fish

LANDSP Landings, Small Pelagics

LANDCR Landings, Crustaceans

LANDMOL Landings, Mulluscs

MEANTL Mean Trophic Level

PPREQ Primary Production Required, Landings

PPREQHER Primary Production Required, Herring

PPREQMAC Primary Production Required, Mackerel

VES Vessels

LANDINGS Landings

VALUE Value

POP Population

INNY Income, New York

INRI Income, Rhode Island

INCT Income, Connecticut

INMA Income, Massachusetts

INME Income, Maine

 34 
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