Marine Species Distribution
Identification
1.	Indicator Description
This indicator examines the changes in the distribution of fish and invertebrate species in North
American oceans from 1973 to 2019. Marine animals are sensitive to the physical conditions of their
environment, including water temperature. Changes in the temperature of ocean water could result in
animals moving to areas of the ocean beyond their historical ranges. This indicator uses data from large
fish-sampling surveys to determine the average geographic position (i.e., latitude, longitude, and depth)
for the entire population of one or more species. In general, deeper or more northerly waters tend to be
colder. Movement of individual species, or groups of species, to these areas may be a natural outcome
offish seeking cooler water. Such shifts have implications for interspecies competition, the economics of
fishing, and overall ocean ecosystem health.
Components of this indicator include:
•	The annual average change in the latitude and depth of the center of distribution for 140 North
American marine species from 1982 to 2019 (Figure 1).
•	Year-to-year movement of three selected species in the Northeast from 1973 to 2019 (Figure
2).
•	Year-to-year movement of three selected species in the eastern Bering Sea from 1982 to 2018
(Figure 3).
2.	Revision History
August 2016: Indicator published.
April 2021:	Updated indicator with data through 2019.
Data Sources
3.	Data Sources
This indicator is based on data from research trawl surveys conducted by the National Oceanic and
Atmospheric Administration's (NOAA's) National Marine Fisheries Service (NMFS). Survey results have
been processed and managed by the Pinsky Lab of Rutgers University and published in various peer-
reviewed studies, including Pinsky et al. (2013) and the U.S. Global Change Research Program's National
Climate Assessment (USGCRP, 2018). Mike Kolian of EPA developed this indicator in collaboration with
Roger Griffis of NOAA and Malin Pinsky of Rutgers University.
4.	Data Availability
All data for this indicator are available from the OceanAdapt website at:
https://oceanadapt.rutgers.edu. This website provides query tools and data descriptions. It is
maintained by the Rutgers University School of Environmental and Biological Sciences. At the time of
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publication, data were available through 2019 for the Northeast and through 2018 for the eastern
Bering Sea and the multi-region species composite shown in Figure 1.
Methodology	
5.	Data Collection
This indicator is based on data collected through research trawl surveys that NMFS conducts annually
along various parts of the U.S. continental shelf. These bottom trawl surveys involve dragging a large net
at a set depth behind a research vessel for a set time and distance. The trawl haul is brought aboard the
vessel, where scientists sort the catch by species and record their size and abundance. They may also
record additional information such as sex, maturity, and evidence of disease. Species recorded include
fish (particularly fish that live near the ocean floor), shellfish, and other invertebrates such as sea stars,
anemones, and ascidians (sea squirts).
NMFS conducts systematic trawl surveys on a regular basis to provide information for use in fisheries
management. In the Northeast, for example, NMFS conducts 300 half-hour trawl sets at random sites in
both spring and fall.
The length of trawl survey records varies by region. Some of the first NOAA survey trawling vessels in
the Northeast were in use as early as 1948 (the Albatross III) and 1950 (the Delaware). Regular collection
of surveys began in the 1960s in the Northeast, the late 1970s along the West Coast, and the 1980s in
coastal Alaska and the Gulf of Mexico.
For more information about NMFS bottom trawl surveys, see: www.fisheries.noaa.gov/about/northeast-
ecosvstems-survevs. Pinsky et al. (2013) and the references therein describe sampling methods in
additional detail.
6.	Indicator Derivation
This indicator focuses on the center of biomass for each species, which is the biomass centroid of the
population distribution at any point in time. The centroid is a common way to characterize the general
location of a population. The centroid for a particular species represents the point (latitude, longitude,
and depth) that is in the geographic center of the total "weight" of the entire population of that species.
For example, the latitude of a species' centroid means that half of the total biomass (or weight) of that
species was caught north of that latitude, while half was caught south of that latitude. As a result, if a
population were to shift generally northward, the biomass centroid would be expected to shift
northward as well. Tracking the depth of the centroid is also useful, as it also indicates whether marine
species are shifting to deeper and presumably cooler waters.
The analyses presented in this indicator focus on two areas: the Northeast and the eastern Bering Sea.
Although data have also been collected from the Southeast, the Gulf of Mexico, the West Coast, and
other parts of Alaska, these regions were excluded for one or both of the following reasons:
• Data for several of these areas were too sparse to support meaningful long-term trend analysis.
Some of these areas have only been sampled every few years—not annually—or have not had
consistent survey methods in use over the course of several decades.
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• Some of these regions—for example, the Gulf of Mexico—have coastlines that would prevent
marine species from moving northward in response to warming waters. Such physical barriers
mean that the data from these regions cannot be used to test the hypothesis that coastal
species are moving northward in response to warming water.
Northeast data come from spring surveys, which have historically been more complete than fall surveys.
Northeast time series in this indicator start in 1973, which is when spring surveys in the Northeast
became systematized. Data from the eastern Bering Sea come from summer surveys that have been
conducted consistently since 1982.
Figure 1. Change in Latitude and Depth of Marine Species, 1982-2019
Figure 1 shows the latitude and depth of the average center of biomass for each year, averaged across
all 140 Northeast and eastern Bering Sea species that had sufficient data available (i.e., species that
were routinely caught in sufficiently large numbers to estimate a centroid). The figure also shows
region-specific averages, with the Northeast consisting of 53 species and the eastern Bering Sea
consisting of 78 species. Both metrics are based on an unweighted average of all species. Thus, no
adjustments are made for population differences across species. Although Northeast species have
downloadable data from 1973 onward, Figure 1 begins in 1982, based on eastern Bering Sea data
availability. EPA converted northward distance from latitude to miles using a conversion factor of 69
miles per degree. Although the length of a degree of latitude is fairly standard worldwide (unlike
longitude, which shrinks as one moves poleward), there are slight differences because the Earth is not a
perfect sphere. Many sources, however, use 69 as a reasonable approximation for unit conversion. Both
parts of Figure 1 show cumulative change since the first year of data, with the first year shown as zero
on the y-axis.
Figures 2 and 3. Average Location of Three Fish and Shellfish Species in the Northeast, 1973-2019, and
the Bering Sea, 1982-2018
Figures 2 and 3 show the position of the biomass centroid for three species in each region of interest.
Each species was selected for some or all of the following reasons, based on recommendations from
NOAA experts:
•	These species represent a variety of habitats and taxonomic groups, including two benthic
invertebrates (lobster and snow crab).
•	These species are thought to be minimally impacted by factors such as overfishing and
associated population rebound effect, which may influence their population centers.
•	These species are present throughout the region in consistently large numbers across the time
period.
•	These species have been highlighted in other peer-reviewed studies using survey data that
examine distribution shifts.
•	Several of these species are important for commercial, sport, and/or subsistence fisheries. For
example, Alaska pollock is one of the nation's largest commercial fisheries; Pacific halibut is a
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large commercial and sport fishery; and American lobster is a large fishery and an iconic part of
the culture and cuisine of New England.
The maps in Figures 2 and 3 show the annual position of each species using the latitude and longitude
calculations provided by the data source. Individual years are identified by the saturation of the color
scale indicated in the legend. Lighter colors represent an earlier point in the time series, whereas darker
colors represent later years. The depth component to this indicator is not depicted on either map. The
small graphs to the right of each map show each species' northward/southward movement in miles,
using the same distance conversion and cumulative position approach as Figure 1.
Indicator Development
An earlier version of this indicator reported Northeast trends starting in 1968. Since then, the
OceanAdapt team has conducted retroactive data reviews and identified some concerns with
inconsistent spring sampling of strata from 1968 to 1972. Therefore, to ensure the integrity of the
results, they removed pre-1973 data from their main database and from the analysis that feeds into this
indicator.
Earlier versions of this indicator also reported national averages from the two regions (Northeast and
eastern Bering Sea) based on a smaller number of species (e.g., 105). As more species are observed,
sometimes in new places, the number of species available to be included in the national average can be
expected to increase over time. The number of species in the composite national average is meant to be
representative of species data that are available over the full time period (1982-present). At the time of
EPA's 2021 update, EPA added the averages for each region to Figure 1 based on a representative set of
species.
7. Quality Assurance and Quality Control
NOAA scientists and other experts have performed several statistical analyses to ensure that potential
error and variability are adequately addressed. These analyses and results are described in Pinsky et al.
(2013). For more information about methods to ensure data quality in NMFS's bottom trawl surveys, see
resources linked from: www.fisheries.noaa.gov/about/northeast-ecosvstems-survevs.
Analysis	
8.	Comparability Over Time and Space
Trawl surveys have been conducted since at least the 1950s in some regions, but the data used in this
indicator begin in 1973 for the Northeast and 1982 for the eastern Bering Sea. These start dates ensure
comparable data collection over the entire period of study, including sufficient sample sizes and
consistent methods, survey design, and frequency. To ensure that the time series in Figure 1 are
comparable over time and space, this figure begins in 1982, and it uses a consistent set of 140 widely
measured species.
9.	Data Limitations
Factors that may impact the confidence, application, or conclusions drawn from this indicator are as
follows:
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1.	Water temperature is not the only factor that can cause marine animal populations to shift.
Other factors could include interactions with other species, harvesting, ocean circulation
patterns, habitat change, and species' ability to disperse and adapt. As a result, species might
have moved northward for reasons other than, or in addition to, changes associated with
climate.
2.	This indicator does not show how responses to climate change vary among different types or
groups of marine species. For example, there are likely to be large differences among species,
which have varying abilities to adapt to temperature changes. Some species could have moved
significantly in one direction while others moved in the opposite direction or did not have a
discernible change.
3.	Some data variations are caused by differences between surveys, such as variation in start and
end locations of the surveys. Such differences, however, are not expected to unduly influence
the results of this analysis.
4.	By focusing on the center of biomass for each species, this indicator does not characterize the
complete range that each individual species inhabits and how the shape of that range may be
changing. For example, northward movement of the centroid for American lobster does not
reveal whether the northern range of the lobster is expanding, the southern edge is
contracting, both, or neither.
5.	The biomass centroid metric relies not only population, but also on the weight of individuals.
Thus, if a fish population were to benefit from large feedstocks in one area, but suffer from a
lack of food in another, the biomass centroid could shift in the "healthy" direction regardless of
a change in population.
6.	NMFS follows general boundaries for conducting its surveys. If populations of one or more
species were to move outside of the study area, this would affect the location of the biomass
centroid in a way that the indicator would not detect accurately.
10.	Sources of Uncertainty
The sources of uncertainty in this indicator have been analyzed, quantified, and accounted for to the
extent possible. The statistical significance of the trends suggests that the conclusions drawn from this
indicator are robust.
One potential source of uncertainty in these data is uneven geographic sampling among surveys. Basic
information on analytical methods can be found in Pinsky et al. (2013), including methods that have
been used to account for variability in survey collection data.
11.	Sources of Variability
Rare or difficult-to-observe marine species could lead to increased variability. Figure 1 addresses this
concern by focusing on 140 widely observed species, while Figures 2 and 3 address this concern by
focusing on a smaller set of relatively common species.
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12. Statistical/Trend Analysis
Pinsky et al. (2013) document the statistical significance of distribution shifts for each species. Using
annual data points, EPA applied an ordinary least-squares (OLS) regression to determine long-term
trends in movement for all species in Figure 1 and for each individual species in Figures 2 and 3. Table
TD-1 shows the slope and statistical significance of each trend. Northward and downward movement of
the combined set of 140 species in Figure 1 was significant to a 95 percent level, as was the northward
movement of all three highlighted Northeast species and two of the three highlighted Bering Sea species
(Pacific halibut and snow crab). Regression slopes were multiplied by the length of the period of record
to estimate the total movement described in the "Key Points" section of this indicator. EPA used Sen's
slope analysis to verify the apparent trends; the Sen slope results matched the OLS regression results in
sign and approximate magnitude.
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Table TD-1. Linear Regression of Annual Centers of Biomass
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All 140 species across
both regions
OLS
trend
(per
year)
Latitude
(miles)
0.559
<0.001
Y
e
s
Sen's slope
trend (per
year)
0.528
All 140 species across
both regions
Depth (feet)
0.582
<0.001
Y
e
s
0.579
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1







9







8





All Eastern Bering Sea
species

2
2
0
1
8
Latitude
(miles)
0.309
<0.001
Y
e
s
0.310


1







9







8





All Eastern Bering Sea
species

2
2
0
1
8
Depth (feet)
-0.024
0.718
N
o
-0.014


1







9







7





All Northeast species

3
2
0
1
9
Latitude
(miles)
0.887
<0.001
Y
e
s
0.884


1







9







7







3



Y

All Northeast species

2
0
1
9
Depth (feet)
1.31
<0.001
e
s
1.32


1







9







7





Homarus americanus
American
lobster
3
2
0
1
9
Latitude
(miles)
2.14
<0.001
Y
e
s
2.16
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1







9







7





Centropristis striata
Black sea
bass
3
2
0
1
9
Latitude
(miles)
3.19
<0.001
Y
e
s
3.51


1







9







7





Urophycis chuss
Red hake
3
2
0
1
9
Latitude
(miles)
2.01
<0.001
Y
e
s
1.83


1







9







8





Gadus chalcogrammus
Alaska
pollock
2
2
0
1
8
Latitude
(miles)
0.444
0.059
N
o
0.428


1







9







8





Hippoglossus stenolepis
Pacific
halibut
2
2
0
1
8
Latitude
(miles)
0.570
<0.001
Y
e
s
0.597


1







9







8





Chionoecetes opilio
Snow crab
2
2
0
1
8
Latitude
(miles)
0.609
0.032
Y
e
s
0.638
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References
Pinsky, M.L., B. Worm, M.J. Fogarty, J.L. Sarmiento, and S.A. Levin. 2013. Marine taxa track local climate
velocities. Science 341(6151):1239-1242.
USGCRP (U.S. Global Change Research Program). 2018. Impacts, risks, and adaptation in the United
States: Fourth National Climate Assessment, volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E.
Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart, eds. U.S. Global Change Research Program.
www.globalchange.gov/nca4. doi: 10.7930/NCA4.2018.CH9
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