NAFO Sci. Coun. Studies, 33: 11–28
The Realized Annual Niche Space of Common Fish
Species off Newfoundland
Johanne Fischer
Institut für Seefischerei, Bundesforschungsanstalt für Fischerei
Palmaille 9, D22767 Hamburg, Germany
and
Richard L. Haedrich
Eco-Research Program, Memorial University
St.John's, Newfoundland, Canada A1C 5S7
Abstract
Data from groundfish research surveys on the continental shelf of northeast Newfoundland were used to examine the relationship between abundance of fish species at individual stations, bottom temperature, and depth in the period 1978 to 1993. The observed
abundance of 24 common fishes within temperature and depth categories (-2 to +6°C, 50
to 1 000 m) was compared with the expected abundance, and preferences and avoidance
were thus determined. The individual pattern of preferred categories defines the niche shape
that is assumed to represent the realized niche of a species. Comparison of realized annual
niche spaces showed that a pronounced shift towards deeper waters occurred in numerous
fish species during the study period. These preliminary results suggest that reduction or
expansion of realized niche space could be useful as an indicator for displacements and
changing habitat occupation by continental shelf fishes.
Key words:
abundance, depth, fish, Newfoundland shelf, niche breadth, temperature, visualization
Introduction
The aim of our study is to describe what the
available data from groundfish research surveys on
the continental shelf off Newfoundland convey
about ecological shifts in abundant fish species. Our
perspective is that of "niche space", a term introduced by Hutchinson (1957). In his concept, biotic
and abiotic characteristics of the environment are
represented by multi-dimensional niche axes along
which each species can be located according to its
specific requirements and physiological tolerances
(as determined from experiments). This describes
the fundamental niche space of a given species. The
realized niche space is that fraction of the fundamental niche space that a species or population will
actually occupy in a particular ecosystem during a
determined time period. Our niche space has two
axes, temperature and depth, and we use these to
discriminate different realized annual niche spaces
of common fish species off Newfoundland during
the autumn season over the period 1978 to 1993.
Based upon Hutchinson's niche concept, we
developed a graphical presentation that is rich in
information. The value of publishing these sets of
visualized niche space, all of which can be analysed
from various different perspectives, consists in offering a tool to help interpret all kinds of other ecological and fisheries data within this geographical
region. Our data sets should be useful to specialists and fisheries biologists concerned with single
species and to community ecologists concerned with
matters such as competition, habitat use, and predation.
Materials and Methods
The database used in this research was developed by Villagarcía (MS 1995) based on information from the annual autumn survey cruises conducted by Department of Fisheries and Oceans,
Canada, from 1978 to 1993 in the Northwest Atlantic Fisheries Organization (NAFO) Divisions 2J,
3K and 3L (Fig. 1). These surveys have been
12
Sci. Council Studies, No. 33, 2000
˚
55
1991 survey
2J
˚
54
˚
53
Labrador
˚
52
˚
51
3K
˚
50
˚
49
3L
Newfoundland
˚
48
˚
47
˚59
˚
46
Fig. 1.
˚
58
˚
57
˚
56
˚
55
54
˚
53
˚
˚
52
51
˚
˚
50
49
˚
˚
48
˚
47
NAFO Div. 2J, 3K, and 3L with an example of survey stations distribution in 1991 .
conducted by stratified random trawls (for more
details see Bishop et al., MS 1994). The analyses
included 24 common fish species in the area (Table
1). Seven temperature categories ranging from -2 to
+6°C and seven depth categories ranging from
50 to 1 000 m were established. The number of stations falling into each of the combined temperature/
depth (which is described in this study as niche)
categories determined the sampled niche space in
regard to bottom temperature and depth. Categories with less than 3 stations were omitted from our
analyses. Expected values for the abundance of
every analysed fish population in each niche category (E f ) were calculated based on station distribution within the sampled niche space (where N f is
the total number of individuals of the analysed fish
species, n s is the number of stations in a particular
niche category, N s is the total number of stations
considered in the analysis):
E
f
N f ns
=
Ns
The observed numbers of fish (O f ) falling into
each niche category were then compared with the
expected numbers and relative deviations in each
cell calculated as γ -values (based on the selectivity index E i proposed by Ivlev, 1961):
γ =
(O
(O
)
+E )
f
− Ef
f
f
Glyptocephalus cynoglossus
Hippoglossoides platessoides
Limanda ferruginea
Reinhardtius hippoglossoides
21 Pleuronectidae
22 Pleuronectidae
23 Pleuronectidae
24 Pleuronectidae
Northern alligotorfish
Leptagonus decagonus
Cyclopterus lumpus
19 Agonidae
20 Cyclopteridae
Arctic deep-sea sculpin
Cottunculus microps
18 Cottidae
Golden redfish
Greenland halibut
Yellowtail flounder
American plaice
Witch flounder
Lumpfish
Deep-sea redfish
Sebastes marinus
Sebastes mentella
16 Scorpaenidae
Spotted wolffish
Atlantic wolffish
Broadhead wolffish
Checker eelpout
17 Scorpaenidae
Anarhichas lupus
Anarhichas minor
14 Anarhichidae
15 Anarhichidae
Anarhichas denticulatus
13 Anarhichidae
Arctic eelpout
Lycodes reticulatus
Lycodes vahlii
Marlin spike
Nezumia bairdii
11 Zoarcidae
Roughhead grenadier
Macrourus berglax
9 Macrouridae
10 Macrouridae
12 Zoarcidae
Roundnose grenadier
Coryphaenoides rupestris
8 Macrouridae
Arctic cod
Atlantic cod
Boreogadus saida
Gadus morhua
6 Gadidae
Blue hake
Capelin
Smooth skate
Thorny skate
Black dogfish
Common names
7 Gadidae
Mallotus villosus
Antimora rostrata
4 Osmeridae
Raja senta
3 Rajidae
5 Moridae
Centroscyllium fabricii
Raja radiata
1 Squalidae
Species
2 Rajidae
Family
220 550
5 388
413 166
32 001
1 375
1 636
1 072
556 437
16 294
2 676
9 963
5 582
11 879
8 798
3 640
18 403
33 411
268 007
85 837
2 517
122 044
2 905
41 309
1 951
numbers
3.5
1.1
5.4
2.9
3.7
3.6
2.9
2.6
2.2
5.3
3.8
5.4
4.6
4.7
1.8
3.7
0.9
4.2
3.0
1.0
3.1
3.2
5.4
1.0
Average Ht
-0.49
0.33
0.67
-0.74
0.04
0.45
-0.10
-0.43
0.08
-0.77
-0.36
-0.77
-0.40
0.36
-0.42
-0.93
-0.17
-0.68
0.58
-0.02
0.49
-0.68
-0.22
-0.16
Trend in Ht r
TABLE 1. List of fish species included in the analyzes, their total numbers in survey catches (including all years from 1978 to
1993), their average annual Ht values, and Ht trends (correlation coefficient r) over the study period. Bold numbers
indicate statistically significant coefficients (α = 0.05).
FISCHER and HAEDRICH: Niche Space of Common Fish
13
14
Sci. Council Studies, No. 33, 2000
A positive deviation from the expected value
is interpreted as preference for and a negative deviation as avoidance of that particular temperature/
depth cell. The visualisation of the realized niche
space is based on the γ -values (see Fig. 2 to 13).
could eventually lead to a marked disappearance of
individuals in once densely occupied habitats with
preferred niche characteristics leaving only remnant
populations in habitats with less favourable niche
characteristics.
Linked to the variability in shape (as visualised in Fig. 2 to 13), the realized niche space has a
size/width component. To facilitate comparisons, a
numeric representation of the relative width of a
species realized niche space (Ht) is determined
based on chi-square ( χ 2 serving as a measure of
the deviation from an expected distribution and not
as a statistical test for correlation). Ht is expressed
as 1/K' (based upon the K-value of Sachs, 1988;
modified); K' corrects χ 2 for both the total number
of fish (N f ) and the number of cells (n c):
Relative to other continental shelf areas, variability in temperature off Newfoundland (ranging
from approximately -2°C to +6°C) is much narrower
than is variability in depth (ranging from approximately 50 m to 1 000 m). This is especially true for
areas deeper than 500 m where a very narrow range
of temperatures of only 4°C to 6°C is observed. As
an important effect of the narrow temperature window on the Newfoundland continental shelf, thermal niche segregation in fish populations is relatively indistinct. Some species occurring in waters
shallower than 500 m tend to avoid the higher temperatures within the range (Arctic cod, Arctic
eelpout, and northern alligatorfish), others tend to
avoid the very low temperatures (smooth skate,
Atlantic cod, checker eelpout, all wolffish, both
redfish, witch flounder, and yellowtail flounder),
and others seem to occupy equally all temperatures
within the range (thorny skate, capelin, lumpfish,
and Greenland halibut). Although these temperature
preferences are not very sharp, they appear to be
fairly constant throughout the study period. There
is not even one case in our analysis where a shift in
realized temperature niche took place that was not
connected to a shift in depth niche.
K' =
X2
1
×
N f nc
→ Ht =
1
K'
A low Ht value (<2) indicates a relatively small
realized annual niche space and a high Ht value (>4)
points to a large realized annual niche.
Trends of a species niche width (Ht) on an annual basis were estimated through regression analyses and calculation of the correlation coefficient r.
Total numbers of species caught during surveys
in each year is given with the figures (Fig. 2 to 13).
Results and Discussion
The approach used in this paper allows determining and comparing annual temperature/depth
distribution of fish independent of their abundance.
To examine possible changes in niche width and
shape during the period of investigation, preference/
avoidance patterns were plotted for each year and
annual measures of the width of the realized niche
space (Ht) were performed (Fig. 2 to 13). When
comparing the graphs for different years in any species one should keep in mind that a shift in preferred niche space does not necessarily imply that
individuals of a population displayed different niche
selection patterns in each year. In the situation encountered on the Newfoundland shelf where abundance of so many fish species declined from 1978
to 1993 (e.g. Haedrich and Fischer, 1996), niche
space shifts might simply reflect a situation where
change in environmental conditions or human predation affects some habitats more than others. This
In contrast to the relative constancy in the realized temperature niche axis, the realized depth
niche axis often changed noticeably over the 16
years of the study. In half of the species analysed,
a trend towards an apparent occupation of deeper
waters was observed (Fig. 2 to 13). This trend was
most common in abundant species like Arctic cod,
A t l a n t i c c o d , r o u g h h e a d g r e n a d i e r, A t l a n t i c
wolffish, golden redfish, deep-sea redfish, witch
flounder, American plaice, and Greenland halibut.
However, there were some less abundant species
that followed the same trend, i.e. broadhead and
spotted wolffish and northern alligatorfish.
Those species that did not exhibit discernible
shifts in realized niche space were mostly either distinctly shallow-water fish or distinctly deep-water
fish. The shallow-water category included thorny
skate, capelin, Arctic eelpout, lumpfish, and
yellowtail flounder. The deep-water category included mostly fish that realized a small niche space
1.2
1.1
Ht
1.0
1990
Ht
1986
Ht
105
240
1.1
0.7
Ht
1.7
1991
Ht
1987
Ht
1983
1982
0.9
1979
Ht
136
0
Ht
1978
62
122
210
53
1.3
0.9
0.8
Ht
1.1
1992
Ht
1988
Ht
1984
Ht
1980
7
50
112
210
0.9
1.3
0.7
Ht
0.9
1993
Ht
1989
Ht
1985
Ht
1981
22
48
267
141
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Centroscyllium fabricii
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
6.2
2.5
3.2
Ht
4.3
1990
Ht
1986
Ht
1982
Ht
1978
3535
2249
2366
687
6.6
8.0
7.2
Ht
4.0
1991
Ht
1987
Ht
1983
Ht
1979
3697
2559
2183
1112
5.3
6.3
7.3
Ht
4.1
1992
Ht
1988
Ht
1984
Ht
1980
4484
3274
1133
945
4.4
5.4
6.5
Ht
4.4
1993
Ht
1989
Ht
1985
Ht
1981
2701
3208
3920
1904
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Raja radiata
Fig. 2. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
FISCHER and HAEDRICH: Niche Space of Common Fish
15
m
Ht
Ht
Ht
294
111
1.9
53
Ht
274
115
2.4
77
Ht
229
96
3.1
Ht
53
1993
Ht
207
124
2.9
Ht
43
Ht
1.2
Ht
121
1.0
1.0
1.0
Ht
1.7
89
Ht
126
25
1.1
75
24
0.7
1993
Ht
290
1.3
1989
Ht
129
0.9
1985
Ht
0.6
1992
1981
Ht
0.9
1988
Ht
266
0.8
1984
Ht
101
1991
1980
Ht
242
1987
Ht
181
1.0
1983
Ht
0.9
1990
<100
200
300
400
500
700
>700
263
145
1979
Ht
1986
<100
200
300
400
500
700
>700
0
Ht
1982
<100
200
300
400
500
700
>700
2.6
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
1978
<100
200
300
400
500
700
>700
2.8
1989
m
186
3.5
1985
Ht
3.0
1992
1981
Ht
3.7
1988
Ht
274
4.5
1984
Ht
2.4
1991
1980
Ht
3.0
1987
Ht
323
4.9
1983
Ht
3.5
1990
<100
200
300
400
500
700
>700
Ht
3.9
1986
<100
200
300
400
500
700
>700
1979
°C
99
0.9
Fig. 3. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
Sci. Council Studies, No. 33, 2000
Ht
367
3.1
1982
<100
200
300
400
500
700
>700
Antimora rostrata
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
1978
<100
200
300
400
500
700
>700
16
Raja senta
°C
Mallotus villosus
°C
m
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
1978
Ht
2.1
1982
<100
200
300
400
500
700
>700
Ht
Ht
Ht
3397
3441
3.2
5561
Ht
2753
10954
3.0
13248
Ht
903
11892
4.3
10069
1993
Ht
8438
5.3
Ht
7975
Ht
6304
Ht
Ht
3079
2.9
3.3
2.6
Ht
3.8
7161
Ht
2811
10435
2.8
8464
8079
3.6
1993
Ht
15275
4.2
1989
Ht
3449
2.3
1985
Ht
2.5
1992
1981
Ht
2.9
1988
Ht
2395
1.9
1984
Ht
1945
1991
1980
Ht
2815
1987
Ht
1824
1.3
1983
Ht
3.2
1990
<100
200
300
400
500
700
>700
3898
2748
1979
Ht
4.4
1986
<100
200
300
400
500
700
>700
274
1.4
1982
<100
200
300
400
500
700
>700
2.9
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
1978
<100
200
300
400
500
700
>700
5.1
1989
Ht
15999
0.5
1985
Ht
2.3
1992
1981
Ht
2.4
1988
Ht
12114
1.0
1984
Ht
3.0
1991
1980
Ht
4.2
1987
Ht
5956
0.7
1983
Ht
3.4
1990
<100
200
300
400
500
700
>700
1979
Ht
5.9
1986
<100
200
300
400
500
700
>700
2
m
8647
4.5
FISCHER and HAEDRICH: Niche Space of Common Fish
<100
200
300
400
500
700
>700
Boreogadus saida
°C
Fig. 4. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
17
5.2
5.9
2.8
Ht
2.9
1990
Ht
1986
Ht
1982
Ht
1978
19146
30416
16667
7858
4.9
6.6
5.7
Ht
3.1
1991
Ht
1987
Ht
1983
Ht
1979
28873
17200
18838
10616
4.5
4.9
4.0
Ht
2.8
1992
Ht
1988
Ht
1984
Ht
1980
12257
16988
11581
8342
4.3
4.0
3.4
Ht
2.8
1993
Ht
1989
Ht
1985
Ht
1981
2612
23439
22466
11586
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Gadus morhua
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
Ht
0.8
0.7
0.9
1990
Ht
1986
Ht
1982
Ht
1978
1137
1283
1784
0
0.7
Ht
0.8
1991
Ht
0.9
1.0
1987
Ht
1983
1979
1253
258
3668
5381
0.6
Ht
0.8
1992
Ht
1.2
0.9
1988
Ht
1984
Ht
1980
159
382
2569
4131
0.4
Ht
1.5
1993
Ht
1.1
1.3
1989
Ht
1985
Ht
1981
821
409
5224
1380
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Coryphaenoides rupestris
Fig. 5. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
18
Sci. Council Studies, No. 33, 2000
4.8
4.7
3.0
Ht
2.6
1990
Ht
1986
Ht
1982
Ht
1978
1053
1107
2139
430
5.1
4.0
3.4
Ht
2.5
1991
Ht
1987
Ht
1983
Ht
1979
1180
1430
1401
998
6.2
4.8
2.7
Ht
1.9
1992
Ht
1988
Ht
1984
Ht
1980
611
746
938
1310
4.7
4.2
3.0
Ht
1.7
1993
Ht
1989
Ht
1985
Ht
1981
680
629
1586
1059
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Macrourus berglax
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
2.4
1.9
1.6
Ht
2.0
1990
Ht
1986
Ht
1982
Ht
1978
279
275
293
28
2.3
1.2
1.5
Ht
1.6
1991
Ht
1987
Ht
1983
Ht
1979
397
174
138
134
1.9
2.0
1.5
Ht
1.6
1992
Ht
1988
Ht
1984
Ht
1980
254
103
111
242
1.8
1.7
1.2
Ht
2.2
1993
Ht
1989
Ht
1985
Ht
1981
335
82
425
108
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Nezumia bairdii
Fig. 6. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
FISCHER and HAEDRICH: Niche Space of Common Fish
19
3.9
5.0
5.1
Ht
3.9
1990
Ht
1986
Ht
1982
Ht
1978
633
460
752
650
4.4
5.2
Ht
5.6
1991
Ht
1987
Ht
1983
Ht
1979
357
791
689
0
4.1
5.2
Ht
4.7
1992
Ht
1988
Ht
1984
Ht
1980
171
975
276
0
3.6
5.3
6.0
Ht
4.2
1993
Ht
1989
Ht
1985
Ht
1981
183
897
1023
695
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Lycodes reticulatus
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
6.0
5.0
4.3
Ht
2.3
1990
Ht
1986
Ht
1982
Ht
1978
377
372
877
2325
6.0
4.6
3.5
Ht
4.0
1991
Ht
1987
Ht
1983
Ht
1979
325
450
721
1376
5.3
5.3
3.4
Ht
5.7
1992
Ht
1988
Ht
1984
Ht
1980
304
408
448
1316
4.8
4.6
3.7
Ht
6.0
1993
Ht
1989
Ht
1985
Ht
1981
433
731
431
541
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Lycodes vahlii
Fig. 7. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right
corner, depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure
indicates years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom
of each annual figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the
species in question was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference;
small circles = week avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
20
Sci. Council Studies, No. 33, 2000
4.8
8.2
4.7
Ht
2.8
1990
Ht
1986
Ht
1982
Ht
1978
95
246
742
319
12.8
6.7
3.9
Ht
3.3
1991
Ht
1987
Ht
1983
Ht
1979
79
188
599
498
7.8
6.7
4.4
Ht
3.8
1992
Ht
1988
Ht
1984
Ht
1980
54
219
394
618
6.2
4.5
3.9
Ht
1.8
1993
Ht
1989
Ht
1985
Ht
1981
19
110
516
481
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Anarhichas denticulatus
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
4.2
4.3
3.0
Ht
2.8
1990
Ht
1986
Ht
1982
Ht
1978
259
322
971
1103
4.7
4.3
2.8
Ht
4.3
1991
Ht
1987
Ht
1983
Ht
1979
404
486
822
1052
4.2
4.4
3.1
Ht
4.1
1992
Ht
1988
Ht
1984
Ht
1980
305
518
500
891
3.8
3.4
3.6
Ht
4.2
1993
Ht
1989
Ht
1985
Ht
1981
252
345
801
591
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Anarhichas lupus
Fig. 8. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
FISCHER and HAEDRICH: Niche Space of Common Fish
21
9.0
5.4
5.0
Ht
3.9
1990
Ht
1986
Ht
1982
Ht
1978
88
116
382
154
5.5
6.5
5.0
Ht
4.2
1991
Ht
1987
Ht
1983
Ht
1979
127
144
244
169
5.9
6.6
4.8
Ht
4.6
1992
Ht
1988
Ht
1984
Ht
1980
79
156
126
188
5.5
5.1
3.4
Ht
4.0
1993
Ht
1989
Ht
1985
Ht
1981
45
142
167
233
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Anarhichas minor
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
3.6
2.8
1.2
Ht
1.1
1990
Ht
1986
Ht
1982
Ht
1978
251
362
554
250
2.6
1.0
3.1
Ht
1.9
1991
Ht
1987
Ht
1983
Ht
1979
234
344
3822
566
1.9
2.4
2.0
Ht
3.3
1992
Ht
1988
Ht
1984
Ht
1980
29
187
490
5567
1.1
1.5
2.0
Ht
3.6
1993
Ht
1989
Ht
1985
Ht
1981
20
656
822
1898
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Sebastes marinus
Fig. 9. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
22
Sci. Council Studies, No. 33, 2000
3.0
3.1
2.5
Ht
2.3
1990
Ht
1986
Ht
1982
Ht
1978
15097
22876
48477
24627
1.9
2.4
2.6
Ht
2.7
1991
Ht
1987
Ht
1983
Ht
1979
8570
16632
1E+05
35982
4.4
4.0
2.0
Ht
2.0
1992
Ht
1988
Ht
1984
Ht
1980
5533
21631
24056
35019
2.2
2.5
1.9
Ht
2.0
1993
Ht
1989
Ht
1985
Ht
1981
3643
10068
52070
70428
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Sebastes mentella
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
4.4
2.4
2.9
Ht
1.0
1990
Ht
1986
Ht
1982
Ht
1978
66
53
41
63
3.3
3.0
2.8
Ht
1.7
1991
Ht
1987
Ht
1983
Ht
1979
206
55
42
48
2.6
1.2
Ht
1.1
1992
Ht
1988
Ht
1984
Ht
1980
91
14
23
0
2.5
3.0
Ht
0.9
1993
Ht
1989
Ht
1985
1981
189
67
46
0
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Cottunculus microps
Fig. 10. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
100
200
300
400
500
700
<100
100
200
300
400
500
700
<100
100
200
300
400
500
700
<100
100
200
300
400
500
700
m
°C
FISCHER and HAEDRICH: Niche Space of Common Fish
23
2.2
5.1
3.8
Ht
1.0
1990
Ht
1986
Ht
1982
Ht
1978
103
76
49
123
3.4
3.2
3.9
Ht
1.7
1991
Ht
1987
Ht
1983
Ht
1979
132
74
49
53
2.1
5.2
3.3
Ht
1.1
1992
Ht
1988
Ht
1984
Ht
1980
192
66
29
21
2.0
3.0
5.4
Ht
0.9
1993
Ht
1989
Ht
1985
Ht
1981
262
216
117
13
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Leptagonus decagonus
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
2.1
5.8
3.1
Ht
1.0
1990
Ht
1986
Ht
1982
Ht
1978
70
181
70
38
3.1
6.1
1.6
Ht
1.7
1991
Ht
1987
Ht
1983
Ht
1979
97
96
35
100
2.6
4.1
1.8
Ht
1.1
1992
Ht
1988
Ht
1984
Ht
1980
85
234
24
32
4.0
4.7
4.4
Ht
0.9
1993
Ht
1989
Ht
1985
Ht
1981
29
142
67
36
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Cyclopterus lumpus
Fig. 11. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
24
Sci. Council Studies, No. 33, 2000
3.4
3.1
2.8
Ht
1.8
1990
Ht
1986
Ht
1982
Ht
1978
1413
1686
2801
1475
4.0
3.2
2.0
Ht
2.1
1991
Ht
1987
Ht
1983
Ht
1979
941
1911
3453
2274
4.0
3.9
2.9
Ht
2.1
1992
Ht
1988
Ht
1984
Ht
1980
493
1469
3277
2551
2.4
3.0
2.8
Ht
2.3
1993
Ht
1989
Ht
1985
Ht
1981
301
1057
3062
2694
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Glyptocephalus cynoglossus
<100
<100
200
300
400
500
700
<100
<100
200
300
400
500
700
<100
<100
200
300
400
500
700
m
<100
<100
200
300
400
500
700
°C
4.5
3.7
4.9
Ht
4.6
1990
Ht
1986
Ht
1982
Ht
1978
22210
23185
47943
10356
5.0
4.2
5.2
Ht
8.2
1991
Ht
1987
Ht
1983
Ht
1979
15913
31077
52269
7404
4.7
5.6
3.9
Ht
10.6
1992
Ht
1988
Ht
1984
Ht
1980
10349
36201
9282
11323
3.8
4.9
5.0
Ht
8.3
1993
Ht
1989
Ht
1985
Ht
1981
4995
23059
53893
41598
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Hippoglossoides platessoides
Fig. 12. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
FISCHER and HAEDRICH: Niche Space of Common Fish
25
0.7
1.2
Ht
1.0
1990
Ht
1986
Ht
154
220
1.2
1.4
Ht
1.7
1991
Ht
1987
Ht
1983
1982
1979
Ht
124
0
Ht
1978
169
500
601
0
1.4
Ht
1.1
1992
Ht
1988
Ht
1984
Ht
1980
156
578
0
0
0.8
1.2
1.0
Ht
0.9
1993
Ht
1989
Ht
1985
Ht
1981
139
155
1890
121
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Limanda ferruginea
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
3.5
4.0
2.7
Ht
2.7
1990
Ht
1986
Ht
1982
Ht
1978
13652
15500
15931
6390
4.8
4.1
2.7
Ht
3.0
1991
Ht
1987
Ht
1983
Ht
1979
10658
14605
14117
9567
5.5
3.7
2.5
Ht
4.2
1992
Ht
1988
Ht
1984
Ht
1980
9900
14390
15043
9977
2.8
4.4
1.9
Ht
3.2
1993
Ht
1989
Ht
1985
Ht
1981
15513
18674
16060
10402
-1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4 -1 0 1 2 3 4 >4
Reinhardtius hippoglossoides
Fig. 13. Realized annual niche space of analyzed species. Temperature categories (1°C width, starting with <-1°C to >4°C) run from the left to the right corner,
depth categories (100 m width, starting with <100 m to >700 m) from the upper corner down. The upper left number in each annual figure indicates
years. The upper right number in each annual figure gives total catch numbers in each year. Annual Ht values are given at the bottom of each annual
figure. Each figure has a unique shape representing the sampled niche space in a given year. White fields indicate space where the species in question
was never caught. Grey fields indicate presence of the species in question. Open circles = avoidance, black circles = preference; small circles = week
avoidance or preference (γ<0,2); large circles = strong avoidance or preference (γ>0,5).
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
<100
200
300
400
500
700
>700
m
°C
26
Sci. Council Studies, No. 33, 2000
FISCHER and HAEDRICH: Niche Space of Common Fish
like black dogfish, blue hake, roundnose grenadier,
marlin spike, and Arctic deep-sea sculpin. None of
these species displayed a shift towards more shallow grounds. A drift towards deeper grounds in
these species would not have been detected in this
study because sampling effort usually did not exceed 1 000 m.
For Atlantic cod, shifts in temperature and
depth preferences on the Newfoundland shelf or
neighbouring areas have been analysed before.
Swain (1993) reports age-dependent density/depth
correlation for Atlantic cod in the southern Gulf of
St. Lawrence where younger cod were found in
shallower water than were older cod. He attributed
this pattern to varying strategies of resource utilisation. On the Newfoundland shelf, since 1978 the
average age of Atlantic cod has declined steadily
(Hutchings and Myers, 1994). Based on the results
of Swain (1993), a shift in realized niche space towards more shallow waters could have been expected. However, realized niche space shifted to
deeper areas, indicating that common resource use
strategies probably did not apply in this case. Another important species on the Newfoundland shelf
is capelin, a key prey species for many larger animals, e.g. Atlantic cod. The decline of capelin in
the area since the late-1980s has been discussed as
a possible factor contributing to the decline of Atlantic cod (Rose et al. 1994). Nakashima (1996)
hypothesises that cooler water temperatures in the
1990s are the predominant reason for changes in
capelin behaviour, distribution, and biology that
have been observed since 1991. We therefore expected to find capelin in a relatively warm temperature niche. The contrary was true. Our data indicated that in most years a relatively large temperature-depth niche for capelin with frequently pronounced preferences for very cold temperatures
below 0°C (e.g. in 1981, 1985, and 1988 to 1991)
and general avoidance of temperatures above 3°C
(Fig. 4).
An interesting question in connection with general deep-water shifts regards the trends over time
in the Ht values (Table 1). The Ht value serves as
an indicator for the size/width of the realized niche
space. A large Ht indicates that the species in question occupies a broad temperature/depth spectrum
whereas a small Ht points to a sharp selection of a
few particular temperature/depth locales by a given
species. Shifts in realized niche space such as the
observed trend towards deeper waters can be the
27
result of either niche space expansion or niche space
reduction of the species concerned. An expansion
of realized niche width is caused by more even distribution over the available niche space, e.g. over
the total depth range, of a species and is indicated
by larger Ht values over time. An increase of Ht
values in connection with deep-water shifts was
observed in only three cases, with statistically significant positive Ht trends in Arctic cod and American plaice, and non-significant but still conspicuous positive trends in northern alligatorfish. A reduction of realized niche space takes place when a
species no longer occupy once preferred areas with
specific habitat characteristic, e.g. shallow waters,
in which case Ht values ought to become smaller.
In two-thirds (8 out of 12) of the species exhibiting trends towards deeper grounds, the shift in realized niche space resulted in an overall reduction
of its width. These trends are statistically signific a n t i n A t l a n t i c c o d , r o u g h h e a d g r e n a d i e r,
broadhead and spotted wolffish, and witch flounder. Ht value trends in Atlantic wolffish, deep-sea
redfish, and Greenland halibut were not statistically
significant, but still suggested that the realized
niche space was reduced.
Conclusions
The method described allows visualizing depth/
temperature preferences (realized niche space) of
fish populations in a given area independent of their
abundance. Annual plots show that the realized
niche space in various species does not remain fixed
but varies from year to year. During the study period, a conspicuous trend towards deeper water was
discernible in many species, which may be connected to changes in the environment or to declines
in fish abundance. The period 1978 to 1993 was one
during which disturbance, from declining sea temperature and heavy fishing effort, increased across
the Newfoundland shelf ecosystem (Haedrich et al.,
1997, Drinkwater, 1996, Colbourne et al., 1997,
Borovkov and Stein, MS 1997). Most fish
populations analysed, including both commercial
and non-commercial species, suffered a decline in
population abundance or average size of individuals, a fact that has been reported in a number of
studies (e.g. Sinclair and Murawski, 1997, Haedrich
and Fischer, 1996, Taggart, et al., 1994, Haedrich
and Barnes, 1997, Bowering and Brodie, 1995).
Ht values reflect the width/size of realized
niche space. The analyses showed that the observed
28
Sci. Council Studies, No. 33, 2000
trends towards deeper water were mostly accompanied by a significant reduction in the size of realized niche space. We thus conclude that trends in
Ht values can be used as an indicator for
displacements and changing habitat occupancy by
continental shelf fishes.
Acknowledgements
We thank Dr David Schneider (Memorial University, St. John's, Newfoundland, Canada) for his
excellent advice concerning the methodology. We
also acknowledge Manfred Stein (Bundesforschungsanstalt für Fischerei in Hamburg, Germany) for his useful remarks on oceanographic
questions. Our research has been supported by
grants from SSHRC, the Tri-Council Eco-Research
Program, and NSERC, Canada, and the GermanCanadian Agreement on Co-operation in Scientific
Research and Technological Development.
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