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Incomes, Attitudes, and Occurrences of Invasive Species:An Application to Signal Crayfish in Sweden
Ing-Marie Gren Æ Monica Campos ÆLennart Edsman Æ Patrik Bohman
Received: 27 December 2007 / Accepted: 28 August 2008 / Published online: 23 October 2008
� Springer Science+Business Media, LLC 2008
Abstract This article analyzes and carries out an
econometric test of the explanatory power of economic and
attitude variables for occurrences of the nonnative signal
crayfish in Swedish waters. Signal crayfish are a carrier of
plague which threatens the native noble crayfish with
extinction. Crayfish are associated with recreational and
cultural traditions in Sweden, which may run against
environmental preferences for preserving native species.
Econometric analysis is carried out using panel data at the
municipality level with economic factors and attitudes as
explanatory variables, which are derived from a simple
dynamic harvesting model. A log-normal model is used for
the regression analysis, and the results indicate significant
impacts on occurrences of waters with signal crayfish of
changes in both economic and attitude variables. Variables
reflecting environmental and recreational preferences have
unexpected signs, where the former variable has a positive
and the latter a negative impact on occurrences of waters
with signal crayfish. These effects are, however, counter-
acted by their respective interaction effect with income.
Keywords Attitudes � Income � Interest rate �Invasive species � Signal crayfish � Sweden
Introduction
Invasive alien species, defined as ‘‘alien species which
become established in natural or semi-natural ecosystems
or habitat, is an agent of change, and threatens native
biological diversity’’ (IUCN 2000), is not a new phe-
nomenon, but can be traced back to the arrival of
agriculture 10000 years ago. During the last decades,
scientists have documented a number of alien and inva-
sive species that have detrimental economic effects, and
on biodiversity (e.g., Pimentel and others 2001). Esti-
mated annual costs of invasive alien species (IAS) for
different countries show a considerable variation with a
range of 3 Euro/capita and 344 Euro/capita (Gren and
others 2008). However, in spite of ecologists’ and biolo-
gists’ relatively early recognition and concern about
eventual damage and social costs associated with invasive
species, there is relatively little environmental economic
research on this topic (e.g., Shogren and Tschirhart 2005).
Since most of the scant research has been focused on
theoretical analysis of efficient management strategies
(e.g., Perrings and others 2000; Horan and Lupi 2005;
Knowler and Barbier 2005; Shogren and Tschirhart 2005;
Gren 2008), or on cost benefit calculations of programs
preventing, controlling, or eradicating damage from spe-
cies’ invasion (see Born and others 2005; Lovell and
others 2006; Olson 2006), there is insufficient under-
standing of the causes for spread of IAS, in particular
within a national territory. The purpose of this article is to
derive and test hypotheses on the spread of an invasive
I.-M. Gren (&) � M. Campos
Department of Economics, Swedish University of Agricultural
Sciences, Box 7013, 750 07 Uppsala, Sweden
e-mail: [email protected]
M. Campos
e-mail: [email protected]
L. Edsman � P. Bohman
Freshwater Laboratory, Bars Holm Road 2,
178 93 Drottningholm, Sweden
e-mail: [email protected]
P. Bohman
e-mail: [email protected]
123
Environmental Management (2009) 43:210–220
DOI 10.1007/s00267-008-9210-7
species in Sweden, signal crayfish (Pacifastacus lenius-
culus), which include economic and attitude variables as
explanatory factors.
To the best of our knowledge there are only two other
studies testing the explanatory power of different factors
for introduction and spread of alien species, and both
these studies are applied to international spread of inva-
sive species (Dalmazzone 2000; Vila and Pujadas 2001).
Trade is then regarded as an important vector of IAS,
which can ‘‘hitchhike’’ with cargoes and goods or be
traded in the international markets for exotic plants or
animals (e.g., Perrings and others 2000). The trade
hypothesis has been tested by both studies on spread of
invasive species. Dalmazzone (2000) also includes income
per capita as an explanatory variable which is supposed to
reflect the economic activity in a country. This study is
complementary to the two earlier studies on causes of
occurrences of invasive species in two respects: One is the
analysis and empirical test of different factors explaining
spread of an invasive species within a single country,
which is based on unique panel data on occurrences of
signal crayfish in Swedish municipalities. Similar to Dal-
mazzone (2000), economic activity is introduced as an
explanatory variable. The other contribution is the analysis
and test of the explanatory power of variables reflecting
attitudes for the spread of signal crayfish, which extends
the scarce empirical literature on attitudes as determinants
of environmentally friendly behavior (Owen and Videras
2007; Kahn 2007).
By the inclusion of income as explanatory variable to
spread of an invasive signal crayfish in Sweden, the study
is also related to the relatively large literature on the so-
called environmental Kuznets curve, which, since the
seminal contributions of Grossman and Krueger (1995),
has been testing the relation between changes in income
and environmental performance in countries and regions
(see Dinda 2004 for a review). A common result is that
environmental degradation, often measured as emissions
of different pollutants, increases at relatively low income
levels and decreases at higher incomes. An interesting
policy conclusion is then that environmental problems
may vanish as average income grows in a country or
region. In spite of the considerably large number of
studies, there are few studies estimating the relation
between biodiversity-related changes and income (Dal-
mazzone 2000; Ehrardt-Martinez and others 2002;
McPherson and Nieswiadomy 2005). Since these studies
apply cross-country data, this study constitutes a contri-
bution by estimating an environmental Kuznets curve for
biodiversity-related changes by using panel data within a
country. Furthermore, since there is a direct linkage
between action, introduction of signal crayfish, and envi-
ronmental impact, decline of the number of populations of
the endemic noble crayfish (Astacus astacus), this study is
one of the few studies estimating environmental Kuznets
curves for local action and associated environmental
impact.
The article is organized as follows. First, a brief pre-
sentation is provided on traditions and environmental
concern with respect to Swedish signal crayfish. It provides
a basis for the modeling of crayfish introduction, which is
used for identifying explanatory variables in the econo-
metric test. Chapter 4 presents data retrieval of included
variables, which is followed by a chapter presenting the
econometric model and results. The article ends with a
brief summary and discussion.
Background
Sweden has a long tradition of enjoying crayfish as a
delicious food and also as giving recreational pleasure and
economic benefits at harvesting times. The noble crayfish is
the only native crayfish in the country and it is believed to
have immigrated into the country after the last ice age
(Skurdal and others 1999). The species has been appreci-
ated for centuries as a delicacy and was enjoyed already in
the sixteenth century by the Swedish Wasa kings (West-
man and Ackerfors 1992). However, the situation changed
during the nineteenth century when the popularity of
crayfish increased significantly also outside the royal house
and the aristocracy. Stories about crayfish can also be
found by famous authors, such as August Strindberg
(Swahn 2004). Today, Sweden has the highest consump-
tion of crayfish worldwide, which corresponds to 0.5 kg/
person and year. Most is consumed on a few occasions
during the more or less ritual crayfish parties, in which
most Swedes take part, and which are held on the mellow
nights of August. Crayfish caught in Swedish lakes and
rivers accounts for approximately 35% of the total con-
sumption while the rest is imported. Signal crayfish today
account for approximately 85% of the crayfish that is
harvested nationally. However, it is not only the eating of
crayfish that is appreciated but also the harvesting. Rec-
reational fishing by fishing right owners accounts for more
than 90% of the total catch of crayfish in Sweden as
compared to what is caught by commercial fishermen (SBF
2000).
The signal crayfish, originating from North America,
was introduced into Sweden in the 1960s by the authorities,
to substitute for the native noble crayfish fishery which had
been lost, mainly due to the disease crayfish plague caused
by a fungus (Aphanomyces astaci). It was then assumed
that the signal crayfish would fill the ecological niche once
held by the noble crayfish and also be the basis for a
productive fishery, since the species was thought to
Environmental Management (2009) 43:210–220 211
123
resemble the noble crayfish in both morphology and ecol-
ogy (Fjalling and Furst 1985). The plague is a parasite on
crayfish and is spread by infected crayfish and spores in the
water. Infected populations of native crayfish can be wiped
out within a few weeks. The plague was carried to Sweden
in 1907 by infected crayfish from Finland, and 50 percent
of the native noble crayfish populations had been struck by
1960 (Unestam 1969).
The signal crayfish (Pacifastacus lenisculus) is more
resistant to the plague, and for that reason it was introduced
to compensate for the losses in the noble crayfish fishery.
However, in the early 1970s it was realized that the signal
crayfish is a chronic carrier of crayfish plague (e.g., Une-
stam 1972; Cerenius and Edsman 2002), and may also be
susceptible to acute plague when stressed (Cerenius and
Edsman 2002). This, in turn, implies that noble crayfish and
signal crayfish cannot coexist in the same water since the
population of noble crayfish will be infected by the plague.
If signal crayfish is introduced into waters with noble
crayfish, the latter disappears (Fiskeriverket and Natur-
vardsverket 1998). Owing to these impacts on the native
species, a regulation was introduced which requires permits
for introducing signal crayfish in waters. A liberal appli-
cation of this regulation has resulted in a steady increase in
the number of waters with signal crayfish, which now
constitute approximately 25% of all waters where the signal
crayfish population can survive (Bohman and others 2006).
A Simple Model of Signal Crayfish Harvesting
in Sweden
In order to test for causes of spread of signal crayfish in
Sweden, a simple model of a representative water owner’s
decision to introduce and harvest signal crayfish is con-
structed. The main purpose is to identify relevant
parameters and their expected signs in the regression
equation presented in Chapter 5. Admittedly, due to lack of
data, there is no perfect match between the variables in this
theoretical chapter and in the reduced regression form,
which allows for a thorough test of the model. Neverthe-
less, we argue that the theoretical exercises carried out in
this chapter are useful by its guidance of choice of inde-
pendent variables included in the econometric test and in
assessing their impact on occurrences of signal crayfish.
The basic assumption is then that a representative water
owner introduces signal crayfish, S, when the streams of
discounted net utility of introducing crayfish, V(S), at the
steady-state level of the stock, S*, is positive, i.e. when
V(S*) [ 0 where V(S) is the value function.
Utility from crayfish introduction arises from provision
of several different attributes, such as recreational values
and environmental impacts. Following Lancaster (1966),
we derive demand for introducing signal crayfish from the
attributes that the signal crayfish populations, S, provide.
This approach has been greatly applied in environmental
economics for deriving demand for recreational services
(e.g., Bockstael and McConnell 1981; Smith 1991). Let
ai = a1,…,am be the different attributes possessed by
either the populations as such or by harvesting of signal
crayfish. The amount of attribute i the individual obtains
from S is a function of the ‘‘technology’’ parameter ai
which transforms the stock of signal crayfish into attribute
i, ai = aiS. In this article, this technology parameter
is interpreted as reflecting attitudes. The stronger attitude
for providing recreational values, for example, the higher
is ai in generating recreational attribute from signal
crayfish.
There is a large literature on the formation of values,
attitudes and beliefs related to environmental and other
issues (e.g., Ester and others 2004), and two distinct lines
of thought can be identified. One is the extensively
applied idea in environmental economics on the trade-off
between economic growth and environmental concern
that depends on income level (e.g, Inglehart 1977, 1995).
The other line of reasoning originates mainly from psy-
chologists and emphasizes the role of value clusters, such
as self-interest, concern for others and the biosphere,
from which environmental and other attitudes can be
derived (e.g., Schwartz 1992, 1994). In this article we
therefore decompose the attribute productivity parameter
into two parts: one reflecting a basic or intrinsic attitude,
ai; and the other depending on the income level, Y, which
is given a simple linear form and written as
ai ¼ ai þ biY:
In addition to affecting attitudes, crayfish harvesting, x,
may contribute to utility as a source of income from sales
of crayfish. Incomes are obtained from sales of crayfish, px,
where p is the unit price, minus cost from harvesting, cx,
where c is the unit harvesting cost. A simplification is made
by assuming that the harvesting cost is independent of the
crayfish population. Total income for a water owner then
includes income from other sources, Yo, and from sales of
crayfish, which gives Y = Yo ? (p - c)x. Utility in each
period of time is then U = U(a1,…,am, Y), which is
assumed to be increasing at a decreasing rate in income,
and can be either increasing or decreasing in the attribute
parameters.
Once introduced, the growth in signal crayfish, _S, is
determined by its natural growth, G(S), minus harvesting,
x. Given all assumptions, the water owner maximizes
current and future streams of net utility given the growth
function of signal crayfish and the attribute generating
relations according to:
212 Environmental Management (2009) 43:210–220
123
Max V ¼R1
t¼0
Uða1; . . .; am; YÞe�qtdt
x s:t:_S ¼ GðSÞ � xai ¼ aiS; i ¼ 1; . . .;mY ¼ Yo þ ðp� cÞxSð0Þ ¼ S
ð1Þ
where q is the discount rate. Assuming sustainable
harvesting, i.e., the natural growth equals harvest or
G(S) = x, the optimal level of signal crayfish, S*, is
determined where the discount rate equals return from
signal crayfish according to:
q ¼ GS þP
i Uaiai
ðP
i Uai biSþ UYÞðp� cÞProof: see Appendix A
ð2Þ
which shows that optimal steady-state level of the stock,
S*, and harvesting of signal crayfish occur where the dis-
count rate q equals the rate of return on the signal crayfish.
The discount rate is the marginal cost of keeping signal
crayfish since it shows the return on investment that can be
obtained elsewhere in the economy. The marginal benefit
from keeping signal crayfish, the right hand side, includes
the natural growth rate and the marginal stock effect, the
second term at the right-hand side. Incentives to keep
signal crayfish are thus decreasing in higher discount rate
and increasing in natural growth and marginal stock
effects.
The marginal stock effect is, in turn, determined by the
marginal impacts on utility from attribute changes in the
numerator and the net impacts on income and associated
change in utility from the income determined part of the
attributes in the denominator. When marginal utility is
negative from an attribute, such as the perception of an
increase in threat to the noble crayfish from a larger signal
crayfish stock, the marginal return decreases whereas it
increases from an attribute generating positive marginal
utility, such as recreational values. The denominator shows
the effect on the stock from harvesting of crayfish, which
includes obtained incomes from harvesting and associated
effects on attitudes.
The impact on the populations from changes in intrinsic
attitudes and income can be obtained by applying the
implicit function theorem on Eq. 2. Since both attitude and
income parameters affect several variables, the final
expressions can be quite involved and indeterminate. When
simplifications are made with respect to the utility function,
it is shown in Appendix A that an increase in intrinsic
attitudes generating negative marginal utility, such as
environmental preferences for preservation of noble cray-
fish, has a negative impact on the populations of signal
crayfish (see Eq. A6 in Appendix A). Similarly, an increase
in income generates either an increase or a decrease in the
populations depending on if the marginal utility from
associated attribute change is negative or positive (see
Eq. A7 Appendix A). Since several attributes may act
simultaneously, the final outcome is theoretically indeter-
minate. Environmental concern for protection of the native
noble crayfish acts for a decline in the population of signal
crayfish, while demand for recreational experiences is a
driving force for a larger population.
Description of Data
From the simple model exercise in Chapter 3, we can
identify the following explanatory variables needed to be
included in the regression equation: intrinsic attitudes,
income, unit price, and harvesting cost of signal crayfish,
discount rate, and natural growth rate. However, as will be
reported in this chapter, it is not possible to obtain data on
all these variables.
Starting with the dependent variable, populations of
signal crayfish, the econometric estimates made in this
article rely on the availability of unique panel data for the
number of waters (lakes running waters and ponds) with
signal crayfish in Swedish municipalities, which is used for
defining the dependent variable (SBF 2006). The data set
covers 188 Swedish municipalities where occurrences of
signal crayfish have been recorded on different occasions
between 1983 and 2004 (SBF 2006). This includes
approximately 2/3 of all Swedish municipalities, where the
remaining municipalities are located in northern Sweden
where it is probably too cold for the signal crayfish pop-
ulations to survive (Fiskeriverket and Naturvardsverket
1998). The panel is unbalanced since the observed time
period for each municipality is discontinuous. This, in turn,
is due to local reports of signal crayfish occurrences, the
time period of which differs between municipalities. In
total, the panel consists of 556 observations.
The reports on water with signal crayfish contain no
further description of the waters, such as area or length. In
order to account for heterogeneous waters and the scale
effect associated with different sizes of the municipalities
with respect to number of waters, the dependent variable,
S in Chapter 3, is defined as the number of waters with
signal crayfish divided by the total number of waters,
where total number of waters is obtained from SMHI
(2006). This is not the ideal measurement of the depen-
dent variable, which, as presented in the foregoing
Chapter 3, would be a measurement of the total stock of
signal crayfish. However, such data is not recorded and
need to be modeled based on harvesting effort and cat-
ches. This is made for only one lake in Sweden for which
Environmental Management (2009) 43:210–220 213
123
necessary data exist (Kataria 2007). Instead we use the
share of waters with signal crayfish in relation to total
number of waters in each municipality as a dependent
variable. The maximum value of the variable is unity,
which occurs when there is signal crayfish in all waters.
We can think of heterogeneous waters in each munici-
pality with respect to natural growth, and an increase in
the discount rate ceteris paribus will then decrease the
share of waters with signal crayfish.
The choice of attribute parameters is restricted by the
availability of panel data at the municipality level, and two
types of attributes are therefore included: preferences for
environmental preservation and recreational values. Attri-
bute productivity parameter for environmental preferences
is approximated by preferences as expressed by voting
behavior at the municipality level. Alternative approxi-
mations are participation in different environmental NGOs,
such as Greenpeace or World Wide Fund for Nature. It is
not possible to obtain such data at the municipal level for
the period under study, and voting behavior is therefore
used as an indicator of the environmental preservation
attitude.
Swedish citizens vote for central and local (municipal-
ity) governments every fourth year. There are seven major
parties to choose between: the Conservatives (Moderater-
na), the Liberal party (Folkpartiet), the Centre party
(Centerpartiet), the Christian Democratic party (Krist-
demokraterna), the Green party (Miljopartiet), the Social
Democrat party (Socialdemokraterna) and the Left party
(Vansterpartiet). Three parties—the Green party, the Cen-
tre party and the Left party—signal environmental
ambitions, where the Green party identifies environmental
concern as its main political issue. According to the elec-
tion manifest of the Green party, the title of which is
‘‘Greener Sweden—for a better quality of life,’’ eight out of
36 points of declaration refer to environmental issues such
as saving the Baltic Sea, green local environment, and
mitigation of catastrophic climate change (MP 2006).
Votes for the Green party are therefore used as a variable
on environmental preferences. Votes for a relatively green
party have also been used as an explanatory variable in
Kahn (2007) for testing differences in consumption
patterns.
Attitudes towards recreational values are measured by
subscriptions to a magazine specialized in fisheries man-
agement, ‘‘Fiskevard’’ (Swedish federation of fishing right
owners 2008). Subscriptions concern households and this
variable is weighted by the number of inhabitants in each
municipality. Admittedly, the variable is likely to measure
general interest in recreation from fishery, and not only
from crayfish. It is still of interest if there is positive cor-
relation between recreational values from general fishery
and from signal crayfish.
Income is measured by the reports in annual tax decla-
rations and is expressed in 2006 price levels (Swedish
Statistics 2006). This excludes all nondeclared incomes
from, for example, sales of signal crayfish and others.
Owing to the conflicting interests mentioned in Chapter 3,
a priori hypothesis on the impact of income on occurrence
of waters with signal crayfish is difficult to formulate. If
only incomes from signal crayfish and preservation of
noble crayfish were at issue, an inverted U-shape between
occurrences of signal crayfish could be hypothesized,
where needs for side incomes increase up to a certain level
of income and then decrease. In other words, environ-
mental improvements (here, provision of noble crayfish)
are affordable first after a certain income level and then
increase. However, the recreational values from the cul-
tural tradition of fishing and eating crayfish in late summer
may be strong enough to offset this relation if the demand
for tradition is stronger than that for environmental
improvements.
Unfortunately, no records exist for market prices of
Swedish signal crayfish, biological growth and harvesting
cost. The only interest rate records available during the
entire period are those of Treasury bills, which have a
duration of three months (Sveriges Riksbank 2007). A real
interest rate is obtained by deflating the nominal rate by the
consumer price index.
In total, the data set contains 556 observations, and
descriptive statistics are presented in Table 1.
The total number of waters and waters with signal
crayfish vary considerably among municipalities, with an
average share of water with signal crayfish amounting to
0.25. Furthermore, the range of income per capita is high,
being approximately five times higher in the richest
municipality (Stockholm) as compared to the poorest
(Ydre). Real interest rate has fluctuated considerably being
lowest in 2005 and highest during the economic crisis in
early 1990s. Descriptive statistics also indicate that the
number of subscriptions to the fishery magazine ‘‘Fis-
kevard’’ is approximately two per thousand inhabitants.
The subscription rate is relatively high in municipalities in
different parts of the country, on the West coast of Sweden
and in mid Sweden. The average share of votes on the
Green party is 0.04, but it can be four times as high which
occurs in a municipality at the West coast of Sweden.
The Econometric Model and Results
The unbalanced panel consists of heterogeneous clusters
due to irregular records on crayfish, variables that are
constant over time and/or over space. Collected informa-
tion on number of accumulated signal waters, income and
voting behavior varies over time, where the length of the
214 Environmental Management (2009) 43:210–220
123
observed period for each municipality varies between
13 years and one year. The number of total waters is
constant over time and varies over municipalities while the
discount rate varies over time but not over municipalities.
These properties of the unbalanced panel introduce a par-
ticular type of heteroscedasticity imposing difficulties in
taking advantage of panel data properties to specify the
econometric model as a fixed effect model which is com-
monly applied in the Kuznets literature (Dinda 2004).
Hence, the econometric model is specified as a lognormal
regression model and it is estimated by the maximum
likelihood method (ML). The model is weighted by
municipality clusters in order to take advantage of panel
data properties. The model assumes that a random variable
is lognormally distributed if the logarithm of the random
variable is normally distributed making the heterogeneous
variance proportional to the square of the mean in order to
correct heteroscedasticity problems. According to Weems
and Smith (2004), when data exhibit overdispersion this
simple assumption on distribution facilitates the computa-
tional work, assuring robustness maximum likelihood
estimates.
Potter (2005) carried out tests in favor of lognormal
models where moderate-sized data indicate a good infer-
ence of maximum likelihood estimates. Chan and others
(2005) analyze residential air leakage in the US, explained
by household income level, housing characteristics and
energy programs, assuming a lognormal and normal dis-
tributions. Their findings show that in the presence of
irregularities in data a lognormal distribution assures
robustness estimates. Balintfy and Goodman (1973) ana-
lyze socio-economic factors in income inequality assuming
that income follows a lognormal distribution considering
group variances. Their main conclusion is that income
distributions can be approximated by a lognormal distri-
bution over much of their range, but their fit remains
poorest at the upper end.
From the theoretical analysis in chapter 3 it is noticed
that income changes can have effects on occurrences of
signal crayfish through two channels, directly and also
indirectly by the impacts on the attitude variables. In this
article we therefore test whether (1) attitude variables have
explanatory power, and (2) interaction effect between
income and attitudes are significant. Furthermore, the
income variable is given a quadratic form in order to test
for turning points with respect to negative and positive
effects of income on the occurrences of signal crayfish.
Such a relation is found in several studies testing impacts
of changes in income on environmental damages in dif-
ferent countries (see Dinda 2004 for a review), and also for
environmental concern showed by Swedish municipalities
(Folke and Gren 2008). We also introduce a time variable
that reflects the changes during time not covered by the
explanatory variables, such as changes in general aware-
ness of environmental issues and climatic changes. A
dummy variable is also introduced for the three largest and
most densely populated cities in Sweden. This may reflect
specific characteristics such as distance to fishing waters,
which partly accounts for the missing harvesting cost
variable. Three different regression equations are then
specified according to
Model I (only economic factors):
Si;t ¼ ai þ b1Yi;t þ b2Y2i;t þ b3rt þ b8dt þ b9dsþ ei;t
Model II (economic factors and direct attitude
variables):
Si;t ¼ ai þ b1Yi;t þ b1Y2i;t þ b3rt þ b4Ei;t þ b5Mi;t þ b8dt
þ b9dsþ ei;t
Model III (economic factors, direct attitude variables
and interaction effect between income and attitudes):
Si;t ¼ ai þ b1Yi;t þ b1Y2i;t þ b3rt þ b4Ei;t þ b5Mi;t
þ b6Ei;tYi;t þ b7Mi;tYi;t þ b8dt þ b9dsþ ei;t
where i = 1,…,188 are the municipalities and
t = 1983,…,2004 are the observed years which are dis-
continuous for each municipality. The dependent variable
Si,t is the share of waters with signal crayfish, Yi,t is income
per capita, rt is the real market discount rate, Ei,t are votes
Table 1 Descriptive statistics; n = 556
Variable name Mean Std. dev. Median Min. Max.
Number of waters with signal crayfish 16.67 17.73 10.00 1.00 87.00
Total waters 154.51 130.68 135.00 1.00 1268.00
Share of signal waters 0.25 0.49 0.10 0.08 1.00
Income per capita, thousand SEKa 138.56 31.37 133.50 89.20 460.75
Real interest rate 5.27 3.64 4.42 1.13 10.84
Number of magazine subscription per 10000 ind. 17.14 16.8 10.66 0.00 92.24
Green party, share of votes 0.04 0.02 0.03 0.00 0.16
a 1 Euro = 9.52 SEK (August 11, 2008)
Environmental Management (2009) 43:210–220 215
123
for the Green party, Mi,t is the magazine subscriptions,
YI,tEi,t is the interaction effect between income per capita
and votes for the Green party, Ii,tMi,t is the interaction
effect between income per capita and magazine subscrip-
tions, dt is a time-specific dummy and ds is a site-specific
dummy for big cities Stockholm, Goteborg and Malmo.
Finally, ei,t denotes the model error term. Regression
results are presented in Table 2.
All three models show an expected negative impact of
the discount rate. The results also indicate a U-shaped
effect of increases in income, which support most of the
results in the related literature. However, the turning
points, where the negative impact of income changes
switches to a positive effect is high, differ between the
model specification, ranging from 280 thousand SEK/
capita (model III) to approximately 800 thousand SEK/
capita (model II). Considering that the median income is
SEK 133 000/year, the positive relation between income
and the share of water with signal crayfish occurs for
relatively few municipalities. This relatively high income
level for the turning point is in contrast with much previ-
ous results, where the turning points for emissions of
several types of pollutant are lower (see Stern 2004 for a
review).
Common to all models is also the positive impact factor
of time, which can be caused by exogenous changes not
included in the model, such as increased general awareness
of the threat of signal crayfish to noble crayfish at the
national level. Another common result is the positive, but
insignificant effect of the dummy for the three largest cit-
ies, which can reflect lower costs for access to waters in
densely populated municipalities. It is also interesting to
note that the successive inclusion of direct attitude
variables and interaction effects between attitude variables
and income increases the explanatory power of the equa-
tions. Furthermore, all variables except for the dummy
representing the three largest cities are significant irre-
spective of model design.
A likelihood ratio test (LR) is conducted in order to test
for the explanatory power of each model. The result of the
test supports the specification of model II and model III
against model I, at a 5% significance level LR = 2.15 and
2.31, v(2,0.95)2 = 5.99 and v(4,0.95)
2 = 9.49, respectively. The
test is also performed to confirm the validity of model III
against model II, where the result of the test confirms the
specification of model III, LR = 2.15. It can also be noted
that the explanatory power of the results presented in
Table 2 is significantly higher then those obtained from
ordinary least square (OLS) estimates (see Table B2 in
Appendix B).
However, the positive and significant effect of votes on
the Swedish Green party on the dependent variable is
unexpected from the theoretical analysis carried out in
Chapter 3. One possible explanation can be that votes for
the Green party express concern about environmental
problems at a larger scale such as climatic change.
Another unexpected result from the theoretical analysis is
the negative effect of subscriptions on the fisheries mag-
azine, if this variable reflects interest in recreational
fishery. One possible explanation is misspecification in the
model in Chapter 3 where recreational values were
assumed to be related to the signal crayfish population.
Recreational values may instead be obtained from har-
vesting of signal crayfish, which implies a pressure on the
population. Another explanation can be that subscription
does not measure only recreational values but also reflects
Table 2 Lognormal model; regression results
Variable Model I Model II Model III
Coeff. t-value Coeff. t-value Coeff. t-value
Intercept 0.71 8.87 1.29 8.17 1.18 5.17
Income (Y) -0.0055 -7.12 -0.0096 -7.83 -0.0091 -5.04
Income2 (Y2) 0.000009 5.46 0.000016 7.62 0.00002 5.11
Real discount rate (r) -0.0118 -3.62 -0.0207 -6.65 -0.0122 -5.41
Time (dt) 0.0122 3.83 0.0104 3.47 0.0096 5.26
Three largest cities (ds) 0.34 1.45 0.31 1.10 0.42 1.64
Votes for Green party (E) 1.40 7.27 8.72 3.90
Magazine (M) -0.0073 -8.25 -0.0126 -4.79
Interaction (EY) -0.0542 -3.18
Interaction (MY) 0.000039 5.26
Variance 2.11 32.37 3.30 27.61 6.20 31.06
Log likelihood -953.65 -1025.55 -1099.85
216 Environmental Management (2009) 43:210–220
123
knowledge on the threat of signal crayfish to the noble
crayfish, and thereby partly captures environmental
concerns.
The interaction effects included in Model III counteract
the unexpected impacts of the attitude variable in Model II.
The negative interaction effect between voting on the
Green party and income indicates that higher incomes lead
to decreases in the share of waters with signal crayfish due
to increased environmental preferences as expressed in the
voting variable. Interestingly, the total impact of the Green
party is negative at income levels exceeding 160 thousand
SEK, which is well within the data range. Similarly, the
positive interaction effect between magazine subscriptions
and incomes can be interpreted as an increase in recrea-
tional demand as measured by the subscription variable at
higher income levels. However, the total negative effect of
a marginal change in subscriptions is the same for Models
II and III when evaluated at the mean income level. The
negative effect is then decreased only for relatively large
income levels, and becomes positive at annual income
exceeding 323 thousand SEK.
Summary and Discussion
The main purpose of this article has been to analyze and
test impacts of economic factors and attitudes on the
occurrences of signal crayfish in Sweden. A simple model
was used where attitudes were modeled within the frame-
work of dynamic harvesting model with multi-attribute
utility from signal crayfish. Independent and measurable
variables derived from the model were discount rate,
income, and attitudes to signal crayfish. An econometric
test was carried out based on a unique set of data on
number of signal crayfish waters in different Swedish
municipalities during the period 1983–2004. In order to test
the explanatory power of economic and attitude variables
on impact of attitude variables, three regression models
were estimated and compared: (1) inclusion of only eco-
nomic variables (income and discount rate), (2) economic
and direct attitude variables, and (3) economic, direct
attitude variables and interaction terms between income
and attitudes. All models resulted in a significant U-shaped
relation between signal crayfish occurrences and income
and a negative impact of the real discount rate. Inclusion of
attitude variables turned out to increase the explanatory
power of the regression equation significantly. Votes for
the Green party showed an unexpected positive sign, but
the total effect was negative when accounting for the
interaction effect with income. Subscription on a fisheries
magazine revealed a negative and significant effect, which
was unexpected if the variable reflects recreational
attributes.
However, although the data set is relatively large, the
results need to be interpreted with caution. One reason is
that the dependent variable measures share of waters with
signal crayfish and not the stocks of signal crayfish in
different municipalities. Furthermore, preferences for
environmental and recreational attributes can be revealed
in other ways, such as membership of nongovernmental
organizations. On the other hand, the econometric results
are robust with respect to alternative functional forms and
estimation methods. Furthermore, the U-shaped income
effect is supported by other studies. The results also adhere
to the unclear relation between attitudes and behavior,
which is the subject of much research in social sciences
(see e.g., Ester and others 2004)
What are then the potential policy conclusions from the
study? One observation is that the net impact on occur-
rences of signal crayfish from changes in income may be
positive. The spread of the species is then not likely to
decrease from economic development as measured by
increases in average income, which is one reason for
implementing policies in order to prevent further spread.
The significant impacts of the discount rate and attitude
variables indicate that both economic incentives and
information campaigns aimed at affecting attitudes have
impacts on the occurrences of waters with signal crayfish.
The expected negative impact of discount rate, which
reduces the streams of net utility from a crayfish popula-
tion, points to the relevance of economic incentives for
mitigating spread of signal crayfish, such as charge pay-
ments for waters with signal crayfish. The results also
support the use of information campaigns for affecting
attitudes, which have been used in Sweden during two
decades for combating spread of signal crayfish. However,
economic instruments have not yet been implemented, and
might therefore contribute to a larger decrease in the
occurrences of signal crayfish then continuous use of
information campaigns.
To the best of our knowledge, there is only one addi-
tional study testing the explanatory power of income
changes on occurrences of invasive species, Dalmazzone
(2000), which is applied to different countries. The results
from our study support those obtained by Dalmazzone
(2000) with respect to the significant and positive impact of
income changes on the occurrence of invasive species.
Similar to Sweden, several countries have introduced
information campaigns and command and control like
instruments, such as bans on imports of hazardous species,
for combating intentional spread of invasive species among
countries. As demonstrated theoretically by several studies,
such a policy might be quite expensive as compared to a
policy based on economic incentives (see Gren 2008 for a
review). The results from this study show that economic
factors affect spread of signal crayfish in Sweden, and,
Environmental Management (2009) 43:210–220 217
123
hence, economic policy instruments may have a potential
in mitigating further spread. However, the research on
appropriate choice of policy instrument at the international
and national scales is currently in its infancy state, in
particular with respect to empirical research on causes of
spread and design of policy instruments, which is needed
for making robust policy conclusions (e.g., Perrings and
others 2000; Gren 2008).
Acknowledgments We are much indebted to the Swedish Envi-
ronmental Protection Agency for financial support to the AquAlien
research program, and to two anonymous referees for valuable
comments. The authors are responsible for any remaining errors.
Appendix A: Derivation of Optimal Stock of Signal
Crayfish
The decision problem in Eq. 1 is solved by use of optimal
control. The Hamiltonian is then written as
H ¼ Uða1; . . .; am; YÞ þ kðGðSÞ � xÞ; ðA1Þ
which gives the first order condition for a maximum as
oH
ox¼ ðp� cÞðUY þ
X
i
Uai biSÞ � k ¼ 0 ðA2Þ
_k ¼ kðq� GSÞ �X
i
Uaiai ðA3Þ
_S ¼ GðSÞ � x ðA4Þ
where sub-index denotes partial derivatives and k is the
costate variable showing the change in V from a marginal
change in the stock of signal crayfish. By solving for
steady-state values, i.e. where _k ¼ 0 and _S ¼ 0; and
inserting (A2) into (A3), we obtain
q ¼ GS þP
i Uaiai
ðP
i Uai biSþ UYÞðp� cÞ : ðA5Þ
The impact of changes in the attribute productivity
parameters can be derived by applying the implicit function
theorem on (A5). In order to simplify the analysis, we
assume that the cross derivates of ai and Y are zero and that
the second derivatives of the utility function with respect to
the attribute parameters are zero. The impact of a marginal
change in ai is then
oS�
oai ¼Uaik
DðA6Þ
where D ¼ � GSSk2 � bðp� cÞ2GSUYY þ ðp� cÞ
Pi Uai
�
biðGSk� bÞÞ; k is derived from (A1) and b ¼P
i Uaiai:
When all Uai \ 0, the denominator, D, is positive,
since, by assumption UYY \ 0, and, for a simple logistic
crayfish growth function, GSS \ 0. When Uai [ 0, D [ 0
for small enough bðp� cÞ2UYY . Equation A6 is then
positive/negative when Uai [ ð\Þ0. Thus, the stock of
signal crayfish is increasing in intrinsic attributes with a
positive marginal utility such as recreational values, and
negative in attributes associated with negative marginal
utility such as preferences for preservation of noble
crayfish.
Similarly, the impact of a change in income, Yo, is
oS�
oY[ ð\Þ0 for
kP
i Uai bi � bðp� cÞUYY
D[ ð\Þ0
ðA7Þ
According to (A7), the impact of a marginal income
change on S* is negative(positive) for Uai \ ([)0.
Appendix B: Tables
Table B1 Correlation matrix
S Y r E M
S 1.000
Y .008 1.000
r .100 .411 1.000
E .085 .175 -.192 1.000
M -.210 -.208 -.040 -.117 1.000
S: share of waters with signal of total waters, Y: Income per capita, r: real discount rate, E: share of votes on the Green party, M: subscriptions on
the fisheries management magazine in relation to population
218 Environmental Management (2009) 43:210–220
123
References
Balintfy JL, Goodman SS (1973) Socio-economic factors in income
inequality: a log-normal hypothesis. Zeitschrift fur Nationalo-
konomie 33:389–402
Bockstael NE, McConnell KE (1981) Theory and estimation of the
household production function for wildlife recreation. Journal of
Environmental Economics and Management 8(3):199–214
Bohman P, Nordwall F, Edsman L (2006) The effect of the large-
scale introduction of signal crayfish on the spread of crayfish
plague in Sweden. Bulletin Francais de la.Peche et de la
Pisciculture 380–381:1291–1302
Born W, Rauschmayer F, Brauer I (2005) Economic evaluation of
biological invasions—a survey. Ecological Economics 55(3):
321–336
Cerenius L, Edsman L (2002) Protection of natives in a plague
situation. Bulletin Francais de la.Peche et de la Pisciculture
367:909–910
Chan WR, Nazaroff WW, Price PN, Sohn MD, Gadgil AJ (2005)
Analyzing a database of residential air leakage in the United
States. Atmospheric Environment 39:3445–3455
Dalmazzone S (2000) Economic factors affecting vulnerability to
biological invasions. In: Perrings et al (eds) Economics of
biological invasions. Edward Elgar, Cheltenham, UK, pp 17–
30
Dinda S (2004) Environmental Kuznets curve hypothesis: a survey.
Ecological Economics 49:431–455
Ehrardt-Martinez K, Crenshaw E, Jenkins C (2002) Environmental
strategies and policies deforestation and the environmental
Kuznets curve: a cross-national investigation of intervening
mechanisms. Social Science Quarterly 83(1):226–243
Ester P, Simoes S, Vinken H (2004) Cultural change and environ-
mentalism: a cross national appraoch of mass publics and
decision makers. Ambiente & Sociedade VII(2 Jul/Dec):43–65
Fjalling A, Furst M (1985) Information fran sotvattenslaboratoriet,
Swedish Fishery Board, 178 93 Drottningholm, Sweden, p 29
Fiskeriverket and Naturvardsverket (1998) Action plan for the
restoration of Noble crayfish. Swedish Environmental Protection
Agency, Stockholm, Sweden (in Swedish)
Folke O, Gren IM (2008) Environmental policy performance of
Swedish local governments: is it the mind or the money?
European Association of Environmental Economics Conference
June 25–28, 2008. Gothenburg, Sweden
Gren IM, Isacs L, Carlsson M (2008) Costs of invasive alien species
in Sweden. Ambio, in revision
Gren IM (2008) Economics of management of invasive alien
species—choosing target and policies. Boreal Environmental
Research 13:17–32
Grossman G, Krueger A (1995) Economic growth and the environ-
ment. Quarterly Journal of Economics 60:353–377
Table B2 Regression results from OLS estimates
Variable names Model I Model II Model III
Coeff. t-value Coeff. t-value Coeff. t-value
OLS-nonlinear
Intercept 0.711 2.44 1.287 4.23 1.175 2.79
Income (Y) -0.005 -1.77 -0.010 -3.11 -0.009 -2.48
Income2 (Y2) 0.000009 1.44 0.000016 2.54 0.00002 2.89
Real discount rate (r) -0.012 -1.43 -0.021 -2.48 -0.022 -2.57
Time dummy (dt) 0.012 1.68 0.010 1.46 0.010 1.34
Big cities dummy (ds) 0.343 1.48 0.305 1.35 0.417 1.76
Green party (E) 1.397 1.25 8.718 1.27
Magazines (M) -0.007 -5.65 -0.013 -1.65
Interaction (EY) -0.054 1.08
Interaction (MY) 0.417 1.76
R2 0.20% 0.79% 0.83%
Log-likelihood -389.73 -372.36 -371.16
OLS-logarithmic
Intercept 17.392 1.93 28.623 3.23 39.588 3.77
Income (Y) -16.972 -2.10 -25.829 -3.27 -32.508 -3.75
Income2 (Y2) 3.654 2.03 5.456 3.11 6.137 3.38
Real discount rate (r) 0.281 2.27 0.135 1.07 0.166 1.30
Time dummy (dt) 0.070 7.33 0.069 7.44 0.072 7.58
Big cities dummy (ds) 0.471 1.78 0.276 1.07 0.333 1.24
Green party (E) 0.121 1.47 5.762 2.24
Magazines (M) -0.279 -6.41 0.108 0.09
Interaction (EY) -2.688 -2.19
Interaction (MY) -0.187 -0.35
R2 12.01% 19.54% 20.25%
Log-likelihood -465.98 -445.91 -443.48
Environmental Management (2009) 43:210–220 219
123
Horan R, Lupi F (2005) Tradable risk permits to prevent future
introductions of invasive alien species into the Great Lake.
Ecological Economics 52:289–304
Inglehart R (1977) The silent revolution. Changing values and
political styles among Western publics. Princeton University
Press, Princeton, NJ
Inglehart R (1995) Public support for environmental protection: the
impact of objective problems and subjective values in 43
societies. PS: Political Science and Politics 28(1):57–71
IUCN (2000) IUCN guidelines for the prevention of biodiversity loss
caused by alien invasive species. Approved by the 51st meeting
of the IUCN Council, Gland, Swizerland, February
Kahn M (2007) Do greens drive Hummers of hybrids? Environmental
ideology as a determinant of consumer choice. Journal of
Environmental Economics and Management 54:129–145
Kataria M (2007) A cost-benefit analysis of introducing a nonnative
species: the case of signal crayfish in Sweden. Marine Resource
Economics 22:15–28
Knowler D, Barbier E (2005) Managing the Black Sea anchovy
fishery with nutrient enrichment and biological invader. Marine
Resource Economics 20(3):263–275
Lancaster K (1966) A new approach to consumer theory. Journal of
Political Economy 74(2):132–157
Lovell SJ, Stone S, Fernandez L (2006) The economic impacts of
aquatic invasive species: a review of the literature. Agricultural
and Resource Economics Review 35(1):195–204
McPherson M, Nieswiadomy M (2005) Environmental Kuznets
curve: threatened species and spatial effects. Ecological Eco-
nomics 55:395–407
MP (Green party) (2006) A greener Sweden—for a better quality of
life! At http://mp.se/files/107300-107399file_10371.pdf. Acces-
sed 1 Oct 2007
Olson L (2006) The economics of terrestrial invasive species: a
review of the literature. Agricultural and Resource Economics
Review 35(1):178–194
Owen A, Videras J (2007) Culture and public goods: the case of religion
and the voluntary provision of environmental quality. Journal of
Environmental Economics and Management 54:162–180
Perrings C, Williamson M, Dalmazzone S (2000) The economics of
biological invasions. Edward Elgar, Cheltenham, UK
Pimentel D, McNair S, Janecka J, Wightman J, Simmonds C,
O’Conell C, Wong E, Russel L, Zern J, Aquino T, Tsomondo T
(2001) Economic and environmental threats of alien plant,
animal, and microbe invasions. Agriculture Ecosystems &
Environment 84:1–20
Potter DM (2005) A permutation test for inference in logistic
regression with small- and moderate-sized data sets. Statistics in
Medicine 24:693–708
SBF (Swedish Board of Fisheries) (2000) En undersokning om
svenskarnas sport-och husbehovsfiske. Finfo 2000:1, p 89
SBF (Swedish Board of Fisheries) (2006) The database of crayfish
occurrences. Stockholm, Sweden
Schwartz SH (1992) Universals in the content and structure of values:
theoretical advances and empirical tests in 20 countries.
Advances in Experimental Social Psychology 25:1–65
Schwartz SH (1994) Are there universal aspects in the structure and
content of human values? Journal of Social Issues 50(4):19–46
Shogren J, Tschirhart J (2005) Integrating ecology and economics to
address bioinvasions. Ecological Economics 52:267–271
Skurdal J, Taugbøl T, Burba A, Edsman L, Soderback B, Styrishave
B, Tuusti J, Westman K (1999) Crayfish introductions in the
Nordic and Baltic countries. In: Gherardi F, Holdich DM (eds)
Crayfish in Europe as alien species. How to make the best of a
bad situation. A. A. Balkema, Rotterdam, pp 193–219
SMHI (Swedish Meteorological, Hydrological Institute) (2006)
Register of lakes and rivers in Sweden. Norrkoping, Sweden
Smith VK (1991) Household production functions and environmental
benefit estimation. In: Kolstad C, Braden J (eds) Measuring the
demand for environmental quality. North-Holland, Amsterdam
Stern DI (2004) The rise and fall of the environmental Kuznets curve.
World Development 32(8):1419–1439
Swahn JO (2004) The cultural history of crayfish. Bulletin Francais de
la Peche et de la Pisciculture 372–373:243–251
Sveriges Riksbank (2007) Svenska marknadsrantor—statsskuldsvax-
lar. Stockholm
Swedish federation of fishing right owners (2008) Fiskevard. At
www.fiskevatten.org. Accessed 15 May 2008
Swedish Statistics (2006) Taxerad och beskattningsbar forvarvsink-
omst samt antal inkomsttagare, samtliga skattskyldiga, efter
kommun. Taxeringsar 1983–2006
Unestam T (1969) Resistance to the crayfish plague in some
American, Japanese and European crayfishes. Report of InstituteFreshwater Research, Drottningholm, 49:202–209
Unestam T (1972) On the host range and origin of the crayfish plague
fungus. Report of Institute Freshwater Research. Drottningholm
52:192–198
Vila M, Pujadas J (2001) Land-use and socio-economic correlates of
plant invasions in European and North African countries.
Biological Conservation 100:397–401
Weems KS, Smith P (2004) On robustness of maximum likelihood
estimates for Poisson-lognormal models. Statistics and Proba-
bility Letters 66:189–196
Westman K, Ackerfors H (1992) Kraftor—biologi, odling, fiske.
Kiviksgardens Forlag, Ystad, Sweden
220 Environmental Management (2009) 43:210–220
123
