BIOGEOPHYSICAL AND SOCIAL VULNERABILITY INDICATORS:
COASTAL CASE STUDIES INFORMATION SHEET: GULF OF GABÈS, TUNISIA
Summary
Important shoreline changes and coastal erosion have occurred along the Gabès coastline during
recent decades. Most of this is related to human activity but it also indicates a high vulnerability to
climate. The observed increase in maximum swell height together with sea-level rise reinforces the
high vulnerability of the coasts. According to the data used, more severe storms may be expected
probably leading to sudden and substantial shoreline modification.
► There is an increasing trend in the number of alien marine species discovered in the Gulf of Gabès.
This increase is explained by the warming of the gulf waters. It leads to an increase in biodiversity
vulnerability and has negative consequences for fishing activity through induced competition
between traditional/highly-valued species and exotic ones. Warming sea water, accentuated by heat
waves, can also induce mortality of species in the gulf and increase the vulnerability of fishing
activity.
► Warming of sea and air masses has lead to both positive and negative effects on the potential tourist
attractiveness of Djerba in the southern Gulf of Gabès. Warmer temperatures have extended the
tourist season. In winter, the region has become more attractive through an increased number of
‘highly favorable’ days. However, the frequency of very hot days has increased and the total number
of days ‘favorable’ for tourism has declined particularly in summer. Beach loss has the largest
negative impact on tourism activities further accentuated by jelly fish and phytoplankton blooms.
► A simple theoretical model shows that economic and employment losses are related to climate
warming and beach retreat for the tourism sector in the Djerba-Zarzis area.
►
1. Introduction
An information sheet focused on observed
climate-marine conditions (Harzallah, 2010),
showed that maximum air temperature is
increasing particularly in summer and autumn.
Rainfall trends are not significant and differ
according to season and location; winter trends
are for example slightly positive in Sfax and
negative in Gabès. There is no evident tendency
towards drought in the Gulf of Gabès region for
the period studied. The summer ‘tourist season’
has lengthened over the observation period with
a tendency for an earlier start date and later end
date.
The main objectives of the present
information sheet are to establish a set of
environmental, biological and socio-economic
indicators that allow the analysis of past and
future dynamics of these systems. Due to
limitations in the length of data series,
assessments are not all based on quantitative
information. The indicators presented here
comprise the most salient vulnerabilities and
impacts related to (i) Air-sea warming, and (ii)
Coastal changes.
2. Vulnerability indicators
The indicators for each category are:
Air-Sea warming
► Marine water temperature
► Alien marine species
► Fish production
► Daily Climate-Tourism Potential Index
► Socio-economic losses due to changes in
climate-tourism potential
Coastal changes
► Maximum swell height
► Shoreline modification
► Coastal Vulnerability Index
► Socio-economic losses due to beach
erosion
1
2.1 Air-sea warming
Marine water temperature
What is it?
An estimate of the long-term temperature trend over marine areas of the Gulf of Gabès is obtained
using data compiled from MEDATLAS and data available at INSTM. The trend is estimated using all
available data in the Gulf for depths up to 30 m.
Figure 1: Water temperature anomalies in the Gulf of Gabès for depths < 30m. Anomalies are calculated
relative to the MODB-med6 climatology (Brasseur et al, 1996). The linear trend is shown by the red line.
Upper text shows the decadal trend (mid value) with upper (right) and lower (left) 95% confidence limits.
What does this show?
Sea-water temperature is warming at a rate of
+0.12°C/decade in the Gulf of Gabès (Figure 1).
At the 95% probability level, the estimate lies
between 0.09 and 0.15°C/decade. Due to the
relatively low number of data points available
this trend is only indicative of the long-term
trend.
Why is it relevant?
Changes in the physical characteristics of marine
water, and in particular temperature, may have
important consequences for the fauna and flora
A
2
of the gulf. The warmer waters pose a potential
risk to human health, tourism and fisheries (e.g.,
through jellyfish and phytoplankton blooms). It
also creates favorable conditions for invasive
species and reduces biodiversity with potential
negative consequences for fishing activity.
Biologically, some species may not support an
excessive temperature increase. During heat
waves (due to the shallowness of the gulf) the
most vulnerable species (particularly the
sedentary ones) may die, for example, following
toxic phytoplankton blooms. Jelly fish blooms
may also have negative effects on fish stocks.
B
Jellyfish blooms in
Gabès. A: Ghannouch
beach where fishermen
use a beach seine (net).
B: Situation observed
during a trawling survey
in 2009 (Photos M.N.
Bradai).
Alien marine species
What is it?
This is the first recording (compiled from papers, thesis and reports) of alien (non-native) marine
species (fauna and flora) in the Gulf of Gabès. Figure 2 shows examples of some alien species recently
observed in the Gulf of Gabès which seem to have become established in the area. The indicator is
expressed as the cumulative number (logarithm) of observed alien species in the Gulf of Gabès as a
function of the year of observation (Figure 3). The linear trend is to some extent biased by an increase
in the number of studies of alien species. To remove this bias, an estimate of the trend related to the
increasing number of studies is obtained using the number of references (467) cited in a recent thesis
on exotic species (Zouari-Ktari, 2008). An estimate of the unbiased rate of increase in alien species is
the difference between these two rates.
1. Hemiramphus far
2. Halophila stipulacea
3. Sphoeroides
pachygaster
4. Erosaria
turdus
5.Fistularia
commersonii
6.Sphyrena
chrysotenia
Figure 2: Examples of some alien marine species recently recorded and established in the Gulf of Gabès
(Photos: M.N. Bradai).
3
Figure 3: Cumulated number of observed alien species (logarithm) in the Gulf of Gabès per observing year.
The linear trend line is shown in red. First records are based on a compilation of the observed alien species
(40) from available papers, thesis and reports. The inner plot shows the increasing number of studies on alien
species (to remove the bias introduced by the increased research activity).
What does this show?
Without correcting for bias, the mean number of
observed alien species increases by +67% per
decade. The mean increase in research papers is
+52% per decade. Thus an unbiased estimate of
the decadal increase in the appearance of alien
species in the Gulf of Gabès is +15% (67 minus
52%).
Why is it relevant?
Tunisian fish fauna is composed of a total of 348
species (2009 data). Most species (294) have an
Atlantic origin, 16 species are considered widely
distributed and 25 are endemic to the
Mediterranean. The Tunisian coast is vulnerable
to alien species originating from the tropical
Atlantic (8 species) and Indo-pacific areas (13
species; Bradai, 2010). Lessepsian migrants
(from the Red Sea) are mostly confined to the
southern Tunisia marine water (Gulf of Gabès)
where the mean sea surface temperature and
salinity are more similar to the Red Sea than to
northern Tunisia waters. During the last 30
years, 58 alien species were observed in Tunisia.
Alien species have brought mixed consequences
4
to the Gabès fisheries, biodiversity, human
health and economy in the Mediterranean Sea.
Some of the alien fish species have become
economically important after establishing
sustainable populations, such as Spanish
mackerel Scomberomorus commerson and
Sphyraena chrysotenia. Similarly some of the
crustacean species have also commercial
importance, such as Metapenaeus monoceros
which has rapid expansion and may be a threat
for Penaeus kerathurus fisheries in the Gulf of
Gabès. Expansion of Caulerpa racemosa may
negatively impact fisheries and biodiversity due
to changes in the ecosystem and associated
species.
In addition to the impact of Lessepsian
migrants, the subtropical character of fish fauna
in the Gulf of Gabès is accentuated by the arrival
of warm-loving Atlantic fish species such as
Seriola fasciata, Sphoeroides cutaneous and
growth in
populations of warm-loving
indigenous fish species such as Balistes
carolinensis, Caranx crysos, C. rhonchus,
Synodus saurus, Sparisoma cretense.
Fish production
What is it?
The indicator shows the weight (in tons/year) of the fish catch in all harbours of the Gulf of Gabès,
1995-2006. The four species shown are: Common Pandora (Pagellus erythrinus), Caramote prawn
(Penaeus kerathurus), Hake (Merluccius merluccius) and Grey trigger fish (Balistes carolinensis).
Data are from ‘Direction Générale de la Pêche et de l’Aquaculture’, Tunisia.
Figure 4: Fish catch (in tons/year) for four leading species.
Data are from ‘Direction Générale de la Pêche et de l’Aquaculture’, Tunisia
What does this show?
The fishing catch exhibits considerable
interannual variability (Figure 4) due to multiple
causes, of which one may be climate variability
(Caramote prawn has a relatively short life
which explains part of its high variability). In
addition to the interannual variability there are
some long-term trends. For example, there is a
dramatic decrease in the catch weight of the
Caramote prawn, which was the leading species
caught during the 1990s. The catch weight of
Common Pandora also decreases but that of
Hake and Grey triggerfish increase.
Why is it relevant?
There are four possible reasons for the depletion
in Caramote prawn catch. The first is overexploitation of the shrimp stock. The second is
habitat destruction by trawling. The third is the
introduction of invasive small shrimps
(Metapenaeus monoceros). The fourth is the
increase in water temperature. The first two
causes are related to human activity whereas the
latter two are related to climate change. It is
possible that each of these pressures is acting at
different levels. The decrease in Caramote prawn
catch, a highly-valued species, leads to economic
difficulties for the gulf fishermen. The large
variability in catch and their long-term trends
shows the high degree of vulnerability of fishing
activity in the Gulf of Gabès.
5
Daily Climate-Tourism Potential Index
What is it?
The Daily Climate-Tourism Potential Index (DCTPI) evaluates climate as a resource for tourism
activity based on daily air temperature (mean, minimum and maximum), precipitation, relative
humidity and wind speed (Henia and Alouane, 2007). DCTPI is a combined measure of thermal
comfort (Thom and Bosen, 1959), the cooling effect (Siple and Passel, 1945) and weather conditions
that influence outdoor activities. Five classes are defined, 0: ‘highly unfavorable’ days; 1:
‘unfavorable’ days; 2: ‘acceptable’ days; 3: ‘favorable’ days; 4: ‘highly favorable days’. The index is
calculated for the period 1972-2003, for winter, summer and intermediate seasons.
DCTPI class frequency Observation data 1973-2003
Favorable
Highly
favorable
Acceptable
Unfavorable
DCTPI class
Figure 5: Histogram of the Daily Climate-Tourism Potential Index (DCTPI) for Djerba shown as the mean
annual (1972-2003) percentage of days corresponding to a given class, 1: ‘Unfavorable’ days; 2: ‘Acceptable’
days; 3: ‘Favorable’ days; 4; ‘Highly favorable’ days. (Data from http://www.tutiempo.net/en/Climate)
What does this show?
Djerba Island is characterised by a climate with a
majority of days (~55% annually) that are
‘favorable’ for tourism (Figure 5), nearly 35% of
days are ‘highly favorable’, there are very few
days that are classified as ‘acceptable’ (<10%)
and almost no ‘unfavorable’ days for tourism
(<1%). During the 31-year period 1973-2003
(Figure 6), some ‘favorable’ and ‘highly
favorable’ days are replaced by ‘acceptable’
days (+3.2% per decade; nearly 12 days). This
change is most prominent in summer when the
percentage of ‘acceptable’ days increases by
about 9% per decade (Table 1). In winter, the
change corresponds to an increase in the
percentage of ‘highly favorable’ days. Changes
in intermediate seasons reflect both summer and
winter trends. Long-term trends in the DCTPI
6
concur with an increase in the number of very
hot days (+0.7 days /month /decade) presented in
the previous information sheet.
Why is it relevant?
Tourism is an important economic sector
especially in the southern gulf. The DjerbaZarzis area accounts for more than 20% of the
Tunisian accommodation capacity. The DCTPI
reveals changes in the tourism attractiveness of
the region. The number of ‘favorable’ days for
tourism activity increases in winter and
decreases in summer, mainly as a result of air
warming. However, the decline in the summer
attractiveness of the climate is greater than the
increase in winter attractiveness. The net change
in the climate resource is a reduction in the
potential tourist attractiveness of the region.
However, climate is only one of many social,
economic and environmental factors influencing
tourism. In addition, the lengthening of the
summer ‘tourist season’ may lessen the negative
impacts of a less attractive summer climate.
a
)
b
)
Figure 6: DCTPI time series (1972-3003) for the classes ‘favorable days’ (a) and ‘acceptable days’ (b) for
Djerba. Linear trends are shown with the trend rates (in % days/decade).
Table 1: Decadal trends (1972-2003) in the annual and seasonal
percentage of days corresponding to a given DCTPI class (% days
/decade) for Djerba.
Season
Annual
Winter
Summer
Intermediate
‘Acceptable’
+3.2
-0.093
+8.8
+0.37
DCTPI Class
‘Favorable’
‘Highly favorable’
-2.0
-1.2
-2.5
+2.7
-6.0
-2.8
-0.9
+1.1
7
Socio-economic losses due to changes in climate tourism potential
What is it?
This socio-economic indicator (Figure 7) is based on a theoretical simulation of socio-economic
impacts due to changes in the number of ‘favorable’ days in the Djerba-Zarzis touristic area. Impacts
are estimated using the annual changes shown in Table 1. The basic hypothesis is that hotels are
devalued when weather conditions become ‘acceptable’ rather than ‘favorable’ such that prices equate
to inland hotels (-20 Tunisian dinar /night devaluation; MEDD/PNUD, 2008). Changes are assumed to
start in 1960 and increase progressively. The capital and gains losses are based on the calculations
given in MEDD/PNUD (2008) and are relative to GDP (2007 rates). Employment is considered
dependent on hotel capacity. Tourism statistics in the Djerba-Zarzis area are based on ONTT (2007).
Figure 7: A theoretical simulation of socio-economic impacts of days becoming “acceptable” in the DjerbaZarzis tourist area. Results are shown as annual percentages of 2007 GDP. Direct and indirect employee loss
should be multiplied by 100,000. Economic losses are based on 2007 rates.
What does this show?
According to this simulation, the number of days
degraded from “favorable” to ‘‘acceptable” is 51
(0.14 x 365) in 2007 (relative to 1960). The
consequent loss of capital is slightly less than
0.1% of the 2007 GDP, and the loss of annual
gains is nearly 0.07% of the 2007 GDP. Such
losses induce a reduction in the direct and
indirect number of employed persons of 2,800
and 8,600 respectively (14% of the employed
persons in 2007).
8
Why is it relevant?
The socio-economic impacts of a decline in days
‘favorable’ to tourism activity in the DjerbaZarzis area are a loss of capital and number of
employed persons. Such losses constitute a non
negligible negative impact on the tourism sector,
and losses increase continuously. However, the
present simulation takes into account only
thermal comfort effects of weather warming;
other climate effects (such as, tourist season
lengthening, larger domestic tourism demand
during excessively hot days, and warmer
swimming water) and non-climate effects (such
as trends in holiday destinations, and price of air
travel) may mitigate the negative impacts.
2.2 Coastal Changes
Maximum swell height
What is it?
This indicator measures the annual maximum significant swell height in three illustrative locations of
the Gulf of Gabès (Figure 8). The data are from Direction Générale des Services Aériens et Maritimes,
(DGSAM, 1995). The indicator is obtained from statistical analysis of a 20-year (1974-1994) wind
data set. It indicates the long-term evolution of swells with largest amplitudes, and hence tendency for
the largest storms.
G17
G28
G35
Figure 8: Annual maximum significant wave height in three illustrative locations of the Gulf of Gabès. Data
are from ‘Direction Générale des Services Aériens et Maritimes’, 1995.
What does this show?
There is a clear increase in the maximum swell
height in each of the three sites (Figure 8). This
is consistent with the increase of wind speed
found for Djerba wind data (~+5 km/h/100year). Substantial erosion found along all the
Gulf of Gabès coasts is attributed mainly to the
low-lying characteristics of the gulf (beaches,
salt flats “Sebkhas”) and to human construction,
but can also result from a change in marine
dynamics including swell height.
Why is it relevant?
The increase in maximum swell height together
with sea-level rise (a rate of +2.6 cm/decade in
Sfax harbour) may accentuate erosion
particularly in low-lying areas. An increase in
maximum swell height implies more severe
storms with likely sudden changes to the
coastline. This indicates increasing vulnerability
of the Gabès coast especially to exceptional
climate-marine events.
9
Shoreline modification
What is it?
Shoreline modification is a measure of the long-term advance or retreat of the shoreline due to climate
effects (e.g., sea-level rise and inundation of salt-flats) and human impacts (e.g., coastal urbanisation
and construction of harbours). To minimise the human effect, selected sites are located as far as
possible from urban areas. Aircraft photos (from Office de la Topographie et du Cadastre, Tunisia),
are available for at least two observing periods (with a minimum separation of 40 years) to identify
shoreline changes.
Figure 9: Three illustrative examples of shore line modification in the Gulf of Gabès. Upper panel: southeast of
Djerba; lower right panel: northeast of Djerba; lower left: northwest side of Kerkennah). The reference year is
1963. Shorelines are based on aircraft photos provided by ‘Office de la Topographie et du Cadastre’, Tunisia.
What does this show?
There is clear shoreline modification (advance or
retreat) in the three illustrative sites (Figure 9).
For example, important retreat can be seen along
the entire coastline northwest of Kerkennah.
Sites with substantial shoreline modification are
commonly found in the Gulf of Gabès. At least
15 such areas with shoreline modification have
been identified. However, most of these are
related to human activity (e.g., harbour
construction).
10
Why is it relevant?
Shoreline retreat can induce beach loss and
reduce tourism activity, particularly for the
tourist resort of Djerba Island. It is however very
difficult to separate impacts attributed to climate
from those attributed to human activity.
Nevertheless, observed increases in maximum
swell height and sea level contribute to shoreline
modification and reinforce the high vulnerability
of the Gulf of Gabès.
Coastal Vulnerability Index
What is it?
The index is a measure of the vulnerability of the coasts of the Gulf of Gabès to erosion. For each slice
of coast, a value for the vulnerability index is given based on a dimensionless scale from 1 (low
vulnerability) to 5 (very high vulnerability).
Table 2: Stable and unstable coasts indicator (PNUD/MEDD, 2007)
Coasts slice
Total
length (km)
Stable
(km)
Unstable (km)
unprotected
Chebba to Sfax
Kerkennah
islands
Inner gulf
130
174
125
171.5
5
3.5
164
164
-
Southern gulf
Djerba coast
332
146
319
127.2
11
 Sfax
 Kerkennah
13
6.5
946
906.7
What does this show?
The Gulf has high vulnerability to coastal
erosion particularly in the islands of Kerkennah,
Kneis and Djerba (Table 2). The total linear
coastal erosion is estimated as 40 km,
corresponding to 4.3 % of the total coastline
(MEDD/PNUD, 2007). Djerba island and Zarzis
appear to be among the most vulnerable areas
(60 % of their coasts are very vulnerable). The
northwest and southeast coasts of Djerba Island
are particularly affected by erosion. Coastal
retreat occurs at a rate of 0.5 to 1.5 m / year,
reaching 10 m / year in some locations
(MEDD/PNUD, 2007).
Vulnerability
index
Protected by
constructions
1.3
Total
Corresponding
site
40.3
3 moderate
4 high
3 moderate
 Mahres
 Ghannouch
4 high
 Zarzis
4 high
 NW coast of
Djerba
 North of Aghir
 South of Aghir
harbour
Rate of coastal retreat 4.3%
Why is it relevant?
Agriculture is among the key economic sectors
affected by coastal erosion through the loss of
arable land. Coastal erosion also has a dramatic
impact on beaches which are essential to the
region’s balnear (coastal) tourism. Some hotel
resorts have already suffered from extensive
erosion. Erosion may also affect harbours since
the transported eroded material results in
sedimentation of the harbour entrance. Nearly
40% of fishing harbours in the Gulf of Gabès are
vulnerable to coastal erosion (MEDD/PNUD,
2007).
11
Socio-economic losses due to beach erosion
What is it? The indicator shown in Figure 10 presents results of a theoretical simulation of economic
and social impacts of beach retreat in the Djerba-Zarzis tourist area. Impacts are based on the
assumption of a 1m/year beach retreat (MEDD/PNUD, 2007) starting from 1960 (when the beach
width is taken as 90 m). Loss calculations are similar to those performed for the climate tourism
potential. Here the basic hypothesis is that the complete disappearance of beaches devalues the hotel
price so that it equates to a hotel situated far inland (-1/3 employed persons; -20 Tunisian dinar/night;
MEDD/PNUD, 2008).
Figure 10: A simulation of the socio-economic impacts of beach retreat in the Djerba-Zarzis tourist area.
Results are shown as percentages of 2007 GDP. Direct and indirect employee loss should be multiplied by
100,000. Economic losses are based on 2007 rates.
What does this show?
According to this simulation a beach retreat rate
of 1m/year leads to a loss of capital in 2007 of
nearly 0.3% of GDP. The annual loss is also
important and reaches 0.25% by 2007. The loss
of direct and indirect employed persons amounts
to 3,500 and 10,500 respectively, which is nearly
18% of the number of employed persons in
2007.
Why is it relevant?
Beaches constitute a fundamental component of
tourism in the Djerba Island. The loss of beach
12
by erosion and sea-level rise will reduce the
attractiveness of hotels, lowering prices and
leading to economic losses and negative social
consequences. The present simulation indicates
that due to beach retreat alone, the number of
employed persons is reduced by nearly 1/5 in
2007. According to these simulations, beach
retreat appears to have more severe socioeconomic consequences for tourism activity than
a loss of ‘favorable’ days. However, it should be
noted that this simulation does not consider other
non-climate drivers, such as trends in holiday
destinations, fuel costs and exchange rates.
3. Thresholds and coping ranges
Thresholds and coping ranges have been
estimated for the fishing and tourism sectors
based on rather arbitrary but plausible criteria.
To a large extent such thresholds are based on
simple extrapolation of the observed trends,
although stakeholder discussions can provide
valuable further insight.
3.1 Fishing sector
The replacement of highly-valued indigenous
species with alien ones is one threshold. The
observed increasing rate of alien species is +15%
/decade, while the rate of sea-water warming is
around +0.12°C/decade. This translates to an
alien species increase of +125% / 1°C warming.
One can arbitrarily assume a threshold when
alien species comprise 10% of total species. A
very approximate number of total species in the
Gulf of Gabès is 1100. At the present rate of
change, this 10% threshold would be reached
after 7 to 8 decades (using 30%, the threshold
would be reached in nearly 15 decades).
However, the coping range may be expanded if
new species are appreciated by the consumer.
3.2 Tourism sector
Beach erosion has the greatest negative impact
on tourism in the southern part of the gulf. One
threshold for tourism is that beaches become
severely eroded. Assuming a continuous loss of
beach at a rate of 1m / year, this threshold will
be reached in about 90 years (beach width is
~90m). Although artificial beach nourishment is
very expensive it helps maintain the character of
the seaside resorts and thereby extends the
coping range.
An extended summer tourist season may be
beneficial but an increase in the frequency of
‘very hot’ days and a reduction in days
‘favorable’ for tourism could have negative
impacts. A possible hypothesis is that a tourist
spending a week in Djera-zarzis cannot tolerate
an additional ‘very hot’ day compared to present
conditions. At the present rate of increase (+0.7
days/month/decade), this will occur in 60 years.
The coping range may be expanded through an
extension of the summer tourist season (+8 days
/decade; approximately +0.6 days/week/decade).
An additional threshold can be defined on the
basis of the Climate Tourism Potential Index, as
the point at which all June-September days
become ‘acceptable’. According to current
trends this threshold would be reached in nearly
60 years. However, more ‘favorable’ days in
winter may stretch the coping range.
4. Risks of climate hazards to social and
biogeophysical systems
4.1 Current climate hazards
Observed trends in climate and marine hazards
for the Gulf of Gabès can be summarized as:
►
►
►
►
►
►
►
►
►
Increased daily mean air temperature:
~+0.5°C/decade
Increased daily maximum air temperature:
~+0.6°C/decade
Increased frequency of very hot days: +0.7
days/month/decade
Increased water temperature: ~0.12 °C/decade
Increased annual maximum swell height:
1m/decade
Sea level rise: +2.6 cm/decade
Beach erosion: 10m/decade
Tourist season expansion: +8 days/decade
Reduction of days ‘favorable’ for tourism: -12
days/decade
4.2 Vulnerability assessment of
biogeophysical and social systems
Agriculture & Fishing and Tourism are two
important economic sectors in Tunisia. They
respectively contribute around 11% and 13% of
the Tunisia GDP (years 2006-2008) and 16.2%
and 3.7% of the total Tunisian workforce
(RGPH, 2004). In comparison, 19.4% of the
workforce
is
employed
in
industrial
manufacturing. The large economic reliance on
fishing and tourism in Tunisia increases the
vulnerability of these activities to climate
change.
13
4.2.1 Fishing activity
Warmer air and sea temperatures lead to an
increase in alien species and a decrease in
indigenous species (Figure 11). This increases
competitiveness between species and results in a
decline in biodiversity. An increase in high
temperature events leads to more frequent
blooms (e.g., jelly fish) and fish mortalities.
These changes, together with an increase in
maximum swell height, bring economic losses to
the fishing sector.
Increased daily mean air temperature
(~+0.5°C/decade)
Increased daily maximum air
temperature (~+0.6°C/decade)
Blooms (e.g., Jelly fish)
Fish mortality
Increased sea water temperature
(~+0.12 °C/decade)
Alien species increase
+15% /decade
+125% /°C water temperature
Decline in indigenous species
Increased maximum swell height
Increased competitiveness
between species
Decreased biodiversity
Decreased catch of traditional
highly valued species
Economic losses for fisherman
Figure 11: Alien species-fishing activity vulnerability linkage diagram for the Gulf of Gabès.
4.2.2 Tourism activity
The vulnerability of the tourism sector to climate
change is difficult to gauge since climate acts
both positively and negatively on this sector
(Figure 12). The greatest vulnerability is related
to beach erosion since most tourism activity in
the region is balnear (coastal). Coastline retreat,
proceeding at 10m/year in some places, is
indicative of the highly negative impact of
erosion. Accompanied by sea-level rise, coastal
erosion may discourage investment in this
14
sector. Increases in maximum swell height also
contribute negatively to tourism activity,
although the influence is strongest in winter. The
increased frequency of very hot days and
warming of mean and maximum air
temperatures also has negative consequences,
leading to increases in water demand and air
conditioning, tropical diseases and jelly-fish
blooms. On the positive side, warmer winter airand sea temperatures result in more days
‘favorable’ to tourism activity. The extension of
the summer season reduces some of the
vulnerability of the tourism sector by allowing
easier management of tourist activities. Although
climate impacts amount to both economic losses
and gains for the tourism sector, the climaterelated losses are estimated to be larger than the
-
gains. However, climate is only one of multiple
forces acting on the tourism sector. Despite the
climate impacts described, tourism investment
and the number of tourists visiting the DjerbaZarzis area are increasing.
+
Increased air temperature in winter
Increased maximum swell height:
1m / decade
Seasonal shift +8 days / decade
Sea level rise 2.6 cm / decade
Increased beach erosion +1m / year
Increased water temperature
+0.12°C / decade
Increased frequency of very hot days
+0.7 days/month/decade;
Increased mean (+0.5°C/decade) and
max air temperature (+0.5°C/decade).
Less days ‘favorable’ for tourism
(-3.2% / decade)
Increased water demand
Increased air conditioning
Increased tropical diseases
More frequent jellyfish blooms
More days ‘highly favorable’ for tourism
in winter (+2.7% / decade)
Economic and social gains
Economic and social losses
Figure 12: Positive and negative climate impacts on tourism activity in the Gulf of Gabès
4.3 Case-study: Fishing bluefin tuna by net trap
In Tunisia, tuna has been fished since ancient
times. Fixed net traps were established due to the
seasonal migration of tuna close to the coast
(reproductive migration). The Sidi Daoud trap is
located in the Gulf of Tunis, approximately 20
km South-West of Cap Bon. Landings of bluefin
tuna in the Sidi Daoud trap have fallen
significantly since 1863 (Figure 13a). This
seems to contradict the general phenomenon of
long-term fluctuations of trap catch for other
fish, such as small pelagic fish (Toresen and
Oestvedt, 2000), salmonids (Beamish et al.,
15
1999) and Gadidae (Bjørnstad et al., 1999). It
has been suggested that the decline in bluefin
tuna catch is related to a change in the migration
path as the bluefin tuna avoid the warming
coastal waters. As a consequence of this
warming, the bluefin tuna catch period, usually
from late May-early July has shifted to early
March-end of May (Figure 13b). Since the year
2000, bluefin tuna have been caught at Hakl El
Bouri (70 nautical miles offshore from the
Tunisian-Lybian border) in the Gulf of Gabès
(Figure 13c). Hakl El Bouri is a protected fishing
area where bluefin tuna are caught by purse
seine. It is also a spawning area for this specie
and provides ideal conditions for its
reproduction. The fishing quotas from several
countries are only fulfilled by June catches in
this new spawning area (which due to its warmer
waters has replaced the previous spawning area
further north).
b
a
Beginning
and end of
bluefin tuna
trap
landings
c
Figure 13: a- Landing of bluefin tuna at Sidi Daoud Tunisian trap 1865-2003 (Hattour, 2005a); b – Beginning
and end of bluefin tuna landings at Sidi Daoud Trap (1931-2003) (Hattour 2005b); c – Landing of bluefin
tuna from Hakl el Bouri (Gulf of Gabès, 1998-2007, Hattour, 2009)
Table 3 summarizes the main biogeophysical and social vulnerability indicators for the Gulf of Gabès
and their associated climate hazards. Some suggestions of system thresholds are presented.
16
Table 3: Summary table of biogeophysical and social vulnerability indicators to current climate
Key impact
indicators
Tourist nights
spent in hotels:
Fish
production:
Climate/marine hazard
indicators
Vulnerability indicators
System
thresholds
Current impacts
 Warmer mean and
maximum summer
temperature.
 Higher frequency of
very hot days.
 Fewer days
‘favorable’ for
tourism.
 Capital and gain
losses.
 Employment loss.
 More Jelly fish
blooms.
 No ‘favorable’
days during
the summer
season.
 Based on a
theoretical model,
the estimated
impact on the
tourism sector is
negative with both
capital and
employment
losses.
 Maximum swell height
increase.
 Sea level rise.
 Coasts erosion.
 Beach retreat.
 Coastal
management.
 Entire beach
eroded.
 Some hotels suffer
from beach retreat.
 Extension of the
summer tourist
season.
 Increase of winter air /
sea-water
temperatures.
 Easier management
of the tourist season.
 The climate
attractiveness of the
region increases;
vulnerability is
reduced.
 Sea-water warming.
 Increased
competition between
alien and endemic
species.
 Increased
competition within
the fishing industry.
 Replacement
of endemic
species with
less-valued
alien species.
 Increased frequency
of very hot days.
 Eutrophication of the
ecosystem.
 Mass mortality
episodes.
 Jelly fish blooms.
 Human
stresses
(marine
pollution,
exploitation of
fish stocks)
reinforced by
water warming
 Based on a
theoretical model,
the estimated
impact on the
tourism sector is
negative for both
capital and
employment
losses.
 40 alien species
observed. A
reduction in the
catch of some
species is
observed.
 Economic losses
for the fishing
sector.
 Aquaculture activity
has stopped in the
lagoon of
Boughrara (DGPA,
2002).
5. Summary
The coastline of the Gulf of Gabès has
undergone several shoreline modifications
(retreat or advance). Much of the coastline is
highly vulnerable to erosion especially on Djerba
Island where several beaches already suffer from
severe erosion. Erosion is caused in part by an
increase in the maximum swell height in the gulf
probably related to an increase in wind speed.
The increase in maximum swell height is
indicative of storms being more severe, and
sudden shoreline modification is expected. Sea
level rise may also play some role in reinforcing
the vulnerability of the coast to erosion.
The discovery of alien marine species (based
on first recordings) has become more frequent in
recent decades. This may accelerate the
17
replacement of traditional highly-valued species
with alien ones. Sea-water warming accentuated
by summer heat waves has negative impacts on
the species living in the Gulf of Gabès,
especially the sedentary ones. The fishing
industry, already vulnerable to intrinsic social
pressures, is also vulnerable to the impacts of
climate change. The reduction of highly-valued
and traditional species in favour of nonindigenous ones may cause supplementary
pressures on the gulf fishermen. A threshold for
fishing activity is that new species are no longer
marginal. However, the coping range may
expand if the consumer develops a taste for
exotic species.
An increase in air and sea-water temperatures
appears to have a positive impact on winter
tourism in the Gulf of Gabès. The generally
warmer winter conditions increase its tourist
attractiveness and facilitate management through
a longer summer tourist season. On the other
hand, warmer weather is accompanied by an
increased frequency of very hot days in summer,
which can lead to negative impacts on tourist
comfort. The number of days ‘favorable’ for
tourism activity decrease in summer and increase
in winter but the summer decrease is much larger
than the winter increase. Beach erosion has the
largest negative impact on the tourism sector.
Greater coastal erosion and sudden shoreline
change due to more severe storms, heightens the
vulnerability of the tourism sector. A theoretical
model applied to tourism activity in the DjerbaZarzis area, suggests significant economic and
employment losses based on observed climate
trends. A threshold for tourism activity is the
point at which a beach is lost through severe
erosion. However, the extended summer tourist
season and generally warmer conditions may
expand the coping range.
Acknowledgements
CIRCE (Climate Change and Impact Research: the Mediterranean Environment) is funded by the
Commission of the European Union (Contract No 036961 GOCE) http://www.circeproject.eu/. This
information sheet forms part of the CIRCE deliverable D11.5.4. The following data sources were
used:
►
►
►
►
►
►
►
►
Historical water temperature data collected by INSTM.
Weather station data for Sfax, Gabès and Djerba, (http://www.tutiempo.net/en/Climate)
Relative sea level for the Sfax harbour provided by Centre d’Hydrographie et d’Océanographie de la
Marine Nationale, Ministère de la Défense Nationale, Tunisia.
Aircraft photos provided by Office de la Topographie et du Cadastre, Ministère de l’équipement, de
l’Habitat et de l’Aménagement du Territoire, Tunisia.
Number of tourist nights, provided by Office National du Tourisme Tunisien, Ministère du Tourisme and
Institut National de la Statistique, Ministère du Développement et de la Coopération Internationale,
Tunisia.
Significant swell height provided by Direction Générale des Services Aériens et Maritimes, Ministère de
l’Equipement, de l’Habitat et de l’Aménagement du Territoire, 1995.
Fish production data provided by Direction Générale de la Pêche et de l’Aquaculture, Ministère de
l’Agriculture, des Ressources Hydrauliques et de la Pêche, Tunisia.
Alien species observations are based on a series of published papers and theses.
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