The current status of Adriatic ichthyofauna
Slide 1
The title of this presentation shows the main attention of authors and this is to presents
collected data about state of Adriatic ichthyofauna with all new records in last 10
years. It will also give as an insight in future trends. I have to stay that majority of this
data was collected by dr. Ivan Jardas, who is probably one of leading Croatian
ichthyologist and I feel honoured by presenting them.
Slide 2
Contents of this presentation will be:
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a short introduction about environmental factors of Adriatic Sea because it is
important to have a good knowledge of the Adriatic characteristics in order to
have a better understanding of living conditions and life in the sea.
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Basic features of the Adriatic ichthyofauna
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Its zoogeographical belonging
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New and endemic species
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And of course, some words about future trends
Slide 3
The current fauna of the Adriatic Sea is a result of numerous geological, geographical,
climatic and biological influences that took place over the earth's past. Those different
environmental factors, mostly of a hydrographic nature, are crucial even today. The
Adriatic Sea is a gulf in the Mediterranean, which derives from the former Tethys Sea,
a large geosyncline that extended between two continents – European in the north and
African in the south. Throughout the tertiary, Tethys was gradually separated into
several discrete basins, as a result of the elevation of large massifs. So, western Tethys
extended into the present Atlantic, and eastern part divided into what are today the
Mediterranean, Black, Caspian and Aral Seas.
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Slide 4
The Adriatic is usually for practical purposes divided into northern, central and
southern parts. According to this division, northern Adriatic stretches to an imagined
diagonal line from Karlobag to Ancona, central part stretches from this line to line
between Split and M. Gargano, while south Adriatic comprises the area to the south of
this line. The north Adriatic is the northernmost part of the Mediterranean and by
physical features partially influences the eastern Mediterranean and by biological
features has boreal properties. Central Adriatic is characterised by Jabuka pit, and
south Adriatic as deepest part with the depth of 1330 m. The Adriatic, which covers
about 4,6 % of the entire Mediterranean, is linked with its other parts by the Strait of
Otranto.
Slide 5
Depth: The Adriatic Sea is shallow sea in which continental shelf covers about 74%
of its surface. The depth of the Adriatic gradually increases from the northwest to the
southeast. An isobath of 100 m is located on the line passing through Kornati
Archipelago. Depths greater than 200 m are found around Jabuka Pit (273 m) and in
the South-Adriatic Pit (1330m). The mean depth is 251 m.
Considering the configuration of the sea floor, the bathymetric characteristics and the
general scheme of a bathymetric division of the zones in the Adriatic Sea, the pelagic
zone includes an epipelagic, a mesopelagic and perhaps a bathypelagic zone. In the
benthal zone there is an intertidal zone, a continental shelf and a continental slope or
bathyal zone.
Slide 6
Salinity: The Adriatic basin is distinguished by relatively high salinity of about 38.3
psu, which is somewhat, less than in the eastern Mediterranean (39 psu) and more
than the salinity in the western Mediterranean (37psu). Generally, salinity falls from
the south towards the north, and from open sea towards the coast. This can be
explained by the influx of more salty eastern Mediterranean water into the Adriatic on
the one hand, and by the influence of continental waters on the other.
Besides the normal annual fluctuation of salinity, in some years there is a more
powerful influx of the more salty eastern Mediterranean water into the Adriatic Sea,
called Adriatic ingression. The phenomenon is related to shifting of water masses
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between eastern Mediterranean and Adriatic Sea due specific distribution of low
pressure in eastern Mediterranean, and probably play important role regarding the
presence of some rare and new species in Adriatic.
Temperature: Temperature in Adriatic indicates that it is a warm sea. The water in its
deepest layers is almost always above 12°C. In the open sea summer surface
temperature is usually between 22-25°C falling to around 12°C in deepest parts.
During winter, south Adriatic is wormer than central and north, and open sea is
wormer than coastal waters. But difference in temperature between CA and SA is not
significant. During summer months, thermocline is formed at a depth of about 10-30m.
But, in autumn, and particularly during winter, because of the cooling and mixing of
water layers caused by bora wind blowing, isotherms is created, firstly it is about 1819°C, and than fall to 11-12°C.
Movement of water masses: The movement of the water masses in the Adriatic Sea
depends primarily on its geomorphological, meteorological (heating, winds) and
hydrographic characteristics. Except geomorphological, all factors have a seasonal or
local significance for the dynamics of the water masses.
Generally, Adriatic Sea can be divided in three distinct horizontal layers: the surface,
intermediary and bottom layers, all with more or less independent systems of
circulation, influencing one another to a certain extent. The flow in surface layer is
basically cyclonic, the water flow in from the eastern Mediterranean along the eastern
coast, and flow out along the western coast. This flow has strong seasonal
characteristics, with grater influx in winter and grater outflow in summer. This rhythm
is also additionally influenced, mostly in positive way, by winds. In the intermediary
layer, inflow predominates throughout the year, especially in summer, due
compensation for surface outflow. The current in bottom layer is least known. Otflow
predominates, particularly in winter, when it appears as a compensatory current to the
inflow in surface and intermediary layers. In winter this water is created in norh
Adriatic by blending of cold and heavy water.
Slide 7
The current checklist includes a total of 437 Adriatic fish species and subspecies
(Myxini 1, Cephalaspidimorphi 3, Chondrichthyes 55, Actinopterygii 379), which
make about 65% of Mediterranean species and subspecies (about 672). The quoted
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number of fish species has been grouped into 2 classes, 22 orders and 124 families. Of
total number of families, 21 belong to Chondrichthyes. However, the list comprises
about 20 species whose findings are old, questionable and/or imprecise, so their
presence needs to be confirmed. Also, the greatest part of the south Adriatic basin,
particularly depths under 500m has not been sufficiently explored. The third reason
for the uncertainty about the exact number of Adriatic fish is some unsolved
taxonomic questions of some fish species especially of gobids.
Slide 8
According to biogeographical determination, the highest number of Adriatic fish
belongs to Atlanto-mediterranean species (> 65%) and Mediterranean species (20%).
Others are cosmopolites and species of wider geographical distribution (11% - tunas,
some meso and bathypelagic species). There are also 9 lessepsian migrants and 6
endemic species. If mediterranean-atlantic biogeographic elements are considered, the
greatest number of the Adriatic representatives belongs to the eastern Atlantic boreal
zone (40%). This boreal elements gives a special character and place of Adriatic Sea
in Mediterranean (genus Raja Mustelus, Pleuronectes, Scophthalmus, gadides,
Sprattus, Belone, Dicentrachus, ,…).
Around 18% of the Adriatic ichthyofauna is belonging to Mediterranean species.
There are not endemic mediterranean species, but those in a wider sensethat can be
found also in neighbouring section of eastern Atlantic, in the region of Gibraltar,
between Portugal and Mauritania, and sometimes including the Azores, Medeira and
the Canary islands. Also, there are 3% of species that are distributed only in
Mediterranean and Black Sea.
Generally speaking, the greatest differences are found between ichthyofauna of the
Black Sea and the rest of Mediterranean. Also, greater similarities exists between
Adriatic and western Mediterranean (by number of typical fish species) although the
Adriatic is both geographically and physiograpically a part of the eastern
Mediterranean. But those differences become less prominent due global changes.
Slide 9
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This slide presents 32 new species recorded in last decade and those in yellow are
Lessepsian migrants, the species that originate from Indo-Pacific region, and entered
in Mediterranean from Red Sea through Suez channel. The entering was impossible
until to the moment when salinity becomes similar to those of the eastern
Mediterranean, but after that more than 30 species entered in it. Besides salinity, high
turbidity and length of channel are main obstructions for the fishes on that way.
Slide 10
Adriatic endemic species is also rare. There are only some species and subspecies
(among the Atlantic-Mediterranean species) of the families of Gobiidae, Syngnathidae
and Acipenseridae. In mediterranean ichthyofauna, also, is the highest number of
endemic species from the family of Gobiidae. Moreover, all Adriatic endemic species
are found in shallow zone, from 0-50 m of depth. But all this records are under
question, because every day we have informations, which are still not confirmed,
about records of this endemic species in other regions out of Adriatic Sea.
Slide 11
The highest number of fish species is recorded in whole Adriatic (56.5%), following
by those distributed in middle and southern part (16.7%) or just in southern part
(15.8%), respectively. Moreover, number of fish species falls from southern to
northern Adriatic. Every of Adriatic division (north, central, south) have few typical
elements of the ichthyofauna, which distinguish them from one another. Thus,
northern Adriatic is characterised by boreal features and boreal elements of the
ichthyofauna more than other parts (Sprattus, Solea,..). Central and South Adriatic
due certain environmental similaritirs (depth, water temperature) have more similar
ichthyofauna
with
more
thermophile
elements
(Thalassoma,
Sparisoma,
Brama,…).Central Adriatic especially marked, as was shown earlier, by the Jabuka pit,
where some boreal and termophile elements of the ichthyofauna are complemented by
some batyphile elements; finally, the deep south adriatic with a distinct bathyphile
ichthyofauna and numerous thermophile elements, many of which occur in this region
only.
Slide 12
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The most dominant families are Gobiidae (46), Labridae (18), Sparidae (18),
Blennidae (17) and Myctophidae (15). According to the number of fish species, the
Adriatic Sea is one of the richer seas, although, by the density of populations and
capacity for exploitation it can be compared with poorer seas.
According to ecological affiliation and horizontal distribution, southern Adriatic is
characterized by higher presence of termophilic and batiphilic species while more
boreal species are recorded in northern Adriatic.
Slide 13
According to the annual catch of fish and other sea organisms in Adriatic Sea,
it comprise about 15% of the total catch in Mediterranean, and takes second or third
place between 10 fishing regions in this area (togerther with Italian catch). From 1983,
a constant drop in quantity of fish caught can be followed. The largest biomass in the
Adriatic is made up of small pelagic fish (> 50% of total catch), so that these few
species comprise the greatest share in the eastern Adriatic commercial catch. Another
hundred or so other species have some economic significance, and are therefore more
important than just being members of the Adriatic ichthyofauna. During last 20 years
demersal fishing takes more significant place due greater profitability and higher
market prices of so called white fishes. Special attention has to be directed to coastal
fisheries because more than 50 fishing gears are used in Croatian coastal fisheries of
which many are unique, like tramata fishing. Coastal waters are one of rather
important fishing grounds of the eastern Adriatic Sea. The area is the most productive
Adriatic zone owing to the vicinity of the land and fresh water inflows. The statistics
on marine fishing published by the Institution of Statistics of the Republic of Croatia
shows that in recent years (1983-1999) landings ranged from 2400-5400 mt in the
eastern Adriatic. The coastal part in that total catch provides 12-13%, but one great
part of demersal and small pelagic fishing is also realized from the coastal area.
Changes in the communities of fish and edible invertebrates, manifested as changes in
quantitative and qualitative catch structure, are due to various reasons, particularly to
that intensive fishing. The long-term monitorings of coastal communities could
provide information on the trend and intensity of those changes.
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Slide 14
Adriatic Sea is one of the most productive and most exploited regions in
Mediterranean. Although by its surface area the Adriatic is small sea (5,5 % % of M),
it yields about 15% of total catch in Mediterranean. Taking into account only large
vessels, there are about 8000 trawlers, puirse seiners etc.
We can therefore say that, on the whole, the Adriatic is an overfished sea. This is
particularly the case with the trawling grounds of the open Central Adriatic
(Blitvenica, Jabuka Pit), as well as the channels, western Italian sector, eastern coastal
region, and of the fish species hake and red mullet in particular. Although, the strong
low regulatives are brought, still the application of this regulatives has to be improved.
Also, indirect damages of fishing, particularly of trawling, is very evident.
Slide 15.
Apart from unreasonable and uncontrolled fishing, a certain harmful influence on the
coastal biological resources is the constant growing pollution of the sea, particularly
in urban and industrial centres. The actual influence of pollution on ichthyofauna is
hard to be estimated. While adult fishes will probably escape from polluted area, fish
in early developmental stages is very vulnerable. A special problem is eutrofication,
process by which the sea is enriched with nutrients stimulating primary production.
The special problem is river Po, which contributes more than 50% of total inflow of
nutrients in Adriatic. In open sea, eutrofication is not a problem up to a certain level,
but in semi-open regions represents a threat to marine life. It can be manifested by
anoxia that can cause mortality of numerous marine organisms.
Slide 16.
A large number of fish is protected in various ways by legal measures for fish and
other marine organism conservation by Sea Fishery Act of the Republic of Croatia.
The regulation includes 60 fish species inhabiting the pelagic waters, trawling
grounds or coastal area. On that way, we try to protect population not reproductively
mature. Other measures are: close season, close areas, temporary fishing prohibition,
and control of harmful fishing gear, meshsize. Also, in Croatia there are several areas,
which are declared as special habitats, parks, or marine protected areas as Kornati,
Mljet. And, at the end red book of Adriatic Sea is preparing and will be reported very
soon.
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