Macroplankton and micronekton
LIDIA ORSI RELINI · GIOVANNI PALANDRI · CHANTAL CIMA · MARCO RELINI
Macrofauna in offshore waters is
particularly varied and rich, because
its differing components - plankton,
nekton, benthos - can rely on an
environment ranging from the surface
to a depth of 2500 m. Representatives
of this fauna which may easily be
watched on the surface are relatively
few - for example, velellas, the jellyfish
Pelagia noctiluca, salp chains, flying
fish, sunfish, the large plankton-eating
shark Cetorhinus maximus, and all the
Salp chain (Salpa fusiformis)
vertebrates with lungs, such as turtles
and marine mammals. Fauna at depth is obviously abundant in species, but
only some reach the surface during the night or are occasionally visible during
the day. When this happens, watching unusual organisms becomes exciting:
for instance, all those who have seen an oarfish swimming on the surface in
sunlight - like a large silver ribbon with a scarlet crest - will certainly never
forget the sight.
A systematic description of mesopelagic macrofauna is harder than that of
microfauna, because scientific sampling devices are often unsuitable for
catching rapidly moving organisms and fishing gear must be used. However,
fishing equipment was generally created for some categories or single species
of commercial interest and is too selective, only allowing us to see a more or
less limited part of the pelagic community. But every kind of device applied to
both research aims and exploitation of resources shows us a different set of
organisms.
Study of the mesopelagic fauna of the Sanctuary, which includes essential
components in the trophic chains of the top predators, is still mainly
qualitative, and we must often content ourselves with listing some apparently
important animals, without being able to describe them in terms of biomass
and their role in the ecosystem.
Jellyfish (Pelagia noctiluca)
53
YEARLY AVERAGE (NUMBER)
YEARLY AVERAGE (BIOMASS)
AVERAGE OF MOST ABUNDANT
SEASON (NUMBER)
845
1
845
20
17900
4
12
15
6
60
72
50
20
200
240
117
16
13
5
2
1
585
32
13
20
10
5
2340
160
65
34
54
6
10
44
17
69
38
335
3
1
0.5
2
15
1
4
10
1
102
54
3
20
660
17
276
380
335
15
2
2
7
96
3
15
51
6
510
108
12
70
4224
51
1035
1938
2010
817
220
0.3
0.7
245
154
2
4
1634
880
1040
135
0.1
0.9
104
122
0.2
1.8
208
243
2310
104
0.1
0.9
231
94
0.4
1.6
924
166
19
9
1
5
19
45
25
75
475
675
412
18
0.5
2.5
206
45
5
35
2060
630
TOTAL
79.5
4719
472
38758
of which:
gelatinous organisms
crustacea and mollusca
31
48.5
1292
3427
230
242
22180
16578
SPECIES
Jellyfish
Pelagia noctiluca
Siphonophores
Chelophyes appendiculata
Abylopsis tetragona
Molluscs
Cymbulia peronii
Clio piramidata
C. cuspidata
Crustaceans
Phronima sedentaria
Phrosina semilunata
Scina crassicornis
Eucopia hanseni
Meganyctiphanes norvegica
Nematoscelis megalops
Gennadas elegans
Sergestes arcticus
S. arachnipodus
Sergia robusta
adults
juvenile
Acanthephyra pelagica
adults
juvenile
Pasiphaea multidentata
adults
juvenile
Tunicates
Salpa fusiformis
oozoids
blastozoids
Pyrosoma atlanticum
adults
juvenile
AVERAGE OF MOST ABUNDANT
SEASON (BIOMASS)
INDIVIDUAL BIOMASS (mg)
54
Biomass (mg of dry weight per 5000 m3) of the most important species of macroplankton and micronekton
The mesopelagic fauna of the western Ligurian Sea has been studied with
nets for mesopelagic sampling (IKMT) since the 1970s. One French research
listed over 70 species off the Provençal coast between Cannes and Marseilles,
at depths of 800–2400 m. Meganyctiphanes norvegica, Sergestes arcticus and
Salpa fusiformis turned out to be the most abundant in terms of numbers. Also
present were jellyfish, siphonophores, planktonic gastropods, several species
of shrimps, pelagic tunicates and small fish. The same research also provided
a biomass evaluation of some of these organisms (weight in mg per 5000 m3
of water) (see table, pag. 54).
Many studies have been carried out on the same organisms by the Villefranche
researchers, who used both IKMT nets and the newest and most
sophisticated sampling devices such as Bioness net systems, etc., which can
be opened or closed at a given depth, allowing sampled organisms to be
distinguished according to their vertical distribution.
A recent example of sampling, carried out with the Bioness net system along
some transects between the French coast (Nice) and Corsica during a spring
survey (see table, page 56) lists the 20 most important species and gives
numbers per cubic metre. Note the abundance of gelatinous plankton,
composed of one jellyfish species, three species of Siphonophores and three of
salps, and several species of Euphausiids. However, there are very few species
of pelagic shrimps and fish, probably due to the size of the mouth of the nets.
IKMT sample: cephalopods and small fishes of the genus Cyclothone
55
■ Medusozoans, ctenophores and other gelatinous plankton
56
SPECIES
DAY
NIGHT
Jellyfish
Solmissus albescens
4.8 ± 4.7
5. ± 4.8
1.6 ± 1.4
1.4 ± 1.1
Siphonophores
Abylopsis tetragona
Chelophyes appendiculata
15.9 ± 23.1
9.2 ± 5.1
Lensia conoidea
16.0 ± 11.1
13.7 ± 14.7
Cavolinia inflexa
4.0 ± 3.1
1.7 ± 2.7
Clio piramidata
2.1 ± 2.6
1.6 ± 0.9
Styliola subula
0.3 ± 0.8
0.4 ± 1.5
Eucopia unguiculata
3.5 ± 2.7*
4.4 ± 3.0*
Euphausia brevis
1.4 ± 2.0
0.5 ± 0.9
Euphausia hemigibba
0.8 ± 1.6
0.5 ± 1.1
Euphausia krohnii
3.1 ± 3.6
3.4 ± 4.5
Small
10.0 ± 1.2
10.6 ± 5.2
Large
18.1 ± 1.6
18.4 ± 4.8
Small
5.7 ± 4.4
7.7 ± 16.4
Large
6.3 ± 2.0
7.3 ± 2.7
Stylocheiron longicorne
3.5 ± 3.3
2.7 ± 1.4
Gennadas elegans
1.1 ± 1.1
2.7 ± 1.3
Molluscs
Crustaceans
Meganyctiphanes norvegica
Velellas are cnidarian hydrozoans, colonies of which may be found on the
surface of the sea thanks to their oval float, up to 6 cm in length, which has a
small “sail” set obliquely on it. Both winds and currents therefore govern the
distribution of these organisms and, especially in late spring and early
summer, large quantities of them are stranded on beaches. From such
seasonal occurrence derive the Italian names “St. Peter’s boats” and the
French “St. John’s boats”, because these saints’ feast-days are celebrated in
June. The shores of the Sanctuary are sometimes edged with blue velellas
which, as the days go by, dry and fade in colour, leaving only the thin,
transparent floats.
When hundreds of thousands of velellas reach land and are beached, it is a
good opportunity for scientists and lovers of marine life to study them, because
other pelagic animals associated with velellas may also be observed - for
example, gastropods of the genera Janthina, Glaucus and Fiona, which eat
their soft tissues. Blue or bluish-violet hues, due to carotenoids ingested by
velellas, very often characterise these molluscs. For instance, Janthina, which
looks like a small snail and lives on a platform of bubbles, also has a blue shell
(greatly appreciated by collectors). The nudibranch gastropods lay their eggs
on the discs of the velellas, exploiting them to the full, as observed by Issel. On
Nematoscelis megalops
Tunicates
Pegea confoederata
0.04 ± 0.1
2.9 ± 5.4
Salpa fusiformis
4.1 ± 4.9
4.3 ± 3.7
Thalia democratica
5.9 ± 10.4
6.9 ± 16.0
Cyclothone braueri
40.2±13.3
48.3 ± 10.9
Cyclothone pygmaea
33.3±12.1
30.7 ± 10.2
Bony fish
Organisms present (n / m3) in water column (surface to 700 m depth) off French coast
Velella (Velella velella) and its predator the mollusc Janthina
57
Aequorea forskalea, side view
YEARS WITH PELAGIA
1
0
1985
1980
1975
1970
1965
1960
1955
1950
1945
1940
1935
1930
1925
1920
1915
1910
1905
1900
YEARS WITHOUT PELAGIA
1895
Aequorea forskalea, viewed from beneath
and females, are elegant in shape, and have a rounded umbrella, up to 20 cm in
diameter, with light blue, violet and brown shades on a transparent background,
and a manubrium extending in four long lobes with festooned edges; the long
stinging filaments hang from the edge of the “umbrella”.
Cases of great abundances of this jellyfish have been known since the 19th
century, but only recently have specific research programmes been undertaken
to study it. Researchers at Villefranche-sur-Mer have examined the cyclicity of
abundances over a period of two centuries, and observed cycles of 12±2
years, formed of a sequence of years “with” and “without” jellyfish. These
cycles are related to climatic events, such as a dry spring. A bloom of Pelagia is
associated with changes in the entire plankton community and, in years
“without” Pelagia, other carnivores take its place, but exactly what determines
these changes is not yet known.
Other large jellyfish which may sometimes be sighted, even in coastal waters,
are Rhizostoma pulmo and Cotylorhiza tubercolata.
Ctenophores represent another group of carnivores of gelatinous
macroplankton, easily observable by scuba-divers. They do not use
nematocysts to capture their prey, but adhesive organs. They move by beating
both typically iridescent cilia and muscle cells: examples are Leucothea
multicornis, Cestum veneris and Beroe ovata.
Gelatinous macroplankton has a great number of filter-feeders in the
Tunicates, represented by salps, doliolids and appendicularians. Even salps
produce extensive blooms, especially in winter and, at times, sailing in
offshore waters, ships seem to plough through an enormous broth in which
1890
Rhizostoma pulmo
May 27 of 1928, the famous marine
biologist went to study the velellas
beached at Sturla and Santa
Margherita “after an exceptionally long
period of rough sea, due to strong S-E
and S-W winds”. The biology and role
played by velellas in the pelagic
ecosystem are complex and not wellunderstood. Like all cnidarians, these
predators catch their plankton prey by
means of nematocysts.
Hunting is limited in space, due to their
completely superficial position, and
thus is especially addressed to the
hyponeuston, i.e., a plankton layer
rich in small crustaceans, especially
cladocerans and pontellid copepods,
which are blue in colour. The medusoid
stage of the velella is represented by a
small jellyfish without a mouth (0.1
cm), called chrysomitra. Velellas are
also eaten by plankton-eating marine
vertebrates such as fish, selachians
and turtles. Carrying symbiontic algae,
velellas are able to exploit light in their
particular surface environment, the best
illuminated among all habitats available
to marine organisms.
The most striking jellyfish of the
Sanctuary belongs to the group of the
Scyphomedusae. Pelagia noctiluca
has the worst capacity for stinging,
and the arrival of large numbers of
these animals in coastal waters during
summer is always news-worthy and
causes problems for bathers. No
polypoid stage is known for this
jellyfish, only pelagic forms, from larvae
of 0.1 cm to the adults. These, males
1885
58
On the basis of several climatic characteristics, a model to predict jellyfish abundance (blue line, varying
from 0 to 1) was produced; green areas: years with Pelagia, orange areas: years without, from 1885 to
1985
59
60
the salp chains look like strings of very fine spaghetti. On the whole, in terms
of the trophic network, gelatinous plankton is one of the treasures of the
Sanctuary. Animals which eat this macroplankton have a never-ending source
of food at their disposal, are characterised by rapid growth, and may reach
striking dimensions. In the Sanctuary, cases of this specialisation are seen in
two vertebrates, Dermochelys coriacea and Mola mola. The former is the
leatherback sea turtle, an occasional visitor which, with a weight of more than
900 kg, is the largest living turtle; the latter is the ocean sunfish which,
reaching 2 tons in weight, is the largest living teleost fish.
■ The krill of the Ligurian sea: Meganyctiphanes norvegica
The euphausiid crustacean Meganyctiphanes norvegica reaches its greatest
concentrations in the whole of the Mediterranean in the Ligurian Sea. It is the
favourite prey of the largest filter-feeding animals of the Sanctuary (e.g.,
Balaenoptera physalus and Mobula mobular) and is eaten by many fish,
including bluefin tuna. More in general, it is a key species in the food webs in
both slope and offshore waters. This euphausiid has been studied in terms of its
biology and especially its reproduction, but its distribution and biomass in the
area - a fundamental aspect for knowledge of how the offshore ecosystem
functions - is still not well-known.
Krill: size and age
Lidia Orsi Relini
The size and age structures of krill
populations are divided into two main
groups: rapidly growing juveniles,
which change with the season, and
adults. The two groups are
distributed according to spatial
gradients. Size structure may be
studied even after krill has become
food for the animals which prey on it.
This means that their feeding places
can be more easily studied.
In the case of the rorqual whale
preying on krill, information on size
structure comes from the whale’s
faeces which, being red in colour, are
highly visible in water (see photo).
1000
500
200
AUGUST 1991
AUGUST 1993
JUNE 1994
100
90
80
70
60
50
40
30
20
10
A1
A3 A3bis A5
A7
A9
B1
B2
B3
B4
B5
B6
B7
C2
C4
C6
C8
D1
D2
D2.5 D2B
D3
Quantities of krill found during summer surveys on oceanographic research vessels “Minerva”
and “Urania” (1991-1994)
Meganyctiphanes norvegica
61
62
Krill and fin whale: density of prey and predators
Lidia Orsi Relini · Giovanni Palandri
krill is cumbersome and heavy. In addition,
these tiny shrimps are not found in
superficial waters, but along a water
column of about 1000 m, where they
move up and down in response to the
intensity of light, and form groups with
varying degrees of aggregation or
dispersal. A large specialised krill eater,
like the fin whale, appears to be able to
“home in” on to the most appetising
shoals, targeting them precisely. We do
not know exactly how it does this, but
some researchers believe that the great
acoustic sensitivity of the fin whale allows
it to listen to the noise made by krill
shoals. In any case, it certainly consumes
enormous quantities of these crustaceans.
For two weeks, the “Minerva,” equipped
In August 1991, an international team on
board the Greenpeace research vessel
“Sirius” carried out a survey of whale
sightings between the Ligurian Sea and
the Strait of Gibraltar, in order to describe
the distribution of fin whales and to
estimate their absolute abundance in the
western Mediterranean. At the same time,
within Sanctuary waters, the
oceanographic vessel “Minerva” was
sampling krill, the euphausiid crustacean
Meganyctiphanes norvegica, and was
counting fin whales with the aim of relating
their local density with that of their
preferred prey. Clearly, measuring krill
densities is much more difficult than
counting whales. A large vessel is needed,
because the best type of net for capturing
with a mesopelagic net for macroplankton
with a mouth aperture of about 20 m2,
sampled krill along transects between the
Ligurian-Provençal coast and Corsica,
and created the first map of this resource
on a basin scale. During this period, a
large number of cetaceans were seen,
including not only fin whales but also
striped dolphins and pilot whales. It is
interesting that the number of fin whales
sighted in the Sanctuary was of the same
order as that found in the entire western
Mediterranean - about 50 and 70,
respectively. In fact, all whales observed
by the “Sirius” were in the Ligurian Sea
and off the Gulf of Lions. In the Ligurian
Sanctuary, the densities of fin whales and
krill were correlated.
GENOVA
A1
A3bis
A3
NICE
B1
A5
D3
D2
D2.5
B2
D2B
B3
D1
A7
B4
B5
B6
B7
A9
C2
C4
C6
C8
Correlation between krill and fin whales: circles represent quantity of krill present along some
transects between Liguria and Corsica. The quadrates of different colours represent fin whales
observed per unit of sailing: darker colours indicate higher numbers of whales
IKMT net used on board the oceanographic ship “Minerva” for sampling mesopelagic fauna
63
64
For this reason, oceanographic surveys organised by the University of Genova,
in cooperation with the Physical Oceanography Unit of ISMAR (one of the
centres of the Italian Council for Research), based at La Spezia, are in progress,
aimed at verifying the distribution of krill on a basin scale over different seasons.
Abundant krill shoals are found in summer mainly along a transect between the
French-Italian frontier and near Calvi, in Corsica. The largest numbers of fin
whales have also been recorded in this transect.
■ Mesopelagic shrimps
After krill, pelagic crustacean decapods, i.e., pelagic shrimps, are an important
group as regards abundance and extent of vertical distribution. These
organisms can move hundreds of metres along the water column, following
light gradients: they may be found in great depths, even beyond 1000 m,
during the day, and much closer to the surface at night. However, for some
species, “close” to the surface means 200-300 m depth. One indication of
their distribution in deep waters is given by colour: there are absolutely
transparent species, which turn dull-white when fished, and others which are
red and white, or all red: the sequence of colours is related to depth. The allred species live in the deepest waters and their intensity of colour, like that of
some nail varnishes, should not mislead us, because we are talking of “non-
Pasiphaea sivado
colours”. That is, as sunlight penetrates
the water column, the red wavelength
is one of the first to be extinguished,
so that a bright red appears black at
depth.
A dozen or more species, belonging to
five families, live in offshore waters, to
which we must add, as meroplankton,
the larval and juvenile stages of many
other species of decapod crustaceans
which, when adults, are benthic, living
near the bottom. Pelagic shrimps are
probably very appetising prey and
analysis of the stomach contents of
large predators sometimes reveals just
how many of these crustaceans have
been eagerly swallowed.
Pasiphaeids are represented by two
species: the small, transparent, white
glass shrimp, P. sivado, sometimes
reaches the surface and may be
caught in large quantities even by
epibathyal trawlings. P. multidentata is
larger, lives in deeper water, and is
white with pink or orange parts. It may
be caught by deep trawling, but only in
small quantities, probably because it
swims fast and can avoid the nets.
Sergestids are represented by four
species of the genus Sergestes, all
half-red; one species of Sergia is all
red. The small aristeids of the genus
Gennadas show also scarlet.
The largest quantities of shrimps found
in the stomachs of striped dolphin
(Stenella coeruloalba) belonged to
Pasiphaea multidentata and Funchalia
spp. species in swordfish, and to
Sergia robusta in Delphinus delphis.
65
Crustacean decapod Sergia robusta
Crustacean decapod Sergestes arachnipodus
CRUSTACEAN DECAPODS
Aristaeids
Gennadas elegans
Penaeids
Funchalia villosa
Funchalia woodwardi
%
46.3
0.13
0.06
Sergestids
Sergestes arcticus
Sergestes arachnipodus
Sergestes sargassi
Sergestes vigilax
Sergia robusta
26.0
3.3
2.6
2.9
2.7
Oplophorids
Acanthephyra pelagica
Acanthephyra eximia
2.3
+
Pasiphaeids
Pasiphaea multidentata
Pasiphaea sivado
9.3
4.1
List of pelagic shrimps sampled with a large
IKMT net in the Sanctuary
Cephalopods and fish
LIDIA ORSI RELINI · GIULIO RELINI · MARCO RELINI · FULVIO GARIBALDI
■ Cephalopods
Pelagic cephalopods comprise one of
the most important and at the same
time least known mollusc groups in the
Sanctuary. Half the cetacean species
which appear regularly in the Sanctuary
- the sperm whale, Cuvier’s beaked
whale, long-finned pilot whale and
Greater argonaut (Argonauta argo)
Risso’s dolphin - are exclusively or
essentially cephalopod eaters.
Cephalopods are also part of the diet of the striped dolphin, common dolphin
and bottlenose dolphin (although the latter only eats coastal species), and are
also preyed upon by many species of fish. It is very difficult to catch
cephalopods with nets, except when they are juveniles and have not yet fully
developed their swimming skills. In addition, pelagic cephalopods are not
professionally fished, but only caught occasionally by amateur fishermen in their
leisure time. For this reason, we have little knowledge of them and sometimes
make incredible discoveries. One such event occurred in August 1993, when a
cephalopod weighing over 80 kg was caught in the eastern Ligurian sea. Only
one photograph of it was taken on board, and its identification is still obscure,
except for a generic attribution to the Cranchidae family. A cephalopod of this
size had never been found before in Italian seas (and, if the attribution to the
Cranchidae is correct, not even in the Mediterranean or the Atlantic Ocean).
In the Sanctuary, sampling the first 800 m of the water column with 15-foot IKMT
nets usually yields 18 species (see table, page 68): three octopodids, which are
only meroplanktonic - Pteroctopus tetracirrhus, Scaeurgus unicirrhus and
Octopus defilippi. To these must be added three species of pelagic octopodids
living in surface waters - Argonauta argo, Ocythoe tuberculata and Tremoctopus
violaceus, for a total of about twenty species.
It is harder to describe the populations of cephalopods which live at depths
exceeding 1000 m. Many of the already mentioned species - perhaps all of
Tremoctopus gracilis
67
68
them - may go even deeper. On the sea
bottom, there are also species of
benthic cephalopods which probably
have semi-pelagic behaviour, as may be
deduced from their jelly-like bodies - for
example, Opisthoteuthis calypso, the
latest to be discovered in the Sanctuary.
This small red octopus has two fins on
its head which represent its swimming
A sepiolid
organs. The first specimen found in
Italian waters was caught in the year 2000 off the western Ligurian coast. The
Histioteuthidae family, with two species, is the most abundant group. These
cephalopods are unmistakable, because they have polychrome photophores all
over their bodies which, depending on the degree of environmental illumination,
may stand out on a silvery skin like gemstones on a metal surface - thus giving
rise to their nickname, jewel squid. They are of no commercial interest because
they contain ammonia, i.e., they reduce their specific weight by accumulating
light ions, like ammonia, and therefore have an unpleasant taste. However, many
top predators eat them, and their remains are abundant in the gut of all the
cephalopod-eating mammals of the Sanctuary, from sperm whale to small
dolphins like Stenella coeruleoalba and Delphinus delphis.
FAMILY
ISTIOTEUTIDS
SEPIOLIDS
CRANCHIDS
CTENOPTERIGIDS
CHIROTEUTIDS
OMMASTREFIDS
OCTOPODIDS
ENOPLOTEUTIDS
ONICOTEUTIDS
ARGONAUTIDS
SPECIES
Histioteuthis reversa
Histioteuthis bonnellii
Heteroteuthis dispar
Stoloteuthis leucoptera
Galiteuthis armata
Chtenopteryx sicula
Chiroteuthis veranii
Todarodes sagittatus
Illex coindetii
Ommastrephes bartramii
Pteroctopus tetracirrhus
Scaeurgus unicirrhus
Octopus defilippi
Abralia verany
Abraliopsis morisii
Onychoteuthis banksii
Ancistroteuthis lichtensteinii
Argonauta argo
Cephalopods n. i.
TOTAL
Composition of teutofauna captured in IKMT nets in the Sanctuary
■ Epipelagic and mesopelagic fish
Much important information on surface-living pelagic fish - traditionally
subdivided into small and large species - comes from fishermen. Small pelagic
fish, such as anchovies, sardines, and sprats, etc., are relatively coastal
species - that is, they may be found on the continental shelf and epibathyal
slope waters. In particular, they are strictly coastal during the reproductive
season, which occurs mainly in summer for anchovy and in winter for sardine.
Large pelagic fish are caught at the greatest depths, i.e., in the centre of the
basin: they are found in the Sanctuary with seasonal migratory fluxes. These
are tuna and other kinds of scombroid fish: bluefin tuna (Thunnus thynnus),
albacore (Thunnus alalunga), little tuna (Euthynnus alletteratus), Atlantic bonito
(Sarda sarda), bullet tuna (Auxis rochei), skipjack tuna (Katsuwonus pelamis),
swordfish and other billfish (Xiphias gladius, Tetrapturus belone, T. albidus),
sunfish (Mola mola), dolphin fish (Coryphaena hippurus, C. equiselis) and
bluefish (Pomatomus saltator).
In Sanctuary waters, bluefin tuna is considered a valuable fishery resource (see
page 106); mainly juveniles live in the area and are one, two or three years old.
They aggregate in schools, sometimes in great numbers. Tuna does not originate
in the Sanctuary area, but reaches it when very young. This is because the
western Ligurian Sea is a suitable nursery where young tuna can exploit both
PERCENTAGE
41,8
5,5
20,0
0,9
9,1
4,5
2,7
1,8
0,9
0,9
0,9
2,7
0,9
0,9
1,8
0,9
0,9
0,9
1,8
100,0
Sunfish (Mola mola)
69
70
small pelagic fish and krill. Older (mature) and larger tuna may be present
especially during the post-breeding period. In this phase, they do not gather in
schools, and are only occasionally caught by both professional and leisure
fishermen.
Swordfish is the most valuable fish in off-shore waters. It originates in the
Sanctuary and perhaps also comes from neighbouring areas, thanks to the
abundant food, especially off-shore squid, which it finds along hundreds of
metres of the water column.
Many families of fish, called mesopelagic, are adapted to living at depths of
200-1000 m during the day, and move to the first 200 m of the water column
during the night. The mesopelagic species of the Sanctuary are of great
interest for many reasons:
1. In the off-shore ecosystem - that is, from the edge of the continental shelf to
the deepest parts - they represent the trophic levels between mesozooplankton
and the top predators. Thus, they are the essential food of large fish such as
swordfish, tuna, pelagic sharks and marine mammals, especially striped
dolphins, i.e., the most numerous cetaceans in the Sanctuary.
2. With their morphological characteristics and specific adaptations to living at
depth, such as silver or black skin, photophores for several purposes, and their
predatory skills, mesopelagic species are outstanding examples of deep-sea life
and biodiversity.
3. Research carried out in Italian
waters has been very important for
knowledge of this group of fish, as
may be deduced from the names of
authors who have described genera
and species. Fishermen or researchers
have sometimes caught specimens
which were later to become the
“types” in systematic studies precisely in the Sanctuary waters.
Mesopelagic fish are subdivided into
small and large species, depending on
whether they are under or over 30 cm in
length. The list of Mediterranean
mesopelagic families includes 11 of
large species and 11 of the small ones.
Large mesopelagic Mediterranean fish
number about 20 species in total;
however, some of them are described
as occasional visitors from the Atlantic
Ocean, as they have been caught only
Yellowmouth barracuda (Sphyraena viridensis)
Blackfish (Centrolophus niger)
71
CEPHALOPODS 4%
FISH 23%
EUPHAEUSIACEANS 14%
DECAPOD CRUSTACEANS 13%
OTER CRUSTACEANS 6%
GELATINOUS PLANKTON 39%
PTEROPODS 2%
Average composition of biomass collected
with an IKMT web in September/October
72
Imperial blackfish Schedophilus ovalis
once. Instances are Alepisaurus ferox,
an unmistakable fish with a large sailshaped dorsal fin, recorded in Sicily by
Bonaparte (1846) and Döderlain (1881);
Hyperoglyphe perciformes, very similar
to Schedophilus ovalis, a specimen of
which was caught at Marseilles in 1880;
and Cubiceps capensis, reported off
Alassio in 1972. The largest of all is the
king of herrings, Regalecus glesne,
which, with its ribbon shape, may reach
several metres in length and, in oceans,
up to 8 m. One specimen, caught off
Sanremo in the 1990s, was 4 m long.
Oarfish is a krill eater, like other large
vertebrates of the Sanctuary, e.g., fin
whale, and the devil ray Mobula
mobular.
Only seldom can large mesopelagic
fish be caught by professional
fishermen using deep long-lines, drift
nets, or other specialised equipment.
In the Sanctuary, the most valuable fish
are the Atlantic pomfret (Brama brama),
blackfish (Centrolophus niger), imperial
blackfish (Schedophilus ovalis) and,
although rare, opah (Lampris guttatus),
luvar (Luvarus imperialis) and oilfish
(Ruvettus pretiosus).
Small Mediterranean mesopelagic
fish are represented by 11 families,
28 genera and 38 species. In this
group too, there is one species which
has been caught only once, in the
larval stage - Diogenichthys atlanticus,
considered to have entered the
Mediterranean by accident through the
Strait of Gibraltar. The fish species in
this group are less well-known than the
73
SMALL PELAGIC FISH
Argentinids
(and Microstomatids)
Astronestids
Chauliodontids
Evermannellids
Gonostomatids
Melanostomatids
Mictofids
Paralepidids
Fotictids
Sternoptichids
Microstoma
Nansenia
Borostomias
Chauliodus
Evermannella
Gonostoma
Cyclothone
Bathophilus
Benthosema
Ceratoscopelus
Diaphus
Diogenichthys
Electrona
Gonichthys
Hygophum
Lampanyctus
Lobianchia
Myctophum
Notoscopelus
Symbolophorus
Arctozenus
Paralepis
Lestidiops
Ichthyococcus
Vinciguerria
Argyropelecus
Valenciennellus
Maurolicus
LARGE PELAGIC FISH
Bramids
Centrolofids
Gempilids
Lamprids
Lophotids
Luvarids
Nemictids
Nomeids
Regalecids
Trachipterids
Trichiurids
Brama
Centrolophus
Schedophilus
Hyperoglyphe
Ruvettus
Lampris
Lophotus
Luvarus
Nemichthys
Cubiceps
Regalecus
Trachipterus
Zu
Lepidopus
Trichiurus
Mesopelagic fish of the Sanctuary, grouped
according to families and genera
former ones, because they are of no
commercial interest, and the scientific
instrumentation and support from a ship
equipped for oceanography is needed
to study them. On a simpler level,
detailed research on the mesopelagic
fauna of the Ligurian Sea has been
carried out with a mesopelagic net of
about 20 m2, with a broad mouth,
equipped so that it is kept stable even
when hung to a depth of 1000 m - the
15-foot IKMT net. This net can sample
many mesopelagic organisms, ranging
from macroplankton (jellyfish, salps and
ctenophores) to cephalopods, krill,
pelagic shrimps and small pelagic fish.
The latest sampling surveys (October
2002, September 2003) carried out by
the “Urania”, one of the ships belonging
to the Italian Council for Research, gave
the following average catches, in terms
of filtered volume of water (see figure
on page 71), and the species of small
mesopelagic fish belonging to the
genera listed on page 73.
74
75
Hatchetfish (Argyropelecus hemigymnus)
Sloane's viperfish (Chauliodus sloani)
■ Sharks and pelagic rays
Blue shark (Prionace glauca), the most common pelagic shark in the Sanctuary
Often, during fishing for swordfish and
bluefin tuna, some species of pelagic
Lightfish (Icthyococcus ovatus)
elasmobranchs are caught. They are
mostly by-catch species, which are of
low commercial interest or are discarded at sea (about 5% of all catches). Their
landing give indications about the greater or lesser distribution of various
species in the Sanctuary waters.
The blue shark (Prionace glauca), alone, represents more than 90% of catches
of pelagic sharks in offshore waters. This carcharhinid is able to cover
considerable distances during its migrations, and can dive to great depths.
In the Sanctuary, specimens of medium size, 150–180 cm long, are commonly
76
caught, although larger individuals are not rare. Of enormous interest is the
regular presence in the Sanctuary of very young - sometimes newborn - blue
sharks, which make this area one of the best reproductive and nursery habitats
for this species. Analysis of feeding habits shows that, as the blue shark is not a
fast swimmer, it eats a great variety of prey and is very probably also a
scavenger, eating mainly ammonia squid, dead animals or parts of them, and
even birds and cetaceans. All the other species of pelagic sharks are quite rare.
Relatively more abundant are the shortfin mako (Isurus oxyrinchus) and
porbeagle (Lamna nasus). Sometimes very young specimens are caught,
again proving that this area is a suitable nursery, also for these species.
The thresher shark (Alopias vulpinus), other members of the Carcharhinidae
family, like the sandbar shark (Carcharhinus plumbeus), copper shark (C.
brachyurus) and silky shark (C. falciformis), or Sphyrnidae, like the smooth
hammerhead (Sphyrna zygaena) or great hammerhead (S. mokarran) - the
latter considered to be an alien in the Mediterranean, and of which only one
specimen was caught in the tuna trap at Camogli in 1969 - are very rarely
caught. In many cases, however, these species are widespread, and are
extending their habitats from the southern Mediterranean northwards. Others
occasionally enter the Mediterranean through the Strait of Gibraltar.
One quite rare visitor is the great white shark (Carcharodon carcharias). In
Sanctuary waters, over a period of more than a century, there have been many
sightings and catches in Liguria and Tuscany, well documented by both local
and national museums. Shark attacks on people, a few of them fatal, have also
been recorded. The last two incidents occurred in 1988, when a professional
scuba-diver died, and in 1991, when a woman sunbathing on a surfboard was
attacked, fortunately without serious consequences. Returning to offshore
fishing, judging by by-catch and discard figures, the pelagic stingray
(Pteroplatytrygon violacea) is the most abundant, but knowledge of its biology
and migratory habits is still scanty (as it is of no commercial interest, all
specimens caught by accident are returned to the sea). In general, many
Mediterranean selachian species, which are nowadays considered worthy of
special protection, live permanently in the Sanctuary. They include two species
now listed in the Barcellona Convention. The first is the Mediterranean devil ray
(Mobula mobular), often sighted in the pelagic waters of the Sanctuary, although
very young individuals are sometimes entangled in fishing nets near the coast.
The second is the basking shark (Cetorhinus maximus), whose presence has
been recorded since ancient times, mainly during the spring. It is still not known
whether these animals spend all their lives in the Mediterranean or, as seems
more likely, they enter the Mediterranean through the Strait of Gibraltar. The
numbers of sharks are steadily falling throughout the Mediterranean, including
the area of the Sanctuary. Direct shark fishing, still practised 20 years ago in
what are now Sanctuary waters, has now completely disappeared.
A pair of pelagic stingrays (Pteroplatytrygon violacea)
Basking shark (Cetorhinus maximus), a large planktophagous species
77
Reptiles, birds and mammals
LIDIA ORSI RELINI · LORIS GALLI · FULVIO GARIBALDI · GIOVANNI PALANDRI · SILVIO SPANÒ
■ Reptiles: sea turtles
Among the various fauna inhabiting the
Sanctuary, there are of course animals
representing the reptiles: turtles. The
most widespread species is Caretta
caretta, whose presence is recorded by
both sightings in the open sea and
accidental captures with various kinds
of fishing gear.
It is difficult to estimate the total
number of specimens belonging to this
Some crabs live on turtles
species in the Sanctuary, partly
because numbers fluctuate significantly, both seasonally and annually. From
professional swordfish longline fishermen, we know of some catches in
summer but, fortunately, these have never been frequent, in contrast with the
case in the southern Mediterranean. In the most abundant seasons, it is
estimated that a few dozen turtles are accidentally captured and then
released, still alive, into the sea.
More rarely, turtles are sighted or captured in nets near the coast or even
found on beaches after collisions with boats, as shown by mutilations and
wounds caused by ships’ propellers. Sometimes, tourists themselves carry
ashore turtles which appear to be in difficulties: in such cases, interesting
observations may be made of associated fauna, i.e., cirripeds and crabs,
which take advantage of their unwilling hosts, and are transported
considerable distances. In fact, as shown by both conventional and satellite
tagging, turtles are able to cover great distances in the Mediterranean and
sometimes even cross the Atlantic Ocean. In addition to C. caretta, two other
turtle species appear very occasionally: the green sea turtle, Chelonia mydas,
until now recorded only twice in the Ligurian Sea, and the giant leatherback
sea turtle, Dermochelys coriacea. Due to its enormous size, any capture or
sighting of the leatherback can hardly go unnoticed.
Sea turtle (Caretta caretta)
79
■ Birds of the Sanctuary
80
Pelagic birds (strict definition). This group includes some species belonging
to several systematic groups, but all with strictly pelagic habits (living far from
the coast).
First of all are the Procellariiformes (from the Latin “procella”, storm):
generally speaking, these birds, with their typical sustained, gliding flight,
exploit airstreams and winds sweeping across the surface of the sea to soar
and glide for hours, without moving their wings, thus saving energy. They are
easily identified by their very long, narrow, sabre-shaped wings, and their
tubular nostrils on each side of the bill. The nostrils of these sea birds host
excess salts taken in with diet, which are excreted through glands located
above and slightly forward of their eyes. Water vapour, with which sea air is
saturated, also condenses in the nostrils of these birds when they inhale,
forming tiny droplets of water. These droplets in turn become saturated with
excess salts, and then flow out along the lateral grooves of the bill and drip
from its hooked tip.
Cory’s shearwater (Calonectris diomedea), levantine shearwater (Puffinus
yelkouan) and storm-petrel (Hydrobates pelagicus) mainly build their nests in
natural cavities in the ground, semi-submerged caves or, in the case of Cory’s
shearwater, in burrows abandoned by rabbits (Oryctolagus cuniculus) along
Green sea turtle (Chelonia mydas): an occasional presence in the north-west Mediterranean
Cory's shearwater (Calonectris diomedea)
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82
undisturbed coastal areas and on the Mediterranean islands (in particular, the
storm-petrel prefers small islands), with many nesting sites located in favourite
areas. During the mating season, they leave their colonies for whole days, to
fly over the open sea seeking schools of fish, in relatively shallow waters,
returning periodically to the nesting sites to feed their chicks.
Outside the breeding season, these wanderings become even longer, with
very short rests on the ground between great distances covered, so that these
birds are seen everywhere, in both the open sea and near the coast of the
Sanctuary. To these species, regularly present, we must add occasional ones,
such as Bulwer’s petrel (Bulweria bulwerii), sooty shear water (Puffinus
griseus), balearic shear water (Puffinus mauretanicus), Wilson’s storm-petrel
(Oceanites oceanicus), Leach’s storm-petrel (Oceanodroma leucorhoa) and
Swinhoe’s storm petrel (Oceanodroma monorhis).
During migratory seasons and winter, the gannet (Morus bassanus) may
appear in the Mediterranean. Colonies of these birds build their nests on the
steep rocky cliffs of the North Sea and North Atlantic coasts and islands.
They have been reported in coastal areas particularly rich in fish further out
to sea. One specimen was recently caught (end of December 2003), in a
fishing-net off Noli (province of Savona, Ligurian sea), and was later set free.
Two more specimens were observed off Bergeggi (Savona) in the second
half of June 2005.
Gannet (Morus bassanus)
The razorbill (Alca torda) and puffin (Fratercula arctica), diving seabirds similar
to penguins, build their nests along the coasts of the northern seas,
respectively in mixed colonies in the gaps of cliffs and in crevices and
burrows; these birds are commonly present in the Mediterranean and may
also be sighted near the coast during migrations: the former in autumn and
winter and the latter in spring and summer. There are also occasional reports
of the guillemot (Uria aalge) and little auk (Alle alle) (the latter was even seen
on the deck of a ship in the Gulf of Genoa on April 20, 1980).
Seabirds in general. This group
includes divers and grebes, diving
birds which have adapted to diving to
catch fish or other prey (molluscs,
crustaceans), thanks to their tapered,
hydrodynamic bodies with feet which
are short-webbed (divers) or lobed (the
toes of grebes have lobe-shaped
extensions) located far back on their
bodies, with short tails and sharp,
straight bills. They are good swimmers
and can dive quite deep, remaining
Black-necked grebe (Podiceps nigricollis)
underwater for many seconds.
The red-throated diver (Gavia stellata),
black-throated diver (Gavia arctica) and great northern diver (Gavia immer)
breed north of the 55th parallel, in fiords, lakes and marshlands. In autumn,
they migrate along the coastlines of the North Sea, Pacific and Atlantic
Oceans (up to 25-30° N), Black Sea and northern Mediterranean.
The red-necked grebe (Podiceps grisegena), slavonian grebe (Podiceps
auritus) and black-necked grebe (Podiceps nigricollis) do not nest in Italy but
migrate from their reproductive areas, mainly in Central and Eastern Europe, to
winter along the Mediterranean coasts. Instead, the little grebe (Tachybaptus
ruficollis) and great crested grebe (Podiceps cristatus), commonly nest in
coastal marshy areas in Tuscany, Sardinia and Corsica.
The cormorant (Phalacrocorax carbo) is a well-known diver, even for those
who know little about birds, thanks to its unmistakable aspect and
characteristic behaviour: it perches on natural (trees, rocks) or artificial
supports (wharfs, buoys, lamp-posts) well exposed to the sun or wind, and
opens its wings to dry its feathers, wet after long immersions. In Italy, it nests
in the Po Plain area and along the western coasts of Sardinia, and winters
83
84
Shag (Phalacrocorax aristotelis)
extensively both along the inland
watercourses and along the coasts.
During the day, cormorants tend to
stay in small groups or alone, to visit
their fishing areas. At sunset, they
gather on alders or other trees near
rivers, or on man-made objects (lampposts, etc.). During their migrations,
they fly in V-shaped formations,
sometimes composed of many dozens
of individuals.
The shag (Phalacrocorax aristotelis)
Little grebe (Tachybaptus ruficollis)
differs from P. carbo due to its smaller
size and relatively thinner bill, which is
grey-green in colour instead of yellow, and the lack of the typical white spot
on chin and cheeks that marks the latter. It builds its nest on rocks and steep
cliffs of Corsica, Sardinia and small islands, and may be seen near the
Ligurian and Tyrrhenian coasts from autumn to spring, although less
frequently than P. carbo.
Among diving birds which may be sighted in the Sanctuary area, are some sea
ducks: common scoter (Melanitta nigra), velvet scoter (Melanitta fusca) and
red-breasted merganser (Mergus serrator) whose presence is irregular,
especially in winter, but also during migrations, particularly in spring. To the
same systematic group (Anseriformes Anatidae) belong some more typical
non-diving ducks.
Non-diving ducks may be identified by their legs, which are set half-way along
the underside, so that they walk on land more or less horizontally. When
swimming, the tip of the tail turns up. These ducks do not normally dive deep
enough to disappear entirely under the water, but turn their bodies vertically,
with their tails tilting upwards, and keep their balance by moving their legs.
When they fly, they rise directly from their position in water or in land. Instead,
diving ducks have relatively short legs set well back, and thus walk upright
clumsily. Their bodies are streamlined so that, when swimming, their tails are
just off the surface of the water. They disappear completely when diving. When
they fly, they are obliged first to “run” along the surface of the water and beat
their wings vigorously, in order to gain speed and momentum for take-off. A
non-diving duck is the eider (Somateria mollissima), a large mollusc-eating
“semi-diving” duck (well-known at mussel farms) mainly nesting in circumArctic regions and wintering in the Baltic and North Seas, and secondarily, in
85
86
the Mediterranean, and the occasional king eider (Somateria spectabilis).
During migrations, other species may also be seen, often common species,
such as the garganey (Anas querquedula) and shoveler (Anas clypeata), which
temporarily rest near coasts.
Probably the most common species throughout the study area is the yellowlegged gull (Larus cachinnans). It nests not only on cliffs and small islands but
has also recently used buildings in coastal towns. Some individuals can often
be sighted hovering above schools of fish offshore, or following fishing-boats.
In winter, two species very similar to L. cachinnans in aspect and size, appear
regularly, although in small numbers: the herring gull (Larus argentatus) and
lesser black-backed gull (Larus fuscus).
For its rarity (it is listed in Annex I of the Birds Directive 79/409/EEC, and
marked as endangered on the Red List of Italian Breeding Birds), the presence
in the Sanctuary area of nesting sites of Audouin’s gull (Larus audouinii) is of
great naturalistic importance: endemic in the Mediterranean, this gull builds its
nest along the Corsican and Sardinian coasts and on the small islands of the
Tuscan archipelago.
During migratory periods and in winter, two other species of smaller size
than the above two are widespread, the Mediterranean gull (Larus
melanocephalus) and black-headed gull (Larus ridibundus), quite similar to
each other. The little gull (Larus minutus), common gull (Larus canus) and
kittiwake (Rissa tridactyla) are less common although they are regularly seen
during migrations and occasionally in winter. Very occasional, if not
accidental, are sightings of the laughing gull (Larus atricilla), slender-billed
gull (Larus genei), Iceland gull (Larus glaucoides), glaucous gull (Larus
hyperboreus), great black-backed gull (Larus marinus) and ivory gull
(Pagophila eburnea), as well as three species mainly showing kleptoparasitic
behaviour (these birds follow and attack other birds carrying fish in their
beaks, and harass them until they drop their prey): examples are the
pomarine skua (Stercorarius pomarinus), arctic skua (Stercorarius
parasiticus) and long-tailed skua (Stercorarius longicaudus).
Terns are medium-sized water birds, with quite long, narrow wings, longer and
sharper beaks than those of seagulls’, clearly forked tails and feathers in
white, black and many shades of grey. They are fast fliers which either skim
over the water catching molluscs, crustaceans and small fish on the surface,
or plunging with wings folded, to seize those swimming slightly deeper (on
average 2–3 m depth). The only species nesting in the Sanctuary and in
wetlands and lagoons near the coast are common tern (Sterna hirundo) (with
some colonies in the northern part of Sardinia) and little tern (Sterna albifrons)
(Sardinia and Corsica).
Quite common in the migratory period and regularly wintering along the
Ligurian and Tuscan coasts is the sandwich tern (Sterna sandvicensis). The
Black-headed gull (Larus ridibundus)
Kittiwake (Rissa tridactyla)
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88
caspian tern (Sterna caspia), instead, is a regular migrant and only sometimes
winters in the area. During migrations, much rarer along the coast are gullbilled tern (Gelochelidon nilotica), whiskered tern (Chlidonias hybridus), black
tern (Chlidonias niger), and white-winged black tern (Chlidonias leucopterus).
Of a certain interest, because they are rarely seen in Italy, roseate tern (Sterna
dougallii) and Arctic tern (Sterna paradisaea): Ligurian records go back to the
19th century.
Among the species which may be sighted both offshore and more easily along
the coast, is the osprey (Pandion haliaetus). This is a rare migratory bird, but
appears quite regularly in spring (April) and above all in autumn (September). It
nests along the Corsican coasts (about twenty breeding couples), while in
Sardinia it became extinct as a reproducing species in the 1960s-1970s. In
winter, it may be sighted both near the above-mentioned nesting places, and
along the Ligurian and Tuscan coasts.
Until a century ago, the marine mammals living in the Sanctuary were
cetaceans and one carnivorous pinniped, the Mediterranean monk seal
(Monachus monachus): nowadays there are only cetaceans. The Pelagos
Sanctuary was in any case originally dedicated to all marine mammals, and it
is hoped that the monk seal may come to live in it again. Cetaceans are
mammals which are perfectly adapted to aquatic life: they are divided into two
sub-orders: Mysticetes, provided with filtering apparatus, and Odontocetes,
which grow conical teeth after birth. The filtering apparatus (or baleen) is made
up of many horny plates (up to 800) set in the upper jaw, which are used to
filter food (krill, small fish). Large quantities of water and food are taken: water
is expelled through the baleen and food is trapped behind it.
About twenty species of cetaceans are found in the Mediterranean. They are
distinguished among those which commonly live in it - that is, they spend
there the various stages of their life-cycle, including reproduction - and others
which, due to the rare and occasional finding of individual specimens, may be
defined as occasional visitors.
The first group contains eight species: striped dolphin, bottlenose dolphin,
common dolphin, Risso’s dolphin, pilot whale, Cuvier’s beaked whale, sperm
whale, and fin whale. At least five out of the eight are present in the
Sanctuary, in numbers higher than those of other areas of the Mediterranean.
In addition, it is known that stenella, Risso’s dolphin, pilot whale, Cuvier’s
beaked whale, sperm whale and fin whale give birth to their young in
Sanctuary waters.
Eight other species, rare or very rare, or only known by the finding of a single
individual, are also found in the Sanctuary. These are the minke whale
Common tern (Sterna hirundo)
Bottlenose dolphin (Tursiops truncatus)
■ Marine mammals
89
(Balaenoptera acutorostrata), sei whale (Balaenoptera borealis), humpback
whale (Megaptera novaeangliae), killer whale (Orcinus orca), false killer whale
(Pseudorca crassidens), Gervais’s beaked whale (M. europaeus) roughtoothed dolphin (Steno bredanensis) and dwarf sperm whale (Kogia simus).
For reasons of space, only a few examples of cetaceans, both Odontocetes
and Mysticetes, are mentioned here, starting with the commonest species,
i.e., striped dolphin and fin whale. Several guidebooks are available on this
subject.
The striped dolphin (Stenella coeruleoalba) lives in temperate and tropical
waters all over the world. It is the most abundant cetacean both in
Sanctuary waters and in the entire Mediterranean. In the Sanctuary, its
population density has been estimated at most at 0.45-0.55 individuals per
square kilometre.
Striped dolphins may be recognised at a distance, due to a detail in the colour
of their flanks, where a kind of white “flame” is visible, ascending near the
base of the dorsal fin. The average length of adult females is 190 cm and that
of males 200 cm; the latter may weigh about 100 kg.
Most of our information on the biology of the striped dolphin come from
detailed studies carried out by the “Centro Studi Cetacei” which, in about 20
years of work along Italian coasts, has records of many hundreds of beached
specimens, together with their size and sex. Considering all the coasts of Italy,
90
Pilot whale (Globicephala melaena): mother and calf
False killer whale (Pseudorca crassidens)
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92
The Sanctuary: where the Mediterranean fin whales are born
omitted). It can be seen that the newborn
individuals are found along the coastlines
of the Ligurian and North Tyrrhenian
Seas, and suckling fin whales 6-11
metres long are found not only in the
above areas, but also in southern Italy
along the coasts of Campania and
Calabria and around Sardinia; two of
them have also been found in the North
Adriatic Sea. Fin whales being weaned
may be found all along the Italian
coastline and also in the Tunisian part of
the Strait of Sicily. In this way, an area situated inside the Sanctuary - has been
identified, where fin whales give birth to
their young, and the movements, north
or south, of mothers with their calves can
be followed. These observations on the
distribution of fin whales in the
Mediterranean have been confirmed by
genetic research, in which mitochondrial
DNA (of maternal origin) from fin whales
sampled in the Ligurian Sea differs from
that of the north-eastern Atlantic Ocean.
Whale hunting has allowed much
information on cetacean anatomy,
physiology and behaviour to be
accumulated. However, as regards the fin
whale, two points have remained
obscure: where exactly are the baby
whales born, and what are they like?
Observations regarding these aspects
from the Mediterranean are thus of
enormous interest. The zoological
literature on cetacean strandings from
France, Monte Carlo, Italy and Tunisia
over a period of 150 years (1850-1999)
reports 53 cases of very young fin whales
found beached on the shores of the
above four countries, and measured in
terms of total length by those who gave
news of the event. The animals were all
between 5 and 13.9 metres long, and
therefore included both newborn and
suckling specimens and juveniles at the
onset of weaning. For clarity of
representation, measurements are given
in metres (i.e., decimal points are
Spring
Autumn
Summer
Winter
the number of dolphins found on the shores of the Sanctuary is much higher
than the average number per coast length, and the beached animals are
usually juveniles, indicating that the population is high and that many young
are born in this area.
Striped dolphins are born between July and October, with a peak in August,
when surface waters are warmer. A newborn dolphin is about 90 cm long,
and lives in close contact with adults until it is about two years old and 150
cm long.
Striped dolphins swim with great agility and elegance, and give an exciting
show to watchers as they ride the bow wave of boats or chase fish on the
surface.
Dozens of dolphins may surround schools of fish (e.g., anchovies) and then
swim and leap around them to frighten them and make them more vulnerable
to capture, and the show they put on is spectacular. However, analysis of
stomach contents shows that most dolphins’ food is composed of
mesopelagic fauna, although whether prey is hunted in groups or by
individuals is not known. Prey are small mesopelagic fish (5-25 cm),
mesopelagic cephalopods, both muscular and ammoniacal, and shrimps,
especially pasiphaeids.
Striped dolphins migrate periodically to and from the Sanctuary, where
minimum numbers coincide with the lowest water temperatures.
TRIESTE
10
7
GENOVA
11
NICE
6 5 6 5
6
5
5
6 11
10
5 5
8
5
5
8
9
LIVORNO
5
5
5
ROMA
11
NAPOLI
6
6
10
8
7
6
9
T UNI S I A
Beaching sites of newborn and suckling fin whales; sizes inside circles (in m) and season are reported
Striped dolphin (Stenella coeruleoalba)
93
94
The fin whale is the largest cetacean in the Mediterranean (adults may reach
17-20 m in length, and females are larger) and, worldwide, is second in size
after the blue whale.
Since ancient times (the Romans did not distinguish between fin whales and
true whales), the fin whale was always considered simply “the” whale and, as
mentioned in the Introduction, during the Roman Empire, a short Ligurian
section of the Sanctuary coastline was called the Costa balenae (or whale
coast). From that segment of coast - which today includes the towns of Taggia
and S. Stefano al Mare - we can draw a line linking Calvi, in Corsica, and
obtain a very important transect of the Sanctuary, which crosses the sea area
richest in krill - the very area where the highest numbers of fin whales are
observed in summer.
Fin whales may be sighted in the Sanctuary all year round, but sightings are
rarer in autumn and winter. Calves, between 5 and 6 metres long, are born
between September and February, with a peak in November.
Sightings of fin whales include both single individuals and groups of two or
more, generally up to six; the average is about 1.5 individuals each time.
Mothers and calves, when together as a pair, are easily recognisable, if the
size of the calf is up to 12 metres long. It is obviously more difficult to
distinguish the relationship between the two animals when the calf is even
larger than this.
The Mediterranean population of fin whales is still not well-known in terms of
numbers and relations with the Atlantic population. The first estimates of
about 3,500 specimens in the Western Mediterranean and a thousand in the
Sanctuary - both made in the early 1990s - are to be considered excessive.
However, as the number of whales decreases, their conservation becomes
increasingly urgent.
To this end, genetic research, which has found a distinction between Atlantic
and Mediterranean fin whale, has been highlighted as important. However,
even this is at a preliminary stage.
Information about fin whales recorded in some museums, especially those near
the Sanctuary coasts (France, Italy, Principality of Monaco), is now very
important for better knowledge of these animals. Recently - that is, in the last
30 years - most of the dead whales found have been juveniles; at present, most
deaths appear to have been caused by collisions with ships. It is important to
recall that, of the species living in the Sanctuary, the less numerous and less
well-known may be the most valuable as regards their conservation. Cuvier’s
beaked whale and pilot whale are definitely two of these.
At present, Cuvier’s beaked whale is an important focus of international
attention, due to cases of mass mortality resulting from military activities.
Researchers are currently reporting every aspect of the anatomy, physiology
and behaviour of this species, in order to protect it and help its conservation.
Fin whale (Balaenoptera physalus)
Risso's dolphin (Grampus griseus)
95
However, current researches also include active testing of the effects of
particular sound waves, in such places where Cuvier’s beaked whales are
definitely known to be resident. Carrying out tests in the Sanctuary seems to
be an extreme approach, on the borderline between conservation and scant
consideration for the animals themselves.
The pilot whales of the Ligurian Sea also deserve particular attention, because
the literature on them is scarce. A few decades ago, reports were made of
groups of sometimes more than one hundred individuals, but these numbers
have not been confirmed in recent sightings.
96
■ The trophic webs of the large
pelagic vertebrates
IKMT net for sampling macrozooplankton and micronekton
The previously described mesopelagic
organisms represent a substantial part
of the diet of large pelagic nekton. Given
the depth of the Corsican-LigurianProvençal basin and the productive
characteristics of its off-shore waters,
Beak of ommastrefid squid: cephalopods
the mesopelagic community is very rich
can be identified by the beak
both qualitatively and quantitatively,
although until now data on secondary production do not seem exhaustive.
It is thus normal for fauna in the Ligurian Sea to include many large
predators hunting at depth, such as the Squalidae (e.g., shark) or
teutophagous Odontocetes (toothed whales: sperm whale, Cuvier’s beaked
whale, pilot whale, Risso’s dolphin).
However, even other predators which, because of their livery, are
considered typical examples of surface-dwelling fauna, such as the blue
shark, swordfish, tuna and small dolphins D. delphis and S. coeruleoalba,
eat mesopelagic species, sometimes exclusively and sometimes together
with epipelagic species.
Some specimens of the mesopelagic community are known to cover
hundreds of metres of the water column in the course of a day and, during the
night hours, are found at relatively superficial levels; others seem to be forced
into deep water.
Continuous observations of the behaviour of predators, such as the blue
shark and swordfish, reveal that they do not hunt according to a horizontal
line or route, but by continually ascending and descending in the water
column. This method of hunting also ensures a saving in energy with respect
97
98
The trophic webs
99
101
100
Juveniles (left) and adults (right) of krill (Meganycthiphanes norvegica)
Macrofauna trophic web
to horizontal swimming; it certainly allows the exploration and exploitation of
a huge volume of water. The nekton living in the intermediate waters of the
Mediterranean, very uniform throughout the year as regards temperature and
salinity, probably shows more significant characteristics of stability than
superficial nekton, representing an important alternative to the fluctuations of
the latter.
In this way, epipelagic and other organisms living in deep waters are linked
not only to the whole set of relations which allow the gradual descent of
organic matter, recently synthesised on the surface, towards deep waters,
but to the fact that the mesopelagic biomass is systematically exploited by
the great surface-dwelling predators.
In particular, in the Corsican-Ligurian-Provençal basin, the natural
transformation of mesopelagic biomass into resources of great utility (tuna,
swordfish, etc.) and conservation interest (mysticete and odontocete
cetaceans) indicates that we should not attempt direct exploitation of
mesopelagic organisms.
It is also important to mention the reconstruction of the trophic web of the
great pelagic fauna of the Sanctuary. Research on it involves several types of
competence and is destined to play an important role in terms of
conservation.