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CETACEAN SIGHTINGS AND INTERACTIONS WITH FISHERIES IN THE
ARCHIPELAGO PONTINO CAMPANO, SOUTHERN TYRRHENIAN SEA, 1991-1995.
Mussi, B.1-2, Gabriele, R.2, Miragliuolo, A. 1-2, Battaglia, M. 2
1 Studiomare, via Botteniga 39, 31100 Treviso, Italia
2 WWF Oasi Blu, c.p. 45, 04028 Scauri (LT), Italia
INTRODUCTION We chose this area because in the past it has never been object of a detailed
systematic study on marine mammals. This is a preliminary report of five years observations.
The purpose of this project was to initiate a long term study on cetaceans in a sample area, to record
the most common species, analyse seasonal variations in their presence, verify the existence of
resident cetaceans and study interaction with fishery.
METHODS: The archipelago Pontino Campano is composed by nine volcanic islands, forming
three distinct groups, old eruptive centres, separated from each other by about 40 km. During the
research we adopted two different methods: between June 1991 and June 1993 data were collected
by ferries, cargo and fishing boats sailing in the area. The recordings were discontinuous but allow
to find out the winter presence of cetaceans in the area. From 1993 to 1995 to get more information
we used a 15 m. sailing boat, “Barbarian”, equipped for high seas navigation with a GPS, recording
data base and a hydrophone system. A constant watch was kept for cetaceans and all sightings
noted with their position, group size, behaviour, associated species, presence of juveniles, sea state
and wind strength. Trips were conducted daily from May to October. No trip was started in
conditions greater than sea state 5. Travel was always made by sails.
RESULTS A total of 330 sightings comprising 3494 individuals of seven cetacean species were
recorded during the period of the research (fig.1). Seasonal changes in sightings frequency are
presented in fig.2. We tried to quantify the observers' effort from 1993 to 1995. Despite all
dependent variables (sea state, light condition, observers' height, boat and cetacean behaviour) a
sightings frequency was calculated dividing the number of individuals by the travelled distance
(Km). These indices varied between 0,09 in 1993, 0,12 in 1994 and 0,13 in 1995 (mean frequency
1,11).
Striped dolphins (Stenella coeruleoalba) They were the most frequent cetacean encountered, with
a total of 183 sightings, comprising 2557 individuals. The great majority were sightings of groups
of 6-10 individuals (mean group size = 13.97) with a maximum group of 350 animals and
concentrated in the south waters of the islands, at an average depth of 700 m. The number of
sightings increased to a peak in the month of September. In the same month we recorded the highest
concentration of juveniles in striped dolphin’s groups.
Bottlenosed dolphins (Tursiops truncatus) They were distributed in coastal waters particularly at
the mouth of the river Volturno, and around Ventotene and Ischia islands at an average depth of 100
m. A total of 68 sightings comprising 501 individuals were recorded during the study. Most
sightings were groups of 2-5 individuals (mean group size = 7.36) with a maximum group size of
100 individuals. Sightings frequency increase to a peak in June, with the highest concentration of
juveniles from May to August. A resident group of 15 individuals had been photo-identified and
studied since 1993: the group was composed of four females, six males, one subadult and four
juveniles. The home range of this group was extended from Ischia to Ponza, but the most frequently
observations were made around Ventotene.
Sperm whales (Physeter macrocephalus) They were recorded during the survey with 29 sightings
of 39 individuals. Sightings were largely confined to the southern waters of the islands at an
average depth of 700 m.; most sightings were of a single animal (mean group size = 1.34) and with
greatest frequency in August and September. They were recorded near the coast at night, during the
breeding season of “European flying squids” (Ommastrephes sagittatus), making use of the high
concentration of squids near fishermen's lights.
Risso’s dolphins (Grampus griseus) They were relatively uncommon, with 13 sightings of 101
individuals. They were encountered very closed to the shore of the islands, in groups of 7-10
individuals (mean group size = 7.76) with a maximum of 15 individuals. Sightings occurred in all
years, decreasing in winter and increasing in September. Juveniles were recorded in April, May,
June and September.
Long finned pilot whales (Globicephala melas) They were rarely encountered in the area, with six
sightings comprising 64 individuals. They were observed most frequently in groups of 6 (mean
group size = 10.66) with a maximum of 35 individuals and were most abundant in October, in south
westerly waters of the islands. Photo-ID studies revealed the seasonal presence of recognisable
individuals in a single location (around Ventotene).
Common dolphins ( Delphinus delphis) They were the rarest cetacean in the area with only four
sighting of seven individuals. They were always in association with large groups of striped
dolphins. Two juveniles were recorded near Ponza, swimming near their mother. In 1996 (data still
being analysed) one sighing of 15 individuals of common dolphin was recorded without any
association with striped dolphin.
Fin Whales (Balaenoptera physalus) They were recorded throughout the area with 16 sightings of
28 individuals. The majority were sightings of single animals (mean group size = 1.75), with a
maximum group size of three individuals. They were most abundant in summer time, from May to
September. The number of juveniles reached a peak in the month of September.
Unidentified They were recorded mainly in 1991-1993 during the ferry-census, for a total of 12
sightings comprising 197 individuals.
Interactions with fishery were recorded in the area with illuminated handlines for squids, surface
longlines, trawling nets, bottom gillnets and drift nets.
Illuminated handlines for squids: interactions occurred with striped dolphins, Risso’s dolphins,
long finned pilot whale and sperm whale. In all cases an opportunistic feeding was completed by
small groups (of 2-5) or single animal (sperm whale); cetaceans waited near the fishing boats until
gear's light had attracted a great number of squids under the boats and then they quickly swam to
catch their prey; this technique may be repeated several time in one night.
Surface longlines: one interaction was recorded with a sperm whale. We found an abandoned gear
in which a decomposed sperm whale was entangled, probably drowned in the course of capturing
his prey.
Trawling nets: interactions were recorded with striped and bottlenosed dolphin, in both cases
involving an opportunistic feeding by small groups (of 2-5): making long dives, dolphins fed all
around and within the net especially at the end of the haul.
Bottom gillnets are used in the area only by artisanal fishermen. Around the island of Ventotene
and Ischia, interactions were recorded with bottlenosed dolphins: every year, in the months of
March, May and September they were observed preying from the nets. Dolphins made long dives
around the net, and produced large rips to catch their prey.
Drift nets are used in all the area especially in June, July and August. Interactions recorded were
with striped dolphin and sperm whale: we found on the high sea, two specimens of striped dolphin
without their tails (sometimes fishermen cut the tail to more easily extract the cetacean from the
net); a juvenile of sperm whale probably caught, was found dead near Naples with an oblique cut
from throat to tail. In 1995 we spent 28 nights from June to August with the boat adrift, between
about 55 swordfish boats that were in the area. Our aim was to record the vocalisations of any
cetaceans in difficulty. Every night, from Ponza to Capri (about 120 km.) fishermen set two
interrupted barrages (exactly along 1000 m. and 700 m. depth’s lines): the boats are co-ordinated
by radio and the nets set one after another, leaving a minimal security distance between the boats;
drift nets were set at 20:30 hours and retrieved at 03:00 hours. During 243 hours of workable
underwater listening we never heard a click: cetacean biosonar regularly entered in our hearing
range at 05:30 hours and disappeared at 21:00 hours.
CONCLUSIONS: Five years of observations have allowed to establish the rich variety of cetacean
species around the archipelago Pontino Campano: seven species were identified in total, one baleen
whale, three toothed whales and three small dolphins. We also verify the existence of resident
bottlenosed dolphins and a seasonal presence of five photo-identified individuals of long finned
pilot whale around Ventotene island.
Our main objective is to make a long-term study in a sample area of the Mediterranean sea. Long
term study provides a powerful way for developing an understanding of the social lives of long
lived animals such cetaceans, besides which we are interested in improving our knowledge about
fishing interactions so that a conservation programme can be initiated despite all the difficulties
involved. Of course, in general, several years will be necessary to adequately conduct analyses of
such observations.
ACKNOWLEDGEMENTS: The research was funded by Studiomare and WWF Italia. Thanks to
Antonio Di Natale and AQUASTUDIO for their valuable comments and assistance during all the
different phases of the study.
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