original scientific paper UDK 599.5(262.3-17) 574.9:5995(262.3-17) A COMPARISON O F THE PRESENT OCCURRENC E O F BOTTLENOSE DOLPHINS, TURSiOPS TRUNCATUS, AN D COMMO N DOLPHINS, DELPHINUS DELPHIS, IN THE KVARNERIC! (NORTHERN ADRIATIC SEA) Giovanni BEARZI BSc, marine biologist, Tethys Research institute, 20121 Milano, víale C.B . Gadio 2, IT dipl. bšo!., morski biolog, Tethys Research Institute, 20121 Milano, víale C.8 . Gadio 2, IT Giuseppe NOTARBARTOLO di SOARA PhD, marine biologist, Tethys Research Institute, 20121 Milano, víale G.B. Gadio 2, IT dr., morski biolog, Tethys Research Institute, 20121 Milano, víale G.B. Gadio 2, IT ABSTRACT tn the course of a long-term study focusing on bottlenose dolphin social ecology and behaviour, conducted in the Kvarneric since 1987, bottlenose dolphins (Tursiops truncatus) and common dolphins (Delphinus delphis) were the only cetacean species observed. A total of 879 bottlenose dolphin groups were encountered, compared to three sightings of common dolphins. The sighting frequency for bottlenose dolphins was about 87 times higher than for common dolphins. The first of the common dolphin sightings, in August 1991, involved four adults, while the following two (August 1994 and July 1995} were of a single specimen, found both times in association with bottlenose dolphins. Photoidentificalion data showed that, the same individual common dolphin was present in all three encounters. These observations reflect the almost complete disappearance of common dolphins from the Northern Adriatic Sea, a region in which both dolphin species were historically abundant. Key words: common dolphin, Delphinus delphis, bottienose dolphin, Tursiops truncatus, Mediterranean Sea, Adriatic Sea, sighting frequency, occurrence, interspecies association Ključne besede: navadni delfin, Delphinus delphis, velika pliskavka, Tursiops truncatus, Sredozemsko morje, jadransko morje, frekvenca opazovanj, pojavljanje, medvrstna združevanja ÎNTRODUCTION predators at the top of the marine food chain, represent excellent biological indicators of the status of the envi-The degradation of any ecosystem is first indicated ronment they inhabit. Their long lifespan (30 years or by the disappearing of the most vulnerable, less adapt-more) make them important bioaccumulators of man-able species, and by a progressive impoverishment of its made polluting substances such as organochlortne com­biological diversity. The general lack of attention given pounds and heavy metals, whose toxic potential is well to the marine environment often makes such processes known. Therefore, the decrease of a dolphin population difficult to detect, and the scarce availability of circum-represents a signal that should be carefully evaluated, stantial historical information in the scientific literature and the assessment of the status of the dolphin popula­may prevent the understanding of the ongoing trends. tions is of foremost importance to determine trends and Consequently, the feeling that something is wrong in a to suggest measures to prevent a possible decline. In the given marine environment often rests upon fishermen's shallow and largely degraded Northern Adriatic Sea, lit-stories and memories of the "good old times", value tle methodical effort has been made in the past to whose cannot be objectively assessed. Dolphins, as document the density and distribution of free-ranging ANNALES 7/'95 Giovanni SEARZ!, Giuseppe NOTARB ARTOLO di SC1ARA: A COMPARISON OF THE PRESENT OCCURRENCE OF BOTTLENOSE DOLPHINS, ..., 61-68 cetaceans, with most of the information deriving from stranded specimens, second-hand reports, or occasional sightings. Only since the late 1980s have Adriatic ceta­ceans attracted some scientific interest, and preliminary data were collected through surveys at sea (Notarbartolo di Sciara et al., 1993). This study represents a further contribution to the understanding of the present occur­rence of two cetacean species in the Kvarnerii, a small but representative portion of the Northern Adriatic Sea. MATERIALS AND METHODS The study area, measuring roughly 900 km2, is situ­ated in the southern portion of the Croatian Kvarneriri {Fig. 1). its sheltered and clear coastal waters, east of the islands of LoSinj and Cres, encompass a variety of differ­ent marine habitats, including rocky coastline and bot­tom, submerged reefs, seagrass flats, and a mud sea bed with a mean depth of about 70 m. The maximum depth is 96 m. Figure 1: The study area. Slika 1: Območje raziskave. Data presented here are part of a larger effort focus­ing on the social ecology and behaviour of the hot­tlenose dolphin community frequenting the area (Bearzi ef al. 1992, 1994, in press). Observations were carried out from September 1987 to July 1995, with a total of 41 months spent in the field (September 1987; April 1988; July - October 1988; July - September 1990; July - Sep­tember 1991; without interruption from March 1992 ­October 1993; April - September 1994; April - July 1995). A total of 453 days were spent at sea during the study: 14 in 1987-88, and 439 from 1990 to 1995, to­talling more than 2,000 h. Surveys were conducted from inflatable boats with fiberglass keels, equipped with 25 to 50 HP outboard engines. Over 18,700 photographs were taken with a reflex camera Minolta 80001 AF equipped with a zoom Minolta AF 80-200 AP O f 2.8 lens, using Ektachrome EPR 64 fSO color transparency film. A chronological catalogue for the identification of individual dolphins was built using 14,300 of these slides. Sighting frequencies were computed based on searching bouts. Each bout consisted of the sum of all periods spent searching for dolphins at a mean speed of 30 km/h under "adequate" sighting conditions, from the beginning of a survey to the time of sighting. A bout could include survey fragments on consecutive days. Sighting conditions were considered "adequate" only when: 1) at least one experienced observer continuously scanned the sea surface, searching for dolphins; 2) the sea state was 0 or 1 (flat, with capillary waves, or with wavelets prior to breaking). The time spent with either dolphin species and the time spent at sea following the first sighting of the day were not considered as searching time and were therefore excluded from the calculation of the sighting frequencies. Due to the unequal survey procedure in 1987-88, only data from 1990-95 were considered in the computation, RESULTS Bottlenose dolphins A total of 843 h 50 min were spent observing and photographing 879 dolphin schools of different size and composition, averaging 6.6 individuals (SD=5.78, SE-0.195, range=1-65, mode=2). Bottlenose dolphins were the only species consistently sighted throughout this study, and the only one found in 1987-88. The mean time spent searching for bottlenose dolphins from the beginning of a survey with "adequate" conditions was 145 minutes (SD=152.35, SE-9.45, N=260, range 1-1139 min). The shortest seasonal mean search time occurred in spring 1994 {76 min), the longest in fall 1993 (313 min); however, despite such wide variation, the difference in search time among years was insignifi­cant (F=1.66, df=5, p<0.14), indicating that the bot­tlenose dolphin density in the area shows little temporal patterns. Until the end of 1994 a total of 106 individuals were photoidentified by means of permanent natural marks on their dorsal fin (Wursig & Wursig 1977, Wursig & Jefferson 1990). The rate at which individual dolphins were identified during the study is presented in Fig. 2. Individual frequency of re-sighting ranged from 1 to 59 different days (mean^13.2, SD=11.48, SE=1.11, Giovanni BEARZI, Giuseppe NOTARBARTOLO di SCI ASA: A COMPARISON OF THE PRESENT OCCURRENCE OF BOTTLE NOSE OOLPHINsT..-, 61-68 00 <30 1990 1991 1992 1993 1994 120 tmiito ^ oopoQQQooggc^ogooopQgooo o —> 'Ni oi xr ir.> '•o F- fa o -^-i cm co i « r - í o a o m w •r^ -»-4 —« —4 *-t « v M ^ 0-j ^ PHOTOIDENTIFICATION SURVEYS Figure 2: Cumulative rate of identification of new individual bottlenose dolphins over time ("rate of discovery"}. Slika 2: Kumulativno število identificiranih osebkov velike pliskavke z metodo fotoidentifikacije v terenskih pre gledih od 1987 do 1994. mode=6); only four identified individuals (3.8%) were sighted once. Most animals were encountered fre­quently, although there were remarkable differences in site fidelity among individuals, and even the most "resident" animals ranged in an area that was larger than the one selected for this study (Bearzi et a!., in press). Common dolphins Common dolphins were observed three times. A group of 4 adult individuals was sighted on 2 August 1991 and followed for 96 min (12:03 - 13:39). No bot­tlenose dolphins were seen in the area on that day. O n 4 August 1994 a single adult individual was seen in a group of 11 bottlenose dolphins including 5 calves and was observed for 27 min (13:03 - 13:30). The following year, on 11 July, a single individual was again found in a bottlenose dolphin group composed by 6 aduits and 4 caives. During this observation, totalling 102 min (18:51 - 20:33), four more adult bottlenose dolphins joined the group. Ail observations were photographically docu­mented; in addition, the 1995 sighting was partly video­taped. The analysis of the photographs showed that the dolphin seen in 1995, recognizable by its dorsal fin's shape, permanent marks, and pigmentation pattern, was the same as the one seen in 1994, and was also present in the group of four individuals sighted in 1991 (Fig. 3). The cumulative time spent before finding common dol­phins in 1990-91, 1991-94, and 1994-95, was 6934, 22646, and 8163 min respectively, averaging 12581 min (SD=8738.2, SE=5045.0). DISCUSSION Many cetacean species have been reported to occur in the Northern and Central Adriatic Sea, including the fin whale, Balaerioptera physalus, the sperm whale, Physeter catodon, Cuvier's beaked whale, Ziphius cavi­rostris, the false killer whale, Pseudorca crassidens, the long-finned pilot whale, Globicephala me!as, Risso's dolphin, Grampus griseus, and the stripped dolphin, Stenella coeruleoalba. However, these species were rep­ ANNALES 7/'95 Giovanni 6 EAR Z). Giuseppe NOTARS ARTOI O d i SCIARA: A COMPARISON OF THE PRESENT OCCURRENCE OF BOTTLE NOSE DOLPHINS, .... SS-68 l§ l 111 SEEEEEEEEEEKE till® •••••••dBBMWBM I Figure 3: The common dolphin sighted on 11 July 1995, associated with a bottlenose dolphin. This same individual was encountered in 1991 and 1994 (Photo: G. Bearzi). Slika 3: Navadni delfin, opažen 11. julija 1995 v družbi z veliko pliskavko. Isti osebek je bil opazovan v letih 1991 in 1994 (Foto: G. Bearzi). resented by rare occurrences of erratic individuals (KrySiufek & L.ipej, 1 985; Notarbartolo di Sciara & Bearzi, 1992; Krystufek & Lipej, 1993; Notarbartolo di Sciara et al., 1994). Of all cetacean species, oniy bottlenose dolphins and common dolphins are regularly encountered in the region (Ciglioli, 1880; Nardo, 1853; Kolombatovic, 1882, 1894, 1896; Brusina, 1889; Trois, 1894; Ninni, 1901, 1904, 1917; Peksider-Srica, 1931; Vatova, 1932; Filleri & Gihr, 1969, 1977; Pilleri, 1970; Rallo, 1976; Di Natale, 1979; Di Natale & Mangano, 1981; Pilleri & Pilleri, 1982, 1983; Di Natale, 1983; Canestri et al., 1986; Ciovannetti, 1986; KovaCii, 1986; Centra Studi Cetacei, 1987, 1988, 1989, 1990, 1991; Bearzi, 1989; Notarbartolo di Sciara eta!., 1993). Abun­dance ratios of common to bottlenose doiphins in the past are unclear. According to Brusina (1889), D. del­phis was the most common cetacean species in the Adriatic, and Ninni (1904) considered that species very common there in contrast to Delphinus tursio (= T. trim­ catus), which he thought rare in the Adriatic. By con­trast, Vatova (1932) listed D. delphis and Tursiops tursio (= T. truncatus) among the most common marine ani­mals near Rovinj. Pilleri and Gihr (1977) noted a de­crease of common dolphins in the Northern Adriatic with respect to the previous 40 years. !n recent times, only the bottlenose dolphin is considered a regular in­habitant of the Northern Adriatic Sea (Notarbartolo di Sciara & Bearzi, 1992; KryStufek & Lipej, 1993; Notar­bartolo di Sciara et al., 1994). Based on an extensive effort in the field, this study documents the regular presence of bottlenose dolphins in the Kvarnerici. The flattening of the discovery curve strongly indicates that at the end of 1994 most of the naturally marked individuals frequenting the study area were iikeiy to have been identified (Fig. 2). The overall bottlenose dolphin density - as indicated by the mean time spent to find them and by the number of individu­als identified - is low compared to other areas where Giovanni BEARZI, Giuseppe NOTARB ARTOi.O cii SCIARA: A COMPARISON OF THE PRESENT OCCURRENCE OF BOTTLENOSE DOLPHINS, ..., 61-68 bottlenose dolphin communities have been studied (Shane et al. 1986, Scott ef al. 1990, Richard C. Connor, personal communication). However, bottlenose dolphin sighting frequency was remarkably higher in the Kvarneric than in any other Northern Adriatic area sur­veyed by Bearzi (1989). Instead, the presence of com­mon dolphins was limited to the rare occurrence of stray individuals. Only 4 different animals were sighted from 1987 to 1995, one of them being encountered in ail of the sightings. The mean time spent before finding com­mon dolphins was two orders of magnitude greater than the mean time needed to spot bottlenose dolphins. Moreover, the long time spent observing bottlenose dol­phins (about 844 hours) was not considered in comput­ing the mean search time for common dolphins, al­though this species could have been sighted while fol­lowing the former. it is apparent that both dolphin species faced a sub­stantial population decrease in the Northern Adriatic Sea during the recent past. The numerical decline of bot­tlenose dolphins is indicated by their iow present den­sity throughout the area (Bearzi, 1989; Notarbartofo di Sciara ef at., 1993). Nevertheless, bottlenose dolphins, whose ability to adapt behaviouraliy and ecologically even to habitats heavily impacted by humans is well known (Shane et ai., 1986; Leatherwood & Reeves, 1990; Henningsen & Wursig, 1991), seem capable of surviving in the less degraded portions of the Northern Adriatic, despite the worsening environmental condi­tions. By contrast the common dolphin, a species whose adaptability and flexible behaviour and ecology was never investigated, might have been unable to deal with the same environmental degradation. The disappearing of the once "common" common dolphin from the Northern Adriatic Sea dramatically reflects its general­ized decrease throughout its former Mediterranean range (Cagnolaro & Notarbartolo di Sciara, 1992; No­tarbartolo di Sciara & Dernma, 1994; Notarbartolo di Sciara & Gordon, in press). The reasons underlying such a decline possibly include environmental pollution and organochlorine contamination (Cummins, 1988; Tanabe ef ai, 1988; Cockroft ef ai., 1989; Tanabe & Tatsukawa, 1992; Tanabe, 1993; Notarbartolo di Sciara, 1994), the impoverishment of food resources (Anonymous 1989), high levels of ambient noise and boat disturbance (Kruse, 1991; Evans et ai, 1992; Dos Santos et a!, in press), by-catches (Di Nataie & Notarbartolo d i Sciara, 1994), and the heavy impact of deliberate killings oc­curring in the Adriatic up until the early 1960s (Holcer, 1994). These threats deserve further investigation. ACKNOWLEDGEMENTS Special thanks are due to Draško Holcer for provid­ing additional references and relevant information. Our thanks also go to the numerous friends and field assis­tants who have been working with us, including Laura Bonomi, Luca Bucchini, Benedetta Cavalloni, Caterina Maria Fortuna, Giancarlo Lauriano, Daniela Maldini-Feinholz, Mario Matešič, Sylvan Oehen, Melita Peharda, Marta Picciulin, Efena Politi, Sandra Pribanič, Luca Riva, Brigitte Sifaoui, Michele van der Schoot, and many "ecovolunteers" provided by Europe Conservation. We are grateful to Arlen Abramič, Dubravko Balenovici, Vlado Balenovič, Hrvoje Gomerčic?, Gordana Lackovič, Nena and Damir Nosalj-Peršic:, Draško Šerman, Goran Sušič, Zoran Tomič, and all people of Lošinj and Cres for providing support and local assistance. This research was largely funded by Europe Conservation. Additional funds were given by the Centra Interdisciplinare di Bioacustica, University of Pavia. The Whale & Dolphin Conservation Society provided financial help in 1995. The main inflatable boat used for this research was sponsored by Novamarine. POVZETEK Med neko široko zastavljeno študijo na temo socio-ekologije in obnašanja velike pliskavke, ki so jo leta 1987 izvedli v Kvarnerskem zalivu, so opaziti samo dve vrsti kitov: veliko pliskavko {Tursiops truncatus) in navadnega delfina (Deiphinus delphis). Registrirali so 879 skupin velike pliskavke in le tri skupine navadnih delfinov. Pogostost opažanj velike pliskavke je bila kar 87-krat večja od frekvence navadnega delfina. Ko so avgusta 1991 prvič opazili navadne delfine, je šlo za štiri odrasle primerke, medtem ko so ob sledečih dveh priložnostih (avgusta 1994 in julija 1995) opazili samo enega predstavnika vrste, ki se je pridružil velikim pliskavkam. S tehniko fotoidentifikacije je bilo mogoče ugotoviti, da je bil ob vseh treh srečanjih prisoten isti primerek navadnega delfina. Iz teh primerov je razvidno, da je navadni delfin skoraj povsem izginil iz severnega Jadrana, iz območja, na katerem je bilo predstavnikov obeh vrst v preteklosti v izobilju. ANNALES 7/'95 Giovanni BEARZI. Giuseppe NOTARBARTOIO