Ward, CA State Park Ranger, pers. comm. 2002) on 5 December 2002, hauled out at Indian Beach in Tomales Bay State Park, approximately two miles north of Shell Beach. Marine turtles sightings in northern latitudes sometimes have been associated with warm-water years (Eckert 1993), but records from Alaska occurred in warm and normal-water temperature years (Hodge & King 2000). The October 2001 sighting occurred after two months of below normal monthly sea surface water temperatures (lower tercile) and was preceded by several months of normal (mid tercile) or below normal temperatures; and the November 2002 observation occurred during normal monthly sea surface temperatures, but was preceded by 6 continuous months of below normal monthly sea surface water temperatures (ﬁgure 1). At least in these two particular sightings, both of which involved apparently uninjured, free swimming olive ridley turtles, the observations were associated with normal or colder than normal sea surface temperatures. The three plausible explanations for an olive ridley on land are: (1) reproductive activity, (2) stranding due to injury, or (3) thermoregulation. No reproductive activity was observed and the turtle did not appear injured. The ridley that hauled onto the beach may have been attempting to raise its body temperature above that of the cold water it was swimming in. Olive ridley turtles are known to thermoregulate at the water surface and have been reported to crawl out onto ﬂoating debris in the open ocean, but the authors are not aware of this species thermoregulating on land.
Acknowledgements: We thank David W. Pierce (Climate Research Division, Scripps Institution of Oceanography) for sea surface temperature data; Captain Brian Guiles for the capture report and photo; Aaron Ward for the Indian Beach report; Wallace J. Nichols, Pam Plotkin and Robert Pitman for conﬁrmation of turtle species and condition from photos; B.L. Wing for information on condition of turtles sighted in Alaska; Alan Bolten for general information on injured loggerheads; David Owens on ridley thermoregulation and Karen Eckert for manuscript review. EVENS, J.G. 1993. The natural history of the Point Reyes peninsula. Point Reyes National Seashore Association. 224 pp. PITMAN, R.L. 1990. Pelagic distribution and biology of sea turtles in the eastern tropical Paciﬁc. In T.H. Richardson, J.I. Richardson & M. Donnelly (Compilers). Proceedings of the Tenth Annual Workshop on Sea Turtle Biology and Conservation. NOAA Technical Memorandum NMFS-SEFC-278. pp. 143-148. PLOTKIN, P. 2003. Adult migrations and habitat use. In: P.L Lutz, J.A. Musick & J. Wyneken. The Biology of Sea Turtles Volume II. CCR Press. pp. 225-241. Reynolds, R.W. & T.M. Smith, 1994. Improved global sea surface temperature analyses. J. Climate 7: 929-948. HODGE, R. P. & B. L. WING. 2000. Occurrences of marine turtles in Alaska waters: 1960- 1998. Herpetological Review 31:148-151. ECKERT, K.L. 1993. The biology and populations status of marine turtles in the North Paciﬁc Ocean. NOAA Technical Memorandum. NOAA-TMNMFS-SWFSC-186. 156 pp.
Oceanic Habitats for Loggerhead Turtles in the Mediterranean Sea Paolo Casale1, Daniela Freggi2, Roberto Basso3 & Roberto Argano4 1
via Antonio Calderara 29, I-00125 Roma, Italy (E-mail: [email protected]
) 2 Sea Turtle Rescue Centre WWF Italia, CP 92010 Lampedusa, Italy (E-mail: [email protected]
) 3 Museo Civico Storia Naturale del Po, via Roma 4, Ostellato, Italy 4 Dipartimento di Biologia Animale e dell’Uomo, Università “La Sapienza”, I-00185 Roma, Italy (E-mail: [email protected]
Loggerhead turtles span thousands of kilometers and undergo two major ontogenetic stages. In the ﬁrst, turtles feed upon pelagic prey in the oceanic zone. After several years (between 6.5 and 11.5 years in the Atlantic; Bjorndal et al. 2000), they are thought to recruit to neritic zones where they shift to feed upon benthic prey. They are rather difﬁcult to study in the oceanic zone, and only recently information began to be available (Bolten 2003). In the Mediterranean Sea, the coasts where nesting occurs are basically well known, and important neritic habitats are recognized in the few large continental shelf areas, also on the basis of at-sea recaptures of nesting females. Oceanic habitats are, however, proposed basically from the interaction of turtles with ﬁshing gear (Margaritoulis et al. 2003). However, this approach may suffer profound bias due to the distribution of ﬁshing effort. Here we report turtle size frequency of specimens stranded or gathered in the waters around Italy, in the center of the Mediterranean (ﬁgure 1), providing new insights on Mediterranean oceanic habitats for loggerhead turtles. Data were collected by a national sea turtle monitoring network operating for twenty years in Italy (Argano 1992). On the basis of curved carapace length (notch to tip) or other appropriate information (e.g. photographs), we classiﬁed loggerhead turtle specimens in two arbitrary size classes: small individuals (< 40 cm), likely to mostly include specimens in the oceanic phase,
and large individuals (≥40 cm), which is likely to include specimens in the oceanic and neritic phases. We included specimens with a known size found stranded (n=373), gathered at sea (taken from the sea surface by hands or handled tools; n=349), and captured by bottom trawlers (n=303). We assigned specimens found at sea to a sub-area (ﬁgure 1) on the basis of geographic coordinates or of the port of origin of ﬁshing vessels. The proportion of individuals in the small size class differed among areas (western basin: 38.6%, n=166; Sicily Channel: 32.4%, n=108; Ionian: 44.1%, n=177; Adriatic: 50.2%, n=271) (Chi-square test, χ2=12.05; df=3; P<0.05; n=722), with the highest proportions in the Adriatic and Ionian. Because of the relative position of Italian coasts and continental shelves (ﬁgure 1) it is not possible to differentiate deep vs. shallow waters in the Sicily Channel, but it is possible to do so for the Adriatic. In the south Adriatic (basically a deep water area with depths > 200 m) the proportion of small specimens was higher (53.3%) than in the north-central Adriatic (basically a shallow water area, with depths < 200 m) (41.6%) (Fisher exact test; P<0.05; n=271). When specimens caught by bottom trawlers ﬁshing on the continental shelves of the north Adriatic Sea and the Sicily Channel are compared, small turtles were found at a higher proportion in the former (36.1%; n=72) than in the latter area (18.2%; n=203) (Fisher exact test; P<0.05; n=275).
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Figure 1. Study area and sub-areas, with the 200-m isobath. NCA: north-central Adriatic; SA: south Adriatic; SC: Sicily Channel.
Although it cannot be excluded that Ionian/South Adriatic deep-water area is used simply as a migratory pathway, present ﬁndings suggest that this area is preferred to the western basin (deﬁned as in ﬁgure 1) as an oceanic developmental habitat. As some of most important nesting sites for loggerhead turtles in the Mediterranean are in the Ionian coast of Greece (Margaritoulis et al. 2003), it is likely that the Ionian/South Adriatic area is an important developmental oceanic habitat for the Greek population. This hypothesis is supported by the ﬁnding of very small specimens (e.g. 7-8 cm) stranded along the south Adriatic coasts, unlikely to come from distant nesting areas. The only two post-hatchling specimens ever found in the north Adriatic (Affronte & Franzelliti 2004) probably moved from the south Adriatic as a result of an exceptional factor during winter 2002-2003. The trophic importance of the Ionian/South Adriatic area was also suggested by Argano et al. (1992) on the basis of specimens re-encountered in the same area after months or years after release. The high occurrence of small turtles in the catch of trawlers from the Adriatic suggests that the oceanic stage juveniles of the Ionian/ South Adriatic area recruit at a small size to the neritic habitat in the north-central Adriatic. Accordingly, catch rates by trawlers indicate a high abundance of juvenile turtles in the north Adriatic area (Casale et al. 2004). As adult females nesting in Greece are also known to frequent this area (Lazar et al. 2004), the Adriatic seems to be one of the most important areas for Mediterranean loggerhead turtles, and especially for the population which nests in Greece, both for its neritic and oceanic habitats. Acknowledgements: We thank the many persons who participated in the “Progetto Tartarughe” (Univ. Roma/WWF Italy). We also thank two anonymous reviewers for their comments on a earlier version of this manuscript.
AFFRONTE, M. & S. FRANZELLITI. 2004. Recoveries of two posthatchling loggerhead turtles in the northern Adriatic Sea. Marine Turtle Newsletter 104:10-11. ARGANO, R. 1992. Sea turtles and monk seal in Italian seas: conservation and perspectives. Bollettino Museo Ististuto biologia Univiverità Genova 56-57:113-135. ARGANO, R., R. BASSO, M. COCCO & G. GEROSA. 1992. New data on loggerhead (Caretta caretta) movements within Mediterranean. Bollettino Museo Ististuto biologia Università Genova 56-57:137163. BJORNDAL, K.A., A.B. BOLTEN & H.R. MARTINS. 2000. Somatic growth model of juvenile loggerhead sea turtles Caretta caretta: duration of pelagic stage. Marine Ecology Progress Series 202:265272. BOLTEN, A. 2003. Active swimmers – passive drifters: the oceanic juvenile stage of loggerheads in the Atlantic system. In: A.B. Bolten & B. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Institution Press, Washington D.C. pp. 63-78. CASALE, P., L. LAURENT & G. DE METRIO. 2004. Incidental capture of marine turtles by the Italian trawl ﬁshery in the north Adriatic Sea. Biological Conservation 119:287-295. LAZAR, B., D. MARGARITOULIS & N. TVRTKOVIC. 2004. Tag recoveries of the loggerhead sea turtle Caretta caretta in the eastern Adriatic Sea: implications for conservation. Journal of Marine Biology Association of U.K. 84:475-480. MARGARITOULIS, D., R. ARGANO, I. BARAN, F. BENTIVEGNA, M.N. BRADAI, J.A. CAMINAS, P. CASALE, G. DE METRIO, A. DEMETROPOULOS, G. GEROSA, B. GODLEY, J. HOUGHTON, L. LAURENT & B. LAZAR. 2003. Loggerhead turtles in the Mediterranean Sea: present knowledge and conservation perspectives. In: A.B. Bolten & B. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Institution Press, Washington D.C. pp. 175-198.
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