International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409.
MONITORING STAVNIKE FISH-TRAPS AND SEA TURTLE BYCATCH AT PATOKU, ALBANIA Michael White1, Idriz Haxhiu2, Enerit Saçdanaku3, Lazion Petri3, Merita Rumano4, Fundime Osmani2, Blerina Vrenozi2, Prue Robinson5, Stephanos Kouris5 and Lily Venizelos5. Centro Recupero Tartarughe Marine, Lampedusa1; Museum of Natural Sciences, University of Tirana2; Faculty of Natural Sciences, University of Tirana3; Ministry of Environment, Tirana4; MEDASSET5. Correspondence to: Dr Michael White, Centro Recupero Tartarughe Marine-WWF, 92010 Lampedusa (AG), Italy. E-mail: email@example.com
ABSTRACT Research began at Patok Lagoon, Albania, in June 2008, monitoring an important sea turtle foraging ground; the project included researchers from Tirana University. The population structure of loggerhead turtles Caretta caretta captured as bycatch in stavnike fish-traps was investigated. The traps yielded 103 turtles, which were tagged and released; 17 were subsequently recaptured. Ten remigrants had been tagged previously at Patok. Adult and adolescent male loggerheads were encountered. There was one juvenile green turtle Chelonia mydas. Keywords: Loggerhead turtle, Caretta caretta, foraging, bycatch, stavnike fish-traps, Chelonia mydas. INTRODUCTION A yacht-based rapid assessment of Albania’s coastal waters was conducted in OctoberNovember 2005 as part of the MEDASSET (Mediterranean Association to Save the Sea Turtles) Marine Research Programme to determine the current distribution of sea turtles and Mediterranean Monk Seals Monachus monachus. The project works within the framework of the Strategic Action Plan for the Conservation of Biological Diversity in the Mediterranean Region (SAP BIO) and the implementation of the Action Plans for the Management of the Mediterranean Monk Seal and for the Conservation of Mediterranean Marine Turtles under the United Nations Environment Programme Mediterranean Action Plan (UNEP/MAP). During the voyage fishermen throughout Albania were interviewed about their encounters with turtles, seals and cetaceans. An important finding from these interviews was that large numbers (100’s) of marine turtles were reported from Albania’s northernmost bay at Patok; but they were rare,
perhaps 2-6 turtles in some years, in southern Albania. Loggerhead turtles Caretta caretta (Linnaeus, 1758) were caught as bycatch in stavnike fish-traps and trawling operations in the broader Patok area: Gjiri i Drinit (White et al. 2006). A research programme that included researchers from Tirana University was planned for Patok, which would include monitoring the stavnike fish-traps and other fishing activities; this began in June 2008 and continued throughout that summer. Collaborating closely with local fishermen, researchers were able to measure and tag many of the sea turtles that were caught incidentally in the stavnikes. We started work with Rakip Martini’s group of fishermen at Patoku on the 1st of June, and included a second group (Çal) on 18th June.
International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409. MATERIALS AND METHODS 1. Study area Gjiri i Drinit is a shallow sea (maximum depth 47 m) with a sand and mud substratum dominated by bivalves and crabs. Five sediment-laden rivers (Bunës, Drinit, Matit, Droja and Ishmit) enter the bay bringing large amounts of terrestrial garbage, predominantly plastics, into the study area. The project base was established at Patoku Lagoon [N41°38.191′; E019°35.327′]. 2. Stavnikes Stavnikes are a type of fish trap, originating in Russia, introduced into Albania around 30 years ago, and then they were forgotten about until 2000, when the Patoku fishermen started to use them again. Two sets of traps were monitored closely: Ishmit [N41°36.198′; E019°33.349′]; Matit [N41°38.512′; E019°34.126′]. Note: Ishmit stavnikes were out of action for nine days in June & four days in July; the nets were removed for cleaning (algal growth). One trap was damaged in heavy weather (15/7/2008) but rebuilt; and both stavnikes were destroyed on 24th July and not rebuilt in this year (2008).
3. Trap construction A rectangular enclosure is erected in shallow water (depth 5-6 m) some distance offshore, consisting of long wooden posts (length 8-10 m, diameter 10-15 cm) forced vertically into the seabed, with nets secured to them in an arrangement that allows easy access into the traps for fish and other marine animals. The number of posts required depends upon trapsize, but the design is always similar. A stavnike is divided into sections (reception area, ante-chamber, and collection chamber), which is repeated to form a double unit. A long barrier net extends from the fish-traps to the beach (Ishmit stavnike was 1800 m offshore; Matit only 200 m); the traps are constructed to
allow entry from either side of the barrier net. When fish or turtles encounter the barrier they have three choices: to turn left, right, or to go back the way they came; an area they may have just foraged. Turning beachwards leads them into shallower water. Animals entering the reception area are guided into successive chambers; escape from these is difficult although not impossible. 4. Fish catch Traps were emptied early each morning before the sun got too hot; harvesting was not possible in strong winds or heavy seas. Working from a small boat inside the enclosure the fishermen slowly raised the bottom net by hand, reducing the size of the collection chamber, until the catch could be emptied into the boat. Any turtles were lifted manually into the boat, which could be difficult with larger animals. Space in the boats is limited and sometimes turtles were released directly at the traps. Catches were monitored in three ways: i) direct observation at the traps ii) direct observation of the catch when the boats returned to Patoku iii) discussions with different fishermen about their catch (anecdotal evidence). Whether researchers went to the stavnikes or not largely depended upon the fishermen’s planned activities. On some mornings they emptied the traps and returned directly to Patoku about 3-5 hours later, on other days they continued to different types of net elsewhere before returning to Patoku in the evening. 5. Sea turtles Turtles captured as bycatch were usually brought to our field base at Patoku, where animals were measured, photographed, tagged and released. Incidental tagging has been conducted in Albania since 2002 (Dalton’s Rototags: RAC/SPA, Tunis); these are now superseded by Stockbrand’s titanium tags with an Albanian address.
International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409. 6. Morphometric data The curved carapace length (CCL) and curved carapace width (CCW) were measured and turtles allocated into 10 cm size-classes (lengthfrequency distribution) based on their CCL e.g. 40 cm size-class range: 40.0-49.9 cm et seq. (White, 2007). As an indicator of the stage of sexual development three measurements were recorded from the tail: i) Distance from posterior margin of plastron to midline of cloacal opening (Plas-clo) ii) Total tail length (TTL) iii) Distance from tip of tail to posterior margin of the carapace (+/- cara) RESULTS 1. Turtle bycatch There were 103 turtles captured in the two stavnikes during June and July 2008: Ishmit stavnike fished for 39 days and yielded 54 turtles (53 Caretta caretta; 1 Chelonia mydas); Matit stavnike fished for 34 days and yielded 49 loggerheads. 2. Size-classes Almost half of the loggerheads (47%; n = 46 turtles) were in the 60 cm size-class (Table 1). Only two had a curved carapace length (CCL) <50 cm; and two had CCL >80 cm. Mean CCL = 64.0 cm; SD = 7.3 cm; 95% confidence limit = 1.47; CCL range 45.5-83.0 cm; n = 98 loggerheads (4 loggerheads were data deficient due to carapace damage). There was one small juvenile green turtle Chelonia mydas (CCL = 39.0 cm).
but, as the animal was very vigorous, it was released again; and recaptured two weeks later. One loggerhead in Matit stavnike had been caught previously on a longline (monofilament line emerged from its mouth, but the swallowed hook could not be seen and was probably in the stomach). 4. Male turtles Carapace and tail measurements (cm) are given for 18 male loggerheads (4 adults; 14 adolescents) that were captured in stavnikes during June-July 2008 (Table 2). Analyses of variance showed that the carapace measurements between adults and adolescents were significantly different (CCL: F1,16=6.98, P<0.05. CCW: F1,16=5.15, P<0.05). Analyses of variance showed that there were highly significant differences in the three tail measurements between adult and adolescent male loggerheads (Plas-clo: F1,16=34.36, P<0.01. TTL: F1,16=27.15, P<0.01. +/- cara: F1,16=25.30, P<0.01). In two adolescents the tail had not yet extended beyond the carapaceâ€™s posterior margin (+/- cara = -1.0 and -2.5 cm). 5. Serial recaptures Seventeen turtles tagged during this study (16 Cc & 1 Cm) were recaptured in stavnikes on more than one occasion (one was taken five times, two others on three occasions, and 14 turtles were captured twice). Seven turtles (6 Cc & 1 Cm) were captured in both stavnikes (4.5 km apart), whereas the other 10 recaptures were always in the same traps. 6. Remigrants Ten loggerheads had been tagged in previous years (all at Patok); the earliest in 2003.
3. Health status
7. Tag loss
Turtles were generally in good health: 13 loggerheads had visible carapace damage, probably caused by boat propellors. The carapace of one turtle was seriously fractured,
Three Caretta caretta (3%; n = 102 loggerheads) had, apparently, lost their flippertags; the size, shape and location of holes in
International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409. their flippers suggested rototags had been previously applied. The plastic rototags on several loggerheads (n = 5) were heavily encrusted with barnacles; one rototag was barely legible after just five years. 8. Epibiotic fauna Forty-two loggerheads had barnacles (chelonibia or lepas spp.) attached to the carapace and/or head; six turtles were very heavily encrusted with epibiotic fauna. DISCUSSION Stavnikes appear to be a â€˜turtle-friendlyâ€™ method of fishing. Perhaps the most important factor is that turtles entering the traps can swim around and, crucially, surface to breathe normally; whereas in trawls, for example, many captured turtles will drown. There was one observation of a loggerhead eating a fish inside a stavnike, and so in-trap foraging is also a possibility. An important conclusion was that entrapped turtles were not deterred from foraging locally, despite being manhandled out of the nets, and then being landed for measuring and tagging. The evidence for this is that 17 turtles were recaptured in stavnikes on more than one occasion. Such serial recaptures indicate that at least some turtles showed shortterm fidelity to Patoku foraging grounds (16 Caretta caretta; 1 Chelonia mydas). Ten of the loggerheads released from Patok were recaptured in the same trap, either Matit or Ishmit, indicating that they foraged in a localised part of the bay. Another seven turtles (6 Cc & 1 Cm) were captured in both stavnikes (4.5 km apart), perhaps showing that they utilised a more extensive foraging area. Patoku (& Gjiri i Drinit) is frequented by larger juvenile and adult loggerheads (Table 1). Data so far suggest that adult females are not using the Patoku foraging ground (one 80 cm CCL turtle may have been female, but this remains unconfirmed). However, this research
coincided with the egg-laying period in the Mediterranean region, and perhaps adult females will be encountered later in the year (post-nesting). Ten loggerheads had been tagged in previous years (all at Patoku), the earliest in 2003; these indicate repeat migrations either to Patoku or enroute elsewhere. Tag loss (3% seen in this study) can result in a turtle receiving new tag numbers, thus its previous life-history remains incomplete and population assessments may be overestimated (Balazs, 1999; White, 2007). A juvenile green turtle Chelonia mydas (CCL = 39 cm) was in Ishmit stavnike (June); regionally this species nests only in the northeastern Mediterranean, and more usually has a tropical distribution. The distribution and lifestyle of male turtles is not as well known as that of females. Patoku may be a male foraging and developmental habitat, as 20% of loggerheads tagged in June were males (adult=4; adolescent=9); there were five more adolescent males in July. This discovery has added importance because of the potential feminising-effect of climate-change on global turtle populations (Davenport, 1989). The development of secondary sexual characteristics in adolescent turtles occurs across a range of year-classes (Limpus and Limpus, 2003; White, 2007). Morphological changes indicating the onset of male adolescence (proximal thickening and elongation of the tail) were observed in 14 loggerheads at Patoku (Table 2). These animals were mostly in CCL size-classes 60 and 70 cm; the smallest turtle showing clear tail development had a CCL= 59.5 cm. The tail tip of the largest adolescent (CCL= 74.0 cm) was still 2.5 cm short of the carapaceâ€™s posterior margin. These bycatch records represent an unknown proportion of turtles using Gjiri i Drinit: only two traps were monitored regularly, and we do
International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409. not know how many turtles of those present in the area actually enter traps. Saturation tagging has yet to be achieved locally. It was not logistically possible to monitor all the stavnikes in Gjiri i Drinit (we located 18 traps in the bay, which is about 30 km north to south); we lacked a sea-going boat and the local roads were in very poor condition. Fishermen from other areas were interviewed about their encounters with turtles whenever possible. In the Mediterranean region the marine ecology of sea turtles, and their marine distribution patterns, both geographical and temporal, are largely unknown (Margaritoulis et al. 2003; White, 2007). Although the monitoring programme at Patoku is still in its early stages, we can confirm that substantial numbers of Caretta caretta are present in Gjiri i Drinit during the summer months. CONCLUSION Sea turtles described in this study were captured in stavnikes in Gjiri i Drinit (June-July 2008): most were large loggerheads Caretta caretta,
but there was one juvenile green turtle Chelonia mydas. Ten loggerheads had been tagged at Patok in previous years, suggesting that Albania forms part of their migratory route. Tag-loss can lead to population overestimation. Seventeen turtles showed short-term residency in the bay, which was demonstrated through their subsequent recaptures in fish-traps. These serial recaptures also suggest that being caught in a stavnike does not deter turtles from foraging locally. Male sea turtles (4 adults, 14 adolescents) were captured at Patoku, suggesting that they may use the area as a developmental and foraging habitat. This discovery has increased importance due to our presently limited understanding of the distribution and marine ecology of male sea turtles; and the threatened impact of global climate-change, which may force embryonic sex-ratios towards female-dominance. Therefore it is recommended that Gjiri i Drinit is legally recognised as a nationally and regionally important foraging habitat for sea turtles; and that these endangered migratory animals are fully protected under Albanian national law.
International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409. LITERATURE CITED BALAZS, G. H. (1999): Factors to consider in the tagging of sea turtles. Pp. 101-109. In: Eckert, K. L.; K. A. Bjorndal; F. A. Abreu-Grobois and M. Donnelly (Editors). (1999). Research and management techniques for the conservation of sea turtles. IUCN/SSC Marine Turtle Specialist Group Publication No. 4. pp. 235. DAVENPORT, J. (1989): Sea turtles and the Greenhouse Effect. British Herpetological Society Bulletin 29: pp. 11-15. LIMPUS, C. J., LIMPUS, D. J. (2003): Biology of the loggerhead turtle in Western South Pacific Ocean foraging areas. Pp.93-113. In: Bolten, A. B. and B. E. Witherington (Editors). Loggerhead sea turtles. Smithsonian Books, Washington. pp. 319. MARGARITOULIS, D., ARGANO, R., BARAN, I., BENTIVEGNA, F., BRADAI, M. N., CAMINAS, J. A., CASALE, P., DE METRIO, G., DEMETROPOULOS, A., GEROSA, G., GODLEY, B. J., HADDOUD, D. A., HOUGHTON, J., LAURENT, L., LAZAR, B. (2003): Loggerhead turtles in the Mediterranean Sea: Present knowledge and conservation perspectives. Pp. 175-198. In: Bolten, A. B. and B. E. Witherington (Editors). Loggerhead sea turtles. Smithsonian Books, Washington. pp. 319. WHITE, M. G. (2007): Marine ecology of loggerhead sea turtles Caretta caretta (Linnaeus, 1758) in the Ionian Sea: Observations from Kefalonia and Lampedusa. Ph.D. Thesis, University College Cork, Ireland. pp. 300. WHITE, M., HAXHIU, I., KOUROUTOS, V., GACE, A., VASO, A., BEQIRAJ, S., PLYTAS, A. (2006): Rapid assessment survey of important marine turtle and monk seal habitats in the coastal area of Albania, October-November 2005. (Available from www.medasset.org).
This research was co-funded by: MEDASSET; MEDASSET (UK); RAC/SPA; UNDP (GEF/SGP); UNEP-MAP. Partners were: MEDASSET; RAC/SPA; UNDP (GEF/SGP); UNEP-MAP; HAS, ECAT (Tirana); Ministry of the Environment, Tirana; Museum of Natural Sciences; University of Tirana.
International Conference on Biological and Environmental Sciences, Faculty of Natural Sciences, Tirana University, Tirana, Albania (2008) pg 404-409. Table 1. Number of loggerheads in each 10 cm size-class of CCL CCL
Table 2. Carapace and tail morphometric data (cm) for 18 male loggerhead turtles. Legend: CCL curved carapace length; CCW curved carapace width; Plas-clo distance from posterior margin of plastron to midline of cloaca; TTL total tail length; +/- cara tip of tail to posterior margin of carapace. The final four turtles are adult, the others adolescent. *may have just reached maturity. CCL
+/- cara 0.5
Published on Oct 1, 2008
Author: White M., Haxhiu I., Sacdanaku E., Petritaj L., Rumano M., Osmani F., Vrenozi B., Robinson P., Kouris S. and Venizelos L. (2008). I...