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Data were available online <http://www.iattc.org> from two IATTC unpublished reports: documents BYC–4–04 and BIC–4–05a (IATTC 2004a; IATTC 2004b) that were produced from the 4th Meeting of the IATTC–Working Group on Bycatch (4-16 January, 2004, Kobe, Japan). As a normal rule, field and biological data aboard tuna purse seine vessels during fishery operations offshore are obtained from accredited and experienced IATTC–marine observers (e.g., biologists or fishery technicians), who are intensively trained in pelagic fishes, marine mammals and sea turtles species identification and morphometrics. The observers on tuna purse seine vessels recorded every sighting of a sea turtle and every capture in a fishing set type, including floating objects, unassociated tunas (tuna fish not associated with dolphins) and tuna fish associated with dolphins. The estimates of loggerhead mortality due to fishery interactions for the entire fleet were extrapolated from data collected by IATTC observers aboard large purse seiners (over 363 tons carrying capacity) during 1993-2003; data were not collected from a few unobserved trips and from trips by smaller vessels that do not carry observers.

In this review analysis, it is important to mention that the information collected by IATTC–observers on sea turtle species is opportunistic and may reflect only a given proportion of sea turtle distribution that overlaps with the effort distribution of the fishing fleet (IATTC 2004a). Since sea turtle swimming speeds are much lower than those of tuna and dolphins, these epipelagic marine vertebrates more often associate with floating sessile objects rather than herds of dolphins (e.g., Common, Spotted and Spinner dolphins: Delphinus delphis, Stenella attenuate and S. longisrostris, respectively), which are associated with tunas (e.g., Yellowfin tuna, Thunnus albacares) or with unassociated schools of tuna (IATTC 2004a; IATTC 2004b). Generally, the sea turtle-fishery interactions occur when the sea turtles are associated with floating objects (e.g., fish-aggregating devices or FADs) and are captured when the object is encircled by a purse–seine net. Secondly, it is likely that sea turtles can be captured in a given location when a net is set around an unassociated school of tunas or a school associated with dolphins (IATTC 2004b). Finally, misidentification of loggerhead turtles for Pacific olive ridleys is possible (Frazier 1985) during field identification at sea, but the intensive training and experience of high qualified IATTC-marine observers make this relatively unlikely.

During the period 1993–2002, IATTC–observers reported a total of 383 sightings of loggerheads, from which 98% (375/383) were alive and 2% (8/383) were dead. In marine waters off Ecuador, during the same time period, less than 10 sightings of loggerheads were recorded, four of them relatively close to Ecuador mainland, within the 333 km of national marine territory, and two far from the coast, including Galapagos Islands, which are located 1000 km from continental Ecuador. This is an extremely low rate of sightings between the latitudes 0°N and 5°S for a nine years period of recorded data. On the contrary, there were a considerable number of observations along the northwest Ecuador coast, above the Equatorial line (0°N), in international waters, including Central American, between the geographical band 3–10°N during the third quarter (July–September) of the year, with less than 10 records of this species close to southwestern Colombia coast. Similarly, around 5–20°S and 80–90°W, a concentration of loggerheads (~30 individuals) is found north, central and southwestern Peru mainland from January to April. The area with the highest loggerhead concentration in the eastern Pacific ocean is found among the western coast of Baja California, between Cedros Island and María Magdalena (30–20°N; 105–115°W), mainly during the second half of the year (IATTC 2004a). This is consistent with the previous observations regarding with the abundance of this species coming from nesting beaches of Japan (Marquez 1990; NMFS & USFWS 1998a; Bowen 2003; Limpus & Limpus 2003; Pritchard 2003).

Figure 1. Abundance and distribution of olive ridley (large dotted area with dashed boundaries) and loggerhead turtles (scattered red dots) in marine waters off Ecuador. The figure shows the overlapping of distribution areas for both turtles mainly at the southward and northward areas, with olive ridley being the most abundant compared to the sightings of loggerhead. Arrow with solid line depicts the Humboldt Current and arrow with the dotted line depicts the Panama or El Nino Current. Data adapted from Figures 2a and 2b in IATTC 2004a.

From the data analyzed here, it is suggested that loggerheads are not only present in marine waters off western Peru and northern Chile, where they are potentially feeding (Donoso et al. 2000; Alfaro-Shigueto et al. 2004), but also in low numbers offshore Ecuador mainland, which offer one of the most productive marine and estuarine areas along the western coast of South America, the Guayaquil Gulf Estuary (Figure 1). Likewise, the Humboldt Current coming from the Southern Ocean brings cold mass of water rich in nutrients, promoting the production of organisms in lower trophic levels and presence of primary and secondary consumers as well as top predators. This oceanographic scenario could enhance the presence of loggerheads and other sea turtles, and I also hypothesize that a small proportion of the juvenile loggerheads residing or foraging temporally offshore Peru and Chile are actually advected northward by the Humboldt Current, reaching Equatorial oceanic waters. However, this argument is weakened by the fact that loggerhead sea turtles, including juveniles, are not passive drifters but will swim against strong oceanic currents (Polovina et al. 2006). The opposite situation might be present during years when the El Niño event shows up, every four or ten years, with thermal anomalies, decreasing drastically the primary production and causing depletion of local food.

An alternative hypothesis regarding the low numbers of loggerhead in marine waters off Ecuador is derived from population ecology since it is known that large numbers of Pacific olive ridleys (Lepidochelys olivacea) forage in Ecuadorian marine waters (NMFS & USFWS 1998b; Pritchard 2003), thereby causing competition with loggerheads for both prey and habitat (Figure 1). We suggest that this interspecific competition of loggerheads and the more numerous olive ridleys has caused the displacement of loggerheads southward to Peruvian and Chilean waters. Note that interspecific competition does not always result in complete competitive exclusion of a species; rather the “excluded” species may be able to coexist in low numbers by sharing the resources with the dominant species at certain level of homeostasis (Odum 1975).

In addition, the antitropical distribution of loggerheads may explain why they are not present in large numbers in marine waters off Ecuador, which might be the northern extent of their range. Polovina et al. (2004) found different distribution and habitat use patterns between loggerhead and olive ridley turtles from the North Pacific, where loggerhead mainly moved westward and were associated with eddies, fronts and geostrophic currents with sea surface temperatures (SST) ranging 15-25ºC, while olive ridley were primarily distributed mainly south of loggerhead habitat in warmer waters (SST = 23−28ºC). Thus, this might support our hypothesis, the rich-nutrient, cold water masses (SST= 20−24 ºC; see Pennington et al. 2006) associated with the Humboldt Current might offer better resources for loggerheads, moving southward to Peruvian and Chilean waters, whereas the warmer equatorial waters, with SST ranging 22−28 ºC (Pennington et al. 2006), off Ecuador are a better option for olive ridley turtles. These hypotheses need further testing by undertaking field studies on foraging ecology strategies and habitat use (e. g. stable isotope analysis), as well as satellite-telemetry research to determine whether these two species are really competing for the same food resources. This will help our understanding of the natural history of these two species on the southeastern Pacific Ocean and promote conservation actions in benefit of a subpopulations or management unit inhabiting this region.

Figure 2. Fishing effort for loggerhead sea turtles found entangled in observed sets on floating objects during tuna purse-seine fleet operations made by the IATTC observers for the period 1993-2002 (data adapted from IATTC 2004)

The estimated annual mortality of loggerheads from bycatch in large purse–seine vessels during tuna fishery activities is indicated in Table 1. No mortality was reported in 1996 and 2002. The fishing effort from 1993 to 2002, as reflected by the number of sets observed during IATTC tuna purse seine operations, was 40115 sets, with most of the effort taking place in 1997 and 1998 when compared to the early 1990s (Figure 2). This pattern reflecting low bycatch mortality could be linked with the relatively low number of turtles observed these areas of the Eastern Pacific Ocean, mainly around 0°N–5°S offshore Ecuador. Additionally, loggerheads were also seen entangled with floating objects that were both not target and target for fishing set operations from purse–seine tuna fishery (Table 1). The number of dead turtles observed in this kind of interaction is low. However, when the turtles are still alive, mainly associated with floating object, they may eventually drown or die because of the stress associated with entanglement. For this reason, IATTC–resolutions on bycatch have encouraged marine crews and observers to work towards releasing all entangled turtles. Unfortunately, no morphometric data of individuals sighted or captured are available from these IATTC–reports.

Table 1. Loggerhead annual mortality in the purse–seine tuna fishery and entangled individuals in floating objects in the Eastern Pacific Ocean during the period 1993–2002. Mortality in the pursue–seine tuna fishery involved the following set types: tuna associated with dolphin, unassociated and floating objects. Entanglements are related to loggerheads observed in webbing with floating objects either involving fishing set type or not involving fishing gear.

In terms of artisanal fisheries, the data from an experimental study conducted in 2004 (testing the use of circles hook versus J–hooks and introducing dehookers during a program with Ecuadorian fishing communities; Largacha et al. 2004) showed that ten loggerheads interacted with fishing gear: either J-hooks (n = 2) or entangled in other gear (n = 10). The observed turtles appeared to be juveniles because the mean curved carapace length (CCL) was 58.8 cm ±9.91SD (range = 50–80cm) and curved carapace width was 57.8cm ±10.9SD (frequency range = 50–80cm). The largest individual with 80cm CCL was likely overestimated, nevertheless still subadult. These sizes are similar to those recorded by Kelez et al. (2003): CCL = 57.0 cm, range = 48.5–62.5cm; n = 7, and relatively similar to those recorded by Alfaro–Shigueto et al. (2004): CCL = 54.3cm ± 11.1 SD; n = 15 for loggerhead turtles caught in artisanal vessel using longlines for mahi mahi (Coryphaena hippurus), blue sharks (Prionace glauca), mako sharks (Isurus oxyrinchus) hammerhead sharks (Sphyrna zygaena) and thresher sharks (Alopias vulpinus). These pelagic fishes are the same species target for artisanal fishing communities of Ecuador, as well as yellowfin tuna (T. albacares), bigeye tuna (T. obesus), sword fish (Xiphias gladius, sail fish (Istiophorous platypterus) and different species of marlins: striped (Tetraptorus audax), black (Makaira indica) and blue (M. nigricans).

Globally, the loggerhead turtle is categorized as endangered by the IUCN Red List and listed in the Appendix I of CITES (Pritchard 1997). The major threat for loggerheads in the Eastern Pacific Ocean is the mortality caused for bycatch in commercial fisheries operations using longlines, trawls and nets (NMFS & USFWS 1998a; Limpus & Limpus 2003), which need to be mitigated for the recovery of this species. Recently, the preliminary data resulting from the ongoing circle hook experiment in Ecuador indicated that the use of circle hooks, type C16 and C18 hooks, reduced sea turtle bycatch by about 70 and 100%, respectively (Largacha et al. 2004). However, the fate of loggerheads on oceanic waters facing international and commercial-industrial fisheries and marine debris in this region of the Pacific Ocean is poorly unknown.

Identification of loggerhead stocks home ranges using DNA analysis is one of the actions required to reach the species recovery (NMFS & USFWS 1998a). This population genetic approach is important to conduct given that it can help to identify either new stocks or unknown populations showing unique genetic pool or otherwise individuals belonging to known maternal lineage already identified in other regions (i.e. nesting grounds) and facing different conservation threats in the Pacific Ocean. Therefore, a major research area and conservation strategy are genetic studies using mtDNA (as conducted in Peru; see Alfaro–Shigueto et al. 2004) on tissue samples collected from loggerhead captured incidentally by IATTC-purse seine tuna fleet operating in marine waters off Ecuador or from ongoing experiments on circle hooks. This will help to elucidate and confirm the occurrence of loggerhead turtles in Ecuadorian marine waters, and therefore the undertaking of management plan actions for this stock in the southeastern Pacific.

Acknowledgements: The author thanks Eric Largacha from the Inter–American Tropical Tuna Commission (IATTC) for facilitating additional data and information on loggerhead records on the Eastern Pacific and marine waters off Ecuador. The authors specially thank two anonymous reviewers for the valuable suggestions and Matthew Godfrey for editiorial work.

ALAVA, J.J. 2000a. Las tortugas marinas en El Ecuador In: Amorocho, D., F. Campo, J.A. Riascos & E. Parra. (Eds.). 2000. Memorias del Curso Taller en Biología y Conservación de las Tortugas Marinas y III Seminario Internacional de la Red Colombiana para la Conservación de las Tortugas Marinas. RETOMAR, Asociación WIDECAST-Colombia. pp. 14–17.

ALAVA, J.J. 2000b. Estado actual de conservación de las tortugas marinas en El Ecuador In: Amorocho, D., F. Campo, J.A. Riascos & E. Parra. (Eds.). 2000. Memorias del Curso Taller en Biología y Conservación de las Tortugas Marinas y III Seminario Internacional de la Red Colombiana para la Conservación de las Tortugas Marinas. RETOMAR, Asociación WIDECAST–Colombia. pp. 51–58.

ALAVA, J.J., P. JIMENEZ, M. PEÑAFIEL, W. AGUIRRE & P. AMADOR.2005. Sea turtle strandings and mortality in Ecuador: 1994-1999. Marine Turtle Newsletter 108:4-7.

ALFARO-SHIGUETO J., P.H. DUTTON, J. MANGEL & D. VEGA. 2004. First confirmed occurrence of loggerhead turtles in Peru. Marine Turtle Newsletter 103:7-11.

Bolten, A.B. 2003. Introduction. The loggerhead sea turtle—a most excellent fishe. In: A.B. Bolten and B.E. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Books, Washington, DC. pp. 1-3.

Bowen, B.W. 2003. What is a loggerhead turtle? The genetic perspective. In: A.B. Bolten and B.E. Witherington (Eds.). Loggerhead Sea Turtles. Smithsonian Books, Washington, DC. pp. 7-27.

CARR, A. 1952. Handbook of turtles. Cornell University Press, Ithaca, New York.

CORNELIUS, S.E. 1982. Status of sea turtles along the Pacific coast of Middle America. In: K.A. Bjorndal (Ed.). Biology and Conservation of Sea Turtles. Institution Press. Washington, D.C. pp. 211-220.

DODD, C.K., Jr. 1988. Synopsis of the biological data on the loggerhead sea turtle Caretta caretta (Linnaeus 1758). U.S. Fish Wildlife Service Biological Report 88(14):1–110.

DONOSO, M., P. DUTTON, R. SERRA & J.L. BRITO-MONTERO. 2000. Sea turtles found in waters off Chile. In: H.J. Kalb and T. Wibbels, (Compilers). 2000. Proceedings of the Nineteenth Annual Symposium on Sea Turtle Biology and Conservation. NOAA Technical Memorandum NMFS-SEFSC-443, pp. 218-219.

FRAZIER, J. 1981. The Status of Marine Turtles in the East Pacific. Department of Zoological Research, National Zoological Park, Smithsonian Institution. Washington D.C.

FRAZIER, J. 1985. Misidentifications of sea turtles in the eastern Pacific: Caretta caretta and Lepidochelys olivacea. Journal of Herpetology 19: 1-11.

GREEN, D. & F. ORTIZ-CRESPO. 1982. Status of sea turtle populations in the Central Eastern Pacific. In: K.A. Bjorndal (ed.), Biology and Conservation of Sea Turtles, Smithsonian Institution Press, Washington, D.C. pp. 221-233.

HURTADO, M.1987. Cierre de exportaciones de pieles de tortugas marinas en Ecuador. Instituto Nacional de Pesca, Boletín Informativo 2: 8pp.

INTER-AMERICAN TROPICAL TUNA COMMISSION. 2004a. Review of the status of sea turtles stocks in the Eastern Pacific. Document BYC–4–04, IATTC–Working Group in Bycatch, Fourth Meeting, 14–16 January, 2004, Kobe, Japan. 9pp. <http://www.iattc.org>

INTER-AMERICAN TROPICAL TUNA COMMISSION. 2004b. Interactions of sea turtles with tuna fisheries, and other impacts on turtle populations. Document BYC–4–05a, IATTC–Working Group in Bycatch, Fourth Meeting, 14–16 January, 2004, Kobe, Japan. 8pp. <http://www.iattc.org>