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Marine Turtle Newsletter 49:8-13, © 1990

Incidental Capture of Marine Turtles by the Swordfish Fishery at San Antonio, Chile

Jack G. Frazier¹ and José Luis Brito Montero^2
1Programa Regional de Vida Silvestre, Apartado 1350, Heredia, Costa Rica;
²Museo Municipal de Ciencias Naturales y Arqueología de San Antonio, Casilla 93 Llo-lleo, San Antonio, Chile

The resurgence of the swordfish (Xiphias gladius L., known locally as "Albacora") fishery in Chile has taken place rapidly since 1987, and is especially developed in four ports: Chañaral (26°22'S), Valparaiso (33°02'S), San Antonio (33°35'S) and Concepción (36°53'S). This increase in a specialized fishery has come about principally because of modernization of the fleet: vessels with greater operating distances, navigational aids, and more effective synthetic nets. In San Antonio alone there are some 250 vessels dedicated to the swordfish fishery; the majority are 14-15 m long, from 15-45 tons draft and make 7-10 knots. Wooden hulls are most common, but steel, ferro-cement and fiberglass are also used. These vessels are classified as "artisanal" and those of larger dimensions "industrial".

Traditionally swordfish have been harpooned from extended platforms from the prows of these artisanal boats (season: December to April). The use of "enmalle" or "enredo" nylon tangle nets is now widespread, and was adopted by artisanal fishermen in Chile after 1985 to increase swordfish capture during the winter months (May to August/ September) when the fish is not found at the surface and cannot be harpooned. These nets have a mesh opening of up to 45 cm, are 80 cm deep and usually 700 to 800 m long; larger nets can be twice as deep and nearly 3 km long. For nocturnal use the nets are fitted with small chemical submarine lights. The swordfish fishery (harpoons or nets) is virtually inoperative from August to December.

Not surprisingly, a variety of animals other than swordfish are captured in the nets, including marine turtles. Over the past two years, J. L. Brito M. has been contacting fishermen who work out of the San Antonio port and recording opportunistically the turtles which they capture (Table 1). Of these, three Dermochelys (JLBM Dc-3, Dc-6 and Dc-11) have been deposited in the Museo Municipal de San Antonio (MMSA 486-RE-47, MMSA 476-RE-45 and MMSA 494-RE-48, respectively). Detailed measurements for these three museum specimens, as well as for two additional turtles caught in early 1989, are in Table 2.

Table 1. Marine turtles captured in the fishery based at San Antonio, Chile. Data are based on interviews with swordfish fishermen, many are based on reports from Sr. Mauro Gonzáles P. Positions [distances], weights and lengths are estimated and were not directly measured. C.m.a. = Chelonia mydas agassizi, D.c. = Dermochelys coriacea, CL = curved carapace length, CW = curved carapace width, SL = straight carapace length, SW = straight carapace width, TL = total length (nose to tail).

Table 2. Measurements of Dermochelys coriacea caught near San Antonio, Chile. Values in meters (m) except weight (kg); see Table 1 for other details. Carapace lengths are taken at midline.

It is remarkable that mostly Dermochelys have been reported and that there have been relatively few records of other species, e.g., Chelonia mydas agassizi (Bocourt). The most southerly record for any marine turtle is from Chile: C. m. agassizi from Isla Desolaciòn (52°57'S) (Guzmán and Campodónico, 1973). Dermochelys has previously been documented as far south as Valpariso (33°02'S) (Frazier and Salas, 1984) and Santo Domingo (33°37'S) (Pequeño, 1967), although it has been claimed that there are records of the species at Isla Chiloé (42°S) (Frazier and Salas, 1984). Eight records here (JLBM Dc-5, Dc-11, Dc-12 to Dc-16, and Dc-18) extend the known range of Dermochelys as far south as Isla Mocha (38°22'S); captured individuals have included subadults as well as adults.

Captures and sightings of Dermochelys by the San Antonio fishery are clearly concentrated between January and July, with an absence of records from August through December (Table 3). This corresponds exactly with the seasonality of the swordfish fishery and is not necessarily indicative of any biological phenomenon in Dermochelys in Chilean waters.

Apparently in 1985 in the mouth of the Maipo River, south of San Antonio, a turtle with a "red mark" was seen (Mella, pers. comm.). The turtle was presumably not Dermochelys, but no further information is available. As yet, no tags have been reported from turtles captured in Chile.

Table 3. Summary of monthly captures and sightings of Dermochelys coriacea by the San Antonio swordfish fishery during the 1988 and 1989 fishing seasons, San Antonio, Chile.

The observations reported here represent only opportunistic records from a single port over a period of two years. They are relevant only to the artisanal fishery; no contact has been made with the industrial fishery of San Antonio. [However, this may not necessarily be a significant omission. The industrial fishery specializes on anchovey purse seining, normally with 30 km of the coast, and it is said by fishermen that in the San Antonio area turtles are not usually seen this close to the coast] As an indication of the rate of turtle capture, the fisheries technician of the MFV "Poseidon III" stated that during the 1989 swordfish season, their boat alone caught six Dermochelys, of which two were alive; he estimated that the minimum annual average per vessel was one-yielding a minimum total for San Antonio of 250 individuals per annum (Gonzáles, pers. comm.). Taking into account the fishing effort along the entire coast of Chile, it is likely that the accidental capture/ drowning of Dermochelys is at least several hundreds of animals yearly. There is a growing interest in marine turtles in Chile. It is hoped that there will be increased monitoring of the problem of incidental capture and increased efforts to avoid this problem in the future.

Acknowledgements: Sr. Mauro Gonzáles Pino, fisheries technician, and the crew of the Poseidon III were of great assistance in collaboration and the reporting of observations of marine turtles; Prof. Herman Núñez also generously provided invaluable assistance. JGF is grateful to the Chelonia Institute for support.

Anonymous. 1985. Totuga comestible en región Austral (photo by Francisco Etérovic). Mercurio, Santiago; 20 October 1985.

Bizama, L. 1989. Tortuga sin aleta capturan en el sur (photo by Sergio Benitez). La Tercera del Hora, Santiago; 3 April 1989.

Ferrer, C. 1982. Caleta Pichicuy: Conmoción en playa pro tortuga gigante (photo by R. Contreras). Mercurio, Santiago; 17 January 1982.

Frazier, J. and Salas, S. 1984. Tortugas Marinas en Chile. Boletin del Museo Nacional de Historia Natural de Santiago, Chile. (1982) 39:63-73.

Guzmán M., L. and Campodónico G., I. 1973. Presencia de Chelonia mydas agassizi Bocourt en Magallanes. Annals del Instituto de Patagonia 4(1-3):439-441.

Pequeño R., G. 1967. La tortuga laud o tortuga coriácea (Dermochelys coriacea schlegeli) en Chile. Noticiario Mensual, Museo Nacional de Historia Natuaral, Santiago 11(127):6-8.