1Marine Mammal Lab, Central Marine Fisheries Research Institute, Cochin, India

2Fishery Survey of India, Kochi, India

3Fishery Survey of India, Mumbai, India 

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The Central Marine Fisheries Research Institute (CMFRI) in Kochi, the Marine Products Export Development Authority (MPEDA) in Kochi, and the Fishery Survey of India (FSI) in Mumbai, jointly began conducting deep sea surveys in the Indian exclusive economic zone (EEZ) to assess marine mammal populations and estimate marine mammal and sea turtle bycatch on 1st April 2020. On 28th July, along the southwest coast of Kerala, we observed two ghost nets (Table 1) at different locations with entangled turtles. One alive and one dead olive ridley turtle (Lepidochelys olivacea) were entangled in the net at 10.730167° N, 75.389694° E (Figure 1 and 2) and a live green turtle (Chelonia mydas) was entangled in the net at 10.65780° N, 75.546333° E (cover image; this issue). Water depth was between 130-200m and temperature 27-28°C at each location. Algae and goose-necked barnacles (Lepas anserifera) were growing on the nets, and the nets and attached biota may have provided a source of food, shelter, and basking platform for the turtles before entanglement (Whittow & Balazs, 1982; Nichols et al., 2001; Boyle & Limpus, 2008; Stelfox et al., 2019).

Table 1. Characteristics of ghost nets with entangled turtles.

Net Type Twisted/ Braided S/Z Twist Mesh Size (mm) Twine Diameter (mm) # Strands Net Weight (kg) Net Length (m)
Trawl Twisted Z 400 1 3 11 15
Trawl Twisted S 60 1 3 4 10

Figure 1. Live and dead olive ridley turtles found in ghost net off the coast of Kerala. (Photo by Arun Ganesan.)

Figure 2. Dead olive ridley turtle found in ghost net off the coast of Kerala. (Photo by Pradip N. Chogale.)

The sea turtles were successfully disentangled from the ghost net and examined. The live turtles displayed no signs of injury. Curved carapace length (CCL), curved carapace width (CCW), front flipper length (distance from anterior tip of the flipper to where the flipper originated just next to the marginal scutes), and head length (distance along midline from the anterior-most part of the upper jaw to posterior-most bone of the skull; Wyneken, 2001) were measured using a flexible tape measure; Figure 3); scale counts (see Pritchard & Mortimer, 1999) and weight (using a mechanical balance) were also recorded (Table 2). Both live turtles were released back to the sea after examination.

Figure 3. Measuring curved carapace length of turtles rescued from ghost net off the coast of Kerala. a) Olive ridley turtle (Photo Credit: Arun Ganesan); b) Green turtle (Photos by Pradip N. Chogale).

Table 2. Characteristics of sea turtles entangled in ghost nets.

Turtle CCL (cm) CCW (cm) Weight (kg) Head Length (cm) Flipper Length (cm) # Costal Scutes # Vertebral Scutes Live/ Dead
Olive ridley 58.4 63.5 27 14.0 33.0 6 7 Live
Olive ridley 55.9 58.4 23 19.1 29.2 6 7 Dead
Green 33.0 30.5 7 19.1 4 6 Live

Literature cited:

Boyle, M.C. & C.J. Limpus. 2008. The stomach contents of post-hatchling green and loggerhead sea turtles in the southwest Pacific: An insight into habitat association. Marine Biology 155: 233-241.

Macfadyen, G., T. Huntington & R. Cappell. 2009. Abandoned, Lost or Otherwise Discarded Fishing Gear. FAO Fisheries and Aquaculture Technical Paper 523. UNEP FAO, Rome, Italy. Pp. 137.

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Pritchard, P.C.H. & J.A. Mortimer. 1999. Taxonomy, external morphology, and species identification. In: Research and Management Techniques for the Conservation of Sea Turtles (eds. Eckert, K.L., Bjorndal, K.A., Abreu-Grobois, F.A. & Donnelly, M.). IUCN/SSC Marine Turtle Specialist Group Publication No. 4. Pp. 21-38.

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Wyneken, J. 2001. The Anatomy of Sea Turtles. U.S. Department of Commerce NOAA Technical Memorandum NMFS-SEFSC-470. Pp. 172.