MTN 143:14-15 Flying Fish Egg Harvest off Keelung, Taiwan Uncovers Occurrence of Pelagic-Phase Green Turtles

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Flying Fish Egg Harvest off Keelung, Taiwan Uncovers Occurrence of Pelagic-Phase Green Turtles

Ka-yan Ng¹, Tien-Hsi Chen² & George H. Balazs³
¹Department of Biology and Chemistry, City University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China (E-mail: kayng64-c@my.cityu.edu.hk; kayan.ng.connie@gmail.com);
²Institute of Wildlife Conservation, National Pingtung University of Science and Technology, Taiwan (E-mail: chenth@mail.npust.edu.tw);
³Oceania Regional Vice Chair, IUCN SSC Marine Turtle Specialist Group, Honolulu, Hawaii, USA (itsahonuworldinhawaii@hotmail.com)

Fish eggs are considered a nutritionally rich delicacy by humans worldwide and especially in East Asia, including Taiwan. Flying fish eggs that are flavored and colored are known as “tobiko.” Sea turtles are also known to seek out and consume fish eggs in oceanic habitats (Fritts 1981; Richardson & McGillivary 2001; Parker et al. 2005, 2011; Witherington et al. 2012). However, the extent and details of such foraging, like many aspects of sea turtle surface- pelagic ecology, have not been widely documented. In March 2014, we had the unique opportunity to learn about traditional flying fish egg harvest and associated sea turtle foraging habitats from the local Taiwanese fishermen in Keelung (25.131°N, 121.737°E), which is located at the northern end of Taiwan (Fig. 1).

Figure 1. A map showing the locations of Keelung, the East China Sea and the extent of the Kuroshio Current.

A seasonal harvest for the eggs of flying fish from the family Exocoetidae occurs in the offshore waters of Keelung in the Pacific around the time of the Chinese lunar Tuen Ng festival (in Chinese, 端午節), which begins in mid-May and continues to the end of July until the allowable amount of eggs are collected throughout Taiwan is reached (e.g., 350 tons in 2014). The harvest by local fishermen coincides with the occurrence of Sargassum drifts, the natural substrate used by flying fish to deposit eggs in masses that hang down into the water column. The fishermen construct artificial rectangular mats or rafts made of rice straw with synthetic foam strips attached along the edges for floatation (Fig. 2 A-C). Four strips of rice straw mats 15 cm wide are attached longitudinally along the midline of the rafts and hang down into the water, thereby creating more surface area for egg attachment. These mats, measuring about 2 m by 3 m by 1-2 cm thick, are laid out on the sea surface attached to one another in areas where floating Sargassum mats occur. The location of these artificial mats varies annually and may be up to 50 km offshore, depending on the location of the Sargassum drifts. The mats are lifted daily to collect the voluminous quantity of eggs that accumulate on them (Fig. 2 D). These mats are used in one season only and replaced with new ones the following year. We learned from the fishermen that during the egg harvest, green turtles (Chelonia mydas) of approximate carapace length 20 cm have been observed under the mats, presumably feeding on the fish eggs or other organisms associated with the fishing mats; they may possibly be using the mats as shelter as well. The local fishermen appear not to be bothered by the presence of the green turtles, but instead are more focused on harvesting the fish eggs for their business. We observed that the remains of flying fish eggs were gathered on artificial cotton-like materials, likely ocean debris, during our visit, suggesting that the spawning season of flying fish in this region started as early as March prior to the fishery opening. Such spawning grounds established in floating Sargassum or other artificial mats may provide energy-rich food that may be consumed by green turtles.

Figure 2. Panels A-C: Artificial rectangular mats or rafts made of rice straw with synthetic foam strips used to attract flying fish to deposit eggs. Panel D: Flying fish eggs (roe).

In the western North Pacific, Sargassum drifts that serve as habitats for diversified fish communities are known to occur off the southeast coast of Japan near the Kuroshio Current (Uehara et al. 2006) and in the Tohoku area of northeastern Japan along the Kuroshio Extension (Safran & Omori 1990). Komatsu et al. (2008) also reported that drifting seaweed mats, which were exclusively Sargassum horneri , proliferated in March through May and were found in waters off Zhejiang, China between the continental shelf peripheral area and the Kuroshio oceanic front within the eastern East China Sea (Fig. 1). This implies that the seasonal occurrence of Sargassum mats in the offshore waters of Keelung that serve as foraging grounds for green turtles may also be affected by the Kuroshio Current.

We highlight the importance of incorporating local people and their knowledge in creating novel opportunities for sea turtle exploratory studies. Such trustful and respectful communication brings insight into what may be the first-documented habitat use of surface-pelagic green turtles in the Sargassum drifts and man-made floating mats off Keelung. We intend to visit Keelung again in the future to talk with more fishermen for greater insights into their rich oceanic work life that is shared with sea turtles. In addition, visual surveys by observers on fishing boats should be conducted as far as possible to collect, verify and establish baseline information about sea turtles found in and around the fishing mats. The analyses of genetic composition and oceanographic features may also add insights into the geographic natal origin of these pelagic-phase green turtles.

Acknowledgements. Ng and Balazs traveled to Taiwan as tourists at their own expense to visit with friends and experience Taiwanese culture in the Keelung region. Information gathered for this article was incidental to their leisure visit. We express our sincere gratitude to Dr. Peter Chen-Te Tseng of the Fisheries Research Institute in Keelung of Taiwan for his hospitality and the photos used in our article, and to Denise M. Parker, Marine Turtle Research Specialist of JIMAR, NOAA, for her input on the geographic distribution of flying fish species.

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