Vol. 15: 251–260, 2012 AQUATIC BIOLOGY Published June 6 doi: 10.3354/ab00425 Aquat Biol Age validation, growth estimation and cohort dynamics of the bony flying fish Hirundichthys oxycephalus off eastern Taiwan Chih-Wei Chang1,2,*, Chung-Hui Lin3,*, Yung-Song Chen4, Meng-Hsien Chen5, Shui-Kai Chang3,** 1National Museum of Marine Biology and Aquarium, Pingtung 944, Taiwan, ROC 2Institute of Marine Biodiversity and Evolutionary Biology, National Dong Hwa University, Pingtung 944, Taiwan, ROC 3Institute of Marine Affairs, National Sun Yat-sen University, Kaohsiung 804, Taiwan, ROC 4Department of Animal Science, National Ilan University 260, Ilan, Taiwan, ROC 5Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan, ROC ABSTRACT: Flying fishes (Exocoetidae) are commonly found in the epipelagic zone and play an important role in Taiwan in maintaining the stability of the marine ecosystem, local culture and coastal fisheries. However, little is known about their biology and life history, even though several species are of important commercial value in western Pacific countries. Overexploitation of one of the dominant species, the bony flying fish Hirundichthys oxycephalus, is a critical issue in the fish- ery management and resource assessment of this species. In the present study, H. oxycephalus eggs were harvested off northeastern Taiwan, while adult fish were collected mainly off the south- eastern coast of Taiwan. We validated the daily periodicities of the growth increments in 3 otolith pairs based on the successive otolith examination of fish reared in the laboratory from fertilized eggs. The asteriscus was determined to be the most suitable otolith for age determination of the fish. Age (in days) was calculated by counting the number of growth increments on the mounted otolith and adding 11. By using a growth coefficient of 0.0075 d−1, the asymptotic length of these fish was estimated to be 253.86 mm. Back-calculated hatching dates indicated that an occurrence of the summer spawning cohort coincided with the known egg-fishing season off the northeastern coast. On the other hand, the source of the adult fishery off the southeastern coast originated from a new winter spawning cohort. The cohort dynamics of this species were found to be more compli- cated than previously thought. Our findings could be added to the information already known about the reproductive ecology of H. oxycephalus and used to improve the fisheries management of these fish. KEY WORDS: Hirundichthys oxycephalus · Otolith · Age and growth · Hatching date · Cohort dynamics Resale or republication not permitted without written consent of the publisher INTRODUCTION ally on small fish (Lipskaya 1987). The flying fish is also the main prey for the dolphinfish Coryphaena Flying fish belong to the family Exocoetidae and hippurus and various tunas (Rose & Hassler 1974, form an epipelagic group of fishes that are distrib- Oxenford & Hunte 1999, Wu et al. 2006). In addition uted worldwide in both tropical and subtropical to its fundamental ecological relevance, the flying waters (Bruun 1935, Oxenford et al. 1995). These fish is also an important component of traditional fishes are an intermediary in the bioenergetic trans- fisheries and is treated as a cultural emblem in the fer, where the flying fish exists as a low-level con- countries of the Caribbean Sea and the southern sumer feeding mainly on zooplankton and occasion- Pacific, as well as in South and Southeast Asia **These authors contributed equally to this work © Inter-Research 2012 · www.int-res.com **Corresponding author. Email: [email protected] 252 Aquat Biol 15: 251–260, 2012 (Zerner 1986, Dalzell 1993, Resosudarmo 1995, Potts Th228/Ra228 radiometric dating. Oxenford et al. (1994) et al. 2003, Blake & Campbell 2007). studied the age and growth of H. affinis by analyzing Among the 8 genera and 52 species of flying fishes the growth increments in the lapillus. Yoneyama in the world (Nelson 2006), 7 genera and 26 species (2001) used the asteriscus for determining the age of (Shao 2009, but this may increase to 29 species flying fish in the coastal waters off eastern Japan. according to Chang et al. 2012), are recorded mainly Ichi maru (2005) compared the growth increments in off the eastern coast of Taiwan, which is influenced both the sagitta and the lapillus of Cypselurus hete - by the Kuroshio Current. The primary target of the ru rus, C. hiraii and H. oxycephalus off the northeast- flying fish fishery in Taiwan is to capture adults by ern coast of Japan, with the lapillus being used to de - drive-in net, gillnet, and set net fisheries off the east- termine the age of the fish. Generally speaking, even ern and southwestern coasts of Taiwan. Another though the otolith pairs selected for age determina- important harvest of this fishery is flying fish eggs, in tion differed between studies, all otolith-related stud- which the ovulating fish attach onto artificial spawn- ies indicated that flying fishes were quite short-lived ing substrata in waters off the northeastern coast. and had a relatively rapid growth, which had been The fishing season for adult flying fish runs mainly previously indicated by the length-based method. from March to June off Taiwan’s east coast, with an As indicated above, about 50% of flying fishes are average annual catch of approximately 420 t. The distributed in the waters off Taiwan (Nelson 2006, egg fishery runs from April to July and has an annual Shao 2009, Chang et al. 2012), but none of them have harvest of 228 t (Anonymous 2010). yet been studied for age and growth. The aim of the The bony flying fish Hirundichthys oxycephalus is present study was to use otolith analysis to determine a widely distributed fish whose range is the Indo- the age and growth of the important bony flying fish West Pacific from the Arabian Sea to southern Japan, found off the eastern coast of Taiwan and to back- New Guinea and New South Wales, Australia. It is a calculate age to the spawning date to determine the relatively small-sized flying fish and is one of the cohort dynamics. In order to determine the age in main species of flying fishes in Taiwan. In north- days, the microstructure showing the daily rings in eastern Taiwan, their eggs are harvested primarily the otolith must be clearly visible. One of the 3 pairs for food consumption, while in southeastern Taiwan of otoliths — the sagitta, asteriscus or the lapillus — the adults are used as bait fish in the long-line and must be empirically designated as the most suitable trolling fisheries. The increased harvest pressure on for determining the age of that particular type of fish. both the adult populations as well as the eggs is due In addition, the first growth ring and the daily period- to overexploitation during the months of May and icity of the subsequent growth increments in the oto- June, and this has become a crucial issue for the lith should be rigidly validated. Thus, before collect- Department of Fisheries in Taiwan. To assess the sit- ing data from the wild-caught fish, we conducted a uation, managers will have to apply models such as laboratory control to test our ability to fulfill the survivor analysis, virtual population analysis and above-mentioned requirements. age-based stock assessment. All of these models require the use of parameters that are derived from the age and growth data from these fish. Also, the MATERIALS AND METHODS possible relationship between parents and recruits of this exploited species needs to be elucidated. How- Sampling design ever, there is a substantial lack of baseline studies pertaining to the biology and ecology of the flying A hatching experiment and an at-sea survey pro- fishes inhabiting the waters off the coast of Taiwan. gram were conducted to obtain flying fish samples The age and growth of the flying fishes Hirund - for the present study. Fertilized flying fish eggs for ichthys affinis of Barbados and Oxyporhamphus the hatching experiment were collected from the micro pterus of the Philippines have been studied artificial spawning substratum off Keelung Island using length-frequency distribution analysis (Lewis (25° 12’ 14.43” N, 121° 48’ 38.67”E) in northeastern et al. 1962, Yacapin 1991). Brothers (1980) confirmed Taiwan on 17 July 2009 (Fig. 1). Within a 5 h period, that the microstructure in the otolith of the Exocoeti- the eggs were transferred from the sampling site dae was suitable for age and growth studies. Bony partly to the laboratory at the College of Marine fishes have 3 pairs of otoliths, namely the lapillus, Sciences (CMS), National Sun Yat-sen University asteriscus and sagitta. Campana et al. (1993) esti- in southwestern Taiwan and partly to the Marine mated the longevity of H. affinis by using sagitta Research Station (MRS), Institute of Cellular and Chang et al.: Age, growth and cohort dynamics of flying fish 253 within the 46 rearing days in CMS, and 21 fish were Keelung sacrificed within 203 days in MRS for the daily peri- ▲Island odicity validation studies. The maximum lengths of 25ºN the reared fish were 46.9 mm and 78.6 mm in CMS MRS and MRS, respectively. For the at-sea surveys, flying fish were collected from the coastal waters of southeastern Taiwan at 4 sites: Hualien, Taitung, Lyudao and Lanyu (Fig. 1). ○ The majority of the fish samples were collected by ○○○ 24º ○○○○○○○○○ daytime gillnetting between April 2009 and March ○○○○ ○○ Hualien 2010 in Lyudao, on some occasions between April TAIWAN and November 2009 in Hualien and between April and July 2009 in Lanyu. A gillnet set was 3.6 m wide and consisted of 3 nets of 65, 70 and 120 m in length with mesh sizes of 5.6, 4.0 and 2.8 cm, respectively.