Growth and production of the dominant pelagic fish, Acanthobrama terraesanctae, in subtropical Lake Kinneret, Israel

Acanthobrama terraesanctae (local name lavnun), an endemic planktivorous cy prinid, dominates total fish numbers (>80%) in Lake Kinneret, and may have a significant top-down impact on the lake ecosystem. The length of young-of -the-year fish calculated from the von Bertalanffy equation agreed with hel d observations of juvenile growth. An unusual bi-modal length-frequency dis tribution observed in May 1993 provided additional help in age identificati on. Males grew more slowly than females and reached a lower maximum length. Total mortality coefficients (exponents) of males and females >12 cm (mini mal legal size of fish in the catch) were similar (c. 1.52). An average coh ort reaches maximum biomass during its second year. Maximum production is c reated at the end of the second year. The production:biomass ratio of the p opulation was 1.16, and 36% of total lavnun standing stock was taken by fis hing. From the late 1980s to early 1990s, when standing stock and populatio n structure were stable, the average harvest of 1000 t was consistent with a total lavnun biomass of 2800 t, which constitutes 50-70% of the total fis h stock measured acoustically in the lake. Such a biomass could be sustaine d by the known production of zooplankton. Absence of verified growth data f or lavnun contributed to the collapse of the fishery in 1993, because it ha mpered timely revision of fishery policy in response to the drastic changes in the lavnun stock in 1992, (C) 1999 The Fisheries Society of the British Isles.