Egg Abundance and Spawning Biomass of the Hawaiian Anchovy or Nehu, Encrasicholinapurpurea, during 1984-1988 in Kaneohe Bay, Hawaii

Abstract

In Kaneohe Bay, Hawaii, nehu (Hawaiian anchovy, Encrasicholina purpurea) eggs were found primarily in areas where water depth was > 10-12 m and were infrequently encountered near reefs, shorelines, or other shallow areas. Eggs were usually most abundant near the centers of one or both of the two large basins; the more enclosed southern basin usually accounted for the majority of the total eggs present. Nehu eggs were present throughout the year, but abundance was usually higher between July and February or March. There was considerable shorter time-scale variation in egg abundance, but there was no apparent underlying periodicity other than the annual cycle. Egg abundance was poorly correlated with measured environmental factors; the only potential relationship was that abundance tended to be low during the season of strong northeast trade winds. Egg abundance in Kaneohe Bay was poorly correlated with abundance in Pearl Harbor, Hawaii, the other major area where nehu are found. Total numbers of eggs present in Kaneohe Bay reached about 109 during peaks. Based on available knowledge of nehu fecundity, spawning frequency, and sex ratio, the biomass of spawning females was about 2 t and that of all adults about 8 t during peaks of egg abundance. Catches of nehu by the skipjack tuna baitfishery were poorly correlated with estimates of adult standing crop, and most variation in catch was attributed to variation in effort. Annual catches, however, were about five times the highest estimates of adult biomass, and several monthly catches exceeded 8 t. The results indicate that postmetamorphic nehu move into and out of and perhaps between spawning and nursery areas such as Kaneohe Bay and that the total population is much larger than that present in enclosed areas at any given time. Consequently, further studies of the population dynamics of nehu and their interaction with the fishery should be conducted on an island-wide and probably archipelagowide basis.