Sexual Maturation Parameters Determined for Hapu'upu'u in the Northwestern Hawaiian Islands

A study by NOAA scientists has shown that hapu'upu'u Epinephelus quernus, the lone Hawaiian-endemic species of grouper, mature first as females, and that later some mature females transform to become males. The new results pertain to specimens of hapu'upu'u from the Northwestern Hawaiian Islands (NWHI). The hapu'upu'u is a member of the 'Deep-7' bottomfish species complex in the Hawaiian Archipelago that is harvested commercially and recreationally in the main Hawaiian Islands under Federal and State regulations. A bottomfish fishery in the NWHI ended on January 1, 2010.

Hapu'upu'u, <em>Epinephelus quernus</em> (Source: John E. Randall, FishBase)
Hapu'upu'u, Epinephelus quernus (Source: John E. Randall, FishBase)

Histological slides from the gonads of more than 600 individual hapu'upu'u were prepared and examined microscopically. The specimens were collected in all months of the year, during several timer periods (1978-1981, 1992-1993, and 2005-2008) and from multiple reefs and banks of the NWHI.

Microscopic criteria were used to identify the sex of the specimens and to establish that hapu’upu’u in the NWHI are protogynous (female-first sex-changing) hermaphrodites. There was no histological or other evidence for small mature males, suggesting that hapu’upu’u are monandrous (all males are sex-changed females). The adult sex ratio was strongly female-biased and conservatively estimated at more than 5 females to each male.

Complementary microscopic criteria also were used to assign a reproductive stage to each specimen and thereby estimate median body sizes (L50) at female sexual maturity and at sex change from adult female to adult male. The L50 at sexual maturation and sex change were 589 ± 8 mm (95% CI) total length (TL) and 895 ± 20 cm TL, respectively. The relationships are shown in the accompanying graphic.

Gonadosomatic indices constructed from relative gonad and body weights were used to describe the seasonality of spawning. Females demonstrated seasonality in reproductive activity. They began ripening in December and remained ripe through April; a lagged (February-June) spawning period was deduced from the proportion of females whose ovaries contained hydrated oocytes and/or post-ovulatory follicles that indicated imminent reproduction. There was no seasonality in weight of testes; the average weight of testes was only about 0.2 % of body weight—about an order of magnitude less than the average weight of ovaries, which peaked at 1-3 % of body weight.

A manuscript describing the work and discussing management implications of the species' reproductive life history has been drafted by researchers Ed DeMartini and Ryan Nichols of the Pacific Islands Fisheries Science Center and former PIFSC biologist Alan Everson (now with the NOAA Fisheries Pacific Islands Regional Office) for submission to the peer-reviewed journal Fishery Bulletin.

In the Northwestern Hawaiian Islands, hapu'upu'u first become mature as females at a length of about 
             580 mm, on average. Some mature females become mature males; the gender shift occurs at a 
             length of about 895 mm, on average.
In the Northwestern Hawaiian Islands, hapu'upu'u first become mature as females at a length of about 580 mm, on average (Fig. 1). Some mature females become mature males; the gender shift occurs at a length of about 895 mm, on average (Fig. 2). Evidence to date indicates that all males start as females.