Implications of big, old, fat, fecund, female fish (BOFFFFs) for the reproductive potential of a demersal teleost stock

Abstract

The ‘big old fat fecund female fish’ (BOFFFF) hypothesis suggests that larger, older female fish contribute disproportionately more to the reproductive potential of a stock than smaller, younger female fish. As fishing typically differentially removes larger, mature fish, this can negatively impact reproductive potential and impair the recovery of a depleted stock. In this study, the BOFFFF hypothesis was explored quantitatively for the endemic West Australian dhufish (Glaucosoma hebraicum) by estimating the relationships between total length (TL) of females and spawning season duration, spawning frequency and oocyte size. The impacts of these size effects on estimates of reproductive potential of the G. hebraicum stock were also explored using a per-recruit analysis. Larger (900 mm TL), older mature female G. hebraicum were shown to spawn for a longer duration (six versus two months) and on more occasions (155 versus 60 times) than smaller (350 mm TL), younger mature fish, and thus these larger females have higher annual fecundity. Larger, older mature G. hebraicum also spawn, on average, significantly larger oocytes with greater estimated energy content (474.6 μm diameter and 0.234 J versus 379.9 μm and 0.140 J). Due to these size effects, reproductive output of G. hebraicum scales hyperallometrically with fish body mass, rather than isometrically. Not accounting for these size effects in per-recruit analysis resulted in higher estimates of stock reproductive potential and thus stock status. Such overestimates, if used to inform management, have the potential to result in harvest rates being set too high which, in turn, could thus affect stock sustainability.