The world’s largest parrotfish has slow growth and a complex reproductive ecology

The bumphead parrotfish (Bolbometopon muricatum) is an iconic coral reef species of commercial, subsistence, and cultural value that has faced severe declines across the Indo-Pacific. In this study, we summarized the age-based biological characteristics of B. muricatum based on comprehensive surveys of a small-scale but high-yield fishery in Solomon Islands. We examined the full breadth of the life history, including pelagic larval duration, growth patterns throughout the ontogeny (post-settlement, juvenile, and adult), life span, mortality, age at maturity, and reproductive timing, as well as the size-dependent relative contribution of females to overall reproductive effort. The age-based demographic information supports a sexual pattern of functional gonochorism, whereby sex ratios were consistent throughout the lifespan. After a 25-day pelagic larval duration, the species growth pattern is comparatively slow and differs by sex, where males generally reach larger sizes at a given age than females. This growth pattern is associated with a long life span (at least 30 yrs) and low mortality rates (< 0.2 yr−1). Annual and lunar tracking of ovary weights confirmed cyclical spawning activity synchronized just prior to new moon throughout the year. Surprisingly, ovary weights declined in the largest and oldest females, implying lower reproductive output. Instead, lower ovary weights may reflect alternative mating strategies among the largest females whereby spawning frequency and strategy differs among females of different body sizes. These results highlight several novel and previously unknown aspects of this species’ biology, and our analyses generate information that can strengthen population models, facilitate stock assessments, support regional management, and provide a baseline for comparative work.