Age, growth, reproduction and management of Southwestern Atlantic’s largest and endangered herbivorous reef fish, Scarus trispinosus Valenciennes, 1840

Abstract

The Brazilian-endemic greenbeack parrotfish, Scarus trispinosus Valenciennes, 1840, is the largest herbivorous reef fish in the South Atlantic. Following the sharp decline of large carnivorous reef fishes, parrotfishes (Labridae: Scarinae) were progressively targeted by commercial fisheries in Brazil, resulting in a global population decline of 50% for S. trispinosus. Most of its remnant population is concentrated in the Abrolhos Bank, where the present study was conducted. We present novel information on age, growth and the reproductive cycle of S. trispinosus, based on 814 individuals obtained from commercial fisheries’ landings and scientific collections, between 2010 and 2013. Sex ratio was biased toward females (1:8), and spawning occurred year-round with discrete peaks in February-March and June-December. Increment analysis indicated annual deposition of growth rings in otoliths, which presented 1–22 rings. The asymptotic length at which growth is zero (L∞) was estimated from a Bayesian logistic regression at 85.28 cm, growth rate (K) at 0.14 year−1, and the theoretical age at zero size (t0) at 0.16. Subregional demographic structuring was detected, with predominance of slower-growing individuals in shallower inshore reefs and predominance of faster-growing and older individuals in deeper offshore sites. We demonstrate that S. trispinosus is highly vulnerable to over-exploitation due to its large size, long live and slow-growth, and review the management measures proposed since its Red List assessment in 2012.

Demography of the largest and most endangered Brazilian parrotfish, Scarus trispinosus, reveals overfishing

“…Most parrotfishes are considered 'short-lived' with a life span between 5 and 23 yr ) compared with other roving herbivores such as surgeonfishes (Acanthuridae) that reach up to 40+ yr old . Evidence suggests that S. trispinosus may reach up to 22 yr old and 86 cm TL on the Abrolhos Bank (Freitas et al 2019), and 20 kg TW in Arraial do Cabo (RJ), southeast Brazil (Bender et al 2014). This demonstrates that the species is relatively larger and longer-lived among parrotfishes, particularly those from the genus Scarus, which usually reach maximum ages between 5 and 15 yr and maximum sizes around 40 cm TL .…”

“…gov/ erddap/ griddap/ erdHadISST. graph; Freitas et al 2019). Maximum sizes and ages at lower latitudes are expected to be lower, since age-based demography of reef fishes varies with sea temperature (e.g.…”

“…However, the complete absence of males in the sample gives considerable support for a monandric protogynous sexual pattern, given that no primary males were observed across all size classes in our study area. The presence of small and potentially primary males (<L 50 ) in the Abrolhos Bank, however, suggests that S. trispinosus may have a diandric protogynous sexual pattern (Freitas et al 2019), but further investigation is needed. The presence of inactive females in the population suggests that fish do not all spawn at the same times and/or locations, or not all females spawn in all years (Pears et al 2006).…”

“…Photomicrograph of a histological section of Scarus tri spinosus ovaries: (A) immature female, (B) re generating mature female however, was already recorded in deeper outer shelf reefs (between 50 and 60 m deep) of the same region (Feitoza et al 2005), suggesting that deeper habitats may harbor even larger and older individuals. In the Abrolhos Bank, male S. trispinosus become more frequent in the population from age 8 onwards, with older individuals found mainly in offshore reefs composed of rhodolith beds between 24 and 65 m deep (Bastos et al 2013, Freitas et al 2019). In the present study, older age classes were probably under-sampled due to constraints in sampling deeper areas, which may explain the complete absence of males among the samples.…”

“…In some areas, S. trispinosus is even considered ecologically extinct based on how rare it has become (Floeter et al 2007, Bender et al 2014). However, information on the life-history traits of this species that are critical to fisheries management and conservation, including growth, size and age at maturity, is still scarce (but see Freitas et al 2019) or unknown, such as size and age at sex change, thus perpetuating the threat to this species.…”