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

Abstract

Many parrotfishes (Labridae: Scarinae) have life history traits, including late maturation and long lifespans, that make them vulnerable to overfishing. The greenbeak parrotfish Scarus trispinosus is the largest Brazilian endemic parrotfish and has been harvested in reefassociated fisheries along the coast. After a sharp population decline, S. trispinosus is now considered by the IUCN to be an Endangered species. We provide an assessment of age-based and reproductive biology for this species and discuss applications for fisheries management. We sampled 95 individuals from inshore and offshore reefs from Rio Grande do Norte state, northeast Brazil, both obtained from artisanal fishing landings and fishery-independent collections. All sampled specimens were females with fork lengths (FL) ranging from 8.1 to 55.9 cm and ages ranging from 0.3 to 7 yr, with estimated median maturity (L 50 ) of 39.2 cm FL and median age (A 50 ) of 4.2 yr. Size class distributions indicate that the inshore reefs are mostly inhabited by juveniles under L 50 , whereas the offshore reefs are inhabited by mature individuals, suggesting an ontogenetic habitat shift from inshore to offshore reefs around the timing of maturation. The fishing pressure on this species is concentrated in inshore reefs, therefore mostly on immature individuals, which may be severely affecting the reproductive capacity of this species. This information is useful to guide size-based fisheries management, such as regulating minimum capture size and fishing gears that capture individuals smaller than L 50 . Managing fisheries of endangered species with late maturity and complex reproductive cycles such as S. trispinosus is imperative to aid recovery.

Protecting nursery areas without fisheries management is not enough to conserve the most endangered parrotfish of the Atlantic Ocean

“…Overfishing may affect the demographic structure of parrotfish populations by modifying their vital rates of mortality and inducing species to change sex at smaller age and sizes 54,55 . This is especially problematic for a relatively larger, late maturing and longer-lived hermaphrodite parrotfish such as S. trispinosus 21,22 . MPAs may prevent some of these effects by exporting larger older individuals to surrounding areas, and/or by receiving recruits that can fully develop to www.nature.com/scientificreports/ adult sizes within MPA boundaries 6,56 .…”

“…Well-designed networks of MPAs can maintain source-sink population dynamics and its temporal variability if important habitats such as nurseries and breeding areas are effectively protected 5 . For S. trispinosus, which is known to undergo an ontogenetic habitat shift from inshore to offshore reefs, with juveniles being more abundant near the coast and mature adult individuals in deeper offshore reefs 21,22 , protecting inshore and offshore habitats is essential to maintain the species source-sink population dynamics. The Abrolhos Marine National Park (no-take) seems to be a good model of that, since it comprises both inshore and offshore portions.…”

“…59-B) regulated the species fishing under restrict rules, which included the ban on recreational fishing and fishing nets, determined spearguns as the only fishing gear allowed and a slot-size limit for catches between 39 and 63 cm total length. The proposed slot-size limit aims to protect both immature and older mature individuals (including most males) which are those with a greater reproductive capacity, according to the species' demographic traits 21,22 . The plan also proposes that fishing would only be allowed within multiple-use marine protected areas by authorized artisanal fishers, with continuous monitoring.…”

“…In each of the 28 sites, juveniles (i.e. individuals ≤ 10 cm of total length, TL, around 4 months old 22 ) and adults (i.e. individuals > 10 cm of TL) of S. trispinosus were counted through a nested stationary visual census technique 29 .…”

“…In Brazil, some parrotfish species have shown signs of depletion, mainly Scarus trispinosus, the largest southwestern Atlantic parrotfish endemic to Brazil 19 . The species has been intensively targeted in northeast Brazil [20][21][22] and was considered ecologically extinct in southern Brazil 19 . Currently, S. trispinosus is listed as Endangered by the International Union for Conservation of Nature 23 and by the Brazilian Red List of Endangered Species/BRL-EndS (Decree nº 445, Brazil's Red List, 2014), and was considered one of the most endangered parrotfishes in the world 24 .…”