Abstract Carapace width-carapace length (CW/CLRs), carapace width-weight (CW/WRs), and carapace length-weight (CL/WR) relationships are presented for the portunid species Callinectes bocourti A. Milne Edwards, 1879, Callinectes danae Smith, 1869, and Callinectes ornatus Ordway, 1863 from the northern coast of Brazil. A total of 85 crabs were collected between May and October 2015 in intertidal zones of the Caeté, Pirabas and Salinas estuaries. All species had strong relationships between measurements with a coefficient of determination (r 2) ranging between 0.97 and 0.99. The variable most strongly related to CW was CL with 99 % of the variability provided by C. ornatus. These relationships are a useful tool for field ecologists to estimate length and/or mass of portunid species, and it is not necessary to euthanize the organism to collect body measurements. Additionally, this study describes the first reference of CW/CLRs and CL/WRs for these portunid species in the region. The Callinectes species in Amazon estuaries are still poorly studied, and there is a need for monitoring their stocks due to its importance for artisanal fishery. The present data are important for supplying biological information required for an adequate management of this fishery.

RESUMO As relações entre o tamanho corporal do peixe e as medidas do otólito sagitta foram calculadas pela primeira vez para 15 espécies pertencentes a seis famílias de peixes demersais da costa norte do Brasil. Um total de 220 peixes foi amostrado da captura acidental realizada pelo arrasto de fundo da frota pesqueira industrial de camarão entre agosto e setembro de 2016. Todas as espécies apresentaram fortes relações entre as medidas do otólito e o comprimento total do peixe, com o coeficiente de determinação (r 2) variando entre 0,71 e 0,99. A variável mais fortemente relacionada ao comprimento total dos peixes foi o comprimento do otólito sagital (OL) com 98% da variabilidade. Essas relações representam uma ferramenta útil para estimar o comprimento e a massa de peixes predados a partir dos otólitos encontrados no conteúdo estomacal de predadores marinhos.

ABSTRACT The relationships between fish size and sagitta otolith measurements were calculated for the first time for 15 species belonging to six families from the northern Brazilian coast. A total of 220 fish were sampled from the bycatch landed by the bottom-trawl industrial shrimp-fishing fleet between August and September 2016. All species had strong relationships between otolith measurements and fish total length with the coefficient of determination (r 2) ranging between 0.71 and 0.99. The variable most strongly related to fish total length was found to be the sagittal otolith length (OL) with 98% of the variability. These relationships are a useful tool to estimate length and mass of preyed fish from otoliths found in stomach contents of marine predators.

Resumo Cinquenta e nove relações peso-comprimento (RRC) e comprimento-comprimento (RCC) foram estimadas para 18 espécies de peixes, distribuídos em 10 famílias. Os espécimes de peixes foram capturados em poças de maré de 21 locais amostrados, ao longo de um trecho de 4.900 km da costa brasileira, entre as latitudes 00° e 22°S, durante o ano de 2012. Este estudo apresenta a primeira referência disponível para 5 espécies de peixes (Gobiesox barbatulus, Bathygobius geminatus, Labrisomus nuchipinnis, Malacoctenus delalandii, Lutjanus alexandrei) em RCC e 6 (Gobiesox barbatulus, Bathygobius geminatus, Hypleurochilus fissicornis, Omobranchus punctatus, Entomacrodus vomerinus, Diplodus argenteus) em RPC.

Abstract Fifty-nine length-weight (LWR) and length-length (LLR) relationships were estimated for 18 fish species, belonging to 10 families. The fish specimens were captured in rockpools of 21 sites along a stretch of 4,900 km of the Brazilian coast, between latitudes 00° and 22°S, in 2012. This study represents the first reference available for five fish species (Gobiesox barbatulus, Bathygobius geminatus, Labrisomus nuchipinnis, Malacoctenus delalandii, Lutjanus alexandrei) in LLR and six (Gobiesox barbatulus, Bathygobius geminatus, Hypleurochilus fissicornis, Omobranchus punctatus, Entomacrodus vomerinus, Diplodus argenteus) in LWR.