Advances in population monitoring of the mangrove ‘uçá’-crab (Ucides cordatus): reduction of body size variance for better evaluation of population structure and extractive potential

ABSTRACT

Monitoring focusing on target species is an important tool to better understand biodiversity. The density, size, extractive potential and population structure of Ucides cordatus reflects the conservation of the mangrove ecosystem. The Federal Brazilian Institution of Biodiversity Conservation (ICMBio) defined a protocol to standardize and estimate these parameters using an indirect method that does not depend on the capture of individuals of a species. In this protocol are used models to adjust diameter of crabs' gallery (DG) measures into largest carapace width (LC). Because this relationship (LC vs. DG) can differ according to geographic positions, the present study assessed it in three Brazilian mangrove areas (north, north-east, and south-east regions). Linear models of this relationship were compared between sexes, and also applied as a single model considering these Brazilian localities as a fixed factor and in three independent models for each locality separately. Equations did not differ significantly between sex and could be represented as one to each locality. However, a simpler linear model not including mangroves as fixed factors can be used to represent the entire latitudinal gradient, promoting a homogeneity of the estimation error, due to cover the entire body size (LC) variation of the Ucides cordatus crab.

HIGHLIGHTS

• Body size and population structure of Ucides cordatus can be successfully estimated by measurements of the burrows, using an indirect method.

• Indirect method is advantageous in continuous monitoring, avoiding the higher impact promoted by capture in a specific mangrove area.

• Regional models can be more accurate, but a single and simpler model representing the entire latitudinal gradient can promote homogeneity of the estimation error and is more manageable.

KEYWORDS:

• Biometry
• conservation
• fishery management
• monitoring
• sustainable development

Acknowledgements

Our gratitude to UNESP – IB/CLP, UFRB – CCAAB, and UNAMA for providing all laboratory facilities for data analysis in the Brazilian states of São Paulo (MAAP), Bahia (SSR) and Pará (MMTS), respectively. We are also very grateful to Dr Gustavo M. Mori (UNESP IB/CLP), who performed previous statistical analysis carried out, as well as during the reading and review of this work.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This study was supported by the ‘Fundação de Amparo à Pesquisa do Estado de São Paulo’ – FAPESP (‘Uçá’ Project, Phases 1–4 to MAAP: # 1998/6055-0, # 2002/05614-2, # 2009/14725-1, and # 2014/50438-5), by the ‘Conselho Nacional de Desenvolvimento Científico e Tecnológico’ – CNPq (Research Fellowship Grant to MAAP: #303286/2016-4 and # 305957/2019-8; Graduate Grant to TAM: # 88882.424479/2019-01), and by the Project ‘Desenvolvimento do Índice de Qualidade das Florestas de Manguezais Baía de Todos os Santos (BTS), Bahia’: # 441389/2017-1.