Jorge Eduardo Lins Oliveira

Atol das Rocas: an oasis for Octopus insularis juveniles (Cephalopoda: Octopodidae)

The habitat, population density, distribution and diet of Octopus insularis Leite & Haimovici, 2008 were studied in the Atol das Rocas Biological Reserve, based on visual census carried out in fixed quadrants. For each octopus den, we collected data on octopus size, substrate, type of den, and food remains around it. A total of 100 octopus dens were found within the fixed quadrants. The highest density occurred at Mapas area (0.30 inds/100 m2) and the lowest at Crista Algalica (0.07 inds/100 m2). The preferred den type was the one on the reef bed (69%), reinforcing the importance of rocky substrates for this species. A total of 454 food items, classified into 22 distinct taxa, were collected. The class Crustacea was best represented, accounting for 70.5% of the total prey, followed by Gastropoda (22.4%), Bivalvia (6.4%) and Cephalopoda (0.7%). Five species represented more than 80% of all findings: the crabs, Xanthodius denticulatus White, 1848 (38.5%), Microphrys bicornutus (Latreille, 1825) (18.5%) and Mithrax forceps Milne-Edwards, 1875 (7.0%); and the gastropods Hipponix sp. (9.3%) and Collisella sp. (8.4%). The overwhelming preference for small crabs shows that O. insularis is a specialized predator. The strong presence of juveniles inside the ring reef indicates the importance of this location for the development of this octopus species in northeastern Brazil.

Gonadal development and reproductive strategies of the tropical octopus (Octopus insularis) in northeast Brazil

Octopus insularis inhabits shallow waters along the coast and oceanic islands of northeastern Brazil, where it is the main target of commercial fishing of octopuses. This study aims to investigate the hypothesis that the tropical O. insularis has a distinct gonadal development and reproductive features when compare to its congener O. vulgaris from the subtropical regions. In order to describe its reproductive development, 545 octopuses were collected in the Northeastern Brazil. A good correspondence was observed between the gonad morphology and its histological structure. Oocytes in different development stages were observed in mature females. Most female in early maturity stages had sperm stored in the spermathecae, indicating that females copulate when still immature. There was no correlation between testis weight and the Needham complex, suggesting a protracted period of spermatophore production. Octopus insularis has a general gonadal development pattern similar to O. vulgaris, however, some differences were observed, as maturation at a smaller size, probably associated to a shorter life, and lower fecundity. The distinct reproductive features of O. insularis seem to be related to less variable conditions in the tropical environments. Management should take into account the differences and establish specific rules for the Northeast Brazil octopus fisheries.

The use of Local Ecological Knowledge as a complementary approach to understand the temporal and spatial patterns of fishery resources distribution

BackgroundAcquiring fast and accurate information on ecological patterns of fishery resources is a basic first step for their management. However, some countries may lack the technical and/or the financial means to undergo traditional scientific samplings to get such information; therefore affordable and reliable alternatives need to be sought.MethodsWe compared two different approaches to identify occurrence patterns and catch for three main fish species caught with bottom-set gillnets used by artisanal fishers from northeast Brazil: (1) scientific on-board record data of small-scale fleet (n = 72 trips), and (2) interviews with small-scale fishers on Local Ecological Knowledge (LEK) (n = 32 interviews). We correlated (Pearson correlations) the months cited by fishers (LEK) as belonging to the rainy or to the dry season with observed periods of higher and lower precipitation (SK). The presence of the three main fish species at different depths was compared between LEK and SK by Spearman correlations. Spearman correlations were also used to compare the depths of greatest abundance (with the highest Capture per Unit Effort - CPUE) of these species; the CPUEs were descendly ordered.ResultsBoth methods provided similar and complementary bathymetric patterns of species occurrence and catch. The largest catches occured in deeper areas, which also happened to be less intensively fished. The preference for fishing in shallower and less productive areas was mostly due to environmental factors, such as weaker currents and less drifting algae at such depths.ConclusionBoth on-board and interview methods were accurate and brought complementary information, even though fishers provided faster data when compared to scientific on-board observations. When time and funding are not limited, integrative approaches such as the one presented here are likely the best option to obtain information, otherwise fishers’ LEK could be a better choice for when a compromise between speed, reliability and cost needs to be reached.

Identifying fish diversity hot-spots in data-poor situations

One of the more challenging tasks in Marine Spatial Planning (MSP) is identifying critical areas for management and conservation of fish stocks. However, this objective is difficult to achieve in data-poor situations with different sources of uncertainty. In the present study we propose a combination of hierarchical Bayesian spatial models and remotely sensed estimates of environmental variables to be used as flexible and reliable statistical tools to identify and map fish species richness and abundance hot-spots. Results show higher species aggregates in areas with higher sea floor rugosity and habitat complexity, and identify clear richness hot-spots. Our findings identify sensitive habitats through essential and easy-to-use interpretation tools, such as predictive maps, which can contribute to improving management and operability of the studied data-poor situations.