Distribuição, biomassas e ecologia de Macrouridae (Teleostei, Gadiformes) no talude continental do sul do Brasil, com ênfase em Coelorinchus marinii hubbs 1934 e Malacocephalus occidentalis Goode & Bean 1885

Abstract

Os peixes da família Macrouridae apresentaram uma das maiores biomassas entre os peixes demersais em cruzeiros de pesquisa no Sudeste-Sul do Brasil entre 300-600m. Embora não sejam alvo da pesca no Brasil, estão entre os principais itens no descarte da pesca de arrasto no talude, sofrendo impacto similar às espécies-alvo. Dados de dois cruzeiros sazonais de arrasto de fundo foram utilizados para analisar a distribuição, abundância, densidade, composição de comprimentos e estimativas de biomassas para sete espécies de Macrouridae do talude superior do Sudeste-Sul do Brasil: Coelorinchus marinii, Malacocephalus occidentalis, M. laevis, Lucigadus ori, Hymenocephalus billsam, Ventrifossa macropogon e V. mucocephalus. A biomassa total foi estimada em 5,5 e 8,3 kt, respectivamente, no inverno-primavera e verão-outono, das quais C. marinii e M. occidentalis compuseram 98%. Amostras mensais da pesca comercial foram adicionalmente usadas para analisar a ecologia trófica das quatro espécies mais abundantes no talude superior do Sul do Brasil. Foram analisadas a composição da dieta, as mudanças ontogenéticas, as variações sazonais, a sobreposição alimentar intra e interespecífica, a fauna parasitária e aspectos da morfologia funcional relacionada à alimentação. C.marinii consumiu presas pequenas da infauna, epifauna, plâncton, nécton e carcaças, aproveitando presas em manchas ou agregações. M.occidentalis apresentou certa seleção por presas maiores e de coluna d’água, além de caranguejos e carcaças. As duas espécies apresentaram mudanças ontogenéticas e variações sazonais na composição da dieta, ocasionando mudanças nos padrões de sobreposição, mas em geral houve uma baixa sobreposição alimentar. As distintas morfologias funcionais encontradas refletiram em diferenças na dieta e nas estratégias de alimentação das espécies. Para C.marinii e M.occidentalis foram contruídos mapas com densidades, áreas de desova, índice alimentar, proporções de sexos e de imaturos/maturos, que foram relacionadas aos processos oceanográficos, fornecendo uma visão sobre as estratégias de vida e processos que regulam os padrões de distribuição e abundância. Ambas as espécies apresentaram variação sazonal na extensão e localização das áreas de desova. A maioria das fêmeas de C.marinii estavam maturas (90%), sugerindo que assentam ao fundo simultaneamente à maturação e que os juvenis são pelágicos, enquanto M.occidentalis apresentou muitos juvenis e poucas fêmeas maturas, assentando ao fundo bem antes da maturação. São identificados e descritos três processos responsáveis pelos padrões de distribuição e abundância encontrados nestas espécies. Sugere-se que áreas encontradas com elevadas biomassas de Macrouridae (carniceiros) sejam causadas por zonas de ocorrência semipermanente de processos de mesoescala (e.g. vórtices). Esses processos aumentam a produtividade e possibilitam elevadas biomassas de organismos de vida-curta encontradas em camadas superiores, e por outro lado, aumentam a concentração, mortalidade e disponibilidade de carcaças desses organismos, favorecendo predadores carniceiros. Esses processos podem ser responsáveis por inconsistências nas biomassas de magafauna e macrofauna encontradas em alguns estudos, onde biomassas de megafauna foram da mesma ordem de grandeza ou maiores que as de macrofauna, contradizendo o princípio Eltoniano.

Macrourids are among the most abundant and diverse demersal fishes in all deep oceans, including the Southwestern Brazilian continental slope. Although not targeted by Brazilian fisheries, they suffer impact similar than the target species, being among the most discarded fishes by deep bottom trawling. Trophic Ecology: Data from research surveys and commercial fishing were used to analyze the trophic ecology of four species inhabiting the upper slope of southern Brazil: Coelorinchus marinii, Malacocephalus occidentalis, M. laevis and Lucigadus ori. For the two abundant ones, ontogenetic changes, seasonal variations, intra- and interspecific dietary overlap, parasite fauna and aspects of functional morphology are also described. C.marinii had an extremely diverse diet, preying infauna, epifauna, plankton, necton and carcasses. M.occidentalis fed on larger and nektonic prey, but also included crabs and carcasses in the diet. Both species showed ontogenetic shifts and seasonal variations in diet composition, both leading to changes in intra- and interspecific diet overlap patterns. Species showed quite distinct feeding anatomy and proportions of body with mouth size, reflecting on feeding strategies. There was little interspecific food overlap. In most cases when the diet was more similar there was a spatial segregation. The coexistence of these species appears to be facilitated by the development of different functional morphologies and feeding strategies. A considerable portion of the diet of these species is due to the consumption of carcasses of pelagic and mesopelagic organisms, and even insects, bypassing the benthic trophic web. Conservative (minimum) estimates of the mean weight of carcasses in diet ranged from 3 to 20%, increasing with the size of the predators and towards deeper waters. C.marinii showed a lower consumption of carcasses and a high proportion of mesopelagic fishes and cephalopods, however, the analysis of the feeding morphology and prey size leads to believe that most of these two groups of prey were consumed as carcasses. This source of food bypass the detritus food chains and connect the concentrations of macrourids to fluctuations in the abundance of epi and mesopelagic organisms and to oceanographic processes that increase their concentration and mortality (e.g. mesoscale anticyclonic eddies). Distribution, Biomass and Oceanography: Data from two seasonal bottom trawl surveys were used to provide information on distribution, abundances, densities, sizecomposition and biomass estimates for seven species: Coelorinchus marinii, Malacocephalus occidentalis, M. laevis, Lucigadus ori, Hymenocephalus billsam, Ventrifossa macropogon and V. mucocephalus. The total biomass was estimated in 5.5 and 8.3 kt respectively in winter-spring and summer-autumn. C.marinii and M.occidentalis comprised 98% of the biomass. For these two abundant species, surface maps were made with spawning areas, feeding index, sex and immature/mature ratios, and were related to oceanographic processes, providing insights on strategies and important processes regulating distribution and abundance patterns. Both species showed a marked seasonal variation in the extent and location of spawning areas. Most C.marinii females were mature (90%), suggesting an early maturation during pelagic phase and acquiring demersal habit just prior the onset of maturation, while M.occidentalis showed few matures females and settle to bottom well before maturity. Temperature rather than depth seems to be the main factor regulating the batimetric distribution of both species. We describe three processes responsible for distribution and abundance patterns found in these species. Differentpatterns of spatial segregation were found in both species, related with depth, sex and maturity. It is suggested that areas with high biomass Macrouridae (scavengers) are induced by zones of occurrence semi-permanent mesoscale processes (e.g. eddies). These processes increase productivity and enable large biomass of short-lived organisms found in the upper layers, and also increase the concentration, mortality and availability of carcasses, favoring scavenger predators. These processes may be responsible for inconsistencies in biomass of megafauna and macrofauna found in some studies, where biomass of megafauna was of the same order of magnitude or larger than macrofauna, contradicting the Eltonian principle. It is suggested that future studies attempt to relate mesoscale processes with the biomass of potential short-lived prey in surface waters and higher biomass of scavengers. This work highlights the importance of the study of ocean dynamics, combining biological and oceanographic observations, trying to understand the role of mesoscale physical processes on the distribution and abundance patterns of species.