ABSTRACT
Functional morphology investigates the relationships between morphological characters and external factors, such as environmental, physical and ecological features. Here, we evaluate the functional relationships between body shape and trophic ecology of a tropical demersal marine fish community using geometric morphometrics techniques and modelling, hypothesizing that shape variables could partially explain fish trophic level. Fish were collected over the continental shelf of northeast Brazil (4-9°S). Analysed fish were distributed into 14 orders, 34 families and 72 species. Each individual was photographed in lateral view, and 18 landmarks were distributed along the body. A principal component analysis (PCA) applied on morphometric indices revealed that fish body elongation and fin base shape were the main axes of variation explaining the morphology. Low trophic levels (herbivore and omnivore) are characterized by deep bodies and longer dorsal and anal fin bases, while predators present elongated bodies and narrow fin bases. Fin position (dorsal and anal fins) on the fish body is another important factor contributing to (i) body stability at high velocity (top predators) or (ii) manoeuvrability (low trophic levels). Using multiple linear regression, we verified that 46% of trophic level variability could be explained by morphometric variables, with trophic level increasing with body elongation and size. Interestingly, intermediate trophic categories (e.g., low predators) presented morphological divergence for a given trophic level. Our results, which can likely be expanded to other tropical and nontropical systems, show that morphometric approaches can provide important insights into fish functional characteristics, especially in trophic ecology.
Subject(s)
Fishes , Somatotypes , Animals , BrazilABSTRACT
Mycteroperca bonaci (black grouper) is one of the most sought species of grouper along its entire distribution, being a prime target for demersal line fisheries because of its high commercial value. Nonetheless, because of population declines the species is considered near threatened according to the IUCN red list. The present study aimed to determine the population parameters of M. bonaci, including growth, reproduction and mortality, and thus contributes to measures towards its conservation and management in the southwestern Atlantic. The sampling area is in the North Brazil Shelf, off Maranhão State, an area of intense fisheries development and yet poorly known. The large continental shelf harbours unique coral reef formations and has been declared an ecologically or biologically significant marine area (EBSA). Sampling on landing sites was carried out monthly between May 2017 and January 2019. A total of 137 black grouper specimens were sampled from commercial landings of artisanal fisheries. The size of the specimens ranged from 44 to 157 cm, and the weight varied from 0.976 to 54 kg. The length-weight was established: log(TW) = -11.26 + 3.01log(TL). Histological analysis of the gonads confirmed only the presence of female individuals, and the occurrence of individuals in the sexual transition was not recorded. Higher GSI values and higher frequency of spawning capable staged individuals occurred during the months of June to August, indicating spawning peaks. The estimated age of sexual maturity A50 for females was 4.62 years ( x _ 93 cm-TL). The growth parameters for the Von Bertalanffy model were TL∞ (cm): 185.5, k: 0.04, t0 (year): -4.75 (t0 not fixed) and TL∞ (cm): 141, k: 0.11 (t0 = 0 fixed). The total estimated mortality rate (Z) according to catch length presented a Z value = 0.11, and the natural mortality was M = 0.04 year-1 . This is the first study on the age and growth of M. bonaci in the SWA, a region where the species is considered as endangered according to Brazil's red list regional assessment. Only females were present in the samples, results that suggest either differential capturability of sexes because of distinct patterns of behaviour or distribution or an effect of selective mortality upon larger and older individuals, as the species is described as a protogynous hermaphrodite. This indicates the need to closely manage this population to avoid collapses. Recovery plans that have been planned by the Brazilian government but not yet implemented for the species must be put into practice to avoid progressive decline as fisheries target more remote areas.
