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- Trophic interactions of two sympatric small pelagic fishes off the southern coast of AngolaPublication . Quiatuhanga, Domingas; Morais, Pedro; Teodosio, MariaNumerous small pelagic fish species are of great economic importance and link the lower and upper levels of the marine food web. The round sardinella Sardinella aurita and flat sardinella S. maderensis coexist along their distribution range in the southeastern Atlantic Ocean, where we hypothesise that they compete for similar prey. Thus, this study aimed to compare the trophic ecology of these species off the southern coast of Angola during the austral summer and winter, by determining their diet composition and overlap, feeding strategies, trophic positions, and evaluating the correlation between their feeding intensity and remote-derived chlorophyll a concentration (Chl-a) and sea surface temperature. The results demonstarte that both species are generalists and ingest a wide range of protistoplankton and metazooplankton taxa of distinct sizes. Both sardinellas show high flexibility and adaptability to prey availability, using both filter-feeding and particulate-feeding modes. The diets were dominated by diatoms and calanoid copepods in terms of relative abundances and frequencies of occurrence, respectively, in the stomach contents. Tintinnid ciliates, fish eggs, decapod larvae, euphausiids, cladocerans and cnidarians had high wet weight contributions. The diets overlapped by 64% overall, indicating moderate competition for food, with S. maderensis exhibiting a lower trophic position than S. aurita (2.98 versus 3.49). The feeding intensity of S. maderensis was positively correlated with Chl-a, and moderately negatively correlated with SST, suggesting that species is more influenced by environmental variables owing to its lower trophic position. Trophic interactions between the two species appear to be mediated by prey sizes and availability. These findings demonstate the value of satellite-derived data as proxies to estimate the feeding intensity of these species, which will be useful to formulate regional ecological models or to predict the stock trends of S. maderensis in particular.
- Reproduction traits and strategies of two Sardinella species off the Southwest Coast of AfricaPublication . Quiatuhanga, Domingas; Morais, Pedro; Krug, Lilian; Teodosio, MariaSmall pelagic fishes such as Sardinella aurita (Valenciennes, 1847) and Sardinella maderensis (R. T. Lowe, 1838) are key intermediate-level components of the marine food web of the southwestern African coast. Their biomass off Angola has shown significant interannual variability, and information about their reproduction is insufficient in the region for adequate stock management. Thus, we aimed to unveil the reproduction period and reproductive traits of these two Sardinella species and establish a link with the prevailing ocean temperature conditions. Adult fish samples were obtained monthly from artisanal and semi-industrial fleets, and the ichthyoplankton samples were collected with a Hydro-Bios Multinet off southwest Angola by Instituto Nacional de Investigação Pesqueira (Angola). The macroscopic inspection of gonads showed that females of both species were more abundant than males. The gonadosomatic index and maturity stages indicate that S. aurita spawns during the Austral summer (December through March), while S. maderensis has a longer spawning period, from October to April. The spawning peak occurs in February for S. aurita and S. maderensis. The mean monthly condition factor of both species was high before and after spawning seasons. The females of S. aurita reach sexual maturity at a smaller size than males, and 50% of the population reaches sexual maturity at a total length of 31.3 cm. The males of S. maderensis reach sexual maturity at a smaller size than females, and 50% of the population reaches sexual maturity at a total length of 28.4 cm. We also found that both species use the southern coast of Angola as a spawning area during the Austral summer and avoid the area during periods of intense upwelling. Currently, these species are managed as a single unit, and the minimum capture size is set at 22 cm, well below the size at sexual maturity registered in the study area. Therefore, we strongly recommend increasing the minimum capture size to guarantee long-term stock viability.