Leonardo A. Venerus

The Reef-fish Fauna of the Northern Patagonian Gulfs, Argentina, South- western Atlantic

A checklist containing 29 species of reef fishes recorded at the gulfs San Jose and Nuevo in Argentina (~42o- 43oS) is provided. The reef-fish assemblages of the San Jose and Nuevo gulfs are a mix of warm-temperate fauna from the South-western Atlantic Province, and cold-temperate species from the South-American Province; however, warm- temperate fishes dominated in both gulfs. The presence of the families Bovichtidae, Eleginopidae, Nototheniidae, Congiopodidae, Sebastidae and Moridae distinguished the Patagonian region from the rest of the Atlantic coast.

Variability in Abundance of Temperate Reef Fishes Estimated by Visual Census

Identifying sources of sampling variation and quantifying their magnitude is critical to the interpretation of ecological field data. Yet, most monitoring programs of reef fish populations based on underwater visual censuses (UVC) consider only a few of the factors that may influence fish counts, such as the diver or census methodology. Recent studies, however, have drawn attention to a broader range of processes that introduce variability at different temporal scales. This study analyzes the magnitude of different sources of variation in UVCs of temperate reef fishes off Patagonia (Argentina). The variability associated with time-of-day, tidal state, and time elapsed between censuses (minutes, days, weeks and months) was quantified for censuses conducted on the five most conspicuous and common species: Pinguipes brasilianus, Pseudopercis semifasciata, Sebastes oculatus, Acanthistius patachonicus and Nemadactylus bergi. Variance components corresponding to spatial heterogeneity and to the different temporal scales were estimated using nested random models. The levels of variability estimated for the different species were related to their life history attributes and behavior. Neither time-of-day nor tidal state had a significant effect on counts, except for the influence of tide on P. brasilianus. Spatial heterogeneity was the dominant source of variance in all but one species. Among the temporal scales, the intra-annual variation was the highest component for most species due to marked seasonal fluctuations in abundance, followed by the weekly and the instantaneous variation; the daily component was not significant. The variability between censuses conducted at different tidal levels and time-of-day was similar in magnitude to the instantaneous variation, reinforcing the conclusion that stochastic variation at very short time scales is non-negligible and should be taken into account in the design of monitoring programs and experiments. The present study provides baseline information to design and interpret results from visual census programs in temperate reefs.

Genetic structure and different color morphotypes suggest the occurrence and bathymetric segregation of two incipient species of Sebastes off Argentina

Rockfishes of the genus Sebastes are extensively distributed in the Pacific and Atlantic oceans. Although the occurrence of two morphologically similar species in the Southern Hemisphere, Sebastes oculatus and Sebastes capensis, is now clearly established, the taxonomic status and phylogeographic patterns for the genus in the region have not yet been completely resolved. In this study, we provide new insights into the taxonomy and evolutionary relationships of rockfishes inhabiting the Southwestern Atlantic Ocean, off the coast of mainland Argentina, by combining mitochondrial DNA (mtDNA) control region sequences, microsatellite data, and color pattern analyses. Differences in coloration (“dark” and “light” fish) together with bathymetric segregation between color morphotypes were evident from fish collection and literature review. In addition, the mtDNA phylogenetic analysis and Bayesian clustering analysis using microsatellite data separated the fish into two distinct groups (FST = 0.041), most likely representing incipient species. Our results suggest that speciation-by-depth in the absence of physical barriers could be a widespread mechanism of speciation in Sebastes from both the Northern and Southern Hemispheres. Nevertheless, the degree of genetic differentiation found, added to the large number of individuals displaying high levels of admixture, points to the occurrence of incomplete reproductive barriers between color morphotypes. Beyond the taxonomic and phylogeographic implications of our findings, the occurrence of distinct groups of Sebastes off the coast of Argentina being targeted by different fisheries (angling and trawling) has consequences for the design and implementation of appropriate fishery regulations to avoid overharvest of either group.

Spatial dynamics of the Argentine sandperch, Pseudopercis semifasciata (Pinguipedidae), in temperate rocky reefs from northern Patagonia, Argentina

The choice of appropriate conservation strategies for reef fishes depends on their mobility, degree of site fidelity and residence times. Here we report the results of a small-scale mark–recapture and resighting study conducted to investigate the spatial dynamics of the Argentine sandperch, Pseudopercis semifasciata. This is the flagship species of the rocky-reef fish assemblage from northern Patagonia, which has been the target of uncontrolled fishing since the early 1950s. About 19% of the fish tagged were recaptured up to four years after tagging. In total, 180 of 218 recaptured fish stayed in the reef of tagging. Thirty-six of 57 recaptures made at known locations within popular fishing areas of San Jose Gulf, densely covered by patchy reefs, occurred within 100 m of the tagging site, up to 793 days after tagging. Six fish were recovered more than 1 km from where they were tagged. Smaller fish were more prone to relocate, and were recovered farther from the tagging site. Fish stayed in the reefs for periods longer than a year; larger males remained longer in the same reefs. Our results indicate that relatively small reserves (in the order of a few kilometres) could be effective at protecting P. semifasciata populations within the northern Patagonian gulfs.

The reproductive biology of Pinguipes brasilianus Cuvier, 1829 (Osteichthyes: Pinguipedidae) in temperate rocky reefs of Argentina

Pinguipes brasilianus is a conspicuous and abundant rocky-reef fish inhabiting the Northern Patagonian gulfs of Argentina, Southwest Atlantic. This study describes its reproductive biology in this region. We made macroscopic and histological descriptions of the testis and ovary development, analyzed the evolution of the gonadosomatic index (GSI) in both sexes throughout the year, and estimated fecundity and length at 50% maturity for females. Pinguipes brasilianus is a multiple spawner with indeterminate annual fecundity and an extended reproductive season, encompassing austral spring and summer. Low GSI values in males (monthly means ranged between 0.11% and 0.75%) and low relative fecundity in female fish (between 2 and 44 oocytes/g) are consistent with a need of close proximity between male and female during oocyte fertilization, sexual courtship and with spawning in pairs and/or within reef crevices. The estimated length at 50% maturity (± SD) for females was 15.22 ± 0.43 cm total length. Although P. brasilianus shares the main reproductive features of its congeneric species Pinguipes chilensis , male GSI and female length at 50% maturity in P. brasilianus were markedly lower than those reported for P. chilensis , while relative and batch fecundity were greater in fish of the same size.