Highlighting growth regulation processes in fish populations by a simplex simulation approach: application to Merluccius hubbsi stocks in the Southwestern Atlantic

A new simplex-based simulation approach (Spx) was developed to highlight multidirectional and multi-scale relationships between morphometric variables helping to functionally differentiate biological (fish) groups for better stocks definition and monitoring. Application concerned Merluccius hubbsi sampled in 1968–1972 and 2004 in six Southwestern Atlantic areas. Simulation results highlighted negative trends opposing front to back compartments indicating competition for body biomass distribution. However, top and bottom parts within these compartments were positively correlated indicating cooperative processes in favour of target local growth regulation. Positive and negative trends of growth regulation were also highlighted at lower body scale, notably between smaller components constituting body front compartment. On a geographical scale, average regulation levels of same morphometric variables showed monotonic or alternated variations between successive fish groups. This highlighted target and modulated growth regulations governing biomass distribution in different body parts by geographical-dependent ways. Under dynamical aspect (1968–1972 vs. 2004), growth regulation of mouth tended to increase with time leading to conclude on morphometric responses of M. hubbsi to overfishing pressure. Spx results were confirmed by several traditional approaches which showed less integrative aspect.

First data on the age and growth of Brazilian flathead Percophis brasiliensis (Pisces: Perciformes) in San Matías Gulf, northern Patagonia (Argentina)

Brazilian flathead Percophis brasiliensis is a commercially important perciform fish caught as bycatch by trawlers throughout its latitudinal distribution range (from 23° S in Brazil to 47° S in Argentina). It is associated with the catches of Argentine hake Merluccius hubbsi and Patagonian red shrimp Pleocticus muelleri in San Matías Gulf (SMG). The main objective of this study was to describe the first data on the growth of this species in SMG and to compare the results with available information for other areas of the Argentine Continental Shelf (ACS). The study was carried out using 294 specimens (196 females, 97 males and one of indeterminate sex) collected over four non-consecutive years from commercial/recreational fishing and during research cruises. The age of individuals was determined by reading and counting opaque-hyaline rings on the sagittae otoliths. The maximum ages observed were 14 years for females and 12 years for males. Growth parameters were estimated using the von Bertalanffy mode. Significant differences in L∞ parameter between sexes were found (L∞ males = 54.58 cm; L∞ females = 78.31 cm, p < 0.05). Growth parameters were different from those determined in previous studies for the ACS.