Lorena P. Storero

Spatial patterns of the Argentine hake Merluccius hubbsi and oceanographic processes in a semi-enclosed Patagonian ecosystem

Abstract Time-series of fishing position, landings, satellite-derived sea-surface temperature and chlorophyll a concentrations were used to relate the spatial–temporal distribution of the Argentine hake Merluccius hubbsi with seasonal oceanographic processes in San Matías Gulf. Also, the seasonal effect of fishing on the hake population structure was analysed. During summer the fleet was concentrated over the area of the frontal system, obtaining the best catch-per-unit-effort (CPUE) of hake in relatively deep waters. In autumn, the dispersion of the fleet due to a reduction in CPUE coincided with the dissipation of the front, suggesting that the distribution and shoaling of the Argentine hake is associated with seasonal thermal structures. In spring, the thermal structure of the waters and the chlorophyll a blooms seem to modulate the timing of spawning of hake, which occurs mainly in October–November. In addition, the fleet captured a higher proportion of females in the gonadal recovery stage during warm months (November–April). While winter catches (May–October) consisted mainly of males, the intense summer fishing may result in a high impact on the female population. This information is relevant to design of spatial management tools intended to provide biological sustainability to the hake fishery.

Reproductive traits of the small Patagonian octopus Octopus tehuelchus

This study evaluated the reproductive features of Octopus tehuelchus in three coastal environments of San Matías Gulf (Patagonia). Monthly samples of O. tehuelchus were used to estimate size at maturity, compare seasonal changes in oocyte size frequency distributions between sites as well as oocyte number and size between female maturity stage and sites. Females in Islote Lobos had a smaller size at maturity than females in San Antonio Bay and El Fuerte, probably as a consequence of a generally smaller body size. Males in San Antonio Bay were smaller at maturity than females. O. tehuelchus is a simultaneous terminal spawner. Fecundity (expressed as number of vitellogenic oocytes in ovary) was lower in Islote Lobos, and an increase in oocyte number in relation to female total weight was found. Females in San Antonio Bay had the largest oocytes, which may indicate higher energy reserves for the embryo and therefore higher juvenile survival. There was a close relationship between reproduction, growth and condition, represented as size at maturity, number and size of vitellogenic oocytes and period of maturity and spawning. Given the local variation in some reproductive features of O. tehuelchus, studies should focus on the environmental factors, which bring about this variation, and on how it affects the dynamics of local populations.

Genetic evidence and new morphometric data as essential tools to identify the Patagonian seahorse Hippocampus patagonicus (Pisces, Syngnathidae).

A genetic study to support morphometric analyses was used to improve the description and validate the Patagonian seahorse Hippocampus patagonicus (Syngnathidae) on the basis of a large number of specimens collected in the type locality (San Antonio Bay, Patagonia, Argentina). DNA sequence data (from the cytochrome b region of the mitochondrial genome) were used to differentiate this species from its relatives cited for the west Atlantic Ocean. Both phylogenetic and genetic distance analyses supported the hypothesis that H. patagonicus is a species clearly differentiated from others, in agreement with morphometric studies. Hippocampus patagonicus can be distinguished from Hippocampus erectus by the combination of the following morphometric characteristics: (1) in both sexes and all sizes of H. patagonicus, the snout length is always less than the postorbital length, whereas the snout length of H. erectus is not shorter than the postorbital length in the largest specimens; (2) in both sexes of H. patagonicus, the trunk length:total length (LTr :LT ) is lower than in H. erectus (in female H. patagonicus: 0·27-0·39, H. erectus: 0·36-0·40 and in male H. patagonicus: 0·24-0·34, H. erectus: 0·33-0·43) and (3) in both sexes, tail length:total length (LTa :LT ) in H. patagonicus is larger than in H. erectus (0·61-0·78 v. 0·54-0·64).

Coccidian infection may explain the differences in the life history of octopus host populations

The prevalence of coccidian parasites in three Octopus tehuelchus populations from San Matías Gulf (Patagonia, Argentina) is compared. The prevalence was similar between sexes, but varied between seasons (being highest during cold months) and sites. Islote Lobos had the highest prevalence (42.7-100%) followed by San Antonio Bay (0-66%) and El Fuerte (0-24.5%). Octopuses under 27 mm of dorsal mantle length showed a low prevalence (less than 50%), which increased with size. We hypothesize that the high prevalence of parasites, which affect the three populations differentially, could account for the observed variability in life-span and growth, size-frequency distributions, reproduction and densities of O. tehuelchus populations.

FIRST STUDIES ON MORPHOMETRIC RELATIONSHIPS AND SIZE AT MATURITY OF THE RED CRAB PLATYXANTHUS PATAGONICUS (MILNE-EDWARDS) AND VARIATIONS CAUSED BY RHIZOCEPHALAN INFESTATION, IN THE SAN MATIAS GULF, PATAGONIA, ARGENTINA

Abstract The size at onset sexual maturity in brachyurans can be evaluated considering different criteria, including growth allometry, gonad development stages, and presence of sperm in spermathecas or eggs in the abdomen. Morphometric aspects of males and the presence of eggs in females of P. patagonicus from the northern San Matías Gulf were respectively analyzed to determine its size at onset of the sexual maturity. Crab samples were obtained during a fishing experiment with traps (cubical, pyramidal, and conical, of similar internal volume), performed in the gulf during winter 2005. Also, the parasitism by a sacculinid rhizocephalan was analyzed to discuss possible effects on the reproductive success. All crabs caught were sorted by sex, carapace width (CW) and total weight (TW). Size frequency distributions were compared among sexes. Proportion of females bearing eggs were grouped into 16 size intervals of 5 mm to determine the size of first reproductive maturity based on a criterion of L50%. In males, the allometric change of chela length was analyzed for this purpose. Only individuals exceeding 50 mm were caught. Of 807 crabs caught, 36% (289) were males and 64% (518) were females. The size frequency distributions differed significantly between sexes with males larger than females (K-S test). Relationships of total weight (TW) to carapace width (CW) were calculated for all reproductive types and compared by ANCOVA with the following results: parasitized crabs < females < females with eggs = males. The mean size at first maturity of females was estimated to be 87.66 mm. Size at maturity for male crabs could not be determined from morphometric data because there was no significant difference in the relationship of chela length and CW for juvenile and adult males. All parasitized crabs (73) were females, whose mean width and mean weight were significantly lower than those from nonparasitized individuals. Prevalence was 9% and the mean intensity was one parasite per host. The parasitized crabs resembled juveniles. The size at first maturity and the reproductive capacity of P. patagonicus could be affected by presence of the parasite, even producing significant interference at the population level. Parasitism by sacculinid must be monitored after the starting of an emerging fishery to assess the actual contribution of the reproductive stock.

Reply to Luzzatto et al. (2014): "Comment on 'Genetic evidence and new morphometric data as essential tools to identify the Patagonian seahorse Hippocampus patagonicus (Pisces, Syngnathidae), González et al. (2014)'"

Fil: Gonzalez, Raul Alberto Candido. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte; Argentina. Universidad Nacional del Comahue. Instituto de Biologia Marina y Pesquera Almirante Storni; Argentina