Gabriela Noemí Williams

Comparison of AVHRR and SeaWiFS imagery with fishing activity and in situ data in San Matías Gulf, Argentina

Seven years (January 2000 to December 2006) of AVHRR and SeaWiFS data were used to estimate monthly climatological means and to present SST and chlorophyll-a seasonal evolution in San Matías Gulf, located between 40° 47′ S and 42° 13′ S on the Argentine coast. SST and chlorophyll-a satellite maps corresponding to spring–summer showed two well differentiable sectors: the southern zone presented colder waters and higher chlorophyll-a concentration while the northern one showed warm water and lower chlorophyll-a. Hake (Merluccius hubbsi) is the most important resource in terms of landings and economic revenues of the San Matías Gulf. Fishing activity data gathered by a Vessel Monitoring System (2004–2006) were linked with SST and chlorophyll-a maps showing that the fishing vessels operated on the thermal front from November to March and had the maximum hake yields. In addition, AVHRR-SST and SeaWiFS-chlorophyll-a data were compared with temperature and chlorophyll-a measured in oceanographic surveys carried out in 2007.

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.

Environmental Niche Overlap between Common and Dusky Dolphins in North Patagonia, Argentina

Research on the ecology of sympatric dolphins has increased worldwide in recent decades. However, many dolphin associations such as that between common dolphins (Delphinus delphis) and dusky dolphins (Lagenorhynchus obscurus) are poorly understood. The present study was conducted in the San Matías Gulf (SMG) ecosystem (North Patagonia, Argentina) where a high diet overlap among both species was found. The main objective of the present work was to explore the niche overlap of common and dusky dolphins in the habitat and temporal dimensions. The specific aims were (a) to evaluate the habitat use strategies of both species through a comparison of their group attributes (social composition, size and activity), and (b) to evaluate their habitat preferences and habitat overlap through Environmental Niche modeling considering two oceanographic seasons. To accomplish these aims, we used a historic database of opportunistic and systematic records collected from 1983 to 2011. Common and dusky dolphins exhibited similar patterns of group size (from less than 10 to more than 100 individuals), activity (both species use the area to feed, nurse, and copulate), and composition (adults, juveniles, and mothers with calves were observed for both species). Also, both species were observed travelling and feeding in mixed-species groups. Specific overlap indices were higher for common dolphins than for dusky dolphins, but all indices were low, suggesting that they are mainly segregated in the habitat dimension. In the case of common dolphins, the best habitats were located in the northwest of the gulf far from the coast. In the warm season they prefer areas with temperate sea surface and in the cold season they prefer areas with relatively high variability of sea surface temperature. Meanwhile, dusky dolphins prefer areas with steep slopes close to the coast in the southwestern sector of the gulf in both seasons.

Satellite-Measured Phytoplankton and Environmental Factors in North Patagonian Gulfs

An extensive series of high-resolution satellite images from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS, 2000–2006) was used in the characterization of the phytoplankton biomass seasonal cycle of the north Patagonian gulfs (NPG). The NPG system is formed by the San Matias, San Jose, and Nuevo gulfs (between 40°47′and 43°00′S and 63°00′ and 65°1.2′W) and is an area of ecological importance and of great significance for marine conservation in the Patagonian Argentinean Shelf. The spatio temporal variability of phytoplankton biomass in each of these environments was characterized by chlorophyll a data from satellite images (Chla-sat). The observed seasonal variability was explained by factors influencing the growth of phytoplankton: photosynthetically available radiation (PAR from the SeaWiFS sensor) and sea surface temperature (SST from the Advanced Very High-Resolution Radiometer, AVHRR). In situ temperature, nutrient, and chlorophyll a concentration data from oceanographic cruises carried out in Nuevo (four cruises: 1982–1983), San Jose (four cruises: 1984–1985), and San Matias (four cruises: 1986–1994) gulfs were also used to explain the observed patterns. Cycles of phytoplankton and SST over the NPG are typical of temperate waters. However, Chla-sat cycles were different among gulfs. At the same time, Chla-sat cycles over the gulfs were different from that over the adjacent middle continental shelf. SMG was characterized by a bimodal cycle, although in winter mean values were higher than the mean concentration for the whole area. SJG was characterized by a unimodal cycle with relatively high values of chlorophyll a concentration in spring-summer. NG showed a bimodal cycle with maximum values in autumn and spring and minimum values in winter and summer. Particularities of each gulf are discussed in relation to the seasonal hydrographic characteristics of the water column (temperature and nutrients) and in the context of the Patagonian shelf ecosystem.

Local scale variation in the reproductive pattern of the southern geoduck, Panopea abbreviata (Bivalvia: Hiatellidae), in Patagonia

espanolDurante el 2007 se realizaron estudios para explorar la variabilidad espacial a escala local, del ciclo reproductivo de Panopea abbreviata en 3 poblaciones presentes en los golfos Nord-patagonicos (El Sotano y Puerto Lobos, en el Golfo San Matias, y Punta Conos en el Golfo San Jose), Argentina. Estudios previos determinaron que P. abbreviata presenta un patron reproductivo, en ambos sexos, caracterizado por una continua proliferacion y evacuacion de gametos durante todo el ano. Sin embargo, el uso de indicadores cuantitativos (distribucion de frecuencia de diametros ovocitarios, ovocitos por campo ocular y area ovocitaria relativa) para las hembras permitio observar una ligera estacionalidad. Las variaciones en el ciclo reproductivo fueron relacionadas con el regimen anual de temperatura de cada sitio. Las hembras de El Sotano y Puerto Lobos muestran una estacionalidad similar en el patron reproductivo: las fases de proliferacion y maduracion predominan cuando la temperatura disminuye durante otono (marzo-mayo); este patron se revierte, cuando las temperaturas comienzan a aumentar durante primavera (septiembre-noviembre). Mientras que, en Punta Conos este patron es mas irregular. Sin embargo, en todas las poblaciones se encontraron individuos de ambos sexos en estadio de madurez durante todo el ano, evidenciando la ausencia de un periodo de inactividad gonadal. En las 3 poblaciones ambos sexos se caracterizan por multiples pulsos cortos de evacuacion de gametos. Este mismo patron se encontro en otras poblaciones de P. abbreviata y es unico para el genero Panopea. Los 3 sitios estudiados presentaron un patron reproductivo similar. EnglishDuring 2007 was carried out studies to explore local scale spatial variability in the reproductive cycle of Panopea abbreviata in 3 sites of the northern Patagonian gulfs (El Sotano and Puerto Lobos, in San Matias Gulf, and Punta Conos in San Jose Gulf), Argentina. Previous reports have revealed that P. abbreviata exhibits a reproductive pattern characterized, in both sexes, by continuous proliferation of gametes and spawning throughout the year. However, the use of quantitative indicators for females has shown a slight seasonality to this pattern. Local spatial variability in the reproductive cycle of P. abbreviata was observed at 3 sites and related to variation in the annual temperature regime at each locality. The females of El Sotano and Puerto Lobos showed similar seasonality in the reproductive pattern: proliferation and maturation phases prevailed over spawning stages when temperature decreased during autumn (March-May); this pattern was reversed when temperatures began to increase during spring (September-November). At Punta Conos this pattern is more irregular. However, at all localities, mature individuals of both sexes were present throughout the year, without a resting period during the reproductive cycle. The reproductive pattern is similar in the 3 sites with many small pulses in reproductive activity that are difficult to detect and characterized by year-round spawning. The same pattern was found in other localities of P. abbreviata and is unique in the genus Panopea.