Growth of Northwest Iberian juvenile hake estimated by combining sagittal and transversal otolith microstructure analyses

Daily growth of Atlantic juvenile hake from Northwest Iberia has been estimated employing a new approach combining analyses of transversal and sagittal sections of the otoliths along the ventral radius. Age of juvenile hake ranging from 3 to 25 cm collected during a spring 2002 survey was estimated. Somatic growth followed a power fit: Fish size (TL) = 3.3254*age^0.7336 (r² = 0.87, p < 0.001, n = 76), yielding an average individual growth rate of 0.66 mm/day (±0.06). The growth model indicates that after a year's life a juvenile can reach 25 cm. Otolith ventral radius ranged from 401 to 1842 μm and daily increments were between 104 and 387. Fish growth and otolith growth were closely related (r² = 0.92 p < 0.001, n = 76). These first results of daily growth rates for the Southern stock corroborate the fast-growth hypothesis of this species. The evolution of increment widths from hatch dates onwards reveals important seasonal growth peaks during July–August and October–November. A comparison with prior data and discussion is also presented in the light of recent work on hake juveniles and tagging-recapture experiences.     

The influence of diel vertical migration on zooplankton transport and recruitment in an upwelling region: estimates from a coupled behavioral-physical model

Diel vertical migration (DVM) is a common zooplankton behavior in which organisms reside in surface or near‐surface waters at night and at deeper depths during the day. In many upwelling regions, DVM reduces the transport of organisms away from the region. It is unclear, however, what role DVM plays in recruitment (the arrival of larvae or juveniles to locations where they will become reproducing adults) to upwelling regions. In this study, we estimate the influence of DVM on zooplankton transport, the level of recruitment of locally produced propagules (self‐recruitment), and sources of recruits in the upwelling region near Monterey Bay, California, by simulating the trajectories of fixed‐depth and vertically migrating organisms with a drifter‐tracking algorithm driven by climatological velocity fields from a three‐dimensional hydrodynamic model. Our simulations suggest that DVM into subsurface poleward and onshore currents during the day does not fully compensate for equatorward and offshore transport in the surface Ekman layer at night and does not retain zooplankton in the Monterey Bay region. Our simulations also suggest that DVM decreases the ability of zooplankton to return to the region after being transported away and shifts source regions for recruits closer to the bay. While DVM does not appear to substantially increase the potential for self‐recruitment to the region, this study indicates that other mechanisms, such as transport during non‐upwelling periods, continuous transport below the surface, increases in mean transport depth over time, or seasonal changes in hydrography, may still enable relatively high levels of self‐recruitment to this highly advective region.     

Quantifying the effects of wind, upwelling, curl, sea surface temperature and sea level height on growth and maturation of a California Chinook salmon (Oncorhynchus tshawytscha) population

We used retrospective scale growth chronologies and return size and age of female Chinook salmon (Oncorhynchus tshawytscha) from a northern California, USA, population collected over 22 run years and encompassing 18 complete cohorts to model the effects of oceanographic conditions on growth during ocean residence. Using path analyses and partial least squares regressive approaches, we related growth rate and maturation to seven environmental variables (sea level height, sea surface temperature, upwelling, curl, scalar wind, northerly pseudo‐wind stress and easterly pseudo‐wind stress). During the first year of life, growth was negatively related to summer sea surface temperature, curl and scalar winds, and was positively related to summer upwelling. During the second, third and fourth growth years growth rate was negatively related to sea level height and sea surface temperature, and was positively related to upwelling and curl. The age at maturation and the fork length at which three ocean‐winter fish returned were related to the environment experienced during the spring before the third winter at sea (the year prior return). Faster growth during the year before return led to earlier maturation and larger return size.     

Habitat suitability, threats and conservation of isolated populations of the smooth snake (Coronella austriaca) in the southern Iberian Peninsula

During the Pleistocene, climatic fluctuations due to glacial and interglacial periods greatly modified the distribution of boreal organisms. One direct effect of these distribution shifts is that, along the southern edge of the range of some boreal species, populations persist only in isolated patches of suitable habitats, surrounded by less suitable areas. Isolated populations in marginal habitat are vulnerable to several threats, including climate change, anthropogenic threats, and stochastic events. We developed habitat-suitability models using Ecological Niche Factor Analysis for populations of the smooth snake, Coronella austriaca, at the southernmost limit of the species range. These models were based on historical and current records of occurrence, coupled with remote sensing data including elevation, slope, and climatic variables. Our results indicated that C. austriaca in the Iberian Peninsula occurred in areas associated with high slope and precipitation, low temperatures, and low variation in seasonal temperature and precipitation compared to areas of non-occurrence. At a broad scale, the areas classified as highly suitable for the species in the southern Iberian Peninsula were small and fragmented. At a local scale, extensive field work demonstrated that C. austriaca occurs in low densities in these areas. In addition, we detected several human-induced threats like habitat loss, favoured by temperature increase and rainfall reduction. Several life-history traits, such as dietary specialization and low frequency reproduction, also may contribute to the vulnerability of these populations to local extinctions. Although the most suitable southernmost areas are included in protected reserves, specific guidelines for management are needed to assess conservation needs.     

Habitat-based conservation priorities for carabid beetles within the Picos de Europa National Park, northern Spain

Quick biodiversity studies on poorly studied taxa and areas are increasingly popular for setting conservation priorities over a wide range of spatial scales. However, the implementation of such studies is complicated by the variable extent to which the different criteria used in prioritisation are correlated to each other. Using methods of constrained ordination, we examined the species-habitat relationships of carabid beetles based on ground beetle assemblages from 22 sites in the Picos de Europa National Park, northern Spain. We found characteristic species assemblages for subalpine meadows, Genista shrublands, and pastures, whereas mown meadows, heathlands, beech and riparian woodlands were occupied by more habitat generalist species. Species associated with subalpine meadows and Genista shrublands tended to be mostly brachypterous and to have geographic ranges restricted to northern Spain. In contrast, we found no relationship between the degree of species' association with pastures and geographic range-wing size type. Although the species richness was higher in riparian woodlands and mown meadows, we suggest a higher conservation value for subalpine meadows and Genista shrublands across the landscape because they sustain characteristic assemblages dominated by species with restricted ranges and reduced powers of dispersal. Our study suggests that preserving areas in the landscape supporting higher biodiversity will not necessarily preserve those species potentially more susceptible to habitat loss and fragmentation. It also supports the feasibility of biodiversity studies based on multivariate techniques for setting conservation priorities over complex landscapes.     

Characterization of denitrification activity in zones of groundwater exfiltration within a riparian wetland ecosystem

Movement of agricultural nitrogen (N) into riparian buffers often occurs within discrete seepage or upwelling zones which can limit the ability of the ecosystem to process the nutrient delivered by exfiltrating groundwater. Characterization of the biogeochemical processing of N within these zones is important in assessing the effectiveness of riparian buffers for mitigating nutrient loading of surface waters. The biogeochemical potential for denitrification in zones of exfiltration within a riparian buffer wetland dominated by high-carbon mucky soils was found to be highly stratified by profile depth with substantially higher activity in the surface layer of soil. The denitrification enzyme activity (DEA) within these zones was partly related to the population size of denitrifying microorganisms as measured by the most probable number (MPN) as well as the general microbial population as measured by substrate-induced respiration. The addition of glucose to the DEA assay stimulated enzyme activity indicating that carbon substrate was limiting activity. The stratification patterns of microbial populations and DEA are consistent with new carbon inputs to the ecosystem being most important driver of biogeochemical reactions such as denitrification in this high-carbon environment. A survey of carbon inputs to the ecosystem under study identified two major sources that contribute most of the annual biomass carbon inputs to the wetland: skunk cabbage in early summer and tree leaf litter in the fall. Tests of the ability of annually deposited wetland plant residues to stimulate denitrification and microbial respiration indicated that the degree of stimulation was inversely related to the C/N ratio of these carbon sources.     

Otter (Lutra lutra) distribution modeling at two resolution scales suited to conservation planning in the Iberian Peninsula

We used the results of the Spanish Otter Survey of 1994-1996, a Geographic Information System and stepwise multiple logistic regression to model otter presence/absence data in the continental Spanish UTM 10×10-km squares. Geographic situation, indicators of human activity such as highways and major urban centers, and environmental variables related with productivity, water availability, altitude, and environmental energy were included in a logistic model that correctly classified about 73% of otter presences and absences. We extrapolated the model to the adjacent territory of Portugal, and increased the model's spatial resolution by extrapolating it to 1×1-km squares in the whole Iberian Peninsula. The model turned out to be rather flexible, predicting, for instance, the species to be very restricted to the courses of rivers in some areas, and more widespread in others. This allowed us to determine areas where otter populations may be more vulnerable to habitat changes or harmful human interventions.     

Forecasting climate-induced changes in the survival of Snake River spring/summer Chinook salmon (Oncorhynchus tshawytscha)

Effective conservation and management of natural resources requires accurate predictions of ecosystem responses to future climate change, but environmental science has largely failed to produce these reliable forecasts. The future response of Pacific salmon (Oncorhynchus spp.) to a changing environment and continued anthropogenic disturbance is of particular interest to the public because of their high economic, social, and cultural value. While numerous retrospective analyses show a strong correlation between past changes in the ocean environment and salmon production within the north Pacific, these correlations rarely make good predictions. Using a Bayesian time-series model to make successive 1-yr-ahead forecasts, we predicted changes in the ocean survival of Snake River spring/summer chinook salmon (O. tshawytscha) from indices of coastal ocean upwelling with a high degree of certainty (R² = 0.71). Furthermore, another form of the dynamic times-series model that used all of the available data indicated an even stronger coupling between smolt-to-adult survival and ocean upwelling in the spring and fall (R² = 0.96). This suggests that management policies directed at conserving this threatened stock of salmon need to explicitly address the important role of the ocean in driving future salmon survival.     

Evaluating upwelling estimates off the west coasts of North and South America

Both low‐ and high‐resolution studies of wind and upwelling were conducted off the west coasts of North and South America between August 1999 and December 2001. For the low‐resolution study, done at 25 regional sites spanning both coasts, weekly mean winds were calculated from satellite measurements, from geostrophic estimates, and from an operational 100‐km‐resolution global atmospheric model. The satellite‐measured winds, used as the reference, showed that the coastal regions of both North and South America were divided into fairly uniform climatic domains located at higher, mid, and lower latitudes. All three weekly‐mean wind data sets were compared at each of the 25 sites, and then used to estimate upwelling based on the method employed by NOAA's Pacific Fisheries Environmental Laboratory. Within each of the wind domains, model‐derived wind and upwelling estimates agreed with satellite‐derived values better than those from geostrophic‐derived estimates. To investigate variability between the regional sites, a 9‐km‐resolution atmospheric model was run for an area off California which spanned four of the regional sites. This high‐resolution model, verified with satellite measurements, revealed jets of wind curving and intensifying around coastal promontories. These near‐shore wind jets, undetected in the global model, resulted in strong upwelling bands on the order of 50 km alongshore by 20 km offshore. These bands are critical for calculating local upwelling. Our results indicate that regional upwelling estimates for fisheries research can be improved by replacing geostrophic estimates of winds with those from a global atmospheric model. For localized coastal upwelling estimates, however, models with resolution an order of magnitude higher are required.     

Seasonal and interannual variations of oceanographic conditions off Mangalore coast (Karnataka, India) in the Malabar upwelling system during 1995–2004 and their influences on the pelagic fishery

Mangalore coast is well known for its multi‐species and multi‐gear fisheries and the fishery and oceanographic features of this region is a true representation of the Malabar upwelling system. Ten years of study (1995–2004) of oceanographic parameters has been carried out from the inshore waters off Mangalore to understand their seasonal and interannual variations and influences on the pelagic fishery of the region. Attempt has been also made to understand the influence of local and global environmental conditions on the alternating patterns of abundance between the Indian mackerel and oil sardine from the area. Field‐ and satellite‐derived oceanographic data have shown that coastal upwelling occurs during July–September with a peak in August resulting in high nutrient concentrations and biological productivity along the coast. Nearly 70% of the pelagic fish catch, dominated by oil sardine and mackerel, was obtained during September–December, during or immediately after the upwelling season. Catches of scombroid fishes were significantly related to cold Sea Surface Temperature, while such relationships were not observed for sardines and anchovies. Significant positive correlations were observed between the ENSO events (MEI) and seawater temperature from the study area. The extreme oceanographic events associated with the cold La Niña, which preceded the exceptional 1997–98 El Niño event, were responsible for the collapse of the pelagic fishery, especially the mackerel fishery along the southwest coast of India (Malabar upwelling system). Coinciding with the collapse of the mackerel fishery, oil sardine populations revived during 1999–2000 all along the southwest coast of India. Tolerance of oil sardine to El Niño / La Niña events and the low predatory pressure experienced by their eggs and larvae due to the collapse of mackerel population might have resulted in its population revival.