Amoroso, R. O., Parma, A. M., Orensanz, J. M., and Gagliardini, D. A. 2011. Zooming the macroscope: medium-resolution remote sensing as a framework for the assessment of a small-scale fishery. - ICES ...Journal of Marine Science, 68: 696-706. Management of small-scale fisheries targeting sedentary stocks requires integration of information about processes operating and observable at different spatial and temporal scales. An integrated approach was developed with a scallop (Aequipecten tehuelchus) fishery in a small, semi-enclosed Patagonian basin as a demonstration case. Medium-resolution (30 m super(2)) satellite (Landsat) data, used to identify circulation patterns, were combined with information from fishery surveys and recruitment experiments to link oceanographic processes with population dynamics. A frontal system splits San Jose Gulf (northern Argentine Patagonia) into two oceanographic domains (East and West) with distinct hydrographic regimes. In the West Domain, where circulation is highly advective and governed by turbulent vorticial fluxes, larval settlement on artificial collectors was insignificant over five reproductive seasons and no important scallop grounds were ever found. In the East Domain, where the main fishing grounds are, spat abundance varied between sites and years, but was always significant. Growth rates displayed strong clinal variation within the East Domain, decreasing clockwise away from the entrance to the Gulf and reflecting inferred circulation and gradual nutrient extinction. A physical mechanism capable of dispersing larvae over long distances towards the north, into the adjacent San Matias Gulf, was identified from Landsat images. The large-scale patterns of variation in growth, distribution, and recruitment of the Tehuelche scallop stock could not have been interpreted without an integrative approach to data assemblage and analysis, including satellite remote sensing.
Coastal Patagonia, often regarded as a pristine area of the world, has been invaded by non-indigenous species that are rapidly modifying local ecosystems. One of the most conspicuous invaders is the ...kelp Undaria pinnatifida. First recorded near the city of Puerto Madryn (Argentina, 42.75degreesS) in 1992, Undaria's range has expanded more than five degrees of latitude to the south during the last 15 years. By 2007 it was first detected north of Valdes Peninsula (a natural barrier to dispersal), beginning its northward expansion, and between 2007 and 2011 spread along the coasts of San Jose and San Matias gulfs at an average rate of ~50 km yr super(-1). A small population was detected in Mar del Plata (Argentina, 38.04degreesS) in 2011, more than three degrees of latitude to the north, suggesting a new human-mediated inoculation. A thermal tolerance window is hypothesized based on experimental information and remotely sensed sea-surface temperature (SST) at the latitudinal range limits of U. pinnatifida populations worldwide. The window is defined by average SSTs ranging between -0.6 degreesC and 16.8 degreesC in the coldest month, and between 13degreesC and 28degreesC in the warmest month. Using climatologic satellite SST from several locations, a potential latitudinal thermal range extending between Puerto Deseado (Argentina, 47.75degreesS) and Cape Torres (Brazil; 29.35degreesS) is predicted. Salinity and substrate quality however constrain suitable habitat in the Southwest Atlantic to discrete stretches of coastline, suggesting that the northern potential boundary would be around La Coronilla (33.90degreesS), on the Uruguayan coast.
Background Mobile bottom fishing, such as trawling and dredging, is the most widespread direct human impact on marine benthic systems. Knowledge of the impacts of different gear types on different ...habitats, the species most sensitive to impacts and the potential for habitats to recover are often needed to inform implementation of an ecosystem approach to fisheries and strategies for biodiversity conservation. This knowledge helps to identify management options that maximise fisheries yield whilst minimising negative impacts on benthic systems. Methods The methods are designed to identify and collate evidence from experimental studies (e.g. before/after, control/impact) and comparative studies (spanning a gradient of fishing intensity) to identify changes in state (numbers, biomass, diversity etc.) of benthic biota (flora and fauna), resulting from a variety of mobile bottom fishing scenarios. The primary research question that the outputs will be used to address is: "to what extent does a given intensity of bottom fishing affect the abundance and/or diversity of benthic biota?" Due to the variety of gear and habitat types studied, the primary question will be closely linked with secondary questions. These include: "how does the effect of bottom fishing on various benthic biota metrics (species, faunal type, trait, taxon etc.) vary with (1) gear type and (2) habitat, and (3) gear type-habitat interactions?" and (4) "how might properties of the community and environment affect the resilience (and recovery potential) of a community to bottom fishing?"
•Predator rate of increase is uncorrelated with forage fish abundance.•Forage species are affected much more by environmental conditions than by fishing.•Previous analysis of forage fish impacts on ...predators ignored natural variability.•Spatial distribution of forage species may be more important than their abundance.•Predators often take small forage fish that are unaffected by fishing.
This paper explores the impact of fishing low trophic level “forage” species on higher trophic level marine predators including other fish, birds and marine mammals. We show that existing analyses using trophic models have generally ignored a number of important factors including (1) the high level of natural variability of forage fish, (2) the weak relationship between forage fish spawning stock size and recruitment and the role of environmental productivity regimes, (3) the size distribution of forage fish, their predators and subsequent size selective predation (4) the changes in spatial distribution of the forage fish as it influences the reproductive success of predators. We show that taking account of these factors generally tends to make the impact of fishing forage fish on their predators less than estimated from trophic models. We also explore the empirical relationship between forage fish abundance and predator abundance for a range of U.S. fisheries and show that there is little evidence for a strong connection between forage fish abundance and the rate of change in the abundance of their predators. We suggest that any evaluation of harvest policies for forage fish needs to include these issues, and that models tailored for individual species and ecosystems are needed to guide fisheries management policy.
Bottom trawling is widespread globally and impacts seabed habitats. However, risks from trawling remain unquantified at large scales in most regions. We address these issues by synthesizing evidence ...on the impacts of different trawl-gear types, seabed recovery rates, and spatial distributions of trawling intensity in a quantitative indicator of biotic status (relative amount of pretrawling biota) for sedimentary habitats, where most bottom-trawling occurs, in 24 regions worldwide. Regional average status relative to an untrawled state (=1) was high (>0.9) in 15 regions, but <0.7 in three (European) regions and only 0.25 in the Adriatic Sea. Across all regions, 66% of seabed area was not trawled (status = 1), 1.5% was depleted (status = 0), and 93% had status > 0.8. These assessments are first order, based on parameters estimated with uncertainty from meta-analyses; we recommend regional analyses to refine parameters for local specificity. Nevertheless, our results are sufficiently robust to highlight regions needing more effective management to reduce exploitation and improve stock sustainability and seabed environmental status-while also showing seabed status was high (>0.95) in regions where catches of trawled fish stocks meet accepted benchmarks for sustainable exploitation, demonstrating that environmental benefits accrue from effective fisheries management. Furthermore, regional seabed status was related to the proportional area swept by trawling, enabling preliminary predictions of regional status when only the total amount of trawling is known. This research advances seascape-scale understanding of trawl impacts in regions around the world, enables quantitative assessment of sustainability risks, and facilitates implementation of an ecosystem approach to trawl fisheries management globally.
Bottom trawl fishing is a controversial activity. It yields about a quarter of the world's wild seafood, but also has impacts on the marine environment. Recent advances have quantified and improved ...understanding of large‐scale impacts of trawling on the seabed. However, such information needs to be coupled with distributions of benthic invertebrates (benthos) to assess whether these populations are being sustained under current trawling regimes. This study collated data from 13 diverse regions of the globe spanning four continents. Within each region, we combined trawl intensity distributions and predicted abundance distributions of benthos groups with impact and recovery parameters for taxonomic classes in a risk assessment model to estimate benthos status. The exposure of 220 predicted benthos‐group distributions to trawling intensity (as swept area ratio) ranged between 0% and 210% (mean = 37%) of abundance. However, benthos status, an indicator of the depleted abundance under chronic trawling pressure as a proportion of untrawled state, ranged between 0.86 and 1 (mean = 0.99), with 78% of benthos groups > 0.95. Mean benthos status was lowest in regions of Europe and Africa, and for taxonomic classes Bivalvia and Gastropoda. Our results demonstrate that while spatial overlap studies can help infer general patterns of potential risk, actual risks cannot be evaluated without using an assessment model that incorporates trawl impact and recovery metrics. These quantitative outputs are essential for sustainability assessments, and together with reference points and thresholds, can help managers ensure use of the marine environment is sustainable under the ecosystem approach to management.
San Jose Gulf is a small semienclosed bay connected by a narrow mouth to a much larger basin, the San Matías Gulf. Intriguingly, this comparatively small water body, characterized by high biological ...productivity, has contributed most of the historical shellfish production in the region. A remote sensing approach allowed us to advance a composite conjecture aimed at explaining that phenomenon. A combination of circulation, strong tidal currents, and coastal topography leads to the formation of a frontal system inside San Jose Gulf and to the development of turbulent fluxes that drive the hydrographie regime. The front divides the San Jose Gulf in two domains (west and east). The origin of water flowing into the west domain was tracked to the Valdes Frontal System, on the continental shelf. The west domain is highly turbulent due to the formation of vortexes and dipoles during the tidal cycle. Detachable dipoles formed at the edge of jets outflowing from San Jose Gulf can reach the central part of San Matias Gulf, constituting a possible larval transport mechanism between the two gulfs. Our results led us to postulate that (1) nutrients from the continental shelf are "trapped in" and larvae are retained in the east domain of San Jose Gulf, resulting in persistently high biomass of secondary producers, and (2) asymmetrical exchange, in the form of vorticial flows, "pumps out" waterborne material from the San Jose Gulf into San Matias Gulf, affecting the connectivity between the two basins.
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