Sea Surface Chlorophyll Concentration Research Articles

Spatial heterogeneity of long-range dependence and self-similarity of global sea surface chlorophyll concentration with their environmental impact factors analysis

Understanding the long-range dependence and self-similarity of global sea surface chlorophyll concentration (SSCC) will enrich its characteristics description and analysis with global change patterns. The satellite SSCC products were collected from the European Space Agency during the period from 29 July 1998 to 31 December2020. After resampling the SSCC products into the spatial resolution of 1°, the missing values were interpolated by Bayesian maximum entropy with mean absolute error of cross validation equaling to 0.1295 mg/m3. Generalized Cauchy model was employed to quantitatively determine the long-range dependence and self-similarity of SSCC at a global scale by using the Hurst parameter and fractal dimension. Good fitted results were achieved with an averaged R2 of 0.9141 and a standard deviation of 0.0518 across the 32,281 spatial locations of the entire ocean; the averaged values of Hurst parameter and fractal dimension were 0.8667 and 1.2506, respectively, suggesting strong long-range dependence and weak self-similarity of SSCC in the entire oceans. Univariate and multivariate generalized addictive models (GAM) were introduced to depict the influence of sea surface height anomaly, sea surface salinity, sea surface temperature and sea surface wind on the Hurst parameter and fractal dimension of SSCC; and smaller mean absolute error were achieved for the GAM of Hurst parameter than that of fractal dimension. Sea surface height anomaly showed the strongest influence for the Hurst parameter than the other three factors, and sea surface wind depicted similar influence; the sea surface temperature owned opposite influence on Hurst parameter compared to sea surface salinity.

Space–Time Variations in the Long-Range Dependence of Sea Surface Chlorophyll in the East China Sea and the South China Sea

Gaining insights into the space–time variations in the long-range dependence of sea surface chlorophyll is crucial for the early detection of environmental issues in oceans. To this end, 12 locations were selected along the Yangtze River and Pearl River estuaries, varying in distances from the Chinese coastline. Daily satellite-observed sea surface chlorophyll concentration data at these 12 locations were collected from the Copernicus Marine Service website, spanning from December 1997 to November 2023. The main objective of the current study is to introduce a multi-fractional generalized Cauchy model for calculating the values of Hurst exponents and quantitatively assessing the long-range dependence strength of sea surface chlorophyll at different spatial locations and time instants during the study period. Furthermore, ANOVA was utilized to detect the differences of calculated Hurst exponent values among the locations during various months and seasons. From a spatial perspective, the findings reveal a significantly stronger long-range dependence of sea surface chlorophyll in offshore regions compared to nearshore areas, with Hurst exponent values > 0.5 versus <0.5. It is noteworthy that the values of Hurst exponents at each location exhibit significant differences during various seasons, from a temporal perspective. Specifically, the long-range dependence of sea surface chlorophyll in summer in the nearshore region is weaker than in other seasons, whereas that in the offshore region is stronger than in other seasons. The study concludes that long-range dependence is inversely related to the distance from the coastline, and anthropogenic activity plays a dominant role in shaping the long-range dependence of sea surface chlorophyll in the coastal regions of China.

A method to establish marine bio-regions in the pelagic ecosystem based on phytoplanktonic communities. Aplication to the southern Spanish coast

Bioregions in the pelagic ecosystem are frequently established on the basis of remotely sensed properties of the sea surface, such as sea surface temperature or sea surface chlorophyll concentration. Those works dealing with the regionalization of the marine ecosystem by means of the use of properties of the water column are less frequent, and even less those that obtain the data from periodic in situ monitoring programs, which are scarce. In this work we use time series of micro, nano and pico-phytoplanktonic abundances in the upper 100 m of the continental shelves of the Gulf of Cadiz and the Alboran Sea from the projects STOCA and RADMED (southern coast of Spain, Western Mediterranean). The use of times series allows us to estimate the median phytoplanktonic abundances of several phytoplanktonic groups along the water column. These statistics differ substantially from those abundances obtained for one particular campaign, reflecting the large seasonal and inter-annual variability of phytoplanktonic communities. These median profiles, estimated for the four seasons of the year and for several phytoplanktonic groups characterize each of the locations sampled in the aforementioned monitoring programs and are used for establishing the similarity between them. Then, these locations are grouped using a cluster analysis. Using some simulations from numerical experiments we determine which metrics and methods of analysis are the more suitable ones for the regionalization of the area of study. A bootstrap method is also used to determine which differences among bioregions can be considered as statistically significant. Despite the existence of a fast current that connects the Gulf of Cadiz and the Alboran Sea, our results show that the outer part of the Gulf of Cadiz shelf, and that of the Alboran Sea, can be considered as two differentiated bioregions. The latter region shows a higher productivity with a higher abundance of large cells such as diatoms, and the dominance of Synechococcus bacteria over Prochlorococcus ones.

Ecosystem Management Policy Implications Based on Tonga Main Tuna Species Catch Data 2002–2018

Despite the crucial role played by international and regional tuna fisheries in facilitating the successful implementation of the ecosystem approach to fisheries management, there exist disparities in viewpoints among these stakeholders, resulting in gaps between regional fisheries management and local communities. Nevertheless, the Tongan government, under the Ministry of Fisheries, is dedicated to the efficient management of its tuna resources, aiming to establish it as the preferred and optimal approach for ensuring the long-term sustainability of its tuna fisheries and the ecosystem services they provide to the community. Recognizing that an appropriate legal, policy and institutional framework is in place for sustainable management of tuna, the first part of this paper presents a review of current Tonga fisheries laws and policies for its tuna fisheries. This review reflects the implementation of an information-based management framework, namely the Tonga National Tuna Fishery Management and Development Plan. The tuna fisheries in Tonga mainly catch albacore (Thunnus alalunga), bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis), and yellowfin (Thunnus albacares) tuna. These tuna species are caught within Tonga’s exclusive economic zones and play a crucial role in the country’s economy; hence, it is crucial to examine the spatio-temporal distributions of their catch in relation to their environmental conditions. In pursuit of this goal, the tasks of mapping (i) the spatio-temporal distribution of catch landed at ports and (ii) the spatio-temporal of environmental conditions were performed. The study utilizes longline catch per unit effort data spanning from 2002 to 2018 for albacore, bigeye, skipjack, and yellowfin tuna. It also incorporates data on environmental conditions, including sea surface temperature, sea surface chlorophyll, sea surface current, and sea surface salinity. Additionally, the El Nino Southern Oscillation Index is mapped in relation to catch data to examine the potential effects of climate change on the tuna catch. Results show that bigeye, skipjack, and yellowfin CPUE show a central–northernmost distribution and are primarily caught between latitudes 14° S–22° S, while albacore, shows a central–southern distribution. The highest CPUE for all species are in latitudes 15.5° S–22.5° S and longitudes 172.5° W–176.5° W. The data indicate that sea surface current velocities range from −0.03 to 0.04 ms−1, sea surface salinity ranges from 34.8 to 35.6 PSU, sea surface chlorophyll concentration varies from 0.03 to 0.1 mg m−3, and sea surface temperature fluctuates seasonally, ranging from 18 °C to 30 °C. Mapping also reveals that times of reduced catches in Tonga coincide with periods of moderate to strong El Nino events from 2002 to 2018.

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Spatiotemporal variation of the association between sea surface temperature and chlorophyll in global ocean during 2002–2019 based on a novel WCA-BME approach

Sea surface temperature (SST) can influence the phytoplankton biomass, measured as sea surface chlorophyll concentration (SSCC), by affecting the physical and chemical properties of the seawater, living environment, and the consumption of zooplankton in a complex way. Yet, the quantitative assessment of the spatiotemporal variation of the inherent synchronous association between SSCC and SST at large spatial and temporal scales is still lacking. Accordingly, in the present study a synthetic approach was proposed that combines wavelet coherency analysis (WCA) with Bayesian maximum entropy (BME) modeling and hotspot analysis in order to evaluate the association between SSCC and SST globally during the period July 2002-February 2019. The WCA-based statistical results showed that SSCC has strong association with SST; particularly strong synchronous variations between SSCC and SST were found at the 1-year and the 5-year periods. During the 1-year period, cluster characteristics were explored in the BME-generated space–time maps of the association strength as well as in the corresponding hotspot maps. Geographically, high association strengths between SSCC and SST were detected in the mid-latitude regions of the Pacific Ocean, in the south and north of the tropical regions of the Atlantic Ocean, and in the southern part of the Indian Ocean. Temporally, most of the sub-regions exhibited a stable level of association strength during the entire study period (only a few sub-regions exhibited fluctuations or a slightly decreasing association strength trend). In conclusion, by assimilating the available knowledge bases at each grid point the proposed synthetic approach assessed quantitatively the strength of the periodic association between SSCC and SST globally; and the approach could be employed to map the space–time variation of the association strength between related natural attributes in the space–time-frequency domain.

Spatiotemporal BME characterization and mapping of sea surface chlorophyll in Chesapeake Bay (USA) using auxiliary sea surface temperature data

Improving the spatiotemporal coverage of remote sensing (RS) products, such as sea surface chlorophyll concentration (SSCC), can offer a better understanding of the spatiotemporal SSCC distribution for ocean management purposes. In the first part of this work, 834 in-situ SSCC measurements of the SeaBASS-NASA (National Aeronautics and Space Administration) during 2002–2016 served as the empirical dataset. A moving window with ±3 days and ±0.5° centered at each of the in-situ SSCC measurements established a search neighborhood for Moderate Resolution Imaging Spectroradiometer Level 2 (MODIS L2) SSCC and MODIS L2 sea surface temperature (SST) data, and the matched SSCC and SST data were used for building a linear SSCC-SST relationship. The unmatched SST was introduced to the linear model for generating soft SSCC data with uniform distributions. The inherent spatiotemporal dependency of the SSCC distribution was then represented by the Bayesian maximum entropy (BME) method, which incorporated the soft SSCC data as auxiliary variable for SSCC estimation and mapping purposes. The results showed that a 75.3% accuracy improvement of remote SSCC retrieval in terms of R2 can be achieved by BME-based method compared to the original MODIS L2 product. Subsequently, the BME-based method was applied to obtain daily SSCC dataset in Chesapeake Bay (USA) during the period 2010–2019. It was found that the SSCC distribution exhibited a decreasing spatial trend from the upper bay to the outer bay, whereas decreasing and increasing temporal trends were detected during the periods 2011–2014 and 2016–2019, respectively. The generalized Cauchy process was used to quantitatively describe the autocorrelation SSCC function in the Chesapeake Bay. The results showed that the outer bay exhibited the strongest long-range dependence among the four sub-regions, whereas the middle bay exhibited the weakest long-range dependence. Finally, one-point and two-point stochastic site indicators (SSIs) were employed to explore the spatiotemporal SSCC characteristics in Chesapeake Bay. The one-point SSI results showed that nearly 100% of the upper, middle and the lower bay areas experienced a high SSCC level (>5 mg/m3) during the entire study period. The area with SSCC >5 mg/m3 in the outer bay increased a lot during the winter season, but the area with SSCC >10 or 20 mg/m3 decreased significantly in the upper, middle and lower bay. Simultaneously, the SSCC dispersion in these areas was rather small during the winter season. On the other hand, the two-point SSI results showed that although the SSCC levels differ among the four sub-regions, but the SSCC connectivity structures between pairs of points also displayed some similarities in terms of their spatiotemporal dependency. In conclusion, the proposed BME-based method was shown to be a promising remote SSCC mapping technique that exhibited a powerful ability to improve both accuracy and coverage of RS products. The SSIs can be also used to explore the spatiotemporal characteristics of a variety of natural attributes in waters.

Predicting summer fin whale distribution in the Pelagos Sanctuary (north‐western Mediterranean Sea) to identify dynamic whale–vessel collision risk areas

Abstract Mediterranean fin whales aggregating in the Pelagos Sanctuary in summer to feed are exposed to vessel collision risk, particularly from high‐speed ferries. This study developed models to predict summer fin whale distribution using a generalized additive model (GAM) and MaxEnt, with the aim of providing a tool to identify potential high whale–ferry collision risk areas along ferry routes within the Pelagos Sanctuary during summertime. Models were trained using sightings data collected in the summer months of 2009–2018 on board ferries crossing the central area of the Pelagos Sanctuary. Environmental predictors were bathymetry and mean sea surface chlorophyll concentration of the annual spring bloom period. The predictive ability of GAM and MaxEnt was assessed using existing knowledge of summer fin whale distribution in the region. GAM (deviance explained = 20.2%) predictions matched documented distributions more closely than that of MaxEnt, with highest predicted fin whale occurrence in deep offshore waters (>2000 m) encompassing the central north‐western and western regions, and in the south‐eastern region, consistent with known fin whale habitats within the Pelagos Sanctuary. Inter‐annual variability was evident, influencing collision risk areas. Collision risk was estimated as a function of the overlap between the predicted probability of fin whale occurrence and ferry density estimated from Automated Identification System data. Ferry routes that cross the northern and eastern regions of the Pelagos Sanctuary presented relatively higher collision risk. Areas with changes in risk intensity between the years were temporally and spatially dynamic: some appeared intermittently throughout the study period while others persisted over consecutive years or recurred in different years. Due to the vastness of the Pelagos Sanctuary, vessel speed reduction maybe a more practical measure to manage collision risk than re‐routing shipping lanes. A combination of Seasonal Management Areas and Dynamic Management Areas approaches could be adopted for high‐risk areas.

Circulation and Hydrography in the Western South Atlantic Shelf and Export to the Deep Adjacent Ocean: 30°S to 40°S

AbstractHigh sea surface chlorophyll concentration on the Argentine Continental Shelf frequently extends to the deep ocean in the vicinity of the Brazil/Malvinas Confluence (BMC). The offshore transport of shelf waters likely plays a key role in the biogeochemical balance of the western South Atlantic and promotes the offshore transport of planktonic species. We analyze data from an oceanographic survey carried out in the western South Atlantic shelf between 31°S and 38°S in October 2013. We describe the distribution and circulation of the water masses and focus on the exchanges with the open ocean. On‐shelf subsurface intrusions of oceanic waters and river discharge supply nutrients to the shelf. A low‐salinity tongue of Río de la Plata (RDP) waters extends northward to 32°S. Below these waters Subantarctic and Subtropical Shelf Waters (SASW and STSW) meet to form the Subtropical Shelf Front. The main SASW branch, oversaturated in oxygen and with high‐fluorescence mixes with a detachment of Brazil Current waters at 38°S and is exported offshore along the BMC. A second branch of SASW reaches 33°S mixing along its way with RDP and STSW and returns southward after splitting into an onshore and an offshore branch. The offshore branch is exported to the open ocean through the BMC. These export routes are in overall qualitative agreement with those indicated by a high‐resolution reanalysis. We estimate a net off‐shelf transport (geostrophic [96.2%] plus Ekman [3.8%]) of 3.44 Sv to the open ocean between 32.1°S and 37.7°S. The majority of the offshore flow occurs between 34.7°S and 37.7°S.

Variability of the ocean mixed layer depth and the upwelling activity in the Cape Bojador, Morocco

This study examines the seasonality of the patterns of the ocean mixed layer depth (MLD) with the coastal upwelling system, using a model data from marine Copernicus with a resolution of 0.083° × 0.083°. For that, we examined wind forcing, ocean circulation, sea surface temperature, sea surface salinity, sea surface chlorophyll-a, and mixed layer depth seasonality from 2007 to 2017 in the Cape Bojador south of the Moroccan Atlantic coast. We observed that in the fall season the wind speed was low, and the maximum wind speed is in the summer season. Furthermore, we found that coastal areas are related to a generally shallower MLD all the year in the Cape. We also proved that the source of the upwelling is between 25 and 26°N. However, we observed that the sea surface chlorophyll concentration in the same region is minimum, while in the region between 24.5 and 22°N, the CHL-a is maximum. We suggested that the biological richness in Cape Bojador, due to the activity of upwelling, derives to the south because of the northward ocean filament. Despite the different physical and biological parameters used to detect upwelling activity, we found that upwelling detection based on sea surface temperature is the best method to describe the upwelling activity in this region.

Modeling the enhancement of sea surface chlorophyll concentration during the cyclonic events in the Arabian Sea

The response of a marine system to a tropical cyclone is often less studied due to lack of direct observations of such events. In this paper, we demonstrate the multifold benefits of using a fully coupled physical-biogeochemical model, configured using Regional Ocean Modeling System (ROMS), in investigating the biogeochemical response of the upper ocean to a tropical cyclone in the semi-landlocked basin of Arabian Sea in the north Indian Ocean. We show that the model manages to capture the spatio-temporal variability of the biological state variables during and after the passage of cyclones. We also investigate the processes that lead to chlorophyll enhancement during cyclone passage - a benefit that model provides against satellite observations. We show that Ekman pumping leads to the shoaling of thermocline depth – which in turn, triggers productivity in the upper ocean by means of nutrient entrainment. The sea surface chlorophyll concentration reaches its peak approximately with the time-lag of a week after the increase in the nitrate concentration of the surface waters. We also show, using results from our model, that the chlorophyll enhancement followed by phytoplankton bloom is dependent on the intensity of the cyclone and is inversely dependent on the translational speed of the cyclone. Our study provides the first-ever comprehensive insights into the continuous and progressive physical-biogeochemical coupled processes across water column during cyclonic events in the Arabian Sea.

BẤT THƯỜNG CỦA HÀM LƯỢNG CHLOROPHYLL TẦNG MẶT TẠI VÙNG BIỂN VEN BỜ NAM TRUNG BỘ VIỆT NAM LIÊN QUAN ĐẾN HIỆN TƯỢNG ENSO

The studies on the impact of the ENSO phenomenon on climate and environment change have shown that the Bien Dong (Southeast Asia Sea) is strongly influenced by this phenomenon. This paper focuses on analyzing sea surface chlorophyll concentration data in the coastal marine area of Vietnam South Centre from MODIS satellite images of National Aeronautics and Space Administration (US NASA). The analysis results have shown that there is no obvious difference of the chlorophyll anomaly index between El Niño and neutral years. However, in La Niña years the chlorophyll anomaly index is greatly varied and generally inversely proportional to the ONI index, which means chlorophyll anomaly index rises while ONI index falls. The impact has made chlorophyll in summer and autumn of La Niña years higher by 0.22 - 0.38 mg/m3 in comparison with other years. In terms of trends, chlorophyll concentration in the Vietnam South Central Coast fluctuates according to the seasons and months. The average chlorophyll concentration usually reaches its maximum value in the Autumn (Sep. - Nov.), then decreases in the Winter (Dec. - Feb.) and usually reaches the minimum value in the Spring (Mar. - May), then rises gradually in the Summer (June - Aug.). The above results have contributed to improving understanding of the impact of the climatic vagaries on the coastal marine area of Vietnam South Centre, supported scientists and managers in proposing measures to prevent, avoid efficiently, limit and mitigate the damage caused by ENSO, and in having reasonable alternatives in the protection of biodiversity as well as environment in the coastal marine area of Vietnam South Centre. It could be considered as a “small piece” of the overall picture of the impacts of the ENSO phenomenon on global climate change.

Sclerochronological Study of a Glycymeris vangentsumi Population From the Madeira Islands

Despite the positive results obtained using saltwater clam Glycymeris spp. for palaeoenvironmental reconstructions in the extratropical North Atlantic domain, this potential of the species has not been investigated in the subtropical North Atlantic region. The aim of this study was to investigate the driving factors for shell growth in Glycymeris bivalves by analysing growth patterns of G. vangentsumi specimens from an environment that is exposed to relatively minor seasonal contrast in terms of temperature compared to mid/high latitudes around the Madeira Islands. The populations studied comprised a group of sub-fossil shells (n=58) collected near the Desertas Islands, Madeira, in 2014, in a depth range of 80-160 m, together with two live-caught specimens. The shells collected alive were relatively young (<37 years), while the ontogenetic ages of the sub-fossil shells proved to be high (up to 154 years). Compared to those collected at greater depths, the average growth rate of the shells in the shallower environment was higher in the first four years. Subsets of the Madeira (n=16) samples could be arranged into a robust site chronology covering the 1950-2012 period, and these were used to explore shell growth responses to environmental parameters. The composite chronology displayed a negative correlation (r<-0.58, p < 0.01) with the January-April sea surface temperature (SST) around Madeira and a positive correlation (r=0.52, p<0.05) with the March sea surface chlorophyll concentration data of the region, from 1998 to 2012. The results presented here suggest that at this southern collection site, lower water temperature was not a directly limiting environmental variable, and other external environmental effects may exert stronger control on shell growth. These include the effect of late winter ocean mixing on the formation of the deep chlorophyll maximum.

Remote Sensing Observations of the Winter Yellow Sea Warm Current Invasion into the Bohai Sea, China

Using ASCAT, QuikSCAT, and MODIS data, we analyzed the sea surface wind field, temperature, salinity, and chlorophyll concentrations in the mixed zone between the Bohai Sea and Yellow Sea in the winter (the period of winter 2013 included December 2013 and January-February 2014) from 2002 to 2013. We found that the intrusion of the Yellow Sea Warm Current into the Bohai Sea occurred three times in the winters of 2007 (strongest), 2004, and 2013 (weakest) during this 12-year period. We present detailed validation of the intrusion in 2013. This study shows that the intrusion of the Yellow Sea Warm Current into the Bohai Sea occurred when the wind speed, sea surface temperature, and salinity were above (or close to) the multiyear average and the chlorophyll concentration was less than the multiyear average.

Bacterial and archaeal biogeography of the deep chlorophyll maximum in the South Pacific Gyre

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 75:1-13 (2015) - DOI: https://doi.org/10.3354/ame01746 FEATURE ARTICLE Bacterial and archaeal biogeography of the deep chlorophyll maximum in the South Pacific Gyre Emily A. Walsh1,*, David C. Smith1, Mitchell L. Sogin2, Steven D’Hondt1 1Graduate School of Oceanography, University of Rhode Island, Narragansett Bay Campus, 215 South Ferry Road, Narragansett, RI 02882, USA 2Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA *Corresponding author: ewalsh@gso.uri.edu ABSTRACT: We used 16S rRNA gene tag pyrosequencing to examine the biogeography of bacterial and archaeal community composition in the deep chlorophyll maximum (DCM) of the South Pacific Gyre (SPG), the largest and most oligotrophic region of the world ocean. Dominant DCM bacterial taxa, including Prochlorococcus, SAR11, SAR406, and SAR86, were present at each sampled site in similar proportions, although the sites are separated by thousands of kilometers and up to 100 m in water depth. Marine Group II (MGII) and MGIII Euryarcheota dominated the archaeal assemblages of the DCM at these sites. Bray-Curtis indices show that assemblage composition of these sites is >70% similar for Bacteria and >80% similar for Archaea. Despite these similarities, communities of the central SPG, the western SPG margin, and the southern SPG margin are distinguishable from each other. Comparison of our bacterial results to samples from the DCM of the North Pacific Gyre (NPG) and the relatively nutrient- and chlorophyll-rich Equatorial Pacific (EQP) shows that DCM bacterial assemblage composition is >50% similar throughout all 3 regions. Nonetheless, the SPG, NPG, and EQP assemblages are statistically distinct from each other (ANOSIM, p = 0.001), with the communities of the 2 gyres resembling each other more closely than either resembles the EQP community (which lives geographically between them). Variation in assemblage composition correlates with sea-surface chlorophyll concentration (r2 = 0.71, p < 0.003). This study demonstrates that the DCM horizons of different oceanic regions harbor statistically distinct communities that are consistent within regions for thousands of kilometers. KEY WORDS: South Pacific Gyre · Microbial biogeography · Microbial diversity · Deep chlorophyll maximum · Pyrosequencing Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: Walsh EA, Smith DC, Sogin ML, D’Hondt S (2015) Bacterial and archaeal biogeography of the deep chlorophyll maximum in the South Pacific Gyre. Aquat Microb Ecol 75:1-13. https://doi.org/10.3354/ame01746 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 75, No. 1. Online publication date: April 23, 2015 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2015 Inter-Research.

Multi-Criteria Decision Analysis as a tool to extract fishing footprints and estimate fishing pressure: application to small scale coastal fisheries and implications for management in the context of the Maritime Spatial Planning Directive

In the context of the Maritime Spatial Planning Directive and with the intention of contributing to the implementation of a future maritime spatial plan, it was decided to analyze data from the small scale coastal fisheries sector of Greece and estimate the actual extent of its activities, which is largely unknown to date. To this end we identified the most influential components affecting coastal fishing: fishing capacity, bathymetry, distance from coast, Sea Surface Chlorophyll (Chl-a) concentration, legislation, marine traffic activity, trawlers and purse seiners fishing effort and no-take zones. By means of Multi-Criteria Decision Analysis (MCDA) conducted through a stepwise procedure, the potential fishing footprint with the corresponding fishing intensity was derived. The method provides an innovative and cost-effective way to assess the impact of the, notoriously hard to assess, coastal fleet. It was further considered how the inclusion of all relevant anthropogenic activities (besides fishing) could provide the background needed to plan future marine activities in the framework of Marine Spatial Planning (MSP) and form the basis for a more realistic management approach.

Spatio‐temporal variability of zooplankton biomass and environmental control in the Northern Benguela Upwelling System: field investigations and model simulation

AbstractSpatial and temporal distribution patterns of zooplankton are highly variable in the Northern Benguela Upwelling System. We studied the distribution of zooplankton (size class ≥ 0.33 mm) and used field data from four cruises that took place between March 2008 and February 2011, as well as simulation results of a regional ecosystem model. Remotely sensed sea surface temperatures (SST) and surface chlorophyll concentrations were analysed to investigate environmental influences on zooplankton biomass. The Intense Benguela Upwelling Index showed a distinct seasonal signal throughout the years and the highest upwelling peaks in August/September. Even though surface chlorophyll concentrations were very variable throughout the year, the highest concentrations were always detected in September, following the upwelling of nutrient‐rich water. In field catches, zooplankton biomass concentration in the upper 200 m was highest above the outer shelf and shelf‐break in December 2010 and February 2011, i.e. 6 months after the upwelling peaks. In contrast, zooplankton biomass simulated by the model in the surface water was highest in September. In March/April, biomass maxima were typically measured in the field at intermediate water depths, but the vertical distribution was also affected by extensive oxygen minimum zones. The ecosystem model reproduced this vertical pattern. Although general trends were similar, simulation data of zooplankton standing stocks overestimated the field data by a factor of 3. In upwelling systems, food webs are generally considered to be short and dominated by large cells. However, our field data indicate more small‐sized zooplankton organisms above the shelf than offshore.

中西太平洋鲣鱼围网渔业资源的空间热点和空间异质性分析

The western and central Pacific Ocean is one of the most productive purse seine skipjack tuna( Katsuwonus pelamis) fisheries in the world. To understand the structural characteristics of skipjack tuna resources in the western and central Pacific Ocean,based on a Chinese fleet purse seine skipjack tuna catch and effort data from 2005—2009,the datawere summarized by year and by yearly average for 0. 5° × 0. 5° areas,and the spatial autocorrelation and spatial heterogeneity of skipjack tuna resources were calculated by using a spatial statistical method. The hot spot areas of skipjack tuna resources were analyzed with marine environment factors( sea surface temperature and chlorophyll concentration) to determine the reasons for hot spot formation. The methods and conclusions are as follows.( 1) Through conventional statistics calculations we obtained the skewness value,Kurtosis number,coefficient of variation,and global spatial autocorrelation Geary c index of skipjack tuna resources,and found that the density of skipjack tuna resources was low in most of the western and central Pacific,but high density areas could be found in some"hot spot". Fish resources exhibited spatial distribution differences and showed strong concentration distribution spatial patterns. As a whole,there was medium spatial autocorrelation.( 2) Through hotspot analysis,we found that local spatial autocorrelation of skipjack tuna resources was strong. There was more than one"hot spot"and"cold spot"that were statistically significant.( 3) When studying the spatial heterogeneity and directional variation of skipjack tuna resources by using geostatistical methods,we obtained the semivariograms parameters and best-fitting semivariogram models. The best-fitting semivariogram model was the sphere model. The average spatial correlation distance( the geostatistical range) was about 1000 km. Approximately 50% variation was explained by spatial autocorrelation,and the rate of spatial autocorrelation was moderate. In directional variation,the structure of the south-north direction was stronger than that of the east-west direction. The rate of structure variation was67% in the south-north direction and 49% in the east-west direction. This conclusion is consistent with marine environmental structure in which spatial distribution has better regularity and structure in the south-north direction compared with the east-west direction. The fractal dimension value of different directions was from 1. 876 to 1. 9; therefore,spatial autocorrelation was weak.( 4) This paper regards skipjack tuna resource hotspot areas as regional fishing grounds.Respectively mapped fishing grounds overlapped with sea surface temperature and chlorophyll concentration. The fishing grounds of skipjack tuna resources in the western and central Pacific Ocean were divided into two different local fishing grounds: cold-tongue and warm-pool ground. The cold-tongue fishing ground,which is caused by the Middle East Pacific equatorial upwelling,provided more abundant primary productivity in the frontal zone,and hence more food for fish. The warm-pool fishing ground is nearer to the mainland and islands where coastal upwelling system can provide primary productivity.( 5) Finally,we compared the method of hot spot analysis with that of fishing ground gravity and habitat suitability index,and identified advantages and disadvantages of those methods. Future studies will involve using the space residual model to solve spatial autocorrelation problems.

Characterizing the potential habitat of European anchovy Engraulis encrasicolus in the Mediterranean Sea, at different life stages

AbstractIdentification of the potential habitat of European anchovy (Engraulis encrasicolus) at different life stages in relation to environmental conditions is an interesting subject from both ecological and management points of view. For this purpose, acoustic data from different seasons and different parts of the Mediterranean Sea along with satellite environmental and bathymetry data were modelled using generalized additive models. Similarly, egg distribution data from summer ichthyoplankton surveys were used to model potential spawning habitat. Selected models were used to produce maps presenting the probability of anchovy presence (adults, juveniles and eggs) in the entire Mediterranean basin, as a measure of habitat adequacy. Bottom depth and sea surface chlorophyll concentration were the variables found important in all models. Potential anchovy habitats were located over the continental shelf for all life stages examined. An expansion of the potential habitat from the peak spawning (early summer) to the late spawning season (early autumn) was observed. However, the most suitable areas for the presence of anchovy spawners seem to maintain the same size between seasons. Potential juvenile habitats were associated with highly productive inshore waters, being less extended and closer to coast during winter than late autumn. Potential spawning habitat in June and July based on ichthyoplankton surveys overlapped but were wider in extent compared with adult potential habitat from acoustics in the same season. Similarities and dissimilarities between the anchovy habitats as well as comparisons with sardine habitats in the oligotrophic Mediterranean Sea and other ecosystems with higher productivity are discussed.

Utility of Primary Productivity Map for Fishery Forecasting

Ocean colour and thermal data from earth orbiting satellites are being used in fishery resource applications. The location of ocean fronts and circulation features are considered as prospective fishing grounds. Ocean frontal zones, as resolved by strong gradients in the surface temperature distribution, has historically been important as indicators for fishing localities over all the oceans. In the present study, the sea surface temperature and chlorophyll concentration map along with the primary productivity map are used to evaluate the usefulness of the above data in fishery forecasting. In the present study, North Andhra Fishing Zone and Maharastra Fishing Zone, India have been taken for investigation. The analysis of thermal front, chlorophyll front with fish catch indicates a nonlinear relationship. The analysis of sea surface temperature (SST) with fish catch also shows a nonlinear relationship. The analysis of chlorophyll concentration with fish catch shows a linear relationship. However, the coefficient of determination (r2) in each case is found to be inconsistent between the two fishing zones. The analysis of primary productivity front with fish catch shows a non linear relationship. The analysis of primary productivity and fish catch shows a linear relationship. The r2 values in both the cases are found to be closer to each other between the two fishing zones. Therefore, it is suggested to include primary productivity map for improved fishing forecasting.