Organic waste impact of capture-based Atlantic bluefin tuna aquaculture at an exposed site in the Mediterranean Sea

A variety of pelagic and benthic parameters were measured at an aquaculture farm used for the fattening of Atlantic bluefin tuna (Thunnus thynnus) which is located at an exposed site (700 m from the coast, average bottom depth of 45 m and average current speed of 6 cm s⁻¹) in the Mediterranean Sea. The objective was to test whether modern off-shore tuna fattening industries can exert a sustainable organic waste impact on the receiving environment as has been reported for the offshore culture of more traditional Mediterranean species such as sparids. In the water column, the concentration of phytopigments, organic matter, heterotrophic bacteria and the taxonomic abundance of mesozooplankton (at the species level) were assessed. In the sediment, we assessed the concentration of reduced sulphur pools, phytopigments, organic matter, heterotrophic bacteria and the taxonomic abundance of meiofauna (at the taxa level) and nematodes (at the genus level). For most parameters, we found no substantial differences between farm and control sites. Deviations of farm values from control values, when they occurred, were small and did not indicate any significant impact on either the pelagic and benthic environment. Deviations were more apparent in the benthic compartment where lower redox potential values, higher bacterial production rates and a change in nematode genus composition pointed out to early changes in the sediment's metabolism. In addition, indigenous potential pathogenic bacteria showed higher concentration at the fish farm stations and were a warning of an undesirable event that may become established following aquaculture practice in oligotrophic environments. The overall data from this study provide extensive experimental evidence to support the sustainability of modern offshore farming technology in minimizing the hypertrophic-dystrophic risks associated with the rapidly-expanding tuna-fattening industry in the Mediterranean Sea.     

The irony and the exclusivity of Atlantic bluefin tuna management

The eastern stock of Atlantic bluefin tuna (thunnus thynnus) was recently nominated for protection under the Convention on International Trade in Endangered Species of Flora and Fauna (CITES). That nomination failed, which leaves management of the heavily overfished stock in the hands of the International Commission for the Conservation of Atlantic Tunas (ICCAT). This paper reviews the history of ICCAT management of Atlantic bluefin tuna to show that (1) early elimination of competitive forces prevented agreement on management in keeping with scientific advice, resulting in the steep decline of the stock, (2) even just the threat of a CITES listing can provide temporary impetus for marked improvement in ICCAT management, and (3) long-term sustainable management by ICCAT will require continued economic and political pressure.     

Evaluation of Atlantic bluefin tuna reproductive potential in the western Mediterranean Sea

Ovarian tissue samples of Atlantic bluefin tuna (ABFT) spawners (n = 49) caught by purse seine in the Balearic Sea (western Mediterranean) were used to assess the stock reproductive characteristics. The frequency of spawning females estimated by the postovulatory follicle method was 84% and the spawning periodicity 1.2 days. Using an unbiased stereological method, the realized batch fecundity was estimated from counts of postovulatory follicles (POFs), whereas the batch fecundity of the subsequent spawn was estimated by quantification of the number of follicles containing oocytes at maturation stage (OMFs). The number of POFs was used as a reliable proxy of the realized batch fecundity, as it represents the actual number of eggs released in the last spawning event. The average relative realized batch fecundity was estimated to be approximately 48 eggs g^− 1 of total body mass. While the absolute batch fecundity was isometrically related to the fork length, the relative batch fecundity was not dependent on fish size, which leads to the assumption that all length classes contribute proportionally to their size, towards the total number of eggs spawned by the broodstock. Size-related variations in the sex ratio were observed in the study area and in other Mediterranean locations; females were more abundant in mid-size classes while males predominated in large-size classes.     

DNA identification of Pacific bluefin tuna (Thunnus orientalis) in the New Zealand fishery

Muscle samples were collected from 69 specimens identified as Pacific bluefin tuna (Thunnus orientalis) (Temminck and Schlegel, 1844) in the New Zealand Exclusive Economic Zone (EEZ) between 1990 and 2000. Identifications before 1996 were based on body size and colour of the caudal keel; later identifications were mostly based on the shape of abdominal cavity. The tissue samples were tested with a diagnostic mitochondrial DNA marker that distinguishes southern bluefin Thunnus maccoyii (Castelnau, 1872) and Pacific bluefin tuna T. orientalis; 59 specimens were confirmed as T. orientalis and 10 as T. maccoyii. Specimens recorded as Pacific bluefin tuna by the shape of the abdominal cavity were correctly identified as T. orientalis, and this character can be used to identify large specimens landed on tuna vessels. Some specimens recorded as Pacific bluefin tuna on the basis of colour and size were T. maccoyii; and early records of T. orientalis in New Zealand waters, based on these characters, are unreliable. Unusual colour patterns were reported in some specimens of T. orientalis but not T. maccoyii. The Pacific bluefin tuna T. orientalis accounted for less than 0.3% of the bluefin tuna catch in the New Zealand EEZ during the 1990s.     

Species-diverse coral communities on an artificial substrate at a tuna farm in Amami,Japan

Tuna-farming is expanding worldwide, necessitating the monitoring/managing of its effects on the natural environment. In Japan, tuna-farming is conducted on coral reefs that have been damaged by mass-bleaching events and crown-of-thorns starfish (COTS) outbreaks. This study focused on the coral community on an artificial substrate of tuna-farm to reveal the possible effects of tuna-farming on the natural environment. Corals flourished on ropes suspended in the farm in the Amami Islands, southern Japan. These were moored 3 m below the sea-surface in 50-m-deep water. The coral community on the rope was analyzed and compared with those on natural substrata on two adjacent COTS-damaged reefs and with that in a protected reef. Corals were monitored throughout a year. Sixty coral species grew on the ropes, that corresponds to 27.3% of the 220 species known from Amami. The coral community was unique, dominated by massive faviid corals. On the ropes, the water temperature rarely exceeded 30.0 °C and no corals on the rope were severely bleached or covered by sedimentation during the observations. The tuna-farm infrastructure provided corals with a suitable habitat, and species-rich coral communities were established. These coral communities are an important node connecting tuna-farms and the natural environment.     

Habitat mapping of the Atlantic bluefin tuna derived from satellite data: Its potential as a tool for the sustainable management of pelagic fisheries

The feeding and spawning habitats of the overfished Atlantic bluefin tuna (BFT) are mapped in the Mediterranean Sea and used in the present proposal for selecting restricted fishing grounds. The feeding habitat is mainly traced by oceanic fronts of satellite-derived temperature and chlorophyll while the spawning habitat is mostly characterized by an important heating of surface waters. The proposal recommends opening the fishery in feeding areas in case the BFT stock is low (current situation). Only spawning areas at its latest stage could be opened once the stock has recovered to its optimum yield. Due to the possible concentration of fishing vessels if fishing areas are restricted (e.g. four-fold increase with a 1/16th restriction of the Mediterranean Sea) the inspection activities could be better targeted. Identified spawning grounds, opened or closed to fishing, could also be particularly monitored by control operations. Within the authorized areas, the habitat maps would guide fishermen to the favourable habitat reducing their costs. The habitat guided management could be able to adapt the spatial and temporal distribution of the effort to the requirements of both the fisheries’ control and the resource. Its implementation is likely to protect the stock (a) by apparently decreasing illegal fishing which accounts in the recent years for more than 1/3rd of total catches, (b) by protecting the spawners to ensure a suitable recruitment and (c) by distributing the effort to respect the population structure. The first species studied is the emblematic bluefin tuna which is at high risk of collapse due to overfishing. The approach is a priori transposable to other epipelagic species of commercial importance.     

The spectre of uncertainty in management of exploited fish stocks: The illustrative case of Atlantic bluefin tuna

The recent overexploitation of East Atlantic and Mediterranean bluefin tuna stock has been well documented in the media where it has become the archetype of overfishing and general mis-management. Beyond the public debate, the crisis also highlighted how the interactions between science and management can change through time according to the awareness of the public opinion. To reflect these issues, the history of Atlantic bluefin tuna overfishing is first described. Then, the major uncertainties that undermine the current scientific advice are summarized and the importance of reducing their impacts by improving knowledge and developing robust scientific framework is considered. The study also discusses how uncertainty was used by different lobbies to discredit science-based management. The recent improvement in bluefin tuna stock status following the implementation of the rebuilding plan shows that, despite uncertainty in the scientific advice, the management of a heavily exploited fish stock can be positive when there is a political will. However, optimizing long-term yields of modern fisheries implies good science. The study concludes by advocating for the implementation of a scientific quota that should be part of the management framework to support the scientific advice.     

南方蓝鳍金枪鱼渔业和生物学的研究进展

南方蓝鳍金枪鱼(Thunnus maccoyii)是金枪鱼渔业的重要经济鱼种,历史上其全球年产量曾达到8万t水平[1]。由于长期的过度开发,近年来资源衰退严重,渔获量不断下降,各国已纷纷提出并实施一些养护措施[2~4]。目前中国正大力开发远洋金枪鱼渔业,而国内对南方蓝鳍金枪鱼的专项研究匮     

The potential compatibility of offshore wind power and fisheries: An example using bluefin tuna in the Adriatic Sea

Given the increasing competition for marine resources, regulatory strategies that benefit multiple stakeholders are increasingly important. Offshore wind power generating facilities are becoming more common in the marine environment and alter the characteristics of the fisheries in the surrounding area. Floating wind turbines can act as fish aggregating devices (FAD), thereby increasing the catchability for some species. Many marine recreational fisheries are open access without effort restrictions; therefore, control of total harvest is difficult. Creating a limited entry recreational fishery and excluding commercial fishing from the area surrounding offshore wind turbines may aid in controlling total harvest and may benefit several important stakeholder groups: (1) recreational and commercial fishermen in terms of higher recreational catch rates and potentially higher overall yield, (2) fisheries managers in terms of more precise control of recreational fisheries harvest, and (3) owners of offshore wind power facilities in terms of reduced risk of damage to infrastructure due to fishing activity. We discuss the compatibility of wind power facilities and fisheries, conditions conducive to this compatibility, and provide an example from a proposed offshore wind power facility in the Adriatic Sea and its potential to affect the fisheries management there, particularly for bluefin tuna (Thunnus thynnus).     

Investigation of a mushroom-like flow in the shelf edge area of northern seas

The dynamics of the evolution of a mushroom-like flow in the shelf edge area of northern seas in April 1989 are analysed using regular satellite data. The use of hydrologic shipboard observations conducted by a research ice-breaker in the area of development of the mushroom-like flow allowed some insights into the mechanism of its generation.Translated by V. Puchkin.     

南海神狐海域上陆坡区典型浅地层剖面的初步解释

应用Triton SB-Interpreter软件对"大洋一号"DY115-20航次试航A航段在南海神狐海域上陆坡区取得的TOPAS浅地层剖面资料进行后处理,并对处理结果进行初步解释,结果表明:(1) 根据地形特征,南海神狐海域上陆坡区顺坡向下可分为起伏区和平坦区,起伏区地形起伏较大,声波穿透性较差;平坦区地形基本没有起伏,声波穿透性较好.(2) 陆坡凸起可能广泛发育于研究区,并且和天然气水合物关系密切,陆坡凸起的成因可能是泥底辟作用,或泥底辟等因素的存在导致沉积地层在重力作用下发生变形.(3) 研究区沉积层中发育有声空白补丁、局部增强反射和声空白带等声学特征,证明了含气结构的存在,相应的沉积层构成了一个含气结构带,若含气结构带下方发育的断层成为气体向上运移的通道,深部天然气水合物的分解为气体的来源,则由此构成的"气源+运移通道+含气结构带"组合可能成为天然气水合物的找矿标志.综上可见,应用Triton SB-Interpreter软件对TOPAS浅地层剖面资料进行后处理,得到的浅地层剖面对寻找天然气水合物具有一定的指示意义.     

Biomarkers of Middle to Late Jurassic marine sediments from a canonical section: New records from the Yanshiping area,northern Tibet

The Yanshiping section, which includes the Quemo Co, Buqu, Xiali, Suowa and Xueshan Formations (Yanshiping Group) exposes organic-rich Middle to Late Jurassic deposits in the Qiangtang Basin of northern Tibet. The biostratigraphic data, from bivalves, brachiopods as well as dinoflagellate cysts, define a Bajocian to Tithonian age. This study focuses on the biomarkers present in these mudstones and limestones to determine the sources, thermal maturity and depositional environment of the organic matter. Most samples show a clear dominance of short-chain (C₁₅–C₂₀) n-alkanes with a maximum at C₁₉ or C₁₉ with a secondary maximum at C₂₃ except for the sample BP01(22)S1 where the predominant range is C₂₂ to C₂₆ with a maximum at C₂₄, significant CPI and odd-to-even predominance. The hopanoids and steroids suggest that the sources of organic matter were dominated by phytoplankton, especially algae, as the primary source. Furthermore, the Pr/Ph, Pr/nC₁₇ and Ph/nC₁₈, with relatively low values plus high abundance of 17α(H)-hopanes, support deposition in dysoxic to reducing, relatively shallow-water depositional settings, and the presence of gammacerane indicates normal marine salinity and/or water-column stratification. All samples are fairly mature with respect to petroleum generation, a conclusion supported by maturity parameters such as C₃₁ 22S/(22S + 22R) hopanes and C₂₉ ααα20S/(20S + 20R) steranes.     

Methane seepage in the Shenhu area of the northern South China Sea: constraints from carbonate chimneys

Two authigenic carbonate chimneys were recovered from the Shenhu area in the northern South China Sea at approximately 400 m water depth. The chimneys’ mineralogy, isotopic composition, and lipid biomarkers were studied to examine the biogeochemical process that induced the formation of the chimneys. The two chimneys are composed mostly of dolomite, whereas the internal conduits and semi-consolidated surrounding sediments are dominated by aragonite and calcite. The specific biomarker patterns (distribution of lipids and their depleted δ¹³C values) indicate the low occurrence of methanotrophic archaea ANME-1 responsible for the chimneys’ formation via anaerobic oxidation of methane. A significant input of bacteria/planktonic algae and cyanobacteria to the carbon pool during the precipitation of the carbonate chimneys is suggested by the high contributions of short-chain n-alkanes (69% of total hydrocarbons) and long-chain n-alcohols (on average 56% of total alcohols). The oxygen isotopic compositions of the carbonate mixtures vary from 3.1‰ to 4.4‰ in the dolomite-rich chimneys, and from 2.1‰ to 2.5‰ in the internal conduits, which indicates that they were precipitated from seawater-derived pore waters during a long period covering the last glacial and interglacial cycles. In addition, the mixture of methane and bottom seawater dissolved inorganic carbon could be the carbon sources of the carbonate chimneys.     

Rare earth elements in cold seep carbonates from the southwestern Dongsha area,northern South China Sea

The circulation of methane-rich fluids at cold seeps often leads to the precipitation of seep carbonates close to the seafloor along continental margins, which can be used as records of past fluid seepage. Rare earth element (REE) concentrations in seep carbonates have been used to trace fluid sources and provide information on associated biogeochemical processes at cold seeps. The REE concentrations of a series of carbonates collected from cold seeps in the southwestern Dongsha area of the northern South China Sea are analyzed in this study. The total REE contents (ΣREE) of the seep carbonates analyzed show a wide variation from 17 ppm to 523 ppm with an average ΣREE value of 54 ppm, which are higher than the typical marine carbonate values of ∼28 ppm commonly reported and also higher than those of the carbonates from other cold seep areas. A positive correlation between Fe–Mn content and ΣREE was observed. These results suggest that the seep carbonates of this study were primarily controlled by the methane-derived fluid from which they precipitated. The Fe-rich dolomite and siderite, which are the main components of the carbonates, are responsible for the enrichment of the REE. A slight positive Ce anomaly observed in the shale-normalized REE patterns of the studied seep carbonates suggests that they formed in anoxic conditions, and the correlations between Ce/Ce* and La_N/Sm_N, Ce/Ce* and Dy_N/Sm_N, Ce/Ce* and ΣREE further reveal that the REE characteristics of most seep carbonate samples preserve the original redox conditions in which they precipitated and late diagenesis has had little effect on the REE. However, the REE characteristics of sub-samples DS2-2B, DS1-6A and DS1-7A are very different from those of the other sub-samples, indicating a greater impact of late diagenesis and post-oxidation favored REE enrichment.     

南海北部冷泉区深水珊瑚的发现及其特征

冷水珊瑚也称为深水珊瑚, 在生物多样性、生态资源和科研价值等方面具有重要意义。文章对采自南海北部冷泉区的冷水珊瑚骨骼碎屑进行测定, 鉴定出冷水珊瑚2个种(Crispatotrochus sp.1和Crispatotrochus sp.2), 以及4个属[Balanophyllia (Balanophyllia)、Balanophyllia (Eupsammia)、Lochmaeotrochus和Enallopsammia]。测定的冷水珊瑚的δ¹³C为-7.36‰~-1.15‰, δ¹⁸O为-1.38‰~3.67‰, 与全球冷水珊瑚碳氧同位素组成相似, 但明显不同于南海暖水珊瑚、冷泉碳酸盐岩及低温热液成因碳酸盐岩的碳氧同位素组成。