Hauraki Gulf snapper fishery, 1972 and 1973: Some evidence for a declining catch‐rate

The commercial fishery for snapper Chrysophrys auratus (Bloch and Schneider) in the Hauraki Gulf is one of New Zealand's principal marine fisheries. The snapper catch from this area declined by 22% in 1972, and by a further 4% in 1973, following 4 y of high catches by Danish seiners.

Some of the decline can be attributed to economic factors within the industry, and adverse winter weather. However, the 1972 decline in Danish seine catches is an acceleration of an existing trend. It probably results from heavy exploitation of an accumulated stock, and from movement of a few strong year classes past the age at which they have contributed most to the catch. The slight recovery in the 1973 Danish seine catch resulted only from increased effort; catch per day at sea continued to fall. An improvement in catch and catch per day is unlikely for some years at least.

Snapper catches by other methods (trawl, long line, and set net) also declined during 1972, but the available data on fishing effort do not allow a detailed analysis. The trawl catch in the gulf fell further in 1973 as fishing effort was diverted to other grounds, but the catch by lines and nets improved slightly.     

Tagging indicates at least two stocks of snapper Chrysophrys auratus in south‐east australian waters

During 1957 to 1962, 4 155 snapper Chrysophrys auratus (Bloch & Schneider) were tagged and released at a number of sites in Victoria. From 1957 until 31 June 1972, 210 of these fish have been reported, and the relationship between the release and recapture sites indicates the existence of at least two stocks: One stock extends from central Victoria to eastern South Australia, and the other extends from eastern Victoria to northern New South Wales.     

Comparison of the growth rates of two stocks ot snapper (Chrysophrys auratus) in south‐east Australian waters using capture‐recapture data

Between 1957 and 1962, 4155 snapper, Chrysophrys auratus (Bloch & Schneider), were tagged and released at a number of sites in Victoria. By the end of June 1972, 210 had been recaptured, and knowing their lengths at release and recapture and the periods at liberty, we determined the von Bertalanffy growth parameters K and L ₈ ^. The values (with 95% confidence limits) were: eastern stock ‐ K = 0.071 ± 0.040, L₈ = 968 ± 325 mm; western stock ‐ K = 0.068 ± 0.023, L₈ = 1079 ± 209 mm; combined stocks ‐ K = 0.062 ± 0.019, L ₈ = 1119 ± 215 mm. No difference between the stocks was apparent when we compared the estimates of K and L ₈ separately; however, when the estimates of K and L ₈ were compared together, a Wilcoxon's test gave a significance probability of 1.5%, indicating a difference in growth rate between the stocks. For the range of lengths of snapper recaptured, this difference was evidently caused by faster growth of snapper from the western stock.     

Nutrient land–sea fluxes in oligothrophic and pristine estuaries of the Gulf of Bothnia,Baltic Sea

Estuaries are often seen as important filters between land and the sea for inorganic and organic nutrients. This paper aims at estimating the estuarine fluxes of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and dissolved silicate for the major oligothrophic and pristine rivers running into the Bothnian Bay (BB) and the Bothnian Sea (BS), the northern subarctic subbasins of the Baltic Sea. Long-term data sets for these rivers and their estuaries as well as for the BB and BS were analyzed to assess whether these estuaries are sinks for inorganic nutrients. Most studied estuaries can be characterized as salt wedge estuaries with little exchange between the fresh seaward-flowing river water and the inward-flowing seawater. Estimates of water transit times ranged between 1 and 14 days. In most estuaries of the BB, N-depleted river water meets P-depleted seawater during the growth period. These findings were corroborated by mixing diagrams showing that the inner areas of the estuaries were N-depleted in summer. In the BS, on the other hand, both rivers and seawater were mostly N-depleted during summer. Thus, for most estuaries of this region of the Baltic Sea, primary productivity is presumably lower than or equal to that of offshore. The low productivity is also reflected in the sediments. The coastal sediments did not differ from the offshore stations in accumulation rates as well as the content of organic matter and nutrients, indicating that estuarine nutrient burial is not always higher as normally observed in other temperate systems. Finally, the estuaries of the pristine rivers in the northernmost part of the BB import DIN during summer, whereas the estuaries of the rivers in the BS import DIP during winter, from the sea.     

Water mass properties and fluxes in the Rockall Trough, 1975–1998

A time series of a standard hydrographic section in the northern Rockall Trough spanning 23 yr is examined for changes in water mass properties and transport levels. The Rockall Trough is situated west of the British Isles and separated from the Iceland Basin by the Hatton and Rockall Banks and from the Nordic Seas by the shallow (500 m) Wyville–Thompson ridge. It is one pathway by which warm North Atlantic upper water reaches the Norwegian Sea and is converted into cold dense overflow water as part of the thermohaline overturning in the northern North Atlantic and Nordic Seas. The upper water column is characterised by poleward moving Eastern North Atlantic Water (ENAW), which is warmer and saltier than the subpolar mode waters of the Iceland Basin, which also contribute to the Nordic Sea inflow. Below 1200 m the deep Labrador Sea Water (LSW) is trapped by the shallowing topography to the north, which prevents through flow but allows recirculation within the basin. The Rockall Trough experiences a strong seasonal signal in temperature and salinity with deep convective winter mixing to typically 600 m or more and the formation of a warm fresh summer surface layer. The time series reveals interannual changes in salinity of ±0.05 in the ENAW and ±0.04 in the LSW. The deep water freshening events are of a magnitude greater than that expected from changes in source characteristics of the LSW, and are shown to represent periodic pulses of newer LSW into a recirculating reservior. The mean poleward transport of ENAW is 3.7 Sv above 1200 dbar (of which 3.0 Sv is carried by the shelf edge current) but shows a high-level interannual variability, ranging from 0 to 8 Sv over the 23 yr period. The shelf edge current is shown to have a changing thermohaline structure and a baroclinic transport that varies from 0 to 8 Sv. The interannual signal in the total transport dominates the observations, and no evidence is found of a seasonal signal.     

Pockmarks, collapses and blind valleys in the Gulf of Cádiz

Herein we describe a suite of fluid escape depression features, including pockmarks and collapse structures, discovered in the Gulf of Cádiz (Spain) during several recent cruises. We also establish an evolutionary model for these depressions and discuss the generation of bottom undercurrent furrows from fluid-flow structures, considering the oceanographic and tectonic framework and gas expulsion mechanisms. We describe for the first time blind valleys, which we define as giant, elongated (3 to 10 km long), collapsed and complex fault-strike features comprising mega-collapses and mega-pockmarks, generated in gas-venting areas and not associated to the collapse of mud-volcano complexes. We detected the blind valleys above diapiric structures. The collapse processes associated to blind valleys result from fluid escape through migration pathways which, in turn, are created by distension due to diapiric activity or to later tectonic reactivation of these diapirs. The evolution of these blind valleys, and their present-day morphology as furrows, derives from progressive fluid migration as well as from interaction of Mediterranean Outflow Water with the seafloor.

Phytoplankton-pigment signatures and their relationship to spring–summer stratification in the Gulf of Gabes

We investigated the phytoplankton dynamics (determined by CHEMTAX analysis of HPLC pigment data) and its relationships with nutrients and water column structure, during two oceanographic cruises in May–June and September 2006 in the Gulf of Gabes (south-eastern Mediterranean). The May–June cruise coincided with the beginning of the summer stratification, while a strong stratification occurred in September with a more than 30 m deepening of the thermocline, and a reduction of the euphotic depth. This strong stratification resulted in a shift in nitrogen sources from nitrates to ammonium as well as phosphate depletion (0.2 μM) and a decrease in silicate concentrations (<2 μM). With the exception of chlorophyll a, pigment concentrations were higher in September than in May–June samplings. The pico- and nanophytoplankton were the major contributors to phytoplankton total biomass, accounting for 90% and 87% of total chlorophyll a in May–June and September, respectively. Picoplankton persisted throughout the entire survey, occupying different depth layers. Chlorophytes were present at substantial amounts (average 23% of total chlorophyll a) during May–June; however, they declined in September (average 5%). Diatoms were overall poorly represented in this study (2% of total chlorophyll a), due probably to silicate shortage. Apparently, the nutrient availability, but also the water column stability seemed to be among the major factors determining phytoplankton dynamics. Indeed, cyanobacteria were prominent in surface samples during the period of strong stratification, whereas the relative contribution of chlorophytes decreased, probably due to low phosphate availability.     

Recoveries of drift cards released from: Oil rigs around New Zealand, 1975–76 (note)

Drift cards were released in batches of 50 every 2 d at drilling sites off the north and south Taranaki coast (May‐October 1975), Banks Peninsula (July‐August 1975), and in Tasman (January‐March 1976) and Hawke Bays (November 1975‐January 1976). The shortest distance “despatch to recovery” trajectories indicate that only in the South Taranaki Bight are the trajectories predominantly unidirectional, the surface drift being southwards on the west coast of the North Island south of Cape Egmont. The trajectories of cards despatched in both Tasman and Hawke Bays highlight the variable nature of the surface drift in these bays.     

Service vessel activity in the U.S. Gulf of Mexico in support of the oil and gas industry using AIS data, 2009–2010

Offshore exploration and production in the U.S. Gulf of Mexico is supported by a large number of service vessels characterized by complex logistical patterns and demand points distributed across an expansive geographic area. No quantitative data on the spatial and temporal distributions of service vessel activity in the region is available due to the size, complexity and dynamics of the network. The purpose of this paper is to apply Automatic Identification System position data to quantify service vessel activity in the U.S. Gulf of Mexico from 2009 to 2010. A total of 1.1 million vessel arrivals and departures were recorded in 2009–2010, and in 2010, the number of vessel events increased by 40% due in part to the Macondo oil spill and cleanup response. Port-to-port movements comprise the majority of events and about 30% of activity relates to movements offshore. Port Fourchon, Venice, New Orleans, Sabine-Neches, and Lake Charles were the most active ports during the period. A detailed breakdown of vessel counts and the limitations of the analysis are outlined.     

Distribution and seasonal abundance of large cetaceans in the Durban whaling grounds off KwaZulu-Natal,South Africa, 1972–1975

Daily charts of the aerial search effort (432 206 nautical miles) of the Union Whaling Company and 1 099 sightings of 10 497 whales were available from 628 flights off Durban between 1972 and 1975. Densities of whales were analysed by month and water depth distribution over the four-year period. Low observed densities of blue Balaenoptera musculus, right Eubalaena australis, sei B. borealis and humpback Megaptera novaeangliae whales most likely resulted from earlier whaling pressure. Seasonality of blue, sei and humpback whales was bimodal, indicative of winter migrations to the north of the Durban whaling grounds, whereas the unimodal seasonality of fin whales B. physalus and minke whales B. bonaerensis or B. acutorostrata suggest the offshore region as the northern terminus of their migrations. Sperm whales Physeter macrocephalus migrate northwards offshore of the KwaZulu-Natal coast in autumn/early winter and southwards in late winter/spring, with larger males migrating later than the smaller males and females. Killer whale Orcinus orca presence was coincident with that of offshore minke whales and the southward migrations of other baleen whales, whereas densities of animals deemed as bottlenose whale Hyperoodon planifrons suggest strong early and late summer seasonal abundance in the offshore region. Such extensive surveys offshore of the KwaZulu-Natal coast are unlikely to be repeated; hence, data-extraction of whaling records provides a valuable source of seasonal and distributional information for marine management.     

Biooptical characteristics of the surface layer of the Baltic,Norwegian, and Barents seas in summer 2014–2016 from shipboard and satellite data

The article presents the results of shipboard and satellite measurements in the surface layer of the Baltic, Norwegian, and Barents seas during legs from the Baltic to the White Sea in June–August 2014–2016. Special attention is paid to marine phytoplankton blooms of cyanobacteria in the Baltic Sea and coccolithophores in the Barents Sea. No blooms were found in the Norwegian Sea. The efficiency of combined application of in situ and satellite optical methods for studying the parameters of phytoplankton blooms is shown.     

The spreading of eutrophication in the eastern coast of the Gulf of Bothnia,northern Baltic Sea – An analysis in time and space

In the Baltic Sea, the Gulf of Bothnia is the only sub-basin with only minor effects of eutrophication mainly due to physical factors. Most evaluations of the state of the Gulf of Bothnia are based on offshore investigations. In the present study the coastal zone of the eastern Gulf of Bothnia is analysed. Long-term data (1980–2007) of total nitrogen and phosphorus, turbidity and oxygen are analysed using principal component analysis (PCA) for spatial and temporal patterns in the trophic situation. The coastal zone is divided into six regions: inner and outer areas of the Bothnian Sea and the Quark, and the outer areas of the southern and northern Bothnian Bay. The results show a degradation of water quality from north to south, and from outer to inner coastal areas. Eutrophication changes from an almost non-existing problem in the Bothnian Bay in the north to clear signs of nutrient over-enrichment in the Bothnian Sea. This shows that even if eutrophication in the Gulf of Bothnia is not serious, the increasing trends in nutrient levels should be seen as warning signals for the future, and remedies to combat eutrophication should be taken rapidly.     

Population dynamics of the ctenophore Mnemiopsis leidyi and its impact on the zooplankton in the coastal regions of the Black Sea of the Crimean coast in 2004–2008

The abundance, biomasses, and population structure of the ctenophore Mnemiopsis leidyi were monitored in the coastal waters of the northern part of the Black Sea (Sevastopol Bay and the adjacent continental shelf regions) in 2004–2008. The abundance and species composition of the comb jelly’s food in the sea were obtained along with experimental data on the digestion time. Based upon these data, the feeding intensity of the ctenophore in situ was estimated. This information was used to calculate the predatory impact of the comb jelly population on certain groups of forage organisms and the forage zooplankton community as a whole. The predatory impact of the M. leidyi population on the bivalve veligers was the highest (up to 90% of the abundance a day) compared to the Copepoda and Cladocera (30% and 40%, respectively). In the summers of 2004–2008, the daily consumption rates of the zooplankton by the ctenophore population in the shelf zone and in the bay were similar to each other: up to 15% and 12% of the abundance a day, respectively. The highest pressure of the ctenophore upon the zooplankton was observed in 2004 and 2008, when M. leidyi was especially abundant in the plankton for a long time.     

FERC pipeline decommissioning cost in the U.S. Gulf of Mexico, 1995–2015

At the end of its useful life or because of a catastrophic event such as a hurricane, offshore pipelines are decommissioned, which normally involves cleaning the line by pigging or flushing, cutting the pipeline endpoints, and then plugging and burying each endpoint below the seabed or covering with a concrete mattress. The vast majority of decommissioned pipeline in the U.S. Gulf of Mexico is abandoned-in-place if the pipeline does not constitute a hazard to navigation, commercial fishing, or unduly interferes with other uses of the seabed. Using a unique data source from the Federal Energy Regulation Commission, decommissioning cost estimates for 28 gas export pipelines in the shallow water U.S. Gulf of Mexico between 1995 and 2015 are evaluated. The average inflation-adjusted pipeline decommissioning cost was $301,000 per mile ($187,000/km) and $47 per cubic foot ($1660 per cubic meter). Hurricane damaged and leaking pipelines are about three to four times more expensive on a unit cost basis than undamaged and non-leaking lines. No time trends or scale economies were observed. Primary cost drivers are identified and discussed.     

Distribution and abundance of demersal fish from trawl stations in the bay of plenty,New Zealand, 1961–63

Between March 1961 and January 1963 trawling surveys were carried out in the Bay of Plenty. Seasonal comparisons of catch weight were made for the four commercially important species, snapper, tarakihi, trevally, and gurnard, during 1962–63. Only trevally showed any marked seasonal variation in total catch. Tarakihi were most abundant in waters over 50 fathoms and snapper, trevally, and gurnard were most abundant in shallower depths. The best return for fishing effort came from the middle sector of the Bay. There was a marked absence of undersized tarakihi and trevally from the catches. A species composition list for the Bay of Plenty waters and a table of species abundance at the stations sampled has been compiled from the trawl catch data.     

Some numerical experiments of the dynamics of the wintertime circulation in the Northern Huanghai Sea and the Bohai Sea

Some numerical experiments have been developed to explain dynamically the mechanism of the formation of the wintertime circulation in the Northern Huanghai Sea and the Bohai Sea. From the results of the numerical experiments with Coriolis parameter having positive and negative values respectively, it is found that the current pattern characterized by flowing into the Bohai Sea in the northern part of the Bohai Straits and flowing out of the Bohai Sea in the southern part of the Bohai Straits is controlled basically by the bottom topography with "the deepness on the northern side and shallowness on the southern side'in the Bohai Straits, and is not related to Coriolis parameter having positive and negative values. It also shows that the Huanghai Warm Current regarded as the inllow condition passing through the in-ports at the water boundary of the numerical experiments only influences the region near the water boundary and the eastern region of the Northern Huanghai Sea. In addition, the mechanism of the     

Palynology and petroleum potential of the Kazhdumi Formation (Cretaceous: Albian–Cenomanian) in the South Pars field,northern Persian Gulf

The Kazhdumi Formation of the Bangestan Group is a well-known source rock that has produced abundant oil in most petroleum fields in the Zagros Basin, which stretches from northwest to southwest Iran over hundreds of kilometres. The formation reaches a thickness of 230 m at the type section in northwest Zagros but thins out to 40–50 m in wells studied from the South Pars giant petroleum field, where it comprises mainly grey shales with occasional intercalations of marls and sandstones. South Pars, best known as the Iranian part of the world's largest non-associated gas field, contains small quantities of oil above and below the Kazhdumi Formation.     

Seasonal features of the appearance of aerosol scattering in the stratosphere and mesosphere of Kamchatka from the results of lidar observations in 2007–2009

The behavior of the vertical aerosol structure (profiles of the ratio of the coefficients of the backward total and molecular scattering) in the height interval 30–80 km is analyzed from the results of lidar observations in Kamchatka over the period from October 2007 through December 2009. The obtained data revealed a regular two-layer aerosol structure in this height range with the maxima of the ratio of the scattering coefficients in the upper stratosphere at heights 35–50 km and in the mesosphere at heights of 60–75 km, as well as a relation between seasonal variations in the aerosol stratification and the circumpolar vortex affecting dynamic processes in the atmosphere of midlatitudes. The procedure of including the aftereffect of the Hamamatsu-M8259-01 PEM, which influences the error in the calculation of the ratio of scattering coefficients, is described.     

Submarine structures in the Gulf of İzmit,based on multichannel seismic reflection and multibeam bathymetry

Multichannel seismic reflection and multi-beam bathymetry data were used to study the active tectonic and syn-tectonic stratigraphic setting of the Gulf of ?zmit in the Marmara Sea (Turkey). The gulf and its near surroundings are deformed by the northern strand of the dextral North Anatolian Fault. Three connected basins of the gulf, the western (Dar?ca), central (Karamürsel) and eastern (Gölcük) basins are formed by active faults, as observed in the stacked and migrated seismic sections, as well as the bathymetry map. The main branch and its surrounding sedimentary strata are confined by normal faults to the north and south. These normal faults converge at depth towards the main fault, forming a negative flower structure in the gulf. The average maximum sedimentation rate is 0.4 mm/year according to the three most recent seismo-stratigraphic units that are located to the south of the main fault branch within the central basin. A 20° south-dipping major discontinuity along the northern shoreline of the gulf represents the top of Paleozoic basement.     

Acoustic evidence of shallow gas accumulations and active pockmarks in the ?zmir Gulf, Aegean sea

Based on high-resolution Chirp seismic, multibeam bathymetry and side scan sonar data collected in the ?zmir Gulf, Aegean Sea in 2008 and 2010, gas-related structures have been identified, which can be classified into three categories: (1) shallow gas accumulations and gas chimneys, (2) mud diapirs, and (3) active and inactive pockmarks. On the Chirp profiles, shallow gas accumulations were observed along the northern coastline of the outer ?zmir Gulf at 3-20 m below the seabed. They appear as acoustic turbidity zones and are interpreted as biogenic gas accumulations produced in organic-rich highstand fan sediments from the Gediz River. The diapiric structures are interpreted as shale or mud diapirs formed under lateral compression due to regional counter-clockwise rotation of Anatolian microplate. Furthermore, the sedimentary structure at the flanks suggests a continuous upward movement of the diapirs. Several pockmarks exist close to fault traces to the east of Hekim Island; most of them were associated with acoustic plumes indicating active degassing during the survey period in 2008. Another Chirp survey was carried out just over these plumes in 2010 to demonstrate if the gas seeps were still active. The surveys indicate that the gas seep is an ongoing process in the gulf. Based on the Chirp data, we proposed that the pockmark formation in the area can be explained by protracted seep model, whereby sediment erosion and re-distribution along pockmark walls result from ongoing (or long lasting) seepage of fluids over long periods of time. The existence of inactive pockmarks in the vicinity, however, implies that gas seepage may eventually cease or that it is periodic. Most of the active pockmarks are located over the fault planes, likely indicating that the gas seepage is controlled by active faulting.