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New Zealand harbours a considerable number of alien plants and animals, and is often used as a model region for studies on factors determining the outcome of introductions. Alien birds have been a particular focus of research attention, especially to understand the effect of propagule pressure, as records exist for the numbers of birds introduced to New Zealand. However, studies have relied on compilations of bird numbers, rather than on primary data. Here, we present a case study of the alien yellowhammer (Emberiza citrinella) introduced from the UK to New Zealand, to demonstrate how recourse to the primary literature highlights significant data gaps and misinterpretations in these compilations. We show that the history of the introduction, establishment and spread of the yellowhammer in New Zealand can be reconstructed with surprising precision, including details of the ships importing yellowhammers, their survival rates on board, the numbers and locations of release, and the development of public perception of the species. We demonstrate that not all birds imported were released, as some died or were re-transported to Australia, and that some birds thought to be introductions were in fact translocations of individuals captured in one region of New Zealand for liberation in another. Our study confirms the potential of precise historical reconstructions that, if done for all species, would address criticisms of historical data in the evidence base for the effect of propagule pressure on establishment success for alien populations.
Since the 1970s, exports and imports of manufactured goods have been the engine of international trade and much of that trade relies on container shipping. This paper introduces a new monthly index of the volume of container trade to and from North America. Incorporating this index into a structural macroeconomic VAR model facilitates the identification of shocks to domestic U.S. demand as well as foreign demand for U.S. manufactured goods. We show that, unlike in the Great Recession, the primary determinant of the U.S. economic contraction in early 2020 was a sharp drop in domestic demand. Although detrended data for personal consumption expenditures and manufacturing output suggest that the U.S. economy has recovered to near 90% of pre-pandemic levels as of March 2021, our structural VAR model shows that the component of manufacturing output driven by domestic demand had only recovered to 59% of pre-pandemic levels and that of real personal consumption only to 76%. The difference is mainly accounted for by unexpected reductions in frictions in the container shipping market.
Using a novel dataset, we develop a structural model of the Very Large Crude Carrier (VLCC) market between the Arabian Gulf and the Far East. We study how fluctuations in oil tanker rates, oil exports, shipowner profits, and bunker fuel prices are determined by shocks to the supply and demand for oil tankers, to the utilization of tankers, and to the cost of operating tankers, including bunker fuel costs. Our analysis shows that time charter rates are largely unresponsive to tanker cost shocks. In response to higher costs, voyage profits decline, as cost shocks are only partially passed on to round-trip voyage rates. Oil exports from the Arabian Gulf also decline, reflecting lower demand for VLCCs. Positive utilization shocks are associated with higher profits, a slight increase in time charter rates and lower fuel prices and oil export volumes. Tanker supply and tanker demand shocks have persistent effects on time charter rates, round-trip voyage rates, the volume of oil exports, fuel prices, and profits with the expected sign.