Change in lameness risk estimates in piglets due to the modelling of herd-level variation.

In a previous study (Christensen, 1996. Prev. Vet. Med. 26, 107-118), an effect parameter changed from positive to negative depending on the model used. The study considered lameness in suckling piglets and the dataset included 7632 litters from 35 herds from the Health and Production Surveillance (HEPS) system database. To further investigate the change in the effect parameter, we performed a simple test to demonstrate the presence of herd-level variation. Finding substantial herd-level variation, we have re-analysed the data with special attention to the herd-level variation, and how to account for it. When herd-level variation was not accounted for in the model, a detrimental effect of prior treatment of the sow was seen but this turned into a beneficial effect when we accounted for the herd-level variation. The treatment of sow refers to any therapeutic treatment given to the sow after farrowing but before lameness or weaning occurred. This is, therefore, an example where not only the variances but also the effect parameters changed when we accounted for herd-level variation.     

Polycyclic Aromatic Hydrocarbons in the Sediments of the Milwaukee Harbor Estuary, Wisconsin, U.S.A.

From 1990 to 1994, a total of 21 sediment cores and 37 grab sediment samples were collected from the Milwaukee Harbor Estuary. Each sediment core was sectioned and dated using ²¹⁰Pb and¹³⁷ Cs radioisotope techniques. A total of 305 samples were analyzed for sixteen polycyclic aromatic compounds (PAHs). Grain size distribution, porosity, and total organic carbon content as measured by loss on ignition were also determined. The results provide a historical overview of the impact of industrialization in the Milwaukee area. Although highly variable, the concentration profile of PAHs show, in general, peaks in the 1950's through 1980's. The PAH concentrations have declined since then for most sediment cores. The current levels of total PAHs in most surface sediment samples range from 25 to 200 ppm. A few cores, some of which were collected in 1994, have an elevated PAH concentration at the surface. Toxicity of the surface sediments was evaluated by comparing with the benchmark values developed by the United States National Oceanic and Atmospheric Administration (NOAA). The most heavily contaminated area was found in the Kinnickinnic River between the Becher Street Bridge and the Wisconsin Wrecking Company Wharf. The highest total PAH concentration determined from seven vibra cores collected in this area ranges from 380 to 1000 ppm. The former Wisconsin Solvay Coke Company may have been a major point source of PAHs until the 1970's. Highway traffic and various industrial discharges also contribute to the sediment PAHs in this area.     

Fishing down marine food webs

The mean trophic level of the species groups reported in Food and Agricultural Organization global fisheries statistics declined from 1950 to 1994. This reflects a gradual transition in landings from long-lived, high trophic level, piscivorous bottom fish toward short-lived, low trophic level invertebrates and planktivorous pelagic fish. This effect, also found to be occurring in inland fisheries, is most pronounced in the Northern Hemisphere. Fishing down food webs (that is, at lower trophic levels) leads at first to increasing catches, then to a phase transition associated with stagnating or declining catches. These results indicate that present exploitation patterns are unsustainable.