The Eye Lens Weight Technique in Aging of the Atlantic Croaker, Micropogon undulatus

The eye lens weight to age relationship was examined in croaker, Micropogon undulatus. Lenses were removed, fixed, and weighed using standard techniques. Age estimates were assigned based on total length measurements. Lens weight showed good correlation with total length. Age could be estimated by eye lens weight, but no more accurately or precisely than with length frequency analysis. Cumulative percent frequency analysis of lens weights showed distinct inflections in the curve, which correspond to hypothesized length at age points. The data seem to verify age structure based on length frequency analysis

The Eye Lens Weight Technique in Aging of the Atlantic Croaker, Micropogon undulatus

The eye lens weight to age relationship was examined in croaker, Micropogon undulatus. Lenses were removed, fixed, and weighed using standard techniques. Age estimates were assigned based on total length measurements. Lens weight showed good correlation with total length. Age could be estimated by eye lens weight, but no more accurately or precisely than with length frequency analysis. Cumulative percent frequency analysis of lens weights showed distinct inflections in the curve, which correspond to hypothesized length at age points. The data seem to verify age structure based on length frequency analysis

Studies on the herring gull population in North Yorkshire

A census of .Herring Gulls (Larus argentatus) breeding along the Cleveland and Yorkshire coast was conducted during 1978 and 1979. Herring Gulls present between Redcar and Black Nab, south of Whitby and between Black Nab and Filey Brigg were observed throughout the year July 1978 to July 1979. The Herring Gulls observed included a proportion with colour-rings on their legs. Ringing of Herring Gulls was carried out both in the study area and north of it from 1976 onwards by a team from the University of Durham Zoology department. Population estimates are obtained from the census of breeding Herring Gulls as well as from 'mark and recapture’ observations throughout the year. Movements of the Herring Gulls are examined together with the distances of these movements. The behaviour of 1st and 2nd year Herring Gulls is compared with that of Herring Gulls older than 2 years. The data from the census of breeding Herring Gulls, the population estimates and the movement data are compared with data previously obtained in this and other areas by other authors to obtain colony growth rates and establish immigration and emigration patterns to and from the area of study. The rates of increase and the movements throughout the year observed in the study area are discussed

A Probabilistic Development of Nutrient Criteria for Louisiana Rivers and Streams (Eutrophication, Dissoved Oxygen, Algae, Standards, Nitrogen).

The objective of this investigation was the development of quantitative criteria based on the estimation of maximum levels of oxygen demand associated with specific levels of nutrients in algal dominated streams. 1582 intensive survey records were obtained from the Louisiana Department of Environmental Quality (LA DEQ). A sub-set of 225 records was defined by a minimum chlorophyll a of 10.0 ug/l and influential observation analysis to restrict the data to streams where algal processes were likely to be dominant. Nitrogen, as measured by total Kjeldahl nitrogen (TKN) was identified as the principle nutrient of concern in the prediction of algal associated oxygen demand in the streams represented in the data sets. A linear model describes the relationship between TKN and BOD(,20) in the region below 6.0 mg/l TKN. Variability in observed data about the model line required that the model be expressed in a probabilistic format. The probabilistic model relates the risk of exceeding any BOD standard for any given TKN concentration up to 6.0 mg/l. In order to examine the generality of the developed nutrient criteria model, an independent data set of 7227 observations from 36 states was obtained from the STORET database for comparison purposes. A similar process as for the LA DEQ data was used to define a comparison data sub-set of 199 observations where algal processes were likely to be dominant. Of the 5 states well represented in the STORET subset, Ohio and a No State Reported group showed no significant difference from the LA DEQ model, while Delaware, Pennsylvania and Minnesota showed significantly different unit BOD to TKN values in the range of 4.7 to 8.4. There was insufficient data to identify sources of regional differences. The developed nutrient criteria model represents ubiquitous processes, minimizing reliance on site specific parameter estimations, and maximizing the value of historical databases. All evidence suggests that the model is general and will not change substantially as additional verification data becomes available