Environmental variation and striped bass population dynamics: A size-dependent mortality model

Although density-dependent growth and mortality are understood to play a large role in regulating populations of some young fish, many investigators report associations between striped bass population fluctuations and environmental variation, not density. One explanation is that mortality is primarily determined by size, which responds through growth to environmental conditions. Mathematically relating mortality to inverse size explains several aspects of striped bass biology. Numerical decline of the 1975 Hudson River cohort is well predicted. Simulated year-class strength responds more strongly to changes in growth and length at hatch than to direct mortality of eggs. The effect of changes in length at hatch and growth, rate on subsequent population size decreases as fish grow. Small changes in temperature or food density early in life could cause the reported association of year-class strength and environmental variation. Disappearance of larvae from an early spawning in the Hudson River in 1976 is attributed to decreasing water temperature, which decreased growth rate. Increased mortality of young striped bass may also result from sublethal exposure to toxicants that decrease growth rate and size at hatch. The approach to modeling population dynamics developed here should be valid for other estuarine and marine species.     

Using parabolas to describe the cross-sections of glaciated valleys

It is widely accepted that the simple power curve Y = aX^b can be used to describe the cross-section of glaciated valleys. There are, however, good reasons to suppose that this particular form of equation is inappropriate for this purpose.     

Summer phytoplankton production and transport along the shelf break in the Bering Sea

A general model is presented for the production and fate of phytoplankton during summer in two regions over the continental shelf of the Bering Sea. We propose that both regions of productivity are supported by nutrients transported into the area with the Bering Slope Current and that the fate of the phytodetritus produced is significantly affected by advection. We hypothesize that one system of primary productivity is initiated at the Bering Sea shelf-break front and continues into the northern Bering Sea as part of the modified Bering Shelf water mass. Phytodetritus produced in this system is transported north through Anadyr and Shpanberg Straits and we estimate that in 1987 it supplied 26% of the daily carbon demand of the benthos in the Chirikov Basin. The second region of primary productivity is located in the northern Bering Sea. Nutrients from the Anadyr Current, the northern branch of the bifurcated Bering Slope Current, support a highly productive phytoplankton bloom throughout the summer. Phytodetritus produced in this surface bloom is probably advected into the southern Chukchi Sea and deposited in the sediments.     

Hydrothermal clinopyroxenes of the Skaergaard intrusion

Magmatic augites reacted with high temperature aqueous solutions to form secondary calcic pyroxenes during the subsolidus cooling of the Skaergaard intrusion. Secondary, hydrothermal clinopyroxenes replace wall rock igneous augites at the margins of veins filled with calcic amphibole. These veins are up to several millimeters wide and tens of meters in length. Hydrothermal clinopyroxenes are a ubiquitous and characteristic phase in the earliest veins throughout the Layered Series of the intrusion, and occur rarely in late veins that, in some places, crosscut the early veins. Associated secondary phases in early veins include amphiboles ranging in composition from actinolite to hornblende, together with biotite, Fe-Ti oxides and calcic plagioclase. Hydrothermal clinopyroxenes in late veins may be associated with actinolite, hornblende, biotite, magnetite and albite.Hydrothermal clinopyroxenes are depleted in Fe, Mg and minor elements, and enriched in Ca and Si relative to igneous augites in the Layered Series gabbros. Secondary vein pyroxenes are similar in composition to calcic pyroxenes from amphibolite facies metamorphic rocks. Clinopyroxene solvus thermometry suggests minimum temperatures of equilibration of between 500° and 750° C. These temperatures, combined with numerical transport models of the intrusion, suggest that vein clinopyroxenes could have formed during 20,000 to 60,000 year time intervals associated with a maximum in the fluid flux through fractures in the Layered Series.     

International scope of marine pollution damage

Increasing pollution of estuaries and coastal waters causes economic damage to fisheries, tourism and much else. Developing countries are not immune from this, and the growth of tourism as well as the shift of populations to the coast in many parts of the world make pollution control all the more urgent. The problem is an international one and demands international solutions, but before these are likely, a good deal more hard information will be needed.