Growth, mortality, and exploitation of the Engraulidae, with special reference to the anchoveta, Cetengraulis mysticetus, and the colorado, Anchoa naso, in the Eastern Pacific Ocean

ENGLISH: Growth and mortality data for Cetengraulis mysticetus, Anchoa naso, Engraulis mordax, E. ring ens, E. anchoita, E. encraslcbolus, E. japonicus, and E. australis were assembled and compared. Estimates of the coefficients of natural mortality, M, of E. anchoita and Ancboa naso were made from the maximum age of the former and from data for the other species. The relative yields per recruit at different fishing mortality rates and lengths at entry into the fishery were calculated for each species, using what are considered to be the best estimates and other likely values of K, a constant of growth, and M. The maximum yields per recruit are theoretically obtainable at very high fishing mortality rates, except when the length at entry is low relative to the asymptotic length. K and M may be positively related to the temperature and to each other, and if such is the case at higher temperatures greater fishing effort would be needed to attain the maximum yield per recruit. The applicability of the yield-per-recruit approach to the data is discussed, and suggestions for further research are made. SPANISH: Se reunieron y compararon los datos sobre el crecimiento y mortalidad correspondientes a Cetengraulis mysticetus, Anchoa naso, Engraulis mordax, E. ringens, E. anchoíta, E. encrasicbolus, E. japonicus y E. australls. Los estimativos de los coeficientes de la mortalidad natural, M, de E. anchoita y Anchoa naso se obtuvieron según la edad máxima de E. anchoita y según los datos de las otras especies. Se calculó para cada especie el rendimiento relativo por recluta a diferentes tasas de mortalidad por la pesca y a diferentes longitudes de entrada a la pesquería, empleándose lo que se considera que son los mejores estimativos y otros valores probables de K, una constante de crecímíento, y M. El rendimiento máximo por recluta se obtiene teóricamente a tasas muy altas de la mortalidad por la pesca con excepción de cuando la longitud a la entrada es baja en relación a la longitud asintótica. K y M pueden estar relacionadas positivamente a la temperatura y mutuamente, y si este es el caso a temperaturas más altas se necesitará un esfuerzo superior de pesca para obtener el rendimiento máximo por recluta. La aplicabilidad del enfoque a los datos rendimiento-por-recluta es discutido y se hacen sugerencias para otras investigaciones. (PDF contains 66 pages.)

^(18)O/^(16)O and D/H studies on the interactions between heated meteoric ground waters and igneous intrusions: Western San Juan Mountains, Colorado and the Isle of Skye, Scotland

Detailed oxygen, hydrogen and carbon isotope studies have been carried out on igneous and metamorphic rocks of the Stony Mountain complex, Colorado, and the Isle of Skye, Scotland, in order to better understand the problems of hydrothermal meteoric water-rock interaction.

The Tertiary Stony Mountain stock (~1.3 km in diameter), is composed of an outer diorite, a main mass of biotite gabbro, and an inner diorite. The entire complex and most of the surrounding country rocks have experienced various degrees of ¹⁸O depletion (up to 10 per mil) due to interaction with heated meteoric waters. The inner diorite apparently formed from a low-¹⁸O magma with δ¹⁸O ≃ +2.5, but most of the isotopic effects are a result of exchange between H₂O and solidified igneous rocks. The low-¹⁸O inner diorite magma was probably produced by massive assimilation and/or melting of hydrothermally altered country rocks. The δ¹⁸O values of the rocks generally increase with increasing grain size, except that quartz typically has δ¹⁸O = +6 to +8, and is more resistant to hydrothermal exchange than any other mineral studied. Based on atom % oxygen, the outer diorites, gabbros, and volcanic rocks exhibit integrated water/rock ratios of 0.3 ± 0.2, 0.15 ± 0.1, and 0.2 ± 0.1, respectively. Locally, water/rock ratios attain values greater than 1.0. Hydrogen isotopic analyses of sericites, chlorites, biotites, and amphiboles range from -117 to -150. δD in biotites varies inversely with Fe/Fe+Mg, as predicted by Suzuoki and Epstein (1974), and positively with elevation, over a range of 600 m. The calculated δD of the mid-to-late-Tertiary meteoric waters is about -100. Carbonate δ¹³C values average -5.5 (PDB), within the generally accepted range for deep-seated carbon.

Almost all the rocks within 4 km of the central Tertiary intrusive complex of Skye are depleted in ¹⁸O. Whole-rock δ¹⁸O values of basalts (-7. 1 to +8.4), Mesozoic shales (-0.6 to + 12.4), and Precambrian sandstones (-6.2 to + 10.8) systematically decrease inward towards the center of the complex. The Cuillin gabbro may have formed from a ¹⁸O-depleted magma (depleted by about 2 per mil); δ¹⁸O of plagioclase (-7.1 to + 2.5) and pyroxene (-0.5 to + 3.2) decrease outward toward the margins of the pluton. The Red Hills epigranite plutons have δ¹⁸O quartz (-2.7 to + 7.6) and feldspar (-6.7 to + 6.0) that suggest about 3/4 of the exchange took place at subsolidus temperatures; profound disequilibrium quartz-feldspar fractionations (up to 12) are characteristic. The early epigranites were intruded as low-¹⁸O melts (depletions of up to 3 per mil) with δ¹⁸O of the primary, igneous quartz decreasing progressively with time. The Southern Porphyritic Epigranite was apparently intruded as a low-¹⁸O magma with δ¹⁸O ≃ -2.6. A good correlation exists between grain size and δ¹⁸O for the unique, high-¹⁸O Beinn an Dubhaich granite which intrudes limestone having a δ¹⁸O range of +0.5 to +20.8, and δ¹³C of -4.9 to -1.0. The δD values of sericites (-104 to -107), and amphiboles, chlorites, and biotites (-105 to -128) from the igneous rocks , indicate that Eocene surface waters at Skye had δD ≃ -90. The average water/rock ratio for the Skye hydrothermal system is approximately one; at least 2000 km³ of heated meteoric waters were cycled through these rocks.

Thus these detailed isotopic studies of two widely separated areas indicate that (1) ¹⁸O-depleted magmas are commonly produced in volcanic terranes invaded by epizonal intrusions; (2) most of the ¹⁸O-depletion in such areas are a result of subsolidus exchange (particularly of feldspars); however correlation of δ¹⁸O with grain size is generally preserved only for systems that have undergone relatively minor meteoric hydrothermal exchange; (3) feldspar and calcite are the minerals mos t susceptible to oxygen isotopic exchange, whereas quartz is very resistant to oxygen isotope exchange; biotite, magnetite, and pyroxene have intermediate susceptibilities; and (4) basaltic country rocks are much more permeable to the hydrothermal convective system than shale, sandstone, or the crystalline basement complex.

How are Italian and Spanish cities tackling climate change? A local comparative study

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The Colorado River; a source of water and power for Los Angeles

The rapid growth and development of Los Angeles City and County has been one of the phenomena of the present age. The growth of a city from 50,600 to 576,000, an increase of over 1000% in thirty years is an unprecedented occurrence. It has given rise to a variety of problems of increasing magnitude.

Chief among these are: supply of food, water and shelter development of industry and markets, prevention and removal of downtown congestion and protection of life and property. These, of course, are the problems that any city must face. But in the case of a community which doubles its population every ten years, radical and heroic measures must often be taken.