The effect of oceanographic variability and interspecific competition on juvenile pollock (Theragra chalcogramma) and capelin (Mallotus villosus) distributions on the Gulf of Alaska shelf

Results from this study suggest that small-scale variability in the Alaska Coastal Current (ACC) and competition between juvenile pollock and capelin are potential mechanisms affecting the distribution and abundance of fishes in the Gulf of Alaska (GOA). Fish distributions in Barnabus Trough, off the east coast of Kodiak Island, were assessed using acoustic data collected with a calibrated echosounder during August–September 2002 and 2004. Trawl hauls were conducted to determine the species composition of the fish making up the acoustic backscatter. Oceanographic data were collected from moorings, conductivity–temperature–depth (CTD) probes, trawl-mounted microbathythermographs (MBT) and expendable bathythermographs (XBT). National Centers for Environmental Prediction (NCEP) reanalysis data were used to assess area winds, and information on regional transport was derived from current meters deployed on moorings north and south of Kodiak Island. The distribution of water-mass properties and fish during 2002 showed variability at the temporal scale of weeks. Juvenile pollock (age-1 and age-2) were initially most abundant in warm, low-salinity water on the inner shelf, whereas capelin were distributed primarily on the outer shelf in cool, high-salinity waters. During a 2-week period juvenile pollock distribution expanded with the offshore expansion of warm, low-salinity water, and capelin abundance in outer-shelf waters decreased. We hypothesize that wind-driven pulsing of the ACC resulted in increased transport of warm, low-salinity water through the study area. In 2004, warm, low-salinity water characterized the inner shelf and cool, high-salinity water was found on the outer shelf. However, the distribution of water-mass properties did not show the weekly scale variability observed in 2002. Area winds were consistently toward the southwest during 2004, such that we would not expect to see the wind-driven pulsing of ACC water that occurred in 2002. Age-1 and age-2 pollock were not observed in Barnabus Trough in 2004. Instead, the midwater acoustic backscatter was composed of capelin mixed with age-0 pollock, and these capelin were not restricted to the outer-shelf waters, but were found primarily in warm, low-salinity inner-shelf waters that had been previously occupied exclusively by age-1 and age-2 pollock. We suggest that this is consistent with inner-shelf waters being preferred foraging habitat for juvenile pollock and capelin. Further study of the mechanisms linking climate change with variability in the ACC is needed, as are studies of the potential for competition between juvenile pollock and capelin.     

Local ecological knowledge and practical fisheries management in the tropics: A policy brief

This policy brief is a summary product of seven case studies examining the integration of local ecological knowledge in fisheries management. Each case began with a series of in-depth interviews with local fishers, after which their answers were examined using both social and biological approaches to assess the possibility of using the information as the basis of simple, valid and locally acceptable indictors for fisheries management. We found that allocation and knowledge issues are closely interlinked and must be addressed in concert, and that the negotiation of shared understandings between multiple sources of knowledge must be a continuous process within an adaptive framework rather than a question of identifying a fixed set of indicators.     

Dating in the Craven Dales

The Craven Dales of North Yorkshire contain some of the finest examples of limestone geology and landscape in the UK. The extensive limestone pavements with their clints, grikes and other water‐worn features, are a key attraction for both scientists and recreational visitors. Likewise the cave systems attract attention with their remarkable sediment accumulations, some of which are in excess of 500 000 years old and others contain the bones of mammals that are either extinct or no longer present in the British Isles. The glacial erratic boulders at Norber and the loessic sediments that, in places, mask the limestone have also provided stimulus for investigation. Summarized below are the findings of several recent studies that focussed on establishing the age of various features. Whilst the reports answer some long‐standing questions, they also demonstrate that there is still much that can be learned about this seemingly familiar territory.     

Reviews

F. L. Stillwell Anniversary Volume. Australian Institute of Mining and Metallurgy, Melbourne, 302 pages, many plates and figures. 1958.

Our Mineral Resources, by Charles M. Riley; x + 338 pages; 102 figures; John Wiley and Sons, Inc., New York and London. $6.95.

Researches in Geochemistry, edited by P. H. Abelson; John Wiley and Sons Inc., New York, 1959. $11.00.

Basic Geology for Science and Engineering, by Edward C. Dapples; vii + 609 pages; 231 figures. John Wiley and Sons Inc., New York, 1959. $9.50.

Historical Geology, by Carl O. Dunbar; xi + 500 pages; 406 figures. Second Edition, publication date August, 1960; John Wiley and Sons Inc., New York. $7.95.

Time, Life and Man, by R. A. Stirton; xi + 558 pages; 291 figures. John Wiley and Sons Inc., New York, 1958.

Vector Space, by Martin J. Buerger; xiv + 347 pages; numerous line drawings; John Wiley and Sons Inc., New York and London. $12.00.

Geology of the Country Around Polonnaruwa, by Piyadasa W. Vtkanage. 1959. Memoir No. 1, Department of Mineralogy, Geological Survey of Ceylon; ix + 75 pages; 11 figures; 12 plates.     

A lagoonal interlude with occasional hypersalinity in the deposition of the Early–Middle Miocene Brasso Formation of Trinidad

An outcrop of the Early–Middle Miocene age Brasso Formation along the Guaico-Tamana Road of Trinidad was logged and sampled for 20 m at 1 m intervals. The log revealed two sand- and silt-rich successions separated by a claystone-rich interval with thinner sands. One horizon yielded gypsum that is concluded to indicate that conditions occasionally became hypersaline. With the exception of one laminated siltstone interval ～1 m thick, all the beds lacked primary sedimentary structures, but many contained much mollusc debris. The lack of primary structures is thought to reflect bioturbation. Pyrite was common throughout much of the section, but replaced by hematite in two intervals. The pyrite is indicative of anoxic conditions in the sediment below the bioturbated layer, while the hematite shows that conditions occasionally became strongly oxic. The development of low-diversity benthonic foraminiferal communities dominated by porcellaneous-walled Quinqueloculina seminulangulata supports a model of occasional hypersalinity. These conditions are concluded to have developed in a leaky lagoon situated between the carbonate bioherms of the Tamana Formation of Central Trinidad and the mountainous allochthon of the Northern Range. Occasional high numbers of planktonic foraminifera are suggested to result from onshore winds blowing surface seawater into the lagoon. The lagoonal interlude came at the end of a tectonically-induced transgressive–regressive cycle. The influence of tectonics on the deposition of the Brasso Formation complicates at least for the Early–Middle Miocene any attempt to tie the sequence stratigraphy of Trinidad to a global sea-level model. It remains to be seen how much this is true for the remainder of the Neogene succession.     

An assessment of the utility of regional diatom‐based tidal‐level transfer functions

In order to understand natural sea‐level variability, and to enhance future predictions, accurate and precise estimates of Holocene tidal levels are required. Although the application of diatom‐based transfer functions can yield such data, these work best when underpinned by local training sets. Urbanized estuaries offer little prospect of obtaining local training sets and, instead, the reliability of regional transfer functions has to be assessed. The performance of a published regional (UK) diatom‐based tidal‐level transfer function applied to fossil assemblages from two contrasting core sites in the Mersey Estuary, UK, is assessed using modern analogue techniques and sediment isotope data. We find that, although estimated tidal levels coincide with changes in organic matter source, the frequent lack of modern analogues mean that palaeotide estimates are without basis. This is likely a consequence of the site‐specific nature of diatom assemblages in higher intertidal and supratidal areas in particular, where local factors are expected to exert a greater control on their ecology. This situation may be partly resolved by constructing and applying much larger regional training sets from multiple higher intertidal and supratidal sites (where intact). Otherwise the application of alternative techniques, such as regional foraminiferal tidal‐level transfer functions, may be more appropriate. Copyright © 2011 John Wiley & Sons, Ltd.