Quantifying commercial catch and effort of monkfish Lophius vomerinus and L. vaillanti off Namibia

Abundance and exploitation patterns of monkfish Lophius vomerinus and L. vaillanti were investigated for use as inputs into a stock assessment framework to be used for management of the Namibian monkfish resource. Total numbers of monkfish caught per size-class were estimated using industry records of tail products classified into six commercial categories. The proportions per category varied each year. Analysis of the commercial data suggests that large numbers of juvenile monkfish are harvested annually. Catch-per-unit-effort (cpue) data of vessels targeting monkfish and sole (the two species are combined in terms of Namibian fleet legislation) for the period 1991–1999 were analysed using two different methods to construct indices of abundance. Both indices, one standardized on vessel horsepower and the other standardized by means of a Generalized Linear Model, showed an increase in catch rate of monkfish from 1991 to 1994 and between 1996 and 1998, but a decline from 1994 to 1996 as well as during 1999. Conversion factors for landed or tail weight to whole weight for four different tail products of monkfish were estimated. Results obtained from the study suggest that the factor of 3.04 currently applied in Namibia to all tail-weight classes is not appropriate for the current fishery and needs to be amended. For management purposes it is also suggested that four different conversion factors, one for each monkfish tail product, be implemented.     

A Bayesian state-space model for mixed-stock migrations,with application to Northeast Atlantic mackerel Scomber scombrus

Management of fisheries that exploit mixed-stock populations relies on assumptions made concerning stock structure and mixing in different areas. To address the problems of accounting for uncertainty when formulating scientific advice for the management of highly migratory fish stocks, management decisions need to be based upon assessment models that represent plausible alternative hypotheses for stock structure and migration patterns of the exploited populations. We present a multi-stock, multi-fleet, multi-area, seasonally structured Bayesian state-space model in which different stocks spawn in spatially different areas and the mixing of these stocks is explicitly accounted for in the absence of sufficient tagging data with which to estimate migration rates. The model is applied to the Northeast Atlantic mackerel Scomber scombrus population, accounting for the annual spawning-feeding-overwintering migration patterns of the three spawning components, together with uncertainty in the extent to which the southern component migrates north to feed and overwinter, and consequently the extent to which it mixes with the other components and is subject to exploitation. The model allows the effect of exploitation on the individual components to be assessed, and the results suggest that the fishing mortality of southern spawning adults was insensitive to the extent to which they migrated north.     

Lieutenant Murdoch Mackenzie and his Survey of the Bristol Channel and the South Coast of England

Abstract

NetCDF (Network Common Data Form) is a data sharing protocol and library that is commonly used in large-scale atmospheric and environmental data archiving and modeling. The NetCDF tool described here, named NCWin and coded with Borland C + + Builder, was built as a standard executable as well as a COM (component object model) for the Microsoft Windows environment. COM is a powerful technology that enhances the reuse of applications (as components). Environmental model developers from different modeling environments, such as Python, JAVA, VISUAL FORTRAN, VISUAL BASIC, VISUAL C + +, and DELPHI, can reuse NCWin in their models to read, write and visualize NetCDF data. Some Windows applications, such as ArcGIS and Microsoft PowerPoint, can also call NCWin within the application. NCWin has three major components: 1) The data conversion part is designed to convert binary raw data to and from NetCDF data. It can process six data types (unsigned char, signed char, short, int, float, double) and three spatial data formats (BIP, BIL, BSQ); 2) The visualization part is designed for displaying grid map series (playing forward or backward) with simple map legend, and displaying temporal trend curves for data on individual map pixels; and 3) The modeling interface is designed for environmental model development by which a set of integrated NetCDF functions is provided for processing NetCDF data. To demonstrate that the NCWin can easily extend the functions of some current GIS software and the Office applications, examples of calling NCWin within ArcGIS and MS PowerPoint for showing NetCDF map animations are given.     

Gradation as a Communication Device in Area-Class Maps

This paper proposes a methodology to assess gradation as a cartographic tool for communicating information in area-class maps. The communication model is used as a theoretical foundation, suggesting distinction between errors that occur in encoding and decoding of geographic information. The proposed methodology begins with the determination of a target level of encoding error. Map alternatives are constrained to achieve this target, with gradation considered as one variable in the map production process. The result is a series of maps of equal encoding accuracy but varying in the degree of gradation represented. The individual maps of the series can then be evaluated in terms of decoding accuracy. The methodology is demonstrated by producing a series of alternative forest region maps of New York, Pennsylvania, and New Jersey based on U.S. Forest Service data on tree genus distributions. The series ranges from a 4-class graded area-class map to a 13-class crisp map. The results show gradation to be a viable alternative to the proliferation of map classes as a means of cartographic communication.     

Changes in the trophic structure of the southern Benguela before and after the onset of industrial fishing

Despite a human presence in the Benguela region for at least one million years, exploitation of marine resources by European seafarers only began in earnest in the 1400s. Ecopath with Ecosim was used to construct and compare mass-balanced foodweb models of the southern Benguela ecosystem, representing the following eras of human influence: aboriginal (10 000 BP–1651), pre-industrial (1652–1909), industrial (1910–1974) and post-industrial (1975–present). Biomass at higher trophic levels (TLs) decreased over the periods examined, whereas that of sardine and anchovy increased in the early 2000s, reflected by the decline in weighted TL of the community (excluding plankton). Fishing became an important predatory impact, taking over consumption of small pelagics and horse mackerel from declined natural predators such as hake. Harvesting of apex predators such as seals and seabirds during the pre-industrial era meant that the mean TL of the catch declined markedly between the pre-industrial (1900) and industrial (1960) models. Biomass removals by fishing have increased substantially over time. Total biomass, consumption, respiration, production and throughput decreased from the pristine model to 1960 and then increased again in the 2000s, probably influenced by the abnormally high small pelagic biomass in the early 2000s. Three additional alternate scenarios were examined for each of the retrospective models, in particular to explore the effects of removing large fish and forage fish from the system. Although biomasses and consumption of various groups in these scenarios differed from base models, indicators such as TL of the community and piscivore groups, and the diversity indices, were not altered much, suggesting that outputs from such retrospective models in the form of derived, relative indicators, may be more robust than comparisons of absolute flows, although the latter provide supplementary inferences. Although South African fisheries have certainly impacted ecosystem structure since their commencement, these effects are in addition to natural (specifically environmental) forcing that has always been influencing the system. Fishing stress at the ecosystem level and the collapse of small pelagic stocks may lead to a shift toward a bottom-up trophic control mechanism becoming the dominant driver of ecosystem dynamics, increasing the impact of environmental events including climate change. It is thus possible that pristine systems were not as severely affected by environmental anomalies as are modern systems.     

Ecological features of harmful algal blooms in coastal upwelling ecosystems

Upwelling regions are the most complex habitats in which dinoflagellates produce red tides, but the flora is not unique. Many species also bloom in nutrient-enriched, non-upwelling systems, share the collective dinoflagellate trait of low-nutrient affinity, and can achieve relatively fast growth rates. Blooms occur over the range of nutrient – mixing – advection combinations found in upwelling habitats, rather than being restricted to the high-nutrient high-irradiance low-turbulence conditions posited by Margalef's classical Mandala and its Bowman et al. and Pingree versions. The bloom species are primarily ruderal strategists (R-species), which typify "mixing – drift" life-forms adapted to the velocities associated with frontal zones, entrainment within coastal currents, and vertical mixing during upwelling relaxations. Collectively, dinoflagellates appear capable of surviving fairly high turbulence spectra formed at representative Kolmogorov length scale – wind speed conditions. This biophysical protection might be the result of cell size-facilitated entrainment within the micro-eddies formed during turbulent energy dissipation. The swimming speeds of 71 clones of dinoflagellates are compared and related to reported rates of vertical motion in coastal upwelling systems. There are slow and fast swimmers; many exhibit motility rates that can exceed representative in situ vertical and horizontal water mass movements. At least four dinoflagellates from upwelling systems form chains leading to increased swimming speeds, and may be an adaptation for growth in coastal upwelling habitats. Red tides are frequent and fundamental features of upwelling systems, particularly during intermittent upwelling relaxations, rather than dichotomous (sometimes catastrophic) interruptions of the diatom blooms characteristically induced by upwelling. Successional sequences and the "red tide" zone may differ between upwelling and non-upwelling systems. In the latter, red tides diverge from the main sequence and are appropriately positioned in the Mandala's ecological space of high nutrients and low turbulence. An amended Mandala based on Pingree's S-kh model and the Smayda and Reynolds life-form model is presented to accommodate the range of red tide development and their successional routing found in coastal upwelling systems. Ecophysiological data support the Pitcher and Boyd seeding mechanism model, which can lead to red tides in upwelling systems. Nutrients, phyto-stimulation and grazing pressure as triggering factors in upwelling-system red tides are considered. Some red tides may be stimulated by nutrients and growth promoting factors excreted by migrating shoals and "boils" of c1upeoid stocks, with selective zooplankton grazing contributory. Substantial collapses in grazing pressure may be essential in anoxic red tide events. The mass mortalities that accompany anoxia, common to the Benguela and Peru upwelling systems, may be a trophic control mechanism to maintain biogeochemical balance and regional homeostasis, which are vital to upwelling ecosystem dynamics. Some traditional concepts of phytoplankton ecology may not completely apply to dinoflagellate bloom events in coastal upwelling systems.