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Fished Areas (fished + area)
Selected AbstractsA comparison of no-take zones and traditional fishery management tools for managing site-attached species with a mixed larval poolFISH AND FISHERIES, Issue 3 2007William J F Le Quesne Abstract No-take zones (NTZs) can generate higher larval production by sessile, sedentary and site-attached species per unit area than in exploited areas, and may increase recruitment and yield compared to status quo management. Whilst NTZs may be considered an essential part of optimal management, few studies have specifically compared the effects of NTZs with those of correctly applied gear and effort controls. A yield-per-recruit (YPR) population model, based on the sedentary abalone Haliotis laevigata, was used to compare the effects of management by minimum landing size (MLS), effort limitation and NTZs, either singularly or in combination. Initially, a minimum basic YPR model was used. Three additional assumptions were sequentially added to the model to see if they affected conclusions drawn from the model. The additional assumptions were the inclusion of: (i) a length,fecundity relationship; (ii) an age-dependent natural mortality function; and (iii) mortality of undersized individuals due to fishery operations. In the absence of undersized mortality caused by fishing, under virtually all conditions the population is best managed with a combination of MLS and effort control, without any NTZs. For simulations that included mortality of undersized individuals in the fished area, under nearly all circumstances NTZs were considered an essential part of optimal fishery management, and management incorporating NTZs greatly increased the sustainable yield that could be taken. [source] Actual status of the sea urchin Diadema aff. antillarum populations and macroalgal cover in marine protected areas compared to a highly fished area (Canary Islands,eastern Atlantic Ocean)AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2008José Carlos Hernández Abstract 1.The aim was to determine the status of subtidal rocky benthic assemblages in three marine protected areas (MPAs) of the Canary Islands: (1) La Graciosa; (2) Mar de Las Calmas; (3) La Palma. Sea urchin (Diadema aff. antillarum) populations and non-crustose macroalgal cover were surveyed, and used as an indicator of conservation status in the three MPAs as well as in a highly fished area (HFA-Tenerife Island). 2.Comparing characteristics between each MPA and the HFA, and considering issues of management and design, it was concluded that the three MPAs each have a different conservation status. ,Mar de Las Calmas' marine reserve was found to have the most desirable conservation status, followed by ,La Palma' marine reserve based on sea urchin populations and non-crustose macroalgae assemblages. 3.Conversely, ,La Graciosa' had the highest density of D. aff. antillarum and the lowest cover of non-crustose macroalgae out of the three MPAs. Values were comparable to those at the HFA, which shows ,La Graciosa' to have the undesired conservation status. 4.Different spatial distribution patterns of non-crustose macroalgal as well as different algal composition cover were observed between the three MPAs and the HFA. These differences were principally attributed to the intensity of grazing activity of the key herbivore D. aff. antillarum. It is suggested that the different study areas correspond to different phase shifts that imply differing resilience of systems that should be taken into a count in future conservation strategies. Copyright © 2007 John Wiley & Sons, Ltd. [source] Potential of Marine Reserves to Cause Community-Wide Changes beyond Their BoundariesCONSERVATION BIOLOGY, Issue 2 2007PAOLO GUIDETTI arrecifes rocosos templados; cambios a nivel comunitario; cascadas tróficas; estados comunitarios alternativos; exceso de pesca; reservas marinas Abstract:,Fishing and other human activities can alter the abundances, size structure, and behavior of species playing key roles in shaping marine communities (e.g., keystone predators), which may in turn cause ecosystem shifts. Despite extensive evidence that cascading trophic interactions can underlie community-wide recovery inside no-take marine reserves by protecting high-level predators, the spatial extent of these effects into adjacent fished areas is unknown. I examined the potential for community-wide changes (i.e., the transition from overgrazed coralline barrens to macroalgal beds) in temperate rocky reefs within and around a no-take marine reserve. For this purpose I assessed distribution patterns of predatory fishes, sea urchins, and barrens across the reserve boundaries. Predatory fishes were significantly more abundant within the reserve than in adjacent locations, with moderate spillover across the reserve edges. In contrast, community-wide changes of benthic assemblages were apparent well beyond the reserve boundaries, which is consistent with temporary movements of predatory fishes (e.g., foraging migration) from the reserve to surrounding areas. My results suggest that no-take marine reserves can promote community-wide changes beyond their boundaries. Resumen:,La pesca y otras actividades humanas pueden alterar la abundancia, tamaño, estructura y comportamiento de las especies que juegan papeles clave en el modelado de las comunidades marinas (e.g., depredadores clave), que a su vez pueden causar cambios en los ecosistemas. No obstante la evidencia extensiva de que las interacciones tróficas en cascada pueden subyacer en la recuperación de la comunidad dentro de reservas marinas que no permiten la pesca mediante la protección de depredadores de nivel alto, se desconoce la extensión espacial de estos efectos en áreas adyacentes. Examiné el potencial de los cambios a nivel comunidad (i.e., la transición de áreas coralinas sobre pastoreadas a lechos de microalgas) en arrecifes rocosos templados dentro y alrededor de una reserva marina sin pesca. Para este propósito, evalué los patrones de distribución de peces depredadores, erizos de mar y áreas sobre pastoreadas en los límites de la reserva. Los peces depredadores fueron significativamente más abundantes dentro de la reserva que en localidades adyacentes, con un excedente moderado en los bordes de la reserva. En contraste, los cambios a nivel de comunidad en los ensambles bénticos fueron aparentes más allá de los límites de la reserva, lo que es consistente con los movimientos temporales de los peces depredadores (e.g., migración de forrajeo) desde la reserva hacia las áreas circundantes. Mis resultados sugieren que las reservas que no permiten la pesca pueden promover cambios a nivel comunidad más allá de sus límites. [source] Chronic fishing disturbance has changed shelf sea benthic community structureJOURNAL OF ANIMAL ECOLOGY, Issue 3 2000M. J. Kaiser Summary 1.,Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2.,In this study we present convincing evidence that chronic bottom-fishing disturbance has caused significant and widespread changes in the structure of two distinct soft-sediment benthic assemblages and habitats. 3.,Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom-fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long-lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4.,Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller-bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state. [source] Effects of natural barriers on the spillover of a marine mollusc: implications for fisheries reservesAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2003Alexander Tewfik Abstract 1.The movement of organisms and dispersal of propagules is fundamental to the maintenance of populations over time. However, the existence of barriers, created through the spatial configuration of habitats, may significantly affect dispersal patterns and thus influence community dynamics and resource sustainability. 2.Within marine environments unstructured or open habitats may form partial or complete ecological barriers due to elevated risk of predation or physical stresses associated with them. The existence and effects of such barriers may be of particular importance when considering the establishment of marine protected areas with a fisheries enhancement focus. 3.In this paper, the spillover of post-settlement queen conch (Strombus gigas) from a protected area in the Turks and Caicos Islands is investigated. It is hypothesized that the reserve boundaries overlap with a series of shallow, sand habitats that effectively enclose the protected population, reducing the spillover of conch into the adjacent fished areas. 4.To test this, density gradient maps for juvenile and adult conch populations were constructed using underwater visual survey data at 68 sites within and surrounding the protected area. These maps illustrate very low densities coinciding with poor, shallow sand habitats along the two marine boundaries of the reserve where spillover is expected to take place. 5.These sand habitats are thought to create ecological barriers to a slow, sedentary gastropod largely due to their shallowness (physical stresses of solar exposure or anoxia) and lack of food reducing the tendency of individuals to move across these areas, despite the 10-times higher density of adult queen conch observed in the protected area compared with outside. Copyright © 2003 John Wiley & Sons, Ltd. [source] Optimal management of the New Zealand longfin eel (Anguilla dieffenbachii),AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 4 2005Graeme J. Doole Annual recruitment of the New Zealand longfin eel (Anguilla dieffenbachii) has decreased by 75 per cent since significant levels of commercial fishing began in the early 1970s. This motivates application of a multiple-cohort bioeconomic model to a New Zealand longfin eel fishery to investigate its optimal management and ascertain the suitability of existing regulatory policy. The use of historical harvest to calculate total allowable catch is asserted to be unsustainable based on recovery dynamics. In addition, individual transferable quota systems are argued to be fundamentally flawed for the protection of longfin fisheries because of high-grading, low-surplus production and a current lack of effective stock-assessment procedures. Area closure and the spatial definition of harvest rights are attractive alternatives given the territoriality of longfins and high larval spillover. The importance of unfished reserves is reinforced when significant uncertainties regarding population strength, harvest intensity and growth dynamics are considered. Restriction of exploitation to older cohorts in fished areas is demonstrated to maximise economic yield. [source] | ||||||||||