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Adjacent Waters (adjacent + water)
Selected AbstractsEffect of light and predator abundance on the habitat choice of plant-attached zooplanktonFRESHWATER BIOLOGY, Issue 3 2007LEENA NURMINEN Summary 1. The diurnal variations in the habitat choice of the periodically plant-attached cladoceran Sida crystallina together with light environment and predator abundance were studied. 2. The density of S. crystallina attached to floating leaves of Nuphar lutea increased between 18:00 and 20:00 hours, when light intensity underneath the leaves was temporarily increased, and decreased again when light intensity declined. A proportion of S. crystallina remained in the swimming mode underneath the leaves even during daylight, indicating that the water column sheltered by the leaves is safer than the open water. 3. In the water adjacent to the leaves, the density of S. crystallina increased steeply in the dark. The increase was not accompanied by a decrease in S. crystallina attached to plant leaves, indicating that the nocturnal increment in the open water density of S. crystallina was due to migration from daytime refuges other than floating leaves. 4. Sida crystallina was most intensively consumed by perch (Perca fluviatilis). Predation threat by fish had weaker effects on the density of S. crystallina attached to plant leaves than on cladocerans in the adjacent water. Cladocerans underneath floating plant leaves, whether attached or not, are probably less vulnerable to fish predation than those outside the leaf cover. 5. The results suggested that light intensity is the proximate factor regulating the attachment of zooplankton to the lower surfaces of floating macrophyte leaves. Light intensity has a positive effect on the density of S. crystallina attached to the floating leaves and a negative effect on density in the water. Predation threat by fish has a strong effect on the migration of zooplankters into the open water habitat. [source] Determining prey distribution patterns from stomach-contents of satellite-tracked high-predators of the Southern OceanECOGRAPHY, Issue 2 2006J. C. Xavier The distribution of many cephalopod, crustacean and fish species in the Southern Ocean, and adjacent waters, is poorly known, particularly during times of the year when research surveys are rare. Analysing the stomach samples of satellite-tracked higher predators has been advocated as a potential method by which such gaps in knowledge can be filled. We examined the viability of this approach through monitoring wandering albatrosses Diomedea exulans at their colony on Bird Island, South Georgia (54°S, 38°W) over the winters (May,July) of 1999 and 2000. At this time, these birds foraged in up to three different water-masses, the Antarctic zone (AZ), the sub-Antarctic zone (SAZ) and the sub-Tropical zone (STZ), which we defined by contemporaneous satellite images of sea surface temperature. A probabilistic model was applied to the tracking and diet data collected from 38 birds to construct a large-scale map of where various prey were captured. Robustness/sensitivity analyses were used to test model assumptions on the time spent foraging and relative catch efficiencies and to evaluate potential biases associated with the model. We were able to predict the distributions of a wide number of cephalopod, crustacean of fish species. We also discovered some of the limitations to using this type of data and proposed ways to rectify these problems. [source] Shrinking baseline: the growth in juvenile fisheries, with the Hong Kong grouper fishery as a case studyFISH AND FISHERIES, Issue 4 2009Allen W L To Abstract Historic and current information on the grouper fishery from Hong Kong and adjacent waters reveals significant changes in species composition and fish sizes over the past 50 years in this important Asian centre for seafood consumption. Once dominant, large groupers are now rare and small species and sizes prevail in the present-day fishery. Juveniles comprise over 80% of marketed fish by number among the most commonly retailed groupers, and reproductive-sized fish are absent among larger species. Current fishery practices and the lack of management in Hong Kong and adjacent waters pose a significant threat to large species with limited geographic distribution such as Epinephelus akaara and Epinephelus bruneus, both now listed as threatened by the IUCN. The heavy reliance on juveniles, not only for groupers, but for an increasing diversity of desired fishes within Asia, potentially reduces stock spawning potential. The ,shrinking baseline' in terms of a progressive reduction in fish sizes being marketed in the region can seriously undermine fishery sustainability and recoverability of depleted fish stocks. Fishing pressure on groupers and other valuable food fishes within the Asia-Pacific is intensifying, the declining long-term trend of grouper landings in Hong Kong and the increasing focus on juveniles for immediate sale or for mariculture ,grow-out' signal a worrying direction for regional fisheries. Moreover, the common appearance of small groupers for sale will influence public perception regarding what are ,normal-sized' fish. Management attention is needed if these fisheries are to remain viable. [source] Principles and approaches to abate seabird by-catch in longline fisheriesFISH AND FISHERIES, Issue 1 2005Eric Gilman Abstract Mortality in longline fisheries is a critical global threat to most albatross and large petrel species. Here we identify key principles and approaches to identify and achieve broad use of effective seabird by-catch avoidance methods. Despite the availability of highly effective and cost-saving seabird avoidance methods, few longline fleets employ them. Given the political context and capacity of management authorities of the majority of longline fisheries, it is critical to identify seabird avoidance strategies that are not only highly effective, but are also economically viable and commercially practical. Adoption of an international performance standard for longline baited hook,sink rate, and prescribing minimum gear weighting designs that meet this standard that are achievable by all longline fisheries, would be an important step forward towards resolving low use of seabird avoidance methods by vessels, including those in illegal, unregulated and unreported fisheries. Due to differences between fleets, no single seabird avoidance measure is likely to be effective and practical in all longline fisheries. Therefore, testing of seabird avoidance methods in individual fleets is needed to determine efficacy and economic viability. Longline fishers should directly participate in these trials as they have a large repository of knowledge and skills to effectively develop and improve seabird by-catch avoidance techniques, and this provides industry with a sense of ownership for uptake of effective by-catch reduction methods. Establishing protected areas containing seabird colonies and adjacent waters within a nation's EEZ can be an expedient method to address seabird by-catch. However, establishing high seas marine protected areas to restrict longline fishing in seabird foraging areas, which would require extensive and dynamic boundaries and large buffer zones, may not be a viable short-term solution because of the extensive time anticipated to resolve legal complications with international treaties, to achieve international consensus and political will, and to acquire requisite extensive resources for surveillance and enforcement. Analysis of results of research on seabird avoidance methods reveals that the most reliable comparisons of the efficacy of alternative strategies are from comparing the effectiveness of methods tested in a single experiment. Benefits from standardizing the reporting of seabird by-catch rates to account for seabird abundance are described. To provide the most precise inputs for seabird population models, estimates of seabird mortality in longline fisheries should account for seabird falloff from hooks before hauling, delayed mortality of seabirds caught but freed from gear, and mortality caused by hooks discarded in offal. [source] Seasonal changes in the reproduction of three oncaeid copepods in the surface layer of the Kuroshio ExtensionFISHERIES OCEANOGRAPHY, Issue 2004KAORU NAKATA Abstract Seasonal changes in reproduction rates of three dominant oncaeids, Oncaea media, O. venusta f. venella and O. venusta f. ,1, and effects of environmental factors on them were examined in the surface layer (0,30 m) in the Kuroshio Extension and adjacent waters off the Pacific coast of central Japan. The biomass of oncaeid copepods peaked in spring, and remained at about 14% of total copepod biomass throughout the year. Monthly mean specific egg production rates of O. media, O. venusta f. ,1 and O. venusta f. venella ranged from 0 to 0.038 day,1, from 0.026 to 0.051 day,1 and from 0.022 to 0.049 day,1, respectively, and were relatively higher from winter to spring. Specific egg production rates of both O. media and O. venusta f. venella were positively related to primary production in the euphotic layer. Analysis of temperature effects on reproduction parameters indicated that low temperature was one cause for high specific egg production rates of O. venusta f. ,1 in winter, mainly because of an increase in clutch size. Environmental factors thus affect reproduction of the dominant oncaeids in the surface layer of the Kuroshio Extension, and an increase in temperature and decline in primary production would reduce their reproduction. [source] Animal behaviour and marine protected areas: incorporating behavioural data into the selection of marine protected areas for an endangered killer whale populationANIMAL CONSERVATION, Issue 2 2010E. Ashe Abstract Like many endangered wildlife populations, the viability and conservation status of ,southern resident' killer whales Orcinus orca in the north-east Pacific may be affected by prey limitation and repeated disturbance by human activities. Marine protected areas (MPAs) present an attractive option to mitigate impacts of anthropogenic activities, but they run the risk of tokenism if placed arbitrarily. Notwithstanding recreational and industrial marine traffic, the number of commercial vessels in the local whalewatching fleet is approaching the number of killer whales to be watched. Resident killer whales have been shown to be more vulnerable to vessel disturbance while feeding than during resting, travelling or socializing activities, therefore protected-areas management strategies that target feeding ,hotspots' should confer greater conservation benefit than those that protect habitat generically. Classification trees and spatially explicit generalized additive models were used to model killer whale habitat use and whale behaviour in inshore waters of Washington State (USA) and British Columbia (BC, Canada). Here we propose a candidate MPA that is small (i.e. a few square miles), but seemingly important. Killer whales were predicted to be 2.7 times as likely to be engaged in feeding activity in this site than they were in adjacent waters. A recurring challenge for cetacean MPAs is the need to identify areas that are large enough to be biologically meaningful while being small enough to allow effective management of human activities within those boundaries. Our approach prioritizes habitat that animals use primarily for the activity in which they are most responsive to anthropogenic disturbance. [source] Double-Observer Line Transect Methods: Levels of IndependenceBIOMETRICS, Issue 1 2010Stephen T. Buckland Summary Double-observer line transect methods are becoming increasingly widespread, especially for the estimation of marine mammal abundance from aerial and shipboard surveys when detection of animals on the line is uncertain. The resulting data supplement conventional distance sampling data with two-sample mark,recapture data. Like conventional mark,recapture data, these have inherent problems for estimating abundance in the presence of heterogeneity. Unlike conventional mark,recapture methods, line transect methods use knowledge of the distribution of a covariate, which affects detection probability (namely, distance from the transect line) in inference. This knowledge can be used to diagnose unmodeled heterogeneity in the mark,recapture component of the data. By modeling the covariance in detection probabilities with distance, we show how the estimation problem can be formulated in terms of different levels of independence. At one extreme, full independence is assumed, as in the Petersen estimator (which does not use distance data); at the other extreme, independence only occurs in the limit as detection probability tends to one. Between the two extremes, there is a range of models, including those currently in common use, which have intermediate levels of independence. We show how this framework can be used to provide more reliable analysis of double-observer line transect data. We test the methods by simulation, and by analysis of a dataset for which true abundance is known. We illustrate the approach through analysis of minke whale sightings data from the North Sea and adjacent waters. [source] | |||||||||||||