Fishing Effort (fishing + effort)

Distribution by Scientific Domains


Selected Abstracts


SPOTTED DOLPHIN EVASIVE RESPONSE IN RELATION TO FISHING EFFORT

MARINE MAMMAL SCIENCE, Issue 1 2005
Cleridy E. Lennert-Cody
Abstract Spotted dolphins in the eastern Pacific Ocean associate with yellowfin tuna. During the chase and encirclement phases of purse-seining for tunas, dolphin attempt to evade encirclement with the purse-seine net. We used data on evasive behavior (1982,2001) and numbers of purse-seine sets (1959,2001) to study the relationship between evasion and fishing effort. Results show that in nearshore areas first exploited by the fishery in the early 1960s, dolphins exhibited high evasion, but with a limited correlation between evasion and cumulative effort. In areas farther offshore next exploited in the mid-to late-1960s, dolphins showed high evasion and a significant correlation between evasion and cumulative effort. Dolphins in far-western and southern areas, first exploited in the late 1960s to early 1970s, exhibited low evasion, with little relationship to cumulative effort. We hypothesize that this spatial pattern is the result of two types of pressure from fishing: early effort in nearshore areas with a high risk of mortality that generated a lasting evasive response, followed by a longer period of even greater effort but with lower risk of mortality that generated evasion by longer-term learning. [source]


Incorporation of Recreational Fishing Effort into Design of Marine Protected Areas

CONSERVATION BIOLOGY, Issue 5 2006
TIM P. LYNCH
consulta pública; modelos de reservas marinas; pesca con caña; suposiciones de poza dinámica Abstract:,Theoretical models of marine protected areas (MPAs) that explore benefits to fisheries or biodiversity conservation often assume a dynamic pool of fishing effort. For instance, effort is homogenously distributed over areas from which subsets of reserves are chosen. I tested this and other model assumptions with a case study of the multiple-use Jervis Bay Marine Park. Prior to zoning of the park I conducted 166 surveys of the park's recreational fisheries, plotting the location of 16,009 anglers. I converted these plots into diagrams of fishing effort and analyzed correlates between fishing and habitat and the effect of two reserve designs,the draft and final zoning plans of the park,on the 15 fisheries observed. Fisheries were strongly correlated with particular habitats and had negatively skewed and often bimodal spatial distribution. The second mode of intensely fished habitat could be 6 SD greater than the fishery's mean allocation of effort by area. In the draft-zoning plan, sanctuary zone (no-take) area and potential subduction of fishing effort were similar. In the final plan, which was altered in response to public comment, the area of sanctuary zone increased, and the impact on fishing effort decreased. In only one case was a fishery's most intensely targeted location closed to fishing. Because of the discriminating manner with which fishers target habitats, if simple percentage targets are used for planning, sanctuary location can be adjusted to avoid existing fishing effort. According to modeled outcomes, the implication of this may be diminished reserve effectiveness. To address this, reserve area should be implicitly linked to subducted fishing effort when promoting or modeling MPAs. Resumen:,Los modelos teóricos de áreas marinas protegidas (AMPs) que exploran los beneficios para las pesquerías o la conservación de la biodiversidad a menudo asumen que hay una poza dinámica en el esfuerzo de pesca. Por ejemplo, el esfuerzo es distribuido homogéneamente en áreas en las que se seleccionan subconjuntos de reservas. Probé esta y otras suposiciones del modelo con un estudio de caso del Parque Marino Jarvis Bay. Antes de la zonificación del parque, realicé 166 muestreos de las pesquerías recreativas del parque, dibujando la localización de 16,009 pescadores con caña. Convertí estos dibujos en diagramas de esfuerzo de pesca y analicé las correlaciones entre la pesca, el hábitat y el efecto de dos diseños de reserva,el anteproyecto y los planes finales de zonificación del parque,sobre las 15 pesquerías observadas. Las pesquerías se correlacionaron fuertemente con los hábitats particulares y tenían una distribución espacial sesgada negativamente y a menudo bimodal. El segundo tipo de hábitat pescado intensivamente podría ser 6 DS mayor que la asignación promedio de esfuerzo de pesquería por unidad de área. En el anteproyecto de plan de zonificación, el área santuario (sin pesca) y la subducción potencial del esfuerzo de pesca eran similares. En el plan final, que fue alterado en respuesta a comentarios del público, el área del santuario fue incrementada, y el impacto del esfuerzo de pesca disminuyó. En solo un caso fue cerrado a la pesca la localidad de pesca más intensiva. Debido a la forma discriminada en que los pescadores eligen los hábitats, si se utilizan objetivos porcentuales simples para la planificación, la localización del santuario puede ser ajustada para evitar el esfuerzo de pesca existente. De acuerdo con los resultados del modelo, la implicación puede ser la disminución de la efectividad de la reserva. Para abordar esto, el área de la reserva debiera estar implícitamente relacionada con la reducción del esfuerzo de pesca cuando se promueven o modelan AMPs. [source]


CREATION OF MARINE RESERVES AND INCENTIVES FOR BIODIVERSITY CONSERVATION

NATURAL RESOURCE MODELING, Issue 2 2010
QUACH THI KHANH NGOC
Abstract Despite a number of benefits, marine reserves provide neither incentives for fishermen to protect biodiversity nor compensation for financial loss due to the designation of the reserves. To obtain fishermen's support for marine reserves, some politicians have suggested that managers of new marine reserves should consider subsidizing or compensating those fishermen affected by the new operations. The objective of this paper is to apply principal,agent theory, which is still infrequently applied to fisheries, to define the optimal reserve area, fishing effort, and transfer payments in the context of symmetric and asymmetric information between managers and fishermen. The expected optimal reserve size under asymmetric information is smaller than that under symmetric information. Fishing efforts encouraged with a transfer payment are always less compared to those without payment. This reflects the fact that as the manager induces the fishermen to participate in the conservation program, the fishermen will take into account their effects on fish stock by decreasing their effort. Examples are also supplied to demonstrate these concepts. [source]


Incorporation of Recreational Fishing Effort into Design of Marine Protected Areas

CONSERVATION BIOLOGY, Issue 5 2006
TIM P. LYNCH
consulta pública; modelos de reservas marinas; pesca con caña; suposiciones de poza dinámica Abstract:,Theoretical models of marine protected areas (MPAs) that explore benefits to fisheries or biodiversity conservation often assume a dynamic pool of fishing effort. For instance, effort is homogenously distributed over areas from which subsets of reserves are chosen. I tested this and other model assumptions with a case study of the multiple-use Jervis Bay Marine Park. Prior to zoning of the park I conducted 166 surveys of the park's recreational fisheries, plotting the location of 16,009 anglers. I converted these plots into diagrams of fishing effort and analyzed correlates between fishing and habitat and the effect of two reserve designs,the draft and final zoning plans of the park,on the 15 fisheries observed. Fisheries were strongly correlated with particular habitats and had negatively skewed and often bimodal spatial distribution. The second mode of intensely fished habitat could be 6 SD greater than the fishery's mean allocation of effort by area. In the draft-zoning plan, sanctuary zone (no-take) area and potential subduction of fishing effort were similar. In the final plan, which was altered in response to public comment, the area of sanctuary zone increased, and the impact on fishing effort decreased. In only one case was a fishery's most intensely targeted location closed to fishing. Because of the discriminating manner with which fishers target habitats, if simple percentage targets are used for planning, sanctuary location can be adjusted to avoid existing fishing effort. According to modeled outcomes, the implication of this may be diminished reserve effectiveness. To address this, reserve area should be implicitly linked to subducted fishing effort when promoting or modeling MPAs. Resumen:,Los modelos teóricos de áreas marinas protegidas (AMPs) que exploran los beneficios para las pesquerías o la conservación de la biodiversidad a menudo asumen que hay una poza dinámica en el esfuerzo de pesca. Por ejemplo, el esfuerzo es distribuido homogéneamente en áreas en las que se seleccionan subconjuntos de reservas. Probé esta y otras suposiciones del modelo con un estudio de caso del Parque Marino Jarvis Bay. Antes de la zonificación del parque, realicé 166 muestreos de las pesquerías recreativas del parque, dibujando la localización de 16,009 pescadores con caña. Convertí estos dibujos en diagramas de esfuerzo de pesca y analicé las correlaciones entre la pesca, el hábitat y el efecto de dos diseños de reserva,el anteproyecto y los planes finales de zonificación del parque,sobre las 15 pesquerías observadas. Las pesquerías se correlacionaron fuertemente con los hábitats particulares y tenían una distribución espacial sesgada negativamente y a menudo bimodal. El segundo tipo de hábitat pescado intensivamente podría ser 6 DS mayor que la asignación promedio de esfuerzo de pesquería por unidad de área. En el anteproyecto de plan de zonificación, el área santuario (sin pesca) y la subducción potencial del esfuerzo de pesca eran similares. En el plan final, que fue alterado en respuesta a comentarios del público, el área del santuario fue incrementada, y el impacto del esfuerzo de pesca disminuyó. En solo un caso fue cerrado a la pesca la localidad de pesca más intensiva. Debido a la forma discriminada en que los pescadores eligen los hábitats, si se utilizan objetivos porcentuales simples para la planificación, la localización del santuario puede ser ajustada para evitar el esfuerzo de pesca existente. De acuerdo con los resultados del modelo, la implicación puede ser la disminución de la efectividad de la reserva. Para abordar esto, el área de la reserva debiera estar implícitamente relacionada con la reducción del esfuerzo de pesca cuando se promueven o modelan AMPs. [source]


An Evaluation of the Cod Fishing Policies of Denmark Iceland and Norway

EUROCHOICES, Issue 3 2004
R. Arnason
Summary An Evaluation of the Cod Fishing Policies of Denmark, Iceland and Norway Many ocean fisheries are subject to a fundamental economic problem generally referred to as the common property problem. This problem manifests itself as excessive fishing fleets and fishing effort, depressed fish stocks and little or no profitability of the fishing activity, irrespective of the richness of the underlying marine resources. European fisheries represent some of the most dramatic examples of the common property problem. This article employs simple empirical models and recently developed mathematical techniques to examine the economic efficiency of three European fisheries, namely the Danish, Icelandic and Norwegian cod fisheries, The optimal harvesting policies for each of these fisheries are calculated. Comparing these optimal policies with actual harvests provides a measure of the relative efficiency in these three cod fisheries. The comparison confirms the widely held impression that the cod harvesting policies of ail three countries have been hugely inefficient in the past. Moreover, it appears that the inefficiency has been increasing over time. Only during the last few years of our data are there indications that this negative trend may have been halted. Somewhat more surprisingly, in spite of radically different fisheries management systems, we find relatively little difference in the level of stock over-exploitation between these three countries. Politiques compareées de pêhe à la morue au Danemark, en Islande et en Norvège Beaucoup de pêcheries océaniques sont confrontées au problème nique fondamental de la "propriété collective". Celui-ci se manifeste par des flottes de taille excessive, au service d' efforts de péche exagérés, qui aboutissent à détruire les stocks de poisson et la rentabilité des pécheries, en dépit de la richesse des ressources marines sousjacentes. Les pêcheries européennes constituent actuellement l'un des exemples les plus dramatiques des problèmes associés a la propriété collective. On présente ici un modèle empirique assez simple mais associéà de nouvelles techniques mathématiques récemment développé es pour mesurer l' efficacitééconomique de trois types de politiques de pêche à la morue, au Danemark, en Norvège et en Islande. On commence par calculer le volume optimal des prises pour chacun de ces pays. La comparaison entre le niveau optimal et le niveau réel des prises permet de mesurer le degré d' efficacité des politiques suivies. Elle permet de confirmer l'opinion largement répandue selon laquelle les politiques passées ont été extrêmement peu efficaces. En outre, il apparaît que l'inefficacité est croissante avec le temps. C'est seulement dans les toutes dernières années des séries de données que l' on observe un infléchissement de cette tendance négative. Enfin, et c'est le plus surprenant, on trouve peu de differences entre les trois pays en ce qui conceme le degré de surexploitation du stock, et cela, bien que les principes de gestion des pêcheries y soient entiArement différents. Eine Bewertung der Kabeljaufischereipolitik in Dänemark, Island und Norwegen ahlreiche Hochseefischereien tehen einem grundlegenden ftliehen Problem gegenüber, das allgemein als Problem des kollektiven Eigentums bezeichnet wird. Dieses Problem zeigt sich in übermäßig großen Fangflotten und beträchtlichem Fischereiaufwand, geschrumpften Fischbeständen und geringer oder fehlender Rentabilität der Fischerei; dabei ist die Höhe der Fischressourcen unbedeutend für das Problem. Die europäischen Fischereien stellen einige der drastischsten Beispiele für das Problem des kollektiven Eigentums dar. In diesem Beitrag werden einfache empirische Modelle und kürzlich entwickelte mathematische Verfahren angewendet, um die wirtschaftliche Effizienz von drei europäischen Fischereien zu untersuchem der dänischen, der isländischen und der norwegischen Kabeljaufischerei. Für jede dieser Fischereien wird die optimale Nutzungsstrategie berechnet. Aus dem Vergleich dieser optimalen Nutzungsstrategie mit den tatsächlichen Erträgen ergibt sich ein Maß fur die relative Effizienz, die bei diesen drei Kabeljaufischereien vorliegt. Der Vergleich bestätigt den weit verbreiteten Eindruck, dass die Strategien zum Kabeljaufang in alien drei Ländern in der Vergangenheit enorm ineffizient waren. Darüber hinaus wird deutlich, dass die Ineffizienz im Laufe der Zeit zugenommen hat. Lediglich die Daten der letzten jahre enthalten Hinweise darauf, dass dieser negative Trend zum Stillstand gekommen sein könnte. Obwohl sich die Fischwirtschaft in jedem dieser drei Länder sehr stark unterscheidet, lassen sich erstaunlich wenige Unterschiede im Maß der Übernutzung des Fischbestandes finden. [source]


How do individual transferable quotas affect marine ecosystems?

FISH AND FISHERIES, Issue 1 2009
Trevor A Branch
Abstract Published papers were reviewed to assess ecosystem impacts of individual transferable quotas (ITQs) and other dedicated access systems. Under ITQs, quota shares increase with higher abundance levels, thus fishers may request lower total allowable catches (TACs) and pay for monitoring and research that improves fishery sustainability. Mortality on target species generally declines because catches are closer to TACs and because ghost fishing through lost and abandoned gear decreases. High-grading and discarding often decline, but may increase if landings (and not catches) count against ITQs and when there is little at-sea enforcement. Overall, ITQs positively impact target species, although collapses can occur if TACs are set too high or if catches are routinely allowed to exceed TACs. Fishing pressure may increase on non-ITQ species because of spillover from ITQ fisheries, and in cases where fishers anticipate that future ITQ allocations will be based on catch history and therefore increase their current catches. Ecosystem and habitat impacts of ITQs were only sparsely covered in the literature and were difficult to assess: ITQs often lead to changes in total fishing effort (both positive and negative), spatial shifts in effort, and fishing gear modifications. Stock assessments may be complicated by changes in the relationship between catch per unit effort, and abundance, but ITQ participants will often assist in improving data collection and stock assessments. Overall, ITQs have largely positive effects on target species, but mixed or unknown effects on non-target fisheries and the overall ecosystem. Favourable outcomes were linked to sustainable TACs and effective enforcement. [source]


Effects of cryptic mortality and the hidden costs of using length limits in fishery management

FISH AND FISHERIES, Issue 3 2007
Lewis G Coggins Jr
Abstract Fishery collapses cause substantial economic and ecological harm, but common management actions often fail to prevent overfishing. Minimum length limits are perhaps the most common fishing regulation used in both commercial and recreational fisheries, but their conservation benefits can be influenced by discard mortality of fish caught and released below the legal length. We constructed a computer model to evaluate how discard mortality could influence the conservation utility of minimum length regulations. We evaluated policy performance across two disparate fish life-history types: short-lived high-productivity (SLHP) and long-lived low-productivity (LLLP) species. For the life-history types, fishing mortality rates and minimum length limits that we examined, length limits alone generally failed to achieve sustainability when discard mortality rate exceeded about 0.2 for SLHP species and 0.05 for LLLP species. At these levels of discard mortality, reductions in overall fishing mortality (e.g. lower fishing effort) were required to prevent recruitment overfishing if fishing mortality was high. Similarly, relatively low discard mortality rates (>0.05) rendered maximum yield unobtainable and caused a substantial shift in the shape of the yield response surfaces. An analysis of fishery efficiency showed that length limits caused the simulated fisheries to be much less efficient, potentially exposing the target species and ecosystem to increased negative effects of the fishing process. Our findings suggest that for overexploited fisheries with moderate-to-high discard mortality rates, reductions in fishing mortality will be required to meet management goals. Resource managers should carefully consider impacts of cryptic mortality sources (e.g. discard mortality) on fishery sustainability, especially in recreational fisheries where release rates are high and effort is increasing in many areas of the world. [source]


Estimating angling effort and participation in a multi-user, inland fishery in South Africa

FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2010
B. R. ELLENDER
Abstract, Angler counts, on-lake interviews and a household survey were used to estimate angler effort and participation in Lake Gariep, South Africa's largest inland water body. Annual fishing effort was estimated from instantaneous counts at 16392 angler day,1 yr,1. Recreational and subsistence anglers contributed 41 and 59% to the total annual fishing effort, respectively. Household surveys in lakeshore settlements estimated that ,914 anglers fished the lake and minimum daily fishing effort in one of the fishing areas assessed was 77 anglers. As a result of recall bias, these estimates were almost twice as high as those determined by direct counts. A low cost method of assessing participation by applying a mark,recapture model to the proportion of anglers whom had been previously interviewed during eight bimonthly sampling events was tested. The model converged in three of four applications (2 areas × 2 sectors). The mark,recapture method revealed similar numbers of anglers to the estimate of regular anglers (fishing 1,3 times a week) from the household survey and was considered an appropriate estimator for the number of subsistence anglers. Regardless of the assessment method the results show that the resource is of importance to subsistence livelihoods, which is an important management consideration in future fisheries development and rights allocation processes. [source]


Assessment of salmon stocks and the use of management targets; a case study of the River Tamar, England

FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2007
K. HENDRY
Abstract, Over recent years the rod and net catch of Atlantic salmon, Salmo salar L., on the River Tamar in south-west England has decreased markedly, resulting in a consistent failure to meet the minimum egg deposition target (conservation limit). Compliance with the target is by annual assessment using rod catch as the major input variable. Further analysis suggested a disproportionate deterioration in the rod fishery performance of the Tamar compared with rivers locally, regionally and nationally. A concomitant decrease in rod licence sales and fishing effort, above both national and regional trends was also evident. However, examination of juvenile electric fishing and adult fish counter data revealed a different trend for the past 10 years, indicating a stable fish population, albeit at a lower level of abundance than previously. The analyses suggested that without consideration of changes in effort and rod exploitation rate, rod catch alone is not a reliable indicator of stock abundance and hence should not be used as such in stock assessment. [source]


Recent evolution of the fishing exploitation in the Thau lagoon, France

FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2002
V. CRESPI
Fisheries activity in the Thau marine lagoon (Mediterranean coast of France) has an old tradition and involves different types of gears (set nets, traps and lines) that are used seasonally with varying frequencies in different areas. A survey of fishing activity, main fishing methods and main commercial species composition in the lagoon was carried out to assess the current fishing effort and seasonal yield. Many important changes in fishing effort and in the most important target species occurred during the last 10 years. A gradual decline in eel, Anguilla anguilla (L.), catches followed by an increase of other commercially-exploited species, particularly the gilthead sea-bream, Sparus aurata L., was observed. [source]


Can fishermen allocate their fishing effort in space and time on the basis of their catch rates?

FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2001
An example from Spermonde Archipelago, Indonesia, SW Sulawesi
Spatial and temporal patterns in catch rates and in allocation of fishing effort were analysed for the coastal fishery in Spermonde Archipelago, Indonesia, to assess whether fishermen can optimise their strategy from catch information, or whether they fish under great uncertainty and merely minimise risks. On average 517 fishing units operated in the 2800 km2 area, catching 21 t fish day,1. Major gear categories were hook and line (59% of total effort and 5% of total catch), and lift nets (16% of total effort and 70% of total catch). The size of individual resource spaces varied with gear type and was smaller in unfavourable weather conditions. Although spatial patterns in catch rates at the scale of the whole archipelago were evident, fishermen could not differentiate between locations, as catch variance within their individual resource spaces was high relative to the contrasts in spatial patterns. The aggregated distribution of fishing effort in Spermonde must be explained by factors such as the small scale of operations, rather than fish abundance. [source]


Environmental effects on recruitment and productivity of Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus with recommendations for management

FISHERIES OCEANOGRAPHY, Issue 4 2005
AKIHIKO YATSU
Abstract We compared a wide range of environmental data with measures of recruitment and stock production for Japanese sardine Sardinops melanostictus and chub mackerel Scomber japonicus to examine factors potentially responsible for fishery regimes (periods of high or low recruitment and productivity). Environmental factors fall into two groups based on principal component analyses. The first principal component group was determined by the Pacific Decadal Oscillation Index and was dominated by variables associated with the Southern Oscillation Index and Kuroshio Sverdrup transport. The second was led by the Arctic Oscillation and dominated by variables associated with Kuroshio geostrophic transport. Instantaneous surplus production rates (ISPR) and log recruitment residuals (LNRR) changed within several years of environmental regime shifts and then stabilized due, we hypothesize, to rapid changes in carrying capacity and relaxation of density dependent effects. Like ISPR, LNRR appears more useful than fluctuation in commercial catch data for identifying the onset of fishery regime shifts. The extended Ricker models indicate spawning stock biomass and sea surface temperatures (SST) affect recruitment of sardine while spawning stock biomass, SST and sardine biomass affect recruitment of chub mackerel. Environmental conditions were favorable for sardine during 1969,87 and unfavorable during 1951,67 and after 1988. There were apparent shifts from favorable to unfavorable conditions for chub mackerel during 1976,77 and 1985,88, and from unfavorable to favorable during 1969,70 and 1988,92. Environmental effects on recruitment and surplus production are important but fishing effects are also influential. For example, chub mackerel may have shifted into a new favorable fishery regime in 1992 if fishing mortality had been lower. We suggest that managers consider to shift fishing effort in response to the changing stock productivity, and protect strong year classes by which we may detect new favorable regimes. [source]


The relationship between the skipjack tuna (Katsuwonus pelamis) fishery and seasonal temperature variability in the south-western Atlantic

FISHERIES OCEANOGRAPHY, Issue 1 2003
H. A. Andrade
Abstract The spatio-temporal distribution of tuna fishing effort has been related to oceanographic circulation and features in several seas of the world. Understanding the relationship between environmental variables and fishery resource dynamics is important for management decisions and to improve fishery yields. The relationship between sea temperature variability and the pole-and-line skipjack tuna (Katsuwonus pelamis) fishery in the south-western Atlantic Ocean was investigated in this work. Data from logbooks, satellite images (sea surface temperature), and oceanographic surveys were used in the analyses. Skipjack are caught in warm tropical waters of the Brazil Current (BC). The north,south displacement of fishing effort was strongly associated to seasonal variation of the surface temperature, which was coupled to the tropical BC flow. Oceanographic fronts from autumn to spring and a shallow thermocline in summer probably induces the aggregation of skipjack schools over the shelfbreak, favouring fishing operations. Hypotheses are proposed to explain the relationship between peaks of fishing events and the presence of topographic peculiarities of the shelfbreak. [source]


Application of a habitat-based model to estimate effective longline fishing effort and relative abundance of Pacific bigeye tuna (Thunnus obesus)

FISHERIES OCEANOGRAPHY, Issue 3 2002
Keith A. Bigelow
A new habitat-based model is developed to improve estimates of relative abundance of Pacific bigeye tuna (Thunnus obesus). The model provides estimates of `effective' longline effort and therefore better estimates of catch-per-unit-of-effort (CPUE) by incorporating information on the variation in longline fishing depth and depth of bigeye tuna preferred habitat. The essential elements in the model are: (1) estimation of the depth distribution of the longline gear, using information on gear configuration and ocean currents; (2) estimation of the depth distribution of bigeye tuna, based on habitat preference and oceanographic data; (3) estimation of effective longline effort, using fine-scale Japanese longline fishery data; and (4) aggregation of catch and effective effort over appropriate spatial zones to produce revised time series of CPUE. Model results indicate that effective effort has increased in both the western and central Pacific Ocean (WCPO) and eastern Pacific Ocean (EPO). In the WCPO, effective effort increased by 43% from the late 1960s to the late 1980s due primarily to the increased effectiveness of effort (deeper longline sets) rather than to increased nominal effort. Over the same period, effective effort increased 250% in the EPO due primarily to increased nominal effort. Nominal and standardized CPUE indices in the EPO show similar trends , a decline during the 1960s, a period of stability in the 1970s, high values during 1985,1986 and a decline thereafter. In the WCPO, nominal CPUE is stable over the time-series; however, standardized CPUE has declined by ,50%. If estimates of standardized CPUE accurately reflect relative abundance, then we have documented substantial reductions of bigeye tuna abundance for some regions in the Pacific Ocean. A decline in standardized CPUE in the subtropical gyres concurrent with stability in equatorial areas may represent a contraction in the range of the population resulting from a decline in population abundance. The sensitivity of the results to the habitat (temperature and oxygen) assumptions was tested using Monte Carlo simulations. [source]


Chronic fishing disturbance has changed shelf sea benthic community structure

JOURNAL OF ANIMAL ECOLOGY, Issue 3 2000
M. 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]


A framework for assessing the biodiversity and fishery aspects of marine reserves

JOURNAL OF APPLIED ECOLOGY, Issue 4 2009
Phillip S. Levin
Summary 1. ,Resource management agencies are often charged with managing natural resources for economic and social goals, while also protecting and conserving biodiversity and ecosystem function. However, this may not always be possible. Ecosystem-based management is frequently suggested as a way to achieve multiple objectives in resource management and requires that trade-offs among conflicting objectives be identified and an effective means to utilize these trade-offs developed. 2. ,We examine the relationship between area and species richness in a diverse assemblage of fishes along the US West Coast and then use parameters from this relationship as input for a model that considers trade-offs between fisheries yield and the number of species protected by different management strategies. 3. ,The species,area relationship (S = cAz) for fishes along the US Pacific coast is well described by the relationship S = 16·18A0·226. 4. ,There are nearly linear trade-offs between diversity and yield when fishing effort is low. However, the trade-offs become nonlinear as fishing effort increases and imposing MPAs increases both the conservation and fisheries value of the system when the system is overfished. 5. ,Synthesis and applications. Solving conflicts between fisheries and conservation requires attention as to how conservation benefits accrue as fishing effort is reduced. However, scientists often lack quantitative information about the trade-offs inherent in human activities such as fisheries. The approach we develop here can begin to help frame the questions to be posed and evaluate the likely consequences of different management options. [source]


Population structure, growth, mortality and estimated stock size of the introduced tench, Tinca tinca (L.), population in Lake Bey,ehir, Turkey

JOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2009
. Bal
Summary Population structure, growth, length,weight relationship, mortality and stock size of tench, Tinca tinca (L.), was studied in Lake Bey,ehir, Turkey in 2005. Totals of 3360 tench (1865 males; 1795 females) were captured with gill- and trammel-nets of various mesh sizes. Male to female ratio was 1.04 : 1. The study covered length year classes. Fork lengths and total weights ranged from 9 to 37 cm and 13 to 815 g. For all individuals, the von Bertalanffy growth equation and length,weight relationship were Lt = 54.2[1,exp(,0.1350(t + 1.0281)] and W = 0.0151 L2.9993, respectively. Growth performance index and mean condition factor of the tench population were 2.598 and 1.513, respectively. Mortality rates were Z = 1.97 year,1, M = 0.29 year,1 and F = 1.68 year,1 for total, natural, and fishing mortality, respectively. The exploitation rate was E = 0.85, and the percentage of surviving fish was 13.9%. Tench stock was assessed as about 6,7 million individuals and 1450,1500 tonnes in biomass. It was determined that maximum sustainable yield could be obtained with an 80% level of the current fishing effort. [source]


SPOTTED DOLPHIN EVASIVE RESPONSE IN RELATION TO FISHING EFFORT

MARINE MAMMAL SCIENCE, Issue 1 2005
Cleridy E. Lennert-Cody
Abstract Spotted dolphins in the eastern Pacific Ocean associate with yellowfin tuna. During the chase and encirclement phases of purse-seining for tunas, dolphin attempt to evade encirclement with the purse-seine net. We used data on evasive behavior (1982,2001) and numbers of purse-seine sets (1959,2001) to study the relationship between evasion and fishing effort. Results show that in nearshore areas first exploited by the fishery in the early 1960s, dolphins exhibited high evasion, but with a limited correlation between evasion and cumulative effort. In areas farther offshore next exploited in the mid-to late-1960s, dolphins showed high evasion and a significant correlation between evasion and cumulative effort. Dolphins in far-western and southern areas, first exploited in the late 1960s to early 1970s, exhibited low evasion, with little relationship to cumulative effort. We hypothesize that this spatial pattern is the result of two types of pressure from fishing: early effort in nearshore areas with a high risk of mortality that generated a lasting evasive response, followed by a longer period of even greater effort but with lower risk of mortality that generated evasion by longer-term learning. [source]


SUSTAINABLE YIELDS IN FISHERIES: UNCERTAINTY, RISK-AVERSION, AND MEAN-VARIANCE ANALYSIS

NATURAL RESOURCE MODELING, Issue 3 2010
CHRISTIAN-OLIVER EWALD
Abstract We consider a model of a fishery in which the dynamics of the unharvested fish population are given by the stochastic logistic growth equation Similar to the classical deterministic analogon, we assume that the fishery harvests the fish population following a constant effort strategy. In the first step, we derive the effort level that leads to maximum expected sustainable yield, which is understood as the expectation of the equilibrium distribution of the stochastic dynamics. This replaces the nonzero fixed point in the classical deterministic setup. In the second step, we assume that the fishery is risk averse and that there is a tradeoff between expected sustainable yield and uncertainty measured in terms of the variance of the equilibrium distribution. We derive the optimal constant effort harvesting strategy for this problem. In the final step, we consider an approach that we call the mean-variance analysis to sustainable fisheries. Similar as in the now classical mean-variance analysis in finance, going back to Markowitz [1952], we study the problem of maximizing expected sustainable yields under variance constraints, and with this, minimizing the variance, e.g., risk, under guaranteed minimum expected sustainable yields. We derive explicit formulas for the optimal fishing effort in all four problems considered and study the effects of uncertainty, risk aversion, and mean reversion speed on fishing efforts. [source]


OPTIMAL HARVESTING OF A SPATIALLY EXPLICIT FISHERY MODEL

NATURAL RESOURCE MODELING, Issue 2 2009
WANDI DING
Abstract We consider an optimal fishery harvesting problem using a spatially explicit model with a semilinear elliptic PDE, Dirichlet boundary conditions, and logistic population growth. We consider two objective functionals: maximizing the yield and minimizing the cost or the variation in the fishing effort (control). Existence, necessary conditions, and uniqueness for the optimal harvesting control for both cases are established. Results for maximizing the yield with Neumann (no-flux) boundary conditions are also given. The optimal control when minimizing the variation is characterized by a variational inequality instead of the usual algebraic characterization, which involves the solutions of an optimality system of nonlinear elliptic partial differential equations. Numerical examples are given to illustrate the results. [source]


Rivers as resources, rivers as borders: community and transboundary management of fisheries in the Upper Zambezi River floodplains

THE CANADIAN GEOGRAPHER/LE GEOGRAPHE CANADIEN, Issue 3 2007
JAMES ABBOTT
This article examines the recent convergence of community-based and transboundary natural resource management in Africa. We suggest that both approaches have potential application to common-pool resources such as floodplain fisheries. However, a merging of transboundary and community-based management may reinforce oversimplifications about heterogeneity in resources, users, and institutions. A scalar mismatch between the ecosystem of concern in transboundary management and local resources of concern in community-based management, as well as different colonial and post-colonial histories contribute to this heterogeneity. We describe a fishery shared by Namibia and Zambia in terms of hybrid fisheries management. We examine settlement patterns, fishermen characteristics, sources of conflict, and perceptions regarding present and potential forms of fisheries management in the area. We also consider the implications that initiatives to manage resources on the local and ecosystem scale have for these fishing livelihoods. Our findings indicate that important social factors, such as the unequal distribution of population and fishing effort, as well as mixed opinions regarding present and future responsibility for fisheries management will complicate attempts to implement a hybrid community-transboundary management initiative. Les rivières comme ressources, les rivières comme frontières: la gestion communautaire et transfrontière dans la plaine inondable du bassin supérieur de la rivière Zambezi Cet article examine l'état actuel du processus de convergence en Afrique entre gestions communautaire et transfrontalière des ressources naturelles. Nous laissons entendre que les deux approches ont le potentiel pour servir à la gestion de ressources halieutiques communes situées par exemple dans les plaines inondable. Par contre, la fusion des modes de gestion communautaire et transfrontaliers pourrait renforcer l'idée selon laquelle l'hétérogénéité des ressources, usagers et institutions est plus simple qu'elle ne l'est en réalité. Un décalage entre l'écosystème en question dans la gestion transfrontalière et les ressources locales en question dans la gestion communautaire, en plus des diverses histoires coloniales et post-coloniales, contribuent à cette hétérogénéité. Une description de la pêche que partagent la Namibie et la Zambie est présentée en termes d'une gestion hybride de la pêcherie. Nous examinons les schémas de peuplement, les traits distinctifs des populations de pêcheurs, les sources de conflit et les perceptions à l'égard des modes actuels et potentiels de gestion de la pêcherie dans la région. Nous étudions les conséquences que des initiatives en matière de gestion des ressources à l'échelle locale et à celle de l'écosystème peuvent avoir sur ces moyens de subsistance. Les résultats semblent montrer que des facteurs sociaux importants, comme la distribution inégale de la population et l'effort de pêche, ainsi que des opinions partagées concernant l'exercice des responsabilités dans la gestion de la pêcherie peuvent compliquer la tâche de mise en uvre d'une initiative de gestion communautaire et transfrontalière hybride. [source]


Assessing the effectiveness of conservation management decisions: likely effects of new protection measures for Hector's dolphin (Cephalorhynchus hectori)

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2010
Elisabeth Slooten
Abstract 1.Fisheries bycatch affects many species of marine mammals, seabirds, turtles and other marine animals. 2.New Zealand's endemic Hector's dolphins overlap with gillnet and trawl fisheries throughout their geographic range. The species is listed as Endangered by the IUCN. In addition, the North Island subspecies has been listed as Critically Endangered. 3.Estimates of catch rates in commercial gillnets from an observer programme (there are no quantitative estimates of bycatch by amateur gillnetters or in trawl fisheries) were used in a simple population viability analysis to predict the impact of this fishery under three scenarios: Option (A) status-quo management, (B) new regulations announced by the Minister of Fisheries in 2008 and (C) total protection. 4.Uncertainty in estimates of population size and growth rate, number of dolphins caught and other model inputs are explicitly included in the analysis. Sensitivity analyses are carried out to examine the effect of variation in catch rate and the extent to which fishing effort is removed from protected areas but displaced to unprotected areas. 5.These methods are applicable to many other situations in which animals are removed from populations, whether deliberately (e.g. fishing) or not (e.g. bycatch). 6.The current Hector's dolphin population is clearly depleted, at an estimated 27% of the 1970 population. Population projections to 2050 under Options A and B predict that the total population is likely to continue declining. In the case of Option B this is driven mainly by continuing bycatch due to the much weaker protection measures on the South Island west coast. 7.Without fishing mortality (Option C) all populations are projected to increase, with the total population approximately doubling by 2050 and reaching half of its 1970 population size in just under 40 years. Copyright © 2009 John Wiley & Sons, Ltd. [source]


An ecosystem modelling approach to deriving viable harvest strategies for multispecies management of the Northern Gulf of California

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009
Diego Lercari
Abstract 1.An ecosystem analysis was developed focusing on resource exploitation and biodiversity conservation for the Northern Gulf of California. The main tools employed were a trophic ecosystem model and time dynamic simulations. 2.The ecosystem was represented by an Ecopath model that included 34 functional groups, from primary producers to top predators. It included relevant species in the area such as commercially important shrimp (e.g. Litopenaeus stylirostris) and highly endangered species (Phocoena sinus and Totoaba macdonaldi). 3.Temporal simulations of changing fishing effort allowed the evaluation of fishing impact on the ecosystem components and, particularly, on protected species. Formal optimization methods were applied with the purpose of searching viable temporal patterns of fishing effort that might minimize social, economic and conservationist conflicts in the area. 4.The results of those simulations showed the capability of the model to represent reference temporal series of relative biomass. The search for viable fishing strategies resulted in effort allocation consistent with those proposed by other studies; that is, a decrease in the industrial shrimp fleet (35,65%), a decrease in the gillnet fishing fleet (52,57%), and an increase of the artisanal shrimp fishery (63,222%). 5.The main conflicts in the Northern Gulf of California seem to take place between social and conservation interests, while the economic and ecological benefits seem to be relatively independent. The next steps towards conflict resolution and ecosystem management should consider the design and operation of MPAs already established in the region. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Incidental catch of marine turtles by Italian trawlers and longliners in the central Mediterranean

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2007
Paolo Casale
Abstract 1.The fishing effort and turtle catch of vessels harbouring at Lampedusa island and fishing in the wider central Mediterranean area was monitored using a voluntary logbook programme. Two large trawlers were monitored between 2003 and 2005 and six small vessels using trawl nets, pelagic longline or bottom longline were monitored in the summer 2005. 2.The observed turtle catch rates of pelagic longline and bottom trawl were among the highest recorded in the basin, and high catch rates by bottom longline were observed too. This suggests that the area contains major oceanic and neritic habitats for the loggerhead turtle Caretta caretta in the Mediterranean Sea. 3.When fishing effort is considered, these results suggest a very high number of captures by Italian trawlers and longliners in the area, as well as by fleets from other countries. This is reason of concern for the conservation of the loggerhead turtle within the Mediterranean Sea. 4.Different fishing gear have different technical/operational characteristics affecting turtle catch and mortality and the present knowledge about associated parameters of these gear varies too. 5.All this considered, specific actions are recommended: (i) an awareness campaign to fishermen to reduce post-release mortality, (ii) technical modifications to pelagic longline gear to reduce turtle catch, (iii) further investigation into turtle bycatch in all fishing gear, with priority given to bottom longline fishing and quantification of mortality caused by trawlers, (iv) assessment of the turtle populations affected by fishing activity in the area, and (v) international cooperation in undertaking threat assessments, and implementing regulations, management measures and monitoring. Copyright © 2007 John Wiley & Sons, Ltd. [source]


A conservation trade-off?

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2007
Interspecific differences in seahorse responses to experimental changes in fishing effort
Abstract 1.A 2-year experimental seining programme and underwater visual censuses were undertaken to quantify the direct effects of active demersal fishing on the population structure and relative abundance of two sympatric seahorse species of conservation concern: the European long-snouted seahorse, Hippocampus guttulatus Cuvier 1829 and the short-snouted seahorse, Hippocampus hippocampus L. The influence of habitat preference on population-level responses to changes in habitat structure following a reduction in fishing effort was also investigated. 2.It was predicted that the benthic habitat would be more structurally complex after fishing ceased and that seahorse densities would increase in response to reduced fishing mortality. Furthermore, it was predicted that the magnitude of the increase in density would be greater for H. guttulatus than for H. hippocampus, because the former species prefers complex vegetated habitats while the latter species uses sparsely vegetated habitats. 3.As predicted, the amount of habitat cover increased significantly when seining ceased, primarily through increases in the abundance of drifting macroalgae and unattached invertebrates. Despite similarities in life histories, the two seahorse species responded differently in terms of magnitude and direction to reduced fishing effort: the abundance of H. guttulatus increased significantly while H. hippocampus decreased in abundance. 4.Results suggest that active demersal fishing may influence the magnitude and direction of the responses of benthic marine fishes to exploitation through its impacts on habitat structure. An increase in habitat cover appeared to favour higher densities of H. guttulatus when seining effort was reduced. By contrast, repeated seining, which maintained less complex habitats, appeared to favour greater abundances of H. hippocampus. 5.Given differences in habitat preference among benthic marine fishes subject to incidental capture in fisheries, simultaneous attempts to manage populations of sympatric species may require complementary strategies that support the persistence of diverse habitat types. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Catch Estimation in the Presence of Declining Catch Rate Due to Gear Saturation

BIOMETRICS, Issue 1 2001
Philip C. Dauk
Summary. One strategy for estimating total catch is to employ two separate surveys that independently estimate total fishing effort and catch rate with the estimator for total catch formed by their product. Survey designs for estimating catch rate often involve interviewing the fishermen during their fishing episodes. Such roving designs result in incomplete episode data and characteristically have employed a model in which the catch rate is assumed to be constant over time. This article extends the problem to that of estimating total catch in the presence of a declining catch rate due, e.g., to gear saturation. Using a gill net fishery as an example, a mean-of-ratios type of estimator for the catch rate together with its variance estimator are developed. Their performance is examined using simulations, with special attention given to effects of restrictions on the roving survey window. Finally, data from a Fraser River gill net fishery are used to illustrate the use of the proposed estimator and to compare results with those from an estimator based on a constant catch rate. [source]


An interdisciplinary evaluation of fishery production systems off the state of Pará in North Brazil

JOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2009
V. J. Isaac
Summary The performance of 20 fishery production systems off the state of Pará in the northern region of Brazil was compared using the ,RAPFISH' methodology, with 57 identified attributes distributed among five evaluation fields: economics, sociology, ecology, technology and politics. The results indicated the existence of three large groups of fishery sectors: (i) industrial (red snapper with traps, the Laulao catfish, shrimp trawl) and semi-industrial (lobster) fisheries; (ii) large-scale artisanal fisheries (acoupa weakfish, red snapper with lines, king mackerel, Spanish mackerel, coco sea catfish); and (iii) small-scale artisanal fisheries (shellfish, crab, estuarine longline, fish traps, etc.). While the industrial and large-scale artisanal systems demonstrated greater sustainability from an economic and social standpoint, small-scale fisheries appeared to be more ecologically sustainable. Based on the results, a reduction in industrial fishing efforts is recommended, along with the establishment of licensing quotas for fishing vessels, as well as an increased investment in research on proper guidance and management of the semi-industrial and large-scale artisanal fisheries sectors. For small-scale artisanal fisheries, economic incentives are suggested for the aggregate value of the products and to assist fishers in the development of an appropriate social organization. Finally, it is believed that a greater stakeholder involvement in the decision-making process would improve management actions for all modalities. [source]


Polymorphic tetranucleotide microsatellite markers in the Caribbean spiny lobster, Panulirus argus

MOLECULAR ECOLOGY RESOURCES, Issue 3 2004
F. M. DINIZ
Abstract Ten tetranucleotide microsatellite loci are described for the Caribbean spiny lobster Panulirus argus. Loci were polymorphic (4,15 alleles per locus) and exhibited high levels of expected (0.553,0.921) and observed heterozygosity (0.469,0.906) from samples caught off Belize and Puerto Rico coasts. No significant departure from Hardy,Weinberg equilibrium conditions were observed for any locus. All microsatellite loci should be useful for assessing population discrimination for this valuable marine animal currently subjected to excessive fishing efforts. [source]


SUSTAINABLE YIELDS IN FISHERIES: UNCERTAINTY, RISK-AVERSION, AND MEAN-VARIANCE ANALYSIS

NATURAL RESOURCE MODELING, Issue 3 2010
CHRISTIAN-OLIVER EWALD
Abstract We consider a model of a fishery in which the dynamics of the unharvested fish population are given by the stochastic logistic growth equation Similar to the classical deterministic analogon, we assume that the fishery harvests the fish population following a constant effort strategy. In the first step, we derive the effort level that leads to maximum expected sustainable yield, which is understood as the expectation of the equilibrium distribution of the stochastic dynamics. This replaces the nonzero fixed point in the classical deterministic setup. In the second step, we assume that the fishery is risk averse and that there is a tradeoff between expected sustainable yield and uncertainty measured in terms of the variance of the equilibrium distribution. We derive the optimal constant effort harvesting strategy for this problem. In the final step, we consider an approach that we call the mean-variance analysis to sustainable fisheries. Similar as in the now classical mean-variance analysis in finance, going back to Markowitz [1952], we study the problem of maximizing expected sustainable yields under variance constraints, and with this, minimizing the variance, e.g., risk, under guaranteed minimum expected sustainable yields. We derive explicit formulas for the optimal fishing effort in all four problems considered and study the effects of uncertainty, risk aversion, and mean reversion speed on fishing efforts. [source]


Demo-genetic analysis of a recovering population of otters in Central Sweden

ANIMAL CONSERVATION, Issue 6 2008
M. Björklund
Abstract We performed a demo-genetic population viability analysis on a recovering population of otters Lutra lutra in Central Sweden, using data on population size, survival and genetic data from microsatellites. Population data were obtained from genotyping faeces. At present, the size and genetic variability of the population is increasing. We found that survival to first reproduction was the most crucial demographic parameter, and that even slight changes downward in this parameter, might lead to a declining population trajectory. Human factors that can affect mortality are traffic, fishing equipment and traps, and we argue that efforts to minimize road kills by means of safe passages as well as careful fishing efforts in streams and lakes would reduce the risk of extinction. In general, even though the population is now growing and has no inbreeding problem, its small abundance could make it vulnerable to chance events and environmental perturbations. [source]