Are mean size data adequate to monitor freshwater eel fisheries?

1999 ◽  
Vol 50 (4) ◽  
pp. 355 ◽  
Author(s):  
R. I. C. Chris Francis ◽  
Don J. Jellyman
Keyword(s):  
Sampling Error ◽  
Fish Population ◽  
Fishing Pressure ◽  
Freshwater Eel ◽  
Long Term Changes ◽  
Mean Size ◽  
The Mean ◽  
Natural Variations ◽  
Size Data

As the biomass of a fish population is reduced by fishing, the mean size (length or weight) of individuals in the population can be expected to decrease. Thus, it should be possible, in principle, to detect changes in fishing pressure by monitoring mean size. A simulation experiment was carried out to see whether this might work in practice with New Zealand freshwater eel fisheries. Information on the dynamics of eel populations was used to construct a simulation model of a fishery with a range of exploitation scenarios. It was found that size data, by themselves, could be useful for detecting large long-term changes in stock status, but are not likely to be good indicators for use in year-to-year management. Natural variations in eel recruitment cause substantial year-to-year variations in the mean size of eels, even when fishing pressure is constant. This makes it difficult to detect changes in size caused by long-term changes in fishing pressure. Even without sampling error, biomass would need to drop by more than 40% (or more, if the drop is gradual) before this change could be reliably detected. The presence of typical levels of sampling error makes this detection even harder.

Late endoscopic evaluation of the ostium size after external dacryocystorhinostomy

2020 ◽  
pp. 112067212097604
Author(s):  
Reem R Al Huthail ◽  
Yasser H Al-Faky
Keyword(s):  
Chart Review ◽  
Retrospective Chart Review ◽  
Tertiary Hospital ◽  
Nasal Endoscope ◽  
Long Term Follow Up ◽  
Mean Size ◽  
External Dacryocystorhinostomy ◽  
The Mean

Objective: To evaluate the effect of chronicity on the size of the ostium after external dacryocystorhinostomy (DCR) with intubation. Methods: Design: A retrospective chart review of patients who underwent external DCR with intubation over 10 years from January 2003 at a tertiary hospital. All patients were recruited and examined with rigid nasal endoscope. Results: A total number of 66 (85 eyes) patients were included. The mean age at the time of evaluation was 53.1 years with gender distribution of 54 females (81.8 %). The mean duration ±SD between the date of surgery and the date of evaluation was 33.2 ± 33.6 (6–118 months). Our study showed an overall anatomical and functional success of 98.8% and 95.3%, respectively. The mean size of the ostium (±SD) was 23.0 (±15.7) mm2 (ranging from 1 to 80.4 mm2). The size of the ostium was not a significant factor for failure ( p = 0.907). No statistically significant correlation was found between the long-term duration after surgery and the size of the ostium ( R: 0.025, p = 0.157). Conclusions: Nasal endoscopy after DCR is valuable in evaluating the ostium with no observed potential correlation between the long-term follow-up after surgery and the size of the ostium.

scholarly journals Climatologies and long-term changes in mesospheric wind and wave measurements based on radar observations at high and mid latitudes

2019 ◽  
Vol 37 (5) ◽  
pp. 851-875 ◽  
Author(s):  
Sven Wilhelm ◽  
Gunter Stober ◽  
Peter Brown
Keyword(s):  
Kinetic Energy ◽  
Gravity Waves ◽  
Lower Thermosphere ◽  
Atmospheric Parameters ◽  
Amplitude Response ◽  
Wave Measurements ◽  
Long Term Changes ◽  
The Mean ◽  
Mesosphere And Lower Thermosphere

Abstract. We report on long-term observations of atmospheric parameters in the mesosphere and lower thermosphere (MLT) made over the last 2 decades. Within this study, we show, based on meteor wind measurement, the long-term variability of winds, tides, and kinetic energy of planetary and gravity waves. These measurements were done between the years 2002 and 2018 for the high-latitude location of Andenes (69.3∘ N, 16∘ E) and the mid-latitude locations of Juliusruh (54.6∘ N, 13.4∘ E) and Tavistock (43.3∘ N, 80.8∘ W). While the climatologies for each location show a similar pattern, the locations differ strongly with respect to the altitude and season of several parameters. Our results show annual wind tendencies for Andenes which are toward the south and to the west, with changes of up to 3 m s−1 per decade, while the mid-latitude locations show smaller opposite tendencies to negligible changes. The diurnal tides show nearly no significant long-term changes, while changes for the semidiurnal tides differ regarding altitude. Andenes shows only during winter a tidal weakening above 90 km, while for the Canadian Meteor Orbit Radar (CMOR) an enhancement of the semidiurnal tides during the winter and a weakening during fall occur. Furthermore, the kinetic energy for planetary waves showed strong peak values during winters which also featured the occurrence of sudden stratospheric warming. The influence of the 11-year solar cycle on the winds and tides is presented. The amplitudes of the mean winds exhibit a significant amplitude response for the zonal component below 82 km during summer and from November to December between 84 and 95 km at Andenes and CMOR. The semidiurnal tides (SDTs) show a clear 11-year response at all locations, from October to November.

scholarly journals Long-term changes in the mean trophic level of Central Chile fishery landings

2005 ◽  
Vol 69 (2) ◽  
pp. 295-300 ◽  
Author(s):  
Hugo Arancibia ◽  
Sergio Neira
Keyword(s):  
Trophic Level ◽  
Central Chile ◽  
Long Term Changes ◽  
The Mean ◽  
Mean Trophic Level

scholarly journals Fisheries, the inverted food pyramid

2015 ◽  
Vol 73 (6) ◽  
pp. 1697-1713 ◽  
Author(s):  
Jeppe Kolding ◽  
Alida Bundy ◽  
Paul A.M. van Zwieten ◽  
Michael J. Plank
Keyword(s):  
Global Assessment ◽  
Marine Ecosystems ◽  
Trophic Levels ◽  
Ecosystem Structure ◽  
Fishing Pressure ◽  
Food Pyramid ◽  
The World ◽  
Long Term Changes ◽  
Ecosystem Structure And Functioning

Abstract A global assessment of fishing patterns and fishing pressure from 110 different Ecopath models, representing marine ecosystems throughout the world and covering the period 1970–2007, show that human exploitation across trophic levels (TLs) is highly unbalanced and skewed towards low productive species at high TLs, which are around two TLs higher than the animal protein we get from terrestrial farming. Overall, exploitation levels from low trophic species were <15% of production, and only 18% of the total number of exploited groups and species were harvested >40% of their production. Generally, well-managed fisheries from temperate ecosystems were more selectively harvested at higher exploitation rates than tropical and upwelling (tropical and temperate) fisheries, resulting in potentially larger long-term changes to the ecosystem structure and functioning. The results indicate a very inefficient utilization of the food energy value of marine production. Rebuilding overfished components of the ecosystem and changing focus to balancing exploitation across a wider range of TLs, i.e. balanced harvesting, has the potential to significantly increase overall catches from global marine fisheries.

scholarly journals HYDROLOGICAL CHARACTERISTICS OF THE DNIESTER ESTUARY BY SURVEYS IN THE SUMMER’S OF 2003–2019

2021 ◽  
Vol 26 (1(38)) ◽  
pp. 28-42
Author(s):  
Ye. І. Gazyetov ◽  
V. І. Medinets ◽  
S. M. Snigirov ◽  
N. V. Kovaleva ◽  
S. V. Medinets
Keyword(s):  
Electrical Conductivity ◽  
Spatial Distribution ◽  
River Flow ◽  
Graphical Representation ◽  
Hydrological Regime ◽  
Hydrological Characteristics ◽  
Wide Range ◽  
Long Term Changes ◽  
The Mean

Problem Statement and Purpose. The Lower Dniester delta and the Dniester estuary are very important because they are natural filters of the river water from pollution and suspended matter, as well as they are the habitat of a large number species of flora and fauna. The construction of reservoirs on the Dniester River in past completely changed the hydrological regime of the river itself and of the Dniester estuary. For these reasons a constant environmental monitoring of the aquatic environment are required. Since 2002 Odessa I. I. Mechnikov National University has been carrying out a wide range of environmental studies in the Dniester estuary, one of aspects of which is observation of hydrological characteristics. The purpose of this paper is to study long-term changes in transparency, temperature and electrical conductivity of the Dniester estuary water in the summer periods of 2003–2019. Materials & Methods. Measurements of transparency, temperature and electrical conductivity of water in the Dniester estuary in the indicated years were carried out according to standard methods at 19 ecological stations. Statistical processing, analysis and mapping of the measurements results were conducted in EXCEL, ARCGIS, SURFER software’s. Data analysis was based on a graphical representation of the spatial distribution of characteristics, as well as by identifying the features of long-term changes in these characteristics. Main Results and Conclusions. On the basis of the summer surveys during 2003–2019 more than double decrease of water transparency mean values in the Dniester estuary has been established. It was found that the maximum transparency values were observed in the central parts of the estuary, far from settlements. For theseyears, an increase of the mean water temperature for the estuary northern part and its decrease in the middle and southern parts has been recorded. Also, for the summer period of these years, an increase of the mean water electrical conductivity in all parts of the estuary was established. The established features of spatial distribution of hydrological characteristics indicate to the river runoff, intrusion of seawater into the estuary, and wind activity as the determining factors in formation of the estuary hydrological regime. Recorded long-term trends of the means transparency values decreasing and the means temperature and electrical conductivity increasing of the Dniester estuary water in the summer of 2003–2019 are considered as consequences of the river discharge decreasing due to long-term climatic changes over Europe and man regulation of river flow.

scholarly journals Long-Term Outcome in Patients with a Solitary Peutz-Jeghers Polyp

2019 ◽  
Vol 2019 ◽  
pp. 1-5 ◽  
Author(s):  
Masaya Iwamuro ◽  
Yuki Aoyama ◽  
Seiyuu Suzuki ◽  
Sayo Kobayashi ◽  
Tatsuya Toyokawa ◽  
...  
Keyword(s):  
Gastrointestinal Tract ◽  
Term Outcome ◽  
Long Term Outcome ◽  
Mucocutaneous Pigmentation ◽  
History Of ◽  
Mean Size ◽  
The Mean ◽  
Peutz Jeghers Syndrome

Background. Clinical characteristics and prognosis of patients with a solitary Peutz-Jeghers polyp (PJP) have not been fully investigated. Methods. Solitary PJP was diagnosed when a single hamartomatous lesion was identified in the gastrointestinal tract of patients without mucocutaneous pigmentation or a family history of Peutz-Jeghers syndrome. We retrospectively reviewed 51 patients (32 men and 19 women) with a solitary PJP and analyzed the sex, age at diagnosis, endoscopic features, and outcomes in this patient group. The STK11/LKB1 germline mutation was not investigated in any of the patients. Results. The mean age of the 51 patients was 66.1 years. The polyp was found in the duodenum (N=10), jejunum (N=2), cecum (N=2), transverse colon (N=5), sigmoid colon (N=21), or rectum (N=11). Most of the polyps presented as a pedunculated lesion (N=40), followed by semipedunculated (N=9) and sessile (N=2) morphologies. The mean size of a solitary PJP was 15.6 mm (range: 5 to 33 mm). During a mean endoscopic follow-up period of 4.5 years (range: 0.1 to 16.1 years), no recurrence was identified. Eighteen of the enrolled patients had a history of cancer or concomitant cancer. Five patients died due to non-gastrointestinal-related causes. No additional cancer or death directly related to solitary PJP was observed. Conclusions. Solitary PJPs did not recur in this study. Although examination of the entire gastrointestinal tract using esophagogastroduodenoscopy, enteroscopy, and colonoscopy is desirable to exclude Peutz-Jeghers syndrome, follow-up endoscopy after endoscopic polyp resection may be unnecessary, once the diagnosis of a solitary PJP is made.

scholarly journals Long-term changes in the snow–firn pack stratigraphy on Ürümqi glacier No. 1, eastern Tien Shan, China

2007 ◽  
Vol 46 ◽  
pp. 331-334 ◽  
Author(s):  
Feiteng Wang ◽  
Zhongqin Li ◽  
R. Edwards ◽  
Huilin Li
Keyword(s):  
Ablation Rate ◽  
Tien Shan ◽  
Coarse Grained ◽  
Climatic Warming ◽  
The West ◽  
Branch Site ◽  
Snow Stratigraphy ◽  
Long Term Changes ◽  
The Mean

AbstractWe report on changes to the snowpack of Ürümqi glacier No. 1, eastern Tien Shan, China, resulting from climate change between 1961 and 2005. Data from more than 120 snow pits were used to investigate temporal changes in the snow stratigraphy for three periods 1961–62, 1980–83 and 2002–05. Both the thickness and structure of the snow were found to be significantly altered by climatic warming. The proportion of coarse-grained firn, which is usually formed by infiltration water, was found to have increased from 40% to 65% over the period 1961–2005, and the distribution of the glacier zones also changed significantly, with all boundaries moving up-slope. The recrystallization–infiltration zone disappeared in 1989. The mean ablation rate over the melt season increased by ~26% from 1962 to 1980 at the west branch site and by ~75% from 1980 to 2004 at the east branch site.

Balancing Fisheries Management and Water Uses for Impounded River Systems

2008 ◽  
Keyword(s):  
Largemouth Bass ◽  
Micropterus Salmoides ◽  
Adult Population ◽  
Wild Fish ◽  
Adult Size ◽  
Catch Per Unit Effort ◽  
Adult Age ◽  
Mean Size ◽  
The Mean

<em>Abstract</em>.—Despite the widespread use of supplemental stocking, survival of age-0 and age-1 stocked fish is often variable and stocking success is not commonly evaluated through adult size-classes. We evaluated the long-term contribution of stocked largemouth bass <em>Micropterus salmoides </em>from three annual stockings in 15 reservoirs in Illinois. Stocked largemouth bass were marked with fin clips and sampled for 5 years. Contribution of stocked fish to the population was highest for age-0 (21%) and age-1 largemouth bass (17%) but decreased significantly in adult fish (5%). Contribution of stocked bass was not associated with either populations of wild largemouth bass or latitude. Survival of stocked fish was similar to survival of wild fish through age 1. Age-0 abundance of wild and stocked largemouth bass were positively correlated in the fall following stocking, suggesting that similar factors may influence initial survival. Survival of stocked fish from age-1 to adult age decreased significantly compared to wild fish, resulting in low contribution of stocked bass to the adult population. Adult and age-1 catch per unit effort of stocked largemouth bass were positively correlated with the mean size of stocked bass in the first fall after stocking and the following spring, indicating that lakes with higher growth rates have increased contribution of stocked fish. We found limited contribution of stocked fish to adult largemouth bass populations due to low survival from age-1 to adult age. Assessments of fish stocking success should evaluate survival of stocked fish through adult ages or they may omit a critical period for mortality.

scholarly journals Impact of meteorological analyses and chemical data assimilation on modelled long-term changes in stratospheric NO<sub>2</sub>

2012 ◽  
Vol 12 (5) ◽  
pp. 12023-12050
Author(s):  
L. N. Gunn ◽  
M. P. Chipperfield ◽  
W. Feng ◽  
M. Van Roozendael ◽  
M. Gil ◽  
...  
Keyword(s):  
Transport Model ◽  
Three Dimensional ◽  
Tracer Transport ◽  
Chemical Transport Model ◽  
Wind Fields ◽  
Basic Model ◽  
Long Term Changes ◽  
Ozone Trends ◽  
The Mean

Abstract. We have used a three-dimensional (3-D) off-line chemical transport model (CTM) to investigate long-term changes in stratospheric NO2. The basic model was integrated from 1977 to 2001 using ECMWF (European Centre for Medium-Range Weather Forcasts) ERA-40 reanalyses. Additional model runs were performed which assimilated HALOE observations of long-lived tracers to constrain the model trace gas distributions. Assimilation of a single long-lived species (CH4) improves not only the distribution of all other long-lived species, via tracer-tracer correlations, but also shorter lived radical and reservoir species. Assimilation of the long-lived species corrects for errors in the model, due to horizontal transport from the ERA-40 reanalyses, and allows a more direct test of the model's chemistry. The basic model significantly underestimates the observed column NO2 from mid-latitude ground-based sites in the mid-late 1990s. The mean underestimate is ~ 26% for summertime values between 1992 and 1998. Moreover, as the model agreement is better in the early 1990s, it underestimates the increasing trend throughout the decade. However, when the model assimilates HALOE CH4 data both comparisons are greatly improved. The mean model-observation difference reduces to 8% for summertime values and the trend improves. This indicates that given realistic wind fields to constrain the tracer transport, the model chemistry and aerosol schemes are able to reproduce the observed trends in NO2. Implications of this for using analysed wind fields to determine dynamical ozone trends are discussed. Ozone trends derived directly from transport models forced by analysed winds are likely subject to similar errors.

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