scholarly journals Towards more selective Mediterranean trawl fisheries: are juveniles and trash excluder devices effective tools for reducing undersized catches?

2018 ◽  
Vol 82 (S1) ◽  
pp. 215 ◽  
Author(s):  
Sergio Vitale ◽  
Giacomo Milisenda ◽  
Michele Gristina ◽  
Pasquale Baiata ◽  
Sara Bonanomi ◽  
...  
Keyword(s):  
Ad Hoc ◽  
Fishing Effort ◽  
Bottom Trawl ◽  
Steel Bars ◽  
Generalized Additive Mixed Models ◽  
Commercial Species ◽  
Additive Mixed Models ◽  
Sorting Efficiency ◽  
Trawl Fisheries ◽  
European Hake

Mediterranean trawl fisheries are characterized by a critical combination of high fishing effort and low size at first capture for most commercial species. In this study we tested the use of sorting grids installed on bottom trawl nets to minimize the catch of undersized deep-water rose shrimp (Parapenaeus longirostris, DPS) and European hake (Merluccius merluccius, HKE). The catch of a traditional trawl net was compared with that obtained with the same net equipped with ad hoc designed juveniles and trash excluder devices (JTEDs) during an experimental survey. Three different JTEDs were tested: the first (G1-SM40) was built with a net of 40-mm square mesh; the second (G2-ST20) and third (G3-ST25) with vertical steel bars spaced 20 and 25 mm, respectively. The probability of retaining DPS and HKE by length class in trawl nets with and without JTED was analysed using generalized additive mixed models. With G1-SM40, the reduction of undersized individuals in the cod-end was about 60% and 44% for DPS and HKE, respectively. With G2-ST20, a 34% catch decrease of HKE individuals smaller than 20 cm total length was observed. A loss of marketable fractions of DPS was recorded with G1-SM40 (–25%) and G2-ST20 (30%). Finally, JTD G3-ST25 was efficient at reducing the catch of undersized specimens of DPS and HKE, but showed a higher loss of marketable fractions than the other JTEDs. Although further fishing trials would be required to maximize the sorting efficiency of the grids, the results obtained clearly indicated that grids can substantially reduce unwanted catches of undersized DPS and HKE in Mediterranean bottom trawl fisheries.

scholarly journals Can a square-mesh panel inserted in front of the cod end improve size and species selectivity in Mediterranean trawl fisheries?

2018 ◽  
Vol 75 (5) ◽  
pp. 704-713 ◽  
Author(s):  
Jure Brčić ◽  
Bent Herrmann ◽  
Antonello Sala
Keyword(s):  
Deep Water ◽  
Bottom Trawl ◽  
Horse Mackerel ◽  
Trachurus Trachurus ◽  
Merluccius Merluccius ◽  
Low Probability ◽  
Low Efficiency ◽  
Trawl Fisheries ◽  
European Hake ◽  
Atlantic Horse Mackerel

An experiment was conducted to assess the selectivity in a typical Mediterranean bottom trawl, equipped with a square-mesh panel inserted in front of the cod end, for Atlantic horse mackerel (Trachurus trachurus), European hake (Merluccius merluccius), red mullet (Mullus barbatus), poor cod (Trisopterus minutus), broadtail shortfin squid (Illex coindetii), and deep-water rose shrimp (Parapaeneus longirostris). The release efficiency of undersized individuals through the panel was low. The differences in selectivity between the gear with and without the panel were very small. The low release efficiency of the square-mesh panel was caused by the lack of fish contact with the panel as they drifted towards the cod end, since the average contact probability was estimated not to exceed 9% for any of the species investigated. A low probability of contact with the selection device was thus found to be the reason for the low efficiency of the square-mesh panel.

scholarly journals Assessment of the relative catch performance of hake, red mullet and striped red mullet in a modified trawl extension with T90 netting

2018 ◽  
Vol 82 (S1) ◽  
pp. 19 ◽  
Author(s):  
Iván Sola ◽  
Francesc Maynou
Keyword(s):  
Target Species ◽  
Commercial Catch ◽  
Red Mullet ◽  
Comparison Approach ◽  
Commercial Species ◽  
Nw Mediterranean ◽  
Catch Rates ◽  
Trawl Fisheries ◽  
Discernible Difference ◽  
European Hake

We studied the relative catch performance of a modified trawl fitted with an extension piece using a 90º turned mesh (T90) in comparison with a standard trawl net used in NW Mediterranean bottom trawl fisheries employing a diamond mesh net. The comparison was made by means of paired experimental hauls using the same fishing vessel with alternate deployments of the standard net (control) and the experimental net. We used the catch comparison approach for three target species of the fishery: European hake, red mullet and striped red mullet. Our results show that the experimental net significantly reduces the catches of small-size hake and red mullet (though there was no discernible difference for striped red mullet), reducing unwanted catches of regulated species under the Landings Obligation. The overall catch rates of hake, pooled over all sizes, also increased by an estimated 50%, while the catch rates of red mullet and striped red mullet were significantly lower. However, considering all commercial species, the experimental net produced losses of commercial catch and income estimated at 17% and 18%, respectively, which may pose a barrier to the adoption of this relatively simple, inexpensive solution.

scholarly journals Time Series Analysis of Land Cover Change in Dry Mountains: Insights from the Tajik Pamirs

2021 ◽  
Vol 13 (19) ◽  
pp. 3951
Author(s):  
Kim André Vanselow ◽  
Harald Zandler ◽  
Cyrus Samimi
Keyword(s):  
Remote Sensing ◽  
Time Series ◽  
Land Cover ◽  
Land Cover Change ◽  
Vegetation Index ◽  
Demographic Data ◽  
Mountainous Areas ◽  
Generalized Additive Mixed Models ◽  
Additive Mixed Models ◽  
Irregular Data

Greening and browning trends in vegetation have been observed in many regions of the world in recent decades. However, few studies focused on dry mountains. Here, we analyze trends of land cover change in the Western Pamirs, Tajikistan. We aim to gain a deeper understanding of these changes and thus improve remote sensing studies in dry mountainous areas. The study area is characterized by a complex set of attributes, making it a prime example for this purpose. We used generalized additive mixed models for the trend estimation of a 32-year Landsat time series (1988–2020) of the modified soil adjusted vegetation index, vegetation data, and environmental and socio-demographic data. With this approach, we were able to cope with the typical challenges that occur in the remote sensing analysis of dry and mountainous areas, including background noise and irregular data. We found that greening and browning trends coexist and that they vary according to the land cover class, topography, and geographical distribution. Greening was detected predominantly in agricultural and forestry areas, indicating direct anthropogenic drivers of change. At other sites, greening corresponds well with increasing temperature. Browning was frequently linked to disastrous events, which are promoted by increasing temperatures.

The importance of alien species to the food web and bottom trawl fisheries of the Northeastern Mediterranean, a modelling approach

2020 ◽  
Vol 202 ◽  
pp. 103253 ◽  
Author(s):  
İsmet Saygu ◽  
Johanna J. Heymans ◽  
Clive J. Fox ◽  
Hüseyin Özbilgin ◽  
Ahmet Raif Eryaşar ◽  
...  
Keyword(s):  
Food Web ◽  
Alien Species ◽  
Bottom Trawl ◽  
Trawl Fisheries ◽  
Modelling Approach

scholarly journals Heart rate during hyperphagia differs between two bear species

2019 ◽  
Vol 15 (1) ◽  
pp. 20180681 ◽  
Author(s):  
Boris Fuchs ◽  
Koji Yamazaki ◽  
Alina L. Evans ◽  
Toshio Tsubota ◽  
Shinsuke Koike ◽  
...  
Keyword(s):  
Heart Rate ◽  
Ursus Arctos ◽  
Brown Bear ◽  
Black Bear ◽  
Black Bears ◽  
Brown Bears ◽  
Fat Reserves ◽  
Generalized Additive Mixed Models ◽  
Additive Mixed Models ◽  
Increased Activity

Hyperphagia is a critical part of the yearly cycle of bears when they gain fat reserves before entering hibernation. We used heart rate as a proxy to compare the metabolic rate between the Asian black bear ( Ursus thibetanus ) in Japan and the Eurasian brown bear ( Ursus arctos ) in Sweden from summer into hibernation. In the hyperphagic period, black bears feed on fat- and carbohydrate-rich hard masts whereas brown bears feed on sugar-rich berries. Availability of hard masts has quantitative and spatial annual fluctuations, which might require increased activity and result in intraspecific stress. Using generalized additive mixed models we analysed the differences in heart rate between the two species. Black bears had decreased heart rates during summer but had doubled heart rate values throughout the hyperphagic period compared to brown bears. This letter illustrates the different physiological consequences of seasonal differences in food availability in two species of the same genus dealing with the same phenological challenge.

scholarly journals Seasonal depth and temperature use, and diel movements of lake trout (Salvelinus namaycush) in a subarctic lake

2019 ◽  
Vol 5 (2) ◽  
pp. 71-89 ◽  
Author(s):  
Colin P. Gallagher ◽  
Matthew M. Guzzo ◽  
Terry A. Dick
Keyword(s):  
Lake Trout ◽  
Salvelinus Namaycush ◽  
Diel Migration ◽  
Vertical Activity ◽  
Generalized Additive Mixed Models ◽  
Additive Mixed Models ◽  
Proximate Causes ◽  
Subarctic Lake ◽  
High Degree ◽  
Diel Period

We conducted a multi-year acoustic telemetry study of lake trout (Salvelinus namaycush (Walbaum, 1792)) in a small subarctic lake to investigate depth and temperature occupancy, and vertical activity across seasons (summer, fall, and winter), diel periods (day, twilight, and night), and during summer periods of 24 h light (day and twilight). Analyses using generalized additive mixed models revealed a high degree of individual variation in depth occupancy independent of the factors hour of day, season, and diel period, whereas temperature occupancy and vertical activity were explained using the three combined factors. Habitats occupied were typically 9–20 m and 6–9.5 °C in summer, 1–3 m and 2–15 °C in fall during presumed spawning, and ≤6 m and <3 °C in winter. Lake trout exhibited partial diel migration where individuals displayed a variety of vertical migratory directions within and among seasons or diel period, including during periods of 24 h light. Fish were most vertically active during periods of daylight and in fall. During 24 h light, some lake trout performed crepuscular movements, whereas individual behaviour best explained modelled depth and temperature occupancy and vertical activity. The variety of vertical patterns among individuals and seasons suggests multifactor proximate causes of partial diel migration and crepuscular movements.

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