Improving the selectivity of bottom trawls in the Adriatic and Tyrrhenian sea

U prvom eksperimentu ispitala se selektivnost vreća pridnene povlačne mreže ko će izrađenih od 50 milimetarskog romboidnog i 40 milimetarskog kvadratnog oka. Razlika u selektivnosti između dviju navedenih konfiguracija uočena je kod vrsta Nephrops norvegicus, Galeus melastomus i Trisopterus minutus u korist kvadratnog oka. U drugom eksperimentu ispitana je razlika u selektivnosti vreća izrađenih od 40 mm kvadratnog mrežnog tega, sa razli čitim brojem oka u opsegu, gdje je uočeno da se povećanjem opsega smanjuje vrijednost parametra L50 za vrstu Mullus barbatus. Trećim eksperimentom ispitana je selektivnost pridnene povlačne mreže ko će kojoj je u zadnjem segmentu grla postavljena 90 milimetarska selektivna rešetka . Rezultati su pokazali kako se upotrebom selektivne rešetke može smanjiti koli čina prilova u ulovu, bez značajnog gubitka ulova gospodarski važnih vrsta. U četvrtom eksperimentu ispitala se selektivnost pridnene povlačne mreže ko će kojoj je u posljednjem segmentu grla postavljen selektivni panel izrađen od 50 milimetarskog kvadratnog oka. Rezultati su pokazali da prisutnost selektivnog panela, zbog malog broja riba koje su uopće došle u kontakt s njim, nema značajnog efekta na selektivnost testirane mreže. Temel jem dosadašnjih istraživanja selektivnosti pridnene povla čne mreže ko će na Mediteranu, dati su odnosi između selekcijskih parametara (L50, SR) i različitih tehničkih parametara koće za koje je poznato da utječu na selektivnost.The first experiment was set up to investigate selectivity of 40 mm square and 50 mm diamond mesh codend. The difference in selectivity between two indicated configurations was evident for Nephrops norvegicus, Galeus melastomus and Trisopterus minutus, favouring square mesh codend. The second experiment was set up to investigate the effect of changing the codend circumference made up entirely of 40 mm square mesh netting. The negative effect of increasing the codend circumference was evident only in case of Mullus barbatus, where parameter L50 was significantly reduced. Third experiment was set up to investigate the selectivity of trawl with a selective grid of 90 mm bar spacing in front of the size-selective codend made of 50 mm diamond mesh. The presence of grid proved to be good in bycatch reduction, without affecting commercial catches. Fourth experiment was set up to investigate the selectivity of trawl with the selective panel made of 50 mm square mesh, positioned in front of the size-selective codend made of 50 mm diamond mesh. The results showed no significant effect of panel on the overall selectivity. Finally, by critically reviewing existing literature on bottom trawl selectivity, general relationships between selectivity parameters (L50 and SR) and different codend technical parameters known to affect selectivity are given

Improving the selectivity of bottom trawls in the Adriatic and Tyrrhenian sea

U prvom eksperimentu ispitala se selektivnost vreća pridnene povlačne mreže ko će izrađenih od 50 milimetarskog romboidnog i 40 milimetarskog kvadratnog oka. Razlika u selektivnosti između dviju navedenih konfiguracija uočena je kod vrsta Nephrops norvegicus, Galeus melastomus i Trisopterus minutus u korist kvadratnog oka. U drugom eksperimentu ispitana je razlika u selektivnosti vreća izrađenih od 40 mm kvadratnog mrežnog tega, sa razli čitim brojem oka u opsegu, gdje je uočeno da se povećanjem opsega smanjuje vrijednost parametra L50 za vrstu Mullus barbatus. Trećim eksperimentom ispitana je selektivnost pridnene povlačne mreže ko će kojoj je u zadnjem segmentu grla postavljena 90 milimetarska selektivna rešetka . Rezultati su pokazali kako se upotrebom selektivne rešetke može smanjiti koli čina prilova u ulovu, bez značajnog gubitka ulova gospodarski važnih vrsta. U četvrtom eksperimentu ispitala se selektivnost pridnene povlačne mreže ko će kojoj je u posljednjem segmentu grla postavljen selektivni panel izrađen od 50 milimetarskog kvadratnog oka. Rezultati su pokazali da prisutnost selektivnog panela, zbog malog broja riba koje su uopće došle u kontakt s njim, nema značajnog efekta na selektivnost testirane mreže. Temel jem dosadašnjih istraživanja selektivnosti pridnene povla čne mreže ko će na Mediteranu, dati su odnosi između selekcijskih parametara (L50, SR) i različitih tehničkih parametara koće za koje je poznato da utječu na selektivnost.The first experiment was set up to investigate selectivity of 40 mm square and 50 mm diamond mesh codend. The difference in selectivity between two indicated configurations was evident for Nephrops norvegicus, Galeus melastomus and Trisopterus minutus, favouring square mesh codend. The second experiment was set up to investigate the effect of changing the codend circumference made up entirely of 40 mm square mesh netting. The negative effect of increasing the codend circumference was evident only in case of Mullus barbatus, where parameter L50 was significantly reduced. Third experiment was set up to investigate the selectivity of trawl with a selective grid of 90 mm bar spacing in front of the size-selective codend made of 50 mm diamond mesh. The presence of grid proved to be good in bycatch reduction, without affecting commercial catches. Fourth experiment was set up to investigate the selectivity of trawl with the selective panel made of 50 mm square mesh, positioned in front of the size-selective codend made of 50 mm diamond mesh. The results showed no significant effect of panel on the overall selectivity. Finally, by critically reviewing existing literature on bottom trawl selectivity, general relationships between selectivity parameters (L50 and SR) and different codend technical parameters known to affect selectivity are given

Escape, discard and landing probability of Nephrops norvegicus in the Mediterranean Sea creel fishery

Size selection in creel fishery consists of two processes: the first taking place in the creel on the seabed and the second made by the fisher on the vessel. However, no study has ever considered both processes when assessing the size selection in creel fisheries. This study presents a framework for including both and demonstrates it to predict the effect of mesh size and shape on the creel fishery targeting the Norway lobster (Nephrops norvegicus) in the Mediterranean Sea. For this specific fishery, we demonstrate that both processes play a role in the overall size selection. Furthermore, we predict an optimal creel mesh size, which potentially eliminates the second process taking place on the vessel, while maintaining high efficiency for the first process on the seabed for the targeted sizes of Nephrops. The approach here presented can be also applied to other creel fisheries

Influencia de la temperatura del fondo del mar y profundidad en la estimación del área de barrido en sistemas de arrastre

The methodological approach to data collection and analysis in Mediterranean bottom trawl surveys has changed considerably since their beginnings in the mid-1980s. The introduction of new technologies in surveys greatly improved knowledge on trawl underwater geometry, but also raised a question on the reliability of the data obtained. The most commonly used trawl monitoring systems in the Mediterranean use the constant speed of sound when calculating horizontal distance from one sensor to another. However, the speed of the sound in seawater is not constant because it depends on water temperature, pressure, and salinity. This is known to affect the performance of the horizontally transmitting sonars, and it is reasonable to assume that unless it is properly compensated for, the readings from trawl monitoring systems can be incorrect, resulting in biased swept area estimates, and hence potentially producing bias in abundance estimates. In the knowledge that speed of sound depends on temperature, salinity and pressure, the Del Grosso (1974) equation was used to calculate the compensation coefficient for a series of theoretical depth and temperature data. A simple model is proposed in the current paper for the manual correction of the horizontal net opening and swept area estimates. Temperature and depth data obtained from the MEDATLAS project are used to show seasonal and spatial variation in the near-bottom speed of sound, and the results demonstrate that, unless compensated for properly, the error in the horizontal net spread ranges from –1.5% to 2.9%.El enfoque metodológico para la recopilación de datos y análisis en estudios de arrastre de fondo del Mediterráneo ha cambiado considerablemente desde sus inicios en los años ochenta. La introducción de nuevas tecnologías en los estudios ha mejorado enormemente el conocimiento de la geometría de los artes de pesca de debajo del agua, pero, al mismo tiempo, surge la pregunta de la fiabilidad de los datos obtenidos. Los sistemas de seguimiento más comúnmente utilizados en los artes en el Mediterráneo usan la velocidad constante del sonido cuando calculan la distancia horizontal de un sensor a otro. Sin embargo la velocidad del sonido en el agua marina no es constante ya que depende de la temperatura del agua, de la presión y la salinidad. Se sabe que esto afecta al rendimiento de los sonares que transmiten en horizontal, y es razonable suponer que si se compensan adecuadamente, las lecturas de los monitores de seguimiento del arte pueden ser incorrectos, dando lugar a estimaciones sesgadas del área barrida por el arte, y en consecuencia potencialmente producir sesgo en bastantes estimaciones. Conociendo que la velocidad del sonido depende de la temperatura, salinidad y presión, se ha usado la ecuación de Del Grosso (1974) para calcular el coeficiente de compensación en series de datos de profundidad teórica y temperatura. A continuación, un modelo simple se ha propuesto en el presente artículo para la corrección manual de la obertura horizontal de la red y estimación del área de barrido. Se han usado los datos de temperatura y profundidad obtenidos del proyecto MEDATLAS para mostrar la variación estacional y espacial en la velocidad del sonido cerca del fondo marino, y los resultados demuestran que, a no ser que se compense adecuadamente, el error en la obertura horizontal de la red varía entre –1.5 a 2.9%

Revealing the Shamefaced Crab Calappa granulata (Crustacea: Brachyura) from the Adriatic Sea, Northern Basin of the Mediterranean

This study presents the first data on morphometry, length–weight relationship, diet, reproductive biology, epibionts and genetic identity of the shamefaced crab Calappa granulata from the central eastern Adriatic Sea. A total of 92 crabs were collected during 2011, 2014 and 2015, of which 64 were females and 28 were males. Overall, 11 morphometric characteristics were measured. Carapace length of sampled individuals ranged from 48.46 to 76.09 mm, and body weight from 47.06 to 221.39 g. The length–weight relationship showed negative allometry for males and isometric growth for females. Analysis of the stomach content revealed the crab’s preference for crustaceans (20.28%) and cephalopods (10.58%), less for fish (3.4%) and shellfish (0.28%). Size at first sexual maturity (CL50%) of 59.25 and 66.92 mm was estimated for males and females, respectively. Epibiotic serpulid polychaetes were recorded on the crab exoskeleton with an overall prevalence of 29.3%. Analyses of a partial sequence of mtCOI showed high haplotype (Hd = 0.964) and low nucleotide diversity (π = 0.00598). Phylogenetic inference and estimation of population differentiation (FST = 0.013, p = 0.271) with publicly available Mediterranean sequences currently imply one homogenous population unit. To the best of our knowledge, these are the first nucleotide sequences of C. granulata from the Adriatic Sea made publicly available.publishedVersio

Edad, crecimiento y utilidad de la morfometría de los otolitos como predictor de la edad en el pez Coris julis (Labridae) del Adriático oriental

Age and growth of Coris julis were determined by examining sagittal otoliths belonging to fish sampled between November 2008 and October 2009 in the eastern Adriatic Sea (north-central Mediterranean Sea). A total of 1102 specimens (528 males, 487 females and 87 individuals of indeterminate sex), ranging from 48 to 222 mm total length were analysed. Ninety-two per cent of the otoliths were readable and 68% of the specimens had two readings in agreement. Counting of daily rings revealed that the second opaque ring represents the first annulus (315.1±27.8 daily rings). The maximum observed age was 7 years for males and 5 years for females, with males dominating in higher age classes ( > 3 years) and females in age classes 1+ and 2+. Growth was described by the von Bertalanffy growth curves and significant differences were found between males (L∞=29.10 cm, k=0.12 and t0=–1.48) and females (L∞=21.27 cm, k=0.21 and t0=–1.08). Otolith mass, length, width and thickness were determined for the otoliths belonging to 465 fish and the utility of these morphometrics as a predictor of age was evaluated. The most precise age estimations were obtained from the otolith length data, followed by the otolith mass.Se determinó la edad y se estimaron los parámetros de crecimiento de Coris julis basados en el análisis de los otolitos sagita de ejemplares capturados en el Adriático oriental (Norte del Mediterráneo central) entre noviembre de 2008 y octubre de 2009. Se examinó un total de 1.102 ejemplares (528 machos, 487 hembras, y 87 con sexo indeterminado), con tallas que oscilaron entre 48 y 222 mm de longitud total. El 92% de los otolitos analizados resultó legible y las lecturas fueron realizadas por dos lectores concordando en el 68 % de los individuos. El recuento de los incrementos diarios revelaron que el segundo anillo opaco corresponde al primer año (315,1±27,8 incrementos diarios). La edad máxima observada fue de 7 años para los machos y 5 años para las hembras. Los machos eran dominantes en las clases de edad más alta ( > 3 años) y las hembras en las clases de edad 1+ y 2+. El crecimiento se determinó mediante el modelo de von Bertalanffy y los parámetros de crecimiento estimados para los machos (L∞=29.10 cm, k=0.12 and t0=–1.48) y las hembras (L∞=21.27 cm, k=0.21 and t0=–1.08) fueron significativamente diferentes. La masa de los otolitos, la longitud, la anchura y el espesor se determinaron para los 465 otolitos y se ha evaluado la utilidad de estas medidas morfometrícas como un predictor de edad. Las estimaciones más precisas de edad se obtuvieron a partir de la longitud de los otolitos, y en segundo lugar por la masa de los otolitos

Influence of soak time on catch performance of commercial creels targeting Norway lobster (Nephrops norvegicus) in the Mediterranean Sea

Source at https://doi.org/10.1051/alr/2017035 .Creel catch performance is known to be affected by the soak time in many fisheries. If creels maintained their efficiency over longer periods, increase in soak time should lead to proportional increase in catch quantity. However, the exact shape of this relationship is unknown for creel fisheries targeting Norway lobster (Nephrops norvegicus). If it was known fishermen could adjust their fishing strategy accordingly and maximize their net earnings. We compared catch performance of creels targeting Norway lobster soaked for one and two days in the Adriatic Sea. Results were obtained for three crustacean species, Norway lobster (N. norvegicus), mantis shrimp (Squilla mantis), and blue-leg swimming crab (Liocarcinus depurator) and two fish species, poor cod (Trisopterus minutus) and blotched picarel (Spicara flexuosa). Doubling the soak time from one to two days did not double the catches and for Norway lobster no increase was found. For the other crustaceans, a slight but not significant increase was estimated. Catches of blotched picarel were significantly lower for the longer soak time, while the results were inconclusive for the poor cod

Fisheries Bycatch of Chondrichthyes

This chapter reviews the current state of knowledge about global chondrichthyes bycatch, including how the combination of biological characteristics of these species and the impact of different fishing methods reflect their vulnerability to bycatch. Specifically, it summarizes the present status of elasmobranchs and chimaeras bycatch worldwide. Following this, it illustrates the main ecological consequences behind such incidental captures. Hence, it provides a description of how chondrichthyes bycatch occurs across broad fishing gear categories. Moreover, it outlines potential mitigation options available to reduce bycatch. As such, the main technical measures tested and applied in different fishing practices are listed. In addition, an overview about which are the current management measures implemented at international level to ensure long-term conservation of cartilaginous fish is reported. Then, two case studies summarize how chondrichthyes bycatch occurred in some of the most exploited fishing areas. Finally, the chapter ends with relevant considerations about potential for new research needed to monitor and reduce chondrichthyes bycatch

Mesh sticking probability in fishing gear selectivity: Methodology and case study on Norway lobster (Nephrops norvegicus) and mantis shrimp (Squilla mantis) in the Mediterranean Sea creel fishery

Fish or crustaceans stuck in the fishing gear meshes can lead to operational problems in some fisheries and thereby affect theeconomic gain. However, mesh sticking probability has never been formally quantified as a part of the estimation of fishing gearsize selectivity. Therefore, this study developed a size selection model and estimation procedure that, besides the size dependentretention and escape probabilities, includes the size dependent mesh sticking probability. The new method was applied to quantify the size dependent retention, sticking and escape probabilities for mantis shrimp (Squilla mantis) and Norway lobster (Nephrops norvegicus) in creels with 41 mm square mesh netting. The mesh sticking probability was found to display a bell-shaped curvature with a maximum value for a specific carapace length and decreasing probabilities for both smaller and bigger individuals. For mantis shrimp the maximum sticking probability was found for 32.5 mm carapace length with a value at 13.5%, while 63.1% and 23.4% of that size were respectively retained inside the creels and escaped. For Norway lobster the maximum sticking probabilitywas 2% and occurred for 34.0 mm carapace length. The method and estimation procedure presented in this study might be applicable for quantifying mesh sticking probability as an integral part of future fishing gear size selectivity studies on other speciesand fisheries

Prediction of potential net panel selectivity in mesopelagic trawls

The growing interest in harvesting mesopelagic fish species has increased the need for knowledge about how trawls should be designed for optimizing the catch efficiency of these resources. Since the net herding efficiency for small mesopelagic fish species is unknown, trawls targeting these species need to consider the potential net panel selectivity along the entire trawl body. Therefore, trawl engineers and net makers who design trawls for harvesting mesopelagic species need to know which design parameters, such as mesh size, mesh opening angles, and trawl tapering angles, can be used along the trawl body to avoid potential net panel selectivity, thus maximizing catch efficiency. This study addresses these knowledge gaps using an approach based on laboratory experiments with mesopelagic fish and a simulation model that can help in predicting the potential net panel selectivity. Three trawl designs that have been used in experimental fisheries in the Northeast Atlantic are investigated in this study. Two of them (trawl 1 and trawl 2) had small-mesh liners in the belly and extension piece while the third trawl didn't. The simulation model shows that trawls with small-mesh liners in the belly and extension piece reduces panel selectivity and can increase catch efficiency.publishedVersio