Selectividad de artes de enmalle (betas y trasmallo) en el Egeo septentrional, Turquía

Fishing trials were carried out with gill nets and trammel nets in the northern Aegean Sea from March 2004 to February 2005. Four different mesh sizes for the gill nets and the inner panel of trammel nets (16, 18, 20 and 22 mm bar length) were used. Selectivity parameters for the five most economically important species, bogue (Boops boops), annular sea bream (Diplodus annularis), striped red mullet (Mullus surmuletus), axillary sea bream (Pagellus acarne) and blotched picarel (Spicara maena), caught by the two gears were estimated. The SELECT method was used to estimate the selectivity parameters of a variety of models. Catch composition and catch proportion of several species were different in gill and trammel nets. The length frequency distributions of the species caught by the two gears were significantly different. The bi-modal model selectivity curve gave the best fit for gill net and trammel net data, and there was little difference between the modal lengths of these nets. However, a clear difference was found in catching efficiency. The highest catch rates were obtained with the trammel net. Given that many discard species and small fish are caught by gill nets and trammel nets with a mesh size of 16 mm, it is clear that these nets are not appropriate for fisheries. Consequently, the best mesh size for multispecies fisheries is 18 mm. This mesh size will considerably reduce the numbers of small sized individuals and discard species in the catch.Se realizaron ensayos de pesca con betas y trasmallos en el Egeo septentrional desde marzo de 2004 a febrero de 2005. Se utilizaron cuatro luces de malla distintas (16, 18, 20 y 22 mm) tanto para las betas como para el paño interno de los trasmallos. Se estimaron los parámetros de selectividad de las cinco especies más importantes capturadas por ambos artes: boga (Boops boops), raspallón (Diplodus annularis), salmonete de roca (Mullus surmuletus), aligote (Pagellus acarne) y chucla (Spicara maena). Se utilizó el método SELECT para la estimación de los parámetros de selectividad de varios modelos. La composición en tallas de la captura así como la proporción de las distintas especies capturadas por las betas y trasmallos fueron diferentes. La distribución de frecuencias de tallas de las especies capturadas por ambos artes fueron significativamente diferentes. El modelo de curva de selectividad bimodal fue el que mejor se ajustó a los datos de betas y trasmallos, y se encontraron muy pocas diferencias entre las longitudes modales de ambos artes. No obstante, se encontró una diferencia clara en la eficiencia de captura. Las tasas de captura más altas correspondieron a los trasmallos. Teniendo en cuenta que con betas y trasmallos de luz de malla de 16 mm se obtienen muchas especies que son posteriormente descartadas así como gran cantidad de peces pequeños, parece claro que estas redes no son convenientes para la pesquería. La luz de malla de 18 mm es la mejor para estas pesquerías multiespecíficas. El uso de paños con esta luz de malla resultaría en una reducción considerable del número de individuos de pequeña talla así como de las especies descartadas

A New Record for Occurrence of Symphodus bailloni (Osteichthyes: Perciformes: Labridae) in the Western Black Sea Coast of Turkey

The fish species Symphodus bailloni (Valenciennes, 1839) reported in the present study were collected between June 2010 and June 2011 from the western Black Sea coasts which were previously not recorded from the Black Sea coast of Turkey. A total of 717 specimens of S. bailloni were measured, ranging between 8.9 and 15.4 cm TL. Morphometrics, meristics, and diagnostic characteristics of the species are presented

Report of the ICCAT GBYP international workshop on Atlantic bluefin tuna growth

In the last Atlantic bluefin tuna assessment, an age-length database coming from direct ageing was presented for the first time. It was observed that otolith age estimates for fish younger than 8 years old had a smaller size at age compared to spine (first dorsal fin radius) age estimates. This difference, although small, was enough to misallocate the year class. This misallocation was solved when introducing a vector of bias corrected aged otoliths based on paired otolithspine samples. We have identified two possible causes for over-estimating age in the otolith agelength data: the current age adjustment criterion (to convert the bands counting into ages) and a reading bias in age estimations from some laboratories. Otolith preparation and reading protocols have been reviewed. The edge type and marginal increment analysis showed that the formation of opaque zones would seem likely to occur primarily between December through to June, contrary to what was thought until now, for which a new criterion for age adjustment has been proposed

Historical separation and present-day structure of common dolphinfish (Coryphaena hippurus) populations in the Atlantic Ocean and Mediterranean Sea

The common dolphinfish (Coryphaena hippurus) is an epipelagic, mid-trophic level, highly migratory species distributed throughout the world’s tropical and subtropical oceans in waters greater than 20C. Life-history variables, migratory behaviour, and genetic markers have been used to define major stocks in the central Atlantic Ocean and Mediterranean Sea. Here, we used the mitochondrial DNA gene NADH subunit 1 (688 bp) to test for differences between population groups. A total of 103 haplotypes were detected among 203 fish. Gene diversities in samples were large and similar among populations (mean h ¼ 0.932; range 0.894–0.987), but nucleotide diversities varied widely among samples (range p ¼ 0.004–0.034) and appear to reflect population histories. Principal component analysis revealed two large populations groups, and the analysis of molecular variation and pairwise values of UST resolved population structure within these groups. Populations in the eastern Atlantic and Mediterranean showed the largest amounts of divergence from one another (UCT ¼ 0.331). Adult movement and biophysical barriers to larval dispersal may explain contemporary differences between stocks, but the divergent populations in the Mediterranean Sea are likely due to isolations by cold temperature barriers during Pleistocene glaciations. The geographically large stock groupings require international cooperation in the harvest management and conservation of local dolphinfish populations

Thermal sensitivity of field metabolic rate predicts differential futures for bluefin tuna juveniles across the Atlantic Ocean

Changing environmental temperatures impact the physiological performance of fishes, and consequently their distributions. A mechanistic understanding of the linkages between experienced temperature and the physiological response expressed within complex natural environments is often lacking, hampering efforts to project impacts especially when future conditions exceed previous experience. In this study, we use natural chemical tracers to determine the individual experienced temperatures and expressed field metabolic rates of Atlantic bluefin tuna (Thunnus thynnus) during their first year of life. Our findings reveal that the tuna exhibit a preference for temperatures 2–4 °C lower than those that maximise field metabolic rates, thereby avoiding temperatures warm enough to limit metabolic performance. Based on current IPCC projections, our results indicate that historically-important spawning and nursery grounds for bluefin tuna will become thermally limiting due to warming within the next 50 years. However, limiting global warming to below 2 °C would preserve habitat conditions in the Mediterranean Sea for this species. Our approach, which is based on field observations, provides predictions of animal performance and behaviour that are not constrained by laboratory conditions, and can be extended to any marine teleost species for which otoliths are available

Thermal sensitivity of field metabolic rate predicts differential futures for bluefin tuna juveniles across the Atlantic Ocean

Changing environmental temperatures impact the physiological performance of fishes, and consequently their distributions. A mechanistic understanding of the linkages between experienced temperature and the physiological response expressed within complex natural environments is often lacking, hampering efforts to project impacts especially when future conditions exceed previous experience. In this study, we use natural chemical tracers to determine the individual experienced temperatures and expressed field metabolic rates of Atlantic bluefin tuna (Thunnus thynnus) during their first year of life. Our findings reveal that the tuna exhibit a preference for temperatures 2–4 °C lower than those that maximise field metabolic rates, thereby avoiding temperatures warm enough to limit metabolic performance. Based on current IPCC projections, our results indicate that historically-important spawning and nursery grounds for bluefin tuna will become thermally limiting due to warming within the next 50 years. However, limiting global warming to below 2 °C would preserve habitat conditions in the Mediterranean Sea for this species. Our approach, which is based on field observations, provides predictions of animal performance and behaviour that are not constrained by laboratory conditions, and can be extended to any marine teleost species for which otoliths are available

An investigation of age, growth and mortality of the red mullet Mullus barbatus Linnaeus, 1758 in the western Black Sea

The aim of this study was to determine the age, growth, length-weight relationship, sex ratio and fishing mortality rates of the red mullet off the western Black Sea coast of Turkey. Age, growth and mortality parameters were estimated for the red mullet, M. barbatus, sampled from commercial landings for the demersal trawl fishery in the western Black Sea between October 2012 and April 2014. The age of 1426 individuals was determined using the sagittal otolith reading technique. The total length ranged from 6.3 to 18.9 cm, while weight varied between 3.62 and 62.42 g for 4928 red mullet individuals (1829 males, 1986 females and 1113 unidentified). 3815 individuals were found mature while 1113 individuals as immature. The length-weight relationship for all individuals was calculated as W = 0.0109 x L-2.9886. M. barbatus has a life-span of 4 years, but over 60% of fish were less than 3 years old. The growth parameters were k = 0.17 yr(-1), L-8 = 24.1 cm, and to = -1.98 years for pooled data. According to age-structured analysis, the total, natural and fishing mortalities were Z = 1.32 year(-1), M = 0.45 year(-1) and F = 0.86 year(-1), respectively. The exploitation rate, E = 0.65, suggests a high fishing pressure on the red mullet stock in the studied area

A Record of Fish Anomaly from the Sea of Marmara, Turkiye: European Hake (Merluccius merluccius Linnaeus, 1758) Missing the Right Eye

Abnormalities of shape, color or body deformities such as lack of swim bladders or any parts of the body are an unexplained issue for many fish species. There is a gap of knowledge regarding their causes. Generally, it is an important problem in the rearing technique in aquaculture management due to the high economic consequences. The morphological abnormalities occur in marine fishes as well. Missing dorsal spines or rays, scale disorientation, jaw deformities, eye deformations and the lack of some parts of the body are within the context of abnormality. In the present study, the body abnormality observed in a specimen of European hake (Merluccius merluccius Linnaeus, 1758) missing its right eye which was caught by a fisherman in the Marmara Sea on 13 October 2020, and its causes are reported and discussed. Further studies are needed to correlate the wild fish anomalies caused by pollution

Technical characteristics of demersal set nets, used in Istanbul artisanal fisheries.

Technical characteristics of demersal set nets, used in Istanbul artisanal fisheries were determined with this study. A total of 13 various types pelagic set nets of which 7 gill nets and 6 trammel nets were identified. Technical plans of these nets were introduced for the first time according to the FAO standards