Net Selection Research Articles

Extra-pair paternity, offspring mortality and offspring sex ratio in the socially monogamous coal tit (Parus ater)

Females of many socially monogamous bird species commonly engage in extra-pair copulations. Assuming that extra-pair males are more attractive than the females’ social partners and that attractiveness has a heritable component, sex allocation theory predicts facultative overproduction of sons among extra-pair offspring (EPO) as sons benefit more than daughters from inheriting their father’s attractiveness traits. Here, we present a large-scale, three-year study on sex ratio variation in a passerine bird, the coal tit (Parus ater). Molecular sexing in combination with paternity analysis revealed no evidence for a male-bias in EPO sex ratios compared to their within-pair maternal half-siblings. Our main conclusion, therefore, is that facultative sex allocation to EPO is absent in the coal tit, in accordance with findings in several other species. Either there is no net selection for a deviation from random sex ratio variation (e.g. because extra-pair mating may serve goals different from striving for ‘attractiveness genes’) or evolutionary constraints preclude the evolution of precise maternal sex ratio adjustment. It is interesting to note that, however, we found broods without EPO as well as broods without mortality to be relatively female-biased compared to broods with EPO and mortality, respectively. We were unable to identify any environmental or parental variable to co-vary with brood sex ratios. There was no significant repeatability of sex ratios in consecutive broods of individual females that would hint at some idiosyncratic maternal sex ratio adjustment. Further research is needed to resolve the biological significance of the correlation between brood sex ratios and extra-pair paternity and mortality incidence, respectively.

Relationships between opercula girth, maximum girth and total length of fish species caught in gillnet and trammel net selectivity surveys off the Portuguese coast

Summary The relationships of total length (Lt) to girth at opercula (Gope) and maximum girths (Gmax) were estimated for 39 and 22 fish species, respectively, captured off the Portuguese coast between Povoa do Varzim and Santo Andre (38°05′54′′–41°15′36′′N and 8°46′54′′–9°31′13′′W). The data were collected between April 1994 and September 1995. The best-represented family was Sparidae (five species), followed by Soleidae and Triglidae (four species each). Gope and Gmax were found to increase linearly with length for all species, all r2 values being statistically significant (P < 0.01) and higher than 0.81. When Gope and Gmax were plotted against length for all species combined, three groups were identified, corresponding to general girth–length relationships: G1 = 1.408 + 0.238 ×Lt, G2 = 2.455 + 0.328 × Lt and G3 = −0.72 + 0.60 × Lt for opercula girth and G1 = 3.402 + 0.195 × Lt, G2 = 2.211 + 0.374 × Lt and G3 = -2.514 + 0.717 × Lt for maximum girth. These groups correspond to different body shapes of fishes: G1-round, G2-torpedo-form and G3-compressed body.

Size selectivity of trammel nets in southern European small-scale fisheries

Trammel net size selectivity was studied for the most important métiers in four southern European areas: the Cantabrian Sea (Atlantic, Basque Country, Spain), the Algarve (Atlantic, southern Portugal), the Gulf of Cádiz (Atlantic, Spain) and the Cyclades Islands (Mediterranean, Aegean Sea, Greece). These métiers were: cuttlefish ( Sepia officinalis) and soles ( Solea senegalensis, Microchirus azevia, Synaptura lusitanica) in the Algarve and the Gulf of Cádiz, sole ( Solea solea) in the Cantabrian Sea and mixed fin-fish in the Cyclades. In each area, experimental trammel nets of six different types (combinations of two large outer panel mesh sizes and three small inner panel meshes) were constructed. Fishing trials were carried out on a seasonal basis (four seasons in the Cantabrian Sea, Algarve and Cyclades and two seasons in the Gulf of Cádiz) with chartered commercial fishing vessels. Overall, size selectivity was estimated for 17 out of 28 species for which sufficient data were available. Trammel nets generally caught a wide size range of the most important species, with length frequency distributions that were skewed to the right and/or bi-modal. In many cases the length frequency distributions of the different nets were highly overlapped. The Kolmogorov–Smirnov test also showed that the large outer panel meshes generally had no effect in terms of size selectivity, while the opposite was true for the small inner panel ones. Six different selectivity models (normal scale, normal location, gamma, log-normal, bi-modal and gamma semi-Wileman) were fitted to data for the most abundant species in the four areas. For fish, the bi-modal model provided the best fits for the majority of the data sets, with the uni-modal models giving poor fits in most cases. For Sepia officinalis, where trammelling or pocketing was the method of capture in 100% of the cases, the logistic model fitted by maximum likelihood was judged to be more appropriate for describing the size selective properties of the trammel nets. Our results, which are among the first ones on trammel net selectivity in European waters, will be useful for evaluating the impacts of competing gear for the socio-economically important small-scale static gear fisheries.

Assessment and control of non‐indigenous brown bullhead Ameiurus nebulosus populations using fyke nets in shallow ponds

In order to evaluate fyke nets as a tool for population assessment and mass removal of brown bullhead Ameiurus nebulosus populations, small, shallow ponds were sampled during late summer in 1999 and 2000. Catch efficiency, species and size selectivity of fyke nets were investigated with the mark‐recapture method. Two different strategies were applied: (1) on six occasions, the mark‐recapture method was applied to entire populations, and (2) in six other cases, sampling was done in two replicated enclosed areas (625 m2). When applied to entire populations, fyke nets were found to be size selective, and capture efficiency significantly increased with standard length. Conversely, no size selectivity of fyke nets was found in enclosed areas. Sampling in replicated enclosures yielded reproducible estimates of population density and biomass. The results suggest that double fyke nets, when combined with the mark‐recapture technique, are a very useful tool for the efficient and reliable assessment of brown bullhead populations. The results of the study also suggest that double fyke nets may potentially be a cost‐effective tool for the mass removal of non‐indigenous brown bullhead populations.

Performance of the AMS-02 transition radiation detector

For cosmic particle spectroscopy on the International Space Station the AMS experiment will be equipped with a Transition Radiation Detector (TRD) to improve particle identification. The TRD has 20 layers of fleece radiator with Xe/CO 2 proportional-mode straw-tube chambers. They are supported in a conically shaped octagon structure made of CFC-Al-honeycomb. For low power consumption VA analog multiplexers are used as front-end readout. A 20 layer prototype built from final design components has achieved proton rejections from 100 to 2000 at 90% electron efficiency for proton beam energies up to 250 GeV with cluster counting, likelihood and neural net selection algorithms.

Ruthenium oxide films for selective coatings

Abstract Although commercial selective surfaces are already available, investigation on different deposition methods and materials still goes on at many laboratories. In this work, ruthenium oxide films upon metallic substrates are assessed for this usage. Deposition of the films was made at room temperature by either spraying or dipping method in a ruthenium chloride alcoholic solution. After deposited on titanium substrates, the films were heat-treated at temperatures between 450 and 500 °C. When deposited on no-polished substrates, such films not only exhibit a high solar absorptance ( α ∼ 0.98 ), but also a high infrared emittance ( e ∼ 0.8 ), which yield a low selectivity ( S = α / e = 1.2 ). By deposition of similar films on polished substrates, absorptance decreases ( α ∼ 0.74 ), but emittance significantly decreases as well ( e ∼ 0.12 ), resulting in a net selectivity increase ( S ∼ 6 ). On the other hand, evaporating a thin (∼20 nm) gold film upon the surface of a coating on a no-polished substrate also improves noticeably its emittance value ( e ∼ 0.16 ) and a lower decrease in absorptance is achieved ( α ∼ 0.91 ), resulting in a selectivity increase ( S ∼ 5.7 ). These preliminary promising results indicate the high potential for using these films as solar selective coatings, but in order to optimize such selectivity values, further work to establish a close control on the deposition parameters and the substrate roughness value, should be done.

A versatile net selectivity model, with application to Pacific salmon and freshwater species of the Yukon River, Alaska

Gillnet catch data from the lower Yukon River, AK, collected from 1990 to 2003 in conjunction with a sonar study to estimate the abundance of migrating fish, were assembled. The full dataset contained 92,029 records with complete species and length information. A subset of data for the eight most prevalent groups of fish was selected for the estimation of net selectivity. The reduced dataset contained 89,984 records for Chinook salmon (Oncorhynchus tshawytscha), summer and fall runs of chum salmon (O. keta), coho salmon (O. kisutch), pink salmon (O. gorbuscha), humpback whitefish (Coregonus pidschian), broad whitefish (C. nasus), and various cisco (Coregonus) species. A Pearson function was used as a net selectivity model for all eight groups of fish, though a parameter was added to accommodate the catch of fish that are relatively large for a particular mesh. Because most of these relatively large fish were probably not gilled, but rather caught by body parts other than the operculum, the extra parameter can be thought of as a tangling parameter. The parameters of the modified Pearson model were estimated using maximum likelihood, and variances were estimated through bootstrapping. Gillnets were found to be most efficient, for all eight groups of fish, when fish length is approximately twice as great as the perimeter of a mesh, and the corresponding location parameter of the Pearson model was estimated with high precision. As the Pearson function has apparently not been used previously as a net selectivity model, its suitability was compared to the normal, lognormal, gamma, inverse Gaussian, and bi-normal functions, which are commonly employed as net selectivity models. Model fit was evaluated on the basis of the value of the likelihood function obtained, Akaike's Information Criterion and scaled deviance statistics, and plots of estimated models and scaled catch data. The Pearson model was found to be quite flexible, and fit the data as well as or better than the other models for all eight groups of fish considered. Other researchers may wish to consider its use with their data.

Salt tolerance in Eucalyptus spp.: identity and response of putative osmolytes

ABSTRACTIn four species of salt‐tolerant eucalypts (Eucalyptus raveretiana, E. spathulata, E. sargentii and E. loxophleba), we found substantial concentrations of quercitol – a cyclitol known for its accumulation in seeds of Quercus. Quercitol was absent in old foliage of E. globulus, a species noted for greater susceptibility to salinity, and also absent in the moderately tolerant E. camaldulensis, but, relative to other species, both had higher foliar concentrations of inositol. Simple sugars and cyclitols accumulated to osmotically significant concentrations in all species. The osmotic potential of expressed sap was always less than that of the external ‘soil’ solution and increasing salinity produced predictable reductions in growth and increases in ion concentrations in foliage of saplings of four eucalypt species. The more salt‐tolerant species, E. spathulata, E. loxophleba and E. sargentii, were able to maintain well‐regulated leaf Na+ concentrations even at 300 mol m−3 NaCl. These more salt‐tolerant species also showed an apparent increase in net selectivity for K+ over Na+ as salinity increased, irrespective of the Na+ : Ca2+ ratio of the external medium (range 25 : 1 to 75 : 1; Ca2+ always ≥ 4.0 mol m−3). By contrast, E. globulus was unable to exclude Na+ when exposed to higher NaCl concentrations (e.g. 200 and 300 mol m−3). Carbon isotope signatures of foliage reflected imposed salinity but were not strongly enough correlated with growth to support previous suggestions that isotope discrimination be a means of evaluating salt tolerance. On the other hand, patterns of sugar and cyclitol accumulation should be further explored in eucalypts as traits contributing to salt tolerance, and with potential use as markers in breeding programmes.

Selectivity of penaeid trap nets used in south eastern Australia

Two experiments were done to estimate the selectivity of commercial and modified trap-net configurations in New South Wales (NSW), southeastern Australia. In the first experiment, a commercial trap net made entirely from 25 mm mesh and designed for use in shallow water was alternatively fished with a fine-meshed (9.5 mm netting) trap net (used as a control). In the second experiment, two trap-net configurations designed for use in deeper water and comprising the same anterior section (made from 25 mm mesh), but with different bunts made from (i) the conventional 25 mm mesh and (ii) 31 mm mesh were alternately fished against the control. Both of the conventional trap nets (comprising 25 mm mesh throughout) had low amounts of bycatch and similarly selected eastern king Penaeus plebejus, greasyback Metapenaeus bennettae and school prawns Metapenaeus macleayi across narrow selection ranges (< 3.4 mm) and at 50% retention lengths (between 18.53 and 21.50 mm) that were larger than the average commercially-accepted sizes (15-17 mm CL). Analyses of the selectivities and relative efficiencies of the trap-net configurations comprising the 25 and 31 mm bunts showed no benefit, in terms of maintaining prawn catches and reducing unwanted bycatch, associated with increasing mesh size in these gears. The utility of trap nets for selectively harvesting penaeids is discussed. We conclude that this type of fishing gear appears to have few deleterious impacts.

서해구 자원관리형 자망 &amp;#x00B7; 통발 어구어법 기술개발에 관한 연구 - 피뿔고동 Rapane venosa 통발의 망목선택성 -

피뿔고동(통칭 소라) 통발의 망목선택성 및 적정 망목을 추정하기 위하여 2003년 6월 27일<TEX>${\sim}$</TEX>6월 29일까지 전북 군산시 말도 인근 해역에서 시험조업을 실시하였다. 시험어구는 망목 35mm, 50mm 및 65mm의 3종류의 그물감을 씌운 통발을 교호로 각각 70개씩 210개를 1개조로 구성하여 2개조를 사용하였으며, 망목선택성 곡선의 분석에는 Kitahara(1968)의 방법을 이용하였다. 그 결과를 요약하면 다음과 같다. 1. 피뿔고동 통발의 시험조업 결과 총어획미수는 1,682마리였으며, 피뿔고동 1,268마리 (75.4%), 배꼽고동 225마리 (13.4%), 쥐노래미 113마리 (6.7%), 기타 76마리 (4.5%) 등이었다. 2. 피뿔고동의 최대 각고/망목(max. 1/m)의 값은 1.79로 추정되었다. 3. 50% 선택구간에 대한 각고/망목(max. 1/m)의 값은 1.79로 추정되었다. 3. 50% 선택구간에 대한 각고/망목(1/m)의 값은 1.24<TEX>${\sim}$</TEX>2.72으로 추정되었으며, 그 선택폭은 1.48이었다. 4. 피뿔고동의 어획금지체장(각고) 50mm에 대한 적정 망목은 40.3mm로 추정되었으며, 피뿔고동의 50% 선택각고 범위는 50.0<TEX>${\sim}$</TEX>109.6mm로 나타났다. In order to examine the mesh selectivity and optimum mesh size of trap nets for purple shell, Rapane venosa, the field experiments were carried out during Jun. 27 to 29, 2003 at the coastal area of Mal-Do, Kunsan, Jeonbuk province. The experimental fishing gears were used in two set of trap nets, which one set was consisted of 210 trap nets that were coverd with 35mm, 50mm and 65mm in mesh size. The analysis of mesh selectivity curve was done by Kitahara's method. The results obtained are summerized as follows : 1. The total number of catch by the experimental fishing of trap nets for purple shell was 1,682, and it was consisted of 1,268 purple shells (75.4%), 225 Glossaulax reiniana (13.4%), 113 green lings (6.7%) and 76 other fishes (4.5%). 2. The value of maximum 1/m on the mesh selectivity curve was estimated at 1.79. 3. The value of 1/m on the 50% selection range was estimated at 1.24<TEX>${\sim}$</TEX>2.72, and the selection width was 1.48.. 4. The optimum mesh size of trap nets for purple shell based on the catch prohibition shell height(50mm) was estimated 40.3mm, and the 50% selection range of shell height of purple shell was 50.0<TEX>${\sim}$</TEX>109.6mm.

Efficient algorithm for FPGA board routing

A simple and fast algorithm for solving the two-terminal board level routing problem in FPGA-based logic emulation systems is presented. The method is based on the net scan selection process. Experimental results are the first implemented results for an algorithm presented previously. The comparison results show that the current approach achieves better effectiveness and uses less CPU time.

EVOLUTION AND STABILITY OF THE G-MATRIX ON A LANDSCAPE WITH A MOVING OPTIMUM

In quantitative genetics, the genetic architecture of traits, described in terms of variances and covariances, plays a major role in determining the trajectory of evolutionary change. Hence, the genetic variance-covariance matrix (G-matrix) is a critical component of modern quantitative genetics theory. Considerable debate has surrounded the issue of G-matrix constancy because unstable G-matrices provide major difficulties for evolutionary inference. Empirical studies and analytical theory have not resolved the debate. Here we present the results of stochastic models of G-matrix evolution in a population responding to an adaptive landscape with an optimum that moves at a constant rate. This study builds on the previous results of stochastic simulations of G-matrix stability under stabilizing selection arising from a stationary optimum. The addition of a moving optimum leads to several important new insights. First, evolution along genetic lines of least resistance increases stability of the orientation of the G-matrix relative to stabilizing selection alone. Evolution across genetic lines of least resistance decreases G-matrix stability. Second, evolution in response to a continuously changing optimum can produce persistent maladaptation for a correlated trait, even if its optimum does not change. Third, the retrospective analysis of selection performs very well when the mean G-matrix (Ḡ) is known with certainty, indicating that covariance between G and the directional selection gradient β is usually small enough in magnitude that it introduces only a small bias in estimates of the net selection gradient. Our results also show, however, that the contemporary Ḡ-matrix only serves as a rough guide to Ḡ. The most promising approach for the estimation of Ḡ is probably through comparative phylogenetic analysis. Overall, our results show that directional selection actually can increase stability of the G-matrix and that retrospective analysis of selection is inherently feasible. One major remaining challenge is to gain a sufficient understanding of the G-matrix to allow the confident estimation of Ḡ.

The evolution of static allometry in sexually selected traits.

Although it has been the subject of verbal theory since Darwin, the evolution of morphological trait allometries remains poorly understood, especially in the context of sexual selection. Here we present an allocation trade-off model that predicts the optimal pattern of allometry under different selective regimes. We derive a general solution that has a simple and intuitive interpretation and use it to investigate several examples of fitness functions. Verbal arguments have suggested cost or benefit scenarios under which sexual selection on signal or weapon traits may favor larger individuals with disproportionately larger traits (i.e., positive allometry). However, our results suggest that this is necessarily true only under a precisely specified set of conditions: positive allometry will evolve when the marginal fitness gains from an increase in relative trait size are greater for large individuals than for small ones. Thus, the optimal allometric pattern depends on the precise nature of net selection, and simple examples readily yield isometry, positive or negative allometry, or polymorphisms corresponding to sigmoidal scaling. The variety of allometric patterns predicted by our model is consistent with the diversity of patterns observed in empirical studies on the allometries of sexually selected traits. More generally, our findings highlight the difficulty of inferring complex underlying processes from simple emergent patterns.

Gill net selectivity for European hake Merluccius merluccius from southern Portugal: implications for fishery management

: A study of European hake Merluccius merluccius gill net selectivity was undertaken off the Algarve (Southern Portugal), between 1999 and 2001. Four nominal mesh sizes (70, 80, 90 and 100 mm) were used in fishing trials and the ‘share each length class catch total’ (SELECT) method was used to fit gill net selectivity curves. Hake were caught in the same size range by all mesh sizes, between 17 and 65 cm total length. While most fishes were wedged, significant and similar proportions were entangled in all mesh sizes, contributing to the wide size range, and in some cases, bimodal shape of catch size frequency distributions. Insignificant numbers of undersized hake were caught, with most catches consisting of mature female fish. Catch rates decreased sharply with increasing mesh size. The bimodal model gave the best fit for hake that were wedged, with estimated modal lengths of 40.1, 46.7 and 51.0 cm for the 70, 80 and 90 mm nominal mesh sizes, respectively. The high catch per unit effort of the smallest mesh size, with most fish caught being female, together with the fact that the modal length of the fitted selectivity curve is well below the size at maturity for hake in Portuguese waters, suggests that the 80 mm nominal mesh size is more appropriate for ensuring resource sustainability.

Biaryl analogues of conformationally constrained tricyclic tropanes as potent and selective norepinephrine reuptake inhibitors: synthesis and evaluation of their uptake inhibition at monoamine transporter sites.

A series of novel conformationally constrained tricyclic tropane derivatives containing a biaryl moiety, (Z)-9-(biarylylmethylene)-7-azatricyclo[4.3.1.0(3,7)]decanes, were synthesized and evaluated for their ability to inhibit reuptake of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) by the DA, 5-HT, and NE transporters. Most of the compounds containing a methoxycarbonyl substituent at C-10 exhibit moderate to high inhibitory activity at the NET but lower activity at the DAT and SERT. Among these new compounds, some potent, NET-selective ligands were identified. The p-methoxy derivative 11a has a K(i) value of 39 nM for uptake inhibition at the NET and moderate to high selectivity over the SERT (100-fold) and the DAT (20-fold). Compound 11f exhibits a remarkable potency (K(i) = 9.7 nM) at the NET and a 25-fold selectivity over both the SERT and the DAT. Analogue 23 containing a thiophene ring as a bioisosteric replacement of the phenyl ring Ar(1) displays a high activity (K(i) = 10.3 nM) for the NET and similar selectivity over the SERT (50-fold) and the DAT (37-fold). The selectivity profile of biaryl analogues differs from that of the monoaryl series, as most members of that series display excellent potency at and selectivity for the SERT (J. Med. Chem. 2002, 45, 1930). This finding suggests that the different shape and size of the lipophilic recognition pocket that encompasses the aryl ring(s) of these tropanes are major determinants of a ligand's transporter activity at either the NET or the SERT. Some of the compounds in this series may also be valuable in sorting out the contribution of the individual transporters to cocaine's reinforcing properties.

THE EVOLUTION OF STATIC ALLOMETRY IN SEXUALLY SELECTED TRAITS

Although it has been the subject of verbal theory since Darwin, the evolution of morphological trait allometries remains poorly understood, especially in the context of sexual selection. Here we present an allocation trade-off model that predicts the optimal pattern of allometry under different selective regimes. We derive a general solution that has a simple and intuitive interpretation and use it to investigate several examples of fitness functions. Verbal arguments have suggested cost or benefit scenarios under which sexual selection on signal or weapon traits may favor larger individuals with disproportionately larger traits (i.e., positive allometry). However, our results suggest that this is necessarily true only under a precisely specified set of conditions: positive allometry will evolve when the marginal fitness gains from an increase in relative trait size are greater for large individuals than for small ones. Thus, the optimal allometric pattern depends on the precise nature of net selection, and simple examples readily yield isometry, positive or negative allometry, or polymorphisms corresponding to sigmoidal scaling. The variety of allometric patterns predicted by our model is consistent with the diversity of patterns observed in empirical studies on the allometries of sexually selected traits. More generally, our findings highlight the difficulty of inferring complex underlying processes from simple emergent patterns.

Seasonal variations in selectivity of plaice trammel nets

The size selectivity of plaice trammel nets was measured in an experiment using catch at length data from six different mesh sizes. Three trials at different times of the year were conducted on a traditional Danish gill-netter giving a total catch of 17,163 plaice—one of the largest European gill/trammel net datasets. Maximum likelihood procedure was used to estimate different types of selectivity curves for each set (soak). A bimodal curve was found to fit the data best. The between set variation was taken into account when calculating a mean selectivity curve for each of the three trials. The modal fish length for largest retention was 2.52 times mesh size. Significant seasonal differences in selectivity were found. The optimum mesh sizes were compared to commercial practice and the trammel net selectivity curve was compared to previous results on gill-nets with a low hanging ratio, i.e. tangle nets.

Habitat Selection of Predator and Prey: Atlantic Salmon and Rainbow Smelt Overlap, Based on Temperature and Dissolved Oxygen

Abstract We investigated the predator-prey interactions of two pelagic species, landlocked Atlantic salmon Salmo salar and rainbow smelt Osmerus mordax, in a large-lake ecosystem. Our goal was to determine the overlap of habitats selected, based on profiles of temperature and dissolved oxygen (DO). We used hydroacoustics to ascertain the seasonal habitat selection of rainbow smelt and gill nets to sample Atlantic salmon in the Inland Sea of Lake Champlain, Vermont. We identified patterns of smelt habitat selection by overlaying the acoustically determined vertical distributions of smelt onto profiles of water temperature and DO. To verify species composition of acoustical targets, we performed midwater trawls using a stepped-oblique method and found that rainbow smelt constituted 99.5% of trawl catches. Trawl catches and acoustic fish density were correlated, indicating that acoustic targets represented trawled fish. Atlantic salmon habitat selection was estimated from temperature and DO profiles taken at...

The effect of twine thickness on the size selectivity and fishing power of Baltic cod gill nets

Sea trials were carried out on a Danish commercial vessel measuring the size selectivity and fishing power of gill nets used to catch Baltic cod ( Gadus morhua). A comparison was made of two different twine thicknesses at two different times of the year. Nominal mesh sizes of 70–130 mm were used. Method of capture, condition factor and girths were measured for sub-samples of the cod caught. A model of the size selectivity of the gill nets was adapted to the experimental conditions where two gears were fished on the same population. This model was fitted to the catch data for each set. Subsequently a model was fitted for the mean selectivity taking between-set variation into account. The selectivity curve that fitted the data best was given by the sum of two normal distributions. It was found that twine thickness and trials period had relatively little effect upon the shape of the selectivity curve. Twine thickness had a substantial effect upon the fishing power of the nets.

Trammel net and gill net selectivity for Lithognathus mormyrus (L., 1758), Diplodus annularis (L., 1758) and Mullus barbatus (L., 1758) in the Adriatic and Ligurian seas

The selectivity of a traditional trammel net, a monofilament trammel net and a gill net for Lithognathus mormyrus (striped sea-bream), Diplodus annularis (annular sea-bream) and Mullus barbatus (red mullet) was investigated in two coastal areas (central Adriatic sea and southern Ligurian sea). Three mesh sizes were tested for each set net: 45, 70 and 90 mm (stretched-mesh size). Selectivity was assessed by the indirect Sechin model based on the measurement of maximum body girth and head girth. The 45-mm mesh size was the most efficient for all the target species irrespective of net type. The catches obtained with the 90-mm meshes were always very low as were the catches of D. annularis and M. barbatus with the 70-mm mesh. Although most fishes of the three target species were caught by gilling and/or wedging, with all gears a number of individuals were also caught by virtue of the tangled and/or pocket effects. Their proportion, lowest and generally negligible in the gill net, higher in the monofilament and highest in the standard trammel net, caused a progressive widening of size-catch ranges, confirming the low selectivity of trammel nets. The 45-mm mesh appears to be the most suitable for the exploitation of the target species because it caught the highest number of specimens while it largely spared the juveniles.