Trawl Selectivity Trials on the Deep-water Rose Shrimp (Parapenaeus longirostris) in Sicilian Waters

The selectivity of the traditional commercial bottom trawl net employed in Sicily to catch the Mediterranean deep-water rose shrimp, Parapenaeus longirostris, has been assessed. Two fishing campaigns were carried out in the Strait of Sicily and in the Southern Tyrrhenian Sea, using the covered cod-end method (mesh 20 mm vs. 31 mm). Of a total catch of 11,601 individuals, 23.4% escaped in the cover; the sample length structure from the Strait is unimodal, while that from the Tyrrhenian, polymodal. A logistic curve, fitted with a maximum likelihood criterion, has been used to model the selectivity data, in order to obtain the parameters CL_c50% (50% retention size), SR_75–25% (selection range) and SF (selection factor, i.e. CL_c50%/mesh). The two sets of data, besides a larger selection range for the Strait sample (5.2 mm vs. 2.3 mm), produced very similar estimates (retention sizes of 13.0 mm vs. 12.8 mm CL), fitting the logistic curve well. Almost no shrimp larger than 20 mm does escape from the cod-end; moreover, from the amount of damaged specimens found in the cover, even the evaded shrimps sustain a high fishing mortality. An increase of the present cod-end mesh opening, even above the size required by the EU bylaws (at present, 40 mm stretched) seems necessary for managing the fishery.     

Notes on the biology of Cancer bellianus (Brachyura, Cancridae) around the Canary Islands

Information on biometric and biological parameters of Cancer bellianus Johnson, 1861 (Crustacea, Decapoda, Brachyura, Cancridae) off the Canary Islands is given. Crabs examined were collected during experimental fishing surveys during 1974–1998. Carapace length, carapace width, total wet weight, sex and ovigerous condition were determined. This species was caught at depths from 153 to 750 m, the deepest ever recorded. Size frequency distributions were assembled and size-weight relationships were estimated by sex. Sex-ratio as a function of size and depth was determined. The size at first maturity was calculated by analysing the relative growth between the carapace length and the left chela width: 103.5 mm CL in males, 101.2 mm CL in females. Ovigerous females, egg size and fecundity estimates are reported apparently for the first time.     

Efficiency of flexible sorting grids to improve size selectivity of the bottom trawl in the Balearic Islands (western Mediterranean), with comparison to a change in mesh cod-end geometry

In recent years several studies have been developed to improve the selectivity of the Mediterranean bottom trawl fisheries, which exert high fishing pressure on young individuals. The focus has been mainly on increasing the mesh size in the cod‐end or changing its mesh geometry; few studies have assessed the efficiency of the sorting grid systems. Analysis of 21 trawl hauls carried out at depths of 117–697 m off the Balearic Islands (western Mediterranean) in October–November 2005, studied size selectivity of the trawl using flexible sorting grids with 15 (SG15) and 20 (SG20) mm bar spacing. A divided polyamide bottom trawl designed for commercial purposes demonstrated high efficiency for the simultaneous use of both sorting grid sizes at different depth intervals (DS: deep shelf; US: upper slope; MS: middle slope). The results were also compared with those from the authors’ previous studies in the area where 40 mm diamond (DM) and square (SM) mesh cod‐ends were used. A saturation effect was detected on the DS for both sorting grids, due to the large amount of biomass captured at this depth interval. Size selectivity of 11 species was modelled, which showed an increase in length at first capture (L₅₀) from SG15 to SG20. Values of L₅₀ estimated for the main target species were: 10.9 cm total length (TL) with SG15, and 18.9 cm TL with SG20 for Merluccius merluccius; 21.1 mm carapace length (CL) with SG15, and 23.8 mm CL with SG20 for Nephrops norvegicus; and 15.9 mm CL with SG15, and 19.6 mm CL with SG20 for Aristeus antennatus. Comparison of size selectivity parameters between the sorting grids and cod‐ends of different geometry showed clear differences. For most species, the highest value of L₅₀ was obtained with SM (e.g. 26.6 mm CL for N. norvegicus and 22.1 mm CL for A. antennatus). Exceptions were the round‐fish M. merluccius, the flatfish Lepidorhombus boscii, and the crustacean Parapenaeus longirostris, with values of SG20 (18.9 cm TL, 12.1 cm TL, and 25.7 mm CL, respectively) higher than with SM (15.2 cm TL, 10.2 cm TL, and 20.2 mm CL, respectively). Sorting grid selection ranges were broader than those estimated for DM and SM. Experience shows that the exchange of the DM for the SM and/or the introduction of SG20 can improve selectivity in the Mediterranean trawl, SM being more efficient than SG20 in the Balearic Islands.     

Catch Composition on Red Shrimps’ (Aristaeomorpha foliacea and Aristeus antennatus) Grounds in the Eastern Ionian Sea

In the present study, the catch composition and the catch per unit effort (CPUE) by weight and numbers in red shrimps’ (Aristaeomorpha foliacea and Aristeus antennatus) grounds was examined in the southern part of the eastern Ionian Sea, in order to collect important information for the Greek waters, where no deep-water fishery exists. In the depth stratum 500–700 m, the catch of the commercial species represented a high proportion (>70%) of the total catch. Red shrimps and several other commercial species were found in important quantities. The present results suggest the possibility of developing a deep-water fishery in Greece. In such a case, attention should be paid because of the high vulnerability of A. foliacea – the main deep-water fishing resource in the area – to the fishing pressure.     

The benthic phase of the life cycle ofParapenaeus longirostris (Crustacea,Decapoda, Penaeidae) along the Mediterranean coast of Israel

The population ofP. longirostris along the Mediterranean coast of Israel spends the benthic phase of its life cycle (from body size over 15 mm) on muddy bottom deeper than 45 m. New age groups are recruited within the depth zone of 45–300 m and migrate in both inshore and offshore directions. Inshore migration is limited by unsuitable sandy ground. The limiting line for offshore migration was not found.An age group could be detected during one year within a body size range of TL = 40 mm to TL = 84.5 mm for males and to TL = 102.5 mm for females. Reproductive activity in shallow water, down to a depth of 73 m, takes place during the whole year, while in depths of 150–300 m there is an arrest of reproductive activity from June to August.     

Selectivity of conventional and alternative codend design for five fish species in the Aegean Sea

Currently, traditional Mediterranean trawls are generally made with non‐selective netting and the fishing boats are involved in multi‐species fisheries. As a result, most near‐shore stocks are over‐exploited. Weather permitting, the demersal trawl fleet tends to fish in relatively deeper, international waters of the Aegean Sea, where the catch is usually higher. Therefore, the need for evaluation of the codends used in this fishery and the potential improvements to their selectivity are of prime importance. In the present study, selectivity data were collected for hake (Merluccius merluccius), blue whiting (Micromesistius poutassou), greater forkbeard (Phycis blennoides), blackbelly rosefish (Helicolenus dactylopterus dactylopterus) and fourspotted megrim (Lepidorhombus boscii) in commercial (300 MC) and square mesh top panel (SMTPC) codends. Trawling was carried out at depths of 274–426 m onboard a commercial vessel chartered for a 15‐day sea trial in August 2004. Selection parameters were obtained by fitting a logistic equation using a maximum likelihood method. Results of the selectivity analysis indicated that the commercially used 40 mm nominal mesh size PE codend was rather unselective for the species investigated in this study. In general, the square mesh top panel codend has relatively higher L₅₀ values than the commercial codend. However, except for blue whiting, even this codend is rather unselective when 50% maturity lengths (L_M50) are considered.     

The influence of dredge design on the catch of Callista chione (Linnaeus, 1758)

To evaluate a possible introduction of a new dredge in the fishery of Callista chione (Linnaeus, 1758), IPIMAR has conducted a study with the objective of comparing the efficiency of two dredges (traditional dredge and the new dredge design) and evaluating their impact on the benthic community. The experiments were carried out during March 1999 on the Southwest coast of Portugal, from a site off Troia. Three different tow durations of 5, 10 and 20 min were investigated. A total of 24 hauls were accomplished, 4 for each tow duration and dredge. The experiments were conducted by attaching a cover bag with a 20 mm mesh to the gear. After each haul, the catches in the bag and in the cover were sorted separately. All individuals retained were attributed scores on a scale of 1–4 in which 1 equates to good and 4 equates to dead. The results obtained showed that catches from the traditional dredge (TD) are composed of a great fraction of juveniles of C. chione, while in the new dredge (NDD) catches are composed, almost entirely, by individuals with a superior size to the minimum legal length (50 mm). This result indicates that the mesh of the bag of the TD used in the exploitation of this resource is not adequate. For the 3 different tow durations, the mean fishing yield obtained for the NDD was always superior to the TD, due to its greater efficiency in capture. The proportion of by-catch is significantly higher when the TD is used. For all 3 tow duration, the TD caused mortalities on the target species and on the macrobenthic community in the same order of magnitude as the NDD. Since the fishery of C. chione is managed by daily quotas per boat, when using the NDD the impact on the macrobenthic community is reduced by about 50% due to its greater efficiency of capture. Another advantage in the usage of the NDD relatively to the TD, is to allow the smallest individuals (independently of the species) to escape rapidly through the metallic bars on the grid, increasing their probability of survival.     

Discards in bottom‐trawl fishery in the western Black Sea (Turkey)

The aim of this study was to estimate the discards of target and non‐target species from bottom trawlers (rhombic and 40 mm cod end mesh size nets) in the Black Sea. On‐board sampling was conducted on the southwestern coasts of the Black Sea in the fishing ports of Rumelifeneri and Igneada for a total of 66 hauls on two commercial bottom trawlers from October 2012 to April 2013 and from October 2013 to April 2014. A total of 32 species were captured, including 25 species of fish, three crustacea, two echinodermata and two mollusca. Mullus barbatus and Merlangius merlangus euxinus were the target species, whereas 24 species were always discarded. Scophthalmus maximus and Pomatomus saltatrix were always retained. The two regions were similar in terms of catch and discard compositions, CPUE, DPUE and discard ratio. Discarding is important in the Black Sea commercial bottom trawl fishery and accounts for as much as 31.4% of the total bottom trawl catch. The results showed that the discard rates varied among species, depths (p = .04) and seasons (p = .0001). Finally, it was concluded that in the western Black Sea, when the impacts of depth and season are considered, that the discard quantity can be reduced.     

The impact of fisheries on vulnerable habitats: the case of trawling on circa-littoral grounds in the Strait of Sicily (central Mediterranean Sea)

The Council Regulation (EC) no. 1967/2006 introduced the adoption of the 40 mm square-mesh or alternatively a 50 mm diamond-mesh codend for trawlers of EU Member States. In this context, the main aim of the current study was to compare the catch composition of Lampedusa’s shallow-water trawl fishery, in terms of retained and discarded fraction, using the 24 mm square-mesh codend (illegal and supposed unselective) and the 50 mm current diamond-mesh codend (legal and supposed selective). During 2012, 21 hauls were performed, under commercial conditions, with the 24 mm square mesh codend and 27 with the 50 mm diamond mesh codend in an area of the Strait of Sicily at depths from 40 to 80 m. The introduction of a 50 mm diamond-mesh, although not significantly, reduced the CPUEs of retained and discarded fraction compared with the 24 mm mesh. Moreover, for most target species and their size classes (especially immature individuals), the legal mesh recorded a lower mean number of specimens than the banned mesh size. All these advantages aside, the discard of the shallow-water trawl fishery, in Lampedusa, represented a very important part of the total catch (more than three-quarters) by both mesh sizes and a large amount of this was represented by species and habitat of conservation concern. Our results suggest that spatial restrictions, such as no-take zones, could be a more effective management tool to protect this sensitive ecosystem in the area than the technical measures (e.g. reduction of mesh size) imposed today by the EU.     

Optimum fishing strategies for Isostichopusfuscus (Echinodermata: Holothuroidea) in the Gulf Of California, Mexico

The Isostichopus fuscus fishery in Mexico was heavily exploited until 1994, when it was closed due to overfishing. However, no information existed on the status of the populations. The fishery was evaluated through an age structured simulation model, and according to our analysis of the stock, the fishery can be feasible and sustainable as long as fishing mortality and age of first catch are optimized. In order to evaluate exploitation strategies, several scenarios were simulated considering different combinations of fishing intensities and ages of first catch. Input data for the model included population parameters, commercial catch and costs and benefits of the fishing operations. Yield production was strongly influenced by the fishing pressure and by the age of first capture. When the first one increased, significant decreases in yield and profits occurred. The best exploitation strategy was these parameters: fishing mortality level F = 0.15, age at first capture t(c) = 4 years, and yielding of approximately 430 tons. However, since the species reproduces for the first time at 5 years, extracting younger specimens would collapse the population. The critical value of fishing mortality was detected at Fc = 0.25. If exceeded, the population tends to exhaustion and the fishery is no longer profitable. In conclusion, I. fuscus fishery is highly vulnerable to overfishing and age of catch. It must be taken into account that the management policies should be considered as pilot and used on a regional basis. Continuous monitoring of the stock, control of the number of fishing licenses and extracting only specimens 5 yeasr-old and older (around 20 cm and >400 g), will allow the populations to recover from fishing activities. Rev. Biol. Trop.     

Fish by-catch species from coastal small-scale shrimp trammel net fishery in the Aegean Sea (Izmir Bay, Turkey)

Fish by‐catch from coastal small‐scale shrimp trammel net fishery was estimated from fishery‐dependent surveys in Izmir Bay (Aegean Sea), Turkey, during the 2004 and 2005 fishing seasons. Sampling data were obtained from 170 observations onboard 18 commercial fishing vessels. Fifty‐two species belonging to 31 families of fish, including cephalopods, constituted the by‐catch. Diplodus annularis was the most abundant by‐catch species followed by Loligo vulgaris > Sepia officinalis > Mullus barbatus > Boops boops > and Solea vulgaris. The estimated total ratio of fish by‐catch to shrimp was 1 : 1.09 kg.     

Selectivity Parameters and Size at First Maturity in Deep-Water Shrimps, Aristaeomorpha foliacea (Risso, 1827) and Aristeus antennatus (Risso, 1816), from the North-Western Ionian Sea (Mediterranean Sea)

Selectivity experiments were carried out during trawling targeting deep-water shrimps Aristaeomorpha foliacea (Risso, 1827) and Aristeus antennatus (Risso, 1816) (Crustacea, Decapoda, Aristeidae) in the North-Western Ionian Sea (Eastern-Central Mediterranean). Different criteria were employed to analyse maturity; however, the proportion at 50% of retained, mated and mature specimens was always used to indicate the size, expressed as Carapace Length (CL, mm), at first capture (CL_c), mating (CL_sp) and at first maturity (CL_m), respectively. In order to estimate the size at 50% maturity (CL_m) for females of both species, three criteria were adopted. In particular, CL_m was computed for the mature females not considering the presence of spermatophores, for the mature females with spermatophores and for the mature females intersected by the decreasing proportion with size of females without spermatophores. Three diamond stretched mesh codends of 40, 50 and 60 mm were tested using a cover of 20 mm. The 40-mm stretched mesh size (European Union legal size in the Mediterranean) was not selective for the sampled population of each species. The size at first capture (CL_c), calculated in both species for the two sexes combined, increased significantly with mesh size. Even for the mesh size of 60 mm, the size at first capture was still smaller than the sizes at 50% maturity, whatever the criterion adopted. Since the differences between the size at first maturity and the sizes at first capture are greater in A. foliacea than A. antennatus, the former species appears in this respect to be more vulnerable to trawling than the latter.     

Reproductive biology of the Brazilian guitarfish,Pseudobatos horkelii (Müller & Henle, 1841) from southeastern Brazil,western South Atlantic

This study provides information on the seasonal occurrence, length‐width relationship, sexual development and size at first maturity of the critically endangered Brazilian guitarfish Pseudobatos horkelii in southeastern Brazil. Samples were obtained from September 2007 to August 2009 from commercial fisheries off São Paulo State coast at depths of 10–50 m, with net mesh sizes of 150 mm in the main net and 100 mm in the cod end. A total of 143 specimens (71 males, 72 females) were analyzed. Total length (TL), disc width (DW), sex and reproductive variables were recorded for each individual. Pseudobatos horkelii presents sexual dimorphism in length‐width relationships, with females attaining larger TL and DW. Females also mature at a larger TL, at 81.1% of the maximum TL, while males mature at 67.8% of the maximum TL. No specimens were captured in winter, and only a small sample size was observed in autumn. Males captured in spring and summer presented semen in the seminal vesicle, indicating that this species may reproduce in the warmer months, as already observed for other Rhinobatidae as well as for P. horkelii in southern Brazil.     

Lantern fish (Benthosema pterotum) resources as a target for commercial exploitation in the Oman Sea

The skinnycheek lantern fish Benthosema pterotum (Myctophidae) represents a virgin resource in the Oman Sea. Because of its potential importance for fishmeal production there has been great interest during the last decade in starting commercial exploitation. Acoustic surveys to estimate stock biomass and trial fishing using pelagic trawls were carried out in Iranian waters of the Oman Sea from 1992 to 1998. Lantern fish schools are found in offshore waters, on the edge of the continental shelf wherever sea depth is more than 100 m. During the day the fish occur in two vertical layers, with the densest schools in the shallower layer (80–130 m), whereas at night B. pterotum occur in a single dispersed layer closer to the surface (mainly at 30–70 m). Biomass estimates range from 1 to 4 million tonnes (t), with an average of 2.3 million t. Densities vary seasonally, with the highest densities recorded in spring (May–June) and lowest in autumn (October–November). The highest densities were seen in the western Oman Sea. Although recommendations can be made with regard to the best fishing seasons, areas and depths, trial catch rates were too low (<30 t daily per boat) to support a commercially viable fishery. Further trials are needed to identify the best gear and vessel size.     

Fisheries assessment of Chwaka Bay (Zanzibar) – following a holistic approach

This study investigates the typical East African multispecies fishery of Chwaka Bay (Zanzibar) by assessing growth, mortality, exploitation and stock size of six key target species of the fishery. Analyses are based on monthly length–frequency data collected from January to June and September to December in 2014 from the three main landing sites surrounding the bay. Estimated von Bertalanffy growth parameters using the ELEFAN I routine as implemented in FiSAT II varied among species from 27.6 to 64.4 cm (L_∞) and 0.24 to 0.8 per year (K). Current exploitation rates compared to biological reference points calculated from yield‐per‐recruit analysis for five of the six key species indicate that Siganus sutor, Lethrinus borbonicus and Lethrinus lentjan are harvested beyond maximum sustainable levels (E_max). While juvenile retention rates of these three species are >80% and current L_c‐values are lower than L_opt, fishing mortalities for Siganus sutor and Lethrinus borbonicus are highest for specimens above length at first maturity. Two management measures are discussed: (i) an increase in mesh size; and (ii) closure of the destructive dragnet fishery. The first option seems feasible only if the radius of the fishery were increased to capture larger specimens outside the shallow bay area. The second option would leave approximately 550 fishermen unemployed. Reallocating dragnet fishing effort to other gears would lead to a substantial increase in the number of boats, which might create use conflicts over the limited fishing area. The general status of the fishery in Chwaka Bay is considered as representing a ‘full exploitation to over‐exploitation scenario’, with no scope for expansion.     

Demersal fish assemblages on seamounts exploited by fishing in the Azores (NE Atlantic)

Seamount fish communities are susceptible to variations due to the oceanographic conditions and level of historical fishing effort. In the NE Atlantic, the Azores is considered an “oceanic seamount ecosystem area” because seamount concentration is high relative to other regions. Scientific information on seamounts in the Azores remains scarce and demersal fishery occurs mostly without any knowledge to endorse sustainable harvest strategies. To make available an important baseline information on dynamics of demersal fish populations inhabiting commercially exploited seamounts, the present study has as specific objectives to (a) describe the taxonomic composition of demersal fish assemblages on underwater mountains, (b) examine whether assemblages vary spatial and temporally, and (c) investigate what drives distributional patterns of species in terms of abundance and size composition. For this, three Azorean seamounts (Açores, Princesa Alice and Mar da Prata) exploited by bottom fishing were selected as case study areas. Data were obtained from scientific surveys and commercial fishery over the past c. 25 years. A total of 84 species from 45 families were identified. Sebastidae, Moridae, Sparidae and Centrophoridae were the most abundant families, mainly represented by Helicolenus dactylopterus, Mora moro, Pagellus bogaraveo and Deania profundorum, respectively. Fish assemblages were more distinguishable spatially than temporally. Depth was identified as the main factor responsible for these differences. The higher occurrence of shallow and intermediate (i.e., up to 600 m) habitats in Princesa Alice and Açores seems to favor the occurrence of a greater number of species and higher abundances in comparison to Mar da Prata. Phycis phycis, Pontinus kuhlii, H. dactylopterus, P. bogaraveo, Conger conger and M. moro were the species which primarily contributed to dissimilarities in assemblage structure among sample groups. Abundance indices and fish sizes showed a decreasing trend for many of these species, especially for those with sedentary behaviour inhabiting historically highly exploited seamount areas. These results highlighted the vulnerability of demersal fishes to the expansion of fishing effort in the offshore seamount areas. Spatial management of seamounts should be a priority being fish conservation balanced with strategies that support sustainable fisheries.     

Discards in bottom trawl fishery in the Aegean Sea (Izmir Bay,Turkey)

Sampling was carried out on a seasonal basis during 2007–2009, using a conventional bottom trawl net with 44 mm codend mesh size in Izmir Bay, Aegean Sea. A total of 116 valid hauls: 27 in autumn, 28 in winter, 35 in spring and 26 in summer, were conducted at depths ranging from 30 to 70 m. A total of 112 species: 15 Chondrichthyes, 83 Osteichthyes, 11 Cephalopoda and 3 Crustacea were obtained in the trawl codend. All captures were separated into commercial (C) and non‐commercial (NC) species. The C ratio was 69.6%, while NC (i.e. discards) was 30.4%. Diplodus annularis was the most abundant species in all seasons, followed by Mullus barbatus, Merluccius merluccius, Citharus linguatula, Serranus hepatus, Lepidotrigla cavillone, Spicara maena, Myliobatis aquila, Diplodus vulgaris, and Trisopterus minutus in decreasing order of abundance. These top ten species constituted 75% of total catch weight. Biomass ratios of total discards to commercial species were 0.44 : 1.     

In situ video monitoring of by-catch interactions within commercial rock lobster (Jasus edwardsii) fishing traps

The incidental capture of non-target and undersized target species during commercial fishing operations has been identified as a major issue and ongoing challenge for fisheries management. In the Northern Zone rock lobster (Jasus edwardsii) fishery (NZRLF) of South Australia, escape gaps have been mandatory in all commercial fishing traps since 2002 to reduce non-target species (by-catch) catch rates and juvenile lobster mortality. This study used in situ video monitoring of by-catch species in traps with and without escape gaps to understand how by-catch species interact within commercial fishing traps. Twenty-two different by-catch species were observed entering commercial rock lobster traps, 20 of which were temperate reef finfish. Overall, on-board by-catch rates were significantly higher in hauled traps without escape gaps and were dominated by reef-dwelling finfish species, particularly Meuschenia hippocrepis and Notolabrus tetricus. However, in situ video monitoring within traps showed no difference in the maximum number of finfish by-catch (MaxN) in traps with or without escape gaps. We suggest that the difference in by-catch rates between hauled traps with and without escape gaps may be driven by species-specific behavioural interactions within traps prior to hauling. Overall, this study shows that the implementation of escape gaps in the NZRLF has considerably reduced fishery by-catch rates. Furthermore, the use of in situ video monitoring has provided a better understanding of by-catch behavioural interactions within traps, not previously identified in on-board sampling research, which may partly explain the mechanisms underpinning escape gap effectiveness.     

Species selectivity in the Eastern Mediterranean demersal trawl fishery using grids to reduce non‐target species

Scientific studies have been conducted on size selectivity of trawls with grids in the Mediterranean; however, none has focused on species selectivity. The aim of the present study was to analyze the value of sorting grids with 20 mm bar spacing for species separation, in a demersal trawl fishery mainly targeting deep water rose shrimp (Parapenaeus longirostris) in the Eastern Mediterranean. Fishing trials were carried out 17–24 August 2008 onboard the commercial trawler ‘Hapulo?lu’, using a modified bottom trawl net. The separation rate for silver scabbard fish (Lepidopus caudatus) was highest among all species with 98% by weight and 97% by number in 44 mm diamond (44D) and 40 mm square mesh (40S) codends, respectively. The exclusion of European hake (Merluccius merluccius) by the grid shows differences between 85 and 93%, in weight and 64 and 83% in number for codends of 44D and 40S, respectively. Excluding the ratio for greater forkbeard (Phycis blennoides), the angler fish (Lophius piscatorius) and broadtail short fin squid (Illex coindetii) varied between 93 and 97% in weight, and 81 and 86% in number in both codends. Losses of legal sized rose shrimp were determined as 23 and 25% in 44D and 40S, respectively. The results obtained in the present study demonstrate that substantial separation of fish and shrimp can be achieved in this Mediterranean demersal trawl fishery. However, further developments should be explored; for this purpose the behaviour of species has to be studied in relation to trawl and grid design and where commercial consequences of changes in gear technology need to be considered.     

TheMoegistorhynchus longirostris (Diptera: Nemestrinidae) pollination guild: long-tubed flowers and a specialized long-proboscid fly pollination system in southern Africa

A guild of 20 late spring- and early summer-flowering species ofIridaceae, Geraniaceae andOrchidaceae is pollinated partly or exclusively by the long-proboscid flyMoegistorhynchus longirostris (Nemestrinidae). This large-bodied fly, active in late spring and early summer, has mouthparts 40–70 (90) mm long and forages for nectar from a variety of species. These plants share a suite of convergent floral features including a straight or weakly curved floral tube usually 50–70 mm long but sometimes to 90 mm, relatively short petals or tepal lobes coloured white, cream or salmon with reddish nectar guides, and often violet or red anthers and pollen. Flowers of most species with these characteristics are zygomorphic with the stamens either arcuate (mostIridaceae) or declinate (Geraniaceae and someIridaceae). The flowers are odourless and typically secrete large amounts of nectar of relatively constant sugar concentration, mostly 24–29%, with a high sucrose:hexose ratio. Guild members utilize five separate sites of pollen deposition on the body of the fly, typically utilizing different deposition sites when two or more co-occur, indicating strong selection to aviod pollen contamination.M. longirostris is restricted to the west coast of southern Africa and at least 8 species appear to depend exclusively on the insect for pollination. The remaining species in the guild are pollinated by one or both of the long-proboscid fliesPhiloliche gulosa andP. rostrata (Tabanidae) over other parts of their range. Species and races pollinated entirely byM. longirostris have longer floral tubes which makes nectar unavailable to other insects, including other species of long-proboscid fly. The only insect with mouthparts long enough to forage effectively on these long-tubed flowers isM. longirostris and this fly must be considered a keystone species in the ecosystems in which it occurs.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday