Galeus Melastomus Research Articles

Effects of fishing methods on deep water shark species caught as by-catch off southern Portugal

Deep water sharks are commonly caught as by-catch of longlines targeting bony fishes and trawlers targeting crustaceans in deep water off the southern Portuguese coast. Due to low or no commercial value, these species are most of the times discarded at sea, with only the larger specimens of some species commercialized at very low prices. In this study we present size distributions, maturity distributions, and sex ratios of 2,138 specimens belonging to four different species, namely the lantern sharks Etmopterus pusillus and Etmopterus spinax and the catsharks Galeus melastomus and Galeus atlanticus, caught with these two gears. Trawls generally caught smaller-sized specimens, in a wider length range than longlines. Trawls caught mostly immature specimens of all species, namely 83.7% immature of E. pusillus, 84.3% of E. spinax, 89.5% of G. melastomus, and 95.5% of G. atlanticus, while longlines caught mostly immature E. pusillus (69.2%) and G. melastomus (78.6%) and mostly mature E. spinax (88.2%) and G. atlanticus (87.2%). Trawls tended to catch more males than females of all species except E. spinax, while longlines caught more females than males of E. spinax and G. melastomus and more males than females of the other two species. The main conclusion of this work is that trawls are catching smaller-sized and mostly immature specimens when compared to longlines, meaning that they are probably having a more detrimental effect on these shark populations. The data presented here have significant implications for the conservation of these shark populations since sizes, sexes, and the immature and mature components of the populations are being affected differently by these two fishing gears.

Short-term temporal variability in fish community structure at two western Mediterranean slope locations

Short-term temporal variability in deep-sea demersal fish assemblages is described for two slope areas characterised by different oceanographic conditions, which are situated north (Balearic sub-basin, BsB) and south (Algerian sub-basin, AsB) of the Balearic Islands (western Mediterranean). A total of 75 hauls were analysed from six bottom trawl surveys carried out in the two sub-basins. At BsB, surveys were designed for sampling different slope habitats during April 1991, December 1991, March 1992 and July 1992: (i) a submarine canyon at a depth of around 450 m, (ii) the upper slope at a depth of 600–650 m, and (iii) the middle slope at a depth of around 1200 m. At AsB, surveys were carried out during October 1996 and May 1998, along a continuous transect on the upper, middle and lower slope. The taxonomic composition, ecological parameters (number of species, abundance and biomass) and biomass spectra of the assemblages, as well as the length frequency distribution of the main species, were compared for different seasons and bathymetric ranges. Forty-four demersal species were captured in BsB and 38 in AsB. Helicolenus dactylopterus and Trachyrinchus scabrus were more abundant in BsB, and Hoplostethus mediterraneus, Galeus melastomus and Centroscymnus coelolepis in AsB. Depth was the determinant factor in all the analyses. Species-specific densities (abundance and biomass) showed significant differences between surveys, depth strata and their interaction in BsB. However, survey and its interaction with depth, were not significant in AsB. We also found significant differences in relation to depth and season for the three ecological parameters tested in BsB, but only significant differences in relation to depth in AsB. Biomass spectra showed large differences in relation to depth but only slight between-survey differences, which mainly occurred in the upper slope. The length frequency distributions of single species presented short-term temporal variations, mainly due to the varying presence of a larger proportion of small or large individuals. Depth, geographic area and sampling time were the main factors determining the species composition and structure of deep-sea slope demersal fish assemblages. The effects of short-term temporal variations were observed in both the replacement and the size structure of some dominant and subdominant species throughout the year. The different temporal variation effects observed between the two sub-basins might be related to differences in productivity and its transport to the benthos.

Reproductive biology of the blackmouth catshark, Galeus melastomus (Chondrichthyes: Scyliorhinidae) off the Languedocian coast (southern France, northern Mediterranean)

The blackmouth catshark, Galeus melastomus presents a wide Atlanto-Mediterranean distribution, and is commonly captured off the Languedocian coast (southern France, northern Mediterranean). The males and females sexually matured between 510–550 mm and 520–610 mm total length (TL), respectively. The largest male and the largest female were 620 mm and 640 mm TL, respectively. There was a significant relationship of total liver mass vs TL between males and females. The diameter of the largest yolky oocytes ranged from 15 to 18 mm (16.5 ± 2.7). Production of egg cases was observed throughout the year, except in September. Egg cases had between 36 and 50 mm (mean: 45.3 mm ± 3.9) in length without horns, and between 14 and 21 mm (18.2 mm ± 1.4) in width. Fecundity remained difficult to assess; an estimation based on production of egg cases enabled us to consider 93 egg cases per year as a maximum.

Spatio-temporal variations in deep-sea demersal communities off the Balearic Islands (western Mediterranean)

The spatial and temporal variations of deep-sea megafaunal assemblages from the western Mediterranean are analysed in the present paper. The assemblages from two locations of the Balearic Islands situated 120 km apart were compared using data collected seasonally on a bathymetric stratum covering the 150–750 m depth range during six bottom-trawl surveys. The assemblage structure, in terms of species composition, species dominance and population sizes, was differentially affected by the spatio-temporal variables analysed (depth, location and fishing period). Although depth was the main factor determining the assemblage composition, the differences obtained between the two locations were also relevant. On the upper slope these between-location differences in the dynamics of megafaunal assemblages were found to be related to the effect of fishing exploitation. Population size-based metrics and biomass spectra were good predictors of meso-scale fishing effects, and were mainly reflected by elasmobranchs and demersal teleosts. Nevertheless, the effects of fishing depended on the species considered. Two dominant large-sized fish species found on the upper slope in both localities, Galeus melastomus and Phycis blennoides, had higher biomass values associated with lower fishing effort. Although the mean body weight (MBW) of both species and also the mean maximum body weight (MMBW) of G. melastomus agreed with this pattern, the P. blennoides MMBW did not. This last case could be indicative of natural size-trends such as the bigger–deeper phenomenon which refers to the displacement of large individuals towards the deeper limit of their bathymetric distribution, beyond the maximum depth sampled in this study for this species. By contrast, the target species of the upper slope fishery, the red shrimp Aristeus antennatus, was not negatively affected by the direct impact of fishing activity and other environmental factors, such as the presence of specific water masses could also be important.

Morphological and mitochondrial DNA divergence validates blackmouth, Galeus melastomus, and Atlantic sawtail catsharks, Galeus atlanticus, as separate species

A total of 60 morphometric traits and nucleotide sequences of the entire mtDNA NADH dehydrogenase subunit 2 (ND2) gene [1047 base pair (bp)] in 23 individuals of blackmouth, Galeus melastomus, and 13 individuals of sawtail catsharks, Galeus atlanticus, caught in Southern Portugal, were examined to test the validity of these two taxa. These sharks closely resemble each other, have overlapping geographical ranges and are difficult to identify by morphological characters. Non‐metric multidimensional scaling of morphometric variables indicates a clear separation between the two species, with 10 characters each contributing 2·12–2·45% of the total variability between species. Maximum likelihood, parsimony and neighbour‐joining trees revealed two major mtDNA haplotype clades, corresponding to the two species, with an average corrected sequence divergence between them of 3·39 ± 0·56%. Within species divergences between haplotypes averaged 0·27 ± 0·18% in G. melastomus and 0·12 ± 0·08% in G. atlanticus. A total of 35 diagnostic nucleotide site differences and four restriction fragment length polymorphism recognition sites in the ND2 gene can be used to distinguish the two species.

Dogfish egg case structural studies by ATR FT-IR and FT-Raman spectroscopy

The dogfish egg case is a composite structure that combines mechanical tensile strength, toughness and elasticity with high permeability to small molecules and ions. Presumably, it provides both a protective and a filtering role for the egg/embryo contained within it. In this work, we performed structural studies of the Galeus melastomus egg case at two different stages of the hardening process, utilizing ATR FT-IR and FT-Raman spectroscopy. Based on these data we deduce that: (a) The G. melastomus egg case, in close analogy to that of the related species Scyliorhinus cunicula, is a complex, composite structure which consists mainly of an analogue of collagen IV. This network forming protein appears to have common secondary structural characteristics in the entire egg case. (b) The outermost layer of the non-sclerotized egg case is especially rich in tyrosine, while the innermost layer is rich in polysaccharides, presumably glycosaminoglycans, and lipids. These differences are diminished upon hardening. (c) Disulfide bonds do not appear to play a significant role in cross-linking. However, cross-links involving tyrosine residues appear to sclerotize the egg case. It is proposed that the intensity of the Raman band at ca. 1615 cm −1, which is due to ring stretching vibrations of Tyr, might be a useful indicator of the sclerotization status of a certain proteinaceous tissue, when tyrosines are involved in sclerotization mechanisms.

Ampullary pore distribution of Galeus melastomus and Etmopterus spinax: possible relations with predatory lifestyle and habitat

The number and distribution of ampullary pores present on the blackmouth catshark, Galeus melastomus and the velvet belly dogfish, Etmopterus spinax do not differ with the size/maturity or gender of the specimen and were found to be related to prey preference.

Evolution of high‐performance swimming in sharks: Transformations of the musculotendinous system from subcarangiform to thunniform swimmers

In contrast to all other sharks, lamnid sharks perform a specialized fast and continuous "thunniform" type of locomotion, more similar to that of tunas than to any other known shark or bony fish. Within sharks, it has evolved from a subcarangiform mode. Experimental data show that the two swimming modes in sharks differ remarkably in kinematic patterns as well as in muscle activation patterns, but the morphology of the underlying musculotendinous system (red muscles and myosepta) that drives continuous locomotion remains largely unknown. The goal of this study was to identify differences in the musculotendinous system of the two swimming types and to evaluate these differences in an evolutionary context. Three subcarangiform sharks (the velvet belly lantern shark, Etmopterus spinax, the smallspotted catshark, Scyliorhinus canicula, and the blackmouth catshark, Galeus melanostomus) from the two major clades (two galeans, one squalean) and one lamnid shark, the shortfin mako, Isurus oxyrhinchus, were compared with respect to 1) the 3D shape of myomeres and myosepta of different body positions; 2) the tendinous architecture (collagenous fiber pathways) of myosepta from different body positions; and 3) the association of red muscles with myoseptal tendons. Results show that the three subcarangiform sharks are morphologically similar but differ remarkably from the lamnid condition. Moreover, the "subcarangiform" morphology is similar to the condition known from teleostomes. Thus, major features of the "subcarangiform" condition in sharks have evolved early in gnathostome history: Myosepta have one main anterior-pointing cone and two posterior-pointing cones that project into the musculature. Within a single myoseptum cones are connected by longitudinally oriented tendons (the hypaxial and epaxial lateral and myorhabdoid tendons). Mediolaterally oriented tendons (epineural and epipleural tendons; mediolateral fibers) connect vertebral axis and skin. An individual lateral tendon spans only a short distance along the body (a fraction between 0.05 and 0.075 of total length, L, of the shark). This span is similar in all tendons along the body. Red muscles insert into the midregion of the lateral tendons. The shortfin mako differs substantially from this condition in several respects: Red muscles are internalized and separated from white muscles by a sheath of lubricative connective tissue. They insert into the anterior part of the hypaxial lateral tendon. Rostrocaudally, this tendon becomes very distinct and its span increases threefold (0.06L anteriorly to 0.19L posteriorly). Mediolateral fibers do not form distinct epineural/epipleural tendons in the mako. Since our morphological findings are in good accordance with experimental data it seems likely that the thunniform swimming mode has evolved along with the described morphological specializations.

Reproductive biology of the blackmouth catshark, galeus melastomus (chondrichthyes: scyliorhinidae) off the south coast of portugal

the reproductive biology of 1045 female (9.5–67 cm (total length (tl)) and 1007 male (9.4–64.3 cm tl) blackmouth catsharks, galeus melastomus, was investigated. the sharks were caught off southern portugal by bottom crustacean trawlers at depths from 209 to 754 m. the sex ratio was 1:1, and this species is sexually dimorphic with males approaching maturity at smaller size than females. sexual segregation appears to be given for the stock within the study area. sexual maturity was reached at a total length above 49 cm in males and above 56 cm in females. mating and egg-deposition take place all year round, with two reproductive peaks of activity, in winter and summer. egg capsules are, on average, 54 mm long and 21 mm wide, with a maximum of 63×25 mm encountered. morphometric measurements of claspers, testes, ovaries, and oviducal glands were suitable for determining sexual maturity of blackmouth catshark.

Trophodynamics of a deep-sea demersal fish assemblage from the bathyal eastern Ionian Sea (Mediterranean Sea)

Daily food consumption of the eight dominant demersal fish species of the bathyal eastern Ionian Sea were determined from field data on four seasonal cruises (April 1999, July August 1999, November 1999 and February 2000). Daily ration (DR) estimates ranged from 0.198 to 4.273% WW/WW. Overall, DR estimates were independent of the model used, and they were comparable to the daily consumption of other deep-sea fauna (e.g. fish and crustaceans). Both sharks studied ( Galeus melastomus and Etmopterus spinax) exhibited the highest values of DRs, together with the macrourid Coelorhynchus coelorhynchus in August. Among osteichthyes, DR estimates were related (in a multi-linear regression model) to the nature of their diet (i.e. their trophic level deduced from δ 15N isotopic composition, the mean number of prey and trophic diversity). Thus, species feeding at a lower trophic level, ingesting a large number of prey items and with a very diversified diet had higher DR than species from higher trophic level and feeding fewer prey items. By season, the DR of species feeding mainly on mesopelagic prey ( Hoplostethus mediterraneus and Helicolenus dactylopterus) were higher in summer, while DR for benthos/suprabenthos feeders (i.e. C. coelorhynchus and Nezumia sclerorhynchus) were higher in spring. Higher food consumption coincides with maximum food availability, both among mesopelagic feeders (higher availability of euphausiids, Pasiphaea sivado and Sergestes arcticus in summer) and among Macrouridae (higher suprabenthos densities in spring). In a tentative estimate the energy intake deduced from diet (i.e. mean energy value of food ingested) was constant in all seasons for each species studied. Results for the energy intake also indicate higher energy intake in the diet of mesopelagic feeders than in the diet of benthic feeders. Overall results are discussed in relation to the deep-sea ecosystem structure and functioning.

Feeding ecology of five commercial shark species of the Celtic Sea through stable isotope and trace metal analysis

In order to trace their feeding habits, stable carbon and nitrogen isotope ratios (delta15N and delta13C), as well as trace metal concentrations (Zn, Cd, Fe, Cu, Se and Hg) were analysed in the tissues of five commercial shark species from the Celtic Sea: the tope shark Galeorhinus galeus, the black-mouthed catshark Galeus melastomus, the starry smooth hound Mustelus asterias, the spiny dogfish Squalus acanthias and the lesser-spotted dogfish Scyliorhinus canicula. Our results were compared to previously described stomach contents and isotopic composition of potential preys. Isotopic ratio delta15N suggested that tope sharks fed at a higher trophic level (16.7 per thousand in the muscle) than the other species, reflecting its piscivorous diet. The lower values of spiny dogfish (11.6 per thousand in the muscle) might be explained, amongst other things, by either its migratory behaviour or its preference for preys from lower trophic levels. Cd and Hg were correlated with isotopic ratios delta13C and delta15N, and were shown to be diet-related whereas Zn, Fe and Cu seemed much more linked to species-specific metabolism. Although this multidisciplinary approach is revealed as a useful tool for the study of shark ecology, the lack of known trophic fractionation suggests that isotopic data be compared to traditional diet analyses.

Semi-pelagic Longline and Trammel Net Elasmobranch Catches in Southern Portugal: Catch Composition, Catch Rates and Discards

In Portugal, elasmobranch landings have decreased substantially in recent years. In this work, elasmobranch catches in experimental hake near bottom semi pelagic longlines (1997 and 1998) were compared with those of experimental trammel nets (2000). In the hake semi pelagic longline fishery, 7 elasmobranch species represented 33.4% (2185 specimens) of the total fish captures. The most abundant species were Galeus melastomus (63.3%), Etmopterus pusillus (21.7%) and Scyliorhinus canicula (14.2%). Most of these elasmobranchs (68.3% in total) were discarded. In the trammel net fishery, 16 different elasmobranch species represented 4.3% (597 specimens) of total fish catches and the most important species were Raja undulata (43.6%) and Scyliorhinus canicula (10.2%). The majority of the elasmobranchs caught with this gear had commercial value, and only 5.4% were discarded. In both fisheries, intra -specific catch rates varied with depth. Length frequency distributions for the only species with relatively high catches in both fisheries, the small-spotted catshark, showed that in general, trammel nets catch larger specimens and in a more restricted length range than longlines. Introduction Elasmobranch fishes have life strategies that make them especially vulnerable to overexploitation (Pratt and Casey, 1990; Smale and Goosen, 1999; Wintner and Cliff, 1999; Hazin et al., 2002; Coelho and Erzini, in press). Worldwide, the problem of elasmobranch overexploitation has been well documented for the case of targeted fisheries (Bonfil et al., 1990; Campbell et al., 1992; Hurley, 1998; Stevens at al., 2000) as well as those with high levels of by-catch of these species (Buencuerpo et al., 1998; Mckinnell and Seki, 1998) and for other fishing activities, such as recreational fishing (Francis, 1998). Elasmobranch fishes are a very important component of the by-catch of the artisanal fisheries in Portugal (Erzini et al., 2000; Erzini et al., 2001), but no management program has been established yet. In the past few years, catches decreased 46.3% in the Algarve (from 888.1 t in 1988 to 447.0 t in 2000) and 30.1 % at a national level (from 5634.4 t in 1997 to 3938.6 t in 2000) (DGPA, 2000). In some cases, those reductions have been very drastic and might even indicate that these species are at high risk. Such is the case of the gulper shark (Centrophorus granulosus) where there was a catch reduction of 92.3 % at a national level and 80.4 % in the Algarve, or the smooth hounds (Mustelus spp.) that registered reductions of 79.4% at a national level and 54.2% in the Algarve. The rays and skates (Raja spp.) have also suffered great reductions, namely 43.8 % at a national level 48.7 % in the Algarve.

Comparison of Elasmobranch Catches from Research Trawl Surveys and Commercial Landings at Port of Viareggio, Italy, in the Last Decade

A program to monitor commercial elasmobranchs was put into effect at Viareggio, the most important fishing port of the Tyrrhenian and Ligurian seas. Size structure of the catches and spatial information on fishing effort distribution were collected monthly by species and gear over the period 1990–2001. Data on catch rates and geographical distribution were also obtained from annual research trawl surveys during 1985–2001 in the same area that the fish landed at Viareggio were caught. The distribution of the fishing effort for every major fishery was compared with catch rates of research trawl surveys for the more important elasmobranch species; two batoids, Raja asterias and Raja clavata and two sharks, Scyliorhinus canicula and Galeus melastomus. Trends in catch rates derived from fishery independent and fishery dependent sources appear inconsistent. This is probably due to spatial shifts in the effort allocation of the fisheries as a consequence of changes in target species that occurred during the analysed period. The current level of fishing pressure and fishing pattern, that remained almost unchanged for the last 10 years, seems sustainable for each one of the four species studied. This may be related to a relatively low fishing pressure on some grounds where certain species are concentrated, to the discarding of a portion of the individuals caught as well as to life history characteristics of some species that make them less sensitive to increased fishing mortality.

Deep-water fish assemblages in the Mediterranean Sea

Data collected during the DESEAS survey carried out in three areas of the Mediterranean Sea (Balearic Sea, western and eastern Ionian Sea) were used to describe the structure and spatial distribution of the fish assemblages at depths between 600 and 4000 m. A total of 55 species (8 chondrichthyes and 47 teleost fish) were sampled, 38 of them in the Balearic Sea, 30 in the western Ionian and 37 in the eastern Ionian. Multivariate analysis showed a clear pattern of zonation with depth and geographic area. Three main assemblages were identified across the vertical gradient investigated: on the upper slope around a depth of 600 m, on the middle slope between 800 and 1300 m, and on the lower slope below 1300 m. The geographic characterisation of the ichthyofauna structure was mainly observed on the upper and middle slope. The highest abundance and biomass values were found at depths of 1000-1200 m due to the presence of larger species with high energy requirements, such as Alepocephalusrostratus, Mora moro and Galeus melastomus. On the middle slope, significant differences in the abundance, biomass and mean fish weight were detected between the three areas. Significant differences for these parameters were also shown between the middle and lower slope assemblages. A significant decrease in species richness and diversity was shown with increasing depth, indicating an impoverishment of the megafauna with depth and a higher similarity between the Balearic Sea and the Ionian Sea with regard to the greatest depths. The dominant species on the deepest bottoms were Bathypteroismediterraneus, Chalinura mediterranea and Coryphaenoides guentheri. On the lower slope, the shark Centroscymnuscoelolepis was also found to be relatively abundant off the Balearic Islands, Etmopterusspinax in the eastern Ionian Sea and the teleost fish Cataetyx laticeps throughout the three study areas. The deepest bottoms of the Mediterranean Sea shelter an ichthyofauna dominated by small-medium species living in a food scarce environment in which some large mobile fishes are widespread. The results are discussed in relation to previous studies mostly carried out in the Atlantic and western Mediterranean.

Chondrichthyes species in deep waters of the Mediterranean Sea

Data collected during the DESEAS survey carried out in three areas of the Mediterranean Sea (Balearic Sea, western and eastern Ionian Sea) were used to describe the distribution and abundance of chondrichthyes species at depths between 600 and 4000 m. A total of 8 chondrichthyes species were recorded, 5 of them in the Balearic Sea, 4 in the western Ionian and 6 in the eastern Ionian. A decrease in abundance with depth was observed in each species with the exception of Centroscymnuscoelolepis. The most abundant species were Galeus melastomus and Etmopterusspinax. The depth range of some species was updated. G. melastomus was caught down to 1500 m, exhibiting a smaller-deeper pattern in females, while E.spinax was captured down to 2200 m with a bigger-deeper trend. Mature females of these two sharks were found between 600 and 1500 m. A wide size-range was shown in both species. C.coelolepis was only collected in the Balearic Sea down to 2800 m. The presence of a pregnant female was sampled from a depth of 1500 m. The distribution of the species is discussed in the context of the present knowledge of the Mediterranean ichthyofauna.

Trophic Relations of Lesser-Spotted Catshark (Scyliorhinus canicula) and Blackmouth Catshark (Galeus melastomus) in the Cantabrian Sea

The feeding habits of Scyliorhinus canicula and Galeus melastomus were investigated by analysing the stomach contents from 6 036 individuals collected on research surveys in the southern region of the Bay of Biscay during the autumns of 1988–2001. These catshark species are the most abundant scyliorhinids on the Cantabrian shelf. Their depth ranges partly overlap, although they occur in different habitats. Both catshark species are opportunistic scavengers, with their main prey being fish and crustaceans. Diets of the two species overlap; they are most similar in individuals <30 cm total length (TL) where euphausiids are important prey, but, for individuals ≥30 cm TL, fish (mainly discarded from trawlers) are important prey. Lesser-spotted catshark are mostly benthic feeders and they feed on a greater diversity of prey than blackmouth catshark, which are more suprabenthic. Resource partitioning between the two species appears to depend on the better vision of the blackmouth catshark, which feeds more in the water column whereas the better developed olfactory sense of the lesser-spotted catshark is an adaptation to benthic feeding. The broad diets of these catshark species and their consumption of fish discarded from trawlers may make them good indicators of fishinginduced change in the Cantabrian Sea ecosystem.

Distribution and Biology of the Blackmouth CatsharkGaleus melastomusin the Alboran Sea (Southwestern Mediterranean)

The distribution, population size structure and reproductive biology of blackmouth catshark Galeus melastomus in the Alboran Sea were studied from 438 bottom trawls performed at depths of 40 to 796 m during twelve surveys carried out between 1994 and 2002. The species was only captured at the two deepest strata (below 200 m), reaching its maximum abundance and biomass between 501 and 800 m. Maximum indices, obtained in 1997 and 2002, indicate no specific trend in abundance, whereas the biomass showed a slightly decreasing trend from 1994. Similarly, seasonal variation of abundance and biomass during the last two years showed maximum values of biomass in autumn but with no trend in abundance. The size of the specimens ranged from 10 to 63 cm and all size groups were well represented in the length frequencies during all seasons. Juveniles and adults were restricted to depths below 500 m, while recruits were distributed throughout the whole bathymetric range in which the species was found. Both recruitment and spawning were continuous throughout the year and the total length at first maturity was calculated as 44.3 and 48.8 cm for males and females, respectively. Finally, the great abundance and biomass of the species as well as its wide population structure are compared and discussed with other Mediterranean areas.

Coplanar polychlorinated biphenyl congeners in the liver of Galeus melastomus from different areas of the Mediterranean Sea.

Coplanar polychlorinated biphenyl congeners in the liver of Galeus melastomus from different areas of the Mediterranean Sea.

Reduction of elasmobranch by-catch in the hake semipelagicnear-bottom longline fishery in the Algarve (Southern Portugal)

: Elasmobranch fish, particularly deep-sea sharks, are the mostimportant component of the by-catch of the hake semipelagic near-bottom ‘pedra-e-bola’ longlinefishery in the Algarve (South Portugal) and most of these fish arediscarded. The effects of the removal of the lower hooks were evaluated,in terms of target and by-catch reductions, by quantifying the catchesof each hook relative to the distance from the bottom. The analysisshowed that most European hake (Merluccius merluccius), thetarget species of this fishery, were caught in the middle rangeof the hooks, with very few individuals caught near the bottom,whereas for sharks the situation was the opposite, with most hookednear the bottom. The removal of the lower three pairs of hooks wouldresult in a small reduction in the catch of the target species,but a much more significant reduction in elasmobranch by-catch.In the specific case of the blackmouth catshark (Galeus melastomus),discard mortality would be further minimized due to the fact thatthe lower hooks capture significantly smaller animals that are alwaysdiscarded compared with hooks that are more distant from the bottom.

Biological Observations on Shark Species Taken in Commercial Fisheries to the West of Ireland

During an investigation into the biology of three shark species commonly taken in Irish fisheries, biological information was also collected from an additional six less-common species: Galeorhinus galeus, Lamna nasus, Mustelus asterias, Galeus melastomus, Hexanchus griseus and Dalatias licha. Data on age, reproduction, feeding and parasites were collected from a total of 137 sharks. Age data from G. galeus and M. asterias suggest possible differences in growth-rate relative to other areas. The state-of-maturity of all specimens agreed with earlier studies, although data regarding the reproductive cycle of M. asterias and G. melastomus were inconsistent with data commonly reported for these species. Stomach contents were unremarkable, with the exception of 1.3kg of cetacean material recovered from a specimen of H. griseus. Results from the parasite component of the investigation extend the known range of two monogenean species, while a further three parasites were recorded from new hosts.