Enric Massutí

Weight-length relationships of littoral to lower slope fishes from the western Mediterranean

Weight–length relationships (WLRs) are presented for 103 fish species inhabiting littoral to lower slope habitats of the Balearic Islands and the Iberian coast (western Mediterranean). Samples were collected using seven types of fishing gear and at depths ranging from 0.5 to 1713 m. Captures were made between the years 1991 and 2001. The b values in the WLR W = aL b varied between 2.072 and 3.847 and showed a mean value of 3.03 (S.E. =± 0.03). Whenever possible, the b values for the species obtained both in this study and some of the previously reported in the Mediterranean Sea were compared, showing the existence of spatial variation whose causes are discussed.

Fish assemblages on the slope in the Catalan Sea (western Mediterranean): influence of a submarine canyon

The analysis of 35 bottom trawls taken on the slope in the Catalan Sea (western Mediterranean) has shown the existence of two different demersal fish assemblages occurring on the upper (350–650 m) and middle (1150–1300 m) slope. The middle slope assemblage is characterized by much higher values in some ecological parameters such biomass and mean fish weight, resulting from the dominance of middle to large size species ( e.g. Alepocephalus rostratus, Trachyrhynchus trachyrhynchus, Mora mom ). On the upper slope two different stations were considered, one inside and the other outside a submarine canyon. Only slight differences were found in species composition, and hence sample and species were not clearly separated by a correspondence analysis. However, some interesting ecological differences exist between these two stations. Much higher values in abundance and biomass inside the canyon were indicative of higher food availability there. Moreover, a drop in mean fish weight was also noted inside the canyon. The analysis of size distributions in the commonest species along the upper slope showed that the submarine canyon acts as a recruiting ground for some of them.

Distribution and biology of five grenadier fish (Pisces: Macrouridae) from the upper and middle slope of the northwestern Mediterranean

Abstract Specimens of five Macrouridae species ( Trachyrhynchus trachyrhynchus, Nezumia aequalis, Hymenocephalus italicus, Coelorhynehus coelorhynchus and Coelorhynchus labiatus ) were obtained from 76 bottom trawls in the Catalan Sea at depths between 147 and 1290 m. Abundance, biomass and length distribution by depth varied depending on the species. For T. trachyrhynchus , maximum abundance and biomass were found between 900 and 1000 m. In H. italicus , abundance and biomass decreased below 500–600 m, whereas abundance and biomass showed a bimodal trend for N. aequalis . In these species, the mean length of the specimens increased with depth. The sex-ratio was 50% for intermediate sizes while larger fish were predominantly females. Reproduction patterns were different for each species. Ripe females of N. aequalis and H. italicus were found all year round, while C. coelorhynchus and C. labiatus ripe females were found in spring-summer and autumn winter, respectively. No ripe females of T. trachyrhynchus were found. Size at attainment of 50% maturity for N. aequalis and H. italicus was 4.5 and 2.7 cm pre-anal length (PAL), respectively. The PAL-otolith length (OL) and OL- otolith weight (OW) relationships showed a negative allometry, except for C. labiatus whose OL-OW relationship was isometric. Seasonal growth was detected in the otoliths of all five species; fast growth rings were laid down in summer. All the species reach ages of at least 9 years, and growth rates were relatively high and greater for females.

Demersal assemblages and depth distribution of elasmobranchs from the continental shelf and slope off the Balearic Islands (western Mediterranean)

The analysis of 131 hauls from four bottom trawl fishing surveys carried out between depths of 46 and 1713 m in two different areas off the Balearic Islands yielded a total of 23 elasmobranch species belonging to eight families. Cluster analysis and multidimensional scaling (MDS) ordination were applied to detect zonation patterns and some ecological parameters (e.g. species richness, abundance and biomass, mean weight, diversity and evenness) were calculated for each assemblage. For each area, analysis of similitude (ANOSIM) and similarity percentage analysis (SIMPER) were also applied to detect differences between seasons and depths. For the most important species (Galeus melastomus, Scyliorhinus canicula, Centroscymnus coelolepis, Etmopterus spinax, Squalus blainvillei, Raja naevus, Raja asterias, Raja clavata, Raja miraletus and Raja oxyrhinchus), abundance and size distributions were analysed by depth.

Fish catch composition of the deep-sea decapod crustacean fisheries in the Balearic Islands (western Mediterranean)

The catch composition of two commercial vessels of the trawl fleet operating from Mallorca (Balearic Islands, western Mediterranean) was analysed. A total of 4959 kg resulting from 144 fishing hours was sampled from October 1996 to December 1997. The fishes represented the major proportion with respect to the total catch. The analysis of the fish discards assembled them in three depth related groups: group A (mean depth 300 m); group B (mean depth 489 m); and group C (mean depth 616 m). Species richness, number of individuals and biomass decreased with depth. The diversity and evenness indices also varied with depth, but no significant differences were found. Fishes, with around 70%, dominated the biomass discarded in the three depth groups. Within the landings, fish biomass also represented the major proportion in groups A and B, but in group C the crustaceans biomass dominated. Our results confirm that an important fraction of the catch of the two deep-sea decapod crustacean fisheries is discarded.

The seascape of demersal fish nursery areas in the North Mediterranean Sea, a first step towards the implementation of spatial planning for trawl fisheries

The identification of nursery grounds and other essential fish habitats of exploited stocks is a key requirement for the development of spatial conservation planning aimed at reducing the adverse impact of fishing on the exploited populations and ecosystems. The reduction in juvenile mortality is particularly relevant in the Mediterranean and is considered as one of the main prerequisites for the future sustainability of trawl fisheries. The distribution of nursery areas of 11 important commercial species of demersal fish and shellfish was analysed in the European Union Mediterranean waters using time series of bottom trawl survey data with the aim of identifying the most persistent recruitment areas. A high interspecific spatial overlap between nursery areas was mainly found along the shelf break of many different sectors of the Northern Mediterranean indicating a high potential for the implementation of conservation measures. Overlap of the nursery grounds with existing spatial fisheries management measures and trawl fisheries restricted areas was also investigated. Spatial analyses revealed considerable variation depending on species and associated habitat/depth preferences with increased protection seen in coastal nurseries and minimal protection seen for deeper nurseries (e.g. Parapenaeus longirostris 6%). This is partly attributed to existing environmental policy instruments (e.g. Habitats Directive and Mediterranean Regulation EC 1967/2006) aiming at minimising impacts on coastal priority habitats such as seagrass, coralligenous and maerl beds. The new knowledge on the distribution and persistence of demersal nurseries provided in this study can support the application of spatial conservation measures, such as the designation of no-take Marine Protected Areas in EU Mediterranean waters and their inclusion in a conservation network. The establishment of no-take zones will be consistent with the objectives of the Common Fisheries Policy applying the ecosystem approach to fisheries management and with the requirements of the Marine Strategy Framework Directive to maintain or achieve seafloor integrity and good environmental status.

Biology and fisheries of western Mediterranean hake (M. merluccius)

The European hake (Merluccius merluccius, Linnaeus 1758) is an economically important species in the western Mediterranean. It is one of the principal target species of the trawl fishery in this area, worth not less than 125 million ECU per year at dockside prices. Although it has been intensively studied, some information on its biology and its state of exploitation is still lacking.

Life history of the red mullet Mullus surmuletus from the bottom-trawl fishery off the Island of Majorca (north-west Mediterranean)

The red mullet Mullus surmuletus is one of the main target species of the trawling fishery along the continental shelf off the Island of Majorca. The size distribution of the catches, and the reproduction, age and growth of this species have been studied based on sampling carried out from 1990 to 1992. The length range of the catches was between 10 and 32 cm, with a main distribution between 15 and 20 cm, but this included small specimens (recruits of 10 to 11 cm) from August. In the >19 cm length-class, females clearly dominated. Monthly variations in the gonadosomatic index (GSI) and in the percentage of mature specimens showed that males spawn from December to June, whereas the reproductive activity of the females centres around spring. Fifty percent of males and females mature at 15 and 16.8 cm, respectively, corresponding to 1 yr of age. Otolith age-readings indicate that the population exploited in the trawl fishery consists of six age-groups, including a very high proportion of individuals between 0 and 4 yr old. Population growth curves revealed that females grow comparatively slowly over a longer period of time and attain greater asymptotic sizes than males. The growth parameters for the whole population are: asymptotic length, L∞=31.28 cm; growth coefficient, K=0.211 yr-1; theoretical age when length is zero, t0=-2.348 yr.

Reproductive biology of dolphin-fish (Coryphaena hippurus L.) off the island of Majorca (western Mediterranean)

Abstract The reproductive aspects of Coryphaena hippurus were studied in 410 specimens collected by long line (60–120 cm fork length) and surrounding net (14.4–66 cm fork length) in Majorcan waters (western Mediterranean) during the 1990 and 1991 fishing seasons. Sexual dimorphism was observed, males from 50 cm fork length developing a vertical forehead. The sex ratio was 1:1. Fish smaller than 25 cm fork length were predominantly females, while males were more abundant over 115 cm fork length. The composition of each sex during the study period was around 50% except in December, when females were clearly predominant. A high proportion of fishes caught by long line were mature and showed gonadosomatic values higher than those obtained from surrounding net catches, in which there were only immature fish. Nevertheless, hepatosomatic index and condition factor did not show any specific trend related to the spawning condition. The size at which the population attain 50% maturity was 54.5 cm fork length in females, and 61.8 cm fork length in males. In 14 pre-spawning females, the relative fecundity ranged from 71 to 197 eggs g −1 , with a mean value of 120 ± 31.3 eggs g −1 . The size distribution of oocytes, with at least two groups of oocytes in the ovaries, suggests that C. hippurus is a multiple spawner, with an extended spawning season in the study area.

Distribution and population structure of the rockfish Helicolenus dactylopterus (Pisces: Scorpaenidae) in the western Mediterranean

The distribution and spatio–temporal variation of Helicolenus dactylopterus (Pisces: Scorpaenidae) population was studied from 816 bottom trawls developed along the Iberian coast. Multifactor analysis of variance was used to test the differences in abundance and biomass and cluster analysis was applied to detect differences in population structure. The results showed a bathymetric and latitudinal gradient in abundance and population structure along three geographic sectors in the surveyed area. In the southern area, the species was more frequent and showed a wider bathymetric distribution range than northwards. The depth range with the maximum frequency of occurrence was also wider in the southern area than northwards. Similar trends were observed in terms of abundance and biomass, with the highest and lowest indices in the southern and northern areas, respectively. The age composition of the catches showed that the population consisted mainly of young-of-the-year and juvenile fish. This fraction of the population is well represented, at a mesoscale, along the whole surveyed area, but adults are well represented only at a local scale, at the deepest strata surveyed in the southern area. In this case, recruits of age 0 and juveniles up to 4-y old were restricted to depths shallower than 500 m, while adult fish older than 6 y of age appeared below this depth. In the southern area, seasonal changes in the population structure were also observed, with modes of small fish (3–6 cm) from March to June, as a consequence of the species recruitment to the bottom. Some direct and indirect factors of biogeographic, environmental and anthropogenic origin affecting the observed gradient are discussed.