Beatriz Morales-Nin

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.

Review of the growth regulation processes of otolith daily increment formation

Abstract Otolith growth is a complex phenomenon integrating various factors that can be considered either as endogenous or exogenous, although they are always regulated by the physiology of the fish. Both types of factors may operate upon the anabolism and catabolism of the fish, and these processes are reflected in the rhythmic deposition of the two main constituents of the otolith: the organic matrix and the aragonite layers. Both components reflect the endogenous process in their periodicity, and the exogenous process in the amount of material laid down in the otolith, resulting in how and where the increments are formed. At the endogenous level, several morphological and functional aspects are relevant. The main one is the role of the otolith as a mechano-receptor in the inner ear. Thus, inner-ear anatomy and function regulate otolith growth and morphology, which in turn determine the daily growth rates. Environmental conditions, transmitted through the physiology of fish, affect the otolith growth rate (increment width) but increment periodicity may be disrupted only in extreme cases of physiological stress. The current state of the art is reviewed and the otolith growth paradigm is summarized. Relevant subjects not yet studied are pointed out for future research.

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.

Larval growth of anchovy, Engraulis encrasicolus, in the Western Mediterranean Sea

Engraulis encrasicolus (Linnaeus, 1758) were sampled in July/August 1985 in the Western Mediterranean Sea; they were aged by means of growth rings in the sagittal otoliths. Daily growth rings were observed and subdaily rings were visible starting with the third or fourth daily increment. The Gompertz growth equation, commonly employed in larval growth analysis, suitably describes the growth of this species in the length range sampled; however, extrapolation to greater lengths is not reliable. An instantaneous growth rate of ca. 0.9 mm d-1 was calculated for 8 mm larvae at a temperature of 20°C. This rate is higher than those reported by other authors for the related species E. mordax from colder waters.

Growth of juvenile Merluccius merluccius in the Gulf of Lions ( NW Mediterranean) based on otolith microstructure and length-frequency analysis

Abstract First-year growth rates of European hake in the Gulf of Lions and hatch-date distribution were analysed. Trawl-collected samples were obtained monthly from January 1990 to March 1991. Age was determined by otolith daily increment interpretation. Results were analysed and compared with those of a modal progression analysis, based on length-frequency histograms. A mean length increase of 1.15 cm month −1 was obtained, indicating that the growth rate of young European hake is faster than previously thought in this area. The growth rate agrees with results of recent studies in other Mediterranean areas. The hatch-date distribution, determined from estimated age in days and date of capture, indicated hatching throughout the year, with a main season between November–December and March, in accordance with reproduction data.

Seasonality in the deep sea and tropics revisited: what can otoliths tell us?

The accepted idea that fish otoliths from supposedly aseasonal environments, such as the deep sea and tropics, do not present seasonal growth increments is questioned and re-evaluated. The main seasonal fluctuation in deep seas is a result of the transfer of organic material from the productive upper layers to the abyssal depths. There is some evidence for seasonal patterns of otolith growth, although the validation of seasonal structures is limited owing to the difficulties inherent in deep-water studies. Tropical regions have an extremely high diversity of aquatic environments but in fact very few are aseasonal, and almost all areas have strong hydrological seasons, mainly annual, interacting with temperature variations. These climatic fluctuations have undoubtedly an effect on otolith growth, therefore leading to a succession of different incremental zones. The lack of previous knowledge on this impact of seasonality is probably a result of the previous low level of exploitation or economic interest of target species, and consequently the absence of age-based assessments. This trend has now changed possibly as a result of the increased exploitation of the resources, and to the greater involvement of international and national fishery management bodies. The number of studies showing apparent or validated seasonal marks has recently increased for these environments.

Sagittal otolith size and shape variability to identify geographical intraspecific differences in three species of the genus Merluccius

A study was carried out on the morphology (size and shape) of the saccular otolith (sagitta) by means of image analysis on three species of the genus Merluccius (M. gayi, M. hubbsi and M. merluccius). By digitization of the sagittae, morphometry and outline (Fourier harmonic) as form descriptor measurements were obtained, that were subsequently analysed by means of multivariant methods, allowing the intraspecific variability to be quantified. The differences in the intraspecific sagittal otolith variability confirmed spatial differences of predicted groups. The results were associated with environmental and population aspects. The use of combined morphometric measurements for the whole otolith and its corresponding sulcus acusticus were very appropriate for determining the origin of the analysed otoliths. Using both principal components analysis and discriminant analyses, a clear geographical differentiation was obtained for Merluccius gayi (from Chile and Peru) and M. merluccius (from the Atlantic and Mediterranean). In both species, the discriminant analysis predicted that all the sagittae could be correctly assigned within each of the groups studied. However, it was a little less effective at differentiating between the two groups of M. hubbsi (from the San Matias Gulf on the Patagonian Shelf and Argentinian-Uruguayan Common Fishing Zone). As a result, the morphometric analysis of the sagittae otoliths acted as a clear diagnostic tool to differentiate individuals from different geographical distribution areas.

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.

Life history and fishery of the common dentex ( Dentex dentex) in Mallorca ( Balearic Islands, western Mediterranean)

Abstract Age, growth, mortality, maturity and diet were analysed for 210 common dentex from 17 to 83 cm TL collected off the island of Mallorca from 1993 to 1995. The length composition by sex showed no differences between females and males. The length-weight relationship was identical for both sexes: W = 0.011 TL 3.06 . Age at 50% maturity was reached between 2 and 4 years old. The reproductive period was centred in the second quarter of the year. Ages were estimated from whole sagittal otoliths. Marginal-increment analysis showed that a single annuli formed each year during autumn-winter. Common dentex ages ranged from 0 to 28 years. The von Bertalanffy growth equation for males was TL = 844 (1 − e( −0.1(t + 2.854) ) and for females was TL = 856 (1 − e( −0.1(t + 2.874) ). The estimate of the instantaneous rate of total mortality ( Z ) was 0.24. Empirically derived estimates of natural mortality were similar to total mortality estimates suggesting that fishing mortality is low.

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.