Juan Freire

Morphometry and Sexual Maturity in the Spider Crab Maja Squinado (Decapoda: Majidae) in Galicia, Spain

Ontogenetic changes in the relative growth of males and females of the spider crab Maja squinado were analyzed and related to their reproductive (maturity) status in order to define criteria to assign individuals to each growth phase. The sampling was carried out in two different areas of southern Galician waters, northwestern Spain, in shallow water ( 20 m) with soft bottoms (adult habitat). A Principal Component Analysis (PCA) of morphometric variables and a nonhierarchic K-means cluster of PCA scores differentiated two morphometric groups defined as juvenile and adult phases. A significant change in allometry of cheliped size was detected in juvenile males with a break point at a 109-mm carapace length (CL). This point may indicate a change in the relative growth of juveniles, separating the immature and adolescent phases. Histological analysis of a subsample of males showed that sperm were present in most adolescent crabs, but not in immature crabs. Bivariate morphometric linear discriminant functions allow for the identification of juvenile and adult males (classified previously by K-means cluster) with over 99% correct classification using CL and the length or height of the right cheliped. Carapace length at the onset of sexual maturity was estimated to be 132.7 mm (50% of adult males), although in a broad range, 112-165 mm, the size of juveniles and adults overlap. The life history of male spider crabs shows 3 phases differentiated by the relative growth rate of chelipeds separated by two 2 critical molts: prepubertal molt (immature-adolescent) determines a slight increase in allometry, and pubertal or terminal molt (adolescent-adult) determines an increase in the relative size and allometry of chelipeds and the onset of functional maturity. Females showed only 2 phases separated by the terminal molt. Growth of chelipeds in females showed no changes in allometry and was similar to juvenile males. Juvenile females presented a smaller relative width and a higher allometry of the abdomen with regard to adult females. Unlike juvenile females with a flat abdomen, adult females with a domed abdomen have well-developed pleopods, gonads, and seminal receptacles. Carapace length at the onset of sexual maturity was estimated to be 130.4 mm (50% of adult females). The range of overlap of the size of juveniles and adults (114-143 mm) was smaller than in males. The spider crab Maja squinado (Herbst) inhabits the Northeast Atlantic from the British Isles to Guinea and the Mediterranean Sea (de Kergariou, 1984; Le Foll, 1993). It is subject to an intense fishery, especially in the waters along the coast of the English Channel and Galicia, northwestern Spain. As for other species of the Majidae, the postlarval life history of Maja squinado consists of two main phases, growth and reproduction, which are separated by a terminal molt (Vernet-Cornubert, 1958; Hartnoll, 1963, 1978; Conan and Comeau, 1986; Comeau and Conan, 1992; Meyer, 1993; Gonzalez-Gurriaran et al., 1995; Freire et al., in press). The first morphometric study done on this species (Teissier, 1935) distinguished three main developmental phases in males, separated by two critical molts. In males, the most obvious morphological change throughout growth is the development of the chelipeds. This led morphometric studies to be based primarily on changes in relative growth rates, or allometric levels, of different variables measuring the size of the chelipeds. Females undergo changes in morphology and in the allometry of the width of the abdomen. Later, these changes in external morphology were used in growth and maturity studies of other species of the Majidae (Vernet-Cornubert, 1958; Hartnoll, 1978; Conan and Comeau, 1986). In studies carried out on other majids, the different phases of the life history and critical molts were based on morphological, morphometric, physiological (gonad maturation), and behavioral criteria (Fig. 1). In males, the first postlarval phase, known as immature or juvenile, gives rise to a second phase, known as prepubertal, juvenile, or adolescent, after a prepubertal, pubertal, or juvenile molt.

MIGRATORY PATTERNS OF FEMALE SPIDER CRABS MAJA SQUINADO DETECTED USING ELECTRONIC TAGS AND TELEMETRY

Abstract Migrations play a key role in the life history of the spider crab Maja squinado (Herbst, 1788) and affect fishery catches. Migrations involve important changes in depth and in the environment. Ultrasonic telemetry has a number of drawbacks due to the difficulties in the continuous tracking of crabs while they are moving to deep waters. The recent introduction of electronic data storage or archival tags permits continuous monitoring of depth and temperature in crabs habitat and reconstruction of the movement patterns using baseline data on habitat characteristics. On the Galician coast (NW Spain) we calibrated and used electronic tags as a tool to study spider crab migrations. In the summer of 1996, 17 crabs were tagged with both ultrasonic transmitters and electronic tags. Tracking was carried out discontinuously at intervals of approximately 1 wk. We obtained a recapture rate of approximately 70%. The information provided by telemetry and electronic tags indicates autumn migrations along the bathymetric gradients (from <10 m down to 100 m) within short periods (mean = 5.7 d, range = 1.3–13.6). During these movements crabs travel through habitats characterized by different temperatures and substrates. Bathymetric and oceanographic data as well as localisation records from the electronic tags make the reconstruction of the animal tracks possible.

New approaches to the behavioural ecology of decapod crustaceans using telemetry and electronic tags

Decapod crustaceans have complex life histories and behaviour in aspects such as foraging, mating and reproduction, moulting and growth, habitat selection and migration. New technologies have enabled us to use an individual, field-based approach to analyze these problems, although they have been less developed in decapods than in marine vertebrates. These new possibilities are discussed here mainly from a biological point of view. There is a brief review of previous applications of telemetry to analyze habitat selection, foraging behaviour, energetics, moulting site selection and migrations in decapods, and two case studies are discussed in more detail. The first one refers to the study of differences in habitat use and movement patterns in juveniles and adults of coastal species that show ontogenetic habitat shifts, related to differences in selective pressures affecting both life history stages (predation risk, and growth and reproduction optimization). The second case study is dedicated to the migratory patterns in spider crabs combining telemetry and electronic tags. Operational limitations in tracking make it impossible to get detailed information on movement patterns during migration, which in turn involve an important bathymetric gradient and a change in the oceanographic environment (mainly temperature). Monitoring depth and temperature in the immediate habitat of the animals, using electronic data storage tags recovered by the fishery, allow for movement patterns to be modeled using supplementary information on the topography and hydrography of the study area. This approach is being tested using both telemetry and electronic tags simultaneously.

HOW GENERAL IS THE CENTRAL-PERIPHERY DISTRIBUTION AMONG SEABIRD COLONIES? NEST SPATIAL PATTERN IN THE EUROPEAN SHAG

Abstract The central-periphery distribution model of nest dispersion suggests that nests located in the center of a colony are less accessible to predators and that birds breeding in the central area are of better physical quality and have greater reproductive success. Another hypothesis, the central-satellite distribution model, suggests that low-quality birds build their nests near those of high-quality pairs, which do not necessarily settle in the colonys center. Advantages of this type of association include increasing the opportunity for extra-pair copulation by low-quality females and increasing the potential for low-quality individuals to obtain a better breeding site or partner in the following season. Here we test these hypotheses on two colonies (Portelo and Faro) of the European Shag (Phalacrocorax aristotelis) on the Cíes Islands, Galicia, northwest Spain. Spatial distribution of pairs differing in quality was analyzed using residuals of reproductive success, eliminating the effect of physical quality of the nest site. A negative autocorrelation of these residuals between nests at short distances was detected for the Portelo colony. In Faro there was no evidence that nest distribution differed from a random distribution. Occupation of nest sites (measured as new nest or reoccupied nest) showed negative autocorrelation at short distances, implying that there was an association between new and reoccupied sites. These results demonstrate that nest distribution of European Shag colonies does not fit the central-periphery model, but rather corresponds to either the central-satellite model or to a random distribution. ¿Es Generalizable el Modelo Centro-Periferia a Todas las Colonias de Aves Marinas? Distribución Espacial de los Nidos en Phalacrocorax aristotelis Resumen. La distribución de los nidos en aves coloniales puede ser explicada por dos modelos. El modelo centro-periferia implica que las aves que crían en el centro de una colonia son menos accesibles a los depredadores, poseen una mejor condición y tienen un mayor éxito reproductivo. En cambio, el modelo centro-satélite sugiere que aves de baja calidad construyen sus nidos cerca de parejas de alta calidad para obtener ventajas como un mayor número de cópulas extrapareja por parte de hembras de baja calidad o un mejor sitio de cría o pareja en la siguiente estación de cría. En el presente estudio, nosotros contrastamos estos modelos con la distribución de la calidad de las parejas de Phalacrocorax aristotelis en dos colonias (Portelo y Faro) de las Islas Cíes situadas en Galicia, noroeste de España. Hemos utilizado como indicador de la calidad de la pareja los residuales del éxito reproductor, eliminando el efecto de la calidad del sitio de nido. En la colonia del Portelo se observó una correlación negativa entre la calidad de las parejas a una distancia menor de 4 m; en el Faro, en cambio, no hubo evidencias de una distribución diferente al azar. Además, se encontró una correlación espacial negativa entre los sitios de nido en los que se construyó un nido por primera vez y los sitios que fueron reocupados. En global, estos resultados muestran que la distribución de las colonias del P. aristotelis no corresponde al modelo centro-periferia, sino más bien al modelo centro-satélite o en todo caso, a una distribución al azar.

Population modelling of European shags ("Phalacrocorax aristotelis")at their southern limit: conservation implications

The European shag (Phalacrocorax aristotelis) population at Cies Islands (the most important breeding area in its southern limit) increased rapidly from 1986 to 1992, and afterwards the population suffered a slight decline. This study analyzed population data obtained from ringing recoveries and reproductive monitoring between 1993 and 1997. The reproductive success was highly variable and associated with adverse weather events. Adult survival rate was very low compared with other colonies, probably due to high accidental capture in gill-nets. In recent years, the fishing effort with gill-nets increased in the study area. Sensitivity analysis of parameters showed that the population is more affected by changes in adult survival than in reproductive success. When dynamic simulations were run with an increase in shag mortality of 5% above the present level, population extinction occurred in all simu- lations. In contrast, when a reduction of mortality of 5% was introduced in the simulations, the population increased in all cases. The main lines of action to study and protect this population should be: (1) ringing schemes to obtain better estimates of survival variability; (2) studies on the interaction of feeding areas and fishing vessels; (3) regulations on gill-netting; and (4) the incorpora- tion of population models as an adaptive management tool to synthesize assessment work and management scenarios. # 2002 Elsevier Science Ltd. All rights reserved.

EROD activity and stable isotopes in seabirds to disentangle marine food web contamination after the Prestige oil spill

In this study, we measured via surgical sampling hepatic EROD activity in yellow-legged gulls from oiled and unoiled colonies, 17 months after the Prestige oil spill. We also analyzed stable isotope composition in feathers of the biopsied gulls, in an attempt to monitor oil incorporation into marine food web. We found that yellow-legged gulls in oiled colonies were being exposed to remnant oil as shown by hepatic EROD activity levels. EROD activity was related to feeding habits of individual gulls with apparent consequences on delayed lethality. Capture-recapture analysis of biopsied gulls suggests that the surgery technique did not affect gull survival, giving support to this technique as a monitoring tool for oil exposure assessment. Our study highlights the combination of different veterinary, toxicological and ecological methodologies as a useful approach for the monitoring of exposure to remnant oil after a large oil spill.

Nephrops norvegicus in the Galician continental shelf (NW Spain): abundance and distribution

Abstract This paper examines the abundance and distribution of Nephrops norvegicus during 13 fishery survey cruises carried out between 1980 and 1991 on the Galician continental shelf (NW Spain). Average annual abundance values fluctuate between 3 and more than 90 specimens per 30 min tow, with the highest densities found between 100 and 200 m in the Mino to Fisterra area, and at over 200 m in the Fisterra to Estaca de Bares area. Catches of this species were very scarce in the area between Estaca and Ribadeo. Mapping of N. norvegicus distribution, carried out using geostatistical analysis techniques, points to the existence of patches ranging in size between 20 and 117 km in length in the different cruises, which are located in two major areas, off the Rias Baixas and north of Fisterra. Depth is not a determining factor of N. norvegicus abundance and distribution within the area under study. There is a coincidence, on a medium scale, between the presence of this species and areas having fine sediment (between 20 and 60% of fine fraction less than 62.5 μm) on the shelf, and the distribution was restricted to the area between Mino and Estaca.

GROWTH AT MOULT, INTERMOULT PERIOD, AND MOULTING SEASONALITY OF THE SPIDER CRAB MAJA BRACHYDACTYLA: COMBINING INFORMATION FROM MARK-RECAPTURE AND EXPERIMENTAL STUDIES

Abstract Growth at moult (for both the prepubertal and terminal moults), and moulting seasonality in the spider crab Maja brachydactyla in the Ría de A Coruña (NW Spain) was quantified within a mark-recapture experiment. Crabs 70-130 mm carapace length (CL) underwent a mean increase at moult of 32.4% from their pre-moult size, with no significant differences between sexes or moult types. Generalised Linear Models (GLMs) were used to construct growth models, employing a combination of information from the mark-recapture study and previous studies performed in laboratory and extensive culture to characterize driving factors. The first model revealed that study method growth did not differ between males and females. However, the effects of the study method (mark-recapture, laboratory, and extensive culture), the pre-moult CL and the interaction between them were significant. The smallest-sized crabs underwent a greater increase in size in the laboratory and culture studies, while the largest individuals underwent greater growth in the field. In the second model, the significant effects were pre-moult CL, moult type, and the interaction between the two variables, indicating that larger crabs showed higher growth rates in prepubertal moults. Mean intermoult period estimated for prepubertal moults in the field ranged 50-86 days, which was slightly lower than the 84.7 days observed in the laboratory. Prepubertal moults occurred primarily in spring and autumn in the field, while under culture conditions, the crabs moulted mainly in the spring. The intermoult period for terminal moults was estimated to be 90 days, slightly lower than the 104 days from the laboratory. The terminal moult took place generally in summer (June-September) both at sea as well as in culture. The intermoult period of juveniles at sea was highly variable, and some of the specimens did not moult for more than 5 months.

Nest Site Characteristics, Occupation and Breeding Success in the European Shag

Abstract The European Shag (Phalacrocorax aristotelis) breeds in a wide range of nest-sites depending on the locality, such as crevices under fallen rocks, open ground caves and open ledges on craggy cliffs. In this paper the habitat selection of shags breeding in cavities on the coastal slopes of Islas Cíes (Galicia, Northwest Iberian Peninsula) are examined. Shags selected sites with more lateral and overhead cover, with better drainage and with average visibility. In addition, sites where breeding was successful differed from unsuccessful sites. Nest-site characteristics especially affected the hatching success. In this colony, shags showed adaptive responses to site-quality variability. Thus, nest-site quality declined with density and with seasonal occupancy. Shag colonies seem to follow an ideal despotic distribution, where some individuals monopolize high quality sites and prevented other individuals from settling in the good sites. Further studies are required to assess the proximal mechanisms used for nest-site selection in this species.

TIMING AND SEASONALITY OF THE TERMINAL MOLT AND MATING MIGRATION IN THE SPIDER CRAB, MAJA BRACHYDACTYLA: EVIDENCE OF ALTERNATIVE MATING STRATEGIES

Abstract Timing and synchronization at individual and population levels of the processes related to the terminal molt, gonad maturation, accumulation of energy reserves and migration in the spider crab Maja brachydactyla are analyzed. Also, the intra and intersexual variability is established. Two hypotheses are tested to explain the temporal and population variability: (1) physiological hypothesis: males and females begin migration when they reach the appropriate physiological stage (the optimum level of energy reserves) and (2) mating opportunities hypothesis: the timing of the migration maximize mating opportunities and mate quality. Our results show that males carry out the terminal molt before females, the former having a peak in July and the latter in August. The onset of gonad maturity in females occurs between two and three months after they have reached morphometric maturity (starting in October), coinciding with the period prior to and during the mating migration to deep waters. In an analysis of the spermathecae of primiparous females, it was found that practically no mating activity occurred in shallow waters, whereas the first copulations took place in the migration corridor. However, probably most of the mating activity occurs in deep mating grounds. Males reached gonad maturity prior to morphometric maturity. No differences were observed in the physiological status (muscle, gonad and hepatopancreas relative mass) between migrating and nonmigrating crabs, which is a clear indication that the physiological hypothesis does not hold true for this species. A higher percentage of postmolt crabs were caught in the migration corridor than in shallow waters. The physiological condition improved over time in males and females in the specimens caught in the shallow area as well as in the migration corridor. Therefore, the crabs that start migrating first did so in poorer physiological condition. Moreover, the early migrators had a significantly lower mean size than the late migrators. Our results suggest that variability within populations and between sexes are related to the different reproductive strategies and not to a physiological limitation. Thus, the poor-quality males (with a reduced competitive ability) would migrate at the beginning of the season to maximize the mating opportunities that would not be feasible if they had to compete with the late migrators, which are larger in size and in better physiological condition. Sperm competition is not clear in M. brachydactyla, but all evidences point at last male preference for fertilization of eggs.