Morphometric and gonad maturity in the spider crab "Maja brahcydactyla". A comparison of methods for the estimation of the size at maturity in species with determinate growth

[Abstract] Ontogenetic changes in the relative growth of males and females of the spider crab Maja brachydactyla, a species with terminal moult and determinate growth, were analyzed and related to their reproductive (maturity) status. Sampling was carried out in the Ría de A Coruña (NW Spain) from December 1997 to November 1999. A combination of principal component analysis of morphometric variables, nonhierarchical K-means cluster and discriminant analysis allowed to differentiate two morphometric groups of males defined as juvenile and adult phases and develop statistical methods to assign maturity status to individual crabs. A significant change in allometry of cheliped size was detected in juvenile males with a breakpoint at 96.2 mm carapace length (CL), separating the inmature and adolescent phases. Histological analysis of males showed that more than 60% of morphometrically juveniles and 100% of morphometrically adults presented spermatophores in the gonad. Size at gonad maturity in males (estimated as CL50) was 96.2 mm CL. Size at morphometric maturity was estimated comparing two methodologies: the size at 50% maturity (CL50) and the median size of adult cohorts. For the whole sampling period, two adult-year classes, CL50 was estimated to be 136.5 mm for males and 130.3 mm for females, while median size of adult cohorts for the same period was estimated to be 139.9 mm for males and 148.7 mm for females. In all cases the size at maturity obtained from the median of the cohort was greater than the one resulting from the CL50 method with differences of over 20 mm, showing the bias that methods based in CL50 could cause in animals with determinate growth. Due the spatial segregation of adults and juveniles and the availability of morphological and morphometrical methods to estimate the maturity status of any crab, we propose a combination of spatial closures and direct protection of juvenile habitat as management strategies alternative to minimum landing sizesXunta de Galicia; XUGA10301B97Ministerio de Ciencia y Tecnología; REN2000-0446MA

Estacionalidad de la muda terminal y la migración reproductiva en la centolla, "Maja brachydactyla" : evidencias de estrategias de apareamiento alternativas

[Resumen] Se analiza la temporalidad y sincronización de los procesos de muda terminal, maduración gonadal, acumulación de reservas energéticas y migración en la centolla, Maja brachydactyla, tanto a nivel individual como poblacional, y su variabilidad intra- e intersexual. Para explicar esta variabilidad en la temporalidad se plantean dos hipótesis: 1) hipótesis fisiológica: machos y hembras inician la migración cuando alcanzan un estado fisiológico adecuado (un nivel de reservas energéticas óptimo), y 2) hipótesis de oportunidades de apareamiento: la temporalidad de la migración trataría de maximizar las oportunidades de apareamiento y la calidad de las parejas. Nuestros resultados muestran que los machos llevan a cabo la muda terminal (con un pico en Julio) antes que las hembras (Agosto). En las hembras, el inicio de la madurez gonadal se produce entre dos y tres meses después de alcanzar la madurez morfométrica (a partir de Octubre), coincidiendo con el período previo y durante la migración de apareamiento a aguas profundas. El análisis de las espermatecas de las hembras primíparas reveló que en la zona somera no se producen prácticamente apareamientos, en el corredor migratorio se producen las primeras cópulas, y es en los deep mating grounds donde se producen probablemente la mayor parte de los apareamientos. En los machos la madurez gonadal se produce antes de la madurez morfométrica. El día promedio de inicio de migración obtenido para los machos fue el 8 de Octubre, mientras que para las hembras fue el 16 de Octubre, lo que confirma evidencias previas de un adelanto de los machos en el inicio de la migración. No se observaron diferencias en la condición fisiológica (índices de condición de músculo, gónada y hepatopáncreas) entre migradores y no migradores, lo que indica claramente que la hipótesis fisiológica no se cumple en esta especie, dado que incluso se capturó un mayor porcentaje de ejemplares en postmuda en el corredor migratorio que en aguas someras. La condición fisiológica mejoró con el tiempo en ambos sexos tanto en los ejemplares capturados en el área somera como en el corredor migratorio, y por tanto los ejemplares que migran primero lo hacen en peor condición fisiológica. Además, los migradores tempranos presentaron una talla media significativamente menor que los migradores tardíos. Nuestros resultados sugieren que la variabilidad intrapoblacional e intersexual estaría relacionada con diferentes estrategias reproductivas, y no con una limitación fisiológica. Así, los machos de peor calidad (y menor capacidad competitiva) deberían migrar al inicio de la temporada (antes o coordinadamente con las primeras hembras), mientras que los machos de alta calidad podrían retrasar la migración al momento en que sus reservas fueran máximas dado que podrían desplazar a los machos de baja calidad en los hábitats de apareamientoMinisterio de Ciencia y Tecnología; REN2000-0446MARXunta de Galicia; XUGA10301B9

Dynamics of the small-scale spatial structure of a local population of the spider crab, "Maja brachydactyla"

Presentado no Sixth International Crustacean Congress, University of Glasgow, Scotland, 18-22 July 200

Population dynamics of "Maja squinado" in the Ría de A Coruña (Galicia, NW Spain), using mark-recapture experiments

8th Colloquium Crustacea Decapoda Mediterranea, 2-6 September 2002, Corfu, Greec

Growth at moulth, intermoult period and moulting seasonality of the spider crab "Maja brachydactyla" : combining information from mark-recapture and experimental studies

[Abstract] An analysis of growth at moult (for both the prepubertal and terminal moults), moulting seasonality and the intermoult period in the spider crab Maja squinado in the Ría de A Coruña (NW Spain) was carried out based on a mark-recapture experiment. Crabs between 70 and 130 mm carapace length (CL) undergo a mean increase at moult of 32.4% from their pre-moult size. Generalised Linear Models (GLMs) were used to construct growth models, employing a combination of information from the mark-recapture study and other previous studies performed in both laboratory and extensive culture, to estimate the effects of the biological variables and the study method. No differences were found in the growth rate between males and females. However, the effects of the study method, the premoult CL and the interaction between them were significant. The smallest-sized crabs undergo a greater increase in size in the laboratory and culture studies, while the largest individuals undergo greater growth in the field. The mean intermoult period estimated for prepubertal moults in the field ranged from 50 to 86 days, which Corgos et al., GROWTH AT MOULT OF MAJA BRACHYDACTYLA is similar to the 84.7 days observed in the laboratory study. The 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 around 90 days, slightly lower than the value of 104 days obtained in the laboratory. The terminal moult took place generally in summer (June-September) both at sea as well as in culture experiments. The intermoult period of juveniles at sea was highly variable, and some of the specimens did not moult for more than 5 months.Ministerio de Ciencia y Tecnología; REN2000-0446MARXunta de Galicia; XUGA10301B9

Timing and seasonality of the onset of maturity, gonad maturation and mating in the spider crab "Maja squinado" : relationships with habitat use and social structure

Fifth International Crustacean Congress, 9-13 July 2001, University of Melbourne, AustraliaXunta de Galicia; XUGA10301B97Ministerio de Ciencia y Tecnología; REN2000-0446/MA

Movements of juvenile and adult spider crab ("Maja squinado") in the Ría da Coruña (NW Spain)

Presentado no Fifth Conference on Fish Telemetry held in Europe, 9-13 June 2003, Ustica, Palermo, Italy[Abstract] In August 2002, 12 juvenile and 12 adult (recently terminal moulted) spider crabs were tagged using ultrasonic pingers (Sonotronics, USA) in the Ría da Coruña (NW Spain). Both adults and juveniles were released in the same sandy shallow bottoms (5-10 m) in which they were caught. This area, as known from previous studies, is a typical juvenile area where juvenile spider crabs carry out their terminal moult before the autumn migration to deep bottoms. The tracking was carried out daily for a period of two weeks, although not all the crabs were located every day. Juvenile crabs were found to move small distances, performing non-directional movements near the coast, in protected areas up to 10 m deep. Two of the adult crabs performed small scale movements in the outer (more exposed) part of the estuary, at depths of up to 20 m. The rest of the adult crabs remained in the juvenile area, performing the same non-directional movements as the juveniles. Four male adult crabs were recaptured by commercial fisheries in the following months, three of them at more than 40 m deep, in the central channel of the estuary, probably while performing their seasonal descent migration. A female carrying eggs was recaptured in December near the coast, probably after carrying out both a descent and ascent migration.Ministerio de Ciencia y Tecnología; REN2000-0446/MA

Inter-specific comparative analysis of distribution and habitat use patterns of benthic decapod crustaceans in shallow waters

[Abstract] Coastal areas have been widely considered as nurseries for many marine species. New approaches to this concept take into account interactions among environmental variables and ecological variations related to geographical location, as well as complex life cycles of marine invertebrates. We present a comparative approach to assess the relevance of environmental variables on the determination of patterns of distribution and habitat use of benthic decapod species in coastal areas. We hypothesize that this approach allows us to infer processes originating these patterns and to identify the main habitat use models. An intensive fine-grain sampling design was used to take into account the environmental gradients occurring at different spatial scales (defined by substrate type, depth, exposure and geographical location) in a temperate oceanic bay (Ria de A Coruña, Spain). A high proportion of juveniles were found in most populations, but the results do not allow us to generalize the idea of coastal areas as potential nurseries, except for few species with a marked spatial segregation between juveniles and adults. Larval transport seems to be the main process regulating mesoscale distribution patterns, while microscale distribution responds to a complex interaction among different processes, i. e. habitat selection at settlement, differential mortality among habitats, post-settlement dispersal and ontogenetic habitat shifts. Sandy substrates showed low-diversity communities dominated by hermit crabs. In rocky bottoms, variability in spatial patterns was mostly related to substrate type and geographical location. Caridean shrimps showed higher densities on flat rock surfaces, with similar juvenile and adult patterns. Anomuran species occurred mainly on cobbles. Distribution patterns of brachyurans varied among species, but did not change greatly from juveniles to adultsMinisterio de Ciencia y Tecnología; REN2000 –0446MARMinisterio de Ciencia y Tecnología; REN2003-04816Xunta de Galicia; XUGA10301B9

Management strategies for sustainable invertebrate fisheries in coastal ecosystems of Galicia (NW Spain)

The original publication in avaliable at www. springerlink.comArtisanal coastal invertebrate fisheries in Galicia are socio-economically important and ecologically relevant. Their management, however, has been based on models of fish population dynamics appropriate for highly mobile demersal or pelagic resources and for industrial fisheries. These management systems focus on regulating fishing effort, but in coastal ecosystems activities that change or destruct key habitats may have a greater effect on population abundance than does fishing mortality. The Golfo Artabro was analysed as a representative example of a coastal ecosystem in Galicia, and the spider crab "Maja squinado" used as a model of an exploited coastal invertebrate, for which shallow coastal areas are key habitats for juvenile stages. The commercial legal gillnet fishery for the spider crab harvests adults during their reproductive migrations to deep waters and in their wintering habitats. Illegal fisheries operate in shallow waters. The annual rate of exploitation is higher to 90%, and lower to 10% of the primiparous females reproduce effectively at least once. A simple spatially-explicit cohort model was constructed to simulate the population dynamics of spider crab females. Yield- and egg-per-recruit analyses corresponding to different exploitation regimes were performed to compare management policies directed to control the fishing effort or to protect key habitats. It was found that the protection of juvenile habitats could allow increases in yield and reproductive effort higher than in the present system, with such protection based in the control of the fishing effort of the legal fishery. Additionally, there is an urgent need for alternative research and management strategies in artisanal coastal fisheries based on the implementation of a system of territorial use rights for fishers, the integration of the fishers into assessment and management processes, and the protection of key habitats (marine reserves) as a basic tool for the regulation of the fisheries.Xunta de Galicia; XUGA10301B9

Habitat diversity and postlarval benthic decapod crustacean assemblages in shallow waters of the Ría de A Coruña (NW Spain)

38th European Marine Biology Symposium, Aveiro (Portugal), 8-12 September 200