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Trophic ecology of Mustelus schmitti (Springer, 1939) in a nursery area of northern Patagonia
Abstract
Mustelus schmitti is an endangered endemic shark of the southwest Atlantic, and an important economical resource in Argentina, Brazil and Uruguay. The objective of this study was to describe the trophic ecology of M. schmitti in Anegada Bay, its feeding strategy and diet composition, along with the possible dietary shifts, due to season, sex, ontogeny and the different geographical features of the bay. Our results show that M. schmitti is a carnivorous opportunistic predator, feeding on a variety of benthic invertebrates. The diet presented seasonal and ontogenetic variations, while no differences in diet composition were observed between sexes or the different sampling sites. This species behave as a generalize feeder, with a wide trophic spectrum and a diverse diet.Research highlights► Mustelus schmitti is an opportunistic predator, feeding on a variety of benthic invertebrates. ► The species uses a generalized feeding strategy. ► Diet was influenced by season and individuals' maturity stage. ► Neohelice granulata and polychaete were the principal component of the smoothhound's diet.
... This area, covering approximately 45,000 km 2 , is the main fishing ground for the industrial fleets targeting this shark [29]. The literature on M. schmitti from the authors of this article alone covers reproduction, trophic ecology, age and growth, and metabolic dynamics [26,[30][31][32][33][34], ...
... The parameter values used as input in the model were specified based on research and experimental results (most of them published in [15,26,30,31,33,34,[50][51][52]) or from literaturereported results on closely related species. The individual processes and parameters are described below. ...
... All rates except the caloric conversion rate between prey and shark (CAL p /CAL s , unitless) are in the units of grams prey/gram shark/day (g prey × g shark −1 × d −1 ). M. schmitti caloric density was set to be 1294 cal × g shark −1 , based on calorimetric determinations (Molina, unpublished data); 1100 and 991 cal/g prey −1 was used for the prey, either polychaetes or crabs [30]. ...
Bioenergetic models are tools that allow the evaluation of the effect of environmental variables on fish growth. Successful implementation of this approach has been achieved in a few elasmobranch species. Our objective was to develop a bioenergetic model for Mustelus schmitti. The model developed showed a good fit to the field data available and accurately described the growth of this species. The practical example developed in this study provides novel population estimates of prey consumption and daily ration for the species. Results also indicate that this species would be susceptible to the effects of climate change. In the simulated climate change scenarios, the energy budget of M. schmitti was significantly altered, with increased food consumption and impaired growth. While there exists a number of limitations for the model developed in this article, namely its limitation to immature individuals, and its restricted temperature model, it provides an important tool for the management of this and other shark populations under heavy exploitation.
... Larger juveniles found in spring suggest that the young of the year remain in Anegada Bay all year long, as happen in other protected areas for other species of elasmobranches inhabiting Bahía Blanca estuary, Río de la Plata estuary and Anegada Bay(Lopez Cazorla, 1987; Jaureguizar et al., 2003; Colautti et al., 2010;Molina and Lopez Cazorla, 2011), while adults of M. goodie enter the bay during spring and summer. By means of the GSI values it can be inferred that the mating and spawning season for M. goodei in Anegada Bay may ocur in summer, although a complete series of GSI values for a complete year would be needed to accuratedly demostrate this. ...
... It is then likely that the differences found in the diet of M. goodei are due to prey assemblage differences between studies rather than active selection by the predator. Such phenomena have been suggested for M. schmitti in Anegada Bay byMolina and Lopez Cazorla (2011) and for other elasmobranches byBarry et al. (2008). ...
... Information on seasonal availability of benthic invertebrates is lacking for the study area, and would be needed to test this assumption. If so, the seasonal differences observed might represent ontogenetic shifts in the diet, as have been reported for other elasmobranches(Bethea et al., 2007; Chiaramonte and Pettovello, 2000, Lucifora et al., 2006, 2009Molina and Lopez Cazorla, 2011).Trophic level of M. goodie in Anegada Bay (TL:3.2) constitutes the first reference for this species, characterizing it as a secondary consumer. For direct comparison, TL was estimated from feeding ecology data of this species presented by Ruocco (2012), obtaining a TL of 3.3. ...
Chondrichthyans play an important role in structuring marine communities. Myliobatis goodie is an eagle ray reported from South Carolina in USA (35°N) to Santa Cuz, Argentina (44°S), however little is known about this species, which is considered Data Deficient by the IUCN. In order to create adequate management strategies for this species, biological information is sorely needed. The objective of this study was to describe the biology of the population of M. goodei and its relationships with season, sex and the geographic features of Anegada Bay, Argentina (from 39.96°S to 40.60°S and from 62.10°W to 62.46°W) during 2008. Specifically, the population structure of M. goodie was studied by sex, seasons and sites, its food habits by seasons and sites, and the reproductive biology by seasons and sex. The results show that M. goodei exhibits seasonal migrations. Young-of-the-year remain in the bay all year long, while adults enter during spring and summer. Juveniles in spring are likely to become first-time mating individuals that migrate into open sea at the end of summer. These individuals would return to give birth for the first time and mate for the second time during the next year at summer. Anegada Bay would then be a mating and nursery area for the species. M. goodei behave as a generalist feeder with a uniform diet composed mainly of bivalves. Seasonal differences in the diet found arise from differences in prey diversity between summer and spring. Spatial differences, however, arise from the different abundances of caprelids and bivalves. Trophic level was 3.2 and it constitutes the first reference for this species, characterizing it as a secondary consumer.
... Debido a la situación de explotación comercial y tendencias poblacionales observadas durante el pasado en la región del Atlántico Sudoccidental (ASO), el tiburón gatuzo ha sido incluido en la Lista Roja de la Unión Internacional para la Conservación de la Naturaleza (UICN) como especie Amenazada 1989199519992003 Las características biológicas de M. schmitti en cuanto a su reproducción, estructura poblacional (Cousseau 1986, Massa 1998 Mustelus schmitti es considerado un mesopredador generalista con un amplio espectro trófico. Se alimenta principalmente de crustáceos (en su mayoría decápodos), peces y poliquetos, existiendo cambios dietarios con diferencias en la proporción de sus presas en relación con variaciones geográficas, ontogenéticas y de la talla (Molina y Cazorla 2011, Bellegia et al. 2012). ...
... , Sidders et al. 2005, Cortes y Massa 2006, Pereyra et al. 2008, Colautti et al. 2010, Cortes et al. 2011, Cortes 2012, Elisio et al. 2016) y alimentación(Molina y Cazorla 2011, Bellegia et al. 2012) han sido descriptas para diferentes zonas de su rango de distribución en el ASO. ...
En el presente trabajo se estudiaron las características de historia de vida en cuanto a edad, crecimiento, longevidad y talla-edad de madurez del Tiburón gatuzo, Mustelus schmitti, en el Golfo San Matías, Argentina. La edad y crecimiento fueron calculadas a partir de la lectura de bandas en secciones vertebrales evaluando cinco modelos de crecimiento. El rango de tallas registrado en los muestreos de los desembarques comerciales fue de 37 y 89 cm de longitud total (LT) para machos y entre 39 y 106 cm para hembras. Las edades observadas fueron entre 1 a 15 años para machos y 1 a 21 años para hembras. El modelo de von Bertalanffy de 2 fases para ambos sexos juntos fue seleccionado como el más adecuado según el ajuste estadístico y el criterio biológico, estimándose los siguientes parámetros: edad a la talla cero t0= -3,56 años (talla de nacimiento L0= 35,7cm); talla asintótica L∞= 103,12cm; y coeficiente de crecimiento K= 0,12 años-1. La longevidad estimada fue de 21 años. Los machos y hembras maduran a una edad y talla media similar de 5,6 años y LT50% de 66,9 cm. No se encontraron diferencias entre sexos en las curvas de crecimiento. Este estudio contribuye al conocimiento de las características de historia de vida de la especie en el sur del Atlántico sudoccidental (ASO) reportando que M. schmitti tiene un crecimiento moderado, es una de las especies más longevas dentro del género y tiene una edad media de madurez temprana que representa aproximadamente un cuarto de la longevidad estimada.
... Debido a la situación de explotación comercial y tendencias poblacionales observadas durante el pasado en la región del Atlántico Sudoccidental (ASO), el tiburón gatuzo ha sido incluido en la Lista Roja de la Unión Internacional para la Conservación de la Naturaleza (UICN) como especie Amenazada 1989199519992003 Las características biológicas de M. schmitti en cuanto a su reproducción, estructura poblacional (Cousseau 1986, Massa 1998 Mustelus schmitti es considerado un mesopredador generalista con un amplio espectro trófico. Se alimenta principalmente de crustáceos (en su mayoría decápodos), peces y poliquetos, existiendo cambios dietarios con diferencias en la proporción de sus presas en relación con variaciones geográficas, ontogenéticas y de la talla (Molina y Cazorla 2011, Bellegia et al. 2012). ...
... , Sidders et al. 2005, Cortes y Massa 2006, Pereyra et al. 2008, Colautti et al. 2010, Cortes et al. 2011, Cortes 2012, Elisio et al. 2016) y alimentación(Molina y Cazorla 2011, Bellegia et al. 2012) han sido descriptas para diferentes zonas de su rango de distribución en el ASO. ...
Conocer los parámetros de historia de vida de las diferentes especies de condrictios es uno de los principales requisitos para evaluar el estado de sus poblaciones y su vulnerabilidad a la explotación pesquera. En este trabajo se estudiaron las características de historia de vida en cuanto a edad, crecimiento, madurez, longevidad y mortalidad de tres especies de condrictios pertenecientes a diferentes grupos taxonómicos y capturadas frecuentemente en el Golfo San Matías: el pez gallo Callorhinchus callorynchus (Holocephali), el tiburón gatuzo Mustelus schmitti (Selachii) y la raya ojona Atlantoraja cyclophora (Batoidea). Los ejemplares analizados de cada una de las especies se obtuvieron de diferentes fuentes: campañas de investigación pesquera anuales realizadas entre los años 2004-2007, muestreos de desembarques de la flota comercial y a bordo durante los periodos 2005-2009 y 2011-2012. La edad y crecimiento fueron calculadas a partir de la lectura de secciones vertebrales para el caso del gatuzo y la raya ojona evaluando cinco modelos de crecimiento. En cambio, para el pez gallo se evaluaron dos metodologías: la interpretación de marcas de crecimiento en la espina de la primer aleta dorsal y el análisis de estructura de tallas.
The knowledge of the chondrichthyans life history traits is one of the most important issuess for the stock assessments and to know their vulnerability to the fisheries. In this thesis the life history traits of age, growth, maturity, longevity and mortality of three chondrichthyans species from different taxonomy groups and caught frequently in the San Matías gulf were studied. The species were: the elephant fish Callorhinchus callorynchus (Holocephali), the shark narrownose smoothhound Mustelus schmitti (Selachii) and the eyespot skate Atlantoraja cyclophora (Batoidea).
The specimens analyzed were obtained from three different sources: annual fishery research cruises during 2004-2007, landings samplings of commercial fleet and on-board samplings between 2005-2009 and 2011-2012. The age and growth of the narrownose smooth-hound shark and eyespot skate were estimate from growth bands counts in vertebral sections and fit to five growth models. Instead, for the elephant fish two methodologies were evaluate to study growth, the age readings (growth bands counts) in the dorsal fin spine sections and the analysis of length frequency data.
... These shallow systems are well represented along the coastal areas of Patagonia and, particularly Anegada Bay, act as feeding and nursery grounds for both teleosts and cartilaginous fish (Lucifora, 2003;Lucifora et al., 2009a, b;Llompart, 2011;Molina & López Cazorla, 2011). Moreover, recreational and artisanal fisheries occur simultaneously in this bay Llompart et al., 2012). ...
... The neonates and juveniles of this species, however, because of food availability, persisted during the entire year until reaching sexual maturity . For this reason Anegada Bay should be considered a nursery area (Molina & López Cazorla, 2011). Moreover, certain authors have suggested that the concentration of C. guatucupa through seasonal migration into the coastal areas between November and April likewise occurs for reproduction (Cosseau et al., 1986;López Cazorla, 1996). ...
The seasonal variation of the inshore fish assemblage of Anegada Bay, North Patagonia, Argentina is described here. Three areas were seasonally sampled from 2007 to 2009 by means of a gang of bottom gill-nets. We found 21 coastal fish species, but species richness and fish number and weight changed throughout the year. The six species classified as dominant have national and regional value for artisanal and recreational fishing and were responsible for the seasonal variation in the fish assemblage. Both cluster and non-metric multidimensional scaling analyses based on fish number and fish weight indicated two major sample groups encompassing spring and summer (the warmer seasons) and autumn and winter (the colder seasons). The fish assemblage had higher species richness, dominance and abundance during the warmer seasons than during the colder seasons in the same years and at the same sites. Water temperature was the main environmental factor structuring the fish assemblage in Anegada Bay. We suggest that partial breeding migration toward the bay during warmer months could explain the seasonal pattern observed. Nevertheless, variation in temperature conditions agreed well with the pattern of seasonal changes, leading to an interaction between abiotic and biotic influences in determining the variability in this seasonal fish assemblage. We conclude that an understanding of species temporal and spatial patterns in areas of high ecological and economic value, as exemplified by Anegada Bay, are essential for the implementation of a management approach oriented toward ecosystem sustainability.
... Thus, M. schmitti was described as a carcinophagous species (Chiaramonte and Pettovello, 2000;Belleggia, 2012). The diet of this shark also includes polychaetes and fishes (Oliver et al., 1968;Menni et al., 1986;Capitoli et al., 1995;Chiaramonte and Pettovello, 2000;Van der Molen and Caille, 2001;Molina and Cazorla, 2011;Belleggia, 2012). Ontogenetic diet shifts have been observed in Northern and Southern Patagonia; the consumption of fishes and crustaceans increased as M. schmitti grew in size, whereas the consumption of polychaetes decreased (Chiaramonte and Pettovello, 2000;Belleggia et al., 2011). ...
The study compares the diet composition between juveniles and adults of the narrownose smooth-hound Mustelus schmitti in areas with and without commercial bottom trawling using stomach contents. Individuals (n = 291) were caught as by-catch by the bottom-trawl shrimp fishery and by coastal sport anglers in Central Patagonia (Southwestern Atlantic between 43° and 45° S). Results showed that M. schmitti is a mesocarnivorous with a mean trophic level of 3.58. The diet was based mostly on crustaceans (decapods, stomatopods, isopods and amphipods), polychaetes, fishes and cephalopods, in a decreasing order of importance. The diet varied between juveniles and adults, and between individuals captured by the trawling fishery and sport anglers. Crabs were the main prey item observed in the stomach of individuals caught by anglers while the shrimp Pleoticus muelleri was the most consumed prey by individuals caught as by-catch. Juveniles consumed more polychaetes than adults, while the latter consumed mostly shrimp. The presence of shrimp in stomach contents of M. schmitti caught by the commercial fishery is evidence of a trophic interaction between M. schmitti and the fishery. The interaction may be due to the shark and the fleet targeting the same resource, or due to the shark using the discarded shrimp as a food source.
... C. guatucupa is a demersal, estuarine-dependent fish and an important fishing resource (Sardiña and Lopez Cazorla, 2005b), juveniles spend their whole first year of life within the BBE since they use it a nursery and growing area (Sardiña and Lopez Cazorla, 2005b) and therefore they have been suggested as suitable bioindicators for PAHs (Recabarren-Villalón et al., 2019) and OCs (Lanfranchi et al., 2006) pollution. M. schmitti is a small shark, currently considered vulnerable by the International Union for Conservation of Nature (IUCN), and it is an important economical resource (Molina and Lopez Cazorla, 2011). M. schmitti has been suggested as a bioindicator for metal pollution in the BBE (Marcovecchio et al., 1991), identified as a nursery area for this species (Lopez Cazorla, 2004). ...
Polycyclic aromatic hydrocarbons (PAHs) are pollutants of global concern in coastal environments. They have a wide range of biological toxicity and due to their inherent properties, can easily bioaccumulate in organisms and concentrate in the environment. This work evaluated, in an integrated way, the seasonal PAH distribution patterns in sediments and four bioindicators fish species in a highly impacted estuary of Argentina; besides, their bioaccumulation patterns were assessed for the first time as indicator of ecological risk. The highest PAH levels in fish were found for Ramnogaster arcuata with an average of 64 ng g⁻¹ w.w., followed by Micropogonias furnieri (45 ng g⁻¹ w.w.), Cynoscion guatucupa (28 ng g⁻¹ w.w.), and Mustelus schmitti (16 ng g⁻¹ w.w.). Fish presented the highest PAH levels in fall with a predominance of petrogenic PAHs in colder seasons and pyrolytic PAHs in warmer seasons. Sediments presented an average of 233 ng g⁻¹ d.w. with the same seasonal composition pattern of the fish tissues. Additionally, the data suggested that the main source of PAHs are wastewater discharges. The bioaccumulation factor (BAF) of PAHs in the tested fishes were found to range from 0.3 to 8. The highest values were observed during fall and winter, while bioaccumulation did not occur in moist spring and summer samples, which would suggest a high biotransformation process during these seasons. Results suggested that class III of juvenile C. guatucupa and M. furnieri, and adults R. arcuata are more sensitive bioindicators of chronic PAH contamination and that their bioaccumulation is independent of the compound hydrophobicity; this could have a positively influence on the criteria used for biological monitoring programs along the Atlantic coast. In addition, the presented BAF data on the target species will serve as a useful pollution indicator for South Atlantic coastal fish.
... The availability of adequate food, suitable thermal and salinity ranges, and the oceanic circulation that favors a retention mechanism would facilitate fish larval recruitment and growth of valuable commercial species (Marrari et al. 2004;Delgado et al. 2015). Also, this area is essential for spawning, calving, and breeding of different emblematic species of the coastal fish complex (Molina and Lopez Cazorla 2011;Militelli et al. 2013). ...
The aim of this introductory chapter is to provide the readers some insight into the regional context of the Bahía Blanca Estuary. We begin this chapter with a description of the geological settings along the Atlantic coast of South America. Central to this issue is the evolution of the relative sea level during the Holocene, which shaped the landscape structure of major coastal wetland systems. Regarding the regional climate, central east Argentina is characterized by a large interannual rainfall variability and by a strong gradient of decreasing rainfall from the northeast to the southwest. Vegetation types along this area are strongly associated with the regional precipitation gradient, ranging from grasslands in the northeast to xerophytic shrublands and bushy steppes in the southwest. In the marine realm, the Bahía Blanca Estuary belongs to the Large Marine Ecosystem called Patagonian Shelf, characterized by the extensive mixing of the Malvinas and the Brazil Currents. El Rincón, in the coastal zone off the Bahía Blanca Estuary, is a highly productive area due to the occurrence of elevated densities of fish and zooplankton. The availability of adequate food, suitable thermal and salinity ranges, and the oceanic circulation that favors a retention mechanism would facilitate fish larval recruitment and growth of valuable commercial species.
... En este sentido, Cortés et al. (2011) sugieren que debido a las características de vida del gatuzo la selección de áreas nursery se debería principalmente a la mayor disponibilidad de alimento (opción 2), lo que le permitiría maximizar la tasa de crecimiento y alcanzar más rápidamente la madurez sexual. Al respecto, un análisis de la disponibilidad de alimento y dieta de gatuzos de la Bahía demostró que la riqueza y diversidad de presas aumentan en la dieta desde neonatos hasta adultos (Molina & López Cazorla 2011). Estos autores también mencionan que el bajo número de estómagos vacíos en neonatos y juveniles y su dieta diferencial con respecto a los adultos sugieren que los primeros encuentran suficiente alimento dentro de la Bahía. ...
... M. schmitti was the sole cartilaginous fish species and occupied the highest trophic position within the fish species under analysis. M. schmitti is also the main exploited shark species in Argentina (Molina and Lopez Cazorla, 2011). With this in mind, the higher mean THg concentrations achieved could be the result, at least in part, of the anatomical, physiological and life-history characteristics that distinguish chondrichthyan fishes from teleosts. ...
This study evaluated-for the first time-the occurrence and distribution of total Hg in abiotic (dissolved and particulate water fractions) and biotic (gills and muscle tissues of six commercial fish species) compartments within a South American coastal environment with anthropogenic pressure. This study dealt with environmental issues on developing countries which, as they are in continuous growth, face the highest rate of coastal transformation. Total Hg content was determined by acid digestion and measured using a cold vapor atomic absorption spectrophotometer. Results revealed that dissolved Hg exceeded the recommended levels for superficial saline waters in 67% of the cases. Hg concentrations varied among fish species and its tissues. The results suggested that metal burden in fishes achieved a mean maximum accumulation towards the muscle, with concentrations below the international maximum permitted values. The estimated daily intakes calculated suggest that people would not experience significant health risks through fish consumption.
... Mustelus sharks as opportunistic predators are supported by other diet composition studies. For example, diet composition studies of M. mustelus (Linnaeus, 1758) ( Saïdi et al. 2009), M. punctulatus Risso, 1827 ( Lipej et al. 2011), M. schmitti Springer, 1939(Manuel Molina & Lopez Cazorla 2011), M. lunulatus Jordan & Gilbert, 1882(Moreno-Sánchez et al. 2012), and M. henlei ( Gill, 1863) ( Espinoza et al. 2012;Rodriguez-Romero et al. 2013) suggest crustaceans as preferred prey for Mustelus sharks, but variation in diet composition is high both within and between Mustelus species. Taxonomic richness in diet composition is often reported as being greater than 10 taxa, including in this study, and the second most important prey item, as indicated by %IRI values, varies widely. ...
Mustelus canis, one of two species in the genus Mustelus found along the Northwest Atlantic coast and the second most abundant shark in the region, is beginning to comprise large portions of by-catch in various commercial fishing industries. This study analysed the gut contents of sharks taken from three locations in Long Island, NY (Long Beach, Shelter Island and Gardiners Bay) to examine sex- and site-specific diet composition. Our study indicates that smooth dogfish in these waters are opportunistic predators, showing a preference for crustaceans (i.e. Cancer irroratus, Libinia spp., Squilla empusa and Upogebia affinis). Dietary niche breadth was found to vary significantly and niche overlap was moderately low between sexes and between sites. While dietary components of M. canis discovered in this study corroborate other studies performed within the Northwestern Atlantic migratory range of M. canis, smooth dogfish diet varies considerably with region and time of year. Thus, future studies should include surveys of distribution patterns for common prey items and studies of caloric components of these prey items.
... This would make the crab less suitable for mating and more vulnerable to physiological stress (including starvation and dehydration) and predation (including cannibalism which is common among individuals of this species). Neohelice granulata face an intense predation pressure from fishes and several birds, both with high developed sense of sight (Delhey et al., 2001;Molina & López Cazorla, 2011;Suárez et al., 2012). In this sense, the elevated contrast of colors derived from the presence of white barnacles growing over brown crabs that walk on dark substrate, might alert potential predators. ...
Neohelice (Chasmagnathus) granulata is an ecosystem engineer endemic of salt marshes and mudflats of the southwestern Atlantic coast, where several Patagonian salt marshes were invaded by the acorn barnacle Balanus glandula, a typical rocky shore species. In this work, we supply the first report of the occurrence of epibiosis of B. glandula on N. granulata in these salt marshes and we describe the major ecological features of this invader/native association in order to generate sound baseline for further investigations and management decisions. Our results show that barnacles are found in the entire dorsal and lateral surface of the crabs, and specially in vital zones such us the basal insertion of the chelipeds, walking appendages, ocular peduncles, jaws, mouth with the carapace. Furthermore, the size reached by barnacles suggest that they are sexually mature and can reproduce while fouling on the crabs, being the maximum size of barnacles tightly associated and determined by the duration of the crab's inter-molt span. Our results highlight the mechanisms by which an invasive rocky shore invader can exploit an unfavorable environment (i.e. mobile substratum) to persist on soft bottom systems.
... Mustelus schmitti Springer 1939, is a medium-small carchariniform shark that extends from Rio de Janeiro (Brazil) to Patagonia (Argentina). Due to its migratory habits, this shark is caught by different fishing fleets which affect different stages of its life cycle (Oddone et al., 2005;Molina and López Cazorla, 2011). Their stock decline, shrinking size of captures and decrease in the LT 50 is well documented (Massa and Hozbor, 2011). ...
This work provides information about the sexual commitment and the folliculogenesis of the gatuzo, Mustelus schmitti. A total of 112 females of all maturity stages were fished in the Bahía Blanca estuary, between 2009 and 2010. The oogonia were present throughout the life cycle of the animals. The folliculogenesis follows a pattern similar to other elasmobranchs. The granulosa layer keeps monolayered throughout the folliculogenesis, but with two cell types in the vitellogenic follicle. The zona pellucida forms in the primordial follicles. The thecal system shows a connective inner layer and a glandular outer sheath. The microscopic beginning of the sexual commitment, indicated by the vitello hoarding, takes place in follicles from 500 micrometres, while the macroscopic evidence appears in follicles of 2500-3000 micrometres. The results presented in this study suggest that the fishery pressure may affect a susceptible range of sizes of the species, not previously considered and provides a biological framework for the development of fisheries policy.
... In Brazil, the depth range extends down to 195 m (Heemstra 1997). Its diet consists mostly of crabs (Capitoli et al. 1995;Chiaramonte and Pettovello 2000;Molina and López Cazorla 2011), but polychaetes and fish could be the most important prey in some regions as the total length of the predator shifts (Belleggia et al. 2012). The specific goals of the present paper are (1) to provide a quantitative and qualitative analysis on the dentition of M. schmitti and (2) to estimate the tooth-replacement rate. ...
The present study provides a quantitative and qualitative analysis on the dentition of Mustelus schmitti, and estimates the tooth-replacement rate. In total, 47 males and 56 females of M. schmitti were collected on scientific trawl surveys conducted by the National Institute of Fisheries Research and Development (INIDEP) in Argentina during the months of November 2007, November 2008 and December 2008. The dental laminas were extracted from the jaw cartilage and attached to onionskin paper for dehydration treatment, maintaining the original jaw position. Tooth replacement rate was estimated following established methods used for fossil sharks, instead of the established technique of clipping teeth, based on the premise that tooth length within each row decreases from the lingual to the labial side of the jaw as a consequence of wear. The length difference between consecutive teeth in four representative rows should be proportional to the tooth-replacement rate. Mustelus schmitti exhibited homodont dentition, where teeth were similar in shape or design, and are arranged in a semi-pavement-like dentition. The dental formula was 47-63/50-63 for juveniles and 50-77/50-69 for adult specimens. The estimated mean replacement rate was 4 days series–1.
... En este sentido, las presas están condicionadas por el estilo de vida del depredador, pues generalmente los tiburones oceánicos depredan principalmente sobre cefalópodos (Stilwell & Casey, 1976;Smale, 1991;Vaske-Junior & Rincón-Filho, 1998;Aguilar-Castro, 2003;Cabrera, 2003;Estupiñán-Montaño et al., 2009;Vaske-Junior et al., 2009;Markaida & Sosa, 2010;Preti et al., 2012), mientras que tiburones de hábitos bénticos, costeros y demersales de las familias Triakidae, Heterodontidae y Squalidae, así como las rayas de las familias Dasyatidae, Rhinobatidae, Urotrygonidae, Rajidae, entre otras y algunos géneros de Carcharhinidae o especies pequeñas de Sphyrnidae, se alimentan en gran parte de crustáceos y/o moluscos (Lyle, 1983(Lyle, , 1987Menni, 1985;Pedersen, 1995;Ellis et al., 1996;Orlov, 1998;Muto et al., 2001;Valadez-González, 2001;Koen-Alonso et al., 2002;Kyne & Bennett, 2002;Navia, , 2009Gómez et al., 2003;Mabragaña & Giberto, 2007;Cabrera-Chávez-Costa et al., 2010;Bornatowski et al., 2010;Bethea et al., 2011;Drymon et al., 2011;Marion et al., 2011;Molina & Cazorla, 2011;Payán et al., 2011;Valls et al., 2011;Bellegia et al., 2012; e incluso de poliquetos (Brickle et al., 2003;Ebert & Cowley, 2003;Mabragaña & Giberto, 2007;Flóres-Ortega et al., 2011;. ...
... Therefore , Brazilian sharpnose shark fisheries can be sustainable when management strategies are provided ( And - rade et al . , 2008 ; Molina and Cazorla , 2011 ) . In addition , small sharks can respond relatively rapidly to reductions in populations of their predators if the relaxation of predation rates is not offset by fisheries - induced mortality . ...
Stomach contents of 175 Brazilian sharpnose sharks, Rhizoprionodon lalandii, were examined to assess their feeding habits. Caught by artisanal fishers between June 2006 and July of 2007 at Ipanema Beach, on the central coast of the state of Paraná, southern Brazil, R. lalandii appears to be piscivorous (89.7% IRI), feeding mainly on families of Clupeidae (5.1% IRI) and Sciaenidae (3.7% IRI) and secondarily on squid Lolliguncula brevis (8.6% IRI). Diets were similar between sexes and seasons. However, there were ontogenetic changes in their diets. The major items for neonates were Penaeidae crustaceans (%IRI = 56.4) and Engraulidae fishes (%IRI = 29.3); for the juveniles, Sciaenidae (%IRI = 62.5) and Clupeidae (%IRI = 19.7), and for adults Clupeidae (%IRI = 45.8) and Sciaenidae (%IRI = 15.9). Only neonate sharks consumed crustaceans, whereas all size classes consumed cephalopods and teleosts. Neonates had the lowest trophic level (TR = 3.8), with the diet of juveniles and adults the highest (TR = 4.2). Given its abundance and diet, R. lalandii may be an important predator of demersal and pelagic prey in coastal waters of Brazil.
... On the other hand, Rhizoprionodon species may have a greater recovery potential, due to be smaller, early maturing (2.6 years for R. lalandii, see Lessa et al., 2009), relatively short-live inshore coastal species (Stevens et al., 2000;Lessa et al., 2009;Froese and Pauly, 2011). Therefore, Brazilian sharpnose shark fisheries can be sustainable when management strategies are provided (Andrade et al., 2008;Molina and Cazorla, 2011). In addition, small sharks can respond relatively rapidly to reductions in populations of their predators if the relaxation of predation rates is not offset by fisheries-induced mortality. ...
Resumo: O cação-frango Rhizoprionodon lalandii é um dos principais elasmobrânquios capturados por pescarias artesanais ao longo da costa brasileira. Entre junho/2006 e julho/ 2007 foram observados desembarques pesqueiros em uma comunidade pesqueira artesanal do balneário de Ipanema, costa central do Paraná. Exemplares do cação-frango Rhizoprionodon lalandii foram obtidos para estudos de limentação e reprodução. Esta espécie apresentou uma dieta generalista, consumindo presas pelágicas e demersais, basicamente peixes das famílias Sciaenidae e Clupeidae, e lula Lolliguncula brevis. Não ouveram diferenças entre os sexos e sazonais. No entanto, diferenças ontogenéticas foram detectadas. Somente neonatos consumiram crustáceos, enquanto que todas as classes consumiram cefalópodes e teleósteos. Através da sua dieta generalizada, R. lalandii possivelmente seja um predador importante de presas pelágicas e demersais em áreas costeiras do Brasil. Para estudos de reprodução, um total de 211 exemplares foi estudado, sendo representado por 119 fêmeas e 92 machos. O tamanho de maturidade para machos e fêmeas foi estimado em 58,2 e 60,6 de comprimento total (cm) respectivamente. Dados indicam um período gestacional de 10 a 12 meses, sendo que o parto ocorre entre os meses de setembro e novembro, com indivíduos com aproximadamente 31 cm de comprimento total. Os resultados do resente trabalho indicam que R. lalandii possui todo ciclo de vida em água costeiras, sugerindo a costa paranaense como um berçário primário e secundário. Medidas de gestão e ordenamento pesqueiro são de alta prioridade para a conservação dessa espécie e outros elasmobrânquios.
We assessed the trophic roles of 13 medium-sized elasmobranchs in central Patagonia (41°-47°S) by identifying their interspecific relationships and trophic overlap using stomach contents and δ ¹⁵ N and δ ¹³ C values. We also conducted a literature review of the available diet information for Argentina. Specimens were collected from the bycatch of the Patagonian red shrimp Pleoticus muelleri trawling fishery and from the sport coastal fishing in areas without trawling. Results showed spatial differences in the diet composition of species between capture sites and from those previous diets reported for Argentina. Trophic levels assessment showed a group of top predators (TP ~ 4) and mesopredators (TP ~ 3.5). Beyond these differences, there was a dietary overlap among almost all elasmobranch species mainly related to the consumption of P. muelleri , an item which had not been reported as a significant prey for several of the studied species. This consumption may be due to the change in prey supply produced by local fisheries' discards and/or to the increased abundance of crustaceans in Central Patagonia during the last decade. These findings underscore the importance of continually updating trophic information in a scenario of global change to contribute with scientific evidence to the development of adaptative management.
In this chapter we summarize the current state of knowledge regarding the assemblages of fish species inhabiting the waters of Bahía Blanca Estuary. We begin by exploring the diversity of habitats and resources available for fish species and then describe the different guilds of fish present in the estuary, based on historical data collections and current biological surveys. A list of the species of each guild and a brief description of the key biological features, such as habitat, distribution, reproduction, and feeding habits of each species, is given. Spatial and temporal fluctuations in species composition within the estuary are described. We conclude this chapter with a section dedicated to the challenges that fish species are subject to in the Anthropocene and the temporal fluctuations in species composition within the estuary in the last 30 years. The chapter concludes with a text box that deals with the artisanal fishery that operates within the estuary and that has been subjected to various degrees of pressure from the industrial fleet operating in open waters outside the boundaries of the estuary. This chapter highlights the astounding abundance and diversity of fish living in this estuary and the pressing need to ensure their conservation.
The feeding habits and trophic ecology of Mustelus lunulatus and Mustelus henlei in the central coast of the Colombian Pacific were evaluated and compared to determine whether there was trophic niche overlap or resource partitioning between these two sympatric shark species. A total of 59 prey items were identified and grouped into 10 taxonomic categories. Mustelus lunulatus fed in large proportion on Stomatopoda and Brachyura, whereas M. henlei fed almost exclusively on Teleostei. Dendrobranchiata, Cephalopoda, Anomura and Polychaeta complemented the diets of both species. There were significant differences in diet between the two species, and there was an ontogenetic diet shift in Mustelus lunulatus,with Stomatopoda being the main prey item of juveniles and Brachyura the main prey item of adults. Dietary overlap (by sex and size) was low between species, but it was high for each species, with significant overlap between juveniles and adults of M. lunulatus and M. henlei, and between males and females of M. henlei. There were differences in the trophic levels of the species, sexes and sizes. This study suggests there is food resource partitioning, and differing ecological function of the two Mustelus species in the food web of the study area.
The reproductive biology of M. schmitti collected from the commercial bottom trawl fishery operating in Puerto Quequén, Argentina is investigated in the present study. The specimens were sampled seasonally during 2003–2004. The number of sharks collected was 637 (298 males and 339 females), including 190 pregnant females with 1,103 embryos. Size ranges for males were 419 – 819 mm total length (LT) and 417 – 951 mm LT for females. Total length and body weight relationship was different between sexes (P<0.05). In contrast, embryos did not show differences between sexes (P>0.05). Size frequency shows that females attain larger length and weight than males. Fifty percent (50%) of maturity size shows that males mature at a lower LT (567 mm) than females (598 mm). The left testis reached larger weight and length than the right one (P<0.01). Average values of the IG and IH per season varied significantly for males and females (P<0.05). Average values of the white and yellow ova per season showed significant differences (P<0.05). The maximum diameter of the left oviducal gland was greater than the right one (P<0.05) and both exhibit seasonal changes (P<0.05). At greater LT the females had more embryos per brood (P<0.01) than bigger puppies (P>0.05).
The relationship of body weight and total length (L(T)) of Mustelus schmitti in southern Patagonia was different between sexes. Changes in maturity stages in males appear at larger sizes in Ria Deseado specimens than in the Mar del Plata area. Mature females ranged from 795 to 913 mm while all male specimens >759 mm L(T) were mature. The data suggest that mating occurs before parturition, with simultaneous ovulation. The diet of adult M. schmitti was mainly carcinophage and the diet of young-of-the-year and adults differed. The young-of-the-year use the Ria Deseado as a pupping area.
The shark species Carcharhinus brachyurus, C. obscurus and Sphyrna zygaena, which attain more than 2 m when adult, occur in coastal waters of the Southern Cape as juveniles. They use these coastal waters as nursery areas and their relative abundance there varies through the year, possibly because of seasonally varying oceanographic conditions. Adult C. brachyurus occur in the same geographic area but usually deeper, although there is some overlap in juvenile and adult depth ranges. Adult C. obscurus prefer the warmer subtropical and tropical waters north of the study area. Adult S. zygaena are found over deep reefs at the edge of the continental shelf. There was considerable dietary overlap between the three species, the prey of all three being dominated by small schooling fish, such as pilchard, and squid. For the three species, animals of total length >2 m took larger prey, such as elasmobranchs, with greater frequency, although they continued to prey on squid and schooling fish. It is postulated that the nursery areas are in the study area because of the abundance of food there, and that avoidance of cannibalism would be enhanced by the use of such nurseries.
The morphology of a submarine dune field developed in a tidal inlet that connects the Argentinean
continental shelf with Anegada Bay (southern Buenos Aires province) was studied. The sediment circulation
was inferred from the differential displacements of the bedforms evaluated by comparing consecutive
surveys. An echosounder and a Phase Measuring Bathymetric System (PMBS) called GeoSwath were used to obtain a detailed submarine morphology. Large dunes, with heights between 4.5 and 5.0 m and from 100 to 120 m separating them, were present near the southern limit of the dune field at 24 m depth. These dunes
move towards the outer part of the channel at a speed of 18 to 75 m year-1. At the northern end of the dune
field, at 21 m depth, the dunes are smaller, being 2.0 to 2.5 m in height and separated by 40 to 80 m. The
smaller dunes move towards the interior of Anegada Bay at 18 to 36 m year-1. The distribution of the water
flow in the entire water column was obtained through a perpendicular profile of the channel by means of an
ADCP. Maximum current speeds were 2 m s-1, and were found during flood tide. The results obtained indicate a circulatory transport model of sedimentary sands, with the formation of ebb and flood deltas at both ends of the deep inlet throat, which lacks of unconsolidated sediments.
The impact of fishing on chondrichthyan stocks around the world is currently the focus of considerable international concern. Most chondrichthyan populations are of low productivity relative to teleost fishes, a consequence of their different life-history strategies. This is reflected in the poor record of sustainability of target shark fisheries. Most sharks and some batoids are predators at, or near, the top of marine food webs. The effects of fishing are examined at the single-species level and through trophic interactions. We summarize the status of chondrichthyan fisheries from around the world. Some 50% of the estimated global catch of chondrichthyans is taken as by-catch, does not appear in official fishery statistics, and is almost totally unmanaged. When taken as by-catch, they are often subjected to high fishing mortality directed at teleost target species. Consequently, some skates, sawfish, and deep-water dogfish have been virtually extirpated From large regions. Some chondrichthyans are more resilient to fishing and we examine predictions on the vulnerability of different species based on their life-history and population parameters. At the species level, fishing may alter size structure and population parameters in response to changes in species abundance. We review the evidence for such density-dependent change. Fishing can affect trophic interactions and we examine cases of apparent species replacement and shifts in community composition. Sharks and rays learn to associate trawlers with food and feeding on discards may increase their populations. Using ECOSIM, we make some predictions about the long-term response of ecosystems to fishing on sharks. Three different environments are analysed: a tropical shelf ecosystem in Venezuela, a Hawaiian coral reef ecosystem, and a North Pacific oceanic ecosystem. (C) 2000 International Council for the Exploration of the Sea.
The smooth-hound Mustelus schmitti is a commercially important and common target shark inhabiting the southwestern Atlantic coastal system and is usually found in shallow waters. Using experimental and artisanal fishing records, we assessed seasonal biological and demographic characteristics related to fishing of the smooth-hound and its potential impact on this species. We found that after birth, juveniles remain in Anegada Bay until sexual maturity. The young adults mate in spring and then leave the bay in summer. The older adults come back to the bay in early spring to give birth, and mate and finally return to the open sea in late spring. This pattern suggests that the bay acts as a seasonal nursery and reproductive area. This species represents 95% of the fishery captures in this bay, although the fishery is highly seasonal. The average harvest during the years 2003–2008 was 164tons, which represented only 2% of the total Argentinean smooth-hound landings. Fishing effort in the bay can be considered moderate due to the narrow time window and the use of selective gear that prevents the capture of juveniles. Future research should be directed at developing management plans at a broader regional scale to allow the recovery of M. schmitti stocks under heavy fishing pressure in other fishing areas.
The foraging ecology of the school shark Galeorhinus galeus was studied in Anegada Bay, Argentina, during the seasonal occurrence of this species in Argentinean waters (October to April) from 1998 to 2001. Of the 408 individuals examined, 168 (41.2%) had food remains in their stomachs. The proportion of individuals with food remains was negatively correlated with total length. In general, the diet was composed mainly of teleosts (98.5 % IRI [index of relative importance]), with invertebrates and chondrichthyans as minor prey. The diet varied ontogenetically and seasonally. Juveniles and adults differed in their consumption of invertebrates, with juveniles preying more on benthic invertebrates, mainly the octopus Octopus tehuelchus, and adults on squid. From December to February, adults preyed mainly on benthic teleosts (almost exclusively the Atlantic midshipman Porichthys porosissimus), while from March to April the consumption of squid increased. A comparison of numbers of prey in stomachs with abundance of prey in the environment in March and April showed that, in these months, juveniles selected invertebrates and demersal teleosts and avoided pelagic teleosts and chondricthyan prey, and adults selected squid and avoided pelagic teleosts. This indicates that, during this period, G. galeus is not an opportunistic predator. The mean size of prey increased with increasing shark length, but even large sharks consumed small prey. All shark sizes consumed prey fragments that were significantly larger than other prey consumed whole. This indicates that G. galeus is able to overcome gape limitation by mutilating prey, and that the ontogenetic diet shift was not due to a change in the ability to seize prey.
Sharks may have an important role in marine ecosystems in relation to populations of fish and invertebrates at lower trophic levels. Fishery management plans stress the need for an ecosystem approach, but few quantitative studies on the foraging ecology of sharks have been published. Stomach contents and catch data of early life stages of Atlantic sharpnose Rhizoprionodon terraenovae, blacktip Carcharhinus limbatus, finetooth Carcharhinus isodon, and spinner sharks Carcharhinus brevipinna taken from fishery independent surveys in Apalachicola Bay, Florida, USA, were examined to test for overlap in resource use. Young-of-the-year Atlantic sharpnose sharks were found to feed mainly on shrimp, juveniles on sciaenids, and adults on clupeids. Young-of-the-year blacktip sharks were found to feed mainly on sciaenids, whereas juveniles fed on clupeids. The primary prey of young-of-the-year and juvenile finetooth and spinner sharks was clupeids. Eight of 10 prey size-selectivity tests showed neutral selection. Compared to relative prey sizes published for teleost piscivores, Atlantic sharpnose and finetooth sharks consume relatively small-sized prey while blacktip sharks consume relatively large prey. Regardless of maturity state and species, diet overlap was high for species-life stage combinations that are similar in size; however, species-life stages did not show significant habitat overlap. Prey categories shared by similar-sized species may not be limiting, although shark species may have alleviated competition pressure by partitioning the resource of time or space.
We utilized a long-term data base collected over a broad geographic range to examine predator size - prey size relationships for 18 species of marine fish predators from continental shelf waters off the northeast US coast. Regression analysis was used to illustrate interspecific variation in ontogenetic patterns of prey size use, gape allometries, and ratio-based trophic niche breadths. Size- based feeding strategies were assessed through comparison of frequency distributions of relative prey sizes eaten and were related to general predator feeding tactics and gape morphology. The results demonstrated that the range of prey sizes eaten expanded with increasing predator body size for each of the marine predators examined, leading to asymmetric predator size - prey size distribu- tions. Absolute maximum prey size and slopes of maximum prey size versus predator size varied widely among predator taxa. Distinct size-based feeding strategies were evident, as diets of some predators were dominated by prey that were 10 to 20% of predator size, whereas other predators frequently consumed prey >50% of predator size. Gape sizes and allometric relationships with body size were also diverse among predators and often were closely associated with maximum prey sizes. Ratio-based trophic-niche breadths generally did not expand with predator ontogeny and tended to narrow for the largest predators, which may be common for animal taxa.
Using real data sets of elasmobranch fishes as examples, this paper presents a critical review of selected methods and statistical approaches used in fish feeding studies and makes recommendations on the application of such methodology. The percent index of relative importance is proposed as a standardized measure in dietary analyses, and a three-dimensional graphical representation of the diet is introduced. Multiway contingency table (log-linear) analysis is recommended to test for dietary variations. Caution is advised when using rank correlation to study dietary overlap and parametric tests when stomach content data do not satisfy parametric assumptions. Sampling gear type, experimental design, and statistical tests can affect results on diel feeding chronology, and stomach content weights do not suffice to interpret diel feeding chronology. On the basis of sampling requirements and model assumptions, the Diana and Olson-Mullen methods appear to be the most appropriate approaches for estimating daily ration in sharks. Use of resampling techniques is highly desirable because they provide a measure of the error in daily ration estimates. Using several criteria to evaluate the best-fitting model of gastric evacuation in fishes is also strongly advocated. Overall, increased consolidation of methods and analyses is recommended to facilitate comparative studies.
Reproduction and feeding habits of Mustelus dorsalis (Pisces: Triakidae) in the Gulf of Nicoya, Costa Rica: Elements for a sustainable management. A total of 311 sharptooth smooth-hound Mustelus dor� salis were collected in the Gulf of Nicoya, Costa Rica from March 1999 to May 2000 to determine reproduction and feeding habits. The fishes were collected using hook and line. 250 females and 61 males were identified. The females are bigger (550-660 mm) and heavier (400-1 000 g) than males (500-585 mm and 200-300 g, respectively). All samples collected were mature and the minimum length to first maturity observed is 500 and 541 mm for females and males, respectively. From September to March individuals were mature, while samples caught during April and August were immature. A total of 1 259 embryos were analyzed. Number of embryos per liter ranged from two to six, the total length is from 130 to 205 mm and the weight from 6 to 35 g. This shark is a polyphagous opportunistic carnivore that preys on crustaceans ( Squilla hancocki, S. parva, Litopenaeus sp.), fishes (Anchoa sp., Caranx sp., Lutjanus sp., Engraulis sp.) and mollusks (Loligo sp. and Octopus sp.). Main prey item was S. hancocki. The presence of mature sharks of both sexes along the year and the consumption of food items associated to shallow coastal rocky waters suggest that this sector of Nicoya Gulf is a nursery ground and an essential habitat. Based on these results the establishment of an integral management plan is proposed. Rev. Biol. Trop. 54 (3): 861-871. Epub 2006 Sept. 29.
Theoretical models of coastal shark populations have remained largely unchanged since the 1960s despite limitations in applicability to many species. Smaller bodied coastal species are poorly represented by the current models. A new theoretical model is proposed to represent those species that spend most or all of their life within nearshore waters but do not show use of discrete nursery areas. Description of this new model outlines the importance of nearshore areas to these smaller species. While all coastal shark populations are susceptible to environmental and anthropogenic impacts, species that fit the new model are more vulnerable to varying coastal processes, habitat degradation, and fishing pressure than are species that use nearshore areas for only part of their life-span. The dynamic nature of nearshore areas and their proximity to human populations present all sharks that occur in them with a range of advantages and disadvantages. This paper reviews how different species utilise nearshore areas and how they overcome the challenges they face in inhabiting these areas. Improving and expanding theoretical models of coastal shark populations will provide a better understanding of how sharks use nearshore environments and assist in making conservation and management decisions for these regions.
Feeding habits of blackmouth catshark Galeus melastomus and velvet belly lantern shark Etmopterus spinax were studied throughout the Spanish Mediterranean, from the Alboran Sea to the Gulf of Lion, between 400 and 790 m depth. Diets were studied taking into account size and depth differences. Included within the trophic guild of non-migratory macroplankton feeders, both species preferably exploited mesopelagic resources (mainly natantian decapods, euphausiids, mesopelagic fish and cephalopods). G. melastomus mostly preyed on decapod crustaceans (46% in terms of IRI), with cephalopods, euphausiids and mesopelagic fish as a secondary prey item. The diet of E. spinax was composed primarily of mesopelagic fish (61.4% in terms of IRI), with decapod crustaceans and cephalopods of secondary importance. Both species showed ontogenetic changes in their diets: small blackmouth catshark specimens (between 150 and 350 mm total length) mainly consumed cephalopods, medium size individuals (351–450 mm TL) consumed decapod crustaceans, while larger specimens (larger than 451 mm TL) seemed to be more generalist-feeders. Smaller specimens of E. spinax (150–250 mm TL) mostly fed on small crustaceans and cephalopods, whilst an increase in the consumption of mesopelagic fish (mycthophids and Stomiiformes) was detected in larger individuals (251–450 mm TL). Diet of G. melastomus also changed throughout the narrow depth range explored, mainly consumed euphausiids and mesopelagic fish between 400 and 500 m depth, whilst preferably exploiting natantian decapods and cephalopods below 500 m of depth. However, this trend may be correlated to the larger-deeper trend found for this species. Slight but not significant differences were found in E. spinax diet by depth, with euphausiids mainly consumed at lower depths (400–500 m). In a multispecies MDS analysis, diets of G. melastomus and E. spinax were separated and the anosim test proved evidence for significant differences in the diets of the two species (R = 0.25; P = 0.05), mainly attributed to the stronger pelagic habits of E. spinax in comparison with G. melastomus. Low overlap (by Schoener Index) also occurred when comparing specimens of the same size range. In general, the higher occurrence of benthic prey in the diet of G. melastomus (i.e. the brachyuran crab Geryon longipes, the thalassinid shrimp Calocaris macandrae) than in E. spinax pointed to a stronger pelagic behavior for the velvet belly lantern shark. Both multivariate analysis and the Levins Index pointed to a narrow niche breadth for the two sharks. A trend of increasing fullness was found for both species in the highly productive areas of the Alboran Sea and Vera Gulf, probably related to higher resource availability, enhanced by local upwellings.
The diet of the smooth-hound shark, Mustelus mustelus, from the Gulf of Gabès (southern Tunisia, central Mediterranean Sea) was investigated with respect to fish size and season. Stomach contents were analyzed from 540 specimens with total lengths ranging from 34 to 158.5 cm. Of the total number of stomachs examined, 63 were empty (11.67%). Smooth-hound shark fed mainly on crustaceans, fishes and cephalopods. Sipunculids, polychaetes and echinoderms were occasional preys. No differences were found between the diets of males and females. Ontogenetic changes in diet of M. mustelus were apparent, with crustaceans forming a greater proportion of the diet of smaller sharks. Both teleosts and molluscs increased in importance with increasing shark size. Consumptions of polycheates, sipunculids and echinoderms were not related to predator size. Prey diversity also increased with size, with large and mobile prey species found more commonly in the diet of larger sharks. The limited overlap in the dietary compositions of juveniles, subadults and adults suggests the possibility of resource partitioning. Seasonality in food habits was in accordance with the dynamics of the predator and the prey species.
This study analyses the seasonal fisheries and sexual proportion of the narrownose smooth-hound Mustelus schmitti from the Uruguayan oceanic coast. The maximum catches took place during the fall. Of a total of 2105 individuals, 1483 were males and 622 females, being females larger than males. Females were dominant at maximum depths of 50 m (inner shelf), whereas males occupied major depths of 50 m (outer shelf). The great proportion of mature females on the inner shelf during spring and summer, and mature males in summer are related to the mating, ovulation and delivery time as previously proposed for this shark in this area. The length in which 50% of the females were retained was below or on the length of sexual maturity of the narrownose smooth-hound, indicating that these are more affected by the fishing activity. Nevertheless, an important fraction of the population that distributes on the inner and outer shelf during the time of parturition, ovulation and mating would be protected in spring and summer by the establishment of fishing bans of the fishes Cynoscion guatucupa and Merluccius hubbsi.
The Bahía Anegada is the coastal zone of the southern part of Buenos Aires Province (Argentina), where several environments are recognized: islands, inlets, marshes, tidal plains and different types of beaches. The Bahía San Blas is located at the southern part of the Bahía Anegada, where the San Blas channel separates the mainland from an island (Fig. 1). The San Blas channel is 2.5 km wide and 12 km long. The study area has a tidal amplitude characterized by a mean of 1.62 m, being 2.20 and 0.58 m the high and low tide respectively. The present study shows the results of a bathymetric survey of the San Blas channel and an analysis of the behavior of the tidal currents that affect sediment transport and promote the generation of different bedforms. The aim of this study was to analyze the submarine geomorphology related to the dynamic conditions in order to characterize in detail the sedimentary conditions in this area. A detailed bathymetric study was conducted over a zone of 50 km2, covering the San Blas channel, through a digital echosounder Bathy-500 positioned by DGPS operating in real time. Fifteen transversal tracks and three longitudinal tracks were made at the San Blas channel in order to obtain the necessary bathymetric profiles to make a bathymetric chart of the area. Over a zone of 1.5 km2, characterized by a field of subaqueous dunes, a Phase Measuring Bathymetric System (FMBS), called swath bathymetry system "GeoSwath Plus" from GeoAcoustics Lt. (UK), was employed in order to determine the detailed dune morphology. This survey yielded details and disposition of the bedforms present on the channel bed with centimetric precision. Bottom sediment samples were collected and tidal currents were measured using an Acoustic Doppler Current Profiler (ADCP) mounted on a ship. The tidal currents were measured during a whole tidal cycle, obtaining the distribution of velocity and direction over the water column, on a track carried out transversally to the channel. These values were computed with the associated WinRiver software. The entire field work (bathymetry, sampling, FMBS and ADCP) was performed with the 6.5 m long boat IADO IV. The coastal features display geomorphological differences in response to a changing dynamic regimen along the channel (Fig. 2). Remarkable morphological and textural differences occur along the coast. Close to the mouth, a dissipative beach, with medium sand and a gentle slope is present. Mobile coastal dunes are common crowning the beach. Nearly the central part, the beach is steeper and composed of gravels developing then a reflective beach. Towards the north, in the inner part of the Bahía Anegada (north of Punta Ramirez), wave-cut platforms and marshes covered with Spartina alterniflora appear, sheltered by cliffs formed by deposits from the Río Negro Formation. The bathymetric map allows distinguishing the existence of significant changes in the morphology throughout the San Blas channel. Based on these differences, the area was divided into 4 zones (Fig. 3), each one with distinctive profiles (Fig. 4). Zones I and II are characterized by a 28 m-depth flat bottom, free of unconsolidated sediments and with steep flanks. These features allow establishing an analogy with a tidal throat. A subaqueous dune field, covering an area of more than 1.5 km2, was found in Zone III. Zone IV is a shallow area where sand bars are exposed during low tide. The dune field was characterized by large dunes, with spacing between 40-80 m and heights of 2.5 m, identified at 21 m depth (Fig. 5). Higher dunes occur in deeper zones, reaching values of 4.5-5 m height at around 24 m depths. Most of the subaqueous dunes located on the southern portion of the dune field exhibit a symmetrical cross section and are covered by smaller bedforms of 0.3-1 m high and 0.7 to 0.9 m of spacing. On the other hand, dunes located on the northern side of the field are asymmetrical, with the steeper side towards the inner part of the channel. The mean grain size in the field dune is between medium and coarse sand (1.8 a 0.28 phi) that is in equilibrium with the strong velocities of tidal currents. The results obtained from the current measurements over a tidal cycle show that maximum velocities measured in the San Blas channel reached 2 m s-1 during flood and 1.8 m s-1 during ebb (Fig. 6). The maximum velocities of the flood currents were attained mainly on the northern flank and central part of the channel almost reaching the bottom. On the other hand, the maximum velocities of the ebb currents were found on the deepest site of the profile, on the southern flank, from mid-water up to the surface. At both ends of the channel, sand accumulates due to the reduction in the carrying capacity which leads to the formation of an ebb and a flood tidal deltas. The sand bars exposed in low tide in the inward shallow part in the Anegada Bay is the tidal flood delta formed by the loss in the sediment transport capacity caused by the widening of the channel section. This unconsolidated granular sediment is available to be transported by the tidal currents. Towards the outer part of the channel, the bathymetric map shows shallower depths while nautical charts confirm the presence of submarine bars at the entrance of the San Blas channel (Fig. 7). These bars might be evidence of the occurrence of an ebb tidal delta. The present study allowed concluding that the San Blas channel is a narrow strait between the mainland and an island, connecting the Anegada Bay with the outer sea and showing different submarine topography. Towards the mouth, the channel presents a flat bottom over 80% of its width, showing a U shape. The bottom is free of unconsolidated sediments due to the strong currents that wash away any loose material. The submarine topography of the San Blas channel corresponds very well with the tidal inlet significance.
The diet, feeding strategy, and dentition of the Patagonian skate, Bathyraja macloviana, on the northern continental shelf of Argentina were studied from specimens collected during research cruises in September
and October 2001. Of a total of 81 stomachs examined, only 3.7% were empty. Cumulative prey curves showed that sample sizes
were adequate to describe the main prey items of the diet. Quantitative analysis, a graphical method, and trophic niche breadth
indicated the species to be a specialized feeder. The most important prey items were polychaetes, followed by gammarid amphipods,
isopods, and crabs. Cumaceans, ophiuroids, and hydrozoans were likely incidentally consumed by mature females. Sexual dimorphism
in dentition was observed; mature males had longer and sharper tooth cusps than females or immature males. However, there
was a high degree of dietary overlap between mature males and mature females, indicating that dental sexual dimorphism in
the species is more important in reproductive behaviour than in differential prey consumption.
Stomach contents and vertebrae from neonate and juvenile blacktip sharks Carcharhinus limbatus (n= 334) were examined to describe their diet, feeding patterns and growth within the Timbalier–Terrebone Bay complex, LA, U.S.A. In the study area, both neonate and juvenile C. limbatus feed primarily on gulf menhaden Brevoortia patronus. However, based on the index of relative importance (IRI), gulf menhaden constituted a larger portion of the diet of neonates (84·05 %IRI) than for juveniles (47·91 %IRI). An increase in the index of relative fullness between the afternoon and dusk time intervals and a large decrease in the percentage of empty stomachs between the night and early morning time intervals suggested that these fish exhibited a diel feeding pattern with crepuscular periods being the times of highest feeding activity. A higher percentage of empty stomachs (neonates 68% and juveniles 39%) and a significantly lower growth rate (age 0+ year C. limbatus, 0·62 mm day−1; age 1+ year fish, 0·89 mm day−1) could indicate that neonate C. limbatus are less efficient predators than older conspecifics.
Nonparametric multivariate analysis of ecological data using permutation tests has two main challenges: (1) to partition the variability in the data according to a complex design or model, as is often required in ecological experiments, and (2) to base the analysis on a multivariate distance measure (such as the semimetric Bray-Curtis measure) that is reasonable for ecological data sets. Previous nonparametric methods have succeeded in one or other of these areas, but not in both. A recent contribution to Ecological Monographs by Legendre and Anderson, called distance-based redundancy analysis (db-RDA), does achieve both. It does this by calculating principal coordinates and subsequently correcting for negative eigenvalues, if they are present, by adding a constant to squared distances. We show here that such a correction is not necessary. Partitioning can be achieved directly from the distance matrix itself, with no corrections and no eigenanalysis, even if the distance measure used is semimetric. An ecological example is given to show the differences in these statistical methods. Empirical simulations, based on parameters estimated from real ecological species abundance data, showed that db-RDA done on multifactorial designs (using the correction) does not have type 1 error consistent with the significance level chosen for the analysis (i.e., does not provide an exact test), whereas the direct method described and advocated here does.
Sexual segregation occurs when members of a species separate such that the sexes live apart, either singly or in single‐sex groups. It can be broadly categorised into two types: habitat segregation and social segregation. Sexual segregation is a behavioural phenomenon that is widespread in the animal kingdom yet the underlying causes remain poorly understood. Sexual segregation has been widely studied among terrestrial mammals such as ungulates, but it has been less well documented in the marine environment. This chapter clarifies terms and concepts which have emerged from the investigation of sexual segregation in terrestrial ecology and examines how a similar methodological approach may be complicated by differences of marine species. Here we discuss the behavioural patterns of sexual segregation among marine fish, reptile, bird and mammal species. Five hypotheses have been forwarded to account for sexual segregation, largely emerging from investigation of sexual segregation in terrestrial ungulates: the predation risk, forage selection, activity budget, thermal niche–fecundity and social factors hypotheses. These mechanisms are reviewed following careful assessment of their applicability to marine vertebrate species and case studies of marine vertebrates which support each mechanism recounted. Rigorous testing of all hypotheses is lacking from both the terrestrial and marine vertebrate literature and those analyses which have been attempted are often confounded by factors such as sexual body‐size dimorphism. In this context, we indicate the value of studying model species which are monomorphic with respect to body size and discuss possible underlying causes for sexual segregation in this species. We also discuss why it is important to understand sexual segregation, for example, by illustrating how differential exploitation of the sexes by humans can lead to population decline.
Aspects of the life history and biology of two sympatric coastal shark species (Mustelus mustelus and M. palumbes) off southern Africa are described and compared. Free-swimming male M. mustelus measured 390-1 450 mm total length (TL), whereas females were recorded up to 1 650 mm TL. Most specimens of both sexes were found at depths shallower than 100 m. Males mature at 950-1 300 mm TL and females at 1 250-1 400 mm TL. Reproduction is seasonal, and each cycle may take one year or longer, if there is a resting period between pregnancies. Litter size was correlated with female size and varied between 2 and 23. The largest embryo measured 425 mm TL. The hepatosomatic indices were negatively correlated to embryo length in both species. Prey was dominated by crustaceans, although cephalopods became important in larger M. mustelus. There was a good relationship between prey size and fish size. Free swimming malé M. palumbes measured 275-1 008 mm TL, whereas females were recorded up to 1 126 mm TL. M. palumbes males were most often taken from 100-180 m deep and females from 60-140 m. Males mature at 750-850 mm TL and females at 800-100 mm TL. Reproduction appears to be aseasonal in M. palumbes and litters of 3-15 young were recorded, with larger females having larger litters. The largest embryo recorded measured 340 mm TL. The timing of reproductive cycles could not be established, but a high proportion of non-pregnant females suggests that there may be a resting period following pregnancy. Crustaceans were the dominant prey type recorded, although larger prèdators ate a wider variety of prey types than smaller individuals. Although there was overlap in the prey taken by the two shark species, the composition of the diet was strongly influenced by the prey available in different habitats.
The concept of elasmobranch species using nursery areas was introduced in the early 1900s and has been an accepted aspect of shark biology and behavior for several decades. Despite several descriptions of how shark species use nursery areas and what types of regions nurseries may be found in, no explicit definition of what constitutes a shark nursery area has been presented. Here we evaluate the assumptions of the current shark nursery paradigm in light of available data. Based on examination of these assumptions and available methods of quantifying and accurately describing shark nursery areas, a new more quantitative definition of shark nursery areas is proposed. This definition requires 3 criteria to be met for an area to be identified as a nursery: (1) sharks are more commonly encountered in the area than other areas; (2) sharks have a tendency to remain or return for extended periods; and (3) the area or habitat is repeatedly used across years. These criteria make the definition of shark nursery areas more compatible with those for other aquatic species. The improved definition of this concept will provide more valuable information for fisheries managers and shark biologists.
The food habits of 595 houndsharks of four species, Triakis scyllium (n = 179, 42–148 cm total in length), Hemitriakis japanica (n = 57, 42–102 cm), Mustelus griseus (n = 193, 39–100 cm), and Mustelus manazo (n = 166, 43–120 cm), found in the central Seto Inland Sea, Japan, from March 1997 to October 1999 and May 2000 to July 2002, were studied. T. scyllium changed their main food items from shrimps to echiuran worms then to cephalopods with their growth. Comparing food habits by the value of similarity (maximum = 1), the small-sized T. scyllium had a low value (0.17) compared to larger sharks. T. scyllium gradually increased the diversity of food until it reached 700 mm long in total length, however, after that it decreased. H. japanica appeared mainly in summer and autumn and ate cephalopods and fishes. M. griseus preyed on various crustaceans and decreased the diversity of food with growth. M. manazo preferred crustaceans and polychaetes. There was no certain tendency in the diversity of the food habit for M. manazo.
Throughout 1 year, from October 2003 to September 2004, 88 visits to the landing site of a small urban fishery (APREBAN) in Rio de Janeiro city were conducted and 816 specimens of Rhizoprionodon lalandii were analysed. The sample, mostly females, was composed of two cohorts: young-of-the-year were abundant in spring and summer and adults predominated in autumn and winter. Gravid females were most abundant from April to June, whereas post-partum females composed most of the catch in August to September. Adult males were present all year although were more abundant between February and July. No neonates were captured during the study and most embryos collected measured slightly below the reported total length (LT) at time of birth (L0) for the species, suggesting that parturition may occur slightly outside the main fishing grounds or that neonates were not captured in commercial gillnets set at this time of the year. The mean LT at maturity (LT50) for males was 578 mm and females matured between 620 and 660 mm, although a precise estimate of LT50 for females could not be determined. The total length (LT) and total mass (MT) relationship was calculated for both sexes and showed no significant differences. The mean condition factor increased steadily from February to July followed by a steep decrease in values relative to females in August and September, suggesting a pupping season. The present study area can be classified as a coastal juvenile habitat and a probable mating ground for R. lalandii.
The relationship of body weight and total length (LT) of Mustelus schmitti in southern Patagonia was different between sexes. Changes in maturity stages in males appear at larger sizes in Ría Deseado specimens than in the Mar del Plata area. Mature females ranged from 795 to 913 mm while all male specimens >759 mm LT were mature. The data suggest that mating occurs before parturition, with simultaneous ovulation. The diet of adult M. schmitti was mainly carcinophage and the diet of young-of-the-year and adults differed. The young-of-the-year use the Ría Deseado as a pupping area.
Stomach contents were examined from 936 individuals of Mustelus manazo, collected by trawl at five locations: Aomori, Tokyo Bay, Maizuru and Shimonoseki in Japan, and one location off Taiwan. The vacuity index was relatively low (0–6.1%). Based on three indices (%W, %F, RI), the major dietary component was crustaceans at all locations. The most important prey category was crabs in Aomori, Shimonosei and Taiwan, mantis shrimps in Tokyo Bay, and shrimps in Maizuru. Fishes were a minor food category for M. manazo in most locations, except in Maizuru where fishes were second in importance in the diet. Dietary overlap revealed a medium degree of overlap between Tokyo Bay and Aomori, and between Tokyo Bay and Shimonoseki. The other locations showed a high degree of overlap with each other. Significant ontogenetic dietary shifts were found in Tokyo Bay, Maizuru and Taiwan, and prey diversity showed a trend being relatively low in larger size classes. The feeding habit of M. manazo was unique in Tokyo Bay, where crustaceans in the muddy substrata were taken in preference to the most abundant benthic prey item available, such as a southern rough shrimp, Trachypenaeus curvirostris. Mustelus manazo appears to use two feeding strategies based upon stomach contents. One, in Tokyo Bay, involved the digging up or removing of burrowing invertebrates from muddy substrata without crushing them. The other, at the other four locations, involved the crushing of prey on the substrata surface.
The use of a highly selective fishing gear is the main reason for mature individual dominance in the Patagonian smoothhound (Mustelus schmitti Springer, 1939) artisanal fishery in Punta del Diablo, Uruguay. Differences in length–weight relationships (LWR) and size at 50% maturity (L50) within its distribution were also expected. A total of 696 M. schmitti specimens (281 females; 415 males) were examined between July 2005 and October 2006. Length-frequency distribution (LFD) presented a peak at 660 mm total length (L) in both sexes, with females significantly larger in size than males. LWR was W = 1.36E−7 × L3.51 for females and W = 5.12E−6 × L2.93 in males. Of the captured females, 67% were mature, whereas 85% of captured males were mature. The smallest mature females and males were 455 and 495 mm L, respectively; largest immature females and males were 680 and 670 mm L. L50 and the confidence intervals (CI) were 597 mm (577–616) and 566 mm (553–580) for females and males, respectively. These figures are similar to those obtained from other populations in the area (34–41° S), although the L50 values were different from the Uruguayan outer shelf and populations further south. Fecundity ranged from 1 to 14 embryos per female (average = 6; SD = 3) and was positively correlated with female L. The results were compared with previous works comprising most of this species’ latitudinal distribution. This is the first research showing results of M. schmitti bottom-fixed gill-net artisanal fisheries. Different from industrial catches, this type of gear results in catches composed mainly of mature individuals (>80%), thus constituting an adequate scenario for sustainability of this endangered resource.
