Chapter

Ecology and Biology of Fish Assemblages

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Abstract

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.

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... The Bahía Blanca estuary (BBE), located in the southwest Atlantic Ocean, is the second most important estuary in Argentina and was declared a Multiple Use Nature Reserve of international importance by the Convention on Wetlands (RAMSAR) in 2012 due to its highly productive habitat and capacity as a nursery ecosystem for many fish species (Molina et al., 2021). However, this estuarine ecosystem has well-documented environmental impacts due to anthropogenic activity. ...
... The estuary also constitutes an important nursery area for a wide range of valuable fish species with essential regional socio-economic value since it provides several ecosystem resources to the population. More than 30 fish species have been recorded in this area, with Ramnogaster arcuata being the main functional component of the ecosystem (Molina et al., 2021). Samplings at the three sites in the internal part of the BBE were performed during the late summer (March 2020) under daylight hours and tide conditions. ...
... Besides, R. arcuata is a food item for the stripped weakfish Cynoscion guatucupa and the flounder Paralichthys orbignyanus Ronda et al. Science of the Total Environment xxx (xxxx) 164715 (Lopez Cazorla and Forte, 2005;Molina et al., 2021), two of the most economically important fish species in the area. Therefore, knowing the behavior of this small pelagic fish concerning MPs in the environment will enable us to elucidate whether R. arcuata could be employed as a bioindicator of this emergent pollutant and finally to evaluate possible bioaccumulation and biomagnification mechanisms in the coastal food web. ...
Article
The presence of microplastics (MPs) in the fish gastrointestinal tract has been documented in several studies. However, it is unclear whether this ingestion is active or passive and whether it affects feeding activity in natural environments. In this study, three sites with different anthropogenic pressure were selected from the Bahia Blanca estuary, Argentina, and the small zooplanktivorous pelagic fish Ramnogaster arcuata was used to evaluate MP ingestion and its effect on specie's trophic activity. We analyzed the zooplanktonic composition, levels, and types of MPs in both the environment and the stomach contents of R. arcuata. Moreover, we assessed the trophic behavior of R. arcuata to determine electivity, stomach fullness, and vacuity indexes. The results showed that despite the availability of prey in the environment, 100 % of the specimens ingested MPs, and their levels and characteristics were different according to the site. Stomach contents at sites related to harbor activities presented the lowest MPs concentrations, most of them were paint fragments, with the smallest sizes and a low diversity of colors. The highest MP ingestions were found near the principal sewage discharge, being mostly microfibers, followed by microbeads, and with a greater variety of colors. Electivity indices showed that R. arcuata has a passive or active ingestion according to the size and shape of MPs. In addition, the lowest stomach fullness index and the highest vacuity index values were associated with the highest level of MP ingestion near the sewage discharge. Altogether, these results demonstrate a negative effect of MPs in the feeding activity of R. arcuata and help to elucidate some mechanisms by which these particles are ingested by a bioindicator fish used in South America.
... En el estuario de Bahía Blanca esta especie ingresa en primavera para parir y aparearse, alimentándose de las abundantes poblaciones de poliquetos y cangrejos. M. goodei se puede encontrar hasta abril (otoño) (Molina et al., 2021). ...
... El nivel trófico de M. goodei en Bahía Anegada (3,2) 12 lo caracteriza como consumidor secundario (Molina y López Cazorla, 2015). En Bahía Blanca, esta especie anádroma puede penetrar hasta la zona interna del estuario, regida por amplias variaciones de salinidad, accediendo a fuentes de alimento imposibles de alcanzar para otros depredadores bentónicos (Molina et al., 2021). En cuanto a la composición de la dieta de M. goodei, en Bahía Anegada esta especie depreda sobre crustáceos, bivalvos y poliquetos (Molina y López Cazorla, 2015). ...
... En el estuario de Bahía Blanca esta especie ingresa en primavera para parir y aparearse, alimentándose de las abundantes poblaciones de poliquetos y cangrejos. M. goodei se puede encontrar hasta abril (otoño) (Molina et al., 2021). ...
... El nivel trófico de M. goodei en Bahía Anegada (3,2) 12 lo caracteriza como consumidor secundario (Molina y López Cazorla, 2015). En Bahía Blanca, esta especie anádroma puede penetrar hasta la zona interna del estuario, regida por amplias variaciones de salinidad, accediendo a fuentes de alimento imposibles de alcanzar para otros depredadores bentónicos (Molina et al., 2021). En cuanto a la composición de la dieta de M. goodei, en Bahía Anegada esta especie depreda sobre crustáceos, bivalvos y poliquetos (Molina y López Cazorla, 2015). ...
Technical Report
Resumen ejecutivo Los condrictios o peces cartilaginosos comprenden a los tiburones, batoideos (rayas, chuchos y afines) y holocéfalos (peces gallo y quimeras). Este grupo surgió hace más de 450 millones de años, antes que los primeros vertebrados terrestres. Son un grupo pequeño y diverso, con cerca de 1250 especies. Ocupan un gran rango de hábitats, desde ríos y estuarios hasta mares profundos. En el caso de los grandes tiburones, son predadores tope y tienen un efecto regulador en la cadena trófica, ayudando a mantener ecosistemas productivos y saludables. En la actualidad, los condrictios son el grupo de vertebrados más amenazado de los océanos, con el 37% de las especies evaluadas clasificadas bajo alguna categoría de amenaza según la Unión Internacional para la Conservación de la Naturaleza (UICN). La vulnerabilidad debida a su biología (madurez sexual tardía, baja tasa de reproducción, crecimiento lento y amplio rango de distribución), combinada con un manejo pesquero no sostenible, han redundado en una rápida declinación poblacional de varios representantes de este grupo a escala global (70% de tiburones pelágicos han visto sus poblaciones reducidas en los últimos 50 años). En el mar Argentino se han registrado 105 especies de condrictios (55 tiburones, 48 batoideos y 2 holocéfalos), de las cuales 59 (62%) se encuentran amenazadas de extinción. La Reserva Bahía San Blas, localizada al sur de la provincia de Buenos Aires y muy cerca del límite con la provincia de Río Negro, resguarda ecosistemas costeros de importancia para al menos 16 de estas especies de condrictios (9 tiburones, 6 batoideos y 1 holocéfalo), que lo habitan de manera permanente o visitan estacionalmente. Estas 16 especies son capturadas por la pesca deportiva, durante al menos una parte de su ciclo de vida. El 94% de estas especies se encuentra bajo alguna categoría de amenaza de extinción a escala global y/o regional, de acuerdo a los criterios de la Lista Roja de la UICN, con el 44% En Peligro Crítico. Con el propósito de facilitar una protección efectiva de estas especies, se trabajó con especialistas en la materia para sistematizar información acerca del estado del conocimiento sobre los condrictios en la Reserva Natural de Uso Múltiple Bahía San Blas (Reserva Bahía San Blas). Mediante este esfuerzo colaborativo se pretende sentar bases y poner en agenda la necesidad de impulsar la preservación y recuperación de estas especies, en línea con los objetivos de conservación del área protegida, los planes y programas nacionales de protección de condrictios y otras metas nacionales e internacionales relacionadas. De esta forma, este documento tiene el objetivo de convertirse en un aporte a la planificación de la gestión, la conservación y los usos en el área protegida y a la promoción de acciones complementarias que propicien la protección efectiva de las especies de condrictios que habitan la Reserva Bahía San Blas. Hasta el año 2007, en la Reserva había pesca artesanal marcadamente estacional durante la primavera. El arte de pesca utilizado era la red agallera de fondo, arte pasivo y altamente selectivo. La pesca era dirigida directamente a una única especie blanco: el gatuzo Mustelus schmitti, concentrando el esfuerzo sobre la fracción adulta de la población. La pesca artesanal y la pesca deportiva tenían un bajo grado de solapamiento en la utilización de los recursos pesqueros en el área, con una superposición temporal parcial entre ambas actividades. En la actualidad la pesca artesanal se encuentra vedada a partir de un fallo de la Corte Suprema de Justicia. En la Reserva Bahía San Blas se realiza anualmente una intensa actividad de pesca deportiva, principal motor económico y turístico del área, concentrada entre los meses de octubre y abril. Se pescan especies de condrictios al borde de la extinción (gatuzo, cazón y escalandrún En Peligro Crítico). San Blas es conocido como el paraíso del pescador. Con el mayor número de estudios e informes realizados y por sus capturas, se puede considerar el mejor pesquero del Atlántico sur del que se tenga registro. Entre los años 2008 y 2010 se registraron capturas de 22 a 30 Tn de gatuzo y de la raya Sympterygia por la pesquería recreativa de costa. Cerca del 12% del volumen capturado por pesca deportiva de costa corresponde a peces cartilaginosos, y casi un 11% del volumen capturado en la pesca embarcada corresponde al mismo grupo y para el mismo período. El resto corresponde a peces óseos. El gatuzo M. schmitti es la especie de condrictios con mayores capturas tanto en pesca de costa como embarcada. El volumen total capturado mediante la pesca embarcada es superior al de costa (por ejemplo, en las temporadas 2008/9 y 2009/10 se capturó 5 a 21% más en modalidad embarcada). En términos de las capturas por unidad de esfuerzo (CPUE), las capturas por pesca embarcada pueden llegar a cuadriplicar las de la pesca de costa (costa = 2,1 peces/hora vs. embarcada = 7,5 peces/hora). Dicho aspecto debe ser tenido en cuenta a la hora de planificar el manejo pesquero de la Reserva. A pesar de la intensa actividad pesquera, los propios pescadores deportivos notan que la calidad de la pesquería está decayendo. En un estudio reciente de percepción, casi todos los pescadores deportivos encuestados (más del 95%) afirmaron que los peces cartilaginosos en general están en peligro de extinción y reconocieron la necesidad de cuidarlos. Además, declararon que aceptarían medidas de manejo que aporten a la sostenibilidad de los recursos pesqueros. Aún queda mucho por entender sobre los condrictios en el sitio de interés. En la actualidad existen vacíos de información acerca de la distribución local, el comportamiento, la reproducción, la alimentación y otras variables poblacionales para las 16 especies de condrictios registradas para la Reserva Bahía San Blas. Para resolver estos vacíos de información, con miras a la adecuada implementación del área protegida, la promoción de mejores prácticas de manejo y la protección de los condrictios, se recomienda implementar nuevos análisis, integrales y a largo plazo, sobre la biología y ecología del grupo, incluyendo monitoreo de la pesca deportiva, los impactos del esfuerzo pesquero y del cambio climático, entre otros. Los monitoreos deberán incluir: registro de desembarques a nivel de especie, especialmente durante primavera y verano; registro de visitantes mediante encuestas permanentes y estandarizadas; evaluación económica de la pesca deportiva. Es menester analizar la relación entre la pesca deportiva, las percepciones y las prácticas de los usuarios (tanto locales como visitantes). Finalmente, dada la importancia del área para varias especies de peces cartilaginosos, principalmente para los grandes tiburones costeros, resulta imperioso armonizar la normativa actual como base para el ordenamiento de la pesca deportiva, tanto en términos temporales como espaciales, dentro los límites de la Reserva Bahía San Blas.
... 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. ...
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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.
... The fish were divided into classes according to their length. Only fish of the size/age that have been shown to have been in the estuary throughout their lives, i.e., they were born there and have not yet left (Cazorla and Sidorkewicj, 2009;Cazorla, 2018;Molina et al., 2021), were evaluated for the information to be an indicative of the local environmental quality. Each sample was a pool of a variable number of individuals classified by class, species, and location (Table 1). ...
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Marine fishes have been intensively studied, and some of the fundamental ideas in the science of marine ecology have emerged from the body of knowledge derived from this diverse group of organisms. This unique, authoritative, and accessible reference, compiled by 35 luminary ecologists, evolutionary biologists, and ichthyologists, provides a synthesis and interpretation of the large, often daunting, body of information on the ecology of marine fishes. The focus is on the fauna of the eastern Pacific, especially the fishes of the California coast, a group among the most diverse and best studied of all marine ecosystems. A generously illustrated and comprehensive source of information, this volume will also be an important launching pad for future research and will shed new light on the study of marine fish ecology worldwide. The contributors touch on many fields in biology, including physiology, development, genetics, behavior, ecology, and evolution. The book includes sections on the history of research, both published and unpublished data, sections on collecting techniques, and references to important earlier studies.
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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.
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The California sheephead Semicossyphus pulcher Ayres (Labridae) is a temperate, rocky-reef/kelp-bed fish that is sought by recreational and commercial fishermen. Long-term acoustic monitoring was used to ascertain site fidelity and seasonal movement patterns of S, pulcher. We implanted 16 adult (24 to 36 cm standard length) fish with long-term (similar to 1 yr) acoustic transmitters and their presence and movement patterns were monitored in the Catalina Marine Science Center Marine Life Reserve using an acoustic receiver array. A method was developed that explained some of the variability in detection frequencies. A negative relationship between detection frequency and activity (rate of movement) was found for S. pulcher moving within the array. Most fish exhibited high site fidelity to the general area of the reserve, with 13 of the 16 fish detected spending an average of 99 +/- 2% of their total days at liberty in the study area, with a mean of 90 +/- 9% of total residence time spent within a 600 m core area. However, these fish showed some variability in area use between months, exhibiting periods of expansion in their range. Fish also tended to increase activity as seasonal water temperature increased. These expanded movements resulted in some fish crossing the reserve boundary for extended periods or leaving the reserve permanently.
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The Baffin Bay estuary is a hypersaline system in the Gulf of Mexico that supports an important recreational and commercial fishery for black drum Pogonias cromis, a benthic predator. Seasonal measurements of water quality variables, benthic macrofauna densities and biomass, and determination of P. cromis food sources using stomach‐content and stable‐isotope analyses were carried out to determine how P. cromis food sources change with water quality and how this may affect P. cromis diet. Gut‐content analysis indicated P. cromis selectively consumed bivalves Mulinia lateralis and Anomalocardia auberiana. Isotope compositions demonstrated that P. cromis relied on these benthic food resources produced in the Baffin Bay estuary year‐round. Biomass and densities of these bivalves were influenced by changes in water quality variables, particularly salinity and dissolved oxygen. Thus, this paper demonstrates the relationship between water quality variables, benthic macrofauna, and their use as food resources by a carnivorous fish species, and emphasizes the need for integrated assessments when studying the effects of water quality on ecosystem function. Holistic approaches such as these can provide important information for management and conservation of fishery resources and can improve predictions of ecosystem response to climate variability. This article is protected by copyright. All rights reserved.
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This study explores the relationship between ecomorphology and trophic segregation in four closely related sympatric fish species (Teleostei, Sciaenidae) that are known to differ in their trophic habits. Only adult specimens were analyzed: 103 Cynoscion guatucupa, 77 Pogonias cromis, 61 Micropogonias furnieri, and 48 Menticirrhus americanus. The four species presented divergent ecomorphological traits related to swimming agility, prey spotting and capture, and the potential size of prey they were able to swallow. Results suggest that these sciaenid species can partition the food resources, even though they completely overlap in space. Differences in their ecomorphological traits appear to correlate closely with the diet and consequently could explain the trophic differentiation observed. Arguably, these ecomorphological differences play a significant role in the coexistence of the adults of these sympatric fish species.
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Estuaries are well known for their role as nutrient and detrital sinks that stimulate high levels of both primary and secondary production which, in turn, support a large biomass of fishes per unit area. This study reviews available information on coastal fish biomasses (g m−2 wet mass) and productivity (g m−2 wet mass year−1) in order to place South African data on these topics into a global perspective. Using biogeographic fish productivity estimates, together with estuarine water area, the approximate annual teleost production in South African estuaries was calculated at 585, 1706 and 13 904 t in the cool temperate, warm temperate and subtropical regions, respectively. Total annual fish production in estuaries on the subcontinent is conservatively estimated at 16 195 t, but this figure is likely to fluctuate widely, depending on recruitment success and annual environmental conditions pertaining to these systems. Approximately 2000 t of fish are estimated to be harvested by fishing activities in South African estuaries each year, which represents c. 12% of annual fish production. Although this figure may appear sustainable, the reality is that there are a few heavily targeted estuary-associated marine species at the top of the food chain that are being overexploited by both anglers and subsistence fishermen. Natural mortalities due to piscivorous fish and bird predation has been estimated at c. 3% of total fish biomass per month in the East Kleinemonde Estuary, but this figure will vary considerably depending on bird abundance and foraging patterns along the coast. In contrast to catches made by the fishermen, piscivorous fishes and birds are targeting mainly juvenile marine fish and small estuarine resident species that are very abundant and generally low down in the food web.
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The fish diversity and the main environmental factors affecting the spatial distribution of species, life history stages and community structure in the Río de la Plata (RdP) and adjacent waters are reviewed and analysed, with emphasis on the functional guild classification. The functional guild classification indicated that most species in the RdP were marine stragglers, zoobenthivores and oviparous species, although the biomass was dominated by estuarine species. Salinity had a stronger influence than temperature on the spatial pattern for all life stages, shallower and fresher waters are the preferred habitats of neonates and juveniles. During the breeding season (spring-summer), adults showed an intrusion into the inner part of RdP or to its adjacent nearshore waters from the offshore waters for spawning or mating, respectively. Variations in river discharge and wind patterns greatly affected the spatial extent of estuarine water, which ultimately influenced the domain of the main life-history stages (juveniles or adults) for both marine and estuarine fishes, as well as species and fish assemblage composition. The strong environmental gradient restricts some species and life-history stages to a particular section and defines three main fish assemblage areas. The composition of the fish assemblage is indicative of the recruitment of freshwater and marine species to the estuary in opposite ways, determined by the vertical stratification. Seasonal changes in the species composition were related to migration as a result of salinity and temperature variations and reproductive migrations to spawning and mating areas. This overview reveals that the RdP is under environmental variations that are likely to produce modifications to fish distribution and abundance that affect its fisheries. This context plus fish stock declines and changes in exploitation patterns could amplify the magnitude of the variations in the fisheries resources availability and affect the sustainability of fishing communities.
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The Patos Lagoon is part of the coastal province which is geologically defined by the Pelotas Basin and the basement (Villwock 1978). The basement is characterized by the Sul-Rio Grandense shield, composed of crystalline Precambrian rock formations, and by Paleozoic and Mesozoic sedimentary and volcanic sequences of the Paraná Basin, both of which provided the sediments for the marginal Pelotas Basin. Owing to successive transgressions and regressions during the Cenozoic, clastic continental, transitional, and marine sediments of about 8000 m thickness accumulated in the Pelotas Basin. The emersed portion comprises the present flat coastal plain between 29 and 35° S which can geomorphologically be divided into an inner alluvial plain, the Lombas Barrier, the Guaíba-Gravataí Lagoon system, a multiple barrier complex, the Patos-Mirim Lagoon system, and the continental shelf (Fig. 4.1.1; Delaney 1965; Villwock 1984). Geomorphologically, the estuary of the Patos Lagoon is surrounded by tertiary and quaternary deposits of the low lands of the Patos-Mirim Lagoon system and the multiple barrier complex, which are characterized by eolian deposits, beach ridges, sand plains, stable and active dune fields, and lagoonal terraces (Fig. 4.1.2; Godolphin 1976; Zeltzer 1976; Paim et al. 1987).
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O El Niño está associado com excesso de chuvas no sul do Brasil e aumento na descarga continental, acarretando alterações no regime de salinidade em estuários. Este trabalho descreve as mudanças na diversidade e composição de espécies da assembléia de peixes do estuário da Lagoa dos Patos antes, durante e depois do El Niño 1997-1998. Vinte arrastos de praia foram realizados em quatro pontos do estuário entre agosto de 1996 e agosto de 2000. As espécies foram agrupadas em: estuarino residentes (RESI), estuarino dependentes (DEPE), visitantes marinhos (MARI) e visitantes de água doce (DOCE). A diversidade foi calculada usando H’, a riqueza de espécies pelo método de rarefação E(Sn), a equitatividade pelo índice Evar, e os intervalos de confiança (95%) foram obtidos por bootstrap. Durante o El Niño, caracterizado por excesso de chuvas e baixa salinidade no estuário, ocorreu aumento na diversidade de peixes, principalmente pelo marcado aumento do número de espécies do grupo DOCE no estuário, e também devido a queda na abundância dos dominantes RESI e DEPE. Estudos englobando outros episódios El Niño são necessários para comparar os resultados e testar as hipóteses propostas no presente trabalho.
Chapter
A total of 21,734 fish from 121 species was taken in 173 collections from July 1976 to March 1979. Seventeen species had a broad distribution and comprised 82% of total numbers. Twelve species (10%) were thought to be permanent residents, 54 (45%) probably used the lagoon as a nursery or feeding ground or both, and 55 (45%) were occasional visitors. Twenty-two percent were herbivores, detritivores, or omnivores, 51% were second order consumers, and 27% were higher consumers. Clustering was used to construct a dendrogram of faunal similarity; it corresponded to major differences in the physical makeup of the lagoon and demarcated southern and northern shore groups of fish. There is an apparent pattern of migration within the lagoon reflecting prevailing currents. The season of maximum juvenile influx from the sea (Aug. to Oct.) was during maximum river flow. Diversity indices (H′, D, J′) reflected changes in numbers of species and individuals during the year, and some were highly correlated with temperature and salinity. Biomass at different sampling stations ranged from 0.95 to 11.3 g wet wt m–2 and H′ ranged from 0.53 to 2.50. Fishery productivity was as high as 12.0 g m–2 year–1.
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The two only species of Myliobatis Cuvier, that occur in the Brazilian coast, Myliobatis freminvillii Lesueur and Myliobatis goodei Garman, have great similarity in external morphology and possess few diagnostic characters that allow easy identification. In order to discriminate these two species, 34 specimens of M. freminvillii and 19 of M. goodei were measured and twenty morphometric characters were taken from each specimen. The residuals of a previous regression analysis performed on all morphometric variables relative to the disc width were used in the Size Independent Discriminant Analysis. All specimens were correctly allocated to their respective taxa. The analysis showed a clear separation of the specimens, forming two well-defined distinct groups. The fifth interbranchial distance (5ID) was the variable with the highest standardized discriminant coefficient value. The fifth interbranchial distance ( 5ID)-Internarial distance (IND) and fifth interbranchial distance (5ID)-Mouth width ( MW) were the proportions that showed better differentiation between Myliobatis species.
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Most small-scale fisheries are in developing countries and many live in poor and food insecure communities. These guidelines considers how small-scale fisheries can contribute to poverty alleviation and food security, and complement existing technical guidelines on sustainable fisheries. Issues discussed include: participation by small-scale fishers and their communities in development of policy and regulation measures, as well as in management decision-making and implementation processes; cross-sectoral uses of fisheries and related resources; the special role of women in fish marketing, processing and value addition; the significant scope for trade; financing; information research and communication aspects.
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The tremendous advances in electronic data processing are likely to result in revolutionary changes in the theories and practices of taxonomy. The process of classification is being removed from speculations regarding the origin of the taxa being classified. A natural classification is one whose taxa share the largest number of properties and which is most useful for a wide range of purposes. The principles of numerical taxonomy are stated briefly and illustrated by means of diagrammatic examples. The relative roles of the taxonomist and computer are discussed and estimates given of computer time and costs involved in numerical taxonomic work. The numerical taxonomic work done in botany so far is discussed and the paper concludes with a brief mention of several problems of numerical taxonomy with regard to botanical work. These are: scarcity of characters, correlations between cytogenetic work and phenetic similarities, and problems raised by hybridization.
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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.
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Cynoscion guatucupa Cuvier 1829 is a migratory pelagic fish species, which has a wide geographical distribution. It is the most important fishing resource for local communities in Bahía Blanca estuary and has been captured by artisanal fishermen since the 1900’s. The industrial fleet has been fishing this species in the coastal area of Buenos Aires province since the 1950’s, and, since 1970, landings have increased sharply. Between 2000 and 2004, the artisanal fishery in the estuarine waters of Bahía Blanca collapsed. Variations in total landings of the artisanal fleet might have arisen from the environmental variables within the estuary, fishing activity in the surrounding sea region, local pressure within the estuary and/or several other variables. Our results suggest that neither oceanographic parameters nor local pressure seem to have influenced the artisanal fishery of C. guatucupa in the estuarine region. Instead, this fishery seems to have been partially influenced by the increasing fishing pressure exerted by the industrial fishing fleet operating in open waters around the estuary. This study emphasizes the need to take into account fisheries data from both the estuarine environment and the surrounding sea region, particularly when designing management plans for the sustainable use of migrating fish resources.
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Spatial and temporal differences In habitat characteristics of coastal nursery grounds can have a large ~ m p a c t on growth rate survival, and subsequent recruitment of species w ~ t h e s t u a r ~ n e -dependent early life history stages Stone flounder Karelus bicoloratus IS a temperate North Pacific flat-fish species characterized by large recruitment variability and an estuanne-dependent juvenile stage Post-larvae settle from m ~ d -J a n u a r y to early Apnl In inshore and estuanne nursery grounds, and luve-niles subsequently rnove farther inshore using selective t ~ d a l stream transport Laboratory btud~es were conducted to determine the s e n s i t ~ v ~ t y of juven~le stone flounder growth rates to changes In tempera-ture and feeding rates at conditions common durlng settlement (8°C) and post-settlement (12cC) The relat~onship between RNA DNA ratio and growth rate {+as developed in the laboratory, and was used to measure in sltu growth rates of juven~les from 5 dltferent habltats durinq settlement (March) and after (April) Juvenile stone tlounder in the laboratory giew reldt~vely quickly feeding ad l ~ b ~ t u m at 8°C (4 1 body xveiqht d l) and 12°C (7 O", bw d 'I, but growth rate was very sensitive to changes in feed-ing rate at both temperatures Growth rdte of starved juven~les was not significantly different between 8 and 12°C and averaged -1 3 % bw d ' RN,\ DNA ratios were good pred~ctors of growth rate (R--0 881, with temperature as a covariate In situ growth rates at all 5 stat~ons (1 estuary 1 seagrass bed, and 3 deeper inshore settlement areas) were higher In Apnl than in March In sltu growth rates were hlghest during both months at the low-salinity estuanne s t a t ~ o n w h e ~ e fish had h ~ g h e s t gut fullnesses Growth rates wele also h ~ g h at a deeper inshore station near a sewage treatment outfall characterized by higher prey abundances than those typically found in open water aleas of Sendai Bay, Japan Growth rates were consistently lowest at the vegetated (Zostera spp bed) habitat, although retention In this h a b ~ t a t between March and April was hlgh Spatial differences In s e d ~ m e n t grain slze and prey abundances may be the primary factors responsible for the large vanability In habltat-specific growth rates Temperature-corrected compansons of growth l i m ~ t a t ~ o n suggest that d ~ s c r e t e habitats maintaln their relative values as nursery grounds over tune although the magnitude of growth llm~tation was much g ~ e a t e r durlng settlement (March) than post-settlement (Aprll) KEY WORDS Stone flounder Kareius bicoloratus Growth Habitat RNA:DNA . Recruitment
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Cownose rays Rhinoptera bonasus typify the K-selected life history strategy that makes their population dynamics susceptible to variation in natural and anthropogenic factors. We used an individual-based bioenergetics model, coupled to a matrix projection model, to predict how water temperatures warmer and cooler than current conditions would affect the individual growth and the population dynamics of cownose rays. The bioenergetics model simulated the daily growth, survival, and reproductive output of a cohort of female individuals from birth over their lifetime. Warmer and cooler temperature scenarios under alternative assumptions about ray movement were simulated. Under warmer conditions, daily consumption rate would have to increase by about 12 % or weights-at-age would decrease by 10 to 17 %, while under cooler conditions, daily consumption would have to decrease by about 14% or weights-at-age would increase by about 15%. Slowed individual growth under warmer water temperatures translated into slowed population growth rate, decreased net reproductive rate, longer generation time, and higher but delayed age-specific reproductive values. For example, under the scenario that resulted in the slowest individual growth rates, the population growth rate would decrease from 0.027 to 0.005 yr(-1). Population growth rates were more sensitive to variation in survival rates, especially those of mature age-classes, than to fertility rates. Our coupling of an individual-based bioenergetics model with a matrix projection model offers a potentially powerful approach for relating how, with limited to moderate information, changes in environmental variables and habitat that affect individual growth can be expressed as population-level responses.
Article
Based on a large standardised data set, the present study proposed a meta-analysis to describe general patterns in the functional diversity of estuarine fish assemblage in terms of both number of species and density along the European Atlantic coast. Fish species collected from 31 European estuaries from Portugal to Scotland were allocated to functional groups according to their ecological utilization of estuaries. A clustering analysis was performed to compare the overall functional structure of estuaries based on fish composition. Generalised linear models were computed to identify relationships between large-scale abiotic and intra-estuarine descriptors and functional attributes of estuarine fish assemblages. The total number of species, and more especially of marine species, was higher in larger estuaries with a wide entrance and, locally, in polyhaline waters. The total density was mainly related to the proportion of intertidal mudflats and, locally, was greater in mesohaline waters. In terms of relative density, northern systems were dominated by marine and catadromous species, while estuarine species were prevalent in the southern ones.
Article
Species of Paralichthys Girard are the most important flatfishes to commercial fisheries in nearshore waters of Argentina and Uruguay. Recent commercial catches increased from 3000 tonnes (t) in 1984 to 11000 t in 1995, representing more than $65 million in export income for 1995. Although their commercial importance has long been recognized, paralichthyid flounders in this region are not well studied, either from a systematic or an ecological viewpoint. Six nominal species have been reported from Argentinean and Uruguayan waters: Paralichthys bicyclophorus, P. brasiliensis, P. isosceles, P. orbignyanus, P. patagonicus and P. simulans. However, species descriptions are often vague and incomplete, and reported distributions are dubious. Variations in scale morphology, meristic and morphometric characters were used to differentiate among the Paralichthys species co-occurring in this area. Of six species previously reported from this region, only three, P. isosceles, P. orbignyanus and P. patagonicus, are valid. P. bicyclophorus is regarded as a junior synonym of P. patagonicus; P. simulans is a junior synonym of P. orbignyanus; while P. brasiliensis, although reported from coastal waters of Argentina and Uruguay for many years, does not occur there. Paralichthys spp. were collected on the continental shelf and in estuaries in the south Atlantic between 34–55°S. P. orbignyanus and P. patagonicus inhabit marine and estuarine locations and extend as far south as 43°S. The former is a shallow-water, euryhaline species occurring to about 20 m. In contrast, P. patagonicus has higher densities between 36–40°S at 70–100 m depth. P. isosceles occurs mainly on the inner continental shelf between 43–45°S at 70–100 m depth, and reaches its southern limit at about 47°S.
Article
Foveaux Strait is a shallow body of water at the southern tip of New Zealand. It supports nationally significant dredge oyster Ostrea chilensis and blue cod Parapercis colias fisheries. Fish counts and benthic habitat descriptions from drift underwater video (DUV) transects conducted in two seasons over an area of recovering biogenic reef and an adjacent recently dredged area are presented. Over all, seven demersal fish species (5.10 per 100m2, 75% P. colias) were recorded on the recovering area surveyed, whereas only three species (0.47 per 100m2, 91% spiky dogfish Squalus acanthias) were recorded on the recently dredged area. There were few seasonal differences except for S. acanthias. Descriptions of benthic habitat derived from video stills showed topographic complexity was greater on the recovering area; general epifauna cover, sponge cover and macro-algal cover were also greater on the recovering area, but with seasonal interactions. In contrast, the numbers of tunicates and ophiuroids were higher on the dredged area. Sponge cover (absent from the dredged area) was also correlated with the abundance of leather jackets Parika scaber and scarlet wrasse Pseudolabrus miles as well as all color phases of P. colias. Topographic complexity, general epifauna cover, and macro-algae cover were also positively correlated with the abundance of adult P. colias and P. scaber. The drifting video methodology was able to estimate densities of demersal fish and make broad-brush measures of benthic habitat capable of demonstrating the importance of benthic habitat complexity to demersal fish in Foveaux Strait. The potential mitigation of reduced benthic habitat complexity from oyster fishing is then discussed.
Article
Some biological parameters of Jenyns' sprat Ramnogaster arcuata in Bahía Blanca estuary, Argentina, were evaluated during a survey conducted on a monthly basis between September 2005 and August 2006. Jenyns' sprat specimens were observed in the estuary all through the year. Total length (TL; N = 721) ranged from 33 to 131 mm. No significant differences between the length–weight relationships of males and females were detected (P > 0.10). Positive allometric growth was observed in juveniles, males, females and sexes combined. Whole otolith analysis revealed four age groups (0–3), 1-year age being the most abundant. Gompertz growth parameters were L∞: 102.75 mm, k = 0.46 and t0 = 0.98 for males (r = 0.80), and L∞: 125.45 mm, k = 0.33 and t0 = 0.68 for females (r = 0.76). Males and females reached 50% sexual maturity (TL50) at 76 and 77 mm TL (age 1 year), respectively, and all individuals were sexually mature at a 110 mm-length at the age of 3 years. Macroscopic gonad inspection, gonadosomatic index and the high percentage of fish of the smallest size-class captured during spring and summer samplings indicate that the spawning season began in spring. Taken together, our results indicate that the biology of R. arcuata is fairly consistent with the biology of other temperate clupeoids.