No abstract

No abstract

Summary This study evaluates the variation in population abundance overtime of twenty commercial fish species associated with an artificial reef and a reference site. Mean yearly catch rates were computed from data collected monthly from 1988 to 2012 using trammel nets. The log‐transformed ratios of catches obtained at the reef and the reference site were calculated for each species. Statistical methods employed to study the changes in abundance of such fish species were multidimensional scaling (MDS), Min/Max Auto‐correlation Factor Analysis (MAFA), Dynamic Factor Analysis (DFA) and chronological clustering. The time‐series analyses were performed on three groups of species showing similar patterns of temporal cross‐correlation. These time‐series analytical techniques were utilized to identify common trends, the influence of some environmental variables, and changes in group trends. The analyses indicated a decreasing trend in the catch ratio for two species groups (mostly reef‐dwelling species) while the third species group indicated an inverse pattern. Changes in the trends of abundance in some species were likely related to the general deterioration of the artificial reef modules.

SUMMARY: The vertical diel activity of a fish assemblage inhabiting the Senigallia artificial reef (northern Adriatic Sea, Italy) was evaluated from July to November 1996 using enhanced hydroacoustic techniques. Extensive seabed mapping of the area was done using a multibeam echosounder to obtain background imagery of the reef structures and identify the most suitable locations for placing stationary acoustic transducers. Three acoustic transducers were placed inside the reef area, while a fourth was located in the open sea outside the area. Data analysis was conducted on three different depth layers: surface, midwater and bottom. In each layer, diel fish biomass inside the reef showed two peaks, one in the early morning and the other in the late evening. Slightly different behaviour was observed outside the protected area. Comparison of the layers showed that fish biomass was not homogeneously distributed along the water column throughout the sampling period. There were high values in the middle and bottom layers until the end of August. However, no significant biomass variations in time were observed outside the reef where low values were always recorded in each layer.Keywords: Adriatic Sea, artificial reef, fish biomass, multibeam sonar, split-beam hydroacoustic. RESUMEN: DINÁMICA DIARIA VERTICAL DE COMUNIDADES DE PECES ASOCIADOS A UN ARRECIFE ARTIFICIAL (MAR ADRIÁTICO NORTE). -La actividad diaria vertical de la comunidad de peces que habitan en el arrecife artificial Senigallia (Mar Adriatico Norte, Italia), se evaluó desde julio a noviembre de 1996 utilizando técnicas de hidroacústica. Se realizó un mapaje extenso del fondo marino utilizando una ecosonda multihaz para obtener imágenes de las estructuras del arrecife e identificar las áreas más adecuadas para emplazar los transductores acústicos. Tres fueron colocados dentro del área del arrecife, mientras que un cuarto fue situado en mar abierto, fuera del área. El análisis de datos se realizó a tres profundidades: superficie, profundidad intermedia y fondo. En cada profundidad la biomasa diaria de peces en el arrecife mostraba dos picos, uno por la mañana y otro al anochecer. Pequeñas diferencias en el comportamiento de los peces se observaron fuera del área protegida. Comparando entre las distintas profundidades mostramos que la biomasa de los peces no estaba uniformemente distribuida a lo largo de la columna de agua, durante el período de muestreo, con valores altos en las profundidades intermedias y en el fondo hasta finales de agosto. Por otro lado no se observaron variaciones de biomasa significativas en el tiempo fuera del arrecife donde siempre prevalecieron valores bajos en cada profundidad.Palabras clave: mar Adriático, arrecife artificial, sonar multihaz, hidoacústica.of putting the observer in direct contact with the organisms and habitats being surveyed, thereby allowing a considerable amount of useful information to be gathered. The disadvantages are depth constraints, the influence of visual conditions, avoidance, and the variability of behav...

A B S T R A C TArtificial reefs (ARs) are becoming a popular biological and management component in shallow water environments characterized by soft seabed, representing both important marine habitats and tools to manage coastal fisheries and resources. Because of the unstable nature of sediments, they require a detailed and systematic investigation that acoustic systems can provide. An AR into the marine environment acts as an open system with exchange of material and energy, altering the physical and biological characteristics of the surrounding area. The AR stability will depend on the balance of scour, settlement, and burial resulting from ocean conditions over time. The acoustic systems are efficient tools in monitoring the environmental evolution around ARs, whereas water turbidity can limit visual dive and ROV inspections. High-frequency multibeam echosounder offers the potential of detecting fine-scale distribution of reef units, providing an unprecedented level of resolution, coverage, and spatial definition. In 2008 the EM3002 multibeam was used to investigate the first scientifically-planned AR in Italy deployed during 1974-75. After 33 years the AR is almost in perfect condition. A considerable scouring around the structures and some vertical/horizontal movements of the single units have occurred. Moreover a deepening of the whole area hosting the AR was observed. R E S U M OOs recifes artificiais (ARs) estão se tornando um componente biológico e de manejo de ambientes de áreas rasas com substratos característicos não rígidos, representando habitats marinhos importantes e ainda constituindo uma ferramenta para o manejo da pesca e dos recursos costeiros. Devido à natureza instável dos sedimentos, exigem um estudo detalhado e sistemático que os sistemas acústicos podem disponibilizar. Um RA atua no ambiente marinho como um sistema aberto com troca de materiais e energia, alterando as características físicas e biológicas das áreas que o cerca. A estabilidade do RA dependerá do equilíbrio entre a escavação, o assentamento e aterramento resultantes das ações do oceano no decorrer do tempo. Os sistemas acústicos são ferramentas eficientes no monitoramento da evolução ambiental ao redor dos ARs, uma vez que a turbidez da água pode limitar o mergulho visual e as inspeções ROV. A ecosonda multifeixe de alta frequência oferece meios para identificar com precisão a distribuição das unidades recifais, com nível de resolução, cobertura e definição especial. Em 2008, a sonda multifeixe EM3002 foi usada para estudar a primeira implantação cientificamente planejada de RA na Itália, durante 1974-75. Após 33 anos, o RA está praticamente em perfeitas condições. Foram observadas a ocorrência de escavação considerável ao redor das estruturas , alguns movimentos vertical/horizontal das unidades isoladas e ainda o aprofundamento de toda a area que abriga o RA.