Home About us Contact
|
Home About us Contact | ||
|
|
||
Visual Census (visual + census)
Selected AbstractsPrediction and verification of possible reef-fish spawning aggregation sites in Los Roques Archipelago National Park, VenezuelaJOURNAL OF FISH BIOLOGY, Issue 4 2010J. Boomhower This study attempts to predict and verify possible spawning aggregation sites and times in the Los Roques Archipelago National Park, Venezuela, based on physical reef characteristics and the knowledge of experienced local fishermen. Three possible aggregation sites were selected for monitoring based on satellite images, low-cost bathymetric mapping and interviews with experienced local fishermen. Abundances and sizes of 18 species that are known to form reproductive aggregations were monitored at these sites using underwater visual census for 7 days after each full moon from February to August, 2007. While spawning events were not observed, possible indirect evidence of spawning aggregations was found for Lutjanus analis at Cayo Sal and Boca de Sebastopol, Lutjanus apodus at Cayo Sal, Lutjanus cyanopterus at Cayo Sal and Piedra La Guasa and Epinephelus guttatus at Bajo California and Cayo de Agua. Additionally, indirect evidence was identified for the past existence of a spawning aggregation of Epinephelus striatus in the northern part of the archipelago, which may have been eliminated by overfishing c.15 years ago. Bathymetric mapping showed that the shelf edge at sites monitored in this study was shallower than at spawning aggregation sites in other parts of the Caribbean, and that sites were not proximal to deep water. While this study does not prove the existence or locations of spawning aggregations of reef fishes in the archipelago, it does add insight to a growing understanding of generalities in the relationship between seafloor characteristics and the locations of transient reef-fish spawning aggregations in the Caribbean. [source] Fish assemblages and rapid colonization after enlargement of an artificial reef off the Algarve coast (Southern Portugal)MARINE ECOLOGY, Issue 4 2008Francisco Leitão Abstract Artificial reefs (ARs) have been deployed in Algarve (Southern Portugal) coastal waters to contribute to the sustainability of local nearshore fisheries. Herein, we describe the colonization process of the recently deployed Faro/Ancão AR, and assess the time until the fish assemblage reaches stability and their seasonal patterns. In addition, we compare the results from the present study with those previously reported for an older AR. The fish assemblages were monitored monthly over a 2-year period by means of visual census. A rapid increase in fish colonization occurred within the first 4 months. After this initial period the assemblage structure showed high similarity (> 73%). The high rate of colonization of the AR was related to the maturity already achieved by the nearby 14-year-old AR and to the fish migration from the Ria Formosa lagoon, a nearby nursery habitat. The reef fish assemblage structure showed a seasonal pattern, mainly associated with recruitment episodes of occasional demersal species (Boops boops, Trachurus trachurus and Pagellus spp.) in spring and summer. A total of 66% of the species found in AR are of commercial and recreational importance. The overall mean density and biomass were 2.8 ind·m,3 and 207 g·m,3. The occasional demersal species accounted for 42% of the fish density. The most important species in terms of biomass belong to the Sparidae family along with Dicentrarchus labrax. The fish assemblage of the new ARs showed higher mean number of species, diversity, density and biomass values than those reported for the older AR. This result was associated with enlargement of the AR area and with the fishing exploitation of the isolated, small and patchy old AR. Moreover, the high biomass values recorded in the new ARs were mainly due to the increased density of D. labrax after AR enlargement. The results of the present study are used to define guidelines for suitable management strategies for the AR areas that are exploited by the local commercial and recreational fisheries. [source] Fish Assemblages in Shallow Marine Caves of the Salento Peninsula (Southern Apulia, SE Italy)MARINE ECOLOGY, Issue 2002Simona Bussotti Abstract. Fish assemblages of three shallow marine caves from the Salento Peninsula (Apulia, SE Italy) were investigated in July 2000. Data were collected in situ by using visual census. A total of nineteen fish species were recorded inside the caves. The species richness generally displayed a similar pattern in all three caves, decreasing from the entrance towards the innermost sections, whereas the patterns of total fish abundance differed among caves. Apogon imberbis (mainly represented by juveniles) was the most important species in terms of number of individuals (accounting for more than 85% of the censused fish) and showed a fairly even distribution inside the investigated caves. Without the numerical contribution of A. imberbis, fish abundance decreased from the entrance to the inner sections and this pattern was common to all three caves. Juvenile fishes of economic interest (e. g., Diplodus vulgaris and Epinephelus marginatus) were also recorded inside. The present study suggests that: (1) environmental constraints could affect distribution patterns in fish species richness and in the abundance of several fish along the axis of "blind caves" (with a single entrance), as already observed for sessile benthos and plankton assemblages; (2) shallow marine caves of the Salento Peninsula could exert the role of refuge and/or nursery for some littoral fish species during the adult and/or juvenile stages of their life histories. [source] Herbivorous fishes and the potential of Caribbean marine reserves to preserve coral reef ecosystemsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010Dorothée Kopp Abstract 1.The development of macroalgae to the detriment of corals is now one of the major threats to coral reefs. Herbivorous fishes are partly responsible for algal regulation on coral reefs and their overexploitation favours the shift from scleractinian coral-dominated systems towards macroalgae-dominated systems. 2.Marine protected areas (MPAs) that have been established worldwide may benefit coral reefs through the maintenance of high densities of herbivorous fishes which regulate algal growth. 3.The paper assesses whether small MPAs in the Caribbean are able to enhance herbivorous fish stock and by controlling macroalgae help to maintain reef ecosystems. A visual census using band-transects was undertaken around Guadeloupe island where marine reserves have been in place since 1979. The effects of MPAs on both benthic communities and herbivorous fishes are examined. 4.Inside MPAs, herbivorous fish biomass was almost twice as high as outside MPAs and macroalgal cover was significantly lower. Fish size class distributions revealed that large individuals occurred mainly inside MPAs and that few male individuals were found outside MPAs. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||