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1.
European intertidal salt marshes are important nursery sites for juvenile fish and crustaceans. Due to the increasing threat of habitat loss, the seasonal changes of salt marsh fish communities need to be understood in order to appreciate the ecological and economic importance of the saltmarsh habitat. This study was the first in Great Britain to investigate the seasonal changes of salt marsh fish communities and the variation in community structure between closely located marsh habitats. Between February 2007 and March 2008, five marshes on three estuaries of the Essex coastline were sampled using flume nets to block off intertidal creeks at high tide. Fourteen fish species were caught. The community overall was dominated by three species that made up 91.6% of the total catch: the common goby Pomatoschistus microps (46.2% of the total catch), juvenile herring Clupea harengus (24.3%), and juvenile and larval sea bass Dicentrarchus labrax (21.2%). Cluster analysis demonstrated clear seasonal patterns, with some community structures unique to specific marshes or estuaries. The marsh fish community shifts from a highly diverse community during spring, to a community dominated by D. labrax and P. microps in autumn, and low diversity during winter months. Gravimetric stomach content analysis of fish community identified three main trophic guilds; macroinvertivores, planktivores and omnivores. The macroinvertivore feeding guild contained D. labrax and P. microps, the two most frequently occurring species. This investigation demonstrates the importance of British salt marshes as nursery habitats for commercial fish species.  相似文献   

2.
The importance of estuaries for coastal environments is widely acknowledged but their role, structure and ecological status have been the focus of recent scientific efforts mainly concerning large estuarine areas. In this work we used fish assemblages to establish, for the first time, the functional and ecological role of five small estuarine systems along the Portuguese south and southwest coasts. Our results showed that, at a functional approach, fish communities did not differ between estuaries, and that all systems presented a seasonal pattern in diversity values, ecological and feeding guilds. These small estuaries contribute to the support of coastal fish populations by providing temporary habitats to the critical life stages of marine species, shelter and feeding grounds, and should be considered in an ecological and conservation perspective.  相似文献   

3.
Multivariate analyses of estuarine geomorphic variables and fish-catch data support the hypothesis that estuaries in New South Wales can be classified in terms of measurable geomorphic characteristics, and that these geomorphic characteristics exert an influence on estuarine biota. The clearest example of this association is the extent to which the area of seagrass, mangrove and central mud basin relates to geomorphic settings and the extent to which the area of these units in turn predict commercial landings of fish and crustaceans. Infilled estuaries with sand barrier entrances, with higher areas of mangrove and lower areas of seagrass and central mud basin yield a catch of fish different to estuaries which are not infilled, and contain relatively high areas of seagrass and central mud basin, and less mangrove. The species contributing most to these differences in assemblages are those which multiple regression analysis identifies to be consistently associated with seagrass area, and which ecological studies reveal to be dependant upon seagrass in their post-settlement phase.  相似文献   

4.
Freshwater inflow has a strong impact on the biological, chemical and physical characteristics of estuaries, which in turn affect the distribution and abundance of estuarine organisms. Increased climatic variability associated with climate change is predicated to modify precipitation patterns, which will likely intensify floods in estuaries. The demersal fish assemblage of the freshwater-dominated Great Fish Estuary, South Africa, was sampled using beam trawls, monthly, from December 2013 to November 2014. The first six months of the study were characterised by river flooding and high flow, with estuarine conditions found only in the mouth region; this was followed by six months of intermediate flow, with estuarine conditions recorded up to 10 km from the mouth. River flooding and subsequent reduced salinity resulted in a decrease in species richness and abundances of fishes in the estuary, with only two estuarine species (Glossogobius callidus and Psammogobius knysnaensis) and one marine migrant (Solea turbynei) recorded following river flooding (201 m3 s?1), in January 2014. The greatest species richness and abundances among both marine and estuarine fishes were recorded during intermediate flow conditions. We conclude that although freshwater inflow into estuaries is important for the nursery function of these systems, flooding—especially in freshwater-dominated estuaries—may cause a temporary decline in the abundance of most marine and estuarine fish species, including important bentho-pelagic marine migrant fishery species, such as Argyrosomus japonicus and Pomadasys commersonnii.  相似文献   

5.
Determining the nursery habitat of fishes that have moved from estuarine nursery habitats is difficult. The elemental fingerprints of otoliths of three species of sparids were determined to investigate their utility as a natural tag of the nursery habitat. Juvenile Pagrus auratus (snapper), Rhabdosargus sarba (tarwhine) and Acanthopagrus australis (bream) were collected from two sites in each of 15, six and three estuaries, respectively, and their otoliths analysed by solution-based inductively coupled plasma-mass spectrometry. Significant differences in otolith chemistry were found for all three species of juveniles collected from different estuaries. The same patterns among estuaries were not seen for all species, although it was not possible to sample the same sites within an estuary for all species. For bream, significant differences in otolith chemistry were found among all three estuaries, whereas for tarwhine the six estuaries were separated into three groups. For snapper, a number of estuaries could be separated, but there was some overlap for other estuaries. All three species were collected from the same site within one estuary and their otoliths analysed. Significant differences were found among species, but the implication of this finding remains unclear as the three species show differences in microhabitat use and may also differ in age. Because the elemental fingerprints of juveniles vary among estuaries or groups of estuaries, the nursery or recruitment estuary of adult fish could now be determined by analysing the juvenile region of adult otoliths. Thus, connectivity between estuaries and open coastal populations could be determined. Such information will have major implications for fisheries management because it will provide information on the distance that fish have moved from their recruitment estuary and the number of estuaries that contribute to each adult population.  相似文献   

6.
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7.
Estuaries serve as nursery grounds for many marine fish species. However increasing human activities within estuaries and surrounding areas lead to significant habitat loss for the juveniles and decrease the quality of the remaining habitats. This study is based on the data of 470 beam trawls from surveys that were conducted in 13 French estuaries for the purpose of the European Water Framework Directive. It aimed at testing the effects of anthropogenic disturbances on the nursery function of estuaries. With a multispecific approach based on ecological guilds, two fish metrics, abundance and species richness of Marine Juvenile migrant fishes, were used as proxies for the estuarine nursery function. Indices of heavy metal and organic contaminations were used to estimate anthropogenic disturbances impacting these estuaries. Fish metrics were described with statistical models that took into account: (a) sampling protocol, (b) estuarine features and (c) contamination. The results of these models showed that the fish metrics highly depend on the sampling protocol, and especially type of gear, depth and salinity, which highlights the necessity of considering such metrics at the sampling (trawl haul) scale. Densities and species richness of Marine Juvenile fishes appeared to be strongly and negatively correlated to contamination indices. These results are consistent with the hypothesis that human disturbances impact the nursery function of estuaries. Finally, the densities of Marine Juvenile migrant species appeared as a potential robust and useful fish indicator for the assessment of the ecological status of estuaries within the Water Framework Directive.  相似文献   

8.
The elemental composition of otoliths from juvenile English sole Pleuronectes vetulus and speckled sanddab Citharichthys stigmaeus living in estuaries and sandy coastal habitats were compared to determine if a chemical habitat tag existed that could be used to differentiate fish living in the alternative juvenile habitats. Juveniles of both species were collected from seven estuaries and 11 coastal sites along 500 km of the central California coast. Collections occurred in three years: 1998, 1999 and 2000. The chemical composition of the otoliths was analyzed using solution-based inductively coupled plasma mass spectrometry. The multi-elemental composition (Sr, Li, Ba, Mn) of otoliths from estuarine and coastal fish differed significantly for all models (global, region and years models) examined in this study. For each species, discriminant function analysis (DFA) for the global model, which pooled juveniles collected from three regions over multiple years, classified fish into estuarine and coastal groups with close to 80% accuracy. The two main elements in the discriminant models, Sr and Li, differed consistently between habitats; Sr was higher and Li was lower in estuarine fish. Classification success was modestly improved by generating separate discriminant functions for each region (regions model) because of some regional differences in Sr and Li concentrations. Classification success also was improved in some cases by generating separate discriminant functions for each year (years model) because Ba and Mn differed between habitats in only some years. Despite this variability in the concentration of elements in some regions and years, a chemical habitat tag was present in each species that could be used to discriminate coastal and estuarine juveniles over a large geographic area and over three years with very different oceanographic conditions (e.g., El Niño, La Niña). In addition, I found that English sole and speckled sanddab had striking similarities in their chemical habitat tags and that, in some cases, one species could be used as a proxy to classify juveniles of the other species without compromising the accuracy of the habitat tag. The ability to use a proxy classification model would significantly reduce the number of juvenile fish that would need to be collected and analyzed in order to classify members of an ecologically similar species. The chemical habitat tags found in this study appears to be promising tools for identifying fish that have lived in alternative juvenile habitats and, ultimately, the proportional contribution of estuarine and coastal habitats to the central California populations of English sole and speckled sanddab.  相似文献   

9.
In the Northwest Pacific Ocean, the squid jigging fisheries from China, Japan and other countries and regions have targeted the west winter-spring cohort of neon flying squid(Ommastrephes bartramii) from August to November since the 1970 s. This squid is a short-lived ecological opportunist with a life-span of about one year,and its population is labile and recruitment variability is driven by the environment or climate change. This variability provides a challenge for ones to forecast the key habitats affected by climate change. The catch data of O. bartramii from Chinese squid jigging fishery and the satellite-derived sea surface temperature(SST) data are used in the Northwest Pacific Ocean from August to November of 1998 to 2004, the SST preferences of O.bartramii corresponding to high values of catch per fishing day(CPUE) are determined and monthly potential habitats are predicted using a histogram analysis of the SST data. The possible changes in the potential habitats of O. bartramii in the Northwest Pacific Ocean are estimated under four climate change scenarios based on the Fourth Assessment Report(AR4) of the Intergovernmental Panel on Climate Change, i.e., 0.5, 1, 2 and 4°C increases in the SST because of the climate change. The results reveal an obvious poleward shift of the potential habitats of O. bartramii in the Northwest Pacific Ocean.  相似文献   

10.
The structure and temporal variations of the fish community in salt marshes of Chinese estuaries are poorly understood. Fish utilization of a salt marsh intertidal creek in the Yangtze River estuary was studied based on quarterly sampling surveys in July and November, 2004, and February and May, 2005. Fishes were collected by consecutive day and night samplings using fyke nets during the ebbing spring tides. A total of 25,010 individuals were caught during the study. 17 families and 33 species were documented, and the most species-rich family was Gobiidae. Three species, Synechogobius ommaturus, Chelon haematocheilus and Lateolabrax maculatus together comprised 95.65% of the total catch, which were also the most important commercial fishery species in the Yangtze River estuary. The fish community was dominated by juvenile individuals of estuarine resident species. Time of year significantly affected fish use of salt marshes, but no significant effects of diel periodicity on the fish community were found except for fish sampling in July. These findings indicate that salt marshes in the Yangtze River estuary may play important nursery roles for fish community.  相似文献   

11.
This paper outlines the benefits of using the framework for an ecosystem approach to fisheries management (EAFM) for dealing with the inevitable yet unclear impacts of climate change and ocean acidification on coastal fisheries. With a focus on the Asia-Pacific region, it summarizes the projected biological and socio-economic effects of increased emissions of carbon dioxide (CO2) for coastal fisheries and illustrates how all the important dimensions of climate change and ocean acidification can be integrated into the steps involved in the EAFM planning process. The activities required to harness the full potential of an EAFM as an adaptation to climate change and ocean acidification are also described, including: provision of the necessary expertise to inform all stakeholders about the risks to fish habitats, fish stocks and catches due to climate change; promotion of trans-disciplinary collaboration; facilitating the participation of all key stakeholders; monitoring the wider fisheries system for climate impacts; and enhancing resources and capacity to implement an EAFM. By channeling some of the resources available to the Asia-Pacific region to adapt to climate change into an EAFM, developing countries will not only build resilience to the ecological and fisheries effects of climate change, they will also help address the habitat degradation and overfishing presently reducing the productivity of coastal fisheries.  相似文献   

12.
Climate change affects ocean conditions, fish stocks and hence fisheries. In West Africa, climate change impacts on fisheries were projected to be mainly negative through multi-facet ways. However, analysis of adaptation responses of fishers to climate change impacts is scarce. This paper reviews the impacts on climate change on fisheries in West Africa and discusses the potential adaptation strategies adopted by both the artisanal and industrial fishing sectors. Overall, climate change and over-exploitation have altered species composition of fisheries catches in West Africa. The effect of ocean warming on fisheries is indicated by the increase in dominance of warmer water species in the landings, shown from an increase in Mean Temperature of Catch, in the region. Climate change induced changes in potential catch and species composition, which inherently have similar symptoms as over-exploitation, are expected to have repercussions on the economic and social performance of fisheries. Both artisanal and industrial sectors may adapt to these changes mainly through expansion of fishing ground that increases operation costs. Our results highlight that historical changes in target species are more common in industrial than artisanal fisheries. This result challenges the prevailing assumption that artisanal fisheries, given their limited movement capacity, would adapt to climate change by shifting target species and/or gear type.  相似文献   

13.
A total of 248 roving creel surveys along the length of the Berg River Estuary, in the Western Cape, South Africa, recorded 626 shore-angler and 88 boat-angler outings over the period December 2002–November 2005. Catch-and-effort information was obtained from catch inspections with 360 handline and 246 rod-anglers. Average total annual linefishing effort was estimated at 449 ± 29 (mean ± SE) boat-angler days, 1 299 ± 118 recreational shore-angler days and 1 394 ± 57 subsistence (handline) shore-angler days. The estimated total shore-based linefish catch (excluding boat-based catches) from the estuary for the years 2004 and 2005 was 37 231 ± 1 326 fish and 26 938 ± 706 fish (approximately 8 t and 7 t) respectively. Compared with other estuaries along the South African east coast where angler catches have been surveyed, species diversity in catches from the cool-temperate Berg River Estuary was low, with only 15 species caught, of which three, elf Pomatomus saltatrix (56%), harder Liza richardsonii (31%) and carp Cyprinius carpio (11%), dominated the catch. Average linefish catch per unit effort of most species increased significantly in the two years subsequent to the closure of the long-existing commercial gillnet fishery in March 2003. Length frequency distributions revealed significant increases in the average size and an increased contribution of larger size class elf and harder to the linefish catch over the monitoring period, suggesting a degree of recovery of the estuarine icthyofauna after more than a century of intensive gillnet fishing.  相似文献   

14.
Recruitment of early life stages into estuaries is an integral part of the life cycle of many marine fish species. Although estuaries are naturally environmentally dynamic, they also are subject to anthropogenic disturbances, including land use and climate change, which may affect recruitment. Rhabdosargus holubi is an endemic marine-spawning species predominantly associated with freshwater-rich estuaries which serve as nursery areas for postflexion larvae and juveniles. This study assessed the effect of environmental variables on the dynamics of recruitment of R. holubi larvae and juveniles into the Swartkops and Sundays estuaries, South Africa. Over a period of two years, fyke nets were set at each estuary mouth to monitor movement into the estuaries at each tidal phase over a 24 h cycle during two sampling sessions per season. Rhabdosargus holubi larvae recruited into estuaries primarily in summer and autumn and during the ebb tide at night, while juvenile movements showed no pattern. Salinity, turbidity and temperature were significantly important factors affecting R. holubi recruitment, with pH having no significant effect. Turbidity and salinity are affected by rainfall and freshwater abstraction which may thus influence recruitment. Rhabdosargus holubi is dependent on estuaries, so a combination of future changes in turbidity, salinity and temperature due to predicted climate change may place populations at risk.  相似文献   

15.
Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%). The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22). Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries. Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary. Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ～529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries. Despite covering large distances between estuaries, individuals often returned to their tagging estuary. Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity.  相似文献   

16.
Proponents of catch share-based fisheries have claimed ecological stewardship can result from the assignment of individual catch quotas. This claim is examined by analyzing the distribution of benthic habitat protection measures adopted by quota-owning industry sectors within the exclusive economic zones (EEZs) of the U.S. (Alaska), New Zealand, and high seas seamounts within the Southern Indian Ocean Deepsea Fishers Association (SIODFA) competence area. Results suggest the protection of both benthic ecosystems and essential fish habitat (EFH) are marginal at best when quota owners have primacy in determining the boundaries of bottom trawl closures. The majority of the areas in these three regions that are closed to trawling are too deep to fish, may not contain vulnerable marine ecosystems, and do not have high abundances of commercially important species. “Freezing the footprint” of bottom trawling is not the best method for benthic habitat protection in areas where the fishing industry is actively fishing vulnerable habitats. Analytical methods should be applied to help determine boundaries of future bottom trawl closures rather than allowing the fishing industry to place benthic protection areas (BPAs) in areas where they are not interested in fishing.  相似文献   

17.
Stable carbon and nitrogen isotopes (δ13C, δ1?N) were used to analyse food web dynamics of two of the main estuaries of the Portuguese coast: Tejo and Mira. The ultimate sources of organic matter supporting production of some of the most abundant and commercially important fish species were determined; and seasonal, inter- and intra- estuarine differences in the trophic relations among producers and consumers were identified. Stable isotope analysis was performed in different producers, primary consumers (main prey items for fish) and fish species (Solea solea, Solea senegalensis, Pomatoschistus microps, Dicentrarchus labrax, Liza ramada, Diplodus vulgaris and Atherina presbyter) of two areas in each estuary, in July and October 2009. Model calculations showed that the main prey for the fish species in the Tejo estuary used mostly salt marsh-derived organic matter as nutritional sources, with no marked differences between the sampled months. Trophic levels of fish species from the same estuary differed at multiple scales: inter-species, seasonally and spatially (both between and within estuaries). Significant differences in isotopic composition of fish species were more pronounced spatially (between the two sampled areas in the estuary) than seasonally (between sampled months). Trophic relationships in both estuaries demonstrated that organic matter is transferred to higher trophic positions mainly through benthic pathways. This shows the flexibility of these species to share resources and to exploit temporary peaks in prey populations. The present results showed that extensive disturbance in intertidal habitats from both estuaries may potentially change the balance of organic matter in the base of these complex food webs.  相似文献   

18.
We examine the microchemistry of otoliths of cohorts of a fished population of the large catadromous fish, barramundi Lates calcarifer from the estuary of a large tropical river. Barramundi from the estuary of the large, heavily regulated Fitzroy River, north-eastern Australia were analysed by making transects of 87Sr/86Sr isotope and trace metal/Ca ratios from the core to the outer edge. Firstly, we examined the Sr/Ca, Ba/Ca, Mg/Ca and Mn/Ca and 87Sr/86Sr isotope ratios in otoliths of barramundi tagged in either freshwater or estuarine habitats that were caught by the commercial fishery in the estuary. We used 87Sr/86Sr isotope ratios to identify periods of freshwater residency and assess whether trace metal/Ca ratios varied between habitats. Only Sr/Ca consistently varied between known periods of estuarine or freshwater residency. The relationships between trace metal/Ca and river flow, salinity, temperature were examined in fish tagged and recaptured in the estuary. We found weak and inconsistent patterns in relationships between these variables in the majority of fish. These results suggest that both individual movement history within the estuary and the scale of environmental monitoring were reducing our ability to detect any patterns. Finally, we examined fish in the estuary from two dominant age cohorts (4 and 7 year old) before and after a large flood in 2003 to ascertain if the flood had enabled fish from freshwater habitats to migrate to the estuary. There was no difference in the proportion of fish in the estuary that had accessed freshwater after the flood. Instead, we found that larger individuals with of each age cohort were more likely to have spent a period in freshwater. This highlights the need to maintain freshwater flows in rivers. About half the fish examined had accessed freshwater habitats before capture. Of these, all had spent at least their first two months in marine salinity waters before entering freshwater and some did not enter freshwater until four years of age. This contrasts with the results of several previous studies in other parts of the range that found that access to freshwater swamps by larval barramundi was important for enhanced population productivity and recruitment.  相似文献   

19.
This study has analysed for the first time fish composition and assemblage structures of three small macrotidal estuaries of the Eastern English Channel (EEC) and has explored the influences of 19 biotic and abiotic variables on the fish assemblages. Fish from Canche, Authie and Somme estuaries were collected during spring (June 2006 and May 2007) and autumn (September 2006) along the estuarine gradients using a 1.5 m beam trawl. Using identical sampling protocols, the study also analysed and compared for the first time taxonomic and functional aspects of the fish assemblages in 15 estuaries located along the Atlantic and English Channel coasts. SIMPER analysis showed high similarities in fish assemblages in the three EEC estuaries and during either spring or autumn periods. However, intra-estuary similarities were relatively low, indicating that fish assemblage structures (species richnesses or abundances) were more variable within the estuary (salinity gradient) than between estuaries and/or seasons (spring vs autumn). Although numerous environmental variables were included in the study, only 47% of the variability observed in the fish distribution was explained. Fish spatial variations in the EEC estuaries are mostly driven by abiotic variables as opposed to biological interactions. As indicated by CCA, salinity and muddy sediments were the two most important factors structuring the fish assemblages. The macrobenthos being very abundant in the EEC estuaries (580–1121 ind. m−2), the availability of potential prey is probably not a limiting factor in the utilization of estuaries by fish. Contrary to the majority of French estuaries dominated by estuarine species (ES), the fish assemblages of the EEC estuaries are clearly dominated by marine migrant (MM) species (65% on average) with high abundance of juveniles (mostly young-of-the-year). Cluster and SIMPROF's analyses distinguished the functional structure of the 15 estuarine fish assemblages into different clusters. The three EEC estuaries form a similar group with the largest French estuaries (Seine, Loire and Gironde). The latters were characterized by higher MM/ES ratio compared to the other French estuaries. Freshwater flow and tidal range were the main factors associated with this group of estuaries. The results of the present study do not indicate that anthropogenic impacts (chemical contamination) on estuaries affect their ecological functioning as described by the fish ecological guilds. It is suggested that the guild approach may not be useful to provide valuable information on the ecological status of estuaries.  相似文献   

20.
This study investigated whether the current lateral boundary for estuaries in South Africa, i.e. the estuarine functional zone (EFZ), includes all estuarine habitats. The EFZ covers 173 930 ha in 304 estuaries/outlets nationally. Field surveys and analysis of available aerial images showed that 82 (12 956.70 ha) of these estuaries (26%) had estuarine habitats occurring outside of this boundary. As a result of mapping scale, the National Vegetation Map does not represent habitats that are associated with small estuaries (approximately 50% of South Africa's estuaries). For estuaries in the Western and Eastern Cape provinces, most habitats have been lost due to urban development, whereas in subtropical areas (northern Eastern Cape and KwaZulu-Natal), cultivation has removed estuarine habitat. Although delineation of boundaries can be complicated by landcover changes, the estuarine lateral boundary in Cape estuaries could be identified based on sediment characteristics (moisture content, organic content, electrical conductivity), groundwater characteristics (salinity, conductivity and depth) and plant species. The delineation of the EFZ needs to be consistent, inclusive of all estuarine physical and biological processes, and cost-effective to identify so that it can protect estuarine habitats.  相似文献   

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