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1.
The recruitment of distinct year-class cohorts in two sparid species, Rhabdosargus holubi and Lithognathus lithognathus, were linked to records of daily mouth state in the intermittently open East Kleinemonde Estuary, South Africa, between 1995 and 2006. L. lithognathus only recruited into the estuary in years when the mouth opened between late August and January. This was attributed to a limited spawning season and inability to recruit during wave overwash events. In contrast, R. holubi recruitment was uninterrupted and not influenced by seasonality of estuary access opportunities (mouthopening and overwash events). Estuarine-dependent residency periods ranged from 27 months to 48 months for L. lithognathus and 12 months to 23 months for R. holubi. The interannual abundances of these estuarydependent sparids were determined by reproductive seasonality, recruitment strategy and seasonal timing of estuarine access opportunities.  相似文献   

2.
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   

3.
Spatial and temporal variation in fish assemblage structure of Koycegiz Lagoon–Estuarine System (KLES), located on the northwestern Turkish coast of Mediterranean, was investigated along an estuarine gradient where salinity ranged from 5 in upper reaches to 40 in lower reaches during October 1993–September 1994. Throughout the study, 42 species, consisting of marine (25), marine–estuarine-dependent (12), freshwater (3), catadromous (1), and estuarine resident (1) forms, were collected in trammel nets. Although species richness of marine species was greater than that of other groups, numerical contribution by marine species to the total catch was only 16%. Tilapia spp., the most abundant species mostly during summer and early spring at upper reaches, contributed 17% of the total samples. Among the seven species of Mugilidae, which contributed 42% of the total catch, Mugil cephalus, Liza aurata, and Liza salines contributed 10, 13, and 10% of the total catch, respectively. Consistent with findings from other studies, species richness and abundance were highest during late spring and summer and the lowest during winter and early spring. Samples from sites at or near the sea had more marine species. Samples from upper reaches had more freshwater and marine–estuarine-dependent species. Canonical correspondence analysis (CCA) indicated that salinity and turbidity were the most important environmental parameters affecting fishes. Sites near the sea were associated with high salinity and low turbidity, and sites in upper reaches had low salinity and high turbidity. Thus, the pattern observed in fish assemblage structure appears to be strongly influenced by species' responses to dominant salinity and turbidity gradients.  相似文献   

4.
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   

5.
Understanding and characterising movement and area-use patterns of fishes within estuaries, as well as understanding the degree of connectivity between estuaries and the marine environment, can provide important insights into a species’ ecology, which is fundamental for effective management and conservation. Mark-and-recapture data obtained from the 082 TAG FISH Project, a dart-tagging programme, were used to describe movement patterns of juvenile leervis Lichia amia in the permanently open Swartkops Estuary, South Africa, as well as the degree of connectivity with the adjacent marine environment. A total of 628 juvenile leervis were tagged from 2008 to 2015, of which 77 fish (12.3%) were recaptured, with juveniles comprising 85.7% of all measured recaptures. The majority of recaptures (75.3%) were made within the Swartkops Estuary, indicating estuarine philopatry, with 23.4% having moved less than 1 km, revealing site fidelity, but most (51.9%) displaying estuarine roaming. A smaller portion of recaptures (27.7%) had dispersed to other habitats; 16 (20.8%) displayed multiple-habitat connectivity, while only 3 (3.9%) had undertaken long-distance movements (>100 km) and were recaptured up to 825 km northeast of the Swartkops Estuary. Lichia amia that had moved greater distances were characterised by a greater mean size and age at the time of recapture. This study provides valuable information on the philopatry and dispersal of juvenile L. amia.  相似文献   

6.
Stomach content analyses were performed on the Cape stumpnose Rhabdosargus holubi. The contents were identified to species level and the dietary importance of each component assessed by employing unrelated quantifying methods, which were subsequently combined to determine an index of relative importance (IRI). The index was determined on a seasonal basis as well as for individual sampling stations. The aquatic macrophyte Zostera capensis was the single most abundant item and, together with filamentous algae, constituted the major proportion (IRI = 7 314) of the diet. Crustacea were the next most abundant (IRI = 6 534), followed by Mollusca (IRI = 160). Stomach contents from the sampling stations in the lower reaches were dominated by aquatic macrophytes and algae, whereas those from the middle and upper reaches had a higher incidence of Crustacea. Mollusca in the diet were uniformly distributed throughout the estuary. There was considerable flexibility in the feeding pattern of R. holubi.  相似文献   

7.
The role of submerged macrophytes as refugia from fish predation and as possible food sources for the estuarine isopod Exosphaeroma hylocoetes ( Barnard, K.H., 1940) was investigated. Laboratory experiments tested the effectiveness of artificial vegetation, replicating submerged vegetation, in enabling isopods to elude selected fish predators Rhabdosargus holubi, Glossogobius callidus, Monodactylus falciformis and Clinus cottoides. Isopods preferentially hid in the vegetation (>90%), even in absence of fish. The predatory fish had varying success in finding isopods within the vegetation. Isopod mortality ranged from 2% (R. holubi) to a maximum of 87% (C. cottoides) within vegetation, depending on the fish predator present. Stable isotope and fatty acid analyses ruled out the submerged macrophyte Ruppia maritima and inundated fringing grasses as direct food sources, but highlighted the epiphytic biota (mainly diatoms) found on the submerged vegetation and sediments as more likely food sources. These findings are consistent with gut content analyses. The results suggest that the close association of E. hylocoetes with R. maritima is the result of the vegetation providing the isopod with a refuge against fish predation as well as areas of increased food availability.  相似文献   

8.
This study made use of data from three long-term fish tagging projects along the South African coastline to investigate the movement behaviour of the endemic black musselcracker Cymatoceps nasutus (Sparidae). From 1984 to 2016, a total of 3 430 C. nasutus (178–980 mm fork length) were tagged (with small plastic dart tags) throughout the species’ distributional range, with an overall reported recapture rate of 7.2%. Recaptured individuals displayed high levels of residency, moving an average of 14.8 km, with time-at-liberty ranging from 0 to 6 809 days. The majority of recaptures (84.6%) were made within 1 km of the tagging sites; however, some large-scale movements, of up to 528 km, were recorded. Although C. nasutus individuals moving greater distances were characterised by greater mean sizes (mm fork length) at time of recapture, the distances moved by juveniles were not significantly different from those of adults (p > 0.05). Low levels of connectivity among coastal regions were therefore expected due to the high degree of residency displayed by this species. Combining traditional management approaches together with a well-designed network of no-take marine protected areas is likely to be the most effective way to protect this vulnerable species. A lack of data on the movements of adults remains a challenge, but this could be overcome by tracking large individuals tagged with long-life acoustic transmitters.  相似文献   

9.
Understanding movement behaviour is essential for effective management of fishery species. Dart tags were used to study coastal movement patterns of white steenbras Lithognathus lithognathus, an overexploited seabream (Sparidae) in South Africa. In total, 6 962 fish (190–1 080 mm fork length) were tagged throughout the species’ distributional range, in four long-term fish-tagging programmes. The predominant behaviour recorded was residency, with relatively short-ranging movements. More than 60% of the 351 recaptured fish were recaptured within 1 km of their tagging site, some of which were at liberty in excess of three years. Most of the juveniles (93.9%), subadults (71.7%) and adults (64.0%) were recaptured within 10 km. Occasional long-distance movements of up to 800 km were recorded. Recapture distances were positively, but weakly, correlated with fish fork length (n = 257 fish measured at recapture; r2 = 0.166, p < 0.001). Low levels of connectivity among coastal areas suggest that large-scale annual spawning migrations, as previously hypothesised for this species, are unlikely, which raises the possibility of multiple spawning sites. Seventy-seven percent of L. lithognathus tagged within three marine protected areas (MPAs) were recaptured within the same MPA, suggesting that area closures provide protection for L. lithognathus through the post-estuarine juvenile, subadult and adult life stages. We confirm that the country’s current network of coastal MPAs plays a vital role in sustaining this species, and suggest that additional closures, or otherwise substantial reductions in catch rates, are necessary for the species’ recovery.  相似文献   

10.
Rhabdosargus holubi is a small (maximum weight=2.4?kg) yet important fishery species in the estuaries of the south-east coast of South Africa. Little is known of its biology and specifically its growth rate, which is essential for sustainable management of the fishery. We examined and counted the opaque zones in the sectioned otoliths of 134 R. holubi to determine its age and growth parameters. The otoliths from two recaptured fish marked with oxytetracycline confirmed that one opaque zone was deposited annually. The species reached a maximum age of 18 years and growth was adequately described by a von Bertalanffy growth function of the form: Lt = 358.1 (1 – e?0.24(t+0.77)) mm fork length. There were no significant differences between any of the male and female growth parameters (likelihood ratio test: p = 0.3). The growth was slow (omega index: ω = 86.56); however, despite this, the unique life history of R. holubi may provide a degree of resilience to heavy fishing pressure in estuaries.  相似文献   

11.
Fisheries managers are increasingly promoting catch-and-release (C&R) to manage recreationally angled fish stocks. Despite this, there is a scarcity of information on the effects of C&R on estuarine-dependent species. Cape stumpnose Rhabdosargus holubi dominates the recreational fisheries catch and provides an important source of food for subsistence fishers in some temperate South African estuaries. The health and survival of R. holubi exposed to a C&R event was investigated by examining their physiological stress response (blood glucose and lactate), reflex impairment (reflex action mortality predictors [RAMP]) and short-term (12-hour) survival. Fish were captured and exposed to one of three air-exposure treatments: 0 s, 30 s or 90 s. Stress and health were measured either immediately (immediate) or one hour after (delayed) the C&R event. There was no significant difference in blood glucose between air-exposure treatments, but there was a significant difference between the mean immediate and delayed glucose levels within each treatment (F(2,143) = 81.8, p < 0.01). In contrast, blood lactate level was significantly higher in the 90-s treatment (p < 0.05). Immediate blood lactate levels were significantly lower than the delayed samples for each treatment (F = 4.29, p = 0.02; n = 169). Although all fish exhibited at least one reflex impairment, the RAMP score was significantly higher in the 90-s air-exposure treatment (H(2,86) = 9.73, p = 0.007). Also, RAMP scores were significantly lower in the delayed samples (p < 0.01). Although short-term mortality was relatively low (2.3%) for this species, it was highest in the 90-s treatment (7%). These results suggest that physiological stress is higher when R. holubi are exposed to longer periods of air exposure and that the physiological stress of fish subject to a C&R event is best measured after a delay.  相似文献   

12.
Estuaries are regarded as valuable nursery habitats for many commercially important marine fishes, potentially providing a thermal resource, refuge from predators and a source of abundant prey. To assess the extent of estuarine use by juvenile (0+) common sole (Solea solea), whiting (Merlangius merlangus) and European seabass (Dicentrarchus labrax) we: (1) developed techniques to distinguish between estuarine and coastally-caught juveniles using otolith chemistry; and (2) examined the accuracy with which multi-elemental signatures could re-classify juveniles to their region of collection.High-resolution solution-based inductively coupled plasma mass spectrometry (HB-SB-ICPMS) was used to quantify 32 elements within the juvenile otoliths; 14 elements occurred above detection limits for all samples. Some elemental distributions demonstrated clear differences between estuarine and coastally-caught fish. Multivariate analysis of the otolith chemistry data resulted in 95–100% re-classification accuracy to the region of collection. Estuarine and coastal signatures were most clearly defined for sole which, compared to bass and whiting, have low mobility and are less likely to move from estuarine to coastal habitats between larval settlement and later migration to adult stocks. Sole were the only species to reveal an energetic benefit associated with an estuarine juvenile phase. The physiological ability of bass to access upper estuarine regions was consistent with some elemental data, while the high mobility and restricted range of whiting resulted in less distinct otolith chemistries.  相似文献   

13.
Broad-scale movements (10s–100s km) of highly migratory species, such as sharks, present unique management challenges as fish migrate across international boundaries, thereby exposing them to different levels of anthropogenic pressure. Lemon sharks and blacktip sharks are well-studied throughout their range in the western North Atlantic, but broad-scale movements in the Caribbean region are largely unknown. Utilizing 10 years (2004–2014) of acoustic and conventional tagging data, this study presents the post-nursery movements of young of the year (YOY) and juvenile blacktip (n = 198) and lemon (n = 130) sharks tagged in the United States Virgin Islands (USVI). A total of five (2.5%) blacktip sharks were recaptured by recreational and commercial fishers in the greater Caribbean and as far north as the southeastern coast of the United States, moving between 2 and 2,200 km and crossing a minimum of six international boundaries. Of the acoustically tagged blacktip (n = 88) and lemon (n = 45) sharks, 28 (32%) and 16 (24%), respectively, were detected outside the boundaries of the nursery area in which they were tagged, dispersing throughout the USVI territory; blacktip sharks were acoustically detected beyond territorial waters as far as Florida, United States (1,881 km). Both species transited through local marine protected areas but did not establish residency resulting in little protection. This is the first study to examine connectivity between blacktip shark populations of the USVI and the east coast of the United States.  相似文献   

14.
Knowledge of population distribution and movement is crucial for the conservation and management of shark species occurring in coastal waters. From 1984 to 2009, 641 scalloped hammerheads Sphyrna lewini, 1 342 smooth hammerheads Sphyrna zygaena and 1 352 unspecified hammerheads Sphyrna spp. were tagged and released along the east coast of South Africa, with recapture rates of 1.9%, 1.5%, and 0.7% respectively. Maximum and average distance moved was 629 km and 147.8 km (95% CI = 33.0–262.7 km) for S. lewini and 384 km and 141.8 km (95% CI = 99.1–184.5 km) for S. Zygaena respectively. The majority of sharks (68% S. lewini, 74.1% S. zygaena and 33.5% Spyrna spp.) were tagged in the Transkei region, with the largest number tagged in Port St Johns. Across regions, most tagged sharks were >50–100 cm precaudal length (PCL), except in Transkei where more sharks >100–150 cm PCL were tagged. In the Western Cape, Southern Cape and Eastern Cape, few sharks were tagged during the autumn/winter months, whereas in KwaZulu-Natal and Transkei sharks were tagged throughout the year. Large-scale directional movements observed may have been migrations in response to seasonal sea surface temperature changes. We identify coastal locations in Transkei that are of importance to juvenile and subadult hammerhead populations year-round.  相似文献   

15.
Although the recruitment of larvae and juveniles of marine fishes into estuaries has been well documented, little is known about the factors governing the immigration of estuary-associated marine fishes into estuaries. Fishes have a well-developed sense of smell and it has been suggested by several workers that olfactory cues of freshwater or estuarine origin serve as stimuli, attracting larvae and juveniles of estuary-associated species into estuaries. Attraction of postflexion Rhabdosargus holubi larvae to estuary and river water from the Kowie estuarine system, South Africa, was measured using a rectangular choice chamber. In experiments, conducted during peak recruitment periods, larvae selected estuary and river water with a significantly higher frequency than sea water. This study, the first to assess the possible role of olfaction in the recruitment process of an estuary-associated marine fish species, demonstrates that larvae are able to recognise water from different origins, probably based on odour.  相似文献   

16.
The short-term movements of a small temperate fish, the annular seabream Diplodus annularis (Linnaeus 1758), were examined using standard tag-recapture and passive acoustic telemetry in Palma Bay (NW Mediterranean), a marine protected area (MPA). The study aimed to provide valuable information for assessing the recreational fishery and its results suggest that MPAs can be used to protect the adult stock of D. annularis. All the fish tagged with standard tags were recaptured near the release locations, with a maximum distance of ∼300 m. The maximum time between release and recapture was 185 d. Two different arrays of acoustic receivers were deployed, one in 2008 and another in 2009, within the MPA. Twenty adults were surgically tagged with acoustic transmitters. Fish monitored in 2008 (n = 12) were translocated from the point of capture to analyse the movement behaviour after artificial displacement. Upon release at displaced locations, 67% of the fish moved towards the original capture location using a time of return that ranged from 0.75 to 15.25 h. Fish monitored in 2009 (n = 8) were released at the point of capture. They showed high site fidelity with a maximum period of 27 d between the first time and the last time they were detected.  相似文献   

17.
Long-term home-range and movement dynamics of spotted grunter Pomadasys commersonnii and the distribution of their dominant prey, the sandprawn Callichirus kraussi, were investigated in the intermittently open East Kleinemonde Estuary, South Africa. In addition, the effects of fish length, diel cycle, season and other abiotic factors on home range and area use were examined. Nine adult spotted grunter (326–489?mm total length) were tagged with acoustic transmitters, and their movements were studied by manual tracking on six consecutive days and nights during each of five tracking sessions from March to November 2004. In addition, movement patterns were recorded by stationary data-logging receivers. Kernel home ranges (95% utilised distribution) varied in size (mean: 76 797?m2?, range: 26 296–165 321?m2), but were all located in the lower one-third of the 3.6 km-long estuary. There was no effect of season, the diel cycle or fish length on the home-range estimates. However, the distribution of prey corresponded with the home-range distribution of tagged fish. Although sandprawn distribution was highly variable within and among transects and depth classes, sandprawns were most abundant in the lower region of the estuary, which corresponded to the home-range distribution of spotted grunter. Spatial distribution of prey appears to be a dominant factor influencing home-range parameters of this species within an intermittently open estuary.  相似文献   

18.
Increases in the density of exploited species on unfished reefs logically implies that some individuals are at least temporarily resident, or show fidelity to a particular area. We tagged snapper (Pagrus auratus (Bloch & Schneider 1801)) in the Leigh Marine Reserve, New Zealand using visible implant fluorescent elastomer tags, recoverable by diver visual sightings without the need to recapture the fish. Batch tagging of snapper (n = 907) was done during an angling survey in June and December 1996, and individually coded tags were implanted by divers (n = 117) in January 1999. Snapper tagged during both programmes were recovered on irregular intervals from 1997 to 2000. There were 71 recoveries of batch tags within 500 m of their tagging sites, and these recoveries were still being made >3 years after tagging: Of individually coded fish, 49 (42%) were seen, sometimes repeatedly over several months, close to their respective tagging sites. These observations included snapper as small as 23 cm fork length, contradicting the commonly held impression that only large snapper take up long‐term residency on reefs. This preliminary evidence suggests that some snapper exhibit site fidelity to areas only a few hundred metres wide, and in the absence of fishing may occupy the same area for years.  相似文献   

19.
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   

20.
Estuarine and sheltered coastal habitats that contain physical structure are potentially important nurseries for juvenile fish. Many of these structured habitats, however, are potentially vulnerable to stressors such as elevated turbidity. Quantifying the benefits that structured habitats provide to juvenile fish may therefore be an important step in the management process. We investigated the value of structured habitat for juvenile fishes in northeastern New Zealand, using artificial seagrass units (ASUs) with varying blade density. ASUs were predominantly settled by juvenile snapper (Pagrus auratus) and spotty (Notolabrus celidotus). The density of both snapper and spotty was greatest on ASUs with the highest blade density. For snapper, a gradient in abundance was present (with higher abundance closer to the harbour mouth), suggesting either a gradient in the supply of recruits or a potential recruitment shadow effect. The size distribution of juvenile snapper (12–70 mm fork length) was very similar on both sampling trips, despite the 2‐month interim period, suggesting an ontogenetic habitat shift dependent on size. The condition of juvenile snapper from ASUs with the highest blade density was also greater than the other ASU treatments. Overall, these results provide new empirical evidence that habitats with physical structure within shallow estuarine systems are important to early stage juvenile fishes such as snapper, and indicate that the location‐specific context of that habitat is also likely important.  相似文献   

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