Estuarine Nursery Areas Research Articles

Facultative habitat selection in Pacific tarpon Megalops cyprinoides as revealed by otolith Sr:Ca ratios

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 387:255-263 (2009) - DOI: https://doi.org/10.3354/meps08119 Facultative habitat selection in Pacific tarpon Megalops cyprinoides as revealed by otolith Sr:Ca ratios K. N. Shen2, C. W. Chang3,4,*, Y. Iizuka5, W. N. Tzeng1,2,* 1Department of Life Science, and 2Institute of Fisheries Science, College of Life Science, National Taiwan University, Taipei, Taiwan 106, ROC 3National Museum of Marine Biology and Aquarium, Pingtung, Taiwan 944, ROC 4Institute of Marine Biodiversity and Evolutionary Biology, National Donghwa University, Hualien, Taiwan 974, ROC 5Institute of Earth Sciences, Academia Sinica, Nankang, Taipei, Taiwan 115, ROC *‑Corresponding authors. Email: changcw@nmmba.gov.tw; wnt@ntu.edu.tw ABSTRACT: The Pacific tarpon Megalops cyprinoides is a euryhaline fish that is widely distributed in offshore waters of the tropical and subtropical Indo-Pacific Ocean. It spawns in offshore waters and the larvae drift with tidal currents before recruiting to estuarine nursery areas at ~25 to 30 d post-hatching. Young Pacific tarpon are found in coastal waters, rivers, estuaries, inner bays, and mangrove areas. However, their age-specific migratory behavior and habitat selection are still unclear. The strontium (Sr) concentration in seawater is ~100× higher than in fresh water, and the Sr:Ca ratios in fish otoliths are positively correlated with ambient salinity and are thus widely used in studying fish migration between seawater and freshwater environments. To understand the migratory environmental history of the Pacific tarpon, otolith Sr:Ca ratios of leptocephali collected from the estuary and sub-adults collected from both Tadu Creek and offshore waters on the west coast of Taiwan were examined using an electron probe microanalyzer (EPMA). Fish were aged by counting otolith annuli. The Sr:Ca ratios in leptocephalus otoliths were high (7.4 ± 0.03 × 10–3). However, the patterns of otolith Sr:Ca ratios in 1 to 3 yr old sub-adults were diverse and can be divided into 3 types: largely brackishwater residents, largely freshwater residents, and vagrants between brackish and fresh waters. Fish older than 4 to 5 yr all return to the marine environment. This study demonstrates that habitat selection in the Pacific tarpon after the leptocephalus stage is facultative and that their migratory environmental history can be reconstructed from otolith Sr:Ca ratios. KEY WORDS: Megalops cyprinoides · Pacific tarpon · Leptocephalus · Otolith · Sr:Ca ratio Full text in pdf format PreviousNextCite this article as: Shen KN, Chang CW, Iizuka Y, Tzeng WN (2009) Facultative habitat selection in Pacific tarpon Megalops cyprinoides as revealed by otolith Sr:Ca ratios. Mar Ecol Prog Ser 387:255-263. https://doi.org/10.3354/meps08119 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 387. Online publication date: July 28, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Behavioral responses of juvenile weakfish (Cynoscion regalis) to diel-cycling hypoxia: swimming speed, angular correlation, expected displacement, and effects of hypoxia acclimation

Areas of low flushing and high nutrient loading in shallow estuaries are susceptible to diel-cycling hypoxia and also represent important nursery habitat for juvenile estuary-dependent fishes. Swimming speed, angular correlation, and expected displacement were measured in juvenile weakfish ( Cynoscion regalis ) in response to diel-cycling hypoxia (cycling between 7.0 and 0.4 mg O2·L–1). Saturation-acclimated (7.0 mg O2·L–1) weakfish exhibited an active response by increasing swimming speed (to a maximum at 2.8 mg O2·L–1) and angular correlation (to a maximum at 1.4 mg O2·L–1) as dissolved oxygen (DO) decreased, after which weakfish exhibited a passive response and both swimming speed and angular correlation decreased by ~50% and 70%, respectively, at 0.4 mg O2·L–1. Weakfish acclimated to hypoxia (cycling between 2.0 and 11.0 mg O2·L–1for 10 days) did not vary swimming speed during decreasing DO or DO recovery (increasing DO) and had an overall swimming speed 46% lower than saturation-acclimated weakfish at 7.0 mg O2·L–1. At the end of DO recovery, saturation- and hypoxia-acclimated weakfish had recovered 60% and 80% of their initial swimming speeds, respectively. The relationship between previous hypoxia exposure and behavior may be an important determinant of habitat utilization in estuarine nursery areas impacted by diel-cycling hypoxia.

Geographical and typological changes in fish guilds of South African estuaries

A comparative analysis of fish estuary association guilds was undertaken on some 190 South African estuaries. This pioneering study spanned three zoogeographic regions and included three broad estuarine types. The guild compositions of the estuaries were compared based on an importance value, incorporating taxonomic composition, numerical abundance and relative biomass. Multivariate analyses included both inter‐regional (zoogeographic) and intra‐regional (estuarine typology) comparisons. The major estuary‐associated guilds (estuarine species and marine migrant species) were important in all estuary types within all biogeographic regions. Significant differences both between regions and between estuary types within regions, however, were recorded. Cool–temperate estuaries were generally dominated by migratory species (estuarine migrants and marine migrant opportunists) while the importance of species dependent on estuaries (estuarine residents and estuarine‐dependent marine migrants) was higher in warm–temperate and subtropical regions. The significance of estuarine nursery areas, particularly in regions where estuaries are few in number, is highlighted. In terms of typology, migratory species assumed a greater importance in predominantly open systems, while freshwater and estuarine‐resident species were more important in predominantly closed systems. Predominantly closed estuaries, however, were also important for marine migrant species, which further highlights the significance of these systems as nursery areas for fishes.

Latitudinal gradients in growth and spawning of sea bass, Dicentrarchus labrax, and their relationship with temperature and photoperiod

0-group Sea bass, Dicentrarchus labrax, were captured in four estuarine nursery areas along the Portuguese coast, during the spring and summer of 2005. This coast has a North–South orientation which means that it is particularly suited for the investigation of latitudinal trends. Growth and hatch dates were estimated through otolith daily increment analysis. A clear latitudinal gradient in growth rates was detected. D. labrax mean growth rates were 0.48 mm d −1, 0.51 mm d −1, 0.56 mm d −1 and 0.61 mm d −1, from the Ria de Aveiro, the Mondego estuary, the Tagus estuary and the Mira estuary, respectively. A latitudinal gradient also existed in the spawning season of this species, particularly concerning its onset, which occurred earlier in the South. Analysis of sea surface temperature data from the adjacent coastal waters showed that spawning is not triggered by an increase in temperature, as has been argued in other coastal areas at higher latitudes. Photoperiod played a crucial role in the determination of spawning season at the Portuguese coast latitudinal range. The impact of future climate change on the observed patterns is also discussed.

A preliminary survey of the estuaries on the south coast of South Africa, Cape St Blaize, Mossel Bay—Robberg Peninsula, Plettenberg Bay, with particular reference to the fish fauna

The coastal river systems on the south coast of South Africa from Cape St Blaize to Robberg Peninsula were surveyed during October and November 1994. The ichthyofaunal and physico-chemical characteristics of each system are presented and their suitability as estuarine nursery areas is discussed. Five systems (Rooi, Meul, Grooteiland, Kranshoek and Crooks) are outlets of small coastal streams and probably provide little or no habitat for either resident estuarine or migrant marine fishes owing to their small size. Four systems (Maalgate, Gwaing, Skaapkop and Kaaimans) are located within deeply incised valleys and have a permanent connection with the sea. The amount of marginal and intertidal habitat available to fishes, however, is limited due to their morphology. Six systems (Hartenbos, Groot Brak, Touw, Swartvlei, Goukamma and Noetsie) are intermittently open to the sea. Although the Touw and Swartvlei are connected to coastal lake systems, flow within these estuaries is not sufficient to prevent the build up of a sand barrier at the mouth. The Hartenbos, Groot Brak, Goukamma, and Noetsie are also periodically closed by a sand bar. The construction of a dam in the lower catchment of the Groot Brak has affected the hydrology of the system. The two remaining estuaries (Klein Brak and Knysna) are permanently open. In addition to strong tidal currents, the fixing of the mouth of the Knysna Estuary between rocky headlands also serves to maintain a permanent connection with the sea. Mugilidae and Sparidae were represented by the greatest number of species, and also dominated catches numerically and by mass. The fish fauna of all the estuaries surveyed were dominated by the juveniles of estuarine-dependent marine species and estuarine-resident species were also well represented in catches. The estuaries surveyed provide a vital habitat for both marine migrant species and resident species, most of which are endemic to the region.

Interspecific variations of otolith chemistry in estuarine fish nurseries

Otolith chemical composition differed between juveniles of five fish species (Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax) in nursery areas of six estuaries along the Portuguese coast (Douro, Ria de Aveiro, Mondego, Tejo, Sado and Mira). Spatially consistent patterns in the concentration of some elements were responsible for differences between species. Discrimination of estuaries using data from all species simultaneously averaged 44·7% of correctly classified cases, whilst discrimination of species averaged 76·2%. Moreover, species‐related patterns in otolith fingerprints were highlighted when comparing species for each estuarine nursery area, with intra estuarine species discrimination averages ranging from 86·2 to 100·0%. Similarities in the otolith elemental fingerprints were larger between species with close phylogeny and ecology, particularly between flatfish and perciform species. In addition to the differences in physiological regulation of species, specific microhabitat use in a common environment was suggested as a relevant factor for the differentiation of otolith chemistry among species occurring in the same locations. Despite positive results in specific estuaries, variation in otolith composition limited the use of species as proxies to classify others to their system of origin.

Declining catch per unit effort of an estuarine-dependent fish, Rhabdosargus sarba (Teleostei: Sparidae), in the marine environment following closure of the St Lucia Estuarine System, South Africa

Monitoring of catch per unit effort of the tropical stumpnose Rhabdosargus sarba in the St Lucia Marine Reserve between 2001 and 2005 revealed a significant decline. A similar decline was evident from shore patrol data collected by Ezemvelo KwaZulu-Natal Wildlife staff in the southern areas of the Greater St Lucia Wetland Park. As the distribution of fishing effort has decreased considerably since the promulgation of a beach vehicle ban in January 2002, this decline in the abundance of stumpnose has not been attributed to overfishing but rather to the closure of the mouth of the St Lucia estuary and lake system. The reason for this is because tropical stumpnose make extensive use of St Lucia as a nursery area and, since the mouth closure in June 2002, there has been no recruitment of juvenile fish into, or adult fish out of, the system. This emphasises the importance of estuarine nursery areas and highlights the need for ongoing catch and effort monitoring.

Ecological performance of red drum (Sciaenops ocellatus) larvae exposed to environmental levels of the insecticide malathion

Malathion is a highly soluble organophosphate insecticide that is widely used in agriculture and mosquito eradication campaigns. Fish species, such as red drum (Sciaenops ocellatus), that use seagrass beds as nursery areas could be affected by runoff waters contaminated with malathion. We exposed red drum larvae at the size they reach in estuarine nursery areas to environmentally realistic and sublethal levels of malathion (0, 1, and 10 microg/L). We evaluated the effects of such exposure on ecologically significant behaviors (routine swimming and predator evasion), growth, and resting metabolism. Malathion exposure to relatively low but ecologically realistic concentrations did not affect routine behavior, escape behavior, resting metabolic rate, or growth, indicating that reported environmental levels may be safe for young fishes. However, a recent substantial increase in the use of malathion may elevate surface-water concentrations to levels above those tested in the present study.

Spatial and temporal patterns in modeled particle transport to estuarine habitat with comparisons to larval fish settlement patterns

Larval fish settlement in estuarine nursery areas is the end result of numerous biological and physical processes. We used a numerical circulation model coupled to a particle transport model to examine the role that physics play in determining settlement patterns of red drum larvae ( Sciaenops ocellatus) in nursery habitat along the Texas coast. We examined supply at various spatial scales (supply to inlet, bays, and individual settlement sites). Temporal patterns in larval settlement in Aransas Bay, Texas, are correlated with several indices of modeled particle supply (number of particles inside the bays, integrated particle input to Lydia Ann Channel, and cumulative number of competent particles in Lydia Ann Channel). High abundances of recently settled red drum in Aransas Bay result from a combination of high larval input, limited habitat for settlement, and proximity of habitat to the inlet. In contrast, larval settlement in Corpus Christi and Redfish Bays does not appear to be related to modeled measures of larval supply. Modeled particle supply at the bay-scale suggests that difference in the abundance of recently settled red drum between the bays may be related to larval supply normalized by the amount available settlement habitat within the bay.

ORIENTATION OF JUVENILE BLUE CRABS, CALLINECTES SAPIDUS RATHBUN, TO CURRENTS, CHEMICALS, AND VISUAL CUES

Abstract Postlarvae of the blue crab, Callinectes sapidus, settle and metamorphose in beds of submerged vegetation in estuarine nursery areas. They remain there until crab stage IV or V, which disperses throughout estuaries. The study considered orientation of Stage IV–V crabs to chemical and visual cues in the presence of current flow. Crabs were tested in a horizontal rectangular chamber that had test waters entering the ends of the chamber and exiting at the center. An orientation response occurred if crabs moved from a center release site to the end of the chamber. Test waters were “Offshore” odor water and estuarine odors (estuarine water, habitat odor from salt marsh cord grass and oysters, predation odors from mud crabs, and predation event odors from crushed conspecifics). In apparent darkness (red light), crabs did not orient to flow (flow rates = 0–30 ml min–1; current speeds = 0–6.2 cm s–1) but moved away from all estuarine odors. When a visual target representing a predator was placed at one e...

Effects of chemical cues on visual orientation of juvenile blue crabs, Callinectes sapidus (Rathbun)

Stage I crabs of Callinectes sapidus occur in beds of submerged vegetation in estuarine nursery areas. After reaching the IV–V instars, juveniles leave nursery habitats and disperse throughout estuaries. This study tested the hypothesis that I and IV–V stage crabs have different behavioral responses to visual targets in the presence of chemical cues. Orientation to solid (black) and vertically striped (black and white) rectangular targets subtending different visual angles (20° to 350°) as viewed by the crabs was tested in a circular arena in the presence of chemical cues from Offshore water (control), and odor from estuarine aquatic vegetation, and predators (estuarine chemical cues). In the presence of Offshore water Stage I crabs oriented away from almost all solid targets, which was interpreted as an escape response for predator avoidance. Exposure to all estuarine chemicals cues dramatically changed their behavior, as they displayed an alarm response, in which they did not orient to visual cues and their predominant behavior was to remain immobile. Stages IV–V crabs were very responsive to solid targets, as they generally swam away from the 30° and 90° targets and toward the 270° solid targets in all water types. Responses of all stage crabs tested to striped targets were more diverse. Stage I crabs generally did not orient to striped targets in any odor environment. In contrast, Stages IV–V crab responses to striped targets varied with the odor type. Thus, the hypothesis was supported because there was an ontogenetic change in orientation to visual cues. Subtle changes in orientation upon exposure to chemical cues (e.g. aquatic vegetation versus predator odor) were not evident. Crabs appeared to have two sets of behavioral responses. They showed an escape response in Offshore water and a combination of escape and alarm responses in the presence of chemical cues from estuarine nursery areas.

Particle transport through a narrow tidal inlet due to tidal forcing and implications for larval transport

For estuarine‐dependent species, especially those that spawn offshore and whose larvae must reach estuarine nursery areas, advective transport through tidal inlets may be a major factor influencing recruitment variability. We examined the role of tidal forcing on particle transport through a narrow, microtidal inlet along the Texas coast by using a three‐dimensional hydrodynamic and particle transport model. Although tidal forcing is relatively small in the study area, tidal currents through the inlet effectively transport passive particles a distance of about 15 km landward of the inlet. The majority of the particles that enter the inlet are transported to regions that are not suitable for larval settlement. There is limited tidal dispersion of the particles into the bays due to shoreline geometry and bathymetry. Most of the particles that enter the inlet are expelled offshore in the ebb tidal jet resulting in estuarine‐shelf exchange of particles. When acting alone, tidal forcing is not effective at retaining particles in a suitable estuarine habitat, suggesting that other physical or biological mechanisms are required to maintain larvae in an estuarine habitat or that there is substantial along‐shelf transport of larvae.

Elemental fingerprints of otoliths of fish may distinguish estuarine 'nursery' habitats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 201:273-286 (2000) - doi:10.3354/meps201273 Elemental fingerprints of otoliths of fish may distinguish estuarine 'nursery' habitats Bronwyn M. Gillanders*, Michael J. Kingsford School of Biological Sciences A08, University of Sydney, New South Wales 2006, Australia *E-mail: bronwyn@bio.usyd.edu.au ABSTRACT: The elemental fingerprints or composition of otoliths of fish may provide a natural tag of the 'nursery' habitat of juvenile fish. The natural tag could then be used to determine the 'nursery' habitat of adult fish found on coastal reefs. We collected juvenile Pelates sexlineatus from 2 to 5 sites within each of 7 estuaries to determine whether elemental composition of otoliths differed among estuaries and among sites within estuaries. In addition, fish were collected in 2 successive years to determine whether temporal differences may be found in elemental fingerprints that could then confound subsequent assignment of adults to 'nursery' estuaries. Significant differences in elemental fingerprints (Sr, Ba and Mn) were found within and among estuaries, but there was often an interaction with time suggesting that there were differences among estuaries/sites but the difference varied between times. Quadratic discriminant functions (QDFs) generated to discriminate among estuaries suggested that the QDFs calculated from a single year class were more successful at assigning fish to the correct estuary than either (1) QDFs based on both years combined or (2) using the QDFs generated from the first year class to classify the second year class. Small-scale variability among sites within an estuary suggested that for an estuarine fishery we may be able to classify fish to their site of origin; this warrants further investigation. Adult fish from a coastal fishery can now be assigned to their 'nursery' estuary by analysing the juvenile region of their otoliths, provided that discriminant functions are generated from the appropriate year class of recruits. KEY WORDS: Estuarine nursery area · Otolith microchemistry · Trace elements Full article in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 201. Online publication date: August 09, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

The influence of a power station on the survival of juvenile sea bass in an estuarine nursery area

Trawl surveys in the estuary of the River Medway in the autumns of 1987–1991 have shown that the distribution of juvenile sea bass Dicentrarchus labrax is strongly associated with the warm‐water outflow from Kingsnorth power station. In years of low abundance of first‐year bass, very few were caught outside the warm‐water discharge channel, whereas proportionately more fish of abundant year classes occupied the main river. About 15% of the available juvenile bass population died on the cooling‐water intake screens at Kingsworth in the autumn and winter of 1987 and 1988. However, growth and survival of first‐year bass in the Medway Estuary may be enhanced by the power station's warm‐water effluent, such that overwinter mortality due to inadequate nutritional reserves and low temperatures may be considerably reduced.

The influence of a power station on the survival of juvenile sea bass in an estuarine nursery area

The influence of a power station on the survival of juvenile sea bass in an estuarine nursery area

Does salinity affect somatic growth in early juvenile Atlantic croaker, Micropogonias undulatus (L.)?

Factors affecting recruitment of fishes remain one of the most studied but least understood issues of fisheries science. Understanding the causes of recruitment variability remains elusive because factors that affect the growth and survivorship of young fishes are complex and dynamic. Here we focus on the influence of salinity on growth of early juvenile Atlantic croaker, Micropogonias undulatus under laboratory conditions as part of a larger study to relate short-term fluctuations in growth rates of young estuarine-dependent fishes with variability in abiotic environmental factors. Body growth of juvenile Atlantic croaker was significantly (P<0.001) different among all of the three salinity treatments with growth in 5‰>20–5‰=20‰. A linear response to the changing treatment suggests an additive effect of changing salinity on body wet weight (WW) growth. Juvenile Atlantic croaker in the 5‰ treatment grew in WW by a factor of 3.88 relative to initial WW. Fish in the 20–5‰ treatment grew in WW by a factor of 2.90, while fish in the 20‰ treatment grew in WW by a factor of 2.17. Otolith diameter also varied significantly with salinity, and there was a significant positive relationship between changes in body WW and changes in otolith diameter growth (r=0.68, P<0.02, n=12). The correlation between body and otolith growth justified our use of otolith data to infer that substantial fluctuation in the early growth of early juvenile Atlantic croaker from field collections was inversely cross-correlated with salinity and water temperature. Assuming that the probability of survival during the nursery period increases as postlarval fish grow, salinity-induced plasticity in growth rates implies that the site and habitat into which post-larval fish settle can potentially influence recruitment dynamics. This study demonstrates that there is the potential for fluctuations and spatial variability in salinity to cause significant variability in short-term growth rates for juvenile fishes within estuarine nursery areas.

A PRELIMINARY SURVEY OF ESTUARIES ON THE SOUTH-WEST COAST OF SOUTH AFRICA, CAPE HANGKLIP—CAPE AGULHAS, WITH PARTICULAR REFERENCE TO THE FISH FAUNA

SUMMARY The estuaries of the south-west coast of South Africa from Cape Hangklip to Cape Agulhas were surveyed during the period September 1994. The ichthyofaunal and physico-chemical characteristics of each system are presented and their suitability as estuarine nursery areas is discussed. Eight systems drain this area and, apart from a small coastal stream which does not appear to have any estuarine characteristics, range from estuaries which are permanently open to small and large systems which occasionally open to the sea. All these systems have variable temperatures, salinities, water levels and water currents which are linked to the seasonal nature of rainfall and runoff in the region. The fish fauna of the estuaries in this region were dominated by estuarine and estuarine-dependent marine taxa. The dominant estuarine species were Atherina breviceps, Gilchristella aestuaria and Psammogobius knysnaensis while important estuarine-dependent marine fishes included Liza richardsonii, Mugil cephalus and Galeichthys feliceps. Despite their great variability, the reproductive strategies of estuarine and estuarine-dependent marine fishes enable these species to utilise these estuaries as nursery areas.

A PRELIMINARY SURVEY OF THE ESTUARIES ON THE SOUTH COAST OF SOUTH AFRICA, CAPE AGULHAS—CAPE ST BLAIZE, MOSSEL BAY, WITH PARTICULAR REFERENCE TO THE FISH FAUNA

SUMMARY The estuaries on the south coast of South Africa from Cape Agulhas to Cape St Blaize were surveyed during the period September/October 1994. The ichthyofaunal and physico-chemical characteristics of each system are presented and their suitability as estuarine nursery areas is discussed. Eight systems drain this area and, apart from a small coastal stream which does not serve any estuarine nursery function, range from estuaries which are permanently open with a strong marine influence to small estuaries which occasionally open to the sea. All these systems are dominated by estuarine and estuarine-dependent marine species and thus serve as important nursery areas. Dominant estuarine species included Caffrogobius multifasciatus, Gilchristella aestuaria and Psammogobius knysnaensis while the dominant estuarine-dependent marine taxa were Argyrosomus japonicus, Galeichthys feliceps, Lithognathus lithognatus, Liza dumer-ilii, Liza richardsonii, Liza tricuspidens and Mugil cephalus.

Interspecific differences in the distribution of adult and juvenile ponyfish (Leiognathidae) in the Gulf of Carpentaria, Australia

The distribution of leiognathids was investigated at 261 sites spread throughout the Gulf of Carpentaria. Eight species, Gazza minuta, Leiognathus decorus, L. equulus, L. fasciatus, L. leuciscus, L. smithursti, L. splendens and Secutor ruconius, were usually restricted to coastal areas, whereas four species, L. bindus, L. moretoniensis, Leiognathus sp. and S. insidiator, were not. Two other species, L. aureus and L. elongatus, were caught at only one site each. The relationships between size of fish and depth in Albatross Bay were investigated by examining the mean weight and minimum and maximum lengths of different species in 356 trawls. Six of the coastal species showed the common pattern of linear increase in size with depth. This pattern is consistent with the existence of estuarine and/or inshore nursery areas, and supports previous observations of these species. In contrast, three of the widespread species exhibited approximately quadratic relationships between size and depth. This unusual pattern resulted from small fish living in both the shallow inshore areas and deeper offshore areas, and it may reduce competition among the juveniles of the large number of very abundant, coexisting species of leiognathid.

A PRELIMINARY SURVEY OF COASTAL RIVER SYSTEMS ON THE SOUTH AFRICAN WEST COAST, ORANGE RIVER—GROOT BERG, WITH PARTICULAR REFERENCE TO THE FISH FAUNA

SUMMARY The coastal river systems on the west coast of South Africa from the Orange River to the Groot Berg were surveyed during the period September to October 1993. The ichthyofaunal and physicochemical characteristics of each system are discussed in relation to their suitability as estuarine nursery areas. Of the fifteen systems sampled, only three appeared to exhibit any estuarine characteristics in terms of their fish fauna. Of the remainder, one system was a coastal lake system which had been severely altered and eleven were either dry river beds or semi-permanent waterbodies which are normally isolated from the sea and appear to be of little value as habitat for either resident or estuarine-dependent marine fishes. The systems on this arid coast are, however, very important habitats for migratory and resident waterbirds.