Fissuroderes, a new genus of Kinorhyncha (Cyclorhagida) from the deep sea and continental shelf of New Zealand and from the continental shelf of Costa Rica

Specimens of Kinorhyncha collected by RV Sonne from the continental shelf off the coast of Costa Rica and from the deep sea East of New Zealand as well as by RV Kaharoa in the Firth of Thames are identified as five new species of a new genus Fissuroderes gen. nov. which is distinguished from all other kinorhynch genera by a ring-like cuticle in the first trunk segment and a cuticle with midventral and lateral articulations resulting in two sternal plates and one tergal plate in segments 2-10. Fissuroderes higginsi sp. nov. can be distinguished from all other species of Fissuroderes by a laterodorsal spine in segment 2 and the lack of a lateroventral spine in segment 8. Fissuroderes rangi sp. nov. is recognized from all other species by the lack of a ventrolateral spine in segment 2, the lack of a lateroventral spine in segment 5, an extremely elongate spinose tergal extension of segment 11 and a prominent midventral spinose process of the sternal plates in segment 11. Fissuroderes papai sp. nov. is identified by the short spinose process of the sternal plate of segment 11. Only Fissuroderes thermoi sp. nov. possesses bilobed sternal plates in segment 11 and a short conical tergal extension. Fissuroderes novaezealandia sp. nov. differs from F. higginsi sp. nov. in the lack of a laterodorsal spine in segment 2, the lack of an accessory spine in a lateral position in segment 8, the lack of a sublateral spine in segment 10, the existence of a lateroventral spine in segment 8 and in the lack of a subdorsal type 2-gland cell outlet in segment 2. The former species differs from F. papai sp. nov. in the lack of a lateroventral spine in segment 8, the lack of longitudinal indentations in the posterior part of the trunk cuticle of each segment and in the existence of an elongate spinose tergal extension of segment 11 and of many fine hairs on the surface of the cuticle. Fissuroderes is included into the Echinoderidae which is suggested to enclose also the genera Echinoderes and Cephalorhyncha. Echinoderes nybakkeni Higgins, 1988 is now combined as Cephalorhyncha nybakkeni (Higgins, 1988) comb. nov.     

Mangrove forests in a peri-urban setting: the case of Mombasa (Kenya)

The structure and regeneration patterns of the peri-urban mangrove vegetation of Mombasa at Tudor creek were studied along belt transects at two forest sites of Kombeni and Tsalu. Based on the species importance values, the dominant mangrove species were Rhizophora mucronata Lam. (Rhizophoraceae) and Avicennia marina (Forssk.) Vierh. (Avicenniaceae). Lumnitzera racemosa Willd., reported in an earlier floristic survey, was not encountered. Tree density varied from 1,264 trees ha^–1 at Kombeni to 1,301 trees ha^–1 at Tsalu and mean tree height was higher at the former site compared to the latter. The size-class structure at both localities showed the numerical dominance of small trees over larger trees. The spatial distribution pattern of adults and juveniles varied greatly between sites and showed a close to uniform pattern (Morisita’s Index I _δ ≪ 1) for adult trees, but a tendency to clustered distribution (I _δ ≫ 1) for juveniles. The present paper shows that unmanaged but exploited peri-urban mangroves are structurally stressed, having enlarged canopy gaps that are characterised by spatial and temporal site heterogeneity that influences regeneration, implying longer periods for canopy closure. Diversifying uses of mangrove products and establishing reserves as no cut zones with regulated harvesting will minimise canopy gap sizes, and promote conservation practices. The proposed management strategy shall boost the ecosystem resilience to both anthropogenic and natural stressors expected in the peri-urban setting in the long run.     

Reproduction strategies and population dynamics of two Diogenes hermit crabs (Superfamily: Paguroidea) in a tropical mangrove estuary

Two species of sympatric hermit crab, Diogenes moosai Rahayu & Forest, 1995 and D. lopochir Morgan, 1989, spatially defined in the Matang mangrove estuary, and facing high mortality due to tidal emersion, predation and competition are hypothesised to adopt different reproductive strategies for successful recruitment. The crabs were sampled by a small otter trawl at mid-estuary, river mouth, mudflat and shoal area along the estuary to adjacent coastal area. Diogenes moosai was widespread in the mudflat as well as in the subtidal shoal area where D. lopochir was dominant. Diogenes moosai showed year-round reproduction, whereas D. lopochir a discontinuous spawning pattern. Major reproduction in both species, however, occurred in January/February and July which resulted in two major recruitment pulses in a year. Diogenes moosai also suffered very high mortality resulting from cockle harvesting on the mudflat, twice that of D. lopochir. Our results show that the more widespread species at higher risk of exposure to extreme physical conditions (in the mudflat), predation and competition for shell resources, generally spreads its reproduction over the year, while the dominantly subtidal species at greater risk of predation only reproduces less regularly but at the most favourable period.     

Meristoderes gen. nov., a new kinorhynch genus, with the description of two new species and their implications for echinoderid phylogeny (Kinorhyncha: Cyclorhagida, Echinoderidae)

A new kinorhynch genus, Meristoderes gen. nov., and two new species from Spain and the Solomon Islands, respectively, are described. The new genus is distinguished from all other genera by the first segment consisting of a closed cuticular ring, and the second segment having partial tergosternal junctions, and a superficial midventral fold. This is a new cuticular configuration that may shed light into the phylogenetic relationships of echinoderid kinorhynchs. Meristoderes macracanthus gen. et sp. nov. from the Mediterranean coast of Spain is recognised by the presence of middorsal spines on segments 4, 6 and 8, ventrolateral tubules on segment 2, lateroventral tubules on segment 5, lateroventral spines on segments 6-9, lateral accessory tubules on segment 8, one pair of laterodorsal tubules on segment 10. Meristoderes galatheae sp. nov. from the Solomon Islands is recognized by having a middorsal spine on segment 4 only, ventrolateral tubules on segment 2, lateroventral tubules on segment 5, lateroventral spines on segments 6-9, lateral accessory tubules on segment 8 and subdorsal tubules on segment 10. Both species have a pattern of paraventral perforation site clusters on segments 3-9, with conspicuously long bracteate hairs from the posteriormost perforations sites on the segments 3-7 and 3-6, respectively.The new genus Meristoderes gen. nov. is included into the family Echinoderidae Bütschli, 1876 and appears closely related with the genera Cephalorhyncha Adrianov, 1999 and Echinoderes Claparède, 1863. The new information it provides is discussed to clarify the internal phylogeny of Echinoderidae. The terminology for cuticular characters in the overlapping area between consecutive segments is also standardized.     

The comparative distribution and population dynamics in Trinidad of Sceliphron fistularium (Dahlbom) and S. asiaticum (L.) (Hymenoptera: Sphecidae)

Two sphecid wasps, Sceliphron asiaticum (L.) and S. fistularium (Dahlbom), which build mud nests and capture spider prey, had overlapping but distinctly different distributions in Trinidad. Sceliphron asiaticum was associated with drier (<2000 mm mean annual precipitation) and less forested areas. The analysis of existing data on these species revealed a similar differential distribution throughout the neotropics. Based on the dissection of their old nests collected at 42 sites in Trinidad, retrospective life tables were constructed and estimates of fecundity made. Sceliphron asiaticum tended to form denser nesting associations and, while most of the common parasitoids were shared, had overall higher developmental mortality. Although such mortality was density-dependent in both species, where the two wasps nested together mortality from Melittobia (Eulophidae, Chalcidoidea) was higher in S. asiaticum . Both species were protarrhenotokous and had similar field fecundities (7–8/♀), but the rate of oviposition may be greater in S. asiaticum since far less mud was used in the construction of its cells. Both species had >50° mortality of the females between emergence and starting to nest. The regulation of numbers of these wasps in relation to that of S. assimile (Dahlbom) in Jamaica is discussed.     

Spatial and temporal distribution patterns of the macrozoobenthos assemblage in the salt marshes of Tejo estuary (Portugal)

The present study focuses on the spatial and temporal distribution of the macroinvertebrate community of the salt marsh areas of the Tejo estuary, based on surveys conducted from autumn 1998 to summer 2000. Samples were collected quarterly in five different intertidal areas along an elevation gradient in: mudflats, creek mouths, creeks, pioneer salt marsh areas and middle marsh areas. A total of 36 benthic invertebrate taxa were identified. Insect larvae were the most well represented group, with 10 taxa identified. Oligochaetes and ostracods were the most numerically abundant taxa, whereas bivalves dominated in biomass. Benthic macroinvertebrate assemblages were dominated, both in number and biomass, by deposit feeders. Three distinct macroinvertebrate assemblages were distinguished along the elevation gradient, based on species presence, density and biomass: the unvegetated muddy areas with a macrobenthic assemblage composed mostly by infauna; the salt marsh pioneer areas of Spartina maritima in which several epibenthic taxa were found, as well as endobenthic taxa characteristic of muddy sediment; and the creek margins, with epifauna taxa such as insect larvae and crustaceans and a low abundance of benthic infauna. Total biomass in the unvegetated and Spartina areas was higher during spring and summer mainly due to the increase in biomass of Scrobicularia plana and Hydrobia ulvae. No decreases in the salt marsh macroinvertebrate biomass values were observed during the highest densities of their potential nektonic predators (summer). This fact might indicate that macroinvertebrates are not a limiting resource for the nektonic species, and that the natural biomass increment of these invertebrate species could be masking the predation/disturbance caused by the nektonic species.     

On the distribution patterns and population dynamics of sublittoral and profundal oligochaeta fauna from Lake Banyoles (Catalonia,NE Spain)

Oligochaeta assemblages from Lake Banyoles were composed of one species of Naididae and eight species of Tubificidae, Potamothrix heuscheri (8–1350 ind. m^–2) being the most abundant and widely distributed species, followed by Limnodrilus hoffmeisteri (25–858 ind. m^–2) and Psammoryctides barbatus (12–792 ind. m^–2). The remaining species were Potamothrix hammoniensis, Potamothrix bavaricus, Limnodrilus claparedeanus, Branchiura sowerbyi, Aulodrilus pigueti and Dero digitata, all of which occurred at lower densities and with restricted distributions.Regardless of sampling depth, maximum densities of oligochaetes were found in winter (up to 5,142 ind. m^–2 in December) and secondarily in June. Immature Tubificidae with hair setae and mature P. heuscheri were present and dominant throughout the year. Cestode parasites were recorded infesting L. hoffmeisteri and P. heuscheri populations.Oligochaeta densities increased with depth, but low oxygen concentrations (less than 1 mg l^–1) during a long period (4 months) in some basins of the lake acted as a key factor in reducing the density of worms and the species richness to one species, Potamothrix heuscheri.     

Studies on population dynamics and spatial distribution of leafhoppers in vineyards (Homoptera: Cicadellidae)

Thirty-two species of Cicadellidae, including the Macropsinae, Agalliinae, Penthimiinae, Aphrodinae, Cicadellinae, Typhlocybinae and Deltocephalinae, 10 of which were already known as phytoplasma vectors, were captured in vineyards using yellow sticky traps. Adult population dynamics of the most abundant species of Penthimiinae and Deltocephalinae were studied over the whole growing season. Penthimia nigra was captured in May and June, Anoplotettix fuscovenosus in June-August, Fieberiella florii in August-October, Macrosteles sexnotatus in May and October, Scaphoideus titanus in July-September, Thamnotettix spp. (Th. confinis, Th. dilutior, Th. exemtus, Th. zelleri) in April-June, while Euscelidius variegatus, Neoaliturus fenestratus, Platymetopius major and Psammotettix spp. (P. alienus, P. confinis) were trapped throughout the growing season. The aggregation level of the above species was investigated by means of Taylor's power law. A. fuscovenosus showed a nearly random distribution in vineyards (0.95 < b < 1.11), while N. fenestratus, P. major and S. titanus were strongly aggregated (1.32 < b < 1.81). The other species showed intermediate levels of aggregation (1.12 > b < 1.32). The results indicate that at least six Deltocephalinae species, A. fuscovenosus, E. variegatus, F. florii, M. sexnotatus, N. fenestratus and S. titanus, known as phytoplasma vectors and commonly found in vineyards, could play a role in Grapevine Yellows (GY) epidemiology. GY transmission trials with these species are needed.     

Association patterns and population dynamics of bottlenose dolphins in the Strait of Sicily (Central Mediterranean Sea): implication for management

An understanding of the population dynamics and social organization of cetaceans is essential to manage the influence of anthropogenic activities. In this study, the population size, site fidelity and social interactions of bottlenose dolphins in the Strait of Sicily (Italy) were investigated to provide recommendations for their conservation. Mark-recapture analysis was based on the encounter histories of 103 marked dolphins from 2004 to 2015. The POPAN formulation of the Jolly–Seber model in MARK software was used to estimate the size of the super-population. Site fidelity and social organization were estimated for individuals re-sighted ≥3 times. The estimated population size was 140 (SE = 15.75; 95% CI = 106–164). Dolphins had low site fidelity, and both adults and sub-adults move outside the study area. Females with calves used the area longer than other individuals. Based on our results, dolphins’ home range likely extended beyond the study area. The mean value of the Half-Weight Association Index was low and the preferred association was by casual acquaintance. However, we found a distinct aggregation of post-parturition females during the final 2 years of the study. Therefore, the pattern of association was apparently a response to an ecological requirement, which was the possibility to breed in high productivity waters. Whether these individuals are part of a larger pelagic population is unknown; however, we can conclude that the management of only coastal waters is insufficient for the conservation of dolphins in the Strait of Sicily.     

Characterization of microsatellite markers for the apicultural pest Varroa destructor (Acari: Varroidae) and its relatives

Sixteen microsatellite loci were isolated and characterized for Varroa destructor using two procedures to screen genomic libraries. Together with those previously designed, they provide useful markers for the study of this harmful apicultural pest whose populations on Apis mellifera are poorly variable. Observed variability has been expressed as the number of alleles because heterozygosity is only rarely present. The defined primers have been assayed on another species of the same genus (V. jacobsoni) and almost half of them successfully cross‐amplified and revealed polymorphism. These results suggest that the microsatellites isolated here should prove useful for population studies in different Varroa species.     

Reproduction, population dynamics, growth and production ofScrobicularia plana da costa (pelecypoda) in the Bidasoa estuary, Spain

The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m^–2 year^–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).     

Metapopulation dynamics in a regional population of the blue-winged grasshopper (Oedipoda caerulescens; Linnaeus, 1758)

For two consecutive years we registered the presence (or absence) of blue winged grasshoppers (Oedipoda caerulescens; Linnaeus, 1758) on 312 habitat patches of differing size in a region of more than 3000 ha. The data show that presence of grasshoppers on a habitat patch is dependent on patch size as well as on patch isolation. We used an ecological incidence model to describe the metapopulation dynamics of the regional population and derived the parameters for this model from presence-absence data and observations of Oedipoda dispersion. The analysis shows that local extinction of grasshopper populations is influenced by strong fluctuations of environmental conditions and that for a number of small patches in our region recolonization is important for the presence of O. caerulescens. Colonization probability, as derived using the incidence model, is in good agreement with estimates from a population genetical analysis.     

Population dynamics of Mus minutoides and Steatomys pratensis (Muridae: Rodentia) in a subtropical grasslandin Swaziland

The population dynamics of Mus minutoides and Steatomys pratensis are virtually unknown. These two species were live-trapped over a 12-month period in a subtropical grassland in Swaziland. Numbers of M. minutoides were relatively high in winter, declined in spring and the population disappeared in summer and autumn. By contrast, numbers of S. pratensis increased gradually from winter to summer and reached a peak in autumn. There were no differences between the mean weights of male and female M. minutoides and S. pratensis. There were, however, seasonal differences in the mean weight of male S. pratensis, with highest weights recorded in summer. Individuals of both species came into breeding condition in spring (October–November). Reproduction had ceased by the end of autumn (April–May). Monthly survival rates of M. minutoides were highest in winter, but did not vary seasonally in S. pratensis. Burning had a pronounced effect on the distribution of S. pratensis. Steatomys pratensis individuals selected recently burnt but revegetated areas over unburnt areas. The effect of burning on the M. minutoides population is difficult to assess, as this species disappeared shortly after the fire.     

Seasonal and spatial patterns in cellular energy allocation in the estuarine mysid Neomysis integer (Crustacea: Mysidacea) of the Scheldt estuary (The Netherlands)

The seasonal and spatial patterns in cellular energy allocation of the estuarine mysid Neomysis integer (Leach, 1814) were investigated in the Scheldt estuary over a 2-year period. Using the recently developed cellular energy allocation (CEA) assay, energy reserves (protein, lipid and sugar) and energy consumption (as derived from the cellular respiration rate) were integrated into a general indicator of physiological stress. Total energy reserves were relatively unaffected by sampling season or location, whereas the individual energy reserve fractions of N. integer were differentially influenced by sampling location and season. Seasonal effects were apparent for mysid weight and were related to the population biology, whereas spatial effects on the weight of N. integer may depend on pollution-induced effects on cellular energy allocation in the two most upstream sites (Bath and Doel). These upstream sites coincide with the most polluted part of the sampled area and were characterized by a significant increase in energy consumption, resulting in a significantly lower CEA. Due to the recent amelioration in the oxygen concentration at these sites, it can be expected that N. integer will migrate further upstream, similar to what is observed in other European estuaries. It will, therefore, be important to assess the physiological consequences and potential population effects on mysids from these polluted areas in the Scheldt estuary. This study provides evidence that the CEA assay has potential under field conditions as an in situ biomarker of pollutant effects.     

Population dynamics of Turbo militaris (Gastropoda: Turbinidae) on rocky shores in a subtropical marine park: implications for management

Understanding the relative impacts of harvesting across an area such as a marine park is vital if the goals of fisheries management are to be met. Given their accessibility, densities of targeted intertidal turbinids should be relatively simple to quantify; however, natural spatial and temporal variability in these populations has hampered this effort. This study aimed to quantify short-term population dynamics of Turbo militaris in relation to current zoning regulations and accessibility. While our results reflected the variability found by other studies, we also detected significantly lower densities at a headland where harvesting is known to occur, and found a trend towards denser aggregations at more remote locations. Importantly, we found that densities at some locations were so low that current fisheries bag limits may be ineffective for protecting populations at local scales. Comparisons between study sites suggest a combination of no-take zoning and inaccessibility may provide the most effective protection for this species. However, a greater understanding of the wider impacts of harvesting, and processes affecting recovery, are essential to ensure sustainable management of this fishery.     

Combining genetic markers and stable isotopes to reveal population connectivity and migration patterns in a neotropical migrant,Wilson's warbler (Wilsonia pusilla)

We used results from the analysis of microsatellite DNA variation and hydrogen stable-isotope ratios to characterize the population structure of a neotropical migrant passerine, the Wilson's warbler (Wilsonia pusilla). The resulting information was then used to infer migration patterns and population connectivity between breeding grounds in North America and overwintering areas in Mexico and Central America. The microsatellite data revealed genetic structure across the North American continent; populations in the west were found to significantly differ from the east. Minimal genetic structure was observed among western sites. The lack of isolation by distance and low variance in FST values suggests that gene flow could play an ongoing role in limiting genetic differentiation among sites in the western part of the distribution. However, additional information including estimates of effective population size and the proximity of the population to equilibrium is required before the role of gene flow can be assessed fully. Analysis of isotope data showed a negative relationship between latitude and hydrogen isotope ratios in breeding ground individuals. There was a positive relationship between wintering ground latitude and hydrogen isotope ratios for individuals that were genetically western in origin. This is consistent with a leapfrog pattern of migration, in which genetically western birds from the northernmost breeding areas overwinter at the most southerly locations in Central America. Additionally, isotopic ratios of western birds suggest that coastal breeders overwinter in western Mexico, while western birds from further inland and at high elevations overwinter in eastern Mexico. Using information from both genetic an isotopic approaches will probably be useful for identifying patterns of migration and population connectivity between breeding and overwintering areas, both important issues for conservation efforts, and may also contribute to investigation of the evolution of migration.     

Dispersal patterns in a medium‐density Irish badger population: Implications for understanding the dynamics of tuberculosis transmission

European badgers (Meles meles) are group‐living mustelids implicated in the spread of bovine tuberculosis (TB) to cattle and act as a wildlife reservoir for the disease. In badgers, only a minority of individuals disperse from their natal social group. However, dispersal may be extremely important for the spread of TB, as dispersers could act as hubs for disease transmission. We monitored a population of 139 wild badgers over 7 years in a medium‐density population (1.8 individuals/km²). GPS tracking collars were applied to 80 different individuals. Of these, we identified 25 dispersers, 14 of which were wearing collars as they dispersed. This allowed us to record the process of dispersal in much greater detail than ever before. We show that dispersal is an extremely complex process, and measurements of straight‐line distance between old and new social groups can severely underestimate how far dispersers travel. Assumptions of straight‐line travel can also underestimate direct and indirect interactions and the potential for disease transmission. For example, one female disperser which eventually settled 1.5 km from her natal territory traveled 308 km and passed through 22 different territories during dispersal. Knowledge of badgers' ranging behavior during dispersal is crucial to understanding the dynamics of TB transmission, and for designing appropriate interventions, such as vaccination.     

The influence of coastal upwelling on the distribution of Calanus chilensis in the Mejillones Peninsula (northern Chile): implications for its population dynamics

A field experiment was carried out in October 1998 during active upwelling in a coastal area off the Mejillones Peninsula (23° S). Zooplankton was sampled at day and night, during two subsequent days at 4 stations inside and outside of the upwelling plume. Three depth strata were sampled: 0–20 m, 20–80 m and 80–200 m. Oceanographic data were obtained in a grid of 23 stations using a CTDO, a fluorometer and a Doppler current meter. Calanus chilensis was mostly represented by late stages, i.e. copepodid C5 and adult males and females. There were no day/night effects on vertical distribution, and abundance was significantly higher inside the upwelling plume in the upper 20-m layer at nearly 14 ind. m^–3, compared to ca. 5 ind. m^–3 outside the upwelling plume. Temperature at 10 m depth and biomass, estimated from stage numbers and their mean dry weights, were used to estimate growth and daily production of Calanus at temperature-dependent rates. The potential loss of biomass from the upwelling center because of advection in the upwelling plume was estimated from current data in the Ekman layer and biomass density. The mean cross-shelf component of the current was estimated at 10.4 km d^–1 within the upwelling plume. This yielded a loss of biomass of 9.7 mg dry weight m^–2 . Production, estimated by a temperature-dependent approach, ranged between 44 and 35 mg dry weight m^–2 d^–1, at mean temperatures of 14.6 °C and 15.8 °C inside and outside of the upwelling plume respectively. Within the plume, as much as 22% of daily production may be advected offshore. However, a higher concentration of biomass in the upwelling plume allowed a greater production compared to surrounding areas. A mass balance approach suggests that advective losses may not have a major impact on the C. chilensis population, because of very high daily production at temperature-dependent rates.     

Juvenile morphology and occurrence patterns of three Butis species (Gobioidei: Eleotridae) in a mangrove estuary, southern Thailand

Juveniles of three eleotrid Butis species (B. butis, B. humeralis, and B. koilomatodon) are described; their occurrence patterns were examined in Sikao Creek, a mangrove estuary located in southern Thailand. Juveniles of each species were distinguished by the following characters: B. butis with no bands on body and pale pelvic fins; B. humeralis with no bands on body and densely pigmented pelvic fins; and B. koilomatodon with 5–6 regular bands on body and a fleshy process (preorbital knob) on the snout. Although B. butis shared the aforementioned characters with B. amboinensis found in the same estuary, the former was distinguished from the latter by having a greater number of pectoral fin rays (18–21 vs. 17) and a deeper caudal peduncle. Distribution patterns of the three Butis species in Sikao Creek were distinguishable from each other. Smaller B. butis [mean ± SD = 22.7 ± 16.9 mm in standard length (SL), n = 32] occurred in the upper reach of the estuary, while larger specimens (52.4 ± 26.2 mm SL, n = 18 and 51.5 ± 29.7 mm SL, n = 10, respectively) were found in the middle and lower reaches and none in the marine area. In B. humeralis and B. koilomatodon, only juveniles were caught except for one adult specimen each. Juveniles (8.9–16.5 mm SL, n = 79) of B. humeralis occurred in the upper and middle reaches and the marine area. B. koilomatodon juveniles (9.9–13.7 mm SL, n = 30) were distributed in all areas from the lower to upper reaches.