Ian Potter

The lamprey genus Geotria Gray, 1851 currently includes only two species: G. australis and G. macrostoma. However, taxonomic relationships within the genus have traditionally been ambiguous and difficult to establish due to the extreme changes in morphology, dentition, and coloration that lampreys undergo during their life cycles, particularly during upstream migration and sexual maturation. Consequently, several lamprey specimens held in museum collections have remained unidentified, especially those from Argentina. In this study, a series of morphometric characters were subjected to discriminant function analysis (DFA) to identify the lamprey species collected during 1867-2004 from the de la Plata River and Patagonia. These specimens are housed at the Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" in Buenos Aires, the Museo de Historia Natural de Montevideo, and the Naturhistoriska riksmuseet in Stockholm. Based on the proportions of the length of the oral disc, prebranchial, and pre-caudal body regions, and the depth of the trunk, DFA provided conclusive evidence that the specimens corresponded to the recently revalidated G. macrostoma (Burmeister, 1868), which was originally incorrectly named as Petromyzon macrostomus Burmeister, 1868, Exomegas macrostomus (Berg, 1899), Geotria chilensis (Berg, 1895), and Geotria macrostoma f. gallegensis Smitt, 1901, as well as other nontype museum individuals of uncertain taxonomic status. The identifications of these long-preserved museum specimens provided key information on the historical geographic range of Argentinian lampreys and suggest that the disappearance of the species reported from northern localities (the Pampean Region) can be attributed to the degradation of their critical habitats, primarily caused by anthropogenic impact and climate change.

This study determined the ichthyofaunal characteristics of the nearshore, shallow waters of three normally-closed estuaries (Stokes, Culham and Hamersley inlets) on the south coast of Western Australia over three years, during which each system remained closed to the ocean through the recent formation of a sand bar at its mouth. The ichthyofauna in each estuary was depauperate (6 or 7 species) and overwhelmingly dominated by small euryhaline atherinid and gobiid species and a larger sparid, which each complete their life cycle within their natal estuary. The atherinid Atherinosoma elongatum contributed between 74.5 and 94.5% to the ∼168,000 fish collected from these three estuaries. In contrast, marine species were represented solely by six Aldrichetta forsteri (Mugilidae), likely derived from overwash of the bar. The degree to which salinity increased and oxygen declined during the three years of closure varied markedly among the three estuaries. Among estuary basins, the number of species and density of fishes declined most rapidly in Culham Inlet, where mean salinity rose sharply from 52 to 293 and oxygen concentration fell precipitously to 0.6 mg L−1, with only A. elongatum present in salinities up to 147 and oxygen concentrations down to 2.4 mg L−1. In contrast, number of species and density of fishes remained relatively constant in the basin of Stokes Inlet, where salinity rose to only 64 and oxygen concentration declined to only 5.5 mg L−1, with ichthyofaunal and environmental changes in the basin of Hamersley Inlet intermediate between those in Culham and Stokes. While species were variably partitioned between the basin and river, certain species, when subjected to extreme salinities in the basin, moved into the less saline riverine reaches of the estuary, with the isolated pools that form upstream in estuaries during very dry periods providing refugia. In estuaries on the extensive south-western Australian coastline, the number of fish species, and particularly the number and abundance of marine species, undergo an overall progressive decline down the lower west coast and eastwards along the southern coast where they eventually fall to minimal levels. This reflects the overall trend for estuaries to change from permanently-open to the ocean to intermittently-open, to seasonally-open and finally normally-closed.
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This study explored the extent to which the hermaphroditic and reproductive characteristics vary among five congeneric (Choerodon) and co-occurring species of the Labridae, a family in which hermaphroditism is widespread. Sampling was located in the large sub-tropical Shark Bay (26° S, 113° E), one of only twenty World Heritage Properties in Australia. Choerodon cephalotes, C. cyanodus, C. cauteroma and C. schoenleinii live within the main body of the embayment, which approaches the southern limit of their tropical, geographical ranges, whereas C. rubescens lives along its outer western boundary, close to the northern limit of its warm, temperate distribution. A combination of comprehensive length and age compositions, histological analyses of gonads and logistic regressions of lengths and ages at maturity and sex change are consistent with all five species being monandric protogynous hermaphrodites. Choerodon cephalotes, C. rubescens and C. schoenleinii are sexually dichromatic, with the lengths and ages of males at the extreme upper end of those of females and low proportions of males among adults (adult sex ratios, ASR: 11–33%). It is proposed that these species have polygynous mating systems, such as leks or harems. Although C. cauteroma has an ASR of essentially parity, its pronounced sexual dichromatism and the ages of its males typically lying at the upper end of those of its females indicate that this species also has a polygynous mating system. Limited sexual dichromatism and an ASR as high as 71% suggest that C. cyanodus is not polygynous. As the timing of the main spawning period of the four species within Shark Bay increases sequentially between early spring and late summer, the temperature trigger for spawning by those species also presumably increases progressively. This phasing of spawning, allied with some interspecific spatial variation, reduces the potential for competition among the larvae and early juveniles of the five Choerodon species. Choerodon rubescens spawns earlier in Shark Bay than in the cooler waters of the Abrolhos Islands, 230 km further south. The management implications of data for Choerodon species, and particularly of the size compositions and the ASRs of the two largest species, C. rubescens and C. schoenleinii, are discussed. The variations in the hermaphroditic and reproductive features of five congeneric species of labrid, in the region in which their distributions overlap, highlight the evolutionary/biological plasticity of this family and thereby contributes to its diversity and success.
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We review published research on the ingress of larvae and early juveniles of marine fishes into estuaries subjected to different tidal regimes and provide perspectives on the abilities and responses of these early-life stages to the physico-chemical, hydrodynamic and biological drivers that facilitate such ingress. We focus on documenting ingress and the mechanisms employed by early-stage fishes from coastal waters to enter different types of microtidal and macrotidal estuaries but also include information on ingress into mesotidal systems. Spawning localities for estuary-associated marine fishes are assessed with respect to ontogeny of larvae and their ability to ingress estuaries during the preflexion and postflexion stages. The processes and physico-chemical cues employed by larvae and early juveniles to locate estuaries are reviewed, with olfactory cues being recognised as especially important. Particular emphasis is directed to vertical migratory behaviours and selective tidal stream transport (STST) employed by many larvae ingressing macrotidal estuaries, contrasting with mainly passive flood-tide entry and active swimming modes typically used by larvae and early juveniles that enter microtidal estuaries and estuarine lakes and lagoon systems.

The dependence on connectivity and use of estuaries by two major groups of fishes, namely estuary-associated marine and diadromous species, are reviewed. The former group comprises marine estuarine–opportunists and marine estuarine–dependents, and the latter anadromous, catadromous, and amphidromous species. Examples of ingress to estuaries by larvae and juveniles of species from each group illustrate the importance of freshwater-estuarine-marine connectivity to the life cycles of those species. Factors that threaten estuarine connectivity, including the potential/possible consequences of global climate change on the contribution of these key taxa to coastal fish assemblages at pristine or recent historical levels, are highlighted. The implications of reduced connectivity on the current and future status of these major groups in estuaries are also discussed. Finally, it is noted that the abundance of fishes in the above guilds has already declined substantially and that there are no clear prospects for a reversal of this trend. Possible future research on fishes and coastal connectivity include applications of environmental DNA and otolith microchemistry, and the assessment of fish responses to the removal of dams to restore connectivity in catchment rivers.

Data for the Berycidae, collected during extensive past scientific surveys, were used to quantify the depth distributions of the four species of Centroberyx and two of Beryx found in Australian coastal waters and thus elucidate the extent to which these species are partitioned by region and depth. The dietary, jaw and dentitional characteristics of the ecologically and fishery-important Centroberyx gerrardi were then determined, providing the first such account for any Centroberyx species. While Centroberyx gerrardi, Centroberyx lineatus, Beryx splendens and Beryx decadactylus are found throughout southern Australia, the last two species extend further up the west and east coasts. Centroberyx australis occurs on the lower half of the west coast eastwards to the central south coast and Centroberyx affinis on the lower half of the east coast. The four Centroberyx species typically occur at depths <350 m and the two Beryx species at >350 m. On the south coast of Western Australia, depth distributions undergo an overlapping progressive gradation, from C. lineatus in inshore and nearshore shallow waters, to C. gerrardi and C. australis in nearshore deep waters, and then B. splendens and B. decadactylus in offshore deep waters. The main dietary categories of C. gerrardi change with increasing body size from crabs and isopods in small fish to teleosts in the largest fish, in which volumetrically they constituted >60% of the stomach contents. The wide range of teleost prey (at least 39 species from 33 families) ingested by C. gerrardi would be valuable to this species if continuing climate change or other anthropogenic effects lead to alterations in the composition of potential prey. Differences between depth distributions account for the fish prey of C. gerrardi comprising nearshore species, such as those of clupeids, congrids, pomacentrids and platycephalids, whereas those of B. splendens (from studies elsewhere) are dominated by myctophids, which are abundant in deeper waters. The combination of a large mouth and numerous, exclusively small teeth (edentulate morphotype) strongly suggest that C. gerrardi is a suction feeder adapted to engulfing larger prey. While the co-occurring and likewise commercially-fished Oplegnathus woodwardi also ingests substantial volumes of crabs and teleosts, its diet is distinguished from C. gerrardi by large volumes of poriferans and appreciable volumes of echinoderms, likewise reflecting feeding specialisations. Although differing in depth distributions and dietary compositions, berycid species in general are close to the apex of the food web.

This chapter examines how zoogeography and estuarine typology can influence fish assemblages. There is a focus on the global classification of estuary‐associated fish species that places them into functional groups and guilds according to the ways in which they utilise these systems, especially in terms of their life cycle, feeding and reproductive strategies. Such an approach facilitates ecological comparisons of estuarine fish assemblages on a regional, continental and global scale, and is particularly useful in documenting estuarine degradation or rehabilitation using functional fish guilds as indicators of responses to anthropogenic impacts.

The patterns of variation at 12 microsatellite loci are used to determine whether Snapper, Chrysophrys auratus, is genetically homogeneous across its range in Western Australian waters and to elucidate the extent to which the genetic composition of this exploited sparid varies among regions in Australasia. Chrysophrys auratus was collected from seven locations in Western Australia (WA), southwards from Carnarvon (25°05–15′S, 113°25–35′E) on the mid-west coast and eastwards to Esperance (34°30′S, 122°10′E) on the south coast. The levels of genetic differentiation among samples extending 1350 km from Carnarvon to Albany (35°20′S, 117°50′E) on the south coast, but not to Esperance ∼ 410 km further east, were low and non-significant (e.g. DEST = 0.003; P = 0.167). This implies that C. auratus is genetically homogeneous along the majority of its extensive range in WA. It is proposed that this reflects wide-spread dispersal of the early life stages (ELS), facilitated by the southward-flowing Leeuwin current and northward-flowing, wind-driven inshore currents, supplemented by movements of juveniles and adults. The genetic composition of the sample of C. auratus from Gulf St Vincent on the south coast (central) of Australia (34°50′S, 138°10′E) was similar to those from Albany and Esperance on the south coast (west) but typically distinct from those from the south coast (east), west and east coasts of Australia. This genetic structure is presumably related to how the eastwards-flowing Leeuwin current and/or the westwards-flowing Flinders currents disperse ELS. Microsatellite data imply that C. auratus from the Port Phillip Bay on the south coast (east), Sydney on the east coast and from Hauraki Gulf in New Zealand each represent distinct genetic stocks. The genetic composition of C. auratus from the Port Phillip Bay is particularly distinct, indicating that this population is relatively isolated and thus potentially more susceptible to exploitation. The results of the present and other studies indicate, however, that gene flow in C. auratus is typically sufficient to maintain genetic homogeneity over 100s of kilometres, as occurs in Western Australia. Thus, C. auratus spawned in one area can potentially act as a source of recruits for other areas and thereby ameliorate the impacts of fishing.

The lamprey genus Exomegas Gill, 1883, was erected on the assumption that it was distinguishable from Geotria Gray, 1851, by possessing three rather than two cusps on the transverse lingual lamina (TLL). Based on literature review and examination of holotypes and new data, the authors reaffirm that the TLL of Geotria possesses two or three cusps in the adult stage. The reduction or disappearance of the middle cusp at the beginning or during the spawning run constitutes a key feature of Geotria. The resurrection of Exomegas by Firpo Lacoste, Fernández and Scioscia, Journal of Fish Biology, 2021, 1–6, 1507–1512, is therefore unjustified and not supported.

This study has explored the extent to which the predominant faunal component of the diet (benthic macroinvertebrates) of the large, long-lived estuarine-resident Acanthopagrus butcheri is related to particular prey and predator traits. Focus is placed on the location (infaunal vs epifaunal) and species size category (small vs medium vs large) of the prey and feeding behaviour of A. butcheri. Data on the benthic macroinvertebrates in the stomach contents of A. butcheri in a microtidal estuary (Swan-Canning, Western Australia) are compared with those of macroinvertebrates sampled in the benthos at the same sites and times in eight consecutive seasons using an Ekman grab. The eight most abundant small macroinvertebrate species in the benthic samples were infaunal and, apart from the bivalve Arthritica semen that was ingested by only a few fish, were not fed on by A. butcheri. In contrast, the three most abundant medium and large-sized species in the benthos, the epifaunal bivalves Xenostrobus securis and Fluviolanatus subtortus and infaunal nereidid polychaete Simplisetia aequisetis, were preyed on substantially, with the first ingested by 54% of A. butcheri and contributing over 51% to dietary volume. Although the eunicid polychaete Marphysa sanguinea occurred in only 7% of benthic samples and contributed <0.1% to abundance, this large infaunal species ranked second in contribution to dietary volume (12%). This species and S. aequisetis were preyed on when they emerged in part or wholly above the substrata. The above results imply that, in terms of prey, A. butcheri selects predominantly medium and large epifaunal macroinvertebrate species and those medium to large infaunal polychaetes which, at times, move out of the substrata. This reflects non-emergent infauna being present in essentially all benthic samples and contributing 66% to total abundance, whereas this group was found in only 8% of stomach samples of A. butcheri and contributed only 2% to dietary volume. In contrast, emergent infauna and epifauna contributed 12 and 22%, respectively, to abundance in the benthos, but as much as 22 and 75%, respectively, to the diets of A. butcheri. It is concluded that the marked selectivity of A. butcheri for prey was related to certain prey and predator traits, i.e. size category of prey species, and prey located above the substrata, either permanently or at frequent intervals, and to visual acuity and a fast-swimming angled attack by the predator.