Search

Within vertebrates, central pattern generators drive rhythmical behaviours, such as locomotion and ventilation. Their pattern generation is also influenced by sensory input and various forms of neuromodulation. These capabilities arose early in vertebrate evolution, preceding the evolution of the cerebellum in jawed vertebrates. This later evolution of the cerebellum is suggestive of subsumption architecture that adds functionality to a pre-existing network. From a central-pattern-generator perspective, what additional functionality might the cerebellum provide? The suggestion is that the adaptive filter capabilities of the cerebellum may be able to use error learning to appropriately repurpose pattern output. Examples may include head and eye stabilization during locomotion, song learning, and context-dependent alternation between learnt motor-control sequences.

20 pages, 3 tables, 5 figures.-- Samantha Andrzejaczek ... et al.-- Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC), Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements, Data analysis was funded by the Bertarelli Foundation through the Marine Science program through grants to D.J.C., B.A.B., and S.A. D.J.C. is also funded through Research England, UK. S.A. and B.A.B. thank the Moore Foundation and the Packard Foundation. F.G.-M. thanks the Instituto Politecnico Nacional for fellowships (COFAA, EDI). S.B.W. thanks funding from the Darwin Initiative (DPLUS046). A.D.M.D. acknowledges funding from the Research and Conservation Budget at Georgia Aquarium, including philanthropic gifts from several anonymous donors. K.F. acknowledges funding from the Rolex Awards for Enterprise and the Whitley Fund for Nature

Fish bioacoustics is about the sounds produced by fish, how fish hear, and what they hear. The focus of this article is on the hypothesis that some late pelagic stage reef fish larvae use the marine soundscape to locate reef settlement habitat. The hypothesis is evaluated by consideration of the nature of reef sound, hearing ability in late-stage larval fish, and direct behavioral evidence for orientation to reef sound.

The demand for information on mid-trophic level (MTL) organisms in open-ocean marine ecosystems has led to initiatives to collect acoustic data opportunistically in different regions around the world. Although, bulk acoustic data can provide information on the distribution patterns and dynamics of MTL organisms, it is necessary to convert acoustic-derived indices into biologically relevant quantities for parameterising and validating ecosystem and trophic models. A 7-year time series of acoustic data collected by ships of opportunity (SOOP) in the New Zealand sector of the Southern Ocean, information on species’ distribution derived from trawl samples collected in research voyages, and target strength (TS) estimates obtained using a resonance-scattering model and literature TS–length relationships, were used to obtain the first estimates of density of mesopelagic fish in this region. Estimates of mesopelagic fish density decreased from north to south reflecting changes in species composition and scattering properties across three latitudinal regions (Northern, Central and Southern). Density estimates ranged from 16.4–40.1 in the north to 4.4–13.4 g m−2 in the south. Catches revealed that the Northern region was dominated by Lampanyctodes hectoris and Protomyctophum sp. (Myctophidae) and Maurolicus australis (Sternoptychidae); the Central and Southern regions were dominated by the myctophids Electrona antarctica and Protomyctophum sp. and the Antarctic krill, Euphausia superba. Information on species composition was the main source of uncertainty in the density estimates, highlighting the need for more biological sampling. This study demonstrates that it is possible to integrate acoustic data collected opportunistically with auxiliary information from research voyages and literature to provide estimates of mesopelagic fish biomass in remote areas.

Here, we review fish rheotaxis (orientation to flow) with the goal of placing it within a larger behavioral and multisensory context. Rheotaxis is a flexible behavior that is used by fish in a variety of circumstances: to search for upstream sources of current-borne odors, to intercept invertebrate drift and, in general, to conserve energy while preventing downstream displacement. Sensory information available for rheotaxis includes water-motion cues to the lateral line and body-motion cues to visual, vestibular or tactile senses when fish are swept downstream. Although rheotaxis can be mediated by a single sense, each sense has its own limitations. For example, lateral line cues are limited by the spatial characteristics of flow, visual cues by water visibility, and vestibular and other body-motion cues by the ability of fish to withstand downstream displacement. The ability of multiple senses to compensate for any single-sense limitation enables rheotaxis to persist over a wide range of sensory and flow conditions. Here, we propose a mechanism of rheotaxis that can be activated in parallel by one or more senses; a major component of this mechanism is directional selectivity of central neurons to broad patterns of water and/or body motions. A review of central mechanisms for vertebrate orienting behaviors and optomotor reflexes reveals several motorsensory integration sites in the CNS that could be involved in rheotaxis. As such, rheotaxis provides an excellent opportunity for understanding the multisensory control of a simple vertebrate behavior and how a simple motor act is integrated with others to form complex behaviors.

One of the common mitigation measures for increasing fish passage through culverts is the concept of increasing roughness by adding secondary elements, such as artificial baffles. Although field assessments of these baffled culverts have shown an increase in passage performance, specific numbers vary for different baffle sizes and different fish species. This highlights the importance of having an understanding of flow fields and their variation with shape and size of individual baffles for an efficient fish passage solution. Furthermore, we need to better understand the response of different fish species towards these altered flows. In this study, we concentrate on characterizing the flow field downstream of baffles for different baffle lengths. The preliminary results shows that the shorter baffle is likely to produce flow fields more suitable for small-bodied fish species compared to the tested longer baffle.

Culverts that impede or inhibit fish migration are, among other river structures, a growing concern in habitat conservation efforts globally. Small-bodied fish species, which are often weaker swimmers than larger specimen, can be impacted by shallow depths and high water velocities encountered in culverts. Retrofitting of culverts is commonly used to enable fish migration. Here, we present a fish friendly remediation design, imitating filamentous algae, and discuss the suitability for fish passage. We describe how instantaneous turbulent flow structures can be assessed for the remediation design. The studied remediation design is a dense layer of filamentous algae that has been observed to provide small-bodied whitebait with a means to overcome an almost vertical weir. We describe a laboratory model that is used for flow field quantification.

The modification and utilization of rivers in regions where small-bodied diadromous fish are prevalent has largely occurred without fully understanding the migration behaviour of these species. As ...

This paper proposes a unifying evolutionary framework for understanding the genesis of a wide range of psychological disorders. Psychological disorders as a whole appear to develop at significant frequencies only under conditions of “evolutionary mismatch,” where people or animals live in environments, such as modern cities or industrialized cultures in general, that they are not evolutionarily or biologically adapted for. Evolutionarily mismatched environments appear to often cause disruptions in drive states that have evolved to maintain homeostasis. Based on several lines of evidence, I will suggest that painful, distressing emotional states can provide unconscious biochemical rewards in the brain and, under mismatched environmental conditions, can become reinforced, creating unconscious, compulsive “emotional addictions.” This core phenomenon may be the main driving force for the great majority of psychological disorders. The maladaptive drive or force that emotional addictions appear to generate, referred to here as the “non-homeostatic drive” or “addictive drive,” is suggested to dysfunctionally, unnecessarily, and repeatedly throw people out of homeostasis, creating systemic imbalances that can result in a variety of psychological dysfunctions.

The cumulative effect of culverts in impeding upstream fish passage is similar to that of large-scale high-head instream structures. The common solution to overcome this impediment is to add ancillary elements, with the goal to lower water velocities and to create discrete low velocity zones (LVZs) for fish to rest. The addition of spoiler baffles is one example of retrofitting structures with ancillary elements, with their efficacy having been proven in various field studies. The scope of the present work is to conduct a detailed laboratory study to evaluate the arrangement of spoiler baffles of different sizes and spatial density. Chosen baffle arrangements are consistent with the present size and spacing recommendations of the New Zealand Fish Passage Guidelines. Flow fields for two different flow rates within different baffle arrangements were obtained with acoustic Doppler velocimeter (ADV) technology. We show that for the standard design, as recommended in the New Zealand Fish Passage Guidelines, the maximum value of mean streamwise velocity and turbulence parameters (turbulent kinetic energy (TKE) and Reynolds stresses) is less than for two other designs we tested. However, the distribution of flow parameters within the plane is significantly different for all tested designs. In general, a shorter size baffle arranged at medium spatial density exhibits highly heterogeneous flow, with numerous LVZs, as well as providing wider pathways compared to the standard design. Wider pathways can also accommodate various fish species, which generally prefer different water velocity and turbulence, with the generated flow field allowing a lower energy cost of fish swimming whilst resting or station holding. Thus, this study shows the viability of using shorter baffles as an alternative fish passage solution for culverts, which can subsequently be validated with different fish species.

Native freshwater fish populations are among the world’s most threatened taxa due to the combined effects of habitat degradation and invasive alien species. Habitat degradation negatively impacts native species, whereas invasive species tend to possess adaptations, such as thermal and salinity tolerance, that are more suited to the degraded environment. Sensory ecology may also be a contributing factor. Most threatened native species are visual feeders, whereas invasive species found in degraded systems often have nonvisual specializations. Behavioral and distributional characteristics of the invasive Western Mosquitofish Gambusia affinis and the New Zealand native Inanga Galaxias maculatus illustrate the potential for sensory biology to influence foraging success, distribution, and species interaction between degraded and clear habitats. Behavioral trials measured the change in feeding rate in clear (0 NTU) and turbid (100 NTU) water over 30 min for Inanga and Western Mosquitofish feeding on brin...

The elaborate structure of the cerebellum has been long known, although its contribution to a remarkable diversity of behavior is only recently appreciated. Taking an evolutionary perspective, we consider the wider function of the cerebellum based on insight from the function of so-called cerebellum-like structures. Cerebellum-like structures cancel the effects of self-stimulation, a function that has been well characterized in both elasmobranch and weakly electric fish. This function depends on the implementation of an adaptive filter, which provides an input-output transformation modified by specific learning rules. We argue that the broad contribution of the cerebellum to behavior can be understood by thinking of the cerebellum as an array of adaptive filters that can be coopted to a wide range of tasks. Consistent with this, studies of mammalian cerebellum reveal operations characteristic of an adaptive filter, which we review here. We then describe a model for how a cerebellar adaptive filter architecture could interact with central pattern generators and sensory feedback to coordinate sequentially patterned behavior. Finally, we use the acquisition and production of complex vocal motor sequencing in birdsong as an example to explore how this model of cerebellar adaptive filter-central pattern generator interactions may contribute to other important domains of vertebrate neuroethology. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Here, we introduce a novel mechanism for temporal recoding by the cerebellar granular layer based on three key properties: the granule cell-Golgi cell inhibitory feedback loop, bursting behaviour of granule cells and the large ratio of granule cells to Golgi cells. We propose that mutual inhibition of granule cells, mediated by Golgi cell feedback inhibition, prevents simultaneous activation. Granule cells are differentiated by firing threshold, resulting in sequential bursts of spikes. We demonstrate the plausibility of the mechanism through a computational simulation of a firing rate model, and further examine its robustness by developing a spiking model incorporating realistic postsynaptic potentials.

Both the lateral line and the inner ear contribute to near-field dipole source detection in fish. The precise roles these two sensory modalities provide in extracting information about the flow field remain of interest. In this study, evoked potentials (EP, 30–200 Hz) for blind Mexican cavefish were measured in response to a dipole source. Greatest sensitivity was observed at the lower and upper ends of the tested frequency range. To evaluate the relative contributions of the lateral line and inner ear, we measured the effects of neomycin on EP response characteristics at 40 Hz, and used the vital dye DASPEI to verify neuromast ablation. Neomycin increased the latency of the EP response up until 60 min post-treatment. DASPEI results confirmed that neuromast hair cell death was significant in treated fish over this timeframe. These results indicate that the inner ear, whether it is sound pressure or particle motion detection, makes a significant contribution to the dipole-induced EP in blind cavefish at near-field low frequencies where the lateral line contribution would be expected to be strongest. The results from this study imply that under some circumstances, lateral line function could be complemented by the inner ear.

Underwater sound is directional and can convey important information about the surrounding environment or the animal emitting the sound. Therefore, sound is a major sensory channel for fishes and plays a key role in many life-history strategies. The effect of anthropogenic noise on aquatic life, which may be causing homogenisation or fragmentation of biologically important signals underwater is of growing concern. In this review we discuss the role sound plays in the ecology of fishes, basic anatomical and physiological adaptations for sound reception and production, the effects of anthropogenic noise and how fishes may be coping to changes in their environment, to put the ecology of fish hearing into the context of the modern underwater soundscape.

Fish sounds are an important biological component of the underwater soundscape. Understanding species-specific sounds and their associated behaviour is critical for determining how animals use the biological component of the soundscape. Using both field and laboratory experiments, we describe the sound production of a nocturnal planktivore, Pempheris adspersa (New Zealand bigeye), and provide calculations for the potential effective distance of the sound for intraspecific communication. Bigeye vocalisations recorded in the field were confirmed as such by tank recordings. They can be described as popping sounds, with individual pops of short duration (7.9±0.3 ms) and a peak frequency of 405±12 Hz. Sound production varied during a 24 h period, with peak vocalisation activity occurring during the night, when the fish are most active. The source level of the bigeye vocalisation was 115.8±0.2 dB re. 1 µPa at 1 m, which is relatively quiet compared with other soniferous fish. Effective calling range, or active space, depended on both season and lunar phase, with a maximum calling distance of 31.6 m and a minimum of 0.6 m. The bigeyes' nocturnal behaviour, characteristics of their vocalisation, source level and the spatial scale of its active space reported in the current study demonstrate the potential for fish vocalisations to function effectively as contact calls for maintaining school cohesion in darkness.

The utility of marine protected areas (MPAs) as a means of protecting exploited species and conserving biodiversity within MPA boundaries is supported by strong empirical evidence. However, the potential contribution of MPAs to fished populations beyond their boundaries is still highly controversial; empirical measures are scarce and modelling studies have produced a range of predictions, including both positive and negative effects. Using a combination of genetic parentage and relatedness analysis, we measured larval subsidies to local fisheries replenishment for Australasian snapper (Chrysophrys auratus: Sparidae) from a small (5.2 km2), well-established, temperate, coastal MPA in northern New Zealand. Adult snapper within the MPA contributed an estimated 10.6% (95% CI: 5.5–18.1%) of newly settled juveniles to surrounding areas (approx. 400 km2), with no decreasing trend in contributions up to 40 km away. Biophysical modelling of larval dispersal matched experimental data, showing larvae produced inside the MPA dispersed over a comparable distance. These results demonstrate that temperate MPAs have the potential to provide recruitment subsidies at magnitudes and spatial scales relevant to fisheries management. The validated biophysical model provides a cost-efficient opportunity to generalize these findings to other locations and climate conditions, and potentially informs the design of MPA networks for enhancing fisheries management.

A high-resolution 3D biophysical model was used to investigate the patterns of larval transport for an important commercial and recreational temperate fish, snapper Pagrus auratus, from a well-established marine reserve (Cape Rodney to Okakari Point marine reserve, CROP), and spawning ground. Our focus was to study the effects of local hydrodynamics, contrasting larval vertical behaviours and changing El Nino-Southern Oscillation (ENSO) cycles (via their effect on wind forcing) on the potential larval supply to adjacent non-protected areas. The model suggests the CROP marine reserve provides significant larval subsidies within a relatively small scale (≤40 km), the details of which depend on larval behaviour and ENSO patterns. Changing ENSO patterns mostly affected the dispersal direction of larvae, while larval behaviour was a strong driver only under La Nina conditions. Modelling suggests that under El Nino conditions, snapper larvae are more likely to settle successfully and hence make a strong contribution to surrounding fished stocks. Understanding the contribution of MPAs to fisheries management will require multiple approaches. Modelling will help identify the strength of contributing physical and biological factors, and in due course enable site- and time-specific examples of larval subsidy to be generalised.

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail-beat frequency, stride length, caudal fin-beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A0 ) was significantly increased in SN-disrupted fish compared with sham-operated controls. In addition, the orientation of caudal fin-tip relative to the overall swimming direction of SN-disrupted fish was significantly deflected (two-fold) in comparison with sham-operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body-wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN-disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (LF ) s(-1) . In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion.

Fish aggregation devices (FADs) are widely used as tools for facilitating fisheries, however, many questions remain as to the manner in which they work. Sound has been long suggested as a potential attraction and orientation cue but this is yet to be demonstrated. Here the temporal and spatial characteristics of the underwater sound around an operating FAD were characterised to evaluate sound as a potential cue for fish attraction. The FAD was located in the coastal waters of northeast Malaysia where they are locally known as ‘unjam’. The underwater signal of the FAD showed a distinct rise in sound energy between 500 and 2000 Hz across three octave bands. The spectral characteristics of this signal suggest that the source was animals inhabiting the FAD. The daily sound pattern showed that the signal was loudest during dusk, followed by night, dawn and significantly lowest during the day (14–20 dB lower than dusk). There was also a significant relationship between signal loss and distance away from the FAD, however, this did not follow conventional point source spreading models for underwater sound. In comparison to the estimated background noise of the prevailing sea state, the FAD signal was detectable up to 400 m away during the day and up to 1000 m during dusk. The bioacoustically rich unjam signal overlaps the frequency range of the hearing of many fishes, indicating that the acoustic signal emanating from FADs has the potential to attract fish and provide a long range orientation cue.

The purpose of this paper is to highlight the contributions of the Leigh Marine Laboratory to sensory neuroethology. A brief summary of the work done at Leigh, or by Leigh staff, is given across each of the main sensory modalities: chemosense, vision and octavolateralis sensory systems (electrosense, flow sensing and hearing). Within this broad overview, three particular areas have been singled out for more in-depth treatment as examples of Leigh research that have made particularly significant contributions to marine science. These three areas are: electrosensory processing, flow sensing and hearing, in particular the role of passive acoustics in orientation and settlement.

Swim bladder extensions and hearing ability were examined in the temperate reef fish Polyprion oxy- geneios (hapuka). Using the auditory evoked potential (AEP) technique, hearing thresholds were determined in four age-classes of hapuka, from larvae to juveniles. The youngest age-class had poor hearing abilities, with lowest thresholds of 132 dB re 1 lPa, and a narrow auditory bandwidth (100-800 Hz). Hearing ability improved sig- nificantly throughout the remainder of their first year, including decreases in thresholds of up to 27 dB, and an increase in auditory bandwidth (up to 1,000 Hz). Magnetic resonance imaging (MRI) was used to investigate structural mechanisms that may account for this ontogenetic improvement in hearing. These showed rostral extensions of the swim bladder developing early in the juvenile stage, and extending with increasing age closer to the otic cap- sule. It is suggested that this indirect connection between the swim bladder and the otic capsule could impart pres- sure sensitivity closer to the inner ear, accounting for the increase in sensitivity seen during development, although further investigation of older fish is required for conclusive evidence. The improvement in hearing ability in hapuka could be potentially related to a unique life history of extended pelagic durations up to 4 years.

Understanding lateral line function requires a background of lateral line anatomy combined with carefully crafted behavioral and neurophysiological studies. This combination, called neuroethology, provides the best insight into how an unfamiliar sensory system generates biologically useful information, and how this information guides behavior.

Le Port, A., Lavery, S., and Montgomery, J. C. 2012. Conservation of coastal stingrays: seasonal abundance and population structure of the short-tailed stingray Dasyatis brevicaudata at a Marine Protected Area. – ICES Journal of Marine Science, 69: . Elasmobranch (shark, ray, and skate) populations around the world are in decline, and effective conservation measures are urgently needed. Marine Protected Areas (MPA) placed in locations important for key life-history stages may form part of an effective conservation strategy. In this context, we examined the seasonal abundance and population structure of the short-tailed stingray (Dasyatis brevicaudata) at an offshore MPA in northeastern New Zealand, and the reported use of this location as a mating ground. Diver surveys were conducted from 2004 to 2007 at the Poor Knights Islands Marine Reserve (PKIMR). During this time, we observed: (i) a substantial increase in adult and subadult numbers, particularly females during the suggested breeding season, and a corresponding increase in females bearing fresh mating scars; and (ii) large numbers of smaller (probably immature) D. brevicaudata individuals of both sexes from spring to autumn. These results suggest that the PKIMR acts as both a mating aggregation location and a nursery for this species. We suggest that for coastal stingrays such as D. brevicaudata, small MPAs may be effective at protecting key life-history stages, but that as movements outside of reserve boundaries also occur, additional management tools may also be necessary.

In this study, a novel technique using baited underwater video with infrared lighting was compared with traditional underwater census surveys to investigate fish populations in situ . Fish abundance at the baited underwater video was related to the olfactory capability of each species. Olfactory specialists were shown to arrive at baited underwater video drops earlier, and in greater numbers, than non-olfactory species. This pattern was reversed in non-olfactory species, which were found to dominate underwater census surveys and appear less at baited underwater video drops. The sensory capacity of a species was found to be a larger determinant for fish abundance at baited underwater video drops than was the actual density of that species. The result of this study has ramifications for fish sampling techniques that use chemical stimuli to attract fish species, such as in the deep sea. The baited underwater video technique was highly effective at determining the diel activity of fish species.

Underwater sound emanating from reefs has been shown to be attractive to pre-set- tlement larval stages of fish and crustaceans, but its ecological importance depends on the range at which this cue can be detected by these larvae. Here we show, through field measurement and modelling, that the spatially extended sound source of a reef creates a surrounding zone, which extends for a distance offshore equal to the length of the reef, within which there is almost no loss in the sound level. Beyond this zone, the sound level decreases with cylindrical spreading plus any seafloor attenuation. This 'reef effect' means that the sound from a reef would be detectable at a much greater distance from the reef than would be estimated from a spot measurement near the reef or by using theoretical models of sound spreading from a point source. The greater reach for sound emanating from a reef means that reef noise could play a greater role in directing larval reef fishes and crabs to suitable settlement habitats than previously estimated.

SUMMARY Blind Mexican cave fish (Astyanax fasciatus) are able to sense detailed information about objects by gliding alongside them and sensing changes in the flow field around their body using their lateral line sensory system. Hence the fish are able to build hydrodynamic images of their surroundings. This study measured the flow fields around blind cave fish using particle image velocimetry (PIV) as they swam parallel to a wall. Computational fluid dynamics models were also used to calculate the flow fields and the stimuli to the lateral line sensory system. Our results showed that characteristic changes in the form of the flow field occurred when the fish were within approximately 0.20 body lengths (BL) of a wall. The magnitude of these changes increased steadily as the distance between the fish and the wall was reduced. When the fish were within 0.02 BL of the wall there was a change in the form of the flow field owing to the merging of the boundary layers on the body of the fish and the wall. The stimuli to the lateral line appears to be sufficient for fish to detect walls when they are 0.10 BL away (the mean distance at which they normally swim from a wall), but insufficient for the fish to detect a wall when 0.25 BL away. This suggests that the nature of the flow fields surrounding the fish are such that hydrodynamic imaging can only be used by fish to detect surfaces at short range.

All fish can detect the three vector components of particle motion, enabling them to determine source bearing, but particle motion alone cannot resolve which direction is towards the source and which direction is away (i.e., there is a 180° ambiguity). However, fish with swim bladders can also detect acoustic pressure which enables such fish to resolve this 180° ambiguity. Proposed processing algorithms, though, often employ unrealistic restrictions such as sinusoidal time dependence and free-field conditions. We propose a robust algorithm for determining the unambiguous source direction by a fish that can detect acoustic pressure. The method is based on the time-averaged acoustic intensity vector (the time-integral of the product of pressure and particle velocity). This non-oscillatory quantity points in the direction of energy flow and hence directly away from the source. The algorithm has the advantage of being applicable to signals with any time dependence, in any propagation environment. For sharks, which do not have swim bladders, we hypothesize that the vertical component of particle acceleration can be substituted for pressure, provided that the shark is sufficiently close to the water surface. We test the validity of this hypothesis by determining the direction to the source for reef noise, a biologically relevant signal, and boat noise in a range-varying shallow water environment.All fish can detect the three vector components of particle motion, enabling them to determine source bearing, but particle motion alone cannot resolve which direction is towards the source and which direction is away (i.e., there is a 180° ambiguity). However, fish with swim bladders can also detect acoustic pressure which enables such fish to resolve this 180° ambiguity. Proposed processing algorithms, though, often employ unrealistic restrictions such as sinusoidal time dependence and free-field conditions. We propose a robust algorithm for determining the unambiguous source direction by a fish that can detect acoustic pressure. The method is based on the time-averaged acoustic intensity vector (the time-integral of the product of pressure and particle velocity). This non-oscillatory quantity points in the direction of energy flow and hence directly away from the source. The algorithm has the advantage of being applicable to signals with any time dependence, in any propagation environment. For sharks, ...

Several patterns of brain allometry previously observed in mammals have been found to hold for sharks and related taxa (chondrichthyans) as well. In each clade, the relative size of brain parts, with the notable exception of the olfactory bulbs, is highly predictable from the total brain size. Compared with total brain mass, each part scales with a characteristic slope, which is highest for the telencephalon and cerebellum. In addition, cerebellar foliation reflects both absolute and relative cerebellar size, in a manner analogous to mammalian cortical gyrification. This conserved pattern of brain scaling suggests that the fundamental brain plan that evolved in early vertebrates permits appropriate scaling in response to a range of factors, including phylogeny and ecology, where neural mass may be added and subtracted without compromising basic function.

The structure of the cerebellar cortex is remarkably similar across vertebrate phylogeny. It is well developed in basal jawed fishes, such as sharks and rays with many of the same cell types and organizational features found in other vertebrate groups, including mammals. In particular, the lattice-like organization of cerebellar cortex (with a molecular layer of parallel fibres, interneurons, spiny Purkinje cell dendrites, and climbing fires) is a common defining characteristic. In addition to the cerebellar cortex, fishes and aquatic amphibians have a variety of cerebellum-like structures in the dorso-lateral wall of the hindbrain. These structures are adjacent to, and in part, contiguous with, the cerebellum. They derive their cerebellum-like name from the presence of a molecular layer of parallel fibers and inhibitory interneurons, which has striking organizational similarities to the molecular layer of the cerebellar cortex. However, these structures also have characteristics which differ from the cerebellum. For example, cerebellum-like structures do not have climbing fibres, and they are clearly sensory. They receive direct afferent input from peripheral sensory receptors and relay their outputs to midbrain sensory areas. As a consequence of this close sensory association, and the ability to characterise their signal processing in a behaviourally relevant context, good progress has been made in determining the fundamental processing algorithm in cerebellar-like structures. In particular, we have come to understand the contribution to signal processing made by the molecular layer, which provides an adaptive filter to cancel self-generated noise in electrosensory and lateral line systems. Given the fundamental similarities of the molecular layer across these structures, coupled with evidence that cerebellum-like structures may have been the evolutionary antecedent of the cerebellum, we address the question: do both share the same functional algorithm?

There is evidence that ambient underwater sound is used by some pelagic larval reef fishes and decapods as a guide to direct them toward coastal areas. It would be advantageous to these organisms if they were also able to use sound to remotely identify suitable settlement habitats. However, it is unknown whether different coastal habitats produce different sounds that would be capable of providing distinctive cues for larvae. This study identified marked differences in the char- acteristics of ambient underwater sound at 3 distinct types of coastal habitat: a macroalgal-dominated reef, a sea urchin-dominated reef, and a sandy beach. The sea urchin-dominated reef habitat pro- duced sound that was significantly more intense overall in a biologically important frequency band (800 to 2500 Hz), compared with that from macroalgal-dominated reefs and beach habitats. The sound produced by snapping shrimp also exhibited marked differences among habitat types, with the sea urchin-dominated reef having significantly more snaps than the macroalgal-dominated reef or beach habitat. Many of the differences in the sound produced by the 2 reef habitats became more apparent at dusk compared with noon. This study provides evidence that there are significant differ- ences in the spectral and temporal composition of ambient sound associated with different coastal habitat types over relatively short spatial scales. An acoustic cue that conveys both directional and habitat quality information that is transmitted considerable distances offshore would have the poten- tial to be of immense value to the pelagic larval stage of a coastal organism attempting to remotely locate a suitable habitat in which to settle.

The mechanoreceptive lateral line system in fishes detects hydrodynamic stimuli and plays a critical role in many fundamental behaviours, including orientation to water currents and the detection of stationary objects, prey and predators. Interspecific variation in lateral line structure may result from a process of functional adaptation, with the background level of hydrodynamic activity proposed as an important selective pressure. Here we use the eight species of the ecologically diverse New Zealand marine triplefin fish of the genus Forsterygion and one species from the sister genus Notoclinops to investigate interspecific differences in lateral line morphology and to assess the relationship between lateral line characteristics and exposure to wave energy (fetch/depth ratio). Overall, the results show that lateral line traits are divergent between species, and these differences could in part be related to the wave exposure of the habitats that the species occupy. Specifically, numbers of canal neuromasts differed significantly between species, and most canal groupings increased in neuromast number with fetch/depth ratio, while the number and area of some superficial neuromast groupings decreased significantly with exposure. Distribution of superficial neuromasts along the trunk in the semi-pelagic and paedomorphic species F. maryannae differed from the other, demersal species, which may be associated with the unique lifestyle of this species and/or developmental processes. Canal architecture also differed considerably between species, but displayed no relationship with fetch/depth ratio. The results from this study indicate that some interspecific differences in lateral line organs may be a by-product of selection for habitat divergence. Future work should explore additional causal factors that might have influenced the evolution of lateral morphology in these species, including phylogenetic and allometric effects.