Single-unit responses in the auditory cortex of monkeys performing a conditional acousticomotor task

The general goal of the present study was to assess the response properties to tones of single neurons in the auditory cortex (primary auditory area, A1, and middle lateral auditory belt, ML) of two macaque monkeys while performing an acousticomotor discrimination task requiring a controlled level of attention and motivation. For each neuron, an approximation of the frequency receptive field (FRF) was first established. Second, based on the FRF, sets of paired tone frequencies were defined in which two different tone frequencies had to be associated by the monkey, following a trial and error strategy, to a left or a right key-press with the left arm. After acquisition of the association, the two tones of the pair were presented randomly ("instruction stimulus”) and, if the monkey touched the correct key, the stimulus was repeated ("confirmation stimulus”) and a reward was delivered. The majority of units (63%) had a FRF formed by multiple peaks, whereas 25% and 12% of units exhibited a simple U-shaped FRF and a "mosaic” FRF, composed of several separated zones of response, respectively. Five principal response patterns were observed: On, Off, On-Off, Sustained, and Inhibition. In relation to the acousticomotor association task, some auditory cortical neurons (33%) exhibited a different response to the same stimulus when presented, in the same trials, as instruction or as confirmation. It was also observed that the response to the same instruction stimulus could differ when comparing correct trials with erroneous trials (wrong motor response). In conclusion, the response properties of auditory cortical neurons in behaving monkeys are strongly dependent on the physical parameters of sounds (frequency, intensity, etc.) as indicated by FRF characteristics, but a substantial influence of the behavioral context and performance may also play an important rol

Forskningsfangst av ål - Sluttrapport HI-prosjekt 81333

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Report on the scientific eel fishery in Norway in 2017

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Sluttrapport forskningsfangst etter ål (2018) - HI prosjekt 81333

Bakgrunn for prosjektet Europeisk ål er en viktig del av kystøkosystemet, spesielt i Sør-Norge. Anguilla anguilla er en katadrom fisk. Det vil si at den gyter i saltvann og vokser opp i ferskvann (gulålstadiet). Imidlertid vokser en god del av ålen som kommer til Norge opp i saltvann langs kysten. Etter gulålstadiet går ålen over i blankålstadiet. Om høsten, mens den fremdeles er seksuelt umoden, starter ålen gytevandringen. Den svømmer da ca. 6000 km for å nå tilbake til Sargassohavet hvor den gyter. I 2007 ble ål inkludert i CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora). Den omhandler arter som ikke nødvendigvis er truet av utryddelse, men der handel med arten må kontrolleres for å unngå en utnyttelse som er uforenlig med deres overlevelsesevne (se http://www.cites.org/eng/ plate / how.shtml). Oppføringen ble gjennomført i mars 2009. Etter den ble rødlistet som kritisk truet i Norge, ble alt fiske etter ål forbudt i Norge 1. juli 2009. Dette gjaldt også fritidsfiske. Ålebestanden i Norge har vært overvåket av Havforskningsinstituttet siden 1975. Fangst og innsats ble registrert i dagbøker frem til 2010. En del fiskere fikk dispensasjon til å fiske en gitt mengde ål etter at fiskeforbudet ble innført for at overvåkingen av ål skulle fortsette. På grunn av CITES regulering fikk imidlertid fiskerne problemer omsetningen av ål, da det ble ulovlig å importere ål inn til EU. Forskningsfangsten ble derfor avsluttet i 2010. I 2015 fikk ål en ny vurdering av Artsdatabanken, og ble oppført som VU (sårbar) i den Norske Rødlisten, hvor den hadde stått som CR (kritisk truet) siden 2006. I Fiskeridirektoratets «Handlingsplan 2016» vises det til at det er behov for mer kunnskap om bestandssituasjonen for ål, og at en overvåkningsfangst vil kunne bidra til dette. Det ble da startet et prosjekt med forskningsfangst for å vurdere endringer i lokale bestander. Formålet med prosjektet var å få oversikt over bestanden av Europeisk ål langs norskekysten, og i tillegg øke kunnskapen om biologiske egenskaper som alder ved kjønnsmodning (utvandring til gyteområdet), vekstparametere, parasittbelastning m.m. Denne kunnskapen kan forbedre rådgivningen for denne arten i Norge og bidra til ICES sin vurdering av hele bestanden. Prosjektet bestod av 3 deler: 1) registrering av fangst fra utvalgte fiskere; 2) merkeforsøk; 3) biologisk kunnskapsinnhenting (aldersbestemmelse, vekt, parasittbelastning). Dette er en sluttrapport for 2018 som oppsummerer aktivitetene og resultatene av: overvåkning av ål dette året.publishedVersio

Blood-based gene expression as non-lethal tool for inferring salinity-habitat history of European eel (Anguilla anguilla)

The European eel is a facultative catadromous species, meaning that it can skip the freshwater phase or move between marine and freshwater habitats during its continental life stage. Otolith microchemistry, used to determine the habitat use of eel or its salinity history, requires the sacrifice of animals. In this context, blood-based gene expression may represent a non-lethal alternative. In this work, we tested the ability of blood transcriptional profiling to identify the different salinity-habitat histories of European eel. Eels collected from different locations in Norway were classified through otolith microchemistry as freshwater residents (FWR), seawater residents (SWR) or inter-habitat shifters (IHS). We detected 3451 differentially expressed genes from blood by comparing FWR and SWR groups, and then used that subset of genes in a machine learning approach (i.e., random forest) to the extended FWR, SWR, and IHS group. Random forest correctly classified 100% of FWR and SWR and 83% of the IHS using a minimum of 30 genes. The implementation of this non-lethal approach may replace otolith-based microchemistry analysis for the general assessment of life-history tactics in European eels. Overall, this approach is promising for the replacement or reduction of other lethal analyses in determining certain fish traits.publishedVersio

A unifying hypothesis for the spawning migrations of temperate anguillid eels

Anguillid eels grow in freshwater but spawn in the open ocean. The cues that guide eels over long distances to the spawning area are unknown. The Earth's magnetic field can provide directional and positional information and is likely used by catadromous eels during their spawning migration; as magnetosensitivity and compass orientation have been reported in eels. To test whether this is theoretically possible, we compared the migratory routes of five species of temperate eels that undertake long migrations with the geomagnetic field of their distribution/spawning areas. We found that, regardless of the species and although routes are different between life stages, larvae of those species always drift along paths of increasing magnetic inclination and intensity, while adults follow reverse gradients. This is consistent with an imprinting/retracing hypothesis. We propose a general navigation mechanism based on larvae imprinting on a target magnetic intensity (or inclination) at the hatching area and on the intensity (or inclination) gradient during larval drift. Years later, adults retrace the magnetic route by following the gradient of decreasing total intensity (or inclination) values that occurs towards lower latitudes. As they reach the target value, adults switch to compass orientation to stay on the target isoline and reach the spawning area. The proposed mechanism fits for all temperate eels examined. Knowledge about navigational strategies of eels is important to evaluate the effectiveness of management strategies that involve stocking of juveniles displaced from one area to another to rebuild local populations.publishedVersio

Glass eels (Anguilla anguilla) imprint the magnetic direction of tidal currents from their juvenile estuaries

The European eel (Anguilla anguilla) hatches in the Sargasso Sea and migrates to European and North African freshwater. As glass eels, they reach estuaries where they become pigmented. Glass eels use a tidal phase-dependent magnetic compass for orientation, but whether their magnetic direction is innate or imprinted during migration is unknown. We tested the hypothesis that glass eels imprint their tidal-dependent magnetic compass direction at the estuaries where they recruit. We collected 222 glass eels from estuaries flowing in different cardinal directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where the magnetic North was rotated. Glass eels oriented towards the magnetic direction of the prevailing tidal current occurring at their recruitment estuary. Glass eels use their magnetic compass to memorize the magnetic direction of tidal flows. This mechanism could help them to maintain their position in an estuary and to migrate upstream.publishedVersio

Magnetic fields generated by submarine power cables have a negligible effect on the swimming behavior of Atlantic lumpfish (Cyclopterus lumpus) juveniles

Submarine power cables carry electricity over long distances. Their geographic distribution, number, and areal coverage are increasing rapidly with the development of, for example, offshore wind facilities. The flow of current passing through these cables creates a magnetic field (MF) that can potentially affect marine organisms, particularly those that are magnetosensitive. The lumpfish (Cyclopterus lumpus) is a migratory species that is widely distributed in the North Atlantic Ocean and Barents Sea. It migrates between coastal spawning grounds and pelagic offshore feeding areas. We tested whether lumpfish respond to MFs of the same intensity as those emitted by high voltage direct current (HVDC) submarine power cables. Laboratory experiments were conducted by placing juvenile lumpfish in an artificial MF gradient generated by a Helmholtz coil system. The intensity of the artificial MF used (230 µT) corresponded to the field at 1 m from a high-power submarine cable. The fish were filmed for 30 min with the coil either on or off. Swimming speeds, and presence in the different parts of a raceway, were extracted from the videos and analyzed. Juvenile lumpfish activity, defined as the time that the fish spent swimming relative to stationary pauses (attached to the substrate), and the distance travelled, were unaffected by exposure to the artificial MF. The swimming speed of juvenile lumpfish was reduced (by 16%) when the coil was on indicating that the fish could either sense the MF or the induced electric field created by the movement of the fish through the magnetic field. However, it seems unlikely that a 16% decrease in swimming speed occurring within 1 m of HVDC cables would significantly affect Atlantic lumpfish migration or homing.publishedVersio

Atlantic cod (Gadus morhua) larvae are attracted by low-frequency noise simulating that of operating offshore wind farms

The number and size of offshore wind (OW) turbines is increasing rapidly. OW turbines produce continuous, low-frequency noise that could impact marine fish dispersing/migrating through the facilities. Any such impact would be relevant for larval stages, which have limited possibility to swim away from OW facilities. If directional movement of fish larvae at sea is impacted by low-frequency continuous sound is unknown. We observe the behavior of Atlantic cod larvae (N = 89) in response to low-frequency sound while they are drifting in a Norwegian fjord inside transparent drifting chambers. We transmit 100 Hz continuous sound in the fjord, in the intensity range of OW turbines’ operational noise, and measure the sound pressure and 3-D particle motion. Half of the larvae (N = 45) are exposed to low-frequency (100 Hz) continuous sound, while the other half (N = 44) are observed under the same conditions but without the sound. Exposure does not affect the routine and maximum swimming speeds or the turning behavior of the larvae. Control larvae orient to the northwest. In contrast, exposed larvae orient towards the source of low-frequency sound and particle motion. This provides a basis to assess how OW might impact dispersal in this species.publishedVersio

Glass eels (Anguilla anguilla) have a magnetic compass linked to the tidal cycle

The European eel (Anguilla anguilla) has one of the longest migrations in the animal kingdom. It crosses the Atlantic Ocean twice during its life history, migrating between the spawning area in the Sargasso Sea and Europe, where it is widely distributed. The leptocephalus larvae drift with the Gulf Stream and other currents for more than a year and metamorphose into glass eels when they arrive on the continental shelf and move toward coastal areas. The mechanisms underlying glass eel orientation toward the coast and into freshwater systems are poorly known. However, anguillid eels, including the glass eel life stage, have a geomagnetic sense, suggesting the possibility that they use Earth’s magnetic field to orient toward the coast. To test this hypothesis, we used a unique combination of laboratory tests and in situ behavioral observations conducted in a drifting circular arena. Most (98%) of the glass eels tested in the sea exhibited a preferred orientation that was related to the tidal cycle. Seventy-one percent of the same eels showed the same orientation during ebb tide when tested in the laboratory under a manipulated simulated magnetic field in the absence of any other cue. These results demonstrate that glass eels use a magnetic compass for orientation and suggest that this magnetic orientation system is linked to a circatidal rhythm.publishedVersio