Grenadier Fish Research Articles

Distribution patterns of the demersal fish assemblage off central Chile.

Thespatial and temporal distribution of the fish fauna in the fishing area of Pleuroncodes monodon, off Central Chile, is analysed. Haul-by-haul information from four surveys was taken into account (April 1982 and 1983, and March and November 1984). The demersal fish fauna exhibits two boundaries, one at depths of around 250 ± 50 m and the other one at depths of around 100 m. Consequently, three fish assemblages are recognized: inshore over the continental shelf, offshore over the continental shelf, and over the upper continental slope. Temporal and spatial changes in the fish assemblage are clearly recognized with M. gayi as the dominant species, being replaced in depth mainly by the grenadier fish Coelorinchus aconcagua.

Physical evidence of direct antagonistic interactions between trematodes in the host gut: the kiss of death?

Although within-host competition among parasites if often assumed to occur based on statistical patterns, actual physical evidence of direct antagonistic interactions between parasites, either intraspecific or interspecific, is very rare. Here, we report such evidence between and within two species of hemiurid trematodes infecting the deep-sea grenadier fish Coryphaenoides subserrulatus. We found pairs of worms attached together, with one worm using its ventral sucker against another worm, and sucking out a large protuberance on the victim. We also found single worms showing clear signs of past attacks. There was no evidence that these interactions were more common at high intensities of infection, where the conditions would be expected to be more conducive to competitive interactions. Our findings provide evidence that trematodes may cause some harm to co-occurring individuals, suggesting a direct form of interference competition among intestinal helminths.

A tale from the middle Paleocene of Denmark: A tube-dwelling predator documented by the ichnofossil Lepidenteron mortenseni n. isp. and its predominant prey, Bobbitichthys n. gen. rosenkrantzi (Macroridae, Teleostei)

The ichnofossil Lepidenteron provides a unique taphonomic window into the life habits of a tube-dwelling predator, probably an eunicid polychaete, and its fish prey. Here we describe a new tube-like ichnofossil Lepidenteron mortenseni n. isp. from the Kerteminde Marl (100–150 m palaeo-water depth) from the Gundstrup gravel pit near Odense, Fyn, Denmark. 110 individual tubes were examined which contain fish remains, including a variety of disarticulated bones and otoliths, by far dominated by a single gadiform taxon referred herein to as Bobbitichthys n. gen. The isolated otoliths here associated with disarticulated gadiform bones have previously been described, from the time equivalent Lellinge Greensand exposed in the Copen-hagen area, as Hymenocephalus rosenkrantzi, a grenadier fish (family Macrouridae). The abundance of associated bones and otoliths in the examined tubes allowed us to reconstruct part of the cranial configuration of Bobbitichthys rosenkrantzi and to tentatively interpret it as a stem macrourid. Bobbitichthys rosenkrantzi represents the earliest grenadier known in the fossil record. Additional, although considerably less abundant, skeletal remains and otoliths have been tentatively referred to a long-fin bonefish (family Pterothrissidae, Pterothrissus? conchaeformis), a viviparous brotula (family Bythitidae, Bidenichthys? lapierrei), a conger eel (family Congridae, possibly belonging to Rhynchoconger angulosus), and another unidentified gadiform.

A new grenadier of the genus Hymenocephalus from Tosa Bay, southern Japan (Actinopterygii: Gadiformes: Macrouridae)

Hymenocephalus yamasakiorum, a new species of grenadier fishes, is described from a single specimen collected from Tosa Bay off Aki, Kochi, Japan, at a depth of 320–400 m. The species is distinguished from its 26 known congeners in having the following combination of features: pelvic-fin rays nine; pectoral-fin rays i16–i17; first dorsal-fin rays II, 10; chin barbel 55 % of head length (HL), its tip extending beyond the hind margin of orbit when laid back; snout moderately high, not depressed, length 28 % HL; orbit diameter 33 % HL; interorbital width 24 % HL; gill rakers on first arch (outer/inner) 14/20, on second arch 20/19; pyloric caeca 15; dorsal half of posterior part of tail prominently blackish.

Tissue and size-related changes in the fatty acid and stable isotope signatures of the deep sea grenadier fish Coryphaenoides armatus from the Charlie-Gibbs Fracture Zone region of the Mid-Atlantic Ridge

Coryphaenoides armatus is a cosmopolitan deep-sea fish that plays a major role in the ecology of abyssal ecosystems. We investigated the trophic ecology and physiology of this species by determining the δ13C, δ15N and fatty acid signatures of muscle, liver and ovary tissues of individuals collected from ∼2700m to the north and south of the Charlie-Gibbs Fracture Zone (CGFZ) of the Mid-Atlantic Ridge, NE Atlantic. Fatty acid and δ13C data both suggested that C. armatus shows an ontogenetic dietary shift, with the relative contributions of benthic and pelagic prey decreasing and increasing respectively as the animals grow. They also indicated that dietary overlap between animals living to the north and south of the CGFZ increases as they grow, suggesting that larger animals forage over greater distances and are not hindered by the presence of the CGFZ. Comparison of tissue-specific fatty acid signatures with previously published data suggests compositional homeostasis of the fatty acids 20:5(n−3) and 22:6(n−3) in the muscle, and 18:1(n−9) in the liver tissues. We ascribe this primarily to strict physiological requirements for these compounds, rather than simply to their abundance in the diet. We pose several speculative mechanisms to explain the observed trends in tissue-specific δ13C and δ15N values, illustrating some of the numerous processes that can influence the isotopic signatures of bulk tissues.

Review of the literature on age and growth of grenadiers in the Mediterranean and new data on age of Trachyrincus scabrus (Macrouridae) in the Ionian Sea

This paper reviews the existing literature on the age and growth of grenadiers in the Mediterranean Sea and provides new data on ageing of Trachyrincus scabrus in the Northwestern Ionian Sea (Central Medi� terranean). Most studies have been carried out through otolith readings. Seasonal otolith formation also appears to be a general trend in grenadier fish in the Mediterranean even though it seems to be related to fluc� tuations in feeding and activity patterns. From examined literature age ranges of macrourids in the Mediter� ranean Sea varied from youngoftheyear (age 0) to a maximum ages of 23 years. There is a general agree� ment on the growth pattern of the species in the different geographic areas. T. scabrus was collected in the Northwestern Ionian Sea at depths between 400 and 1200 m during four seasonal trawl surveys. The mini� mum and maximum sizes of the whole sampled population were between 58 and 217 mm PAL. Otoliths were removed from 216 specimens. Backcalculation was performed and a maximum age of 10 years was deter� mined. The following von Bertalanffy growth parameters were estimated for the whole sampled population: L ∞ = 247.44 ± 8.39 mm PAL; k = 0.125 ± 0.010/year; t 0 = -1.921 ± 0.127.

Notes on the diet of seven grenadier fishes (Macrouridae) from the lower continental slope of Chatham Rise, New Zealand

Diets of 8 rarely sampled species of grenadiers were examined from the lower continental slope (1178 to 1837 m) on Chatham Rise, New Zealand and includes the first known records of the diet of Bathygadus cottoides, Coryphaenoides mcmillani, C. murrayi, and Idiolophorhynchus andriashevi. Most species fed benthopelagically on small crustaceans, e.g., calanoid copepods, amphipods and mysids and others.

Stable abundance, but changing size structure in grenadier fishes (Macrouridae) over a decade (1998–2008) in which deepwater fisheries became regulated

A ten-year time series (1998–2008) from a trawl survey of the continental slope of the NE Atlantic was analyzed to assess temporal variation in the abundance and length frequency of seven species of deepwater grenadier fish. This period coincided (in 2003) with the regulation of deepwater fisheries in this area. None of the species declined in numbers or biomass over the period, and 2 species significantly increased. This suggests that the declines in abundance of these deepwater species following the onset of fishing in the 1970s may now have stabilized, albeit at much lower levels than the virgin biomass. Although two metrics of body size (mean length and maximum length) did not show any evidence for consistent decrease over time, there were significant changes in the overall length–frequency distributions. The species found in shallower depths (500 m) had a greater number of larger individuals in 2008 whereas those found deeper (1500 m) tended to have a greater number of smaller individuals. This suggests the presence of a lagged indirect effect of fishing on species that live beyond the actual depths that fishing takes place.

A taste of the deep-sea: The roles of gustatory and tactile searching behaviour in the grenadier fish Coryphaenoides armatus

The deep-sea grenadier fishes ( Coryphaenoides spp.) are among the dominant predators and scavengers in the ocean basins that cover much of Earth's surface. Baited camera experiments were used to study the behaviour of these fishes. Despite the apparent advantages of rapidly consuming food, grenadiers attracted to bait spend a large proportion of their time in prolonged periods of non-feeding activity. Video analysis revealed that fish often adopted a head-down swimming attitude (mean of 21.3° between the fish and seafloor), with swimming velocity negatively related to attitude. The fish also swam around and along vertical and horizontal structures of the lander with their head immediately adjacent to the structure. We initially hypothesised that this behaviour was associated with the use of the short chin barbel in foraging. Barbel histology showed numerous taste buds in the skin, and a barbel nerve with about 20,000 axons in adult fish. A tracing experiment in one undamaged animal revealed the termination fields of the barbel neurons in the trigeminal and rhombencephalic regions, indicating both a mechanoreceptory and a gustatory role for the barbel. Our conclusion was that olfactory foraging becomes ineffective at close ranges and is followed by a search phase using tactile and gustatory sensing by the barbel. The development of this sensory method probably co-evolved alongside behavioural changes in swimming mechanics to allow postural stability at low swimming speeds.

Geographic and bathymetric trends in abundance, biomass and body size of four grenadier fishes along the Iberian coast in the western Mediterranean

The present study is a mesoscale analysis of latitude and depth related trends in abundance, biomass and body size of the four grenadier species Caelorinchus caelorhincus, Hymenocephalus italicus, Nezumia aequalis and Trachyrinchus scabrus inhabiting the deep western Mediterranean. We have analysed data from seven annual bottom trawl surveys, carried out down to 800 m depth along the Iberian Mediterranean coast covering a distance of approximately 1200 km. The objectives were to establish general patterns in the mesoscale distribution of abundance, biomass and body size of deep-water grenadier fishes and also analyse the consistency of the bathymetric distribution of these parameters along a large latitudinal gradient. Five complementary series of analyses have been completed. The first focussed on describing the general patterns of abundance and size by correspondence canonical analysis, CCA, in the area. The second and third series focussed on the existence of temporal, geographical and bathymetric trends of abundance, weight and mean size by analysis of covariance, ANCOVA and multiple regression analysis. The fourth series compared the frequency distributions of body length. Finally, the last series focussed on the patterns of abundance versus size. The total number of individuals of all four grenadier species captured in 260 bottom trawls amounted to 27,435 and their weight was 1404 kg. No general trends for the four species have been observed between years. All four species showed a general pattern of increasing size with depth, which, except in the case of C. caelorhincus, was consistent along a large latitudinal gradient. Nezumia aequalis was unique in showing the same noticeable trend of increasing abundance with depth along the entire latitudinal range, but with clear differences in the intercepts. The abundance of N. aequalis and C. caelorhincus decreased significantly northwards. Hymenocephalus italicus was the least abundant species and had a homogeneous distribution without any specific trend along the entire latitudinal range analysed. The distribution of T. scabrus in the Mediterranean seemed to be more localised. Higher abundances were found to the north and south of the latitudinal gradient with lower values between. The grenadiers studied also showed a general trend of decreasing mean size northwards, except in the case of the smallest species, H. italicus. The relation between abundance and body size differed between sectors for the whole grenadier population and species-specific variations were also observed. The relationship between individual body mass and population density fit well to a second-order polynomial function rather than to a linear regression, showing a significant trend for density to increase with increasing size until some mid-point, then to decline with increasing size thereafter. The observed latitudinal gradient in the distribution patterns of grenadiers along the upper slope of the western Mediterranean can be discussed in relation to direct and indirect factors of biogeographic, environmental and anthropogenic origin.

Round and pointed-head grenadier fishes (Actinopterygii: Gadiformes) represent a single sister group: Evidence from the complete mitochondrial genome sequences

The gene order of mitochondrial genomes (mitogenomes) has been employed as a useful phylogenetic marker in various metazoan animals, because it may represent uniquely derived characters shared by members of monophyletic groups. During the course of molecular phylogenetic studies of the order Gadiformes (cods and their relatives) based on whole mitogenome sequences, we found that two deep-sea grenadiers ( Squalogadus modificatus and Trachyrincus murrayi: family Macrouridae) revealed a unusually identical gene order (translocation of the tRNA Leu (UUR)). Both are members of the same family, although their external morphologies differed so greatly (e.g., round vs. pointed head) that they have been placed in different subfamilies Macrouroidinae and Trachyrincinae, respectively. Additionally, we determined the whole mitogenome sequences of two other species, Bathygadus antrodes and Ventrifossa garmani, representing a total of four subfamilies currently recognized within Macrouridae. The latter two species also exhibited gene rearrangements, resulting in a total of three different patterns of unique gene order being observed in the four subfamilies. Partitioned Bayesian analysis was conducted using available whole mitogenome sequences from five macrourids plus five outgroups. The resultant trees clearly indicated that S. modificatus and T. murrayi formed a monophyletic group, having a sister relationship to other macrourids. Thus, monophyly of the two species with disparate head morphologies was corroborated by two different lines of evidence (nucleotide sequences and gene order). The overall topology of the present tree differed from any of the previously proposed, morphology-based phylogenetic hypotheses.

New grenadier fishes of the genus Coryphaenoides (Pisces: Macrouridae); one from off New Zealand and one widespread in the southern Indo‐West Pacific and Atlantic Oceans

Two new species of macrourid fishes of the genus Coryphaenoides from New Zealand are described. Coryphaenoides dossenus n. sp. is widespread on the continental slope at 480–1464 m and shows sexual dimorphism with the largest male about half the length of the largest female. It is also known from the Tasman Sea, Coral Sea, Indian Ocean, and the eastern side of the Atlantic Ocean south of c. 6° S. Coryphaenoides microstomus n. sp. is known only from four specimens collected from a single station at 1550–1720 m off the east coast of the North Island, New Zealand.

Distribution and biology of five grenadier fish (Pisces: Macrouridae) from the upper and middle slope of the northwestern Mediterranean

Specimens of five Macrouridae species ( Trachyrhynchus trachyrhynchus, Nezumia aequalis, Hymenocephalus italicus, Coelorhynehus coelorhynchus and Coelorhynchus labiatus) were obtained from 76 bottom trawls in the Catalan Sea at depths between 147 and 1290 m. Abundance, biomass and length distribution by depth varied depending on the species. For T. trachyrhynchus, maximum abundance and biomass were found between 900 and 1000 m. In H. italicus, abundance and biomass decreased below 500–600 m, whereas abundance and biomass showed a bimodal trend for N. aequalis. In these species, the mean length of the specimens increased with depth. The sex-ratio was 50% for intermediate sizes while larger fish were predominantly females. Reproduction patterns were different for each species. Ripe females of N. aequalis and H. italicus were found all year round, while C. coelorhynchus and C. labiatus ripe females were found in spring-summer and autumn winter, respectively. No ripe females of T. trachyrhynchus were found. Size at attainment of 50% maturity for N. aequalis and H. italicus was 4.5 and 2.7 cm pre-anal length (PAL), respectively. The PAL-otolith length (OL) and OL- otolith weight (OW) relationships showed a negative allometry, except for C. labiatus whose OL-OW relationship was isometric. Seasonal growth was detected in the otoliths of all five species; fast growth rings were laid down in summer. All the species reach ages of at least 9 years, and growth rates were relatively high and greater for females.

Review of trachyrincine grenadier fishes (Pisces: Macrouridae) from New Zealand, with a description of a new species ofTrachyrincus

Abstract Knowledge of the New Zealand trachyrincine grenadiers is reviewed. Idiolo‐phorhynchus andriashevi Sazonov, 1981 and Trachyrincus longirostris (Gunther, 1878) are redescribed and Trachyrincus aphyodes n. sp. is described. T. aphyodes differs from T. longirostris, with which it has been confused, by having more pyloric caeca (119–211 cf. 35–62) and a larger mouth (upper jaw length 29.4–34.0 cf. 24.7–28.2% head length). A key to the three known New Zealand trachyrincine grenadiers is given.

Chondracanthid copepods (Poecilostomatoida) parasitic on Japanese deep-sea fishes, with a key to the genera of the Chondracanthidae

Four species of chondracanthid copepods are reported from grenadier fishes (Macrouridae) taken in the deep waters off Japan. They are Chondracanthus neali Leigh-Sharpe, 1930 from the oral cavity floor of Malacocephalus nippoensis Gilbert et Hubbs; Chondracanthodes deflexus Wilson, 1932 from the gill cover of Coryphaenoides armatus (Hector); Jusheyhoea ryukyuensis sp. nov. from the oral cavity wall of Coelorhynchus anatirostris Jordan et Gilbert, C. gilberti Jordan et Hubbs and C. productus Gilbert et Hubbs; and Chelonichondria okamurai gen. et sp. nov. from the gill cover of Coryphaenoides nasutus Gunther. A key to the 42 genera of the Chondracanthidae is provided.

Seasonal change in activity of abyssal demersal scavenging grenadiers Coryphaenoides (Nematonums) armatus in the eastern North Pacific Ocean

The responses of the grenadier fish Coryphaenoides (Nematonurus) armatus to bait deployed on the sea floor at station M in the North Pacific Ocean (34°50′N, 123°00′W; 4,100 m deep) in February and October were compared. In February 1990 and 1992, the first fish arrived after an average time of 25 min and stayed an average of 150 min. In October 1991, the respective times were 15 and 98 min. The faster response in October is correlated with a higher mean swimming speed of 0.0692 m s−1 compared with 0.0262 m s−1 in February. Fish activity was elevated in October following seasonal enrichment to the benthos by downward flux of particulate organic matter from the surface. Grenadier abundance was estimated from arrival times as 325 individuals km−2, corresponding to a wet weight biomass of 146 mg m−2 or 10.2 mg C m−2.

Temporal change in foraging behaviour of the fish Coryphaenoides (Nematonurus) yaquinae in the central North Pacific

Deep-sea grenadier fish Coryphaenoides (Nematonurus) yaquinae were attracted to a baited free-fall video camera and tracklng vehicle dunng deployments in the central North Pacific (31°N, 159 W) at a depth of 5800 m. The mean time of arrival of the first fish was 31.0 min after landing on the sea floor. The mean number of fish within camera view increased to a peak of 5.25 at 90 min after landing and decreased thereafter The mitial arrival rate was 0.06 fish mm-' , and mean fish staying time was 122 min The staying time was much shorter than in previous work at this site, suggesting a change in food supply with time of year Grenadiers were tracked using ingestible acoustic transmitters. The mean time until transmitter ingestion after the bait landed was 85.1 min. Fish that swallowed transmitters dispersed at radial rates of l to 20 cm S ' , and all had departed to a range of > 1000 m by 13 h after landlng. Movements to an altitude of > 15 m were recorded for 60 % of fish tracked and occupied 12.9 10 of total tracking time. Bottom current speeds were between < 1 and 9 cm S-' with a tidal rhythmicity Deep-sea macrourid fish, Coryphaenoides (Nematonurus) armatus and C. (N.) yaquinae, are attracted to baits deployed at abyssal depths (Wilson & Smith 1984). Movements of these fish can then be tracked since they will swallow (Priede & Smith 1986) and retain (Armstrong & Baldwin 1990) acoustic transmitters. Earlier work has compared arrival rates and staying time of grenadiers at a standard bait in contrasting areas of the Pacific Ocean (Priede et al. 1990). The areas studied were a relatively eutrophic region at 4400 m under the California current (Stn F, 32 50' N, 124 W) and an oligotrophic station a t 5800 m under the central North Pacific gyre (CNP, 31°N, 159 W). Priede et al. (1990) were able to record the range and the degree of vertical movement of acoustically tagged fish at Stn F but not at CNP. Present address SOAFD, Freshwater Fishenes Laboratory, Pitlochry, Perthshire PHI6 5LB, UK O Inter-Research/Pnnted in Germany The present study collected acoustic tracking data from CNP to supplement the previous work. The study was conducted at a different time of the year to earlier work at CNP and therefore allows a n assessment of temporal variation in foraging behaviour of Coryphaenoides yaquinae, the only grenadier species recorded from this area (Wilson & Waples 1983). Methods. First fish arrival times and the change in fish numbers around a standard mackerel bait were recorded using the free-fall vehicle (FVV) described by Priede et al. (1990). Photographic data were collected during deployments of the FVV between 30 March and 23 April 1989. Either 2 or 3 baited acoustic transmitters were included on each of 8 of these deployments; range and altitude of fish that swallowed these transmitters were also recorded on the FVV. The acoustic recording system utilised in this study had a maximum range of over 1000 m, substantially greater than that in the earlier study. Current speed was measured on a separate mooring using a current meter (S10 Model 6 with Savonius rotor and directional vane) suspended at 2 to 3 m above the seabed. Results. The delay between FVV landing and arrival of the first fish seen swimming against the current ranged from 9 to 54 min with a mean of 31.0 min (n = 10, SD = 11.28). On 2 occasions fish that apparently did not detect the food were seen swimming across and down-current; these were excluded from the analysis since they were apparently not responding to the odour plume from the bait (Wilson & Smith 1984). Mean maximum numbers of fish within camera view increased steadily to a peak of 5 fish at ca 90 rnin after landing (Fig. l ) . Thereafter the numbers gradually declined to a mean of less than 1 fish at 12 h from landing. The equation of Priede et al. (1990) was fitted to the data to give estimates of the initial arrival rate of fish (%, min-l), mean fish staying time (p , min) and a 196 Mar. Ecol. Prog. Ser. 76: 195-199, 1991 Fig. l . Coryphaenoides (Nematonurus) yaquinae. Video observations of mean (+ SE) number of grenadier fish within camera view, an area of ca 2 m2 of seafloor, in relation to time after landing from deployments at Stn CNP. Means are given for the maximum number of fish observed in each Yz or l h period, depending on sampling frequency Rangc (m) 0 0 0 0 8 8 8 o c u + a m ~

Foraging behavior of abyssal grenadier fish: inferences from acoustic tagging and tracking in the North Pacific Ocean

Abyssal grenadier fish Coryphaenoides yaquinae were Coryphaenoides armatus and observed arriving at baits deployed within view of a free-fall video vehicle (FVV) camera on the sea floor at two stations in the North Pacific, Sta. F 32°50′N, 124°W, 4400 m deep in the vicinity of the California current and Sta. CNP 31°N, 159°W, a 5900 m deep oligotrophic station. Included within each bait deployment were one or two ingestible acoustic transmitters. A total of 23 fish at Sta. F and 13 fish at Sta. CNP ingested transmitters and were tracked using an acoustic tracking system (ATEX). The number of fish within view of the camera increased to a mean maximum of 4.7 at 60 min at Sta. F and 11.8 by 400 min at Sta. CNP, a paradox in view of presumed lower fish population density at Sta. CNP. Fish that ingested transmitters moved away at radial velocities between 1 and 15 cm s −1, reaching a mean radius of 233 m by 370 min at Sta. F and 622 min at Sta. CNP. Fish appear to be active foragers with no evidence for a “sit and wait” foraging strategy. Grenadiers generally remained near the sea floor as they dispersed. Only one vertical movement to an altitude of ca 25 m was recorded and this comprised less than 0.2% of tracking time. The number of fish present at the bait was found to correspond to the following relationship: N t = α 0 x (1 − c −xf) t ⩽ β α 0 x c −xt(c βx − 1) t > β where N t is number of fish present at time t min after bait reaches the sea floor, α 0 is initial arrival rate of fish, β is mean fish staying time and x is the bait decay constant. In accordance with optimal foraging theory staying time (β) is longer at Sta. CNP.

Acoustic detection and tracking of abyssopelagic animals: description of an autonomous split-beam acoustic array

Importance of pelagic animals in transport of organic matter at abyssal depths has been suggested based on vertical distribution and gut content analysis. We developed an autonomous acoustic instrument to detect individual pelagic animals, measure their target strength, and track their movements across specific depth boundaries in the deep sea. This instrument consists of a split-beam line array with a beam pattern narrow in the vertical and omnidirectional in the horizontal. Animals (acoustic targets) ⩾2 cm in length can be detected in an insonified radius of 100 m around the array with a position resolution of ca 42 cm. The velocity of a target animal can be resolved using a closely spaced ping sequence. The line array is deployed as a bottom-moored free vehicle with controller electronics, preamplifier, and a battery source for deployments up to several weeks at depths to 6 km. A deployment in the central North Pacific at 100 m altitude above the bottom (5762 m total depth) for 25 h recorded four targets moving through the acoustic field. Estimated size of the targets, based on initial target strength analyses, suggests that two are crustaceans and one is a grenadier fish. The fourth target is indicative of an animal larger than any we have observed in video camera deployments or caugh with baited traps and hooks at this station. Our initial measurements show that abyssopelagic fauna can be detected and their target strengths and movements measured with the acoustic array.

Behaviour of the abyssal grenadier, Coryphaenoides yaquinae, monitored using ingestible acoustic transmitters in the Pacific Ocean

Scavenging grenadier fishes, Coryphaenoides yaquinae, were tracked with ingestible acoustic tags at 5800 m depth in the central North Pacific. A free‐fall vehicle comprising a video camera and recording system together with a hydrophone, ultrasonic acoustic receiver and recorder was deployed on the sea bed. Special acoustic transmitters (75 kHz) were wrapped in bait and attached below and in view of the camera. Grenadiers were observed to ingest the baited transmitters and move away to ranges of over 100 m within 5h, some returning several times to within range of the receiving system. Voluntary ingestion of transmitters by this grenadier demonstrates that an inacessible population can be studied and provides a basis for development of automated tracking systems for long‐term monitoring of individual deep‐sea fish.