Michael J. Miller

The University of Tokyo (retired)

The spawning areas of the Atlantic freshwater eels were discovered about a century ago by the Danish scientist Johannes Schmidt who after years of searching found newly hatched larvae of the European eel, Anguilla anguilla, and the American eel, Anguilla rostrata, in the southern Sargasso Sea. The discovery showed that anguillid eels migrate thousa...

What eel larvae feed on in the surface layer of the ocean has remained mysterious. Gut contents and bulk nitrogen stable isotope studies suggested that these unusual larvae, called leptocephali, feed at a low level in the oceanic food web, whereas other types of evidence have suggested that small zooplankton are eaten. In this study, we determined...

The spawning area of the common Japanese conger, Conger myriaster, had remained unknown because spawning adults or its newly hatched larvae were never collected. Using genetic identification, we determined that C. myriaster spawns far offshore in the western North Pacific, just west of the spawning area of the Japanese eel, Anguilla japonica. In Ju...

The natural reproductive ecology of freshwater eels remained a mystery even after some of their offshore spawning areas were discovered approximately 100 years ago. In this study, we investigate the spawning ecology of freshwater eels for the first time using collections of eggs, larvae and spawning-condition adults of two species in their shared s...

Of more than 800 species of eels of the order Anguilliformes, only freshwater eels (genus Anguilla with 16 species plus three subspecies) spend most of their lives in freshwater during their catadromous life cycle. Nevertheless, because their spawning areas are located offshore in the open ocean, they migrate back to their specific breeding places...

Anguilla marmorata, A. megastoma, and A. obscura live in the freshwater habitats of tropical islands spread across the western half of the South Pacific from New Caledonia to French Polynesia, but little is known about their early life histories or spawning areas in the eastern region. Otolith microstructure examinations of 455 glass eels from Moor...

The diverse freshwater fish fauna of the Japanese archipelago is distributed among four main island landmasses, which include Hokkaido in the north, with many diadromous species. One relatively well-preserved river drainage along the southern coast of Central Hokkaido is the Mukawa River. Fish fauna surveys in the Mukawa River were mostly in downst...

To understand the larval distribution, size variation, and stable isotope ratios of Japanese eel leptocephali in relation to the salinity front and their feeding ecology, larvae from 7 research cruises (2002–2013) in the North Equatorial Current (NEC) spawning area were examined. The smallest early‐stage larvae were distributed south of or near the...

Where anguillid eels go to reproduce was historically considered to be one of the major biological mysteries of these species, and when Johannes Schmidt discovered the large overlapping Sargasso Sea spawning areas of the Atlantic eels of the genus Anguilla, it became a famous revelation about fish migration. This was followed by Katsumi Tsukamoto’s...

Context Conger eels in temperate regions migrate offshore to reproduce in similar ways as anguillid eels do, but little is known about Conger life histories in the western South Pacific (WSP). Aims To show the larval distribution and size, species composition, and early life history of WSP conger eels. Methods Morphological and genetic species iden...

H.G. Moser was not particularly well known regarding the Elopomorpha, but he began his seminal 1981 fish larvae morphology review by describing the mysteries of European eels and their leptocephali, and he eventually described some California Current leptocephali. Descriptions of all types of leptocephali and then microscope photographs have reveal...

We review ichthyoplankton research history in Indonesia, which began when H.C. Delsman conducted studies on fish larvae and eggs in the northern Java region (1921–1938). The Danish 1929 eel expedition net sampling in Indonesian waters discovered an Anguilla bicolor bicolor spawning area off West Sumatra by collecting small leptocephali. After > 45...

Northern hemisphere anguillid eel populations declined after continental habitat losses and ocean-atmosphere regime shifts occurred, but the exact causes of declines or recruitment fluctuations remain uncertain. Recruitment variations have been hypothesized to result from variable early larval survival, which could be related to phytoplankton bloom...

Parentage sibship‐inference analyses were conducted using mtDNA sequencing and six microsatellite genotypes of 182 Japanese eel preleptocephali that were collected from one net‐tow near the West Mariana Ridge in May 2014. At least 328 parents were involved in producing the 182 preleptocephali, and several parents may have spawned a few times during...

Although juvenile anguillid eels live in freshwater/estuarine habitats, and marine eels live in diverse ocean environments ranging from shallow-to-deep continental shelf areas and around islands to deep-benthic habitats and deeper meso- and bathy- pelagic zones, the larvae (leptocephali) of all species mix together in the ocean surface layer. All t...

Facultative catadromous eels migrate back to the sea to reproduce, but their spawning behavior and locations have remained elusive. Using environmental DNA (eDNA), we identified a likely spawning site location and time of spawning of the Japanese eel. We detected Japanese eel eDNA at 400 and 600 m and recorded a likely sighting of this species at a...

We evaluated whether a strict fisheries management measure of closure of fishing for recruiting juveniles (glass eels) could have resulted in the recovery of a local population of Japanese eels, Anguilla japonica, when there was no harmonized management of the other life stages, the relevant ecosystem, or local socioeconomic factors (i.e., Ecosyste...

South African coelacanths, Latimeria chalumnae, were intensively studied using submersibles in the Comoros Islands before recent progress in deep-diving techniques led to the discovery of coelacanths living at shallower depths off Sodwana Bay, South Africa, which were then studied by divers in close encounters or from underwater vehicles. However,...

Pop-up satellite archival tags (PSAT) have been used to study the mysterious open ocean spawning migrations of several anguillid eel species including the Japanese eel, Anguilla japonica. To compare migration behaviors of Japanese eels in each general geographic region of their spawning migration, 7 silver eels (852–992 cm, 1095–1809 g) were tracke...

It is unknown how many spawning areas exist for tropical South Pacific eels ( Anguilla marmorata , A. megastoma , A. obscura ) populating island archipelagos between Papua New Guinea and French Polynesia. They could spawn at single centralised eastern and western locations, implying long-distance migrations by some eels, or at several local spawnin...

The Indonesian Seas are at the center of the Coral Triangle, which has the highest marine biodiversity in the world, and the region is under threat from climate change. Freshwater habitats in the region have a high number of anguillid eels compared to other regions of the world, but it is more difficult to capture marine eels to assess their biodiv...

Anguillid eels are found globally in fresh, transitional and saline waters and have played an important role in human life for centuries. The population status of several species is now of significant concern. The threats to populations include direct exploitation at different life stages, blockages to migratory routes by dams and other structures,...

The spawning area of the Japanese eel is located at the southern part of the West Mariana Ridge in the western North Pacific, but their spawning events have not been observed. To further understand Japanese eel spawning ecology, an interdisciplinary research survey by the R/V NATSUSHIMA (NT14-09, 14 May–4 June 2014) was conducted to detect spawning...

The diets of larval (leptocephali) anguillid and marine eels are poorly understood, despite studies on their gut contents or stable isotope ratios suggesting marine snow particles represent a food source. Concerns for Japanese eel Anguilla japonica stock conservation necessitate an improved knowledge of their larval ecology to better understand the...

Small-sized eels of the Tropical Conger, Ariosoma scheelei, appear to be common in shallow Indo-Pacific tropical sheltered-bay and lagoon-type habitats when they are sampled appropriately and their larvae are abundant offshore of these areas, but little is known about their biology. Collections of about 7800 likely A. scheelei larvae in May 1997 us...

Leptocephalus larvae have transparent bodies with tubular intestines that usually lack identifiable food items when they are collected, so mystery has surrounded efforts to determine what they feed on. Artificially spawned and reared first-feeding larvae were found to be highly selective in what they would eat, but they would consume rotifers and e...

Leptocephali are the unique larvae of eels and their relatives of the teleost superorder Elopomorpha that have remained poorly understood despite their ubiquitous presence at tropical to temperate latitudes. This review examines recent advancements in understanding the behavioral ecology and distribution of leptocephali. Their regional distribution...

The mysterious food source of anguilliform leptocephali has been difficult to understand, so this review evaluates potential interrelationships among recent discoveries on this subject. There are typically few identifiable gut-content objects in leptocephalus intestines, which usually contain amorphous materials. Gut content observation studies and...

The ecology of leptocephali remains poorly known but they appear to feed on marine snow that can vary spatially and temporally according to the food web dynamics. This study provided new information about the position of leptocephali within the functional structure of microbial plankton and other food web components of the western South Pacific (WS...

A wintertime net sampling and hydrographic survey was conducted in the Kuroshio Extension (KE) and northern subtropical gyre during 3 cruise-legs in January–March 2006. Conductivity-Temperature-Depth (CTD), expendable CTD (XCTD) and expendable bathythermograph (XBT) surveys were conducted to examine the regional hydrographic structure, which includ...

Seven South Pacific anguillid eel species live from New Guinea to French Polynesia, but their spawning areas and life histories are mostly unknown despite previous sampling surveys. A July–October 2016 research cruise was conducted to study the spawning areas and times, and larval distributions of South Pacific anguillid eels, which included a shor...

Leptocephali of the shallow-water congrid eel Ariosoma balearicum are abundant during February–April in the Sargasso Sea, and larval and adult meristic data indicates this species includes several regional subpopulations/cryptic species. Four multiple-transect larval surveys (2011, 2014, 2015, 2017) were used to examine the geographic size distribu...

Japanese eel (Anguilla japonica) recruitment to Japan was very low during the early 2017−2018 recruitment season when most glass eels are usually caught, but catches increased in the late recruitment season when recruitment usually decreases. Concurrently, the Kuroshio meander south of Japan had formed again after the previous event ended in 2005....

Gelatinous zooplankton (GZ) such as medusae, ctenophores, siphonophores, pyrosomes and salps are important components of oceanic pelagic communities and small calycophoran siphonophores (CS) are typically abundant at shallow depths. The Sargasso Sea spawning area of the Atlantic catadromous freshwater eels has a regular pattern of shallow autumn to...

The oceanic spawning migration of female Anguilla dieffenbachii eels was previously studied using pop-up satellite transmitting tags (PSAT). The swimming depths and experienced-temperature data of 3 eels released in May 2006 were re-examined in relation to water temperature data, and also lunar cycle and regional hydrography as these latter aspects...

To assist in detection of offshore spawning activities of the Japanese eel Anguilla japonica and facilitate interpretation of results of environmental DNA (eDNA) analysis in their spawning area, we examined the eDNA concentration released by each life history stage of artificially reared Japanese eels in the laboratory using quantitative real-time...

It has been known for about a century that European eels have a unique life history that includes offshore spawning in the Sargasso Sea about 5000–7000 km away from their juvenile and adult habitats in Europe and northern Africa. Recently hatched eel larvae were historically collected during Danish, German and American surveys in specific areas in...

The head morphology and body shapes of anguilliform larvae (leptocephali) vary widely by having fewer, much longer teeth in the small larvae and more numerous, but relatively smaller teeth in larger developmental stages. The feeding ecology of leptocephali has been difficult to understand because they do not appear to feed on typical zooplankton li...

The possible effect of directional larval swimming on the recruitment success of the Japanese eel, Anguilla japonica, was examined with a three-dimensional particle-tracking ocean circulation model using horizontal northwestward swimming and diel vertical migration (DVM). Four separate experiments included virtual larvae (v-larvae) movement from th...

Deep-sea midwater “saccopharyngiform” eels of the families Cyematidae, Monognathidae, Eurypharyngidae and Saccopharyngidae (order Anguilliformes) are extraordinary fishes having major skeletal reductions and modifications compared to the general anguilliform body structure. Little is known about most aspects of the systematics, phylogeny, and ecolo...

2018) Sulawesi Island of north-central Indonesia is located in a region where at least 6 species of tropical anguillid eels are present, but the reproductive ecology and biodiversity of these eels in each area of the Indonesian archipelago remains poorly understood. Some information about these species was obtained from collections of their leptoce...

Many diadromous fishes such as salmon and eels that move between freshwater and the ocean have evolved semelparous reproductive strategies, but both groups display considerable plasticity in characteristics. Factors such as population density and growth, predation risk or reproduction cost have been found to influence timing of maturation. We inves...

Japanese eels Anguilla japonica were tagged in order to understand their behavior in their spawning area. Three silver eels (EEL-A, B, C: TL792, 898, 992 mm) were tagged with pop-up satellite archival transmitting tags (PSATs) and released at different locations near/in their spawning area along the southern part of the West Mariana Ridge. EEL-A sh...

Eel larvae (leptocephali) are rarely studied extensively both spatially and temporally, and detailed illustrations of most species are limited. This study uses the unique research reported in the monograph of Blache (Leptocéphales des poissons anguilliformes dans la zone sud du golfe de Guinée. ORSTOM Faune Tropicale 10:1–381, 1977, in French) to d...

The abundance and distribution of leptocephalus larvae of the European eel (Anguilla anguilla, Anguillidae) were examined using ten historic and recent Sargasso Sea expeditions that were selected on the basis of having the largest number of sampling stations and highest catches. The surveys cover the period 1920–2014. Station data were recalculated...

The circumglobal deep-sea gelatinous giant octopod, Haliphron atlanticus , reaches 4 m in length and uses both benthic and pelagic habitats in the upper 3000 m of the ocean during different life history stages, but it is rarely observed due to the deep-depths where it typically lives. It has been collected in trawls and observed a few times near co...

Recruitment of Japanese eels, Anguilla japonica, has declined in recent decades possibly due to both anthropogenic and ocean-atmosphere factors. The potential impact of ocean circulation on the decreasing Japanese eel catches in the western North Pacific was examined based on a three-dimensional particle-tracking method, in which virtual larvae (v-...

The unique semi-enclosed Indian Ocean basin includes large Mascarene Plateau banks, offshore coral-reef islands, seasonal equatorial current jets, and cross-basin westward South Equatorial Current (SEC) flow, making it interesting for studying long larval-duration eel larvae (leptocephali) and regional eel biodiversity. Three surveys for leptocepha...

Environmental DNA (eDNA) analysis is emerging as an innovative tool to assess the distribution and biomass of species in aquatic environments that enables quick and non-invasive surveys compared to conventional sampling methods such as fishing, hydroacoustics, and diving observations. We applied eDNA analysis to spawning ecology research of the Jap...

European eels (Anguilla anguilla) migrate between the southwestern Sargasso Sea and the European and Mediterranean coasts. In a recent paper in Current Biology, Naisbett-Jones et al. [1] claim to “provide the first evidence that they [eels] derive positional information from the Earth's magnetic field” and that this information guides their migrati...

The ecology of leptocephali is poorly understood. We investigated their nighttime vertical distributions and assemblage structure in the North Equatorial Current (NEC) region of the western Pacific in October and November 2013. Of the 1372 collected leptocephali of ca. 66 species, the most abundant taxa were Serrivomeridae, Nemichthyidae, Conger, a...

Several surveys and studies have examined the Atlantic anguillid eels’ larval distributions, but little is known about their larval growth rates. Otoliths of 17 European eel Anguilla anguilla (8.8–46.0 mm) and 19 American eel Anguilla rostrata (9.8–59.9 mm) leptocephali collected in the Sargasso Sea (25–31°N, 58–70°W) in March and April 2011 were a...

The distribution of the leptocephalus larvae of European (Anguilla anguilla) and American (Anguilla rostrata) eels collected during recent Sargasso Sea surveys was used to model larval drift. The drift trajectories of individual larva were back-calculated to the estimated time of spawning, using current data from two global oceanographic assimilati...

The timing of downstream migrations of anguillid silver eels in relation to environmental factors in rivers has been examined using various types of data. Less is known about the factors that affect when silver eels leave estuaries and enter the sea or about the onset of the spawning migrations of eels living in brackish-water coastal areas. The ti...

Recruitment declines of anguillid eels are difficult to understand because both anthropogenic impacts on juveniles and adults and oceanic changes affecting larval survival or dispersal may be contributing. Anguillid larvae may passively disperse widely from offshore spawning areas but late-stage larvae or glass eels apparently must swim directional...

The Indonesian Seas in the center of the Coral Triangle have high marine biodiversity, and a unique area is Sulawesi Island that has the large semi-enclosed Tomini Bay, including the Togian Islands, formed within the island. A sampling survey for leptocephali was conducted in March 2010 at 48 stations in the southern Celebes Sea and in Tomini Bay t...

Catadromous anguillid eels (genus Anguilla) migrate from their freshwater or estuarine habitats to marine spawning areas. Evidence from satellite tagging studies indicates that tropical and temperate eel species exhibit pronounced diel vertical migrations, from between 150-300 m nighttime depths to 600-800 m during the day. Collections of eggs and...

Bonefish leptocephali of the genus Albula are difficult to identify to the species level due to morphological similarities between two different species present in the Northeastern Pacific Ocean, A. esuncula and A. gilberti. In this study, 22 bonefish leptocephali (premetamorphic and early metamorphic), collected from two locations in the southern...

When and where marine eels spawn is poorly known even though species such as those of the family Congridae, Muraenidae and Ophichthidae can be caught in continental shelf habitats. The congrid genus Ariosoma includes small continental shelf eel species whose life histories are not yet known. Mature male and female eels of Ariosoma meeki were observ...