scholarly journals Evidence of different habitat use by New Zealand freshwater eels Anguilla australis and A. dieffenbachii, as revealed by otolith microchemistry

2004 ◽  
Vol 266 ◽  
pp. 213-225 ◽  
Author(s):  
T Arai ◽  
A Kotake ◽  
PM Lokman ◽  
MJ Miller ◽  
K Tsukamoto
Keyword(s):  
New Zealand ◽  
Habitat Use ◽  
Otolith Microchemistry ◽  
Anguilla Australis ◽  
Freshwater Eels

scholarly journals Aspects of the Biology of Juvenile Freshwater Eels (Anguillidae) in New Zealand

2021 ◽  
Author(s):  
◽  
Donald John Jellyman
Keyword(s):  
New Zealand ◽  
Fresh Water ◽  
Habitat Preferences ◽  
Spring Tide ◽  
Age Groups ◽  
Upstream Migration ◽  
Coastal Lake ◽  
Anguilla Australis ◽  
Glass Eels ◽  
Freshwater Eels

<p>The early freshwater life of the two species of New Zealand freshwater eels, Anguilla australis schmidtii Phillipps and A. dieffenbachii Gray was studied involving an examination of 8131 glass-eels, 5275 migratory elvers, and 4291 resident eels of less than 26 cm. Most eels were collected from the Makara Stream, Wellington by set-net, hand-net and electric fishing. These extensive samples together with subsidiary collections from elsewhere in New Zealand show that glass-eels of both species arrive in fresh-water from July to December. Their otoliths indicate a marine larval life of about 18 months but it is not possible as yet to locate the precise oceanic spawning areas. Migratory movements of glass-eels are in two phases: an invasion of fresh-water from the sea and an upstream migration. The former occurs only at night with a periodicity corresponding to the daily ebb-flood tidal rhythms. There is a seasonal reversal in this response which is attributable to the onset of the behavioural transition taking place prior to the second migratory phase. Increased pigmentation and changes in response to light, flowing fresh-water and schooling tendencies characterise this latter migration which occurs primarily at spring tide periods. Such juvenile eels show specific habitat preferences and a high degree of olfactory differentiation of water types. This behaviour, together with pigment development and physical tolerances, was studied in the laboratory. Measurements of invading glass-eels show that mean length, weight and condition all decline throughout the season of arrival but mean vertebral numbers remain constant. An upstream migration of small eels (elvers) occurs each summer and is readily observed at many hydro-electric stations. These migrations, comprising eels of mixed sizes and age groups, penetrate progressively further upstream each year. In both species, scales begin formation at body lengths of 16.5-20 cm. All features of scale formation, including the number of scale rings, are related to length with relative differences in rate of development occurring between the species. In contrast to scale rings, otolith rings are annual in formation and become visible after grinding or burning the otolith. Growth rates established for 273 eels to 29 cm in length from the Makara Stream, Wellington, are slow, with mean annual increments of 2.2 and 2.1 cm respectively for shortfins and longfins. In contrast, shortfins from a coastal lake near Wellington reach 26 cm in their third year of freshwater life. Length-weight relationships for small eels are given together with mean monthly condition factors. Growth studies on elvers held in a multiple tank unit in which temperature, density, and amount and frequency of feeding could be controlled, show that young eels grow more slowly than normal under such conditions. However, growth appears optimum at 20 degrees C with a feeding rate of 5-7% body weight per day. Feeding efficiency decreases with higher temperatures. At both glass-eel and elver stages, shortfins adapt and survive better under artificial conditions.</p>

scholarly journals Aspects of the Biology of Juvenile Freshwater Eels (Anguillidae) in New Zealand

2021 ◽  
Author(s):  
◽  
Donald John Jellyman
Keyword(s):  
New Zealand ◽  
Fresh Water ◽  
Habitat Preferences ◽  
Spring Tide ◽  
Age Groups ◽  
Upstream Migration ◽  
Coastal Lake ◽  
Anguilla Australis ◽  
Glass Eels ◽  
Freshwater Eels

<p>The early freshwater life of the two species of New Zealand freshwater eels, Anguilla australis schmidtii Phillipps and A. dieffenbachii Gray was studied involving an examination of 8131 glass-eels, 5275 migratory elvers, and 4291 resident eels of less than 26 cm. Most eels were collected from the Makara Stream, Wellington by set-net, hand-net and electric fishing. These extensive samples together with subsidiary collections from elsewhere in New Zealand show that glass-eels of both species arrive in fresh-water from July to December. Their otoliths indicate a marine larval life of about 18 months but it is not possible as yet to locate the precise oceanic spawning areas. Migratory movements of glass-eels are in two phases: an invasion of fresh-water from the sea and an upstream migration. The former occurs only at night with a periodicity corresponding to the daily ebb-flood tidal rhythms. There is a seasonal reversal in this response which is attributable to the onset of the behavioural transition taking place prior to the second migratory phase. Increased pigmentation and changes in response to light, flowing fresh-water and schooling tendencies characterise this latter migration which occurs primarily at spring tide periods. Such juvenile eels show specific habitat preferences and a high degree of olfactory differentiation of water types. This behaviour, together with pigment development and physical tolerances, was studied in the laboratory. Measurements of invading glass-eels show that mean length, weight and condition all decline throughout the season of arrival but mean vertebral numbers remain constant. An upstream migration of small eels (elvers) occurs each summer and is readily observed at many hydro-electric stations. These migrations, comprising eels of mixed sizes and age groups, penetrate progressively further upstream each year. In both species, scales begin formation at body lengths of 16.5-20 cm. All features of scale formation, including the number of scale rings, are related to length with relative differences in rate of development occurring between the species. In contrast to scale rings, otolith rings are annual in formation and become visible after grinding or burning the otolith. Growth rates established for 273 eels to 29 cm in length from the Makara Stream, Wellington, are slow, with mean annual increments of 2.2 and 2.1 cm respectively for shortfins and longfins. In contrast, shortfins from a coastal lake near Wellington reach 26 cm in their third year of freshwater life. Length-weight relationships for small eels are given together with mean monthly condition factors. Growth studies on elvers held in a multiple tank unit in which temperature, density, and amount and frequency of feeding could be controlled, show that young eels grow more slowly than normal under such conditions. However, growth appears optimum at 20 degrees C with a feeding rate of 5-7% body weight per day. Feeding efficiency decreases with higher temperatures. At both glass-eel and elver stages, shortfins adapt and survive better under artificial conditions.</p>

Is the subspecies classification of the freshwater eels Anguilla australis australis Richardson and A. a. schmidtii Phillipps still valid?

1999 ◽  
Vol 50 (3) ◽  
pp. 261 ◽  
Author(s):  
L. H. Dijkstra ◽  
D. J. Jellyman
Keyword(s):  
Mitochondrial Dna ◽  
New Zealand ◽  
Fisheries Management ◽  
Gene Pool ◽  
Molecular Evidence ◽  
Analysis Of Molecular Variance ◽  
Molecular Variance ◽  
Anguilla Australis ◽  
Freshwater Eels

The validity of the subspecies classification of Anguilla australis was reviewed by sequencing the control region of mitochondrial DNA. Samples of A. a. australis (Australia) and A. a. schmidtii (New Zealand), collected from two sites within each country were compared by analysis of molecular variance (AMOVA) and neighbour joining. There was no molecular evidence to support the present subspecies designation and they would be more appropriately merged into the single classification of A. australis, the Australasian shortfinned eel. As Australian and New Zealand populations of this species share a common gene pool, fisheries management needs to be carried out cooperatively between the two countries.

scholarly journals Studies on the Reproductive Biology of New Zealand Freshwater Eels

2021 ◽  
Author(s):  
◽  
Peter Robin Todd
Keyword(s):  
New Zealand ◽  
Lunar Cycle ◽  
Immature Stage ◽  
Anguilla Australis ◽  
Stage Of Development ◽  
Spawning Areas ◽  
Growth Zones ◽  
Parallel Features ◽  
Pass Through ◽  
Freshwater Eels

<p>Macroscopic and histological observations of the gonads from 1,739 non-migrant freshwater eels, the shortfin Anguilla australis schmidtii Phillipps and the longfin A. dieffenbachii Gray, showed that they pass through seven stages of development. Shortfins become sexually differentiated at body lengths of 35.0cm to 56.9cm and longfins at lengths of 50.0cm to 67.0cm. No intersexual stage was present, as in A. anguilla L., and although 1% of 350 migrating longfin males examined contained ribbon-like testes, the typical lobed organ of Syrski (testis) can be used as diagnostic of maleness. Histologically, the maximum stage of development attained in the non-migrant, immature stage, was spermatogonia in the males and vacuolated oocytes in females. At the time of seaward migration, based on gonad histology, gonadosomatic indices and ova diameters, migrating longfins were more sexually developed than shortfins. These differences may relate to the location of different oceanic spawning areas: that for the longfin possibly being closer to New Zealand. The autumnal migratory runs, from March to May, of the sexually maturing adults in the Makara stream showed no particular species or sex sequence. The movement of eels was coincident with a rise in stream level and the second half of the lunar cycle. Other relevant environmental factors are discussed. In Lake 0noke peak catches of seaward migrating shortfins were made before the longfins and movements of eels occurred throughout the lunar cycle. Once at sea, the eels apparently disappear. A published note is included on the first eel of the New Zealand species, a longfin female, to be caught at sea. Age determinations from 995 eels were made by otoliths, which were burnt lightly to intensify the growth zones for reading purposes. Shortfin males are younger than females at migration. Longfins are older than shortfins at migration but the males are younger than the females. In the non-migrant stage, sexually undifferentiated shortfins grow more slowly relative to the males, and males relatively more slowly than the females. Similar but less significant differences in growth occur in longfins. Migrant males held in seawater were induced to mature and spawn with injections of mammalian hormones or carp pituitaries, over temperatures of 11.8 degrees C to 28 degrees C. The maturation period was dependent on temperature. Testes of experimental eels that survived maturation regressed to the pre-migrant or migrant stage. Two eels that had regressed were induced to mature a second time. Females held at 20 degrees C and injected with mammalian hormones showed significant increases in sexual development but died before maturity. Females injected with carp pituitaries matured and spawned. Mature longfin eggs, 0.9mm to 1.2mm in diametar, and mature shortfin eggs, 0.9mm to 1.2mm in diameter, are translucent and contain one to many oil globules. A blastodisc formed in water hardened eggs but attempts at fertilization were unsuccessful. Gametogenesis, observed from non-migrant, migrant and hormone injected eels is similar to that described for other teleosts. Electron microscope observations showed parallel features of spermiogenesis in both species. Mature spermatozoa have crescent shaped heads with an anteriorly placed mitochondrion. A flagellum of the unusual 9 + 0 pattern arises from the posterior region of the head, and a short, striated rod-like structure is positioned adjacent to the main flagellum. A complex of subfibrils which extend along either side of the head to the mitochondrion arise from the proximal centriole.</p>

scholarly journals Studies on the Reproductive Biology of New Zealand Freshwater Eels

2021 ◽  
Author(s):  
◽  
Peter Robin Todd
Keyword(s):  
New Zealand ◽  
Lunar Cycle ◽  
Immature Stage ◽  
Anguilla Australis ◽  
Stage Of Development ◽  
Spawning Areas ◽  
Growth Zones ◽  
Parallel Features ◽  
Pass Through ◽  
Freshwater Eels

<p>Macroscopic and histological observations of the gonads from 1,739 non-migrant freshwater eels, the shortfin Anguilla australis schmidtii Phillipps and the longfin A. dieffenbachii Gray, showed that they pass through seven stages of development. Shortfins become sexually differentiated at body lengths of 35.0cm to 56.9cm and longfins at lengths of 50.0cm to 67.0cm. No intersexual stage was present, as in A. anguilla L., and although 1% of 350 migrating longfin males examined contained ribbon-like testes, the typical lobed organ of Syrski (testis) can be used as diagnostic of maleness. Histologically, the maximum stage of development attained in the non-migrant, immature stage, was spermatogonia in the males and vacuolated oocytes in females. At the time of seaward migration, based on gonad histology, gonadosomatic indices and ova diameters, migrating longfins were more sexually developed than shortfins. These differences may relate to the location of different oceanic spawning areas: that for the longfin possibly being closer to New Zealand. The autumnal migratory runs, from March to May, of the sexually maturing adults in the Makara stream showed no particular species or sex sequence. The movement of eels was coincident with a rise in stream level and the second half of the lunar cycle. Other relevant environmental factors are discussed. In Lake 0noke peak catches of seaward migrating shortfins were made before the longfins and movements of eels occurred throughout the lunar cycle. Once at sea, the eels apparently disappear. A published note is included on the first eel of the New Zealand species, a longfin female, to be caught at sea. Age determinations from 995 eels were made by otoliths, which were burnt lightly to intensify the growth zones for reading purposes. Shortfin males are younger than females at migration. Longfins are older than shortfins at migration but the males are younger than the females. In the non-migrant stage, sexually undifferentiated shortfins grow more slowly relative to the males, and males relatively more slowly than the females. Similar but less significant differences in growth occur in longfins. Migrant males held in seawater were induced to mature and spawn with injections of mammalian hormones or carp pituitaries, over temperatures of 11.8 degrees C to 28 degrees C. The maturation period was dependent on temperature. Testes of experimental eels that survived maturation regressed to the pre-migrant or migrant stage. Two eels that had regressed were induced to mature a second time. Females held at 20 degrees C and injected with mammalian hormones showed significant increases in sexual development but died before maturity. Females injected with carp pituitaries matured and spawned. Mature longfin eggs, 0.9mm to 1.2mm in diametar, and mature shortfin eggs, 0.9mm to 1.2mm in diameter, are translucent and contain one to many oil globules. A blastodisc formed in water hardened eggs but attempts at fertilization were unsuccessful. Gametogenesis, observed from non-migrant, migrant and hormone injected eels is similar to that described for other teleosts. Electron microscope observations showed parallel features of spermiogenesis in both species. Mature spermatozoa have crescent shaped heads with an anteriorly placed mitochondrion. A flagellum of the unusual 9 + 0 pattern arises from the posterior region of the head, and a short, striated rod-like structure is positioned adjacent to the main flagellum. A complex of subfibrils which extend along either side of the head to the mitochondrion arise from the proximal centriole.</p>

Eels at the Edge: Science, Status, and Conservation Concerns

2009 ◽  
Keyword(s):  
New Zealand ◽  
Management System ◽  
Stock Assessment ◽  
Catch Per Unit Effort ◽  
Commercial Catch ◽  
The North ◽  
Anguilla Australis ◽  
Unit Effort ◽  
Access Rights ◽  
Quota Management

<em>Abstract.</em>—The New Zealand eel fishery comprises two species, the shortfin eel <em>Anguilla australis </em>and the New Zealand longfin eel <em>A. dieffenbachii</em>. A third species, the speckled longfin eel <em>A. reinhardtii</em>, is present in small numbers in some areas. Major fisheries in New Zealand are managed under the Quota Management System. Individual transferable quotas are set as a proportion of an annual total allowable commercial catch. The Quota Management System was introduced into the South Island eel fishery on 1 October 2000 and the North Island fishery on 1 October 2004. Freshwater eels have particular significance for customary Maori. Management policies allow for customary take and the granting of commercial access rights on introduction into the Quota Management System. Eel catches have remained relatively constant since the early 1970s. The average annual catch from 1989–1990 to 2001–2002 (fishing year) was 1,313 mt. Catch per unit effort remained constant from 1983 to 1989 and reduced from 1990 to 1999. Statistically significant declines in catch per unit effort for New Zealand longfin eel were found in some areas over the latter period. For management, an annual stock-assessment process provides an update on stock status.

Diel feeding and prey selection of three size classes of shortfinned eel (Anguilla australis) in New Zealand

1998 ◽  
Vol 49 (5) ◽  
pp. 421 ◽  
Author(s):  
P. M. Sagar ◽  
G. J. Glova
Keyword(s):  
New Zealand ◽  
Prey Selection ◽  
Microhabitat Use ◽  
Night Time ◽  
Fish Prey ◽  
Size Classes ◽  
Anguilla Australis ◽  
Selection Indices ◽  
Feeding Periodicity ◽  
Selection Of

Benthic macroinvertebrates and three size classes of shortfinned eel (Anguilla australis, Anguillidae) were sampled in a lowland New Zealand stream over a 24-h period in summer to investigate diel feeding periodicity and prey selection. Fish of all three size classes fed mostly from post-dusk to dawn, with larger fish tending to consume a greater proportion of their prey during night-time. The number of prey taxa consumed increased with increasing size of fish. Prey selection indices indicated that: (1) the smallest eels (80–100 mm total length, TL) preferentially consumed ostracods (Crustacea) and larvae of Chironomidae (Diptera) and Psilochorema sp. (free-living Trichoptera); (2) medium-sized eels (101–199 mm TL) preferred larvae of Chironomidae, and Costachorema sp., Hydrobiosis sp. and Psilochorema sp.; and (3) large eels (200–300 mm TL) preferred ostracods, Psilochorema sp. and Hudsonema amabilis (cased Trichoptera). Eels of all size classes showed selection for soft-bodied or easily broken prey over those with hard cases which would have been more difficult to digest. There was considerable overlap in the diets of medium and large eels. Differences in the timing of feeding between the three size classes of eel are explained in terms of microhabitat use; differences in diet are explained in terms of prey size, and are also related to eel size.

Preliminary observations of migrating adult freshwater eels (Anguilla australis australis Richardson) in Tasmania

1984 ◽  
Vol 35 (4) ◽  
pp. 471 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Water Temperature ◽  
Significant Positive Correlation ◽  
River Flow ◽  
Downstream Migration ◽  
Single Male ◽  
Male Specimen ◽  
Anguilla Australis ◽  
Daily Water Temperature ◽  
Daily Water ◽  
Freshwater Eels

The downstream migration of maturing adult short-finned eels, A. a. australis, was recorded at an eel trap on the Clyde River during the 1981-1982 season. 5.2 t of eels entered the trap from November to April with 53% of the catch taken during January. Of the 190 eels examined, only a single male specimen was found. Female A. a. australis migrated downstream at a mean length of 94.5 cm, a mean weight of 1700 g and a mean age of 22.1 years (range 18-30 years). There was a significant positive correlation between catch and water temperature, temperatures above 12�C being associated with eel migration. The peak catch occurred during January and coincided with the highest record of mean daily water temperature (20.5�C). The migration did not appear to be influenced by moon phase, and river flow was controlled.

Observations on granulocyte peroxidase in New Zealand freshwater eels, Anguilla species

1986 ◽  
Vol 29 (6) ◽  
pp. 711-720 ◽  
Author(s):  
P. M. Hine ◽  
J. M. Wain ◽  
D. M. Dunlop
Keyword(s):  
New Zealand ◽  
Freshwater Eels
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