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>

Invasion and upstream migration by glass-eels of Anguilla australis australis Richardson and A. reinhardtii Steindachner in Tasmanian Freshwater Streams

1984 ◽  
Vol 35 (1) ◽  
pp. 47 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Fresh Water ◽  
River Flow ◽  
Condition Factor ◽  
Late Summer ◽  
Upstream Migration ◽  
Larval Life ◽  
Freshwater Streams ◽  
Anguilla Australis ◽  
Glass Eels ◽  
High River Flow

The recruitment of glass-eels into fresh water was investigated by hand-netting and electrofishing at the lowest permanent freshwater riffle on several streams in eastern Tasmania. Measurements of the forward extent of the dorsal fin distinguished the short-finned eel, A. a. australis, from the long-finned eel, A. reinhardtii; this separation was verified by vertebral counts and A. a, australis glass-eels were found to be larger than A. reinhardtii. A. a. australis glass-eels were collected at the first riffle during all seasons of the year except mid-summer. Numbers in the catch declined during mid-winter, probably as a result of an effective seaward movement of the freshwater-estuarine interface during periods of high river flow; A. a. australis glass-eels were still found to be abundant near estuary mouths at such times. A. reinhardtii glass-eels exhibited a more restricted movement into fresh water during late summer and autumn with no collections recorded after mid-winter. For both species, the stage of pigmentation was found to advance as the season progressed, and length, weight and condition factor declined with advancing pigmentation. The otoliths of invading glass-eels of both species appeared similar with a single summer ring, suggesting a larval life of 1-1½ years. The restricted invasion period of A. reinhardtii and the similar size throughout the species range suggests a short and precise larval life. The length of larval life of A. a. australis is probably quite variable, resulting in a more substantial and prolonged influx of glass-eels into Tasmanian waters.

Upstream migration by young pigmented freshwater eels (Anguilla australis australis Richardson) in Tasmania

1984 ◽  
Vol 35 (1) ◽  
pp. 61 ◽  
Author(s):  
RD Sloane
Keyword(s):  
Water Temperature ◽  
Fresh Water ◽  
River Flow ◽  
Late Spring ◽  
Day Length ◽  
Upstream Migration ◽  
Single Specimen ◽  
Anguilla Australis ◽  
And Control ◽  
Freshwater Eels

During late spring and summer, upstream migrations by young pigmented freshwater eels (elvers) can be seen at stream barriers in Tasmania. The elver runs at two major hydro-electric dams, Trevallyn and Meadowbank, were sampled regularly during the period 1977-1981 and migrations at a number of smaller stream barriers throughout Tasmania were also investigated. Migrating elvers were found to be short-finned eels, A. a. australis; only a single specimen of the long-finned eel, A. reinhardii Steindachner, was recorded. Elvers sampled at inland stream barriers were both larger and older than those found nearer the sea, indicating that eels migrate farther upstream for several years in succession. Eels involved in upstream migration were found to be shorter than 25 cm, having spent up to 10 years in fresh water. Day length, water temperature and river flow may all contribute to the initiation and control of elver migrations. The numbers of elvers involved in annual migrations at major hydro- electric dams in Tasmania are substantial: the largest migration occurs at Trevallyn, where between 3 × 106 and 5 × 106 elvers take part each year. These elvers represent a considerable stocking poterltial and could be used to expand the local wild-eel fishery.

The life cycle of Stegodexamene anguillae n.g., n.sp., an allocreadiid trematode from New Zealand

Parasitology ◽  
1951 ◽  
Vol 41 (1-2) ◽  
pp. 1-10 ◽  
Author(s):  
W. V. Macfarlane
Keyword(s):  
Life Cycle ◽  
New Zealand ◽  
Calcium Carbonate ◽  
Fresh Water ◽  
New Genus ◽  
Anguilla Dieffenbachii ◽  
Freshwater Eels

1. A new genus of trematode (family Allocre-adiidae) from the intestine of freshwater eels is described, and named Stegodexamene anguillae.2. The genus is related to Aephnidiogenes, Lepidapedon and Neophasis, but differs significantly from each of them.3. The life cycle followed is from the adult in Anguilla dieffenbachii to the redia in Potamopyrgus antipodum (fresh-water gastropod). The cercaria encysts in the eloetrid fish Gobiomorphus gobioides.4. Progenetic production of eggs and spermatozoa occurs in the metacercariae.5. Metacercarial excretory spherules are composed of calcium carbonate.

scholarly journals Status of New Zealand fresh-water eel stocks and management initiatives

2007 ◽  
Vol 64 (7) ◽  
pp. 1379-1386 ◽  
Author(s):  
Don J. Jellyman
Keyword(s):  
New Zealand ◽  
Fresh Water ◽  
Management Strategies ◽  
Wetland Loss ◽  
Commercial Catch ◽  
Anguilla Australis ◽  
Generation Times ◽  
The Status ◽  
Quota Management ◽  
Average Size

Abstract Jellyman, D. J. 2007. Status of New Zealand fresh-water eel stocks and management initiatives. – ICES Journal of Marine Science, 64: 1379–1386. New Zealand has two main species of fresh-water eel, shortfin (Anguilla australis), which is shared with Southeast Australia, and the endemic longfin eel (A. dieffenbachii). Both species are subject to extensive commercial and customary fishing. The shortfin is the smaller and shorter lived, with typical generation times for females ranging from 15 to 30 years; generation times for longfin females are double this. The distribution and the abundance of both species have been compromised by habitat modifications, shortfins, the more lowland species, being affected by wetland loss, and longfins by weirs and dams. Although there are few concerns about the status of shortfins, there is increasing evidence of overexploitation of longfins, including reduced recruitment, reduction in catch rates, reduction in abundance and average size, and a regional reduction in the proportion of females. Eels are managed under the quota management system, although individual and regional quotas are set from catch histories because biological parameters are inadequate. Maori, New Zealand's indigenous people, have been allocated 20% of commercial quota, with additional quota set for customary take. The annual commercial catch of eels has halved over the past decade, and is now ∼700–800 t, shortfins comprising 66% of catches. Recent management developments have included enhancement of upstream waters with juvenile eels, consolidation of processing into fewer but larger units, setting aside of additional reserve areas to increase escapement of silver eels, increased management involvement of Maori, and development of regional management strategies.

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.

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