Selected Abstracts

[Previous Page] [Up] [Home Page] [Contents]

Selected Abstracts


The Fish of Lake Ellesmere, Canterbury by P.A. Ryan

The fishes of Lake Ellesmere, a large brackish water lake in Canterbury, New Zealand, are listed and notes on the abundance and breeding status of each species are given. One previously unrecorded resident, the carp, Carassius sp. is noted.


A checklist of the brackish and freshwater fish of Fiji by P.A. Ryan

A list of the brackish and freshwater fish species known to occur in Fiji is given together with information on species which are likely to be present but thus far not reported. Where a species has been coillected by the author this information is given also with an indication of its abundance.


Namalycastis vuwaensis n.sp. (Polychaeta: Nereidae) from the Nadrau Plateau, Fiji by P.A. Ryan

This new species of subfamily Namanereinae is probably most closely related to N. tiritae Winterbourn from the North Island of New Zealand, differing from it only in size, some parapodial characters, and the arrangement of peristomial cirri. N. vuwaensis was found in patches of sand and gravel in fairly still water in the lee of large stones in a fast-flowing reach of a montane stream. The presence of identifiable chaetae in faeces suggests that oligochaetes may be its main food.


Energy contents of some New Zealand freshwater animals by P.A. Ryan

Energy contents of several freshwater animal species collected from Lake Ellesmere, Canterbury, were determined by bomb calorimetry. Values are shown to vary seasonally and between size classes. Because of this variability the use of a single energy value of an organsm in an energetics study is not recommended.


Diel and seasonal feeding activity of the short-finned eel, Anguilla australis schmidtii, in Lake Ellesmere, Canterbury, New Zealand by Patrick Ryan

Eel samples from Lake Ellesmere, a brackish water lake in the South Island, New Zealand, were taken at approximately monthly intervals from January 1974 to April 1976. Nets were set for 24 h and emptied every three hours. Total lengths and stomach fullness values of 498 eels were recorded. Analysis using the non-parametric Kruskal-Wallis test showed that eels <40 cm and 40.1—50 cm in length increased in fullness through the night with greatest fullness values at 0300 and 0600 h. Seasonal analyses revealed greatest eel activity in spring, summer and autumn. There was little eel activity in winter.


Seasonal and size-related changes in the food of the short-finned eel, Anguilla australis in Lake Ellesmere, Canterbury, New Zealand by Patrick A. Ryan

An approximately monthly sampling programme in Lake Ellesmere, Canterbury, New Zealand, from January 1974 to April 1976 yielded 487 eels. The stomachs were fixed in l0% neutralised formalin and the contents examined. Preliminary analysis indicated that the mollusc Potamopyrgus antipodarum, the isopod Austroditea annectens, the mysid Tenagomvsis chi1toni, the amphipod Paracalliope fluviatilis, the midge larva Chironomus zealandicus and the teleosts Retropinna retropinna, Galaxias maculatus and Gobiomorphus cotidianus together made up the bulk of the diet. The pre-ingested dry weight (i.e. the reconstructed weight) of the most important of these prey species was obtained by relating the length of a digestion resistant part to actual dry weight in field collected specimens. Regression equations for this relationship in each season enabled the reconstructed dry weight of each stomach item to be calculated. In some instances reconstructed weight was less than the actual digested dry weight of the prey specimen. In every case the larger value was used. This method is referred to as Combination Dry Weight (CDW) and is believed to be new. These data, used in conjunction with the energy content of the species concerned, enabled the caloric dietary contribution of each prey species to be determined. Comparison of relative contribution to eel diet between CDW and energy values calculated from CDW and bomb calorimetry revealed large differences. Marked variations in diet between <40 cm, 40.1—50 cm, and >50.1 cm size classes were also shown. Eels <40 cm feed primarily on invertebrates and become progressively more piscivorous as they grow. Eels >50.1 cm are almost entirely piscivorous. Seasonal differences in diet also exist within each size class examined.


A New Species of Stiphodon (Family Gobiidae: Sicydiaphiinae) from Vanuatu by Patrick A. Ryan

Stiphodon astilbos sp. nov. is described on the basis of specimens from Espiritu Santo island, Vanuatu. The species differs from S. elegans in male colour pattern and some morphometric features. The interrelationships between S. elegans and S. stevensoni are briefly discussed.


The terrestrial crabs Sesarma (Sesarmops) impressum and Geograpsus crinipes (Brachyura, Grapsidae, Sesarminae) recorded from the Fiji Islands by C.L. McLay and P.A. Ryan

Two terrestrial brachyuran grapsid crabs are recorded from the Taveuni Is. in the Fiji group: Sesarma (Sesarmops) impressum, and Geograpsus crinipes. These new records, plus previous records of grapsid crabs (S. (Parasesarma) lenzii, S. (P.) leptosoma, S. (Labuanium) rotundatum, S. (Neosarmatium) smithii, S. (Labuanium) trapezoideum, S. (Perisesarma) bidens, Geograpsus grayi, Varuna litterata) and the gecarcinid crabs (Cardisoma 1ongipes, C. carnifex, C. hirtipes and Gecarcoidea lalandii), bring the total known Fiji fauna to fourteen species. Further collecting is likely to reveal many more species.


Taxonomy of the arboreal polychaete Lycastopsis catarractarum Feuerborn (Namanereidinae: Nereididae), with a discussion of the feeding biology of the species by C.J. Glasby, R. L. Kitching and P.A. Ryan.

Lycastopsis catarractarum
Feurborn, 1931 is redescribed and a neotype designated. A full synonymy is given and all known records of the species are examined. Gut contents are analysed for two populations (Papua New Guinea and Fiji) and the feeding biology and ecology are discussed.


Environmental effects of sediment on New Zealand streams: a review by Paddy A. Ryan

Literature pertaining to sediment in stream ecosystems is reveiewed. Suspended sediment can alter the water chemistry, and cause temperature decreases and turbidity increases. Deposition of sediment may change the character of the substrate, block interstices, and reduce interstitial volume. Turbidity levels as low as 5 NTU can decrease primary productivity by 3-13%. An increase of suspended sediment levels increases the drift fauna and may reduce benthic densities as well as alter community structure. Fish are not so obviously afected, although death resulting from clogging of the gills may occur in sensitive species. Suspended and deposited sediment may alter fish community composition, both by interference with run-riffle-pool sequences and by favouring olfactory feeders over visual feeders. In many situations aesthetic reactions to suspended sediment may be of more concern than biological ones. In already turbid water, a 20-50% reduction in clarity may not be detectable whereas in normally clear water a clarity reduction of 10-15% is distinguishable. Recovery from the effects of suspended sediement deposition is usually rapid, once the source of contamination is removed and as long as the stream is prone to regular spates; the aesthetic recovery may only take days whereas biological recovery may take months.


The success of the Gobiidae in tropical Pacific insular streams by P.A. Ryan

The high islands of the tropical Pacific possess a sparse native fish fauna dominated by the family Gobiidae. Evidence of this domination is presented, together with possible reasons for the success of the Gobiidae. Factors which may have contributed include a marine larval stage, euryhalinity, small size, an excellent climbing ability, a range of trophic level from carnivory through omnivory to herbivory, frequent lack of a gas bladder, and an associated bottom-living life style. The evolution of streams in the high islands of the tropical Pacific is relatively recent, thus there has been little time for colonisation to occur. Furthermore, estuaries in many islands are poorly developed, thereby placing euryhaline estuarine species at a competitive disadvantage.


Mountain streams in Westland, New Zealand: benthic ecology and management issues by M.J. Winterbourn and P.A. Ryan

1. The West Coast of the South Island, New Zealand (Westland) is a region of mountains, forests, high rainfall, and a history of exploitation. The Southern Alps rise to over 3000 m in the east of the region, and a narrow coastal plain supports some agriculture and the main centres of population.
2. Stream waters in the Southern Alps are characterized by low concentrations of major ions, and most can be described as calcium—sodium—bicarbonate waters. Brown waters with low pH and high concentrations of dissolved organic carbon are common at low and intermediate altitudes.
3. Many mountain streams and rivers provide physically harsh environments for aquatic biota with their rapidly changing flows and frequent spates. Hydrological factors and low nutrient concentrations limit periphyton standing crops, and biomass of coarse detritus is often low. Invertebrate populations are usually dominated by insect larvae that feed primarily on Fine Particulate Organic Matter and stone surface biofilms.
4. Features of the macroinvertebrate stream fauna on the West Coast are the wide range of physicochemical conditions tolerated by many common species, and the numerical dominance of the mayfly Deleatidium (Leptophlebiidae) in many streams. The Plecoptera also exhibit high diversity relative to other parts of the country, and an unusual trend towards terrestrialism is shown by larvae of Gripopterygidae.
5. The West Coast has a long history of coal and gold mining, forestry and farming, activities that have had negative impacts on stream communities and water quality. We discuss some ecological and management issues associated with present day mining practices, and a proposal to take large volumes of alpine stream water for export.


An invasion of the blue moon and blue tiger butterflies (Lepidoptera: Nymphalidae) from Australia, April 1995 by Early, J.W., Parrish, G.R., and Ryan, P.A.

Large numbers of two Australian butterflies, Hvpolimnas bolina nerina and Tirumala hamata hamata, were reported in April-June 1995 in New Zealand, mostly in the north and west of the North Island. Meteorological evidence indicates that they probably arrived on 9-10 April from between about 24 degrees and 32 degrees S on Australia’s east coast, and with a trans-Tasrnan passage time of 54-60 hours. A few specimens of other Australian butterflies (Danaus chrysippus petilia, Cynthia kershawi, Junonia rillida calybe and possibly Melanitis leda bankia (Nymphalidae)) and moths (Utetheisa pulchelloides vaga (Arctiidae) and Elvgaea materna (Noctuidae)) were also recorded over the same period.


Cranefly larvae (Diptera: Tipulidae) living in jelly masses by R.A. Beaver and P.A. Ryan

The immature stages of the cranefly, Limonia (Geranomyia) vitiella Alexander. are found mostly on the leaves of Pandanus in moist habitats in the rain forest on the island of Viti Levu, Fiji. The larva lives within a tube of jelly on the upper leaf surface, emerging to feed on decaying and dead epiphylls. and associated microbes. When mature, it usually moves to the lower leaf surface where a larger mass of jelly is produced, within which it pupates. The jelly protects the immature stages against desiccation, and natural enemies. The species occurred patchily in both space and time.


Distribution, ecology, and conservation status of freshwater Idoteidae (Isopoda) in southern New Zealand by Chadderton, W.L., Ryan, P.A., & Winterbourn, M.J.

Three species of Idoteidae, Austridotea lacustris, A. annectens, and A. benhami, are known from the South Island of New Zealand and some of its outlying islands. All three have largely coastal distributions, with A. lacustris and A. annectens inhabiting both fresh and brackish water. They feed mainly on plant detritus and, to a lesser extent, algae and invertebrates. A. lacustris is known from Stewart Island, Campbell Island, Pitt Island, and the south of the South Island. On Stewart Island, many stream populations of A. lacustris occur immediately above the upper limit of tidal influence, but on Campbell island, the species penetrates much further inland. A. annectens has been found on Stewart Island, Pitt Island, and the southern South island as far north as Banks Peninsula. It lives in freshwater streams and brackish lagoons. A. annectens has a 1-year life cycle with young released in spring. A. benhami is known only from a few freshwater streams near Dunedin (South island) and appears to be the most endangered of the three species. Habitat protection by vegetated riparian strips is proposed to reduce potentially harmful effects on its populations.


Impacts of global warming on New Zealand freshwater organisms: a preview and review by Ryan, P.A. and Ryan, A.P

Global warming is a reality and there is evidence that some New Zealand freshwaters have already increased by as much as 1.6 oC over a 17-year period. Temperature increases may cause a southwards retreat of vulnerable aquatic species in New Zealand as a 3 oC temperature increase will shift a derived degree day / latitude regression 670 km southward. Introduced salmonids, stream invertebrates and non-diadromous native fishes may be unable to make compensatory migrations and be extirpated from portions of their range. Diadromous galaxiids may be harmed by egg loss due to increased flood frequency. Existing evidence on genetic heterogeneity of stream insects is ambiguous but some species may have the genetic capacity to cope with increased temperatures. Maintenance or enhancement of riparian vegetation is likely to be important to keep adult stream insects within their temperature tolerance ranges. Higher CO2 levels may result in reductions in nitrogen levels in leaves that fall into streams, thereby reducing food value to aquatic consumers. Higher temperatures may also produce faster growth rates but smaller adult size in some freshwater invertebrates. An increase in the frequency of extreme climatic events will have the capacity to alter aquatic community structure and higher temperatures may enhance the reproduction of parasites with consequent negative effects on their hosts. Furthermore, warmer stream temperatures could increase the possibility of aquarium escapees establishing in northern waters.


[Previous]  Ryan Environmental Reports
[Next]  Paddy's Essay of the "week"
[Home]  Home Page
[Contents]  Dr Paddy Ryan Contents

Ryan Photographic, 2802 East 132nd Circle, Thornton, Co 80241, USA. Phone 303-457-9795.