New Zealand Journal of Marine and Freshwater Research abstracts

---

Diet of the crayfish Paranephrops zealandicus in bush and pasture streams: insights from stable isotopes and stomach analysis

John W. Hollows^*

Colin R. Townsend

Department of Zoology
University of Otago
Dunedin, New Zealand

Kevin J. Collier

National Institute of Water & Atmospheric Research Limited
P.O. Box 11  115
Hamilton, New Zealand
^* Present address: Fish & Game Otago, P.O. Box 76,  Dunedin, New Zealand. email: j.hollows@fish- game.org.nz

Abstract   Crayfish (Paranephrops zealandicus White) stomachs from streams in both native bush (mainly tree leaves and dicotyledonous seeds) and exotic pasture settings (mainly grass stems and monocotyledonous seeds) were dominated by allochthonous material. More detritus occurred in stomachs in autumn–winter than in spring–summer, but quantities were similar in crayfish from native bush and pasture streams. The stomachs of larger crayfish contained a significantly greater proportion of detritus than smaller individuals. Aquatic invertebrates were the second most abundant dietary category by volume, with highest values in winter, but there were no significant differences between land uses or crayfish size classes. A wide range of invertebrates was eaten by crayfish, with mayfly nymphs, chironomid larvae, and snails predominating. The latter were numerically more prominent in crayfish from bush than pasture streams. Terrestrial invertebrates were recorded from 4% of stomachs, but there were no significant differences in relation to land use, season, or crayfish size class. Despite aquatic invertebrates making up <4% of stomach volumes on average, stable isotope analysis indicated a greater importance for invertebrate prey in terms of assimilation and incorporation into crayfish biomass. Allochthonous detritus and moss appeared to be unimportant. Whereas the results of stomach analysis provided some evidence of an ontogenetic shift, with detritus assuming greater importance in larger crayfish, this pattern was not supported by isotope analysis because invertebrate prey appeared more important to the diet than detritus. An unidentified carbon source, depleted in ¹³ C and perhaps of microfloral origin, seems to be an important energy source for crayfish in both stream types.

Keywords  Paranephrops; land use; diet; carbon stable isotopes; nitrogen stable isotopes

M01003 Received 9 January 2001; accepted 10 September 2001
New Zealand Journal of Marine and Freshwater Research, 2002, Vol. 36 : 129–142
0028–8330/02/3601–0129 $7.00 © The Royal Society of New Zealand 2002

PDF file of entire paper: Print-quality

---

This year's abstracts | Journal home page | All abstracts | Publishing home page