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    The relative abundance, movement, and growth of rainbow trout (Salmo gairdneri) and brown trout (Salmo trutta) in the Rangitikei River, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science with Honours in Zoology at Massey University
    (Massey University, 1984) Rodway, Maurice Allan
    The null hypothesis tested was that rainbow and brown trout populations do not move between naturally defined sections of the Rangitikei River. It was found to be true for adult brown trout but false for rainbow trout. Recaptures of tagged brown trout demonstrated that the majority of these fish living in the mid-reaches do not make seasonal movements between river sections. Brown trout dwelling in the lower reaches were smaller than mid-reach brown trout. This difference, and the lack of tag returns indicating movement between the two sections, supports the hypothesis. Recaptures of tagged rainbow trout demonstrated that the majority of these fish migrating from the mid-reaches in autumn and winter travel to the headwaters where they remain the following summer. Those rainbow trout which were recaptured in the headwaters after moving from the mid-reaches tended to migrate earlier in the winter than those captured, then later recaptured, in the mid-reaches. Similarities in the size of rainbow trout spawning migrants captured in the lower reaches and the mid-reaches suggested that both groups spent at least their second and third years in the same area of the river, but low numbers of tag returns meant that no firm conclusions regarding rainbow trout movement between the mid and lower reaches could be made. Limited data concerning movement during the summer period suggested that some rainbow and brown trout move within sections but evidence of individuals remaining in one place for extended periods was found also. Reported behaviour of both species of trout in response to seasonal physiological changes and agonistic pressure, allied with stream bed morphology probably accounted for the observed distribution of young of the year, year one, year two and adult trout in the river. Upstream migrating adults, of both species counted at two traps, were found to respond to fluctuations in water flow and were probably affected by moon phase so that migratory activity was saltatory. Rainbow trout tended to migrate earlier in the winter than brown trout. The movement of female brown trout followed the male brown trout migration but similar differences were not observed in the rainbow trout migrants.
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    Open population mark-recapture models including ancillary sightings : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Statistics at Massey University
    (Massey University, 1995) Barker, Richard J
    A model is proposed for a mark-recapture experiment with ancillary observations obtained from marked animals any time between capture periods and throughout the geographic range of the animals. The model allows three types of emigration from the site where recaptures are made: (1) random emigration, where the probability an animal is at risk of capture at i does not depend on whether it was at risk of capture at i - 1, (2) permanent emigration where animals can leave the area where they are at risk of capture but not return, and (3) Markov emigration, where the probability an animal is at risk of capture at i depends on whether it was at risk of capture at i - 1. Under random emigration the likelihood function can be factored into a set of conditionally independent binomial terms used to estimate the parameters and a set of conditionally independent multihypergeometric terms that do not involve the parameters. Closed-form maximum likelihood estimators are derived under random emigration for models with age-dependence and a temporary marking effect. Contingency table based goodness-of-fit tests are derived from the multihypergeometric terms in the likelihood function. Contingency table tests of the age-dependence and temporary marking effect models are also derived. Explicit estimators do not appear to exist for permanent or Markov emigration. It is shown that the estimator suggested by Jolly (Biometrika 52:239, 1965), and as a consequence the estimator suggested by Buckland (Biometrics 36:419-435, 1980), is only valid if there is no emigration from the study area or if emigration is random. The estimator suggested by Mardekian and McDonald (Journal of Wildlife Management 45:484-488, 1981) for joint analysis of recapture and tag-recovery data is also only valid under no emigration or random emigration. By making appropriate constraints on parameters the models reduce to previously published models including the Jolly-Seber model (with age-dependence and a temporary marking effect), tag-resight models, tag-recovery models, and joint live-recapture/ tag-recovery models. Thus, the model provides a common framework for most widely-used mark-recapture models and allows simultaneous analysis of data obtained in several ways. Advantages of the new models include improved precision of parameter estimates, and the ability to distinguish between different type of emigration. FORTRAN programmes are developed for fitting the models to data with an application to a data set for brown trout (Salmo trutta) tagged in spawning tributaries of Lake Brunner, Westland between 1987 and 1991.
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    Diet overlap between coexisting populations of native blue ducks (Hymenolaimus malacorhynchos) and introduced trout (family: Salmonidae) : assessing the potential for competition : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1996) Towers, Dale Jeffery; Towers, Dale Jeffery
    I investigated diet overlap between blue ducks and trout, to assess the possibility that introduced trout (Family: Salmonidae) may be acting as an agent-of-decline on New Zealand's endemic blue ducks (Hymenolaimus malacorhynchos). Blue ducks inhabit fast-flowing rivers and streams. Both rainbow (Oncorhynchus mykiss) and brown trout (Salmo trutta) were liberated into New Zealand's rivers and streams in the 1870s. Stream macroinvertebrates are consumed by both blue ducks and trout raising the possibility that the two animals may compete for food resources. The importance of different prey in the diets of trout and blue ducks was assessed both in terms of numbers of prey consumed and prey dry weight. To analyse each predator's diet in terms of prey dry weight, I developed regression equations for commonly eaten macroinvertebrates. These allowed for the estimation of dry weight from prey head width and body length measurements. A power equation, y = ax b is used to express the relationship. The precision of dry weight estimation varied between taxa ranging between ± 10% and ± 40%. For the majority of taxa, dry weight could be estimated with greatest precision from body length. The relative abundance of macroinvertebrate prey was measured in trout stomachs and faeces of adult blue ducks collected from Tongariro, Manganuiateao, Ikawetea and Makaroro Rivers in 1991/92. Trichoptera and Ephemeroptera larvae were the most abundant macroinvertebrate prey in the diet of blue ducks inhabiting all rivers. Diptera were also consumed in large numbers by blue ducks on Tongariro and Manganuiateao Rivers but were less important than Trichoptera and Ephemeroptera in terms of dry weight. Prey consumed by blue ducks were also of high importance in the diets of trout in all four rivers. A maximum diet overlap value of 0.69 (Schoener's index) was found using numeric data while a maximum value of 0.89 was found when dry weight data were examined. The highest overlap occurred between blue ducks and trout on Manganuiateao River. Blue ducks on all four rivers were found to take macroinvertebrates having a smaller mean body length than that occurring on average in the benthos. Trout were found to consume prey having a larger mean body length than that occurring in the benthos. The body length of prey consumed by trout was positively correlated with trout fork-lengths (rs = 0.49 p < 0.05). However, the mean body length of prey consumed by small trout (FL < 250mm) was significantly larger than that taken by blue ducks (T199 = -2.74 p = 0.007). To test the hypothesis that foraging by rainbow trout alters the composition of the aquatic macroinvertebrate community, data were compared from reaches of river above and below waterfalls on Ikawetea and Makaroro Rivers. Discriminant analysis indicated that the macroinvertebrate communities occurring in sections of river free of trout were not consistently dissimilar from those in sections inhabited by trout. However, an enclosure / exclosure experiment conducted in Tongariro River in April, 1993 found that in the absence of rainbow trout the density of Trichoptera, Ephemeroptera and Plecoptera in the benthos significantly (F2, 33 = 3.615 p = 0.038) increased. In addition, in those enclosures containing trout the density of large macroinvertebrates (body length > 7.1 mm) was less than in enclosures free of trout after 6 days. To examine the response of blue ducks to trout-induced changes in the benthos I conducted an experiment to assess the foraging behaviour of blue ducks in artificial stream channels varying in prey availability. Blue ducks showed a graded response in respect to relative food availability, with a significant correlation between prey density and number of foraging visits to channels (rs = 0.738, p < 0.05). In addition a significant correlation was found between the proportion of total foraging time spent in a channel and the proportion of total insect numbers in that channel (rs = 0.833, p < 0.05). For those endeavouring to develop a strategy to ensure the long term survival of this unique waterfowl my research indicates that where trout and blue ducks coexist resource partitioning may result in little interspecific competition occurring and hence competition appears unlikely to be a principal agent-of-decline of blue ducks.