Investigation of the diet of nutria
Re-colonisation was facilitated by the efforts of multiple agencies combined within the Joint Otter Group and other agencies working to reverse environmental degradation. Abstract: Monitoring throughout the county of Essex has shown annual widening of otter distribution. Percent frequency occurrence values of prey families within each stream order ( Figure 2 ) provided a description of predation within each stream order, these values were used to calculate related trophic niche breadths ( Figure 3 ). Investigation into the Dietary Habits of the Eurasian Otter ( Lutra lutra ) in the County of Essex. lutra across the county of Essex. Therefore, analysis of data required the use of the Kruskal-Wallis (H) test between trophic niche breadth (TNB) and stream order. 08. Prey remains were identified to family level and data used to calculate trophic breadths over the range of stream orders. Extended research could determine seasonal variation and the extent to which available prey assemblage limits distribution against wider environmental and biological variables. 07. Annual monitoring of the Essex population is tracking progress, which is essential, as the population has yet to reach carrying capacity and still has potential to expand ( Crawford, 2010 ). 09. Investigative comparisons were used to detect changes in diet with stream order. The statistical analyses of data were performed using SPSS software. The dry weight of spraints ranged from 0. Relative percent (%) frequency of prey families within the diet of otters from four orders of stream. In the group of fourth order streams, the distribution was highly skewed and had a median of 0. Stream order was allocated to each sample using the system described by Strahler (1952). Received 12th July 2011, accepted 29th October 2011. 34g to 7. 195). Consistent occurrence across stream orders suggests invertebrates are an important dietary component to this population. 9%). 046g (SE 0. Second order streams had a median value of 0. Essex is a low-lying county in eastern England. To produce a map communicating the distribution of collected samples in relation to the known distribution of this species. Arcsine transformed frequencies of prey families were compared between stream orders using the paired t-test. Six of the samples (11%) came from second order streams. Within the fifth order group of samples the TNB median was 0. Due to problems associated with bulk estimations ( Carss and Nelson, 1998 ) no attempt had been made to estimate the volume of fish eaten, whole or part. The distribution of TNB values within each group was skewed. In this study fish were the most frequently taken food items, 67%. Despite transformation, neither normality nor homoscedasity were achieved. The remaining eleven samples (20%) where collected from fifth order streams. , Tansley, D. Samples were wrapped in aluminium foil, sealed in plastic sample bags, tagged and stored frozen.
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This study aims to complement survey distribution data with additional information, through dietary analysis, on how a growing otter population uses available resources. The Eurasian otter ( Lutra lutra ) population in the county of Essex and East Anglia is experiencing growth and becoming re-established after regional extinction ( Mason and MacDonald 2003 ). (2011). Using descriptive statistics, homoscedasity was assessed for each group before and after various transformations. A survey in 1991 ( Strachan and Jefferies, 1996 ), identified the presence of field signs indicating otter usage. To identify all prey species to family level. Third order streams contributed the highest proportion of 20 samples (37%). Volume 28 Issue 2 Pages 62 - 118 (October 2011). 1. ,1986, 2000 ). This paper reports a snapshot study of spraints collected from within the areas of known distribution, providing additional insight on a growing population. Otters predated animals from four groups comprised of eight families of fish, four families of invertebrate, three families of bird and one family of mammal ( Table 1 ). Insects and crustaceans featured regularly in the diet (19. The Trophic Niche Breadth of otter diet as determined from spraints collected from four orders of stream within the county of Essex. Once separated identification of prey remains to family level was aided by published keys ( Conroy et al. Habitat restoration and targeted re-introductions successfully re-established a small yet viable population ( Jefferies et al. Successive surveys have consistently shown increases in the extent to which the species uses local water courses (Tansley, 2008, 2009, 2011 ). In terms of volume, fish may contribute a larger proportion of diet than has been measured here. Streams originating from source were allocated the first order. , 2005, Teerink 1991, Day 1966 ). The county of Essex incorporating the known otter distribution as 2009 (triangles) and the sites where samples of spraints where collected in 2010 (circles). 91g, mean 2. Investigation into the Dietary Habits of the Eurasian Otter ( Lutra lutra ) in the County of Essex. Citation: Cousins, L. The median TNB value of third order streams was 0. To compare trophic breadth indices to identify geographical patterns in relation to stream order. Seventeen samples were taken from streams of the fourth order (31%). To determine the diet and feeding habits of L. In this system an n th order stream always flows downstream from the confluence of two (n-1) th order streams. Binocular Leica Zoom 2000 and Nikon 104 microscopes were used for analysis. To determine the importance of invasive crayfish species to otter diet. To determine the relative contributions of each family to otter diet in relation to distribution. and Hepburn, L. Historically, the otter was common throughout Britain ( Stephens 1957 ). Dietary composition was consistent within the range and period studied.
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