BTO Research Report No. 515

Carrying Capacity Modelling for the Pied Oystercatcher at Lauderdale and Surrounding Sites. Lauderdale Quay Proposal.

Authors

Philip W. Atkinson1 & Richard A. Stillman2

1British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK & 2School of Conservation Sciences, Bournemouth University, Talbot Campus, Poole, Dorset BH12 5BB, UK.

November 2008

© British Trust for Ornithology & Bournemouth University

Report prepared for Aquenal Pty Ltd

British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU Registered Charity No. 216652

British Trust for Ornithology

Carrying Capacity Modelling for the Pied Oystercatcher at Lauderdale and Surrounding Sites. Lauderdale Quay Proposal.

BTO Research Report No. 515

Philip W. Atkinson & Richard A. Stillman

Published in … 2008 by the British Trust for Ornithology The Nunnery, Thetford, Norfolk, IP24 2PU, UK

Copyright © British Trust for Ornithology 2008

ISBN

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publishers

BTO Research Report No. 515 i November 2008 CONTENTS

Page No.

List of Tables ...... iv List of Figures...... v

Executive Summary ...... vi

1. INTRODUCTION ...... 1

1.1 Background to this study...... 1 1.2. Overview of the model...... 1 1.2.1 Application and testing the model to Eurasian Oystercatchers ...... 2 1.2.2 Parameters required to apply the model to a new system...... 2 1.2.3 Applying the model to Lauderdale and surrounding bays ...... 3

2. METHODS ...... 4

2.1 Study Sites ...... 4 2.1.1 Site selection ...... 4 2.1.2 Division of the study sites into patches...... 5 2.2 Availability of Intertidal Feeding Habitat ...... 7 2.2.1 Introduction...... 7 2.2.2 Methods...... 7 2.2.2.1 Generating tide tables and bathymetry ...... 7 2.2.2.2 Ascertaining patch area available to birds ...... 8 2.3 Calculation of the Energy Content of the Invertebrate Prey...... 11 2.3.1 Introduction...... 11 2.3.2 Ash-Free Dry Mass Estimation...... 11 2.3.3 Results...... 11 2.4 Foraging Studies ...... 20 2.4.1 Introduction & methods...... 20 2.4.2 Results...... 20 2.5 Parameterising the Model for Pied Oystercatcher ...... 26 2.5.1 Single- and multi-bay models...... 26 2.5.2 Environmental parameters ...... 26 2.5.2.1 Time period simulated ...... 26 2.5.2.2 Time step length...... 26 2.5.2.3 Day length...... 26 2.5.2.4 Tidal cycle...... 27 2.5.3 Patch parameters ...... 27 2.5.3.1 Maximum patch area ...... 27 2.5.3.2 Patch area available to birds ...... 27 2.5.4 Food resource parameters...... 28 2.5.4.1 Prey size classes...... 29 2.5.4.2 Numerical density of prey at start of each season...... 29 2.5.4.3 Prey mass during each season...... 29 2.5.4.4 Prey energy content ...... 30 2.5.5 Bird parameters ...... 30 2.5.5.1 Population size...... 30 2.5.5.2 Target body mass and starvation body mass...... 31

Continued…/

BTO Research Report No. 515 ii November 2008 Page No.

2.5.5.3 Energy density of bird reserves...... 31 2.5.5.4 Metabolic rate ...... 31 2.5.5.5 Time and energy cost of moving between patches ...... 31 2.5.5.6 Size ranges of prey diets consumed by the birds ...... 31 2.5.5.7 Individual variation...... 32 2.5.5.8 Day and night variation in foraging efficiency ...... 32 2.5.5.9 Interference competition ...... 32 2.5.5.10 Functional response ...... 33 2.5.5.11 Maximum intake rate ...... 33 2.5.5.12 Assimilation efficiency ...... 33 2.5.5.13 Decision rules...... 33 2.5.6 Modelling habitat loss...... 33 2.5.7 Summary of the parameterised model...... 35

3. MODEL PREDICTIONS OF THE EFFECT OF THE DEVELOPMENT ON PIED OYSTERCATCHER FORAGING CARRYING CAPACITY...... 36

3.1 Quantity of Food in Relation to the Requirements of the Birds...... 36 3.2 Predicted Behaviour, Body Mass and Survival in the Absence of Habitat Loss...... 39 3.2.1 Patch choice...... 39 3.2.2 Diet selection...... 39 3.2.3 Food intake rate ...... 40 3.2.4 Percentage of time spent feeding ...... 40 3.2.5 Body mass and survival...... 40 3.3 Predicted Effect of Partial Habitat Loss on Behaviour, Body Mass and Survival...... 42 3.3.1 Behaviour...... 42 3.3.2 Body mass and survival...... 42 3.4 Predicted Effect of Complete Habitat Loss on Behaviour, Body Condition and Survival...... 42 3.4.1 Site choice ...... 42 3.4.2 Body mass and survival...... 42 3.5 Sensitivity Analysis of Predicted Effect of Habitat Loss ...... 43 3.5.1 Number of birds within the model ...... 43 3.5.2 Water depth within which birds can forage ...... 43 3.5.3 Uncertainty in the density of prey ...... 43 3.5.4 Combined effects...... 44 3.6 Future Increases in Bird Population Size and the Predicted Effect of Habitat Loss...... 44

4. DISCUSSION...... 46

4.1 Impact of the Proposed Development and the Ability of Other Sites to Accommodate Displaced Birds ...... 46 4.2 Observed and Predicted Diet of the Pied Oystercatchers ...... 49 4.3 Future Changes in the Pied Oystercatcher Population ...... 49 4.4 Conclusion ...... 50

Acknowledgements ...... 52

References...... 53 eferences ......

BTO Research Report No. 515 iii November 2008 LIST OF TABLES

Page No.

Table 2.3.1 Number of individuals sampled for AFDM measurements at the seven sites and in the three seasons ...... 14

Table 2.3.2 Parameters that were included in the preferred models for each species group and the amount of variation explained by the model...... 15

Table 2.3.3 Selection of the preferred model for each species ...... 16

Table 2.3.4 Parameter estimates of the preferred models ...... 18

Table 2.3.5 Parameter estimates for the average AFDM-length model with no site or seasonal effects ...... 19

Table 2.4.1 The percentage make up of Pied Oystercatcher diet at the seven study sites in terms of bivalves, polychaetes and gastropods ...... 21

Table 2.4.2 Mean AFDM intake rate per 10 minutes for each of the 7 sites across seasons ...... 21

Table 2.4.3 Mean AFDM intake per 10 minutes during foraging observations broken down by patch and season ...... 22

Table 2.5.1 Patch areas calculated from the bathymetry study...... 28

Table 2.5.2 Bird count data used to parameterise the model: number of Pied Oystercatchers occupying each site during each season...... 30

Table 4.1.1 Summary of model predictions in relation to variation in model assumptions and parameter values...... 46

BTO Research Report No. 515 iv November 2008 LIST OF FIGURES

Page No.

Figure 2.1.1 Sites included in the model...... 4

Figure 2.1.2 Distributions of patches within each bay ...... 6

Figure 2.2.1 Bathymetry maps for each bay ...... 10

Figure 2.3.1 Plots of the transformed Ash Free Dry Mass vs length of the eight invertebrate groups studied in this report...... 13

Figure 2.4.1 Relationship between the length of three polychaete species and their ash free dry mass ...... 23

Figure 2.4.2 Mean AFDM intake per 10 minutes for Pied Oystercatchers foraging at the 7 study sites by season and overall and the proportion of the diet throughout the year made up of gastropods, bivalves and polychaetes ...... 24

Figure 2.4.3 Comparison of the mean intake rates for each site, expressed as a proportion of the site with the maximum intake rate...... 25

Figure 2.4.4 Intake rates at Lauderdale by patch averaged across the three season...... 25

Figure 2.5.1 Proposed amount of habitat to be lost from Lauderdale ...... 34

Figure 2.5.2 Screenshot of the model...... 35

Figure 3.1 Biomass of food available in each bay during each season in relation to the food requirements of the birds ...... 37

Figure 3.2 Biomass of food available at Lauderdale during each season in relation to the food requirements of the birds ...... 38

Figure 3.3 Predicted and observed behaviour of Pied Oystercatcher at Lauderdale in the absence of habitat loss ...... 41

Figure 3.4 Predicted effect of possible future increases in the population size of Pied Oystercatchers at Lauderdale on the percentage of birds surviving the year in the presence and absence of partial habitat loss...... 45

BTO Research Report No. 515 v November 2008 Executive Summary

The Walker Corporation Pty Ltd has proposed the development of a marina village at Lauderdale in southern Tasmania (i.e. the Project). The proposed development site includes a large area of tidal flats (85.76 ha) that is used by a wide range of migratory waders and a significant proportion of the world population of Pied Oystercatchers. Lauderdale forms part of a complex of lagoons and bays situated within the Derwent/Pitt Water region that collectively support approximately 8% of the estimated global population of 11,000 Pied Oystercatchers. Averages of 2.6% and 2.4% of the global population of Pied Oystercatchers occur at Lauderdale in summer and winter respectively (Aquenal 2008b), satisfying Criterion 6 of the Ramsar Convention of 1% of the global population being present at a site. Within the Derwent/Pitt Water region, the South Arm Neck site in Ralphs Bay also exceeded this 1% criterion. The effect of loss of bird habitat (foraging, roosting and breeding) has been identified as an issue that needs to be addressed as part of the Integrated Impact Statement (IIS) for the Project.

The current study assessed one aspect of habitat loss by using a behaviour-based model to determine the likely impact of the proposed development on food resources available to Pied Oysterctachers. This report details the modelling studies and background analyses needed to parameterise the model. A total of seven sites located in south eastern Tasmania were included in the model, and were selected on the basis of supporting large numbers of Pied Oystercatchers and having potential links to the proposed development site. Two of the sites, Orielton Lagoon and Barilla Bay, fall within the existing Pitt Water/Orielton Lagoon Ramsar site. The seven sites included a total of 34 ‘patches’ identified for the model and had a total area of 616 ha. Field data required as input to the model were collected during spring, summer and winter seasons to correspond with important life stages of wader species and hence variation in food availability. Data collected related to bird numbers, invertebrate prey species, and bird foraging activity, while information on sandflat exposure, energy demands by the birds and the energy content of their food were also input to the model.

Surveys by Harrison (2008) provided foraging data input to the model, and identified 20 prey species consumed by Pied Oystercatchers during full surveys. Polychaete worms and two species of bivalve (Katelysia scalarina and Anapella cycladea) accounted for approximately 90% of prey consumed in numeric terms. Inclusion of additional less common benthic infauna bivalves, as well as the gastropod Salinator fragilis and epibenthic bivalves Crassostrea gigas and Mytilus galloprovincialis, meant than data input to the model accounted for 98% of food items. The largest single numerical contributor to the diet was polychaete worms, which accounted for more than 40% of prey during each season.

The benthic invertebrate survey (Aquenal 2008a) provided the densities and sizes of the invertebrate prey available and targeted the species identified as important components of the Pied Oystercatcher diet from the above foraging studies. Energy intake by the birds was determined by calculating the relationship between the length of the organism and the ash-free dry mass (AFDM) for eight species (four bivalves, three polychaetes and one gastropod) for the seven sites and three seasons surveyed. These relationships were applied to the invertebrates observed to have been consumed by Pied Oystercatchers in the foraging surveys and were converted into the ‘common currency’ of AFDM. Analyses found that bivalves comprised on average 88% (range 70-95%) of the energy intake expressed as AFDM across all sites.

Birds at Lauderdale had the highest intake rates (c. 6g AFDM per hour) and, in terms of biomass (expressed as AFDM) also consumed the highest proportion of bivalves. In terms of foraging, Lauderdale was therefore the highest quality site surveyed.

In the absence of habitat loss (i.e. no development) the model predicted that there was a seasonal minimum of four times the amount of food needed to sustain the current number of birds at Lauderdale (mean across seasons of 189 and a maximum of 252 birds). This minimum occurred during the winter season when the quality of food was lowest. European Oystercatchers require between two to eight times the amount of food required to maintain low mortality rates, depending on the dominant prey types. At Lauderdale and surrounding sites, where birds feed largely on dispersed

BTO Research Report No. 515 vi November 2008 rather than aggregated bivalve species, the birds would suffer little intra-specific competition and we initially expected that the amount of food required in the environment would be closer to two, than eight times the amount the birds needed to consume.

After removing the exact area that is covered by the proposed development, the model predicted no deaths or loss of condition of Pied Oystercatchers on the basis of reduced food availability. To ensure removal of any potential bias in the data, a sensitivity analysis was applied by increasing the number of birds to the seasonal maximum and not allowing birds to wade for food, however the same result was achieved. This scenario assumes that the development does not (a) impact on the sediments (and therefore food resources) to the south of the proposed development or (b) impact on the behaviour of the Pied Oystercatchers in the remaining area. These predictions do not take into account the presence of other waders but we expect the interaction between these species and Pied Oystercatcher to be relatively low for two reasons. First, there were relatively low numbers of other wader species present at the sites. Second, other wader species will not depend on bivalves to the same extent as the oystercatchers. As polychaetes only made up 11% of the Pied Oystercatcher diet (in terms of AFDM) overall, there was only a small amount of overlap in their diets.

To allow for the scenario of the proposed development having an adverse impact on areas to the south of its ‘footprint’, additional model simulations were conducted whereby all of the habitat was removed from Lauderdale and birds were forced to move elsewhere. On the basis of food resources, birds were predicted to move to South Arm Neck and Pipeclay Lagoon and, due to the large amounts of food available at those sites, no increase in mortality, or loss of condition, were predicted. The conservative approach of increasing the numbers of birds in the model to their seasonal maximum in each site, and not allowing them to wade for food, also resulted in no increased mortality or decrease in body condition. In these models we assumed that there was no cost to moving to feed at a new site. In reality, other wader species have shown a short term effect of increased mortality in the first year after being forced to move, so there may be a localised effect on the population.

The above default habitat loss simulations also assumed that the Pied Oystercatchers were the only source of prey mortality, whereas other factors may also be important. Additionally, the invertebrate survey may have overestimated the amount of food available to the birds. To account for these possibilities, a further sensitivity analysis was conducted by re-running the model, retaining the above assumptions about the seasonal maximum number of birds present and an absence of wading, but also assuming that only 50% of the observed food supply was actually available to the birds. Given the measured error (5th percentile of the total AFDM in the site) in the invertebrate survey varied seasonally between 31 and 43% of the total AFDM actually measured, and the fact that the preferred prey populations were relatively stable through the year (implying that mortality rates of these prey were relatively low), a 50% reduction of prey density was considered relatively extreme. The combined assumptions of this sensitivity analysis therefore provided a highly conservative assessment, with model output likely to reflect a worst case impact on the basis of reduction of food resource availability alone. For the partial habitat loss scenario (development area only), no increase in mortality or loss of condition were predicted with the 50% reduction in food. However when the other sectors to the south of the proposed development area at Lauderdale were made unsuitable, the model run predicted high mortality rates of 55% on average per year. In this scenario, it was therefore predicted that adjacent sites would not be able to support all birds displaced and mortality would occur.

Given that increased mortality is a possibility, although unlikely, it is important to ensure that the impact of the proposed development on the oystercatcher population is minimised. We also do not know the current degree of interchange of birds between sites and whether birds would suffer increased mortality if forced to move. Therefore, the difference between the full or partial utilisation of this habitat could make the difference between normal survival levels and increased rates of mortality. This highlights the importance of minimising any disturbance to the south of the proposed development site; an issue which should be considered in the impact assessment for the project.

BTO Research Report No. 515 vii November 2008 The model predicted that the current foraging resources at Lauderdale could support a potential maximum of up to 1,000 Pied Oystercatchers, with the area directly affected by the development's footprint supporting up to 300 individual Pied Oystercatchers. Making all of Lauderdale unavailable would therefore reduce capacity for 1,000 birds from the network of sites considered. It is unlikely that the development's impact would be limited to its immediate footprint and it is likely that birds would be forced to move to other sites. Given the current situation (i.e. current Pied Oystercatcher population level and food supplies), the most likely scenario is that there would be sufficient food available to these birds at other sites. If all the habitats at Lauderdale were made unsuitable by the proposed development then, again, the most likely scenario is that there would be sufficient food. It is only in the worst case scenario that mortality dramatically increases.

Based on the current surveys, food does not therefore seem to be the factor limiting Pied Oystercatcher population numbers in south eastern Tasmania. The model indicates that sites such as Lauderdale, South Arm Neck and Pipeclay Lagoon are key sites for maintaining high survival for Pied Oystercatchers in the region. Data obtained by Birds Tasmania (see Aquenal 2008b) show no evidence of significant declines in the population. Based on 1983-2005 biannual wader count data, the Pied Oystercatcher population in the Derwent/Pitt Water region increased in the 1990s although there was a greater variability in numbers in the later years. Although there was an excess of food, if the oystercatcher population undergoes a similar increase in future then food, particularly that available in winter, may become a limiting factor.

BTO Research Report No. 515 viii November 2008 1. INTRODUCTION

1.1 Background To This Study

The Walker Corporation Pty Ltd has proposed the development of a marina village at Lauderdale in southern Tasmania (i.e. the Project). The proposed development site includes a large area of tidal flats (85.76 ha) that is used by a wide range of migratory waders and a significant proportion of the world population of Pied Oystercatchers. The effect of loss of bird habitat (foraging, roosting and breeding) has been identified as an issue that needs to be addressed as part of the Integrated Impact Statement (IIS) for the Project. The current report details the modelling studies and background analyses used to determine the likely impact of the proposed development on the food resources available to Pied Oystercatchers.

This report concentrates on the Australasian Pied Oystercatcher Haematopus longirostris as it is the dominant species of the wader assemblage found in Ralphs Bay, the location of the proposed development. Averaged counts for the period 2001-2005 indicate that the Lauderdale site supported approximately 2.4% in winter and 2.6% in summer of the world population of this species (note: assessments of site significance are based on available data for the most recent five years, consistent with international protocol) (Aquenal 2008b). Averaged counts for the period 2001-2005 indicate that the Lauderdale site supported 32% (29.9% in winter and 33.7% in summer) of Pied Oystercatchers found in the Derwent/Pitt Water region, an area of both national and international significance for this species.

The RPDC guidelines for the Project indicate the need to assess the impact of the proposal on bird species. The current report provides background assessments for the wader component of the impact assessment by investigating the carrying capacity of Pied Oystercatchers at Lauderdale and surrounding lagoons using the individual-based models (IBMs) developed by Stillman et al. (2003). IBMs have a very wide range of applications for coastal birds, and they can directly advise policy and management on a number of issues. They use the foraging behaviour of birds in a simulation model to determine the number of birds that sites can support based on the amount of food available. They are also able to incorporate effects such as human disturbance by making parts of the food supply unavailable during disturbance events and increasing energy expenditure of the model birds, but in this report we have limited the simulations to just investigating how changes in food supply will impact on the birds body condition, survival and intake rates.

1.2 Overview of the Model

The model has been developed as a standalone application called MORPH. MORPH is the latest in a sequence of IBMs that have been developed to address coastal bird conservation issues. The models were originally developed as part of a long term study of Eurasian Oystercatchers on the Exe estuary, UK. The first two of these shorebird models (Goss-Custard et al., 1995; e.g. Clarke et al., 1996) described in increasing detail the oystercatcher-shellfish system in the Exe estuary, UK. The third of these shorebird models was also primarily developed for oystercatchers Haematopus ostralegus on the Exe estuary (e.g. Stillman et al., 2000), but was subsequently parameterised for a wider range of shorebirds and sites (e.g. Stillman et al., 2003; Durell et al., 2005). MORPH and its predecessors have been applied to coastal bird conservation issues in over 20 European sites. Although these models were developed from a study of Eurasian Oystercatchers and have been applied to European sites the principles on which they are based and the conservation issues they are designed to address occur globally.

The MORPH program predicts how environmental change (e.g. habitat loss, changes in shellfishing, changes in human disturbance, climate change and changes in population size) affects foraging animal populations. MORPH’s key assumptions are that individuals behave in order to maximise their perceived fitness (i.e. their expected survival and reproduction associated with alternative behaviours), but that perceived fitness may not always be positively related to the actual chances of

BTO Research Report No. 515 1 November 2008 survival and reproduction (i.e. animals may make sub-optimal decisions). MORPH contains a basic framework to describe animal physiology and foraging behaviour, and the distribution and abundance of resources. It can produce both general predictions (when parameterised in a simple way), and predictions for specific systems (when parameterised using system-specific data).

MORPH is an IBM and tracks the foraging location, body condition and ultimate fate of each individual within an animal population. During each day, each animal in the population must consume enough food to meet its energy demands. It attempts to do this by feeding in those locations and at those times of the day where its intake rate is maximised. Although all individuals decide on the same principle, intake rate maximisation, the actual decisions made by each differ. Their individual choices depend on their particular competitive ability which depends on two characteristics. Interference-free intake rate is the rate at which an individual feeds in the absence of competition and measures its basic foraging efficiency. Susceptibility to interference measures how much interference from competitors reduces its intake rate as competitor density rises. Survival is determined by the balance between an individual's daily rates of energy expenditure and consumption. Energy expenditure depends on metabolic costs. Energy consumption depends on the time available for feeding, intake rate while feeding and the energy content of the food being consumed. When daily energy consumption exceeds daily expenditure, individuals accumulate energy reserves or maintain them if a maximum level has already been reached. When daily requirements exceed daily consumption, individuals draw on their reserves. If reserves fall to zero, an individual dies of starvation.

1.2.1 Application and testing the model to Eurasian Oystercatchers

MORPH, and the previous models from which it has evolved, have been applied widely to the Eurasian Oystercatcher Haematopus ostralegus and predicted the effect of factors such as shellfishing, habitat loss and human disturbance on this species (Stillman et al., 2000; Stillman et al., 2001a; West et al., 2002; Stillman et al., 2003; West et al., 2003; e.g. Caldow et al., 2004; Goss- Custard et al., 2004; Caldow et al., 2007). The model is routinely used to advise on coastal bird conservation issues in Europe, and used to assess the food resources that are required to support coastal bird populations (e.g.Goss-Custard et al., 2004; Stillman et al., 2005c; Stillman et al., 2005b).

If IBMs such as MORPH are to be of applied value they need to produce accurate predictions. MORPH has been tested as thoroughly as possible using all data available for each study system. Two questions can be asked about whether an IBM predicts real events reasonably well. One question asks whether the model captures with good precision the behaviour of real birds in the system being modelled. Because the predictions for survival are derived from the behaviour of the birds in the model, and because decision making by fitness-maximizing individuals is the fundamental feature of the model, it is vital that the model adequately represents the behaviour of real birds. The other question is whether the model accurately predicts the fitness measures (e.g. survival) that are derived from this underlying behaviour. Although the tests have varied between sites, data have been typically available to test the predicted distribution of birds throughout a site and the major prey species consumed by birds. Typically, patch selection and prey choice were accurately predicted for the majority of species (e.g. Durell et al., 2005; Stillman et al., 2005a). In some sites, data were available on the proportion of the time spent feeding each day (an important indicator of the difficulty birds are having in surviving winter) and overwinter mortality rates. Both the proportion of the time spent feeding and overwinter mortality were accurately predicted in all cases (e.g. Goss-Custard et al., 2008). In one of the few tests where survival estimates could be tested, the models performed well and consistently predicted the annual survival of Eurasian Oystercatchers during periods of food shortage (Stillman et al. 2003). These accurate predictions increase confidence that the model provides a realistic description of the European waders and therefore that predictions for novel scenarios, which cannot be tested, are also likely to be accurate.

BTO Research Report No. 515 2 November 2008

1.2.2 Parameters required to apply the model to a new system

To be applied to a new system, the key parameters that need to be measured or obtained from previous studies or the literature are: (i) the distribution of the food supply and how food quality and abundance changes through the season; (ii) the tidal availability of feeding areas; (iii) the rate at which foragers are able to consume food given the abundance of food and competitors; (iv) the amount of food a forager needs to consume each day in order to avoid starvation; and (v) the distribution and seasonal changes in other factors which influence the foraging behaviour and survival of foragers. In practice the only parameters that have been measured for new shorebird systems have been the distribution and abundance of invertebrate prey and the availability of this prey through the tidal cycle. Typically, other parameters have been either obtained from the literature or from previous studies of the site. As a result models have typically been parameterised and applied to conservation issues using one autumn survey of prey populations (sometimes supplemented with a second in the spring), and estimates of the tidal exposure of patches either derived from local knowledge, patch heights on the shore, or existing tidal models. Once data are available, models have typically been parameterised and simulations run to address conservation issues within two months. Once a model is parameterised for a system, simulations can be run to address new issues within a matter of hours. The experience has therefore been that it has been possible to apply MORPH within a time scale that is compatible with the time constraints of coastal conservation issues.

1.2.3 Applying the model to Lauderdale and surrounding bays

Oystercatchers are almost cosmopolitan, occurring in perhaps as many as 20 different forms. All are remarkably similar, but there are limited variations in size, shape of bill and legs, iris and eye ring colour and distribution of the black, white and brown in the plumage (Hayman et al. 1986). They are all bulky waders that feed on shellfish and occupy similar niches across the world. Although the model has not previously been applied to Pied Oystercatchers, it is based on general principles of foraging behaviour and ecology that apply globally, rather than just to the European waders for which it has been developed. Furthermore, the Pied Oystercatcher shares many similarities in physiology, behaviour and diet with the Eurasian Oystercatcher to which the model has been most thoroughly tested. In addition, the behavioural predictions of the model were tested for Pied Oystercatcher (see below) to determine how well it described this system.

The model was run to simulate the annual cycle of Pied Oystercatchers at Lauderdale and surrounding sandflats/lagoons. The model simulated hourly time steps and during each of which predicted the location, diet selection, food intake rate and proportion of time spent feeding by each bird in the population. At the end of the annual cycle, the model predicted the body condition and survival of each bird. Three contrasting scenarios were simulated:

• Current situation – No habitat was removed from Lauderdale. Birds were allowed to freely move between sites. • Partial habitat loss – Habitat was removed in the 'footprint' of the proposed development zone at Lauderdale. Birds were not allowed to move away from Lauderdale. This latter constraint was added to determine if there was still sufficient food available at the southern end of the Lauderdale sandflats. • Complete habitat loss – A scenario where all habitat at Lauderdale became unsuitable and birds had to forage elsewhere. This scenario was added to determine whether, due to disturbance or any other factor that caused Pied Oystercatchers to be unable to forage at Lauderdale, they were able to find adequate food elsewhere if they were able to move.

BTO Research Report No. 515 3 November 2008 2. METHODS

2.1 Study Sites

2.1.1 Site selection

The model comprised Lauderdale and six other bays/lagoons that were considered to have potential links to the Lauderdale proposed development site (Figure 2.1).

Within each site the model comprised the area of intertidal habitat covered by the benthic invertebrate surveys (Aquenal, 2008a), adjusted to mean low tide as described in Section 2.5.3.1. The model did not include any terrestrial feeding habitats that may be exploited by the birds.

Figure 2.1.1 Sites included in the model (enclosed in black rectangles).

BTO Research Report No. 515 4 November 2008 2.1.2 Division of the study sites into patches

The data from each site were divided into one or more patches for the model. These patches are frequently determined on the basis of habitats and distributions of main prey species. However, given that it was necessary to have bird count and invertebrate data for each patch, the boundaries of patches in the current study were determined to a large extent on the basis of zones that were practical for the purpose of recording bird counts and foraging observations. Bird counts were conducted during the wader utilisation surveys (Aquenal, 2008b) and during the foraging ecology observations (Harrison, 2008), and provided data for two sets of patches. During the wader utilisation surveys, bird counts were pooled for the entire intertidal area at each site except at Lauderdale and Pipeclay Lagoon, while Harrison (2008) recorded counts for a larger number of zones at most sites during the foraging ecology surveys. The zones used by Harrison (2008) defined the model patches. Three mussel/oyster survey zones identified during the benthic invertebrate surveys (Aquenal, 2008a) also provided distinct prey resources within clearly mapped areas and hence were included as separate patches. The sites were subdivided into patches (Figure 2.1.2). Patches 6 at Lauderdale and South Arm Neck and patch 4 at Pipeclay Lagoon were oyster/mussel beds.

In addition, each site was assumed to contain one roost patch. The roost patches did not contain any food, but were used when no other patches were available, or when only very poor feeding patches were available. The individual roosts within each site were assumed to represent one or more actual roosts within the real system. This was a modelling assumption as MORPH can specifically model the energetic requirements of flying to a distant roost site. Here we just assumed that roost sites were present on-site and thus the birds did not incur energy costs to get to the roost.

BTO Research Report No. 515 5 November 2008

(a) (b)

(c) (d)

(e) (f) (g)

Figure 2.1.2 Distributions of patches within each bay: a) Five Mile Beach; b) Mortimer Bay; c) Barilla Bay; d) South Arm Neck; e) Orielton Lagoon; f) Lauderdale (the hatched area refers to the area covered by the proposed development); and g) Pipeclay Lagoon. A 500 m scalebar has been included in the map for each site.

BTO Research Report No. 515 6 November 2008 2.2 Availability of Intertidal Feeding Habitat

2.2.1 Introduction

An important factor determining food availability to shorebirds is variation in the area of intertidal habitat exposed through the tidal cycle, as this determines the amount of habitat within which the birds can feed. The model requires parameters measuring the area of habitat that is available during each model time step, potentially taking into account the fact that birds can feed within shallow water or on exposed habitat. Aquenal undertook a field study to collect the necessary data on intertidal habitat exposure using the methods described below. Wading depth of foraging birds was determined by Harrison (2008).

2.2.2 Methods

The exposure study was divided into the following tasks:

1) Generating tide tables specific to each site. 2) Using tide tables, in combination with depths for invertebrate sample sites (i.e. sites illustrated in Aquenal 2008a), aerial photos and Google Earth, to generate bathymetry maps for each site. 3) Ascertaining the area of each patch that is exposed for each one hour interval throughout the 2006-2008 study period. 4) Ascertaining the area of each patch that is available for feeding for each one hour interval throughout the 2006-2008 study period, incorporating the wading depth provided by Harrison (2008).

2.2.2.1 Generating tide tables and bathymetry

In order to create site-specific tide tables, and obtain accurate heights for sample patches, an Aquatec Aqualogger 520 was deployed sub-tidally at each site. This instrument logged pressure over time, which effectively records depth change over time, since pressure is directly related to depth. Readings taken were an average measurement over a burst of eight recordings every 10 minutes.

Once a suitable position for the logger was decided upon a star picket was hammered into the substrate. A hose clamp was attached to the star picket at a point just above the seabed. A Leica 1200 Real Time Kinetic GPS system was used to accurately record the position of the star picket in terms of easting, northing and height above Australian Height Datum. Height was taken from the top of the hose clamp. The Kinetic GPS was calibrated, using a ‘One Point Localisation’, at the closest SPM mark to the bay being surveyed. The locations of these marks, which are a known position and height, can be found on the LISTmap online at www.thelist.tas.gov.au/listmap. The logger was attached to the star picket so that the base was sitting on the hose clamp.

Invertebrate sample site depths were measured with a customised ruler, to the nearest centimetre, while the Aqualogger was logging pressures. The logger was then left to record pressures for one month. This process was repeated for each site.

Resultant data were used to generate site-specific tide tables using a software program developed and implemented by Dr John Hunter at the Antarctic Climate and Ecosystems Cooperative Research Centre of the University of Tasmania. The program is compatible with the analyses performed by the Proudman Oceanographic Laboratory in the U.K. and the National Tidal Centre in Australia, and uses singular value decompression (essentially a least squares estimator) to calculate the harmonic constants.

BTO Research Report No. 515 7 November 2008 Invertebrate sample site depths were corrected for tide using the tables mentioned above. These depths were then used, in conjunction with aerial photos, Google Earth, field observations and Mapinfo Professional (GIS software), to generate bathymetry maps for each bay (Figure 2.2.1).

Other factors, such as wind, will affect tidal heights. However water depths were measured on-site and these depths reflect the various factors influencing water depth. This work provides a snapshot in time (one month), but provides more accurate information than utilising generic data for the nearest port, which may not perform well at some of these sites.

2.2.2.2 Ascertaining patch area available to birds

The bathymetry maps were used, in conjunction with the minimum low tide predicted during the three year study period and bird feeding depth, to ascertain the maximum area of each patch which is available during that period for feeding by Pied Oystercatchers, i.e. the area available at the lowest spring tide. The minimum tide for each site was taken from the relevant tide table and the maximum bird feeding depth was judged by Harrison (2008) as being 120 mm.

Two areas within each patch were recorded for the purpose of the models. One is the area of zone exposed (above water level) at minimum low tide (Area A), and the other is the area of zone available for feeding at minimum low tide (Area B). Area B takes into account the maximum water depth at which a Pied Oystercatcher can feed. It is the area exposed plus the area which is 120 mm or shallower in depth (based on Harrison 2008) at minimum tide. The shoreward side of the areas was delineated by the Mapinfo coastal layer (Mean High Water Mark) supplied by Land Information Services Tasmania at the Department of Primary Industries and Water.

Two types of patches were surveyed in this study; 1) a gently sloping beach from below Low Low Water (LLW) to above High High Water (HHW) and 2) a gently sloping beach from below LLW to the base of a steeply sloping shore bank. The vast majority of the areas surveyed fall into the second category, with only patches 4 and 5 at Lauderdale being exceptions.

For the patches with steep shores, bathymetry maps were used to determine the tide height at which 98% of their area is A) covered by water and B) unavailable for feeding (covered by more than 120 mm of water). ‘More than 98%’ was used as a default for 100% due to a lack of height measurements on the steep banks, from which greater accuracy could be obtained. This tide height was then used as the ‘cut-off’ height, above which the zone is considered A) covered or B) unavailable for feeding.

For most of the patches the ‘cut-off’ is below Mid High Water (MHW) so that the entire zone is unavailable for feeding by MHW. The exceptions are patches 4 and 5 at Lauderdale where at MHW 95% of zone 4 and 80% of zone 5 are covered by water. In these patches we have assumed that there is little foraging habitat available above MHW. The height at which the site-specific MHW line (from bathymetry map and tidal data) is covered by 120 mm of water was then used as the limit above which no food is available to the Pied Oystercatchers.

The relationship between proportion of area exposed/available for feeding and tidal depth was examined by manipulating areas with GIS software (MapInfo Professional Version 8.5). It was found to be close to a linear relationship and was therefore approximated to be such to avoid the hugely complex data tables which would result from more complex relationship formulae.

BTO Research Report No. 515 8 November 2008 Tables of depth over time generated by Dr John Hunter, along with the average rate of area change against depth, the minimum tide and the ‘cut-off’ tide (see above) were then used to create a spreadsheet for each bay. Each spreadsheet consisted of a date, time (in 1 hour intervals), tide height, proportion of Area A exposed, and proportion of Area B available for feeding. The data covered the period from the beginning of 2006 to the end of 2008, with each year having its own spreadsheet.

Oyster/mussel patches were identified in the field at Lauderdale, Pipeclay Lagoon and South Arm Neck. These zones were treated as flat surfaces for the purpose of the models, such that they were either 100% exposed/available for feeding or 0% exposed/available for feeding.

BTO Research Report No. 515 9 November 2008

Figure 2.2.1 Bathymetry maps for each bay: a) Five Mile Beach; b) Mortimer Bay; c) Barilla Bay; d) South Arm Neck; e) Orielton Lagoon; f) Lauderdale; and g) Pipeclay Lagoon. A 500 m scalebar has been included in the map for each bay.

BTO Research Report No. 515 10 November 2008 2.3 Calculation of the Energy Content of the Invertebrate Prey (Ash-Free Dry Mass Measurement)

2.3.1 Introduction

To calculate a bird's energy intake it is necessary to calculate the amount of organic material it is ingesting. It is not possible to estimate this using fresh organisms due to the differing amounts of water and inorganic salts contained in the fresh organism. The ash-free dry mass (AFDM) is the amount of dry organic matter minus the mass of inorganic salts and is a more accurate estimate of diet required for the model than numbers of prey individuals consumed. For each of the main prey species an AFDM-length relationship is required to calculate the biomass density at each sampling site. It is also needed to calculate the potential intake rate of the birds in the model as this depends on the mean AFDM of the prey they are eating.

2.3.2 Ash-free dry mass estimation

The individual prey animals used to derive these relationships were collected during the invertebrate survey (Aquenal 2008a). For each species, the aim was to collect 20 individuals from each site in each season. For low density species this was not always possible; sample sizes are shown in Table 2.3.1. Methods for collection and laboratory processing of AFDM samples are described in Aquenal (2008a). Mussels, oysters and the gastropod Salinator fragilis were only identified as important prey in a subset of sites and hence were only collected from those sites.

Depending on local conditions, the relationship may well be different between sites and seasons. We therefore used an information theoretic approach (Akaike Information Criterion – AIC) to determine whether it was necessary to include site or seasonal factors into the models. AIC is a tool for model selection which attempts to find the model that best explains the data with a minimum number of parameters. It rewards improved goodness of fit, but also includes a penalty that is an increasing function of the number of estimated parameters. This penalty discourages overfitting. The preferred model is the one with the lowest AIC value.

We therefore ran AFDM-length models and included all permutations of site factor, season factor and site*length and season*length interaction terms, thus nine models in total. To select the most parsimonious model, AICc (AIC corrected for small sample size) was calculated and the models ranked by this value. AIC is a measure of the goodness of fit of an estimated statistical model and describes the trade-off between the precision and complexity of the model. It is not a test of the model in the sense of hypothesis testing, rather it is a tool for model selection (Burnham & Anderson 2002). The one with the lowest AICc was selected as the 'best' model and the parameters used to derive the ln(AFDM) – ln(length) relationships. This relationship was back-transformed and the error that is introduced by back-transforming predicted loge AFDM values was countered by adding half the regression error mean square (EMS) to the logged AFDM value before it was transformed back to a predicted AFDM.

2.3.3 Results

In all cases there was significant variation in the length-AFDM relationship between sites (Table 2.3.2) and significant variation between seasons for those species which were collected in all three seasons. Samples of Mytilus galloprovincialis, S. fragilis and Crassostrea gigas were only collected in season three (winter) at sites where it became apparent that the birds were taking these prey. Bay*length interaction terms were significant for Anapella cycladea and M. galloprovincialis and season*length interactions were significant for Katylesia scalarina and the three polychaetes (Leitoscoloplos normalis, Nephtys australiensis, Olganereis edmonsi). The model selection tables are presented in Table 2.3.3, parameter estimates of the preferred model in Table 2.3.4 and plots of the relationships in Figure 2.3.1.

BTO Research Report No. 515 11 November 2008 Model fit of the preferred models was generally good or very good. For the bivalves, the R2 values were greater than 0.9 for three species but lower in C. gigas. For an encrusting thick-shelled species such as this, length probably varies more in relation to AFDM than thinner shelled species. There was more unexplained variation in the polychaetes, which was expected given their susceptability to fragmentation (although every effort was made to use unbroken worms where possible), but the R2 were acceptable and were in the order of 0.6 to 0.7. Perhaps surprisingly, given the ease of measurement, the poorest fit was obtained for the gastropod S. fragilis.

Although these relationships are sufficient to enable translation of the density of each different invertebrate group into biomass, due to the nature of the sampling it was not possible to sample every species group in each site and season. To overcome this, the average relationships together with the R2 values are presented in Table 2.3.5. These may be used to estimate the biomass available for species found on the benthic invertebrate survey where we do not have site or season specific data. The fits, as expected, are poorer but still explain over a third of the variation in the data in all cases. The fits for the bivalve species K. scalarina, M. galloprovincialis and A. cycladea are all extremely good.

One issue was that in the foraging surveys (Section 2.4) it was not possible to conclusively identify the polychaetes being consumed. Two species (N. australiensis and L. normalis) had similar relationships but O. edmonsi were longer and thinner (Figure 2.4.1).

BTO Research Report No. 515 12 November 2008 Figure 2.3.1 Plots of the transformed Ash Free Dry Mass (AFDM) vs length of the eight invertebrate groups studied in this report.

-1 Katelysia scalarina Anapella cycladea -2 0 -3 -2 -4

-4 -5

ln(AFDM) (g) ln(AFDM) (g) ln(AFDM) -6 -6 -7

-8 -8 1.5 2.0 2.5 3.0 3.5 4.0 1.41.61.82.02.22.42.62.83.03.23.43.6 ln(Length) (mm) ln(Length) (mm)

2 2 Mytilus galloprovincialis Crassostrea gigas 1 1 0 0 -1 -1 -2

ln(AFDM) (g) ln(AFDM) (g) ln(AFDM) -2 -3

-4 -3

-5 ln(Length)-4 (mm) 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 3.23.43.63.84.04.24.44.6 ln(Length) (mm) ln(Length) (mm)

0 -2 Leitoscoloplos normalis Nephtys australiensis -3 -2 -4

-4 -5

-6 -6

ln(AFDM) (g) ln(AFDM) (g) ln(AFDM) -7 -8 -8

-10 -9 2.02.53.03.54.04.55.0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 ln(Length) (mm) ln(Length) (mm)

-1 -2.4 Olganereis edmonsi Salinator fragilis -2 -2.6 -3 -2.8 -3.0 -4 -3.2 -5 -3.4 -6

ln(AFDM) (g) ln(AFDM) (g) ln(AFDM) -3.6 -7 -3.8 -8 -4.0 -9 -4.2 2.02.53.03.54.04.55.05.5 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 ln(Length) (mm) ln(Length) (mm)

BTO Research Report No. 515 13 November 2008 Table 2.3.1 Number of individuals sampled for AFDM measurements at the seven sites and in the three seasons. Crassostrea gigas, Mytilus galloprovincialis and Salinator fragilis were only identified as prey items at three sites.

Anapella Crassostrea Katelysia Leitoscoloplos Mytilus Nephtys Olganereis Salinator Season Site cycladea gigas scalarina normalis galloprovincialis australiensis edmonsi fragilis Spring 2006 Lauderdale 43 42 21 42 Mortimer Bay 21 21 5 South Arm Neck 6 Pipeclay Lagoon 21 12 21 21 4 Five Mile Beach Barilla Bay 21 21 21 Orielton Lagoon Summer 2007 Lauderdale 42 42 27 41 21 Mortimer Bay 1 19 3 21 South Arm Neck 21 10 21 21 21 Pipeclay Lagoon 21 1 3 12 21 Five Mile Beach 21 14 21 Barilla Bay 22 4 12 21 Orielton Lagoon 1 4 21 Winter 2007 Lauderdale 42 22 36 39 22 42 42 42 Mortimer Bay 3 21 5 21 21 South Arm Neck 21 51 21 21 50 21 21 21 Pipeclay Lagoon 21 24 21 21 22 21 21 21 Five Mile Beach 21 21 21 1 21 Barilla Bay 21 19 21 21 21 Orielton Lagoon 21 16 21 21 Grand Total 364 97 304 298 94 390 246 84

BTO Research Report No. 515 14 November 2008

Table 2.3.2 Parameters that were included in the preferred models for each species group and the amount of variation explained by the model (R2).

Parameter site* season* R2 Species Group length site season length length Katelysia scalarina X X X X 0.955 Anapella cycladea X X X X 0.939 Crassostrea gigas X X 0.793 Mytilus galloprovincialis X X X 0.922 Leitoscoloplos normalis X X X X 0.593 Nephtys australiensis X X X X 0.732 Olganereis edmonsi X X X X 0.687 Salinator fragilis X X 0.519

BTO Research Report No. 515 15 November 2008 Table 2.3.3 Selection of the preferred model for each species. The nine models were ranked by AICc and the one with the lowest AICc chosen as the preferred model.

Katelysia scalarina Model Number Model Structure Deviance Parameters (N) AICc 1 length site season season*length -67.49 12 160.05 2 length site season -70.48 10 161.72 3 length site site*length season -65.55 15 162.78 4 length site site*length season season*length -63.91 17 163.97 5 length site site*length -84.17 12 193.42 6 length site -92.48 7 199.35 7 length season season*length -93.82 6 199.92 8 length season -97.48 4 203.10 9 length -131.69 1 265.40

Anapella cycladea Model Number Model Structure Parameters (N) 1 length site site*length season 35.17 17 -34.56 2 length site site*length season season*length 35.39 19 -30.56 3 length season season*length 12.28 6 -12.32 4 length season 9.09 4 -10.07 5 length site season 14.08 11 -5.40 6 length site season season*length 15.87 13 -4.69 7 length site site*length 6.19 14 16.82 8 length -17.19 1 36.40 9 length site -13.99 8 44.39

Crassostrea gigas Model Number Model Structure Parameters (N) 1 length site -54.83 4 118.10 2 length site season -54.83 4 118.10 3 length site season season*length -54.83 4 118.10 4 length site site*length -54.75 6 122.43 5 length site site*length season -54.75 6 122.43 6 length site site*length season season*length -54.75 6 122.43 7 length -73.26 1 148.57 8 length season -73.26 1 148.57 9 length season season*length -73.26 1 148.57

Mytilus galloprovincialis Model Number Model Structure Deviance Parameters (N) AICc 1 length site site*length -19.36 6 51.68 2 length site site*length season -19.36 6 51.68 3 length site site*length season season*length -19.36 6 51.68 4 length site -29.2 4 66.84 5 length site season -29.2 4 66.84 6 length site season season*length -29.2 4 66.84 7 length -58.66 1 119.37 8 length season -58.66 1 119.37 9 length season season*length -58.66 1 119.37

Continued…./

BTO Research Report No. 515 16 November 2008 Leitoscoloplos normalis Model Number Model Structure Deviance Parameters (N) AICc 1 length site season season*length -362.34 13 751.96 2 length site site*length season season*length -357.03 19 754.80 3 length site season -367.23 11 757.39 4 length site site*length season -361.22 17 758.65 5 length site site*length -380.20 14 789.90 6 length site -387.71 8 791.92 7 length season season*length -409.91 6 832.10 8 length season -416.23 4 840.60 9 length -427.19 1 856.39

Nephtys australiensis Model Number Model Structure Deviance Parameters (N) AICc 1 length site season season*length -289.55 13 606.08 2 length site site*length season season*length -286.73 17 609.12 3 length season season*length -308.75 6 629.72 4 length site season -325.71 11 674.13 5 length site site*length season -322.50 15 676.30 6 length season -343.08 4 694.27 7 length site site*length -354.71 12 734.26 8 length site -359.74 8 735.86 9 length -372.53 1 747.07

Olganereis edmonsi Model Number Model Structure Deviance Parameters (N) AICc 1 length site season season*length -218.69 13 464.95 2 length site season -223.80 11 470.72 3 length site site*length season season*length -216.49 19 474.34 4 length site site*length season -219.64 17 475.97 5 length season season*length -244.14 6 500.63 6 length season -248.06 4 504.29 7 length site site*length -245.28 14 520.38 8 length site -256.40 8 529.40 9 length -272.17 1 546.36

Salinator fragilis Model Number Model Structure Deviance Parameters (N) AICc 1 length site -0.16 4 8.82 2 length site season -0.16 4 8.82 3 length site season season*length -0.16 4 8.82 4 length site site*length -0.08 6 13.24 5 length site site*length season -0.08 6 13.24 6 length site site*length season season*length -0.08 6 13.24 7 length -6.71 1 15.47 8 length season -6.71 1 15.47 9 length season season*length -6.71 1 15.47

Table 2.3.3 Continued.

BTO Research Report No. 515 17 November 2008 Table 2.3.4 Parameter estimates of the preferred models.

Katelysia Anapella Mytilus Crassostrea Leitoscoloplos Nephtys Olganereis Salinator scalarina cycladea galloprovincialis gigas normalis australiensis edmonsi fragilis Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Estimate SE Intercept -12.381 0.198 -11.016 0.202 -9.572 0.647 -11.987 0.864 -10.072 0.443 -11.558 0.280 -9.770 0.305 -8.775 0.630

Site Lauderdale 0.372 0.074 -1.892 0.397 -3.471 0.874 0.108 0.138 -0.888 0.212 0.045 0.097 -0.237 0.157 0.249 0.066 Mortimer Bay 0.131 0.079 -0.906 1.072 -1.116 0.353 0.197 0.106 0.381 0.186 South Arm Neck 0.304 0.092 -2.035 1.054 -1.750 0.792 -0.545 0.120 0.448 0.230 0.479 0.113 -0.307 0.169 0.176 0.076 Pipeclay Lagoon 0.267 0.086 -0.326 0.460 0.000 0.000 0.000 0.000 -0.970 0.232 -0.014 0.112 -0.768 0.169 0.000 0.000 Five Mile Beach 0.034 0.086 -2.140 0.518 -1.151 0.229 1.244 0.519 -0.066 0.186 Barilla Bay 0.000 0.000 0.197 0.320 -0.916 0.226 -0.070 0.105 -0.041 0.198 Orielton Lagoon 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Season Spring 2006 -0.044 0.304 3.282 0.809 4.079 0.432 2.895 0.899 Summer 2007 0.447 0.309 1.671 0.664 2.858 0.388 2.352 0.511 Winter 2007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Length 3.080 0.069 2.639 0.081 2.166 0.167 2.836 0.201 1.778 0.133 1.990 0.080 1.406 0.081 2.072 0.251

Site*Length Lauderdale 0.625 0.140 1.031 0.227 Mortimer Bay 0.274 0.367 South Arm Neck 0.666 0.341 0.375 0.201 Pipeclay Lagoon 0.089 0.160 0.000 0.000 Five Mile Beach 0.716 0.180 Barilla Bay -0.103 0.120 Orielton Lagoon 0.000 0.000

Season * Length Spring 2006 0.112 0.100 0.258 0.033 -0.763 0.249 -1.133 0.135 -0.535 0.270 Summer 2007 -0.173 0.105 0.044 0.028 -0.387 0.215 -0.713 0.118 -0.455 0.162 Winter 2007 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

BTO Research Report No. 515 18 November 2008

Table 2.3.5 Parameter estimates for the average AFDM-length model with no site or seasonal effects.

Length parameter R2 Species group Intercept estimate Katelysia scalarina -12.1661 3.1079 0.931 Anapella cycladea -11.5713 2.8439 0.918 Crassostrea gigas -13.5375 3.1534 0.698 Mytilus galloprovincialis -10.6342 2.4295 0.820 Leitoscoloplos normalis -9.4119 1.4481 0.369 Nephtys australiensis -9.4132 1.4585 0.589 Olganereis edmonsi -8.4273 1.0523 0.513 Salinator fragilis -8.8112 2.1541 0.436

BTO Research Report No. 515 19 November 2008

2.4 Foraging Studies

2.4.1 Introduction and methods

The foraging survey was carried out for two reasons. First, it was important to determine the make up of the prey Pied Oystercatchers were eating to (a) identify the key prey species and (b) validate the prey choices made by Pied Oystercatchers in the model. Second, the foraging surveys estimated the rate of energy intake by Pied Oystercatchers which, again, could validate the estimates provided by the model. The methodology and results of the foraging surveys are provided in Harrison (2008) and should be read in conjunction with this report. The foraging surveys determined the relative contribution of each prey type to the diet of Pied Oystercatchers in numeric terms. There will, however, be a great deal of variation in the biomass of each different prey type and numeric relationships are not sufficient to determine the relative proportion of the intake of biomass comprised by each prey species. For example worms contain far less biomass than larger bivalves. Conversion of these results into ash-free dry mass (AFDM), i.e. the amount of dry organic matter ingested minus the mass of inorganic salts, is a much better estimate than numbers of individuals consumed. Calculating AFDM is a labour-intensive process and we, therefore, determined the relationship between the length of each species type and it’s AFDM (Section 2.3 in this report). During the foraging surveys, the length of each item ingested was estimated and the length-AFDM relationships used to calculate the amount of food ingested by the birds. All of the individuals sampled during the benthic invertebrate survey (Aquenal 2008a) were measured as well and, therefore, comparisons could be made between what food was available and what was taken (Harrison 2008).

A total of 20 prey species were identified during the foraging surveys (Harrison 2008). Polychaete worms and two species of bivalve (Katelysia scalarina and Anapella cycladea) accounted for approximately 90% of prey consumed in numeric terms. This varied little seasonally - winter = 91%, spring = 87%, and summer = 90%. Inclusion of additional less common benthic infauna bivalves, as well as the gastropod Salinator fragilis and epibenthic bivalves Crassostrea gigas and Mytilus galloprovincialis, meant that data input to the model accounted for 98% of food items. Each item consumed was measured, or estimated in relation to the bill length of the oystercatcher, to determine its length in 5mm categories.

To convert the prey resource types into AFDM we used the ‘best fit’ models (see section 2.3) where possible, but where the resource was not sampled at a particular site, or in a particular season, we used the relationship that was averaged across all sites. This was the case in <5% of samples. For polychaetes, it was not possible to identify species in the foraging survey. On the basis of invertebrate survey data, three species (Nephtys australiensis, Leitoscoloplos normalis, Olganereis edmonsi) were primary candidates and we, therefore, used an average length-AFDM relationship for these. Two species (N. australiensis and L. normalis) had similar length-AFDM relationships (Figure 2.4.1) whereas O. edmonsi were longer and thinner than the previous two species and had a lower AFDM per unit length. We, therefore, used an average AFDM for each size class across all three species. We only included a species in the average if individuals up to the length had been recorded in the benthic invertebrate survey (Aquenal 2008a).

2.4.2 Results

At all seven sites, bivalves made up the majority of the diet expressed as AFDM, being over 70% in all cases and >90% at three sites (Table 2.4.1). Despite polychaetes numerically making up the largest part of the diet, in terms of AFDM they contributed relatively little to the diet and never exceeded 30% of the AFDM consumed and averaged only 15% across all sites. Gastropods made up no more than 3% of the AFDM consumed at any site.

In terms of overall diet, birds predominantly consumed two species of bivalves. The largest contributor was K. scalarina, which on average was consumed at twice the rate of any other prey species on the basis of AFDM (Table 2.4.2). A. cycladea was second at approximately 50% of the rate

BTO Research Report No. 515 20 November 2008

of K. scalarina. Mussels and oysters contributed very little to the overall diet. There was some seasonal variation with a wider variety of prey being taken in summer. In winter, in terms of the main prey species included in the model, the diet was predominantly made up of K. scalarina, A. cycladea (these two comprising >90% of the diet) and polychaetes (Figure 2.4.2).

Lauderdale was the site with the highest intake rate, at approximately 6g per hour (Figure 2.4.3), as well as the highest average number of birds. Orielton Lagoon and Mortimer Bay had intake rates of approximately 80% of that at Lauderdale. South Arm Neck and Pipeclay Lagoon had intake rates of about 60% of Lauderdale and the remaining sites had intake rates of <40% that of Lauderdale. Lauderdale was, therefore, the key site for Pied Oystercatchers and this was reflected in the number of birds using the site (Aquenal 2008b).

Within Lauderdale, the key prey type was the Katylesia group (see section 2.5.4 for definition of groups) which made up 64-82% of the diet across the three seasons, as measured by the mean of the AFDM intake rates across patches in each season (Table 2.4.3). Intake rates were highest in the mussel patch (Patch 6) at Lauderdale, followed by patch 4 (Figure 2.4.4). Intake rates were similar in patches 1, 2 and 5. The patches to be removed by the proposed development (i.e. patches 1, 2, 6 and part of patch 3) include one of the key feeding areas in the site. While the benthic invertebrate survey report did not note a particularly high abundance of K. scalarina in the southern part of Lauderdale (patches 4 and 5) (Aquenal 2008a), the higher intake rates in patch 4 can be explained by a number of ‘other bivalves’ (most notably Tellina deltoidalis) which contributed to the Katylesia group of bivalves.

Table 2.4.1 The percentage make up (expressed as % of total AFDM) of Pied Oystercatcher diet at the seven study sites in terms of bivalves, polychaetes and gastropods.

Site %bivalves %gastropods %polychaetes Lauderdale 95 0 4 Mortimer Bay 91 0 9 South Arm Neck 80 3 17 Pipeclay Lagoon 77 0 23 Five Mile Beach 81 0 19 Barilla Bay 70 1 30 Orielton Lagoon 94 0 6

Table 2.4.2 Mean AFDM intake rate per 10 minutes for each of the 7 sites across seasons.

Site Anapella Crassostrea Katelysia Mytilus Polychaetes Salinator Total cycladea gigas scalarina galloprovincialis fragilis (g AFDM per 10 minutes) Lauderdale 0.179 0.005 1.097 0.054 0.062 0.006 1.403 Mortimer Bay 0.099 0.004 0.89 0.003 0.099 0 1.095 South Arm Neck 0.103 0.01 0.489 0.139 0.154 0.031 0.926 Pipeclay Lagoon 0.161 0.058 0.383 0.028 0.183 0 0.813 Five Mile Beach 0.33 0 0.089 0 0.1 0 0.519 Barilla Bay 0.106 0 0.282 0 0.165 0.003 0.556 Orielton Lagoon 0.704 0 0.447 0 0.076 0 1.227 Mean 0.240 0.011 0.525 0.032 0.120 0.006

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Table 2.4.3 Mean AFDM intake per 10 minutes during foraging observations broken down by patch and season.

Anapella Crassostrea Katelysia Mytilus Salinator Number Season Site Patch cycladea gigas scalarina galloprovincialis Polychaetes fragilis of observations Winter 2007 Lauderdale 1 0.0792 0 1.5843 0 0.1099 0 11 7/8/2007 2 0.176 0 0.94 0 0.0329 0 20 -1/9/2007 3 0.0204 0 1.029 0 0.0517 0 19 4 0 0 1.4319 0 0.0576 0.0173 20 5 0.1022 0 0.6231 0 0.1265 0 20 6 0.1122 0.1041 1.9601 0.7272 0 0 9 Mortimer Bay 1 0.0229 0 1.2779 0 0.1713 0 20 2 0.0115 0.0146 0.386 0.0121 0.0226 0 20 South Arm Neck 1 0.011 0 0.284 0 0.083 0 14 2 0.0072 0 0.0424 0.1125 0.3284 0.0366 20 3 0 0.0549 0.1738 0.2979 0.1655 0 20 4 0 0 0.5133 0 0.1245 0 20 5 0.0373 0 0.6032 0 0.0375 0.018 20 6 0 0 0.0607 2.7352 0.0052 0 6 Pipeclay Lagoon 1 0.2125 0 0 0 0.1185 0 20 2 0 0 0 0 0.1453 0 20 3 0.1229 0 0.0734 0 0.0459 0 20 Five Mile Beach 1 0.2561 0 0.048 0 0.0806 0 20 Barilla Bay 1 0.0591 0 0.6275 0 0.2601 0.0138 20 3 0.009 0 0.119 0 0.1427 0 20 Orielton Lagoon 1 0.3184 0 0.7865 0 0.0365 0 20 Spring 2007 Lauderdale 1 0.3225 0 0.2971 0 0.021 0 18 5/11/2008 2 0.016 0 0.8548 0 0.0076 0.0278 20 -23/11/2007 3 0.0289 0 1.129 0 0.03 0 20 4 0.2157 0 0.8007 0 0.1127 0 20 5 0 0 0.0723 0 0.1317 0 2 6 0 0.0885 0.7585 0.0258 0.0693 0 2 Mortimer Bay 1 0 0 0.4445 0 0.0363 0 20 2 0.0715 0 0.5963 0 0.0923 0 20 South Arm Neck 1 0.0078 0 0.1722 0 0.1293 0 16 2 0 0 0.5562 0 0.0115 0.0131 20 3 0.0423 0.0268 0.8309 0 0.0689 0.0276 20 4 0.0032 0 0.7567 0.0121 0.1008 0 20 5 0.0238 0 0.6557 0 0.0567 0 20 6 0 0.2733 0.4589 1.8429 0 0 4 Pipeclay Lagoon 1 0.0812 0 0.041 0 0.228 0 14 2 0.1765 0 0.0174 0 0.2094 0 20 3 0.1127 0 0.0368 0 0.215 0.0014 20 4 0 0.7778 0.1294 0.6088 0.0141 0 6 Five Mile Beach 1 0.2477 0 0.1589 0 0.0766 0 20 Barilla Bay 1 0 0 0.1795 0 0.0428 0 20 3 0.3276 0 0.1243 0 0.0651 0 20 Orielton Lagoon 1 0.5791 0 0.3075 0 0.0728 0 20 Summer 2008 Lauderdale 1 0.2537 0 0 0 0.0343 0 15 4/2/2008 2 0.2463 0 0.4446 0 0.0239 0 20 -4/3/2008 3 0.2327 0 1.1426 0 0.0266 0 20 4 0.1231 0 2.2217 0 0.0491 0 20 5 0.1659 0 0.2821 0 0.0952 0.0211 20 6 0.4998 0 0.5192 0.8458 0.0032 0 5 Mortimer Bay 1 0.0609 0 0.0918 0 0.0919 0 20 2 0.2279 0 0.8676 0 0.0072 0 20 South Arm Neck 1 0.0004 0 0.0421 0 0.1754 0.054 20 2 0.5675 0 0.1028 0 0.1627 0.0677 20 3 0.1282 0 0.0059 0 0.1121 0.0016 20 4 0.1976 0 0.7031 0 0.2728 0.1478 20 5 0.147 0 0.2106 0 0.145 0.0181 20 Pipeclay Lagoon 1 0.2081 0.0375 0.7104 0 0.2657 0 20 2 0.1365 0 0.4692 0 0.125 0 6 3 0.1667 0.1393 1.5801 0 0.066 0 20 Five Mile Beach 1 0.1634 0 0 0 0.0608 0 19 Barilla Bay 1 0.0816 0 0 0 0.1145 0 20 3 0.0052 0 0.3367 0 0.2073 0 20 Orielton Lagoon 1 0.8621 0 0.0166 0 0.0804 0 20

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Figure 2.4.1 Relationship between the length (mm) of three polychaete species and their ash free dry mass (g).

0.07

0.06

0.05

0.04

0.03 AFDM (g) 0.02 Leitoscoloplos normalis 0.01 Nephtys australiensis Olganereis edmonsi 0.00 0 20 40 60 80 100 120 140 160 180

Length (mm)

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Figure 2.4.2 Mean AFDM intake per 10 minutes for Pied Oystercatchers foraging at the 7 study sites by season and overall (a-d) and the proportion of the diet throughout the year made up of gastropods, bivalves and polychaetes.

0.7 Spring 0.7 Summer 0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3

0.2 0.2

0.1 0.1 AFDM intake 10 minutesAFDM per (g) AFDM intake per 10 minutes (g) minutes 10 per intake AFDM 0.0 0.0 s s s s na lis e li ga i a t i adea i dea l g la rag a inci hae fragili c alarina cyc calar c c tre s ly tor s lychaetes or f s prov o a a t o P n lla cy i Po so ysia i s na pella l ly ali a as e Sal assostrea tgigase at r a S An Cr K Anape C K tilus gall y M Mytilus galloprovincialis

0.7 Winter 0.7 Across all seasons 0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3

0.2 0.2

0.1 0.1 AFDM intake per 10 minutes (g) minutes 10 per intake AFDM AFDM intake 10 minutesAFDM per (g) 0.0 0.0 a a s s lis ilis e is e i ia t ag ial e clade gigas y calarina inc c ea gigas s ea cha tr r rovinc lla s a prov st ia scalarina oly o Polychaetes ella cyclad o s lop P pe p al na Salinator fr ass g Salinator fragil Crasso atelysi A K Ana Cr Kately us ilus gall til Myt My

1.0 87%

0.8

0.6

0.4

12% 0.2 Proportion of AFDM intake AFDM of Proportion 1% 0.0 Gastropods Bivalves Polychaetes

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Figure 2.4.3 Comparison of the mean intake rates for each site, expressed as a proportion of the site with the maximum intake rate.

1.0

0.8

0.6

0.4

(AFDM per 10 minutes) per (AFDM 0.2

0.0 le y n h y Proportion of maximum intake rate average o c a a B go e th Arm a B lla L e ri Lagoon y l a n Lauderdaortimer BaSou a Mi B M ecl ve ielto ip r P Fi O

Figure 2.4.4 Intake rates at Lauderdale by patch averaged across the three seasons (g per 10 minute bout +/- SE). Letters indicate similar means.

3 c

2.5

b,c 2

a,b 1.5

aa 1 a

0.5 Mean (±SE) AFDM intakemiunteper 10 bout 0 123456 Patch number at Lauderdale

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2.5 Parameterising The Model For The Pied Oystercatcher

The proposed development at Lauderdale could impact on Pied Oystercatchers in several ways, including loss of breeding habitat, destruction of nests, disturbance to breeding or foraging activity, loss of feeding habitat, increased predation due to an increase in cats and dogs, and loss or disturbance to roosting sites. The model addressed just one of these potential impacts, loss of feeding habitat. The purpose of the model was to predict whether, on the basis of available foraging resources alone, the proposed habitat loss from Lauderdale would decrease the survival or body condition of Pied Oystercatchers below that predicted in the absence of habitat loss. This section describes how the model was parameterised for Lauderdale and surrounding sites.

2.5.1 Single- and multi-site models

In order to determine whether the survival and body condition of Pied Oystercatchers were influenced by the movement of birds between sites, two versions of the model were developed. In the single-site model birds were not allowed to move between sites, and so the populations of birds on the different sites were independent. In the multi-site model birds were allowed to move between sites under certain conditions, and so the sites were not independent of one another.

2.5.2 Environmental parameters

2.5.2.1 Time period simulated

The model simulated an annual cycle from 1 September until 31 August. The model was parameterised with bird population, tidal and day length data (see below) from 1 September 2007 until 31 August 2008, and so included 29 February. Model simulations therefore ran for 366 days. The model was parameterised with intertidal invertebrate data collected between 1 September 2006 and August 2007.

The annual cycle was divided into three seasons, with mid-point dates approximately coinciding with the timing of the intertidal invertebrate surveys (Aquenal, 2008a). Season 1 ran from 1 September to 31 December (intertidal survey conducted 12 September to 11 October 2006), Season 2 from 1 January to 31 April (intertidal survey conducted 7 February to 6 March 2007) and Season 3 from 1 May to 31 August (intertidal survey conducted 6 June to 5 July 2007). Additionally, each season encompassed one of the Pied Oystercatcher foraging surveys conducted during 5 – 23rd November 2007 (Season 1), 4th February – 4th March 2008 (Season 2) and 7 August – 1st September 2007 (Season 3).

2.5.2.2 Time step length

Time was divided into one hour time steps, during each of which environmental conditions were assumed to remain constant. Birds were assumed to occupy a single patch, and consume a single diet during each time step, but could change patches and diets between time steps. The time of day of each model time step was that for the mid-point of the time step measured in Australian Eastern Standard Time.

2.5.2.3 Day length

Daylight was assumed to occur between sunrise and sunset. The times of sunrise and sunset each day were calculated for Lauderdale (42o 55’ S 147o 29’ E) from the US Naval Observatory website (aa.usno.navy.mil) which can calculate these values for any location on the Earth. All sites were assumed to have the same daily sunrise and sunset times as Lauderdale.

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2.5.2.4 Tidal cycle

The model incorporated the hourly variation in the area of intertidal habitat available to the birds due to the tidal and spring/neap cycles. Tidal data and patch exposure for each site were empirically determined by Aquenal over three years (see Section 2.2).

2.5.3 Patch parameters

2.5.3.1 Maximum patch area

The maximum area of each intertidal patch was empirically determined by Aquenal over the 2006-2008 study period (see Section 2.2). However, this maximum patch area would only be available to birds on a very small percentage of low tides (i.e. extreme spring low tides). To obtain a patch area more representative of that available to the birds on a typical low tide, the mean patch area exposed on low tides throughout the year was calculated. This mean low tide patch area was used to determine maximum patch areas in the model (Table 2.5.1).

Patch areas were calculated by either assuming that birds could not feed in areas covered by water (excluding birds’ foraging depth) or assuming that birds could feed up to the maximum observed foraging water depth of 120 mm (see below for details) (including foraging depth).

The roost patches were not given specific areas, but were assumed to be large enough to potentially contain all birds at each site, and were always available to the birds.

2.5.3.2 Patch area available to birds

The area of each patch available to birds during each time step was determined by Aquenal (see above). These data were used to parameterise the model, with the exception that patch area was prevented from exceeding mean low tide patch area (see above).

Patch availability was calculated by either assuming that birds could not feed in areas covered by water (excluding birds foraging depth) or assuming that birds could feed up to the maximum observed foraging water depth of 120 mm (including foraging depth) (Harrison, 2008).

The roost patches were assumed to always be available.

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Table 2.5.1 Patch areas calculated from the bathymetry study. The areas (ha) used in the model are quoted in terms of the mean patch area exposed across low tides. The maximum extent exposed on the lowest spring tides is also shown. For each of these, two areas are quoted depending on whether the model assumed birds could wade for food.

Site Patch Mean low tide Mean low tide Maximum Maximum patch area patch area extent extent Birds can wade for food? NO YES NO YES Lauderdale 1 16.21 16.64 30.35 31.48 2 16.39 16.94 30.69 32.04 3 28.29 28.53 52.99 53.97 4 9.79 9.75 18.34 18.45 5 15.41 15.15 27.18 27.18 6 (Mussel/oyster) 0.73 0.73 0.73 0.73 Mortimer 1 27.12 32.08 111.5 117.8 2 22.48 26.59 75.9 82.23 South Arm 1 22.56 26.98 103.2 112.6 Neck 2 25.59 29.78 66.71 73.74 3 29.14 31.97 75.98 79.15 4 16.74 19.35 51.52 55.35 5 25.94 33.04 79.83 94.5 6 (Mussel/oyster) 1.01 1.01 1.01 1.01 Pipeclay 1 35.41 34.71 58.85 59.26 Lagoon 2 20.42 21.13 33.94 36.07 3 67.12 70.34 127 134.4 4(Mussel/oyster) 0.39 0.39 0.39 0.39 5 38.14 47.25 90.34 107.7 Five Mile 1 45.69 57.54 117.8 139.6 Beach Barilla Bay 1 26.91 32.14 90.5 99.77 2 18.05 21.62 60.7 67.11 3 21.65 29.81 72.81 92.55 Orielton 1 8.27 12.65 13.99 23.58 Lagoon

2.5.4 Food resource parameters

Based on the results of the benthic invertebrate survey (Aquenal, 2008a), three species or species groups of polychaete, four species or species groups of bivalves and one gastropod were included in the model. In order to minimise the number of species groups in the model, less common species were combined with the more common species that was most similar in terms of size and food value to the birds. The following names were used to refer to the species and species groups used in the model: • Nephtys australiensis (plus other similar, less common polychaetes), • Leitoscoloplos normalis, • Olganereis edmonsi (plus other similar, less common polychaetes), • Anapella cycladea (plus other similar, less common bivalves), • Katelysia scalarina (plus other similar, less common bivalves), • Mytilus galloproviancialis, • Crassostrea gigas, • Salinator fragilis.

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2.5.4.1 Prey size classes

Based on the intertidal survey results, prey groups were divided into the following 5mm size classes (i.e. each ‘main prey’ species is indicated but includes additional grouped species). Anapella cycladea group: 10-14.9, 15-19.9, 20-24.9, 25-29.9, 35-39.9 mm Katelysia scalarinagroup: 10-14.9, 15-19.9, 20-24.9, 25-29.9, 30-34.9, 35-39.9, 40-44.9, 45-49.9 mm Salinator fragilis: 10-14.9 mm Nephtys australiensisgroup: 10-14.9, 15-19.9, 20-24.9, 25-29.9, 30-34.9, 35-39.9, 40-44.9, 45-49.9, 50-54.9, 55-59.9, 60-64.9, 65-69.9, 70-74.9, 75-79.9, 95-99.9 mm Leitoscoloplos normalis: 10-14.9, 15-19.9, 20-24.9, 25-29.9, 30-34.9, 35-39.9, 40-44.9, 45-49.9, 50-54.9, 55-59.9, 60-64.9, 65-69.9 mm Olganereis edmonsi group: 10-14.9, 15-19.9, 20-24.9, 25-29.9, 30-34.9, 35-39.9, 40-44.9, 45-49.9, 50-54.9, 55-59.9, 60-64.9, 65-69.9, 70-74.9, 75-79.9, 80-84.9, 85-89.9, 90-94.9, 95-99.9, 100-104.9, 105-109.9, 110-114.9, 115-119.9, 120-124.9, 125-129.9, 130-134.9, 135-139.9, 140-145.9, 155-159.9, 160-164.9, 205-209.9 mm Mytilus galloproviancialis: 20-24.9, 25-29.9, 30-34.9, 35-39.9, 40-44.9, 45-49.9, 50-54.9, 55-59.9, 60-64.9, 65-69.9, 70-74.9, 75-79.9, 80-84.9 mm Crassostrea gigas: 30-34.9, 35-39.9, 40-44.9, 45-49.9, 50-54.9, 55-59.9, 60-64.9, 65-69.9 mm

2.5.4.2 Numerical density of prey at start of each season

The numerical density of each prey species group on each patch at the start of each season was determined from the benthic invertebrate survey (Aquenal, 2008a). The invertebrate survey recorded the numbers of prey species within each size class from sampling stations located throughout each site. Initially, each of these sampling stations was associated with a model patch based on its location. The mean density of each prey species class within each patch during each season was then calculated.

The invertebrate survey did not record the losses or gains in prey species density due to factors other than the birds. However, overwinter reductions in the prey of Eurasian Oystercatcher Haematopus ostralegus can sometimes be substantial [Mytilus edulis (mussel) = 7% loss (Exe estuary, UK) (Stillman et al., 2000), 0-9mm Cerastoderma edule (cockle) = 60% loss (Burry Inlet, UK) (Stillman et al., 2001b), 10+mm Cerastoderma edule = 10% loss (Burry Inlet, UK) (Stillman et al., 2001b)]. The importance of loss due to factors other than the birds was investigated in a sensitivity analysis. In these simulations, the biomass of resource was reduced by half during each season.

2.5.4.3 Prey mass during each season

The mass of an individual of each prey species on each patch during each season was determined from the benthic invertebrate survey (Aquenal, 2008a). The survey measured the ash-free dry mass (AFDM) of a sample of prey individuals of varying size across all sites in each season. These data were analysed to derive site and season-specific relationships between prey species length and mass (see above). These relationships were used to predict the AFDM of individuals within each prey class in each site during each season. We used a bootstrapping technique to determine the sampling error. AFDM data from sampling stations within each patch were selected (with replacement) 999 times to provide 999 estimates of the total AFDM available to the birds. We calculated the median and 5th percentile of these

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values. In 95% of cases the total AFDM available to the birds would be greater than the 5th percentile.

2.5.4.4 Prey energy content

Prey energy content is the amount of energy (KJ) contained in 1g of prey flesh. The following energy densities were assumed based on published values: molluscs = 22 KJ -1 (Zwarts et al., 1996); polychaetes = 23.5 KJg ash-free dry mass-1 (Zwarts et al., 1996).

2.5.5 Bird parameters

2.5.5.1 Population size

Pied Oystercatcher numbers were recorded at each site during each season in the wader utilisation surveys (Aquenal, 2008b) and opportunistically during the foraging surveys (Harrison, 2008). These surveys derived two estimates of the mean number of birds present at each site during each season (termed ‘observed population sizes’ in the following text). The number of birds present within the model on each site during each season (Table 2.5.2) was set to the largest observed population size derived from either the wader utilisation survey or the foraging survey (e.g. if, for a particular site and season, more birds were recorded in the wader utilisation survey, then the number of birds in the model for this site and season would be set to the observed population size derived from the wader utilisation survey). It was not possible to determine from the survey data whether the same birds were present on a site in each season or whether some or all of the birds changed between seasons (e.g. whether the 186 birds present at Lauderdale during Season 2 were the 128 birds present in Season 1 plus another 58 birds, or whether they were all new birds). Furthermore, the survey data could not determine the amount of turnover of birds on sites within a season (e.g. whether the birds recorded during one day are the same birds recorded on the following day). The model would require this information to follow the movements of birds in a very detailed way, because it follows the behaviour and fate of individual birds throughout the annual cycle. Rather than make unsupported assumptions as to the proportion of birds in a site that changed between or within seasons it was decided to run simulations based on a constant number of birds in each site. Although this meant that the model ignored the patterns of movement between sites that are likely to occur, the model still simulated the observed number of birds present within each site during each season. Hence, the amount of food required to support the model population of birds was expected to be similar to the amount required to support the real population.

Table 2.5.2 Bird count data used to parameterise the model: number of Pied Oystercatchers occupying each site during each season. The figures for each site and season are derived from either the wader utilisation surveys or the foraging surveys. Each of these surveys estimated the mean number of birds on a site during each season. The maximum number estimated from either survey is presented. Model simulations assumed a constant number of birds on each site throughout the annual cycle. This number was either the mean or maximum of the seasonal values shown in the table.

Season 1 Season 2 Season 3 Mean Maximum Lauderdale 128 186 252 189 252 Mortimer Bay 22 72 32 42 72 South Arm Neck 105 148 218 157 218 Pipeclay Lagoon 60 68 58 62 68 Five Mile Beach 17 18 16 17 18 Barilla Bay 26 57 51 45 57 Orielton Lagoon 42 44 23 36 44

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2.5.5.2 Target body mass and starvation body mass

It was assumed that birds arrived at their target body mass and attempted to maintain this mass throughout the year. Birds died of starvation if their mass fell to their starvation mass. Target body mass was the mean mass of male and female Pied Oystercatchers (Marchant et al., 1993) (male mean = 641.7g, female mass = 710.0g, mean mass = 675.9g). As no seasonal data were available, birds were assumed to have the same target mass throughout the annual cycle. In reality, target body mass is likely to vary seasonally, but in the majority of simulations (see below) birds were able to maintain their body mass at their target and hence did not die of starvation. This means that the survival rate predicted by the model was not sensitive to the assumed target mass or whether or not target mass varies seasonally. Starvation masses have not been estimated for Pied Oystercatchers and so were assumed to be the same proportion (0.64) of target mass as observed in Eurasian Oystercatchers (starvation mass of Pied Oystercatcher = 432.5g). Given the morphological similarity between these species, we believe that this is a reasonable assumption.

2.5.5.3 Energy density of bird reserves

Energy density is the amount of energy (KJ) contained in one gram of bird fat reserves and was assumed to be 33.4 KJ g-1 (Kersten et al., 1987). Although this estimate was not derived for Pied Oystercatchers, it is a value that has frequently been used in models of European waders. Bird energy density and prey energy content influenced how birds gained weight. For example, if 1g of mollusc flesh was assimilated, only 22/33.4g of extra fat would be stored because fat can store the energy more efficiently than the mollusc flesh.

2.5.5.4 Metabolic rate

The amount of energy expended per time step by birds was based on body mass using the all bird equation of Nagy (1999). This equation excludes the energy cost of thermoregulation (as it is based on average energy expenditure).

2.5.5.5 Time and energy cost of moving between patches

For simplicity it was assumed that no time and energy costs were associated with moving between patches. If, in reality, birds frequently move between sites, the model will underestimate the time and energy costs of the real birds. However, the standard simulations predicted that birds at Lauderdale could survive without moving to other sites (see below), implying that frequent movements were unlikely to be driven by limitation of food resources (although other factors may cause such movements).

2.5.5.6 Size ranges of prey diets consumed by the birds

Based on the foraging survey (Harrison, 2008), the Nephtys australiensis group, Leitoscoloplos normalis and the Olganereis edmonsi group were aggregated into a single polychaete diet as these prey could not be distinguished in the foraging observations. Based on observations during the foraging survey (Harrison, 2008), the following size classes of each prey group were assumed to be consumed by the birds. Birds were assumed to consume prey from a single diet type during each time step. • Anapella cycladea group: 10-29.9 mm • Katelysia scalarina group: 10-49.9 mm • Salinator fragilis: 10-14.9 mm • Polychaetes: 10-199.9 mm • Mytilus galloproviancialis: 20-84.9 mm • Crassostrea gigas: 30-69.9 mm

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2.5.5.7 Individual variation

Birds were assumed to vary in their foraging efficiency (normal distribution), which influenced the rate at which birds consumed food in the absence of competitors, and dominance (uniform distribution), which influenced a bird’s susceptibility to interference from competitors. The standard deviation of foraging efficiency 0.125 (mean=1) was the average observed in Eurasian Oystercatchers on the Exe estuary, UK (Stillman et al., 2000).

2.5.5.8 Day and night variation in foraging efficiency

Foraging efficiency in Eurasian Oystercatchers is sometimes lower at night than during the day. Foraging efficiency of Eurasian Oystercatchers consuming Mytilus edulis (mussels) has been shown to be the same by day and night (Sitters, 2000), but night time foraging efficiency of oystercatchers consuming Cerastoderma edule (cockles) has been shown to be 61.5% of the day time value (Stillman et al., 2000). The foraging survey (Harrison, 2008) indicated that night time feeding rates of Pied Oystercatchers were approximately 50% of the day time rate, and so night time foraging efficiency was assumed to be 50% of the day time value.

2.5.5.9 Interference competition

Interference competition for food in an important component in any oystercatcher model. As the density of birds increases so will the likelihood that individuals will become territorial and exclude other birds from patches of food. Stillman et al. (2003) illustrated this in a real world test of the model on the Wash, England. Oystercatchers ate mussels Mytilus edulis and cockles Cerastoderma edule at this site and during winters of low food densities, birds were both observed (in the field) and predicted (in the model) to die when only a fraction of the available food was consumed. Within the model at least, this was because interference competition excluded the least dominant birds from part of the food supply and the least efficient foragers died before the food supply was fully depleted. A simplified model, which excluded interference and individual variation, was applied to this system and incorrectly predicted that all birds survived in all years. Models that exclude these two components of behaviour underestimated the effect of mussel and cockle food shortage on oystercatchers. Shellfishery management incorrectly based on such predictions may cause high oystercatcher mortality rates even though enough food would appear to be reserved for the birds.

Interference was incorporated using standard equations (Triplet et al., 1999; Stillman et al., 2005a). Interference competition was assumed to reduce intake rate above a threshold density of 100 birds ha-1 (Stillman et al., 2005a). Above this threshold intake rate decreased with increasing bird density at a rate depending on the prey species and the dominance of a bird (more interference for less dominant birds). For simplicity, it was assumed that the strength of interference was relatively high in mollusc-feeding birds, being the same as that between Cerastoderma edule (cockle)-feeding birds. Interference for these prey was assumed to occur because of prey stealing and so was stronger in more sub-dominant birds that will suffer more from such aggression. Interference in polychaete-feeding birds was assumed to be due to the polychaetes retreating into their burrow when disturbed by birds, with a strength measured in Common Redshank (Tringa totanus), the only system for which such data have been recorded (Yates et al., 2000). This form of interference was assumed to influence all birds equally, regardless of their dominance. Aggregation factors, which measured the fact that birds are not spread evenly over the feeding grounds, but usually aggregated, were assumed to be 10, the value observed in Eurasian Oystercatchers feeding on intertidal sand flats (Stillman et al., 2000; Stillman et al., 2005a). The way in which interference was incorporated into the model was consistent with the approach used for models of European waders. We had no reason to expect that these relationships were inappropriate for Pied Oystercatcher given the similarity in the behaviour of Pied and Eurasian Oystercatchers, and similarities in their prey species.

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2.5.5.10 Functional response

The functional response is the relationship between prey density and the rate at which prey are consumed. The functional responses in the model were based on body mass using the equations in Goss-Custard et. al.(2006) which have been derived for a wide range of wading bird species.

2.5.5.11 Maximum intake rate

Maximum intake rate was based on the maximum daily energy assimilation calculated from body mass using standard equations (Kirkwood, 1983). This assumed that birds could achieve this maximum value by feeding for just 50% of the day to allow them, if possible, to consume their daily requirements from intertidal prey alone. This maximum limited the maximum amount of food a bird could consume within a time step.

2.5.5.12 Assimilation efficiency

Assimilation efficiency is the proportion of the energy within the prey consumed by a bird that is assimilated into the bird’s body. The values used for polychaetes and molluscs were the same as those used in previous studies: polychaetes = 0.75; molluscs = 0.85 (Stillman et al., 2005a).

2.5.5.13 Decision rules

Birds’ decision rules depended on their previous foraging success and, in the case of the multi-site model, their body mass.

In both the single and multi-site models, it was assumed that birds moved to patches and consumed diets that maximised their rate of energy assimilation unless this maximum rate was less than the average they had achieved over the last 24 hours (Kersten et al., 1996), in which case they moved to the roost. In the single site model, birds could only move to patches on their current site.

In the multi-site model, birds with relatively good body condition (body masses greater than 75% of their target body mass) adopted the same decision rules as birds in the single-site model, and could only move to patches on their current site. In contrast, birds with relatively poor body condition (body masses less than 75% of their target body mass) were able to move to patches on other sites.

For simplicity, it was assumed that birds did not suffer any time or energy costs when moving between sites.

2.5.6 Modelling habitat loss

Two sets of simulations were run to determine the consequences for Pied Oystercatcher of reduced foraging resources as a result of habitat loss from Lauderdale.

In the partial habitat loss simulations, the amount of habitat loss as a direct result of the proposed development at Lauderdale (Figure 2.5.1) was removed from the model. This involved completely removing patches 1, 2 and 6, and removing 43% of patch 3.

In the complete habitat loss simulations, it was assumed that the proposed development would adversely affect the whole of Lauderdale and so all Lauderdale patches were removed from the model. In these simulations the model predicted whether adequate food was available at other sites for Pied Oystercatchers displaced from Lauderdale.

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Figure 2.5.1 Proposed amount of habitat to be lost from Lauderdale (shaded area incorporating patches 1, 2, 6 and part of patch 3).

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2.5.7 Summary of the parameterised model

The model (Figure 2.5.2) followed the foraging decisions (i.e. patch and prey choice) of each Pied Oystercatcher, as they attempt to meet their daily energy requirements. The model included the successive exposure and covering of intertidal patches through the tidal cycle, and also included the day / night cycle to account for the possibility that bird behaviour may differ between night and day. The model divided time into a sequence of time steps, during each of which birds either moved to the patch on which their rate of assimilating energy was greatest, or roosted (and did not feed) if no patches were available or if only relatively poor quality patches were available. The density and biomass of intertidal invertebrate food varied between sites and patches, as did the exposure of patches through the tidal cycle. Habitat loss from Lauderdale was simulated by either partial (partial habitat loss simulations) or complete (complete habitat loss simulations) loss of intertidal patches on the site. The model predicted the distribution of birds between sites and patches, which prey species were consumed by the birds, how much time birds needed to feed for to meet their requirements, the body mass of birds and the percentage of birds that survived.

In Figure 2.5.2, a map of each site is shown on the left (with 500m horizontal scale bars), with locations approximating those in the real system (top left: Barilla Bay; top: Five Mile Beach; top right: Orielton Lagoon; centre: Lauderdale; bottom left: South Arm Neck; bottom: Mortimer Bay; bottom right: Pipeclay Lagoon). Land is displayed in green and the sea in white. Intertidal patches are displayed in the same colours as in Aquenal (2008a). Roosts are displayed as grey circles. Each bird is displayed as a small black circle either on an intertidal patch or a roost. Intertidal patches are displayed as white when they are covered by the tide (e.g. leftmost patch on South Arm Neck). Variables associated with the simulation as a whole, patches, resources, bird diets and the birds themselves are displayed on the right. Various graphical displays of simulation predictions can also be obtained by clicking the tabs to the top right. Simulation execution can be controlled by using the buttons to the bottom right.

Figure 2.5.2 Screenshot of the model.

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3. MODEL PREDICTIONS OF THE EFFECT OF THE DEVELOPMENT ON PIED OYSTERCATCHER FORAGING CARRYING CAPACITY

3.1 Quantity of Food in Relation to the Requirements of the Birds

Previous studies have shown that the mortality rate of shorebirds can increase even when there is apparently enough food to support the population. The “ecological requirement” of the birds (i.e. the amount of food that needs to be present to maintain high survival) is larger than the “physiological requirement” (i.e. the amount the birds actually eat). This difference occurs for a number of reasons, including (i) interference competition which excludes sub-dominant birds from some of the food supply, (ii) individual variation in foraging efficiency which means that some birds die when food abundance is sufficient to support more efficient birds and (iii) other factors that reduce food abundance.

The ecological requirement for food in Eurasian Oystercatchers can be 2 to 8 times the physiological requirement, and varies for oystercatchers on different estuaries (Goss-Custard et al., 2004). The major factor thought to determine this variation is the type of prey species, being closer to 2 on estuaries comprised of dispersed bivalves (cockles Cerastoderma edule) and closer to 8 on estuaries comprised of highly aggregated mussel (Mytilus edulis) beds. More food is required with aggregated prey because the more dominant birds can exclude the sub-dominant birds from more of the food supply than is possible with dispersed prey. Lauderdale and the surrounding sites are more representative of the former type of site, and so the initial expectation is that approximately twice the amount of food consumed by the birds will need to be present to maintain high survival rates.

Figure 3.1 shows the biomass of food available in each site during each season in relation to the food requirements of the Pied Oystercatchers (calculated from the assumptions given in the model description section). The food supplies available were estimated from the site-wide numerical abundance (numerical density x patch size) and mass of prey classes within the size ranges consumed. With the exception of Orielton Lagoon the food supply is at least 4 times greater than the requirements of the Pied Oystercatchers for all sites in all seasons. Based on the discussion above, the initial expectation is that the food supply is sufficient to support the bird populations in all sites except Orielton Lagoon. The expectation for Orielton Lagoon is that Pied Oystercatchers initially resident at this site can only survive by emigrating to other sites for at least part of the year.

Figure 3.2 compares the biomass of food available at Lauderdale either with or without the proposed habitat loss. The proposed habitat loss reduces the amount of food available, but in all seasons the amount of food available is at least 3 times greater than the requirements of the Pied Oystercatchers. However, as the mortality of Eurasian Oystercatchers can increase when 2 to 8 times the birds’ physiological requirements are present, this result does not determine whether or not the habitat loss will increase mortality.

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(a) Lauderdale (b) Mortimer Bay 20 20 Available

) Required ) 15 15

10 10

5 5 Biomass (tonnes Biomass (tonnes Biomass

0 0 123 123 Season Season

(c) South Arm (d) Pipeclay Lagoon 20 20 ) ) 15 15

10 10

5 5 Biomass (tonnes Biomass Biomass (tonnes Biomass

0 0 123 123 Season Season

(e) Five Mile Beach (f) Barilla Bay 20 20 ) ) 15 15

10 10

5 5 Biomass (tonnes Biomass (tonnes Biomass

0 0 123 123 Season Season

(g) Orielton Lagoon 20 ) 15

10

5 Biomass (tonnes Biomass

0 123 Season

Figure 3.1 Biomass of food (ash-free dry mass) available in each site during each season in relation to the food requirements of the Pied Oystercatchers. The food supplies available were estimated from the site-wide numerical abundance (numerical density x patch size) and mass of prey classes within the size ranges consumed. The Pied Oystercatcher food requirements were estimated from population size, daily energy requirements and the energy content and assimilation efficiency of the prey.

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(a) Before habitat loss 20 Available

) Required 15

10

5 Biomass (tonnes

0 123 Season

(b) After habitat loss 20 ) 15

10

5 Biomass (tonnes

0 123 Season

Figure 3.2 Biomass of food (ash-free dry mass) available at Lauderdale during each season in relation to the food requirements of the Pied Oystercatchers: (a) observed food supply; (b) food supply after proposed habitat loss. The food supplies available were estimated from the site-wide numerical abundance (numerical density x patch size) and mass of prey classes within the size ranges consumed. The Pied Oystercatcher food requirements were estimated from population size, daily energy requirements and the energy content and assimilation efficiency of the prey.

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3.2 Predicted Behaviour, Body Mass and Survival in the Absence of Habitat Loss

The individual-based model was initially used to predict the behaviour, body mass and survival of Pied Oystercatchers under the current environmental conditions to determine how accurately it represents the system, and whether any birds are predicted to die or have poor body condition in the absence of habitat loss. These simulations were based on a default model which was considered to be the best compromise between simplicity and a model that could accurately describe the real system. It is important to keep individual-based models as simple as possible as it can be very difficult or impossible to interpret output from very complicated models. The rule used while developing the default model was to only include parameters with values that could be measured in the real system or derived from the literature. Similarly, the model only included assumptions that could be validated in the real system or from the literature. A few other simplifying assumptions were made (e.g. to assume that the number of Pied Oystercatchers in each site remained constant during the year, or that Pied Oystercatchers were the only source of prey mortality) as it was initially considered that making such assumptions would not change the key predictions of the model (i.e. the survival and body condition of the birds). However, to test the validity of these simplifying assumptions, sensitivity analyses were conducted to determine whether changing them altered the model’s predictions.

The following sections describe the predictions of the default model in the absence of habitat loss. Simulations were run in which Lauderdale was either treated as an isolated site and hence birds at Lauderdale were unable to move to other sites (single-site simulations), or in which all sites were considered and hence birds at Lauderdale (or other sites) were able to move to other sites (multi-site simulations). As the main aim of the project is to predict the consequences of habitat loss at Lauderdale, predictions associated with Pied Oystercatchers at Lauderdale are given priority here.

3.2.1 Patch choice

In the model, Pied Oystercatchers move to the feeding patch on which their rate of assimilating energy is maximised. Usually this means that they move to the patches that have the highest biomass of their preferred prey species (in the case of oystercatchers, usually large bivalves). Patch choice in the model was recorded every 15 days during the hours of daylight (for comparison with the observed data), as the percentage of birds feeding on different patches. The annual mean percentage of birds in different patches is presented in this report.

At Lauderdale the model predicted that patch 4 should be preferentially used by the birds because they achieved their highest energy assimilation rate on this patch as it contained the highest biomass of their preferred food), on account of a high mass of Katelysia scalarina and bivalve species grouped with it (e.g. the large bivalve Tellina deltoidalis which was more common in patch 4 than other patches) (Figure 3.3a). The foraging survey indicated that the intake rates of the birds (which are positively related to energy assimilation rates) were highest in that patch except the oyster/mussel bed (patch 6). In contrast, the observed data showed that patch 2 supported the largest number of birds.

3.2.2 Diet selection

Diet choice in the model was recorded every 15 days during the hours of daylight (for comparison with the observed data), as the percentage of birds feeding on different diets. The annual mean percentage of birds feeding on different diets is presented in this report.

The model predicted that bivalve groups Katelysia scalarina and Anapella cycladea comprised the vast majority of the birds’ diet (Figure 3.3b). This was consistent with the observation that bivalves were the dominant prey of the real birds on the basis of biomass. The foraging surveys showed that on average, 88% of the diet across all sites by mass comprised bivalves. For Lauderdale specifically across all seasons, the foraging surveys showed that the Katelysia group made up 76% of the diet and the Anapella group 12%, in close agreement with Figure 3.3b.

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3.2.3 Food intake rate

Intake rate in the model was recorded every 15 days during the hours of daylight (for comparison with the observed data) as the daily mean ash-free dry mass intake rate of birds consuming different diets. The annual mean of daily intake rate from different diets is presented in this report.

The model predicted that the birds were able to achieve intake rates of between 4 and 6g ash-free dry mass hr-1 while feeding on the Katelysia scalarina group, Anapella cycladea group or Mytilus galloproviancialis (Figure 3.3c). The value for the Katelysia scalarina group was quite close to that observed, but the model overestimated the intake rate for the Anapella cycladea group and Mytilus galloproviancialis (Figure 3.3c).

3.2.4 Percentage of time spent feeding

The percentage of time spent feeding while on intertidal feeding patches gives an indication of the difficulty birds are having meeting their energy requirements. The closer this percentage is to 100% the less spare time birds have in which to compensate for any deterioration in feeding conditions, brought about for example by habitat loss. The percentage of time spent feeding in the model was recorded every 15 days during the hours of daylight, as the daily mean percentage of time spent feeding by birds while foraging on intertidal patches (i.e. excluding time spent on a roost). The annual mean percentage of time spent feeding is presented in this report.

The model predicted that while foraging on intertidal patches, birds spent less than 40% of the time feeding (Figure 3.3d). This happened because they were able to meet their energy requirements within a relatively short time (the percentage of time feeding would increase to 100% if birds were failing to meet their requirements). This prediction indicated that birds could compensate for any reduction in feeding conditions by increasing the percentage of the time they spent feeding.

From the wader utilisation survey (Aquenal 2008b), in summer, 63% of Pied Oystercatchers were foraging in zone N1 (i.e. patch 1 and 2 combined), 64% in patch 3 and 71% in zone S (i.e. patch 4 and 5 combined). In winter, 30% of Pied Oystercatchers were foraging in zone N1 (i.e. patch 1 and 2 combined), 41% in patch 3 and 65% in zone S (i.e. patch 4 and 5 combined). Therefore, for the whole Lauderdale site, 64% (out of 13,779 observations) and 49% (out of 9,996 observations) of Pied Oystercatchers were foraging in summer and winter, respectively. The model predictions therefore fell within the range of observations, but were towards the lower end of the observed values. These are relatively low percentages of the time feeding compared with Eurasian Oystercatcher in the winter which can spend up to 90% of the low tide feeding (Stillman et al., 2002).

3.2.5 Body mass and survival

In the absence of habitat loss, in both the single- and multi-site simulations, all birds at Lauderdale were predicted to survive and maintain their target body mass on the basis of foraging resources. In the multi-site simulations no birds were predicted to leave Lauderdale because all could maintain their body mass by feeding in Lauderdale alone. These predictions were consistent with the fact that the biomass of food at Lauderdale was greater than four times the birds’ requirements during all seasons.

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(a) Patch selection (b) Diet selection 100 100 Observed Predicted Predicted 75 75

50 50

25 25 Percentage of records of Percentage records of Percentage 0 0 12345 Poly. Anap. Katel. Salin. Mytil. Crass. Patch Patch

(c) Intake rate (d) Percentage of time spent feeding 6 50 Observed Predicted Predicted ) 5 40 -1 4 30 3 20 2

Intake rate (g hr 10 1 time of Percentage

0 ***0 Poly. Anap. Katel. Salin. Mytil. Crass. 123 Patch Season

Figure 3.3 Predicted and observed behaviour of Pied Oystercatcher at Lauderdale in the absence of habitat loss. (a) Percentage of birds feeding in difference patches. (b) Percentage of birds consuming different diets. (c) Intake rates obtained from different diets (* = no model predictions as model birds did not consume these diets; Poly. = polychaetes, Anap. = Anapella cycladea group, Katel. = Katelysia scalarina group, Salin. = Salinator fragilis, Mytil. = Mytilus galloproviancialis, Crass. = Crassostrea gigas). (d) Percentage of time birds spend feeding while on intertidal feeding patches. Predictions were derived from a single simulation of the model, because they varied little between replicate simulations.

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3.3 Predicted Effect of Partial Habitat Loss on Behaviour, Body Mass and Survival

In the partial habitat loss simulations it was assumed that only those patches directly affected by the proposed development were lost to the birds. These simulations considered Lauderdale in isolation, and so birds were not able to move to other sites if the habitat loss meant that they were no longer able to meet their requirements.

3.3.1 Behaviour

The model predicts the body condition and survival of Pied Oystercatchers from underlying behaviour, and so any effects of habitat loss should be apparent in changes in predicted behaviour. After habitat loss, patches 1, 2 and 6 were removed from the model, and patch 3 was reduced in area. These changes did not make any substantial differences to the patch selection of the birds. Patch 4 was still the most preferred patch (72% of records) and patch 3 the second most preferred (24% of records). Similarly, diet selection was unaffected, with the bivalve groups Katelysia scalarina (88% of birds) and Anapella cycladea (9% of birds) comprising the majority of the diet. Furthermore, the intake rate of birds consuming these key prey groups was not reduced (Katelysia scalarina group (6g hr-1) and Anapella cycladea group (4.4g hr-1), and as a consequence the percentage of time for which the birds fed on the feeding grounds was similarly unaffected (annual average 34% of the time). Therefore, there was no evidence that modification of foraging resources would influence any of the behavioural parameters that underlie body mass and survival.

3.3.2 Body mass and survival

Habitat loss had no effect on the predicted survival or body mass of the Pied Oystercatchers on the basis of reduced foraging resources. All birds at Lauderdale were predicted to survive in good condition (i.e. with body masses within 25% of their target body mass). These predictions were consistent with the fact that the biomass of food at Lauderdale was still greater than three times the birds’ requirements during all seasons even after the area of foraging habitat had been reduced.

3.4 Predicted Effect of Complete Habitat Loss on Behaviour, Body Condition and Survival

Even though the proposed development is restricted to the northern section of Lauderdale it is possible that it will adversely affect the site as a whole (for example through disturbance to birds on remaining areas of the site, smothering of sediments, dredging, increased disturbance and predation from dogs and cats). To account for this uncertainty, complete habitat loss simulations were run in which it was assumed that the whole of Lauderdale became unsuitable for birds. These simulations predicted the redistribution of birds from Lauderdale to other sites, whether the birds displaced from Lauderdale could survive on other sites and whether the influx of birds to other sites increased the mortality rate of birds on those sites.

3.4.1 Site choice

After being displaced from Lauderdale, Pied Oystercatchers were predominantly predicted to utilise South Arm Neck (48% of records) and Pipeclay Lagoon (42% of records). This happened because these sites contained a higher prey biomass than the other sites (Figure 3.1).

3.4.2 Body mass and survival

None of the birds displaced from Lauderdale were predicted to die. This is consistent with the relatively high biomasses of food per bird at South Arm Neck and Pipeclay Lagoon (Figure 3.1), which were not reduced substantially by the influx of birds from Lauderdale. Additionally, none of the birds initially resident on the other sites were predicted to die, indicating that the influx of birds

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from Lauderdale was not reducing food resources to the point at which birds were unable to meet their energy requirements.

3.5 Sensitivity Analysis of Predicted Effect of Habitat Loss

The previous predictions of the effect of habitat loss were based on the default model. This section explores the consequences for these predictions of altering the values of some of the more uncertain parameters in the model.

3.5.1 Number of birds within the model

The habitat loss simulations assumed that the number of birds at Lauderdale was the mean number observed through the annual cycle. However, the number of birds at Lauderdale was greatest in winter, when food resources may be more limiting, and it is possible that the lower number of birds in the model were able to survive more easily than would be the case in reality. To test this possibility, the model was re-run assuming that the maximum number of birds observed during any season was present throughout the year.

Increasing the number of birds at Lauderdale and other sites to the seasonal maximum, rather than the seasonal mean, had no effect on the survival or body mass of the birds in either the partial or complete habitat loss simulations. All Lauderdale birds were predicted to survive in good condition (i.e. with body masses within 25% of their target body mass). These predictions were consistent with the amount of food per bird available after the number of birds was increased. In the partial habitat loss simulations, the biomass of food at Lauderdale was still greater than two and half times the birds’ requirements during all seasons. In the complete habitat loss simulations, after the influx of birds from Lauderdale, the biomasses of food at South Arm Neck and Pipeclay Lagoon were still over two times the bird’s requirements during all seasons.

3.5.2 Water depth within which birds can forage

The default habitat loss simulations assumed that Pied Oystercatchers were able to forage while wading in up to 120 mm of water. However, it is possible that wading birds may be less efficient at finding prey, particularly if they are searching for visual cues of prey on the substrate surface, and so this assumption may have meant that the model birds were able to forage at unrealistically high rates while wading. To test this assumption, the model was re-run assuming that birds were not able to forage while wading. This was achieved by assuming that patches were only available to birds when they were exposed by the receding tide, which reduced the time and area over which birds could feed.

Preventing birds from foraging while wading had no effect on the survival or body mass of the birds in either the partial or complete habitat loss simulations. All Lauderdale birds were predicted to survive in good condition (i.e. with body masses within 25% of their target body mass). These predictions were consistent with the amount of food per bird available after the birds had been prevented from wading. In the partial habitat loss simulations, the biomass of food at Lauderdale was still greater than two and a half times the birds’ requirements during all seasons. In the complete habitat loss simulations, after the influx of birds from Lauderdale, the biomasses of food at South Arm Neck and Pipeclay Lagoon were still over two times the bird’s requirements during all seasons.

3.5.3 Uncertainty in the density of prey

The default habitat loss simulations assumed that the Pied Oystercatchers were the only source of prey mortality, whereas other factors may also be important. There was also variation associated with the data collected in the invertebrate survey, as described in Section 2.5.4.3 and also the AFDM calculations. This was addressed by bootstrapping the sample data to calculate confidence intervals. The 5th percentile (see Section 2.5.4.3 as to why 5th and not the 2.5 was used) was 57% of the median

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total AFDM available to the birds in spring, 65% in summer and 69% in winter. Across all seasons and sites, in 95% of cases, the total AFDM of prey measured would have exceeded 64.5% of the median prey total actually measured.

To account for the census error and loss to other sources, the model was re-run assuming that only 50% of the observed food supply was actually available to the birds. Given that the preferred prey populations were relatively stable through the year (implying that mortality rates of these prey were relatively low), a 50% reduction of prey density was considered relatively extreme.

Reducing the food supply by 50% had no effect on the survival or body mass of the Pied Oystercatchers in either the partial or complete habitat loss simulations. All Lauderdale birds were predicted to survive in good condition (i.e. with body masses within 25% of their target body mass). In the partial habitat loss simulations, the biomass of food at Lauderdale was as little as one and a half times the birds’ requirements during all seasons. In the complete habitat loss simulations, after the influx of birds from Lauderdale, the biomass of food at South Arm Neck was still over two times the bird’s requirements during all seasons. The biomass of food at Pipeclay Lagoon was less than two times the birds requirements after assuming that all Lauderdale birds would move to this site. In both the partial and complete habitat loss simulations, the biomass of food was close to the biomass at which mortality would be expected to increase.

3.5.4 Combined effects

The previous sections tested individual assumptions of the model, but it is possible that all of these assumptions were incorrect and meant that the model birds were able to survive more easily than the real birds. To test this possibility, the model was re-run assuming that (i) the maximum number of birds observed during any season was present throughout the year, (ii) birds were not able to forage while wading and (iii) only 50% of the observed food supply was actually available to the birds. The combination of these assumptions provides a very conservative assessment of potential impact.

In the partial habitat loss simulations all birds at Lauderdale were predicted to survive in good condition (i.e. with body masses within 25% of their target body mass). In these simulations the biomass of food at Lauderdale was as little one and a half times the birds’ requirements, and so was close to the biomass at which mortality would be expected to increase.

In the complete habitat loss simulations, survival rates (averaged across all birds on the site) were low on all sites (mean = 45%) and so birds from Lauderdale could not survive by moving to other sites.

3.6 Future Increases in Bird Population Size and the Predicted Effect of Habitat Loss

It is possible that the population size of Pied Oystercatcher may increase in Lauderdale and surrounding sites, and so simulations were run to determine the consequences of increased population size for the predicted impact of habitat loss (Figure 3.4). Simulations were run with the single-site model and so any birds that could not meet their requirements at Lauderdale were predicted to die of starvation.

With both the presence or absence of partial habitat loss, increases in the number of birds at Lauderdale up to 600 did not decrease predicted survival rate. In the absence of habitat loss, predicted survival did not decrease substantially until more than 1000 birds were assumed to be present. With partial habitat loss, predicted survival decreased rapidly when more than 700 birds were assumed to be present. The amount of food that would be physically removed by the proposed development would support up to approximately 300 birds before mortality would increase under the standard model runs (i.e. birds can wade for food).

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100 .

75

50

25 No habitat loss

Percentage survival Percentage Habitat loss 0 0 500 1000 1500 Initial population size

Figure 3.4 Predicted effect of possible future increases in the population size of Pied Oystercatchers at Lauderdale on the percentage of birds surviving the year in the presence and absence of partial habitat loss. Predictions are the mean of 5 replicate simulations.

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4. DISCUSSION

The intertidal flats of Lauderdale and surrounding sites support a complex assemblage of resident and migratory waders. This model looks at one part of this wader assemblage in detail and investigates whether there would be sufficient food supplies available to the adult Pied Oystercatchers at Lauderdale and six other surrounding sites following the loss of foraging habitat associated with the Lauderdale Quay development.

4.1 Impact of the Proposed Development and the Ability of Other Sites to Accommodate Displaced Birds

The data from the benthic invertebrate survey (Aquenal 2008a), and studies of bird numbers (Aquenal 2008b) and foraging (Harrison 2008) together with the bathymetry study were combined in the MORPH model to describe the foraging resources that are available to Pied Oystercatchers throughout the year. It was clear from using the data collected by this study that there was an excess of food both at Lauderdale and at surrounding sites to support the current number of Pied Oystercatchers in the Derwent-Pitt Water region. The fact that Pied Oystercatchers spent a large portion of their time not feeding (c50% in winter and c35% in summer, Appendix 4 Aquenal 2008b) and very rarely fed in terrestrial habitats (Harrison 2008) indicated that they were able to maintain their body condition without having to forage all day. If all of the habitat was made unsuitable at Lauderdale, the default model (i.e. birds can wade for food & the seasonal number of birds in Table 2.5.2 were used) predicted that there was sufficient food (2-3 times the birds' requirements) in the other six sites studied to accommodate the displaced birds.

It is always important to question the assumptions made in any model. Table 4.1 shows the combinations of simulations run to test whether the model’s predictions were sensitive to possible variations in its assumptions and parameter values. These simulations showed that the model predictions and hence our conclusions drawn from these predictions were consistent over a wide range of potential model assumptions and parameter values.

Table 4.1.1 Summary of model predictions in relation to variation in model assumptions and parameter values.

Model Habitat Birds Number of Birds Food Mortality Decrease Loss allowed to birds allowed available increase? in body move? (seasonal to wade to the condition? mean or for birds maximum) food? Lauderdale Partial No Mean Yes 100% No No only No Maximum Yes 100% No No No Mean No 100% No No No Mean Yes 50% No No No Maximum No 50% No No All sites Complete Yes Mean Yes 100% No No Yes Maximum Yes 100% No No Yes Mean No 100% No No Yes Mean Yes 50% No No Yes Maximum No 50% Yes Yes (survival = 45%)

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While discussing potential food requirements we stated that the “ecological requirement” of the birds (i.e. the amount of food that needs to be present to maintain high survival) is larger than the “physiological requirement” (i.e. the amount the birds actually eat). The ecological requirement for food in Eurasian Oystercatchers can be 2 to 8 times the physiological requirement (Goss-Custard et al., 2004), and so we used these figures in our discussion. This occurs for a number of reasons, including (i) interference competition which excludes sub-dominant birds from some of the food supply, (ii) individual variation in foraging efficiency which means that some birds die when food abundance is sufficient to support more efficient birds and (iii) other factors that reduce food abundance. Even though we used the Eurasian Oystercatcher example in our discussion, the assumption that the ecological requirement is larger than the physiological requirement was not incorporated within the individual-based model. Instead, the model calculates the predicted mortality rate directly from the amount of food available and the behaviour of the birds. In fact, in the case of Pied Oystercatchers, the model predicted that low mortality rates were predicted even if the amount of food present was as little 1.5 times the amount the birds actually consumed.

The model assumed that the area of intertidal habitat available to the birds was either the area above the water’s edge or the area with water less than or equal to 120 mm deep. In either case the model assumed that the entire area of this habitat was available to the birds. However, the foraging study (Harrison 2008) showed that most of the birds’ foraging activities occurred close to the tide edge. This may have occurred because birds were able to forager more efficiently on substrates that had recently been exposed by the tide, perhaps because prey were more detectable, or more straightforward to remove from the substrate. An alternative explanation would be that birds were following the tide edge because this allowed them to maintain the furthest distance from potential disturbance sources or threats on the shoreline. The consequences of birds following the tide edge would be to increase their density, hence increasing the strength of interference competition, and reduce the area of habitat actually available at any point in time. Given the generally low densities of birds we do not believe that the strength of interference would have been increased greatly, if at all. It was not possible to model such behaviour in the model, and so the model may have overestimated the total area of habitat available to birds at any one point in time, and the strength of interference.

We increased the number of birds potentially present at each site to the seasonal maximum (rather than average numbers in the default model run) and also did not allow birds to wade for food. In both of these cases there was no decrease in body condition or increase in mortality in either the ‘footprint’ scenario or where all of Lauderdale was made unsuitable.

Although the invertebrate survey was comprehensive, it was possible that there were biases associated with data collected. We therefore halved the prey density to allow for (a) census error in prey density and (b) losses to other sources. It is very unlikely that other wader species present in the area will consume large numbers of bivalves (see Harrison 2008) which are the main resource available to the birds on the basis of mass. The only species likely to do so is the Sooty Oystercatcher (Haematopus fuliginosus), while smaller bivalves may be taken by Bar-tailed Godwit (Limosa lapponica), but both these two species are uncommon in the system and so it is thought unlikely that they would contribute much to the depletion of the Pied Oystercatcher prey resource. Benthic invertebrate densities can, however, exhibit a high degree of inter-annual variation (although bivalves less so) and a halving of the prey density was considered a conservative approximation to an extreme reduction in prey density. Once we did this, made all of the habitat at Lauderdale unsuitable, used the maximum number of birds observed in each site and did not allow the birds to wade for food, mortality of the population increased to over 50%.

One of the main questions is how the development will impact on the Pied Oystercatcher’s ability to use the patches immediately to the south of its ‘footprint’. The proposed development will remove patches 1, 2 and 6 completely and part of 3. The model does not make any assumptions about the impact of disturbance to the birds but it is very likely that there will be disturbance issues, both during the construction phase and afterwards, and these need to be considered in any impact assessment of

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this proposal. The impact assessment should also consider the increased risk of an environmental disaster such as a fuel spill making the surrounding foraging areas unsuitable.

If all of the Lauderdale sandflat became impacted and unsuitable for wader foraging, the default model indicated that there was sufficient food in the rest of the system for the present numbers of Pied Oystercatchers. Therefore, the most likely scenario is that under non-extreme conditions there is sufficient food available in the other six sites studied to support the number of Pied Oystercatcher likely to be displaced from Lauderdale. This assumes that birds can move amongst sites without any increase in mortality, but this has not been tested in Pied Oystercatchers.

The issue of movements between sites was addressed to some extent by correlating counts between sites (Aquenal 2008b). Of the 36 possible permutations tested, only 8 (22%) had correlation coefficients of >0.7 which was the cut off point selected by the author. Although indicative only, it does suggest that there is some degree of (short-term?) movement between sites under certain environmental conditions. An analysis of the existing banding data, or a dedicated radio-tracking study would be required to definitively quantify the degree of movements between sites.

There were strong negative correlations between counts of birds at South Arm Neck and four other sites: Lauderdale, Orielton Lagoon, Barilla Bay and Five Mile Beach. This suggests that bird numbers at South Arm Neck can be volatile and birds move between this site and the other four. Numbers at Lauderdale were also positively correlated with numbers at Orielton Lagoon. Without further examination of the data we cannot be certain if this is due to birds moving from South Arm Neck into these two sites at the same time, thus causing this positive association.

The counts analysis does therefore indicate that there is some movement amongst the three northern sites in and adjacent to the Pitt Water / Orielton Ramsar site (Barilla Bay, Orielton and Five Mile Beach) and the sites to the south (Lauderdale, South Arm Neck, Mortimer Bay and Pipeclay Lagoon). However, without observations of individually-marked birds (e.g. colour-ringed birds) the degree of movement cannot be ascertained.

In other waders, being forced to move can lead to increases in mortality. In wintering Redshank, for example, closure of a barrage in Cardiff Bay (UK) led to the displacement of several hundred birds which experienced a substantially higher mortality and poorer body condition compared with birds normally wintering outside Cardiff Bay (Burton et al. 2006). There is therefore a risk that displacing birds will increase their mortality and decrease their body condition, regardless of estimates of food resources. The example given is analogous as it refers to sudden habitat loss such as would occur in this case.

Based on the counts from the three northern sites in and directly adjacent to the existing Pitt Water / Orielton Ramsar site, the designated Ramsar site supported an average of 1.2% and up to 3.2% of the global population of Pied Oystercachers between 2001 and 2005 (Aquenal 2008b). The linkages between northern Ramsar sites and southern (non-Ramsar) sites discussed above indicate that the proposed development may therefore have an impact of the birds that use the Ramsar site at some point during the year. In fact, greater numbers of Pied Oystercatchers were found in southern sites. Lauderdale supported an average of 2.5% and up to 3.8% of the global population. Two other sites, South Arm Neck (average 1.1% and up to 4.1%) and Pipeclay Lagoon (average 0.97% and up to 1.6%) each supported >1% of the global population which is a criterion for designating a Ramsar site.

Lauderdale is the key site in terms of Pied Oystercatcher foraging as intake rates were highest there and, in winter, the biomass of food was second only to South Arm Neck. These are the two key sites that will act as refuges for extreme events. Making Lauderdale unsuitable would therefore remove one of the two key sites for Pied Oystercatchers in south-eastern Tasmania. The populations of Pied Oystercatcher at Lauderdale and South Arm Neck both meet the Ramsar criterion of a site of international importance. Removal of the habitat at Lauderdale and the resulting effects on birds should therefore be evaluated against Article 3 of the Ramsar Convention that states "The Contracting

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Parties shall formulate and implement their planning so as to promote the conservation of the wetlands included in the List, and as far as possible the wise use of wetlands in their territory." It is important to stress that Lauderdale is not a Ramsar site but the Convention does place an obligation on countries to ensure, as far as possible, the wise use of wetlands.

If a decision is made to implement the proposed development and hence remove part of this key site, then it is important to ensure that there is as much of a buffer (i.e. a safety factor) built in to maximise the food available to the birds. This can be done in one of two ways. First, the amount of food available could be increased at other sites by modifying the habitats or (re)creating foraging areas (such as rehabilitating East Marsh Lagoon at the southern end of Lauderdale). The other option is to make the food that is there more available to the birds. It is therefore important that all possible steps are taken at Lauderdale to minimise the impact of disturbance on the birds both during and after the construction to ensure birds can feed on the remaining resources undisturbed. This will need wider consultation with stakeholders but could include measures such as restricting boat, people and dog access (and other sources of disturbance) to the central and southern parts of Lauderdale and ensuring that birds have safe and undisturbed areas to roost in. Similarly, if in other sites disturbance is thought to be an issue, then measures should be established to reduce this.

In the absence of extreme events keeping the population of Pied Oystercatchers lower than might be expected from the food resources available to them, it is likely that other factors are limiting the population. It is beyond the scope of this study to determine these, but could include factors such as loss or reduction in quality (e.g. human disturbance) of nesting habitat and foraging areas adjacent to nesting habitat or poor rates of recruitment of young birds into the adult population. Having access to good, high quality (i.e. both in terms of food availability and low disturbance) foraging areas is therefore critical to these birds. Should this apparent excess of food be reduced to a point where birds find it more difficult to find food then the combination of factors will lead to increased mortality and lower body condition and recruitment of young birds into the population.

4.2 Observed and Predicted Diet of the Pied Oystercatchers

The model predictions and the results from the foraging surveys (Harrison 2008) were in close agreement. Although the foraging surveys found that worms were the most abundant prey (c40% of all items taken), in terms of ash-free dry mass, bivalves were by far the most profitable prey and made up 88% of the energy ingested overall. Bivalves are, therefore, key prey for the Pied Oystercatcher population and the assumptions made about averaging the AFDM-length relationships of three species of worms will have had relatively little bearing on the overall estimate of energy ingested. This close agreement and the comprehensive nature of the invertebrate survey strengthens confidence in the model predictions.

4.3 Future Changes in the Pied Oystercatcher Population

It is unknown what the historic (i.e. pre-European) population size of Pied Oystercatchers at Lauderdale and surrounding sites was. At present there are no national targets for the population size for this species but when considering the impact of the proposed development it is important to consider not only the current population, but also allow for future natural fluctuations in numbers. In the 1990s, the population rapidly expanded but has become more variable in the early 2000s (Aquenal 2008b).

In terms of food availability, there appears to be room for the Pied Oystercatcher population to expand. If the increasing trend from the 1990s continues then this excess food will be vital to continuing growth. In all sites but one, there was four times the food needed available and using the 2x rule the sites could, therefore, comfortably support a doubling of the population. However, the model results showed that if the current amount of food was halved then it was possible that the

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development could reduce the capacity of the sites considered to support the current number of birds to such an extent that mortality would rapidly rise across the population (see section 3.5.4). This could happen for a number of reasons. First, extreme events such as a series of years of poor spatfall or storms washing out bivalves from sediments could reduce prey availability substantially. In the Wash, England, a combination of high fishing mortality of mussels (Mytilus edulis) and a series of years of poor spatfall of cockles (Cersatoderma edule) led to winter mortality rates of Eurasian Oystercatchers 13 times higher than normal (Atkinson et al. 2003). Although we do not know exactly how Pied Oystercatchers would react to poor food stocks, experience from the very similar Eurasian Oystercatcher is that they tend to die rather then move long distances looking for alternative food sources (Atkinson et al. 2003).

The model simulations showed that the intertidal food resources at Lauderdale could support many more birds than they currently do. The consequence of this was that the model predicted that habitat could be removed, thus decreasing the amount of food available, without increasing the mortality rate of the number of birds currently found on the site. It is not necessarily surprising that the intertidal areas of Lauderdale are not at carrying capacity, defined as the maximum sustainable density of birds. Studies of other shorebirds have in fact shown that it is most unlikely that carrying capacity defined in this way is reached at either local (Goss-Custard et al., 2002) or global scales (Goss-Custard, 1993). This occurs because population size may be limited by other factors (e.g. reproduction), either on the site in question or on other sites on which the species occurs at some stage of the annual cycle.

When considering impacts of the current proposed development, it is important to also consider future events such as predicted climate change and sea level rise. Much of this part of Tasmania is low lying and, as sea levels rise, consideration needs to be given to the impact on estuaries. Sharples (2006) outlines the vulnerability of the sites used in this report to sea level rise. All the sites used in the model were classed to be at 'potential flood vulnerability'. Lauderdale, Mortimer Bay, South Arm, Pipeclay Lagoon and Five Mile were all classed as being sandy shores backed by low sand plains that were vulnerable to both erosion and horizontal recession. Orielton Lagoon was predominantly backed by bedrock, which was classed as 'beach erosion only'. This study was relatively limited in extent and did not take into account local factors such as wave climate, sediment budget or bathymetry which may greatly increase or decrease the potential for recession at particular sites. With a sufficient sediment supply horizontal recession may well not occur if accretion keeps up with sea level (Atkinson 2003, Atkinson et al. 2004). The effect of sea level rise may also be minimal if the beach is allowed to retreat naturally up the land profile. However due to coastal development, this may not be possible in some areas.

Without detailed studies of the likely effects of sea level rise on the Tasmanian coast, it is not possible to formally include this in the carrying capacity models but it is something that should be evaluated during the impact assessment. Similarly, climate change has the potential to impact the Tasmanian coastline through two main processes, the change in mean wind speed and direction and change in the degree of storminess and the number of extreme events. Both of these processes have the potential to radically alter the form and composition of the beaches but again the effects are very dependent on local factors such as the fetch, orientation of the site, sediment budget and bathymetry. Without detailed modelling on a site by site basis it is out of the scope of this study to predict the physical changes to the beaches and estuaries, the resulting impact on the benthic invertebrates and hence the oystercatchers. The predictions for the predicted change in wind speed in Tasmania are unclear (data accessed from http://www.climatechangeinaustralia.gov.au) and the confidence intervals overlap zero. Again this is something that should be evaluated during the impact assessment.

4.4 Conclusion

The data collected in this study indicated that there was an excess of food in all seasons surveyed at the seven sites considered. Lauderdale is the key foraging site (highest energy intake rates) for Pied Oystercatchers and the proposed development will remove, or have a negative impact, on key Pied

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Oystercatcher foraging sites at Lauderdale. Given that there will inevitably be disturbance issues around the periphery of the development both during construction and post-construction periods, it is likely that some of the Pied Oystercatchers currently foraging there would be displaced to other sites.

Waders displaced by a development have been shown to have a higher risk of mortality and experience lower body condition than non-displaced birds. This could be because they have a poor knowledge of the food resources in the surrounding areas, or become less dominant than the resident birds in the areas into which they have been displaced and thus suffer more interference.

The default model which made Lauderdale unsuitable as a foraging site indicated that there would be sufficient food for any displaced birds. Displaced Pied Oystercatchers were predicted to move to Pipeclay Lagoon and South Arm Neck, where food supplies were high.

The model assumes perfect knowledge of food supplies and hence does not factor in any increased mortality due to non-perfect knowledge. Waders displaced by a development have been shown to have a higher risk of mortality and experience lower body condition than non-displaced birds. This could be because they have a poor knowledge of the food resources in the surrounding areas, or become less dominant than the resident birds in the areas into which they have been displaced and thus suffer more interference. It is possible that there may be some small temporary increase in mortality.

Even if this model was made more conservative by not allowing birds to forage in water and increasing the numbers of birds in each site to the seasonal maximum, there was still sufficient food available for the energetic needs of the Pied Oystercatchers. Only when the amount of food was halved in the more conservative model above, did substantial increases in mortality occur. This 'worst case' scenario was included to allow for uncertainty in the invertebrate survey and depletion of invertebrates to other sources (e.g. predation by other birds, fish, extreme weather events etc). This was considered very extreme but does indicate that the food supply is not many orders of magnitude greater then the energetic needs of the birds.

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Acknowledgements

This study is the culmination of a series of long and detailed background studies which have involved many hours in the field and in the laboratory. In particular, we would like to thank Dr Karen Parsons of Aquenal, who has been so supportive of our work over the past three years since PWA’s visit to the proposed development site and has supplied the invertebrate data. Dr Cindy Hull of Aquenal and Annette Harrison provided bird count and foraging data and contributed very useful advice on other bird data, while Sheryl Hamilton and Alejandro Velasco-Castrillón are also thanked for assistance with the bird data. Additional staff at Aquenal prepared the exposure data and assisted with the invertebrate data, particularly Jeremy Dudding, Derek Shields, Kathryn Pugh and Hanna Westmore.

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