spatial and temporal overlap between seabird distribution

SCRS/2008/029 - Preliminary

Spatial and temporal overlap between seabird distribution

in the Atlantic Ocean and ICCAT longline fishing effort

F. Taylor and C. Small

Paper submitted to the 2008 intersessional meeting of the ICCAT Sub-Committee on Ecosystems, 10-14 March 2008, Madrid

ABSTRACT Objectives (ii) and (iii) of the ICCAT seabird assessment are to collate the at-sea distribution of seabird species in the ICCAT area, and to analyse the spatial and temporal overlap between seabird distribution and ICCAT longline fishing effort. The four seabird populations assessed so far exhibit seasonal variation in their overlap with fishing effort, which is a function of seasonal shifts in seabird distribution. The calculated index of overlap is as much as 3-10 times higher in the southern hemisphere winter (Q2, Q3) compared to the southern hemisphere spring (Q4). As would be expected, total overlap is highest for a species whose breeding and non-breeding distribution overlaps with the ICCAT area (e.g. Tristan Albatross). The aim at this intersessional meeting is to (i) simplify the method for estimating the distribution of species for which there are no tracking data and (ii) identify if there are more sophisticated methods for calculating overlap. 1. INTRODUCTION In 2004, initial analysis of the Global Procellariiform Tracking Database indicated that approximately 17% of global breeding albatross distribution is within the ICCAT area (BirdLife International 2004a, 2006). Objectives (ii) and (iii) of the ICCAT seabird assessment have been established to improve knowledge of the spatial and seasonal overlap between the distribution of ICCAT longline fishing effort and the seabird species that are known or considered likely to be vulnerable to bycatch. Objectives (ii) and (iii) are to: (ii) Collate available data on at-sea distribution of seabird species (iii) Analyze the spatial and temporal overlap between species distribution and ICCAT longline fishing effort. Full results will be presented in September 2008, but this preliminary version of the paper presents the methodology and provisional results for the four populations shown in Table 1. Table 1. The four seabird populations assessed in this paper

Common name Scientific name Threat status1 Breeding colony Black-browed Albatross Thalassarche melanophrys Endangered South Georgia Tristan Albatross Diomedea dabbenena Endangered Gough Island White-chinned Petrel Procellaria aequinoctialis Vulnerable South Georgia Sooty Shearwater Puffinus griseus Near Threatened South Georgia

1 Source IUCN 2006, BirdLife International 2004b.


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2. METHODS Over 90% of existing albatross and petrel tracking data have been submitted to the Global Procellariiform Tracking Database, representing 20 of the 22 species of albatross, both species of giant-petrel, White-chinned Petrel, Westland Petrel, and Cory’s, Sooty and Short-tailed Shearwater. However, many gaps in tracking data remain, particularly for the non-albatross species in the ICCAT assessment. In addition, even among albatrosses, tracking data coverage of certain breeding stages (particular juvenile and immature stages) is generally poor. For this reason, estimation of seabird distribution for the ICCAT seabird assessment must rely on a combination of tracking data (where available), and best-available estimates when tracking data are lacking, including estimated total range and foraging radius from breeding colony (Phillips et al. 2007). The analysis for the ICCAT seabird assessment also differs from previous analyses of the Global Procellariiform Tracking Database in that, rather than producing separate density distributions for breeding and non-breeding birds, the analysis requires an estimate of total population distribution, divided seasonally. This requires estimates of the proportion of juveniles, immatures and non-breeding adults within a seabird population (see Section 2.2 below). 2.1 Processing available seabird remote tracking data When satellite tracking (PTT) data are submitted to the Tracking Database, data are processed using standardised methods agreed among data-holders. Data points are first validated using a filter based on McConnell et al. (1992), which calculates the average velocity between the current satellite uplink and the preceding and following two uplinks. Where the velocity is over the maximum velocity vMax (set at 100km.hr-1 for all species) and an alternative latitude and longitude is provided, the filter substitutes the alternative point. In an iterative process, the filter then removes the uplink with the highest velocity over vMax, although a point with high accuracy is not removed (location classes 1, 2 and 3 with accuracies of up to 1km (Argos 1989, 1996)). The velocities for the four points adjacent to the removed point are then recalculated and the process repeated, until no low quality point has a velocity above vMax (BirdLife International 2004a). In order to convert the PTT tracking data into density distributions, the assumption is made that birds travel at constant speed and in a straight line between each pair of uplinks. The path of the bird is then resampled at hourly intervals. If the interval between two uplinks is more than 24 hours (as in the case with duty-cycled data), no resampling is conducted between these points. Geolocator (GLS) devices are generally less accurate than PTTs and provide only two locations per day, but are ideal for tracking the wintering ranges of pelagic species (Phillips et al., 2004a), and, being lighter than PTT devices, can be used on smaller birds. Data holders submit GLS data to the database in a processed form, since the variety of geolocators available make it unrealistic to develop a standardised validation routine. Given that GLS data are only available at c.12-hour intervals and migrating birds can move very rapidly, there may not be a location in a particular 5x5° grid square even though the bird’s flight path did cross part of the area. Therefore, for the purposes of this analysis, the tracks were resampled at six hour intervals. Where there were erroneous locations on land, a straight-line path was assumed between the nearest two points located on water, and this path was interpolated at six hour intervals.


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2.2. Estimating total population distribution To estimate total population distribution, the annual cycle of each species was split into stages, representing groups of individuals that are likely to have different distributions (Table 2). Where tracking data were available, kernel density distributions were derived for each stage (and sex if known) of a particular population. This was done in ArcGIS 8.2 using a smoothing (h) parameter of 1° and a grid size of 0.1° for PTT data (selected on the basis that this was likely to be the smallest practical unit for management on the high seas), and for GLS data a smoothing parameter h of 2°, (corresponding to the nominal resolution of the data) and a cell size of 0.5°. Data points were not separated into ‘commuting’ or ‘foraging’ points. It is thus recognised that not all areas used by the albatrosses and petrels will be areas of foraging, although these still represent areas where there is potential interaction with fisheries. Table 2. Annual stages for seabird species under consideration

Stage Season Age class Notes Proportion time at sea

Incubation Breeding Adult The pre-egg period was included in this stage as no tracking data were available 0.5

Brood-guard Breeding Adult This stage was ignored in the case of burrowing petrels, where the brood period lasts only a few days.

0.5

Post-guard Breeding Adult 1

Early fail Breeding Adult Breeding adults that fail before end of brood-guard 1

Late fail Breeding Adult Breeding adults that fail after brood-guard 1

Sabbatical Breeding Adult Non-breeding adults during the breeding season 1

Immatures (B) Breeding Immature Pre-breeders that have returned to the colony 1

Non-breeders Non-breeding Adult Non-breeding adults during the non-breeding season – in annual breeders this is all adults 1

Immatures (NB) Non-breeding Immature 1

Juveniles Breeding & Non-breeding Juvenile Juveniles that have not returned to the colony

since fledging 1

Grids were then combined to produce an overall density distribution for the population for the entire year and each quarter. Grids were combined based on the length of the stage (start/end dates rounded up to 0.5 months), the proportion of time spent at sea during the stage, and the proportion of birds in the stage. The proportion of a population in non-breeding and juvenile life history stages was estimated using a Leslie-Lefkovitch age/stage-structured matrix model. Input variables are an estimate of survival for each age class (juvenile, immature, adult), the amount of time spent in each age class, and an estimate of fecundity (the number of female offspring produced per female per year), with an assumption of a 1:1 sex ratio. Where separate grids were produced for each sex, grids were combined assuming equal proportions of the sexes.


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If no tracking data were available for a particular stage then distribution was estimated based on the assumptions in Table 3. Details of the parameters used to create the grids for each of the four populations considered in this paper are given in Appendix 2. Table 3. Estimates used for each annual stage when no remote tracking data were available

Stage Season Age class Data used to estimate distribution Incubation Breeding Adult Brood-guard Breeding Adult Post-guard Breeding Adult Early fail Breeding Adult Late fail Breeding Adult Sabbatical Breeding Adult Immatures (B) Breeding Immature

Foraging radius data (use data from nearest available colony) (foraging radii estimates may be based on length of incubation shifts, diet sampling, and at-sea observations)

Non-breeders Non-breeding Adult Immatures (NB) Non-breeding Immature

Juveniles Breeding & Non-breeding Juvenile

Total range (based on data from at-sea observations and ringing recoveries)

An additional point of consideration that applies to all tracking analyses is that care must be taken when interpreting maps which have been based on small sample sizes. Ideally, analysis would be based on at least 10-15 tracks for each breeding stage, and preferably each sex, before results would be considered to approach reliability, though the effect of sample size varies between species (BirdLife International 2004a). Distribution of albatrosses and petrels has also been identified as varying between years, though analysis suggests that while differences do exist, they are not as substantial as other factors, such as breeding stage (Weimerskirch et al. 1993, Prince et al. 1998, Weimerskirch 2004, Phillips et al. 2004a). 2.3 Overlap with ICCAT longline fishing effort data The ICCAT area used for analysis in this paper covers the entire Atlantic Ocean, including the Mediterranean, down to 50°S. Effort data used were those generated at the 2007 intersessional meeting of the Sub-Committee on Ecosystems. This data set was used to calculate the average number of hooks set in each 5x5° grid square for each quarter during the period 2000-2005, as well as the average annual number of hooks for the same period. For each seabird population, the % at-sea time spent within the each 5x5° grid in the ICCAT area during each quarter and for the whole year was obtained using the distribution grids produced in Section 2.2. These grids were then multiplied by the average fishing effort for the relevant the 5x5° grid square and period and the resultant grid summed to obtain an index of risk of seabird bycatch for each population for a particular period. 3. RESULTS 3.1 Proportion of distribution within ICCAT area The proportions of total distribution within the ICCAT area for the four populations analysed in this paper are shown in Table 4. Tristan Albatross spent 90% of their time within the ICCAT area, and this was constant throughout the year. In contrast, Black-browed Albatross and White-chinned Petrels from South Georgia (Georgias del Sur) spent more of their time in the ICCAT area in southern hemisphere winter (Q2 and Q3), corresponding to their non-breeding periods,


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and a lower proportion of their time in the ICCAT area in the southern hemisphere summer (Q4 and Q1). Sooty Shearwater spent a lower (26%) proportion of its time within the ICCAT area, but this was not estimated to vary through the year. Table 4. Percent distribution of each seabird species within the ICCAT area defined as the Atlantic (including Mediterranean) with a southern boundary of 50º South. (Q1=Jan-Mar, Q2=Apr-Jun, Q3=July-Sep, Q4=Oct-Dec).

Species Breeding island Annual Q1 Q2 Q3 Q4

Tristan Albatross Gough Island 89

90

89

89

89

Black-browed Albatross

South Georgia (Georgias del Sur)

49

27

60

77

34

White-chinned Petrel


56

49

59

63

55

Sooty Shearwater Falkland Islands (Islas Malvinas)

26

26

26

26

26

3. 2 Overlap with ICCAT longline fishing effort The calculated overlap between seabird distribution and ICCAT longline fishing effort is shown in Table 5. For Black-browed Albatross and White-chinned Petrel, the seasonal overlap with ICCAT longline fishing effort was highest during the southern hemisphere winter (Q2 and Q3), as would be expected from their seasonal distribution. Tristan Albatross and Sooty Shearwater had highest overlap with ICCAT longline fishing effort in Q2, the quarter when fishing effort below 20ºS is highest. Table 5. Index of overlap between the distribution of four species of albatross, petrel and shearwater and ICCAT fishing effort intensity. Distributions were derived from tracking data held in the Global Procellariiform Tracking Database, and species ranges and foraging radii provided by BirdLife International. Overlap was calculated as the % seabird distribution * fishing effort per 5x5 grid square, where fishing data are the average annual and quarterly number of hooks set per 5° grid square (2000-2005 data) (Q1=Jan-Mar, Q2=Apr-Jun, Q3=July-Sep, Q4=Oct-Dec).

Species Breeding island Annual Q1 Q2 Q3 Q4

Tristan Albatross Gough Island

615,329

149,349

285,835

135,912

44,233



401,043

35,257

208,048

135,992

21,746



320,286

11,170

166,221

119,481

23,414

Sooty Shearwater

Falkland Islands (Islas Malvinas)

210,851

44,912

79,024

59,402

27,513

Discussion The results for four populations presented here indicate that the overlap with ICCAT longline fishing effort varies between year quarter, which is a factor of seasonal variation in seabird distribution and seasonal variation in fishing effort.


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Of the four populations, the overlap for Tristan Albatross was the highest, as would be expected since it is the only one of the four populations considered whose breeding site lies within the ICCAT longline fishing effort area itself, and whose breeding and non-breeding distribution overlaps highly with ICCAT longline fishing effort. Overlap is high in all quarters except the Southern Hemisphere spring (Q4), when pelagic longline fishing effort below 20 degrees is relatively low. For Black-browed Albatrosses from the Falkland Islands (Islas Malvinas) and White-chinned Petrels from South Georgia (Georgias del Sur), the distribution of non-breeding and juvenile birds overlap with ICCAT longline fishing effort, rather than breeding birds. Overlap is significantly higher (factor of 5 or more) in the southern hemisphere winter (Q2, Q3), compared to southern hemisphere summer (Q4, Q1). Future work The intention is to apply this methodology to all seabird populations in the ICCAT seabird assessment (or particularly those that are high priority). At this meeting the intention is to:

• Seek input on whether there is an alternative method for calculating overlap between fishing effort and seabird distribution

• Develop a simplified method for estimating the distribution of species for which there are no tracking data

• Decide whether to continue with the current definition of ‘ICCAT area’ as having a boundary of 50°S, or alternatively to define the ICCAT area using the 5x5° grid squares in which fishing effort occurred in 2000-2005.

Acknowledgements This analysis was made possible with the contribution of tracking data from the following data holders: Black-browed Albatross and White-chinned Petrel (South Georgia) PTT data: John Croxall, Richard Phillips and Andy Wood, British Antarctic Survey Black-browed Albatross and White-chinned Petrel (South Georgia) GLS data: John Croxall, Richard Phillips, Janet Silk and Dirk Briggs, British Antarctic Survey

Tristan Albatross (Gough Island) PTT data: Richard Cuthbert, Royal Society for the Protection of Birds, UK. Percy FitzPatrick Institute, University of Cape Town, South Africa

REFERENCES Argos. 1989. Guide to the Argos System. Toulouse, CLS/Service Argos. Argos. 1996. User’s Manual. Toulouse, CLS/Service Argos. Berrow, S.D., Croxall, J.P. & Grant, S.D. 2000. Status of white-chinned petrels Procellaria aequinoctialis Linnaeus

1758, at Bird Island, South Georgia. Antarctic Science 12(4): 399-405. BirdLife International, 2004a. Tracking Ocean Wanderers: the global distribution of albatrosses and petrels. Results

from the Global Procellariiform Tracking Workshop, 1-5 September 2003, Gordon’s Bay, South Africa. Cambridge, UK, BirdLife International.

BirdLife International, 2004b. Threatened birds of the World 2004. CD-ROM. Cambridge, UK: BirdLife International Bradley, J.S., Wooler, R.D., Skira, I.J., 2000. Intermittent breeding in the short-tailed shearwater Puffinus tenuirostris.

Journal of Animal Ecology 69, 639–650. BirdLife International 2006. Distribution of albatrosses and petrels in the Atlantic ocean and overlap with ICCAT

longline fisheries. ICCAT Col. Vol. Sci. Pap, 59(3): 1003-1013. Brooke, M. 2004. Albatrosses and Petrels Across the World. Oxford University Press, Oxford. 520p. Cuthbert, R.C., Sommer, E, Ryan, P.G., Cooper, J. & Hilton, G. 2004. Demography and conservation of the Tristan

albatross Diomedea [exulans] dabbenena. Biological Conservation 117: 471–481. Croxall, J. P., Prince, P. A., Rothery, P. And Wood, A. G. 1998. Population changes in albatrosses at South Georgia. Pp.

68–83 in G. Robertson and R. Gales, eds. Albatross Biology and Conservation. Chipping Norton, Australia: Surrey Beatty & Sons.

Hall, A.J. (1987) The breeding biology of the white-chinned petrel Procellaria aequinoctialis at South Georgia. Journal of Zoology, 212, 605-617.

IUCN, 2006. IUCN 2006 List of Threatened Species. A global species assessment. Available at http://www.redlist.org . Jones, C. (2002) A model for the conservation management of a ‘secondary’ prey: sooty shearwater puffinus griseus

colonies on mainland New Zealand, a case study. Biological Conservation, 108, 1-12. Marchant, S. 1991. The Handbook of Australian, New Zealand and Antarctic Birds: Volume 1: Ratites to Ducks. Oxford

University Press, Oxford. 1408p. McConnell, B.J., Chambers, C. and Fedak, M.A. 1992. Foraging ecology of southern elephant seals in relation to the

bathymetry and productivity of the Southern Ocean. Antarctic Science 4: 393-398. Phillips, R.A., Arata, J., Gales, R., Huin, N., Robertson, G., Terauds, A., Weimerskirch, H. 2004a. Synthesies of

distribution of breeding birds from different populations of selected species: Black-browed Albatross Thalassarche melanophrys. In: BirdLife International. 2004. Tracking Ocean Wanderers: the global distribution of albatrosses and petrels. Results from the Global Procellariiform Tracking Workshop, 1-5 September 2003, Gordon’s Bay, South Africa. BirdLife International, Cambridge, UK, pp24-25.

Phillips, R.A., Silk, J.R.D., Phalan, B, Catry, P., Croxall, J.P. 2004b. Seasonal sexual segregation in two Thalassarche species: competitive exclusion, reproductive role specialization or trophic niche divergence? Proceedings of the Royal Society, Series B, 271: 1283-1291.

Phillips, R.A., Tuck, G., Small, C. 2007. Assessment of the impact of ICCAT fisheries on seabirds: proposed methodology and framework for discussion. Paper submitted to the 2007 intersessional meeting of the ICCAT Sub-Committee on Ecosystems, 19-23 February 2007, Madrid. SCRS/2007/030

Prince, P.A., Croxall, J.P., Trathan, P.N. & Wood, A.G. 1998. The pelagic distribution of South Georgia albatrosses and their relationships with fisheries. In Robertson, G. & Gales, R. (Eds). Albatross Biology and Conservation. Chipping Norton, Australia, Surrey Beatty & Sons, pp. 137-167.

Ryan, P.G., Cooper, J. and Glass, J.P. (2001) Population status, breeding biology and conservation of the Tristan Albatross Diomedea [exulans] dabbenena. Bird Conservation International, 11, 35-48.

Schreiber, E. A. and Burger, J., eds. (2002) Biology of marine birds. London: CRC Press. Scofield, R.P., Fletcher, D.J. & Robertson, C.J.R. 2001. Titi (Sooty Shearwaters) on Whero Island: Analysis of Historic

Data Using Modern Techniques. Journal of Agricultural, Biological, and Environmental Statistics 6 (2): 268-280. Weimerskirch, H. 2004. Distribution of breeding birds in relation to year: Wandering Albatross Diomedea exulans,

Crozet. In: BirdLife International, Tracking Ocean Wanderers: the global distribution of albatrosses and petrels. Results from the Global Procellariiform Tracking Workshop, 1-5 September 2003, Gordon’s Bay, South Africa. BirdLife International, Cambridge, UK, pp21-23.

Weimerskirch, H., Salamolard, M., Sarrazin, F., Jouventin, P. 1993. Foraging strategy of Wandering Albatrosses through the breeding season: A study using satellite telemetry. Auk 110: 325-342.

Woehler, E.J., Cooper, J., Croxall, J.P., Fraser, W.R., Kooyman, G.L, Miller, G.D., Nel, D.C., Patterson, D.L., Peter, H.U., Ribic, C.A., Salwicka, K., Trivelpiece, W.Z & Weimerskirch, H. 2001. A statistical assessment of the status and trends of Antarctic and Subantarctic seabirds. Report on SCAR BBS Workshop on Southern Ocean seabird populations.

Figure 1. Distribution of Tristan Albatross from Gough Island (99.9% global population), and overlap with average ICCAT longline fishing effort 2000-2005.

Figure 2. Distribution of Black-browed Albatross from South Georgia (Georgias del Sur) and overlap with average ICCAT longline fishing effort 2000-2005.


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Figure 3. Distribution of White-chinned Petrels from South Georgia (Georgias del Sur) and overlap with average ICCAT longline fishing effort 2000-2005.


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Figure 4. Distribution of Sooty Shearwaters from Falkland Islands (Islas Malvinas) and overlap with average ICCAT longline fishing effort 2000-2005.

Appendix 1. Parameters used to calculate the proportion of seabird populations within each breeding stage by month.

Breeding chronology Species Return

datea,b Pre-egg perioda,b Egg datea,b Median

egg datea,b Incubation

(days)a,d Hatch datea,b

Brood-guard perioda,b

End brood-guard datea,h

Fledging (days)a,d

Fledge datea,b

Black-browed Albatross early Sep-early Oct 19-27 Oct (23 Oct) 65-72,

68±1.2

most early Dec

c. 3 weeksf (late Dec) 116-125i late Apr

Tristan Albatross (early Dec)c early Jan (79)e (late Mar) (late Apr) late Jan-k

early Mar

White-chinned Petrel mid Sep 50 days mid Nov-mid Dec 22 Nov 57-62,

mean 58.9 (20 Jan) 3.8 daysg (late Jan) 87-106,j mean 98.1 (late Apr)

Sooty Shearwater late Sep mid Nov-early Dec (end Nov) 52.7-56 24 Jan 5 days (end Jan) 97 late Apr-

mid May

Breeding parameters Species % not

breedingl Breeding frequency Notes on breeding frequency % early

failuresa,r % late

failuresa,v Chicks

fledging Breeding success

Black-browed Albatross (31%)m 69% 75% successful and 67% failed breeders breed the following yearq 38%s (35%) 43%q 27%q

Tristan Albatross (46%) 54%o Biennial 14%t 42%t 44%o

White-chinned Petrel (27.3%) 72.7%p 91% successful and 88% failed breeders breed the following year 32-40%p (17-24%) 66-72%p 44-45%p

Sooty Shearwater (28%)n 72% 29.9%u (22.2%) 68.3%u (47.9%)

Population structurew

Species Adult survival

Immature survival

Juvenile survival

Recruit-ment rate

Age first returna,b

Age first breeda,b

Median age first breed

Observed ann. change

Predicted ann. change

% adults

% immatures

% juveniles

Black-browed Albatross 91.5%x (75%)aa 70%ac 7%x 2-6 7-11 9 - 4.5%, -

6.9%af - 4.3%-6.7%ah 72% 9% 20%

Tristan Albatross 93%o 81%o 76%o 4-5, 6 8-9.7ae 9.7o - 2.9-5.3%o - 3.3% 64% 14% 21%

White-chinned Petrel 88% (90%)y (85%)ac (85%)ac 6.5 6.5 - 2.3%ag - 2.2% 60% 16% 24%

Sooty Shearwater 91.9%z 92%z 85.3%ad 48.9%u 3-5u 5-7 6 + 4.4%u + 4.4% 60% 11% 29%


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Appendix 2. Continued.

Distribution data used Species

Incubation Brood-guard

Post-guard

Early fail Late fail Sabbatical Immatures

(B) Non-

breeders Immatures

(NB) Juveniles

Black-browed Albatross PTT tracking

PTT tracking

PTT tracking

GLS tracking

GLS tracking

GLS tracking Sabbatical GLS

tracking Non-breeders

Non-breeders

Tristan Albatross PTT tracking

PTT tracking

PTT tracking

Breeder see notes

Breeder see notes

Breeder see notes

Breeder see notes see notes Range Range

White-chinned Petrel PTT tracking

Not included

PTT tracking see notes see notes see notes see notes GLS

tracking Non-breeders

Non-breeders

Sooty Shearwater see notes Not included see notes see notes see notes see notes see notes Range Range Range

Notes


Tristan Albatross

As breeding range covers a large proportion of global range, assumed failed and sabbatical bird were distributed as for breeders Biennial breeder with 13 month breeding season, so no non-breeding adults during non-breeding season - all are sabbatical adults.


Distribution of non-breeding birds during breeding season (including sabbatical, failed and immature birds) was assumed to be a combination of the breeding range and non-breeding range, excluding the western portion up the coast of Chile. An even distribution was assumed throughout this range.

Sooty Shearwater

GLS tracking from New Zealand during breeding (Shaffer et al) suggests that breeders travel up to 2800km from the colony, and distribution is clumped throughout this range - i.e. not concentrated at the colony. A 2800km buffer was created around the Falklands and clipped to the species' range. Breeders and non-breeders during the breeding season were assumed to have an even distribution throughout this buffer.

(values in brackets are assumed from similar species or inferred from other data presented in this table)

a Assume the same for all colonies. Brooke 2004 unless otherwise stated b Brooke 2004 unless otherwise stated c No information available - assume the same as Wandering Albatross d Schreiber 2002 unless otherwise stated e Brooke 2004 assumes c.79 days similar to other great albatrosses f Phillips, Silk, Phalan, Catry, Croxall 2004 f Handbook of Australian, New Zealand and Antarctic Birds (Marchant 1991) h Inferred from hatch and brood-guard period unless otherwise stated i Brooke 2004 gives 116 days j Hall 1987 k Ryan et al 2001 l Proportion of adults not breeding during a particular breeding season m Assume all sabbatical adults attempt breeding the following year, and that the number of annual breeding pairs is constant n Bradley et al 2000 (for Short-tailed Shearwater). Used by Jones 2002 for modelling Sooty Shearwater. o Cuthbert et al 2004 p Berrow et al 2000 q Croxall et al 1998 r Percentage of breeders failing before brood-guard s 68% eggs hatch, data from South Georgia (Georgias del Sur) t Cuthbert et al 2004 - 75% of failures occur after incubation u Jones 2002

v Percentage of breeders failing after brood-guard w As no information on populations structure was available, for each species a Leslie-Lefkovitch Matrix Model was used to obtain the stable age distribution, using the three age classes previously mentioned. Parameters for the models were obtained from the literature and are presented in this table. The model was verified by comparing the predicted annual rate of change with observed rates. x Croxall et al 1997 z Scofield 2001 breeder survival, used by Jones 2002 as adult and pre-breeder survival aa Calculated from combination of juvenile survival and recruitment rate ac No information available, so immature survival was assumed to be the same as juvenile survival, and this was adjusted until the model fit the observed rate of decline at South Georgia ad Scofield 2001 non-breeder survival estimate, used by Jones 2002 for juveniles up to age 5 ae Ryan et al 2001 give modal age of first breeding as 8 af Woehler et al 2001 - South Georgia 1976-1999, Croxall et al 1997 - South Georgia 1995-1996 ag Woehler et al 2001 - 28% decrease over 15 years at South Georgia (Georgias del Sur) ah Annual decrease of 6.7% predicted by rates given. Immature and juvenile survival were adjusted to 90 and 80% respectively to give a predicted annual decrease of 4.3%. The average of the two stable age distributions was used

spatial and temporal overlap between seabird distribution

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