The Effects of Longlining on Seabird Populations: by-catch estimation, archival tagging and population modeling

Transcription

1 The Effects of Longlining on Seabird Populations: by-catch estimation, archival tagging and population modeling Dennis Heinemann Neil Klaer Tom Polacheck Geoffrey Tuck Tim Davis Date 1 January 2002 FINAL REPORT AFMA 97/98

2 1 INTRODUCTION 1.1 Background The incidental catch of seabirds in the Southern Ocean s pelagic and demersal longlining fisheries has been identified as an issue of considerable importance to the sustainability of seabird populations. Several albatross species, including the wandering albatross, Diomedea exulans, have shown marked declines in abundance throughout their range (Weimerskirch and Jouventin 1987, Croxall et al. 1990, Gales 1998). Wandering albatross and other species are frequently taken as bycatch from longline fishing fleets, and mortality associated with longlining has been implicated as the primary cause of the declines in abundance (Gales, 1993). With new and expanding fisheries form Patagonian toothfish, Dissostichus eleginoides, and increasing pressure on southern tuna stocks, there is now a critical need to enhance our understanding of the impact of seabird bycatch on bird populations through this internationally collaborative project. This project builds upon the collaborative work begun under the Australian Fisheries Management Authority (AFMA) contracts during 1995/1996, and 1996/1997 and upon the international collaboration which developed between the CSIRO, the British Antarctic Survey (BAS) and the Centre National de la Recherche Scientifique (Centre D etudes Biologiques de Chize, CEBC/CNRS). These latter two institutions are recognised as world leaders in the study of albatross biology. Since 1988, data on seabird bycatch have been collected by the Tasmanian Parks and Wildlife Service and the AFMA observer program. These data, combined with fishery observer data and AFMA logbook data provide essential information on catch rates of seabirds. Estimates of catch rates have been determined in a collaborative project between CSIRO and the Tasmanian Parks and Wildlife Service (Klaer and Polacheck 1995) and have been presented to the first and second meetings of the CCSBT Ecologically Related Species Working Group (ERSWG; Klaer & Polacheck 1995, 1997a, 1997b). These catch and catch rate estimates for the Australian Fishing Zone had required updating on a yearly basis as new data have become available. Now that the Japanese are not fishing in the Australian Fishing Zone, updates are no longer needed. In the place of the AFMA observer program, a Pilot Observer Program to collect similar data from Australia s domestic longline fisheries has been developed by CSIRO, AFMA and EA (Environment Australia). Catch rates currently provide the most feasible measure to analyse the progress of mitigation and to base management objective upon. Long-term monitoring of seabird catch and catch rates is of extreme importance in order to assess the impacts of incidental takes and determine the effect of increased recent use of mitigation measures (e.g. night setting) and changes in gear on seabird catch rates. This was recognised at the second CCSBT ERSWG meeting (Canberra 3-6 June, 1997). Preliminary population modelling assessment results completed under previous AFMA contracts indicate that seabird mortality associated with longlining can provide a reasonable explanation for the historic decline in breeding pairs observed from the South Georgia and Crozet Island wandering albatross populations. The modelling framework produced can assess the effects of the longline fishery on seabird populations, and this preliminary work was 2

3 presented to the CCSBT Ecologically Relation Species Working Group in Wellington, New Zealand in December 1995 (Tuck and Polacheck 1995). A necessary element in the development of the modelling framework was an understanding of the spatial and temporal distribution of longline effort across the Southern Ocean. Effort employed by the various southern hemisphere fisheries will have significant implications for those populations of seabirds caught by tuna longline fleets. A paper describing trends in tuna longlining fisheries in the Southern Ocean and implications for seabird by-catch was presented to the first meeting of the CCSBT-ERSWG (Wellington 1995), and an update was presented at the following meeting at Canberra in 1997 (Polacheck and Tuck 1997). The model framework that has been developed considers a range of possible hypotheses for the spatial distribution of wandering albatrosses. As expected, preliminary results are sensitive to assumptions about the spatial distribution of the birds and so there is a need to reduce this uncertainty and refine our understanding of wandering albatross foraging distributions. An understanding of the spatial distribution is critical to the modelling process and will assist with determining the spatial and temporal interaction of the seabirds with fishery; this is vital for assessing impacts and designing mitigation measures. The at-sea distribution of wandering albatross remains largely unresolved, with limited information coming from banding, bycatch data and satellite tracking. Short term information on the distribution of birds when breeding can be provided by satellite tracking, however information of the distribution of non-breeding birds is critical and archival tags currently provide the best potential technology to produce this information. Pilot work was initiated in 1995 jointly between CSIRO, BAS and CEBC/CNRS to evaluate the potential for archival tags to provide information on the spatial distribution of seabirds. Analysis of the data from the tags deployed in 1996 confirmed that the archival tags have the ability to give not only invaluable positional information, but also behavioural information (Tuck et al. 1998). The abundance of several species of Southern Ocean seabirds has declined substantially over the last three decades. The incidental catch of seabirds during oceanic longline operations has been identified as a potential source of the mortality leading to the observed declines and as such has been declared a key threatening process under Australia s Endangered Species Act. With new and expanding fisheries for Patagonian toothfish and increasing and shifting fishing pressure on southern tuna stocks, monitoring and assessment research is now critical to minmise risk to seabird populations. In order to evaluate the potential effect on seabird populations and make informed management decisions to reduce incidental catches, the estimation of catch rates and catches of seabirds in relation to season, area, fishing practices and mitigation measures is critical. Analyses of the effects of mitigation measures on catch rates of seabirds and target species is of extreme importance. A knowledge of the effect of night setting on catch rates of SBT is vital if night setting is to be used effectively as a mitigation measure, as called for in the Threat Abatement Plan. Currently little is known about the effects of night setting on SBT catch rates. 1.1 Objectives 1. Update estimates of the seabird catch and catch rates and their associated variances within the Australian Fishing Zone by area and season. 3

4 2. Analyses of the effectiveness of various mitigation measures used to reduce seabird bycatch. Explore the consequences of night setting on southern bluefin tuna catch rates, and evaluate the potential for wider adoption of night setting as a mitigation measure. 3. Continue work on the deployment and analysis of data from archival tags. 4. Update the wandering albatross population model in collaboration with BAS and CEBC/CNRS, and explore additional hypotheses regarding the impact of longlining on wandering albatross populations. 5. Extend the albatross model to include other species of Southern Ocean albatrosses. 2 RESULTS 2.1 Bycatch Rates CSIRO Marine Research continued its efforts at providing annual updates to estimates of bycatch rates of seabirds in the Japanese tuna fishery within the Australian Fishing Zone, up until the time they were excluded from the AFZ. Estimates for 1996/1997 were completed and presented to second meeting of the CCSBT-ERSWG in 1997 (Klaer & Polacheck 1997). Those results are reproduced in Appendix 1. Estimates for the 1997/1998 seasons were completed and presented to the third meeting of the CCSBT-ERSWG, 9-12 June 1998, Tokyo, Japan (Klaer & Heinemann 1998). Those results are reproduced in Appendix 1. In addition to these annual updates to Japanese bycatch data, other work on seabird bycatch estimation was completed. Also, presented to the 1998 CCSBT-ERSWG meeting in Toyko, were the results of observations carried out onboard two domestic vessels operating off the east coast of Australia (Young et al. 1998). Those results are reproduced in Appendix 2. In 1999 CSIRO Marine Research completed a contract with AFMA and EA to develop a pilot observer seabird bycatch observer program for Australia s domestic longline fisheries (Heinemann et al. 1999). As part of that work and for the purposes of this contract, all of the available data on seabird bycatch in domestic longline fisheries was collated and analyzed. The relevant text and tables from Heinemann et al were extracted and are presented in Appendix Mitigation & Night Setting Results of analyses on the effects of environmental factors and mitigation measures on the bycatch rates in the Japanese fishery were presented to the third meeting of the CCSBT-ERSWG, 9-12 June 1998, Tokyo, Japan and later published in the journal Emu (Klaer & Polacheck 1998) and is reproduced in Appendix 4. This paper and work by other researchers (Brothers et al. 1999) have identified night setting as potentially the most effective mitigation measure available. However, resistance to the use of night setting has occurred in all tuna fisheries. Concerns range from the potential loss of catch, to inefficient and costly operating procedures, to crew safety issues. Data to assess the potential qualitative and quantitative effect of night 4

5 setting on the catches of tuna in the Japanese fishery were limited because little data met the requirements for inclusion in analyses. Therefore, plans were developed for the analysis of additional datasets, the use of hook monitors and other methods of determining the time at which tuna are caught, inferring catch patterns from information on the natural feeding patterns, and the design of a sampling experiment to collect new data on this specific question. These plans were presented to the third CCSBT-ERSWG meeting in Japan (Heinemann 1998), and are reproduced in Appendix 5. The plans were received favorably at the meeting. An ERSWG working committee modified the plans and put them forward in a technical document with recommendations to CCSBT and its Scientific Committee; the modified plan is reproduced in Appendix 6. Subsequently, some of these ideas were incorporated into research proposals to AFMA s Tuna Ecologically Related Species Working Group (Appendix 7). One proposal was funded, but the project could not be undertaken because the Principal Investigator left CSIRO. 2.3 Archival Tags Technical and logistic problems encountered during the period of this contract prevented the deployment of additional archival tags on wandering albatrosses. The evaluation of positional resolution of the existing archival tag data and analyses of the spatial distribution generated from these data were not completed. 2.4 Update Wandering Albatross Model The modelling framework for the analysis of the population dynamics of wandering albatrosses and their interactions with longline fisheries, first described in Tuck and Polacheck 1995, has undergone continued development. That development has included significant improvements to data inputs, model structure and the fitting algorithm used in the model. The latest version of the model and the modelling results for wandering albatross populations on Bird Island and the Crozet Islands have been submitted for publication (Tuck et al. In Press). That manuscript is reproduced in Appendix Extend Albatross Model Work started on the application of the albatross model to other species. This process involved obtaining data for those species, and modifying the model to handle differences in the demographic system. Specifically, the model was being modified to handle annual breeders, i.e. species that breed every year, and to address more complicated spatio-temporal albatrossdistribution hypotheses. This work was not completed. On Bird Island, sufficient data are available to model the population dynamics of the annually breeding black-browed (Diomedea melanophrys) and biennially breeding grey-headed albatross (D. chrysostoma), both species that have shown population declines possibly related to longline fishing mortality (Croxall et al. 1998, Croxall pers. com.). On the Crozet Islands, sufficient data appear to be available for 3 species: biennially breeding sooty (Phoebetria fusca), biennially breeding light-mantled sooty (P. palpebrata) and annually breeding black-browed albatross (Weimerskirch and Jouventin 1998, Weimerskirch pers. comm.). All of these 5

6 populations have also shown population declines in recent decades, and longline fishing is believed to have been an important factor. ACKNOWLEDGEMENTS Portions of the work reported here build upon previous research sponsored by AFMA and the work on the design of an observer program (Appendix 5) was done as part of a contract to Environment Australia. This Appendix has been included so that the current report provides a comprehensive set of documents on seabird research. We also wish to acknowledge and thank all of the observers who have contributed data that have been utilized in this report. REFERENCES Brothers, N., R. Gales, and T. Reid The influence of environmental variables and mitigation measures on seabird catch rates in the Japanese tuna longline fishery within the Australian fishing Zone, Biological Conservation 88: Croxall, J.P., P. Rothery, S.P.C. Pickering, and P.A. Prince Reproductive performance, recruitment and survival of wandering albatross Diomedea exulans at Bird Island, South Georgia. Journal of Animal Ecology 59: Croxall, J.P., P.A. Prince, P. Rothery and A.G. Wood Population changes in albatrosses at South Georgia. In: Albatross Biology and Conservation. G. Robertson and R. Gales (Editors). Surrey Beatty & Sons, Chipping Norton, Australia. Pp Gales, R Co-operative mechanisms for the conservation of albatross. Australian Nature Conservation Agency. Tasmanian Government Printer, Hobart, Australia, 132 pp. Gales, R Albatross populations: status and threats. In G. Robertson and R. Gales (eds), Albatross Biology and Conservation. Surrey Beatty and Sons, Chipping Norton, Australia. Pp Klaer, N. and D. Heinemann Japanese longline seabird by-catch in the Australian Fishing Zone, April 1997 March Third meeting of the Council for the conservation of southern bluefin tuna ecologically related species working group; 9-12 June 1998, Tokyo, Japan. CCSBT-ERS/9806/24, 9 pp. Klaer, N. and T. Polacheck Japanese longline seabird by-catch in the Australian Fishing Zone April 1991 March 1994: catch and catch rates by area and season and an evaluation of the effectiveness of mitigation measures. CSIRO Division of Fisheries Report. Klaer, N. and T. Polacheck. 1997a. Japanese longline seabird bycatch in the Australian Fishing Zone April 1995 March CCSBT-ERS 1997 Working Group Document. Klaer, N. and T. Polacheck. 1997b. By-catch of albatrosses and other seabirds by Japanese longline fishing vessels in the Australian Fishing Zone from April 1992 to March Emu 97:

7 Klaer, N. and T. Polacheck The influence of environmental factors and mitigation measures on by-catch rates of seabirds by Japanese longline fishing vessels in the Australian region. Emu 98: Tuck, G. and T. Polacheck Trends in tuna longline fisheries in the southern oceans and implications for seabird bycatch: 1997 update. Second meeting of the Council for the Conservation of Southern Bluefin Tuna Ecologically Related Species Working Group; 3-6 June 1997, Canberra, Australia. CCSBT-ERS/9706/35, 9 pp. Tuck, G., T. Polacheck, J. Croxall, H. Weimerskirch, P. Prince and S. Wotherspoon The potential of archival tags to provide long-term movement and behaviour data for seabirds: first results from wandering albatross (Diomedea exulans) of South Georgia and the Crozet Islands. CSIRO draft document. Weimerskirch, H. and P. Jouventin Population dynamics of the wandering albatross, Diomedea exulans, of the Crozet Islands: causes and consequences of the population decline. Oikos 49: Weimerskirch, H. and P. Jouventin Changes in population sizes and demographic parameters of six albatross species breeding on the French sub-antarctic islands. In: Albatross Biology and Conservation. G. Robertson and R. Gales (Editors). Surrey Beatty & Sons, Chipping Norton, Australia. Pp

8 APPENDIX 1 Japanese longline seabird bycatch in the Australian Fishing Zone, April 1997 March 1998 Neil Klaer Dennis Heinemann 15 May 1998 Document prepared for the third meeting of the CCSBT Ecologically Related Species Working Group, 9-12 June 1998, Tokyo, Japan 8

9 Introduction This working paper presents tables of estimates of seabird by-catch by Japanese longline vessels operating in the Australian Fishing Zone from April 1997 to March The tables supply updated information to that given in Klaer and Polacheck 1995, 1996 and The methods used to derive the estimates are the same as those used and documented in Klaer and Polacheck (1995) to derive estimates from April 1991 to March Results are presented here for comparable area and time strata. No analysis of catch and catch rate by species is presented, as information on the species identification of seabirds retained by observers was not available to us. These results underestimate the total number of seabirds actually killed because a fraction of birds captured are lost before the line is hauled, and therefore are not observed. Captured seabirds can be eaten by sharks or other fish before the longline is hauled and some are torn from the line during hauling (Brothers 1991). Some birds are known to escape after being hooked (Weimerskirch & Jouventin 1987; Huin & Croxall in press) and may subsequently die. In addition, crew on some vessels dispose of captured seabirds during hauling by quickly cutting them away, and some of these may be missed by the observers. Brothers (1991) reports that the estimated number of birds observed to have been captured during a set was 27% more than the number subsequently observed to be hauled on board (this includes birds hooked but which escape before being hauled underwater). As such, the estimates of incidental catch based on the observed numbers recovered during hauling operations, as in this paper, may substantially underestimate actual seabird kills. Data Processing and Analyses Observer data was filtered to remove records that appeared to be recorded incorrectly, and those that could not be matched with records on the Japanese AFZ longline logbook database. In 1997, 17% of the sets or 9% of the birds were removed, which was not unusual when compared to the previous two years (Table 1). Table 1. Observer data filtering for by-catch and by-catch rate analyses. The numbers of records rejected by category are given to indicate the importance of different problems, but are not additive, and, therefore cannot be summed to give the total number of invalid records. Sets Birds Total Total Total records Reason for rejection Bad position or outside AFZ mis-match with logbook Other Number valid Percent valid e.g. observed greater than total number of hooks, insufficient data to calculate variances 9

10 Changes in Data Reporting Monitoring of the Japanese fleet within the AFZ moved in 1996 from the collection of paper logbook records and reporting of fishing effort via radio to real-time reporting of catch and effort via satellite (known as the Vessel Monitoring System or VMS). In the past, there was a considerable delay in the receipt of vessel logbooks by the Australian Government as these were often sent when the vessel returned to Japan. Delays were more than a year in some cases. Due to this delay, daily radio reports of numbers of hooks set and noon position of Japanese vessels were often used for the calculation of total effort recently expended by Japanese vessels in the AFZ by area and time. There have always been problems in completely matching observer records with vessel logbook or radio report data for individual vessel sets. A match is required to allow the data to be used in catch calculations such as those presented in this paper. In particular, matching observer records with radio report data was problematic as radio reports give the vessel noon position and hooks set since the previous radio report. Observers record details on start and end times and position for setting and hauling. As Japanese vessels normally carry out one fishing operation per day, to match observer and radio report data it was normally assumed that the radio report refers to the haul completed in the previous 24 hours as recorded by the observer. This was not always the case, and some mis-matching was expected. The introduction of VMS has continued this problem, as VMS reports are made in the same way as the old radio reports. A noon position is reported, as well as catch and effort details for the previous 24 hours. Effort is being made to change this standard to reporting a time and position for some part of the last fishing operation (start of set, end of haul, etc.), which would allow simple crossreference of observer records. Such a change would greatly increase the utility of the data collected via VMS. In the past, our estimates of seabird by-catch and by-catch rate have been stratified by season, area, and gear type (Klaer and Polacheck 1995, 1996 and 1997). To make stratified estimates, it must be possible to stratify both the observed and unobserved data according to the factor of interest. Gear type, actually mainline material (traditional kuralon or lighter monofilament) has been determined to be important for the calculation of seabird by-catch rates. The paper logbook system contained a gear detail sheet in which was recorded a description of the gear used by a Japanese vessel while fishing in the AFZ. Unfortunately, the VMS system that replaced the logbook system does not have a facility for the reporting of gear used by all vessels. Our only record of gear used now comes from those vessels that were observed. In the past, the number of vessels using monofilament has been small, and they were specifically targeted for observer coverage. Up to 1996, we are confident that most or all of the vessels that used monofilament were identified. For 1997, however, this was not possible. We know that some vessels that used monofilament in the AFZ in 1997 were not observed, and that no data was collected on the gear used on non-observed vessels. This means that we now do not have the data required to make estimates of seabird bycatch and by-catch rates in the same manner as for previous years, ie. Using the gear type stratification. Accordingly, calculations are provided in this paper without use of the gear type stratum for For comparative purposes, we present data for the previous years stratified in the same way, ie. By season and area only. In 1997, a number of vessels fished in the zone surrounding Norfolk Island, and an observer was placed in that area. Historically there has not been a large amount of 10

11 Japanese longline effort expended in Australian remote territories. Therefore, to maintain comparability with results produced previously, the fishing effort, and the small number (3) of birds caught in that zone are not included in these analyses. Results The distribution of Japanese longline sets within the AFZ during winter and summer 1997 are shown in Figure 1. Fishing effort was much lower in summer than winter, and the distributions differed, with virtually no fishing occurring on the east coast north of Tasmania and the effort on the west coast shifting north. These seasonal changes were very similar to those in previous years (see figures in Klaer and Polacheck 1995, 1997). Compared to 1996, the total effort in 1997 that could be used for estimating seabird bycatch and by-catch rates was considerably higher in winter (103 versus 78 cruises, and 2238 versus 1884 sets), but the summer effort declined significantly (1 versus 8 cruises, and 5 versus 174 sets). The distributions of fishing effort with observers in 1997 (Figure 2) showed a very similar pattern to the total distribution of effort (Figure 1). The proportion of cruises and sets in 1997 that were included in the analysis with observers was similar to that in 1996; 36% versus 43% and 13% versus 16%, respectively. All seabird by-catch and by-catch rates presented in previous reports have been calculated using a stratification procedure which has included area, season and gear type. Stratification by gear type for the 1997 data was not possible for the reasons described above. Therefore, estimates for 1997 are stratified by area and season only (Table 2); comparable estimates for 1995 and 1996 are shown in Appendix

12 Figure 1. Japanese longline fishing effort in the AFZ April 1997 to March 1998 for winter (left panel) and summer (right panel). Each point represents a single set. Regions used for stratification (North West Australia, North East Australia, South East Australia, Eastern Tasmania, Western Tasmania, Southern Australia and South East Indian Ocean) are overlayed on the maps. 120 E 140E 160 E 120 E 140E 160 E JOP 97 WIN JOP 97 SUM NW Aus NE Aus NW Aus NE Aus 20S 20S 20S 20S SE Aus SE Aus 40S 40S 40S 40S SE Ind SE Ind S Aus W Tas E Tas S Aus W Tas E Tas 120 E 140E 160 E 120 E 140E 160 E Figure 2. Observed Japanese longline fishing effort in the AFZ April 1997 to March 1998 for winter (left panel) and summer (right panel). Each point represents a single set. Regions used for stratification (North West Australia, North East Australia, South East Australia, Eastern Tasmania, Western Tasmania, 120 E 140E 160 E 120 E 140E 160 E OBS 97 WIN OBS 97 SUM NW Aus NE Aus NW Aus NE Aus 20S 20S 20S 20S SE Aus SE Aus 40S 40S 40S 40S SE Ind SE Ind S Aus W Tas E Tas S Aus W Tas E Tas 120 E 140E 160 E 120 E Southern Australia and South East Indian Ocean) are overlayed on the maps. 140E 160 E Of the 31 seabirds observed killed in 1997, 29 were caught in the Eastern Tasmania area during the winter season. The winter by-catch rate in that area (0.15 seabirds per 12

13 1,000 hooks ) was, with the exception of 1994 (see below), higher than in previous years (0.09 in 1996, 0.10 in 1995, 0.04 in 1993, 0.05 in 1992, and 0.04 in 1991). Because all the cruises had observers on board, this by-catch rate scaled-up to an estimated 84 seabirds killed (not all sets were observed). The remaining two birds were caught the South East Indian Ocean area in the winter. Because there were 23 sets with observers and 177 without, the relatively low by-catch rate (0.04 seabirds per 1,000 hooks) scaled up to an estimated 28 seabirds killed. In the past, when observers have been deployed in this area, by-catch rates were considerably higher (0.59 in 1996 and 0.75 in 1993). The lack of seabird by-catch in the North East Australia area is the same as what happened in , although high by-catch rates occurred there in This pattern was similar as what occurred in the South East Australia area no by-catch in 1997, low rates for ( ), and high rates for 1991 to 1993 ( ). Table 2. Estimated by-catch and by-catch rates of seabirds in the AFZ for The shaded values had to be estimated indirectly because of insufficient sampling effort. Area Season Cruises Sets 000 Hooks Birds Variance S.D. C.V. Catch Tot Obs Tot Obs Tot Obs Obs Tot Set Cruise Total Rate NE Aus Summer E Tas Winter NE Aus Winter SE Aus Winter SE Ind Winter Observed strata Southern strata Total strata These comparisons have been made without stratifying by gear type, because of the data limitations in The effect of stratifying by gear type can be examined in a simple manner by looking at the estimates of overall seabird by-catch rate. The southern areas were selected to make this comparison because that is where most bycatch has occurred. As expected, differences were found in overall by-catch rate estimates depending on whether stratification by mainline material was included in the analysis (Figure 3). Figure 3. Overall by-catch rate of seabirds in southern areas and 95% confidence intervals calculated with (+ mono) and without stratification (- mono) by gear type (monofilament and traditional mainline material); the stratification could not be performed in 1997 for the reasons described earlier. 13

14 Ca tch 0.35 rat e 0.30 (pe r 0.25 ' ho ok 0.15 s) 0.10 mean + mono 95% ci + mono mean - mono 95% ci - mono During 1992, monofilament was not used, and so the estimates are identical. In the summer of 1993, a small number of observed vessels that used monofilament caught a large number of seabirds in comparison with other observed vessels using traditional gear in the same areas. In response to this situation, and in consideration of the possibility that monofilament gear increased the time that baits were accessible to seabirds, gear (mainline) type was included subsequently as a stratum in the estimation of by-catch and by-catch rates (Klaer and Polacheck 1995). This results in a much lower estimate of by-catch rate variance, compared to that when the data were not stratified by gear type (Figure 3), and reduces the uncertainty in the overall estimate of by-catch. Stratifying reduced the overall by-catch rate estimate, in this case, because of the particular distribution of observer effort and by-catch. In 1994, observed vessels using monofilament were still few in number, but, unlike 1993, did not catch comparatively larger numbers of seabirds, so the two estimates produced by the different stratifications and their variances are nearly the same. At the time, this change was interpreted as probably due to the scattered and clumped nature of seabird catches. The same situation continued for estimates made for 1995 (Table 2; Klaer and Polacheck 1997). In 1996, in the South East Indian Ocean area during winter, observers were placed on two vessel using monofilament and one using traditional gear (Klaer and Polacheck 1997). This observation effort was unbalanced, as the number of vessels actually using traditional gear was much greater than those using monofilament in that area/time stratum (13 traditional versus 2 monofilament). Contrary to expectations, the vessel using traditional gear caught a large number of seabirds consistently over a number of separate sets. This meant that the high by-catch rate for the single vessel using traditional gear was scaled to a large proportion of the effort in the stratum, leading to the calculation of a high catch rate overall. It was noted at the time that the overall AFZ by-catch rate was heavily influenced by the observations made from this single cruise. Calculations made by pooling the data for that area/time stratum leads to a lower overall AFZ 1996 by-catch rate estimate, but much larger variance (as shown in Figure 3).

15 Table 2. Comparison of observed by-catch rates of seabirds by gear type pooled annually for all southern strata from 1992 to Year Traditional Gear Monofilament Gear Ratio Sets Birds Rate Sets Birds Rate These differences across years in the relative by-catch rates of vessels using the two gear types can be shown to be statistically, significantly different, at least in some years (see Klaer and Polacheck 1995). However, we also recognise that seabird distributions are clumped and that seabird captures are relatively rare events (Klaer and Polacheck 1998), so the significance of these differences is over-estimated if random distribution is assumed and sample sizes are not very large. This aside, the data suggests a change in the effect of monofilament gear from being associated with large by-catch in 1993, to smaller by-catch from 1994 to Anecdotal reports from AFZ observers and our calculations suggested that monofilament did increase chances of catching seabirds when it was first introduced. We cannot give a reason for this change, except to note that Japanese operators may have modified their fishing methods in a way that offset the effect (eg. Better construction of tori poles, thawing of baits, use of bait throwers, more setting at night, line weighting, etc.), or the hypothesised link between the use of monofilament line and higher seabird by-catch rates may have been incomplete. A thorough scrutiny of the written observer reports for monofilament vessels during 1994 to 1996 with regard to these issues, or directed trials may provide some information on this question, but neither has yet been undertaken. One new adjustment reported by observers was the practice of attaching heavy (2kg) weights to the buoy lines. Such practices are not included in the standard set of details collected by observers for entry into the observer database. A modification of the type of data collected routinely by observers on the gear used on longline vessels deserves consideration particularly in relation to how weighting is carried out, or generally on how fast the line sinks. Given that there is evidence to support the case that monofilament and traditional gear type catch rates are different (greater or less depending on the year), estimates based on the full stratification by area, season and gear type will have more validity. Therefore, by-catch rates calculated using the full stratification and previously presented for the period 1992 to 1996 are the most precise. Unless information becomes available to allow us to continue to stratify the data by gear type, our best estimates from 1997 onwards will, of necessity, be less precise. Nonetheless, the overall by-catch rate in was so low that stratification by gear type, in addition to area and season, would not make a large difference. 15

16 References Brothers, N Albatross mortality and associated bait loss in the Japanese longline fishery in the Southern Ocean. Biological Conservation 55, Huin, N. & Croxall, J.P. In press. Fishing gear, oil and marine debris associated with seabirds at Bird Island, South Georgia, 1993/94. Marine Ornithology. Klaer, N. and Polacheck, T Japanese longline seabird bycatch in the Australian Fishing Zone April 1991 March 1994: catch and catch rates by area and season and an evaluation of the effectiveness of mitigation measures. CSIRO Division of Fisheries Report. Klaer, N. and Polacheck, T Japanese longline seabird bycatch in the Australian Fishing Zone April 1994 March CCSBT ERS 1996 Working Group Document. Klaer, N. and Polacheck, T Japanese longline seabird bycatch in the Australian Fishing Zone April 1995 March CCSBT ERS 1997 Working Group Document. Klaer, N. and Polacheck, T The influence of environmental factors and mitigation measures on by-catch rates of seabirds by Japanese longline vessels in the Australian region. Paper modified for publication from the ERS 1997 Working Group Document by the same title. Weimerskirch, H. & Jouventin, P Population dynamics of the Wandering Albatross, Diomedea exulans, of the Crozet Islands: causes and consequences of the population decline. Oikos 49,

17 Appendix 1.1 Estimated by-catch and by-catch rates of seabirds in the AFZ, stratified by area and season, for The shaded values had to be estimated indirectly because of insufficient sampling effort. Area Season Cruises Sets 000 Hooks Birds Variance S.D. C.V. Catch Tot Obs Tot Obs Tot Obs Obs Tot Set Cruise Total Rate E Tas Summer E Tas Winter NE Aus Summer NE Aus Winter NW Aus Summer S Aus Summer S Aus Winter SE Aus Summer SE Aus Winter SE Ind Summer SE Ind Winter W Tas Summer W Tas Winter Observed strata Southern strata Total strata Estimated by-catch and by-catch rates of seabirds in the AFZ, stratified by area and season, for Area Season Cruises Sets 000 Hooks Birds Variance S.D. C.V. Catch Tot Obs Tot Obs Tot Obs Obs Tot Set Cruise Total Rate E Tas Summer E Tas Winter NE Aus Winter NW Aus Summer NW Aus Winter S Aus Winter SE Aus Summer SE Aus Winter SE Ind Winter W Tas Summer W Tas Winter Observed strata Southern strata Total strata

18 APPENDIX 2 The Ocean Colour Project: fishing effort, and shark and seabird by-catch on three domestic tuna longliners in eastern Australian waters Jock W. Young Dennis Heinemann Rosemary Bailey Don C. McKenzie Jessica Farley 2 June 1998 Document prepared for the third meeting of the CCSBT Ecologically Related Species Working Group, 9-12 June 1998, Tokyo, Japan 18

19 Introduction In 1993 a field study supporting ocean colour satellite imagery in Australian waters was funded jointly by Australia s Fisheries Research and Development Corporation and Eastern Tuna Management Advisory Committee (Parslow and Lyne 1994). The aims of the project were to provide ground-truth data to calibrate the satellite imagery and to examine the relationship, if any, between tuna and billfish and ocean colour, a measure of ocean productivity, off eastern Australia. Delays in the launch of the ocean colour satellite meant that the start of fieldwork was postponed until early As a part of the project, CSIRO observers spent time aboard domestic longline fishing vessels operating on the east coast of Australia. They collected catch data and water samples for analysis. A summary of the fishing practices and catch data, including bycatch, are included in this report. Methodology The field program centred around three domestic longlining vessels operating in two very different oceanographic environments and fisheries on the east coast of Australia, one working out of Mooloolaba, a coastal port 90km north of Brisbane, and the other two operating out of the port of Bermagui on the south coast of New South Wales. All boats are ~20m in length and fish for southern bluefin tuna, yellowfin tuna, bigeye tuna and broadbill swordfish depending on the season and area. Each boat is capable of setting over 1000 hooks on 60km of monofilament mainline. Trip duration for these and other boats in the area is for 2 to 3 days, and trips are generally restricted to waters within nm of the coast (on the continental shelf). Each vessel was equipped with an underway sampling device developed by CSIRO Marine Research to collect measurements of salinity, fluorescence (a measure of phytoplankton concentration) and temperature at the sea surface. Each month, a CSIRO observer spent up to 4 days on each boat. Their duties included collecting samples of seawater for determination of salinity and chlorophyll, recording the fishing practices of the vessels and recording details of all fish taken during each set. Results Nine observer trips, 4 out of Bermagui and 5 out of Mooloolaba, have been completed between May 1997 and February 1998 (Table 1), and a further 6 are planned. A total of 5,700 hooks were observed in Bermagui and 16,100 hooks in Mooloolaba. The number and relative proportions of the major fish species caught are shown in Table 2. In total, four seabirds, none of which were albatrosses, were caught during the observer trips. As well, 46 sharks were caught. Fishing Practice and by-catch Bermagui The longline vessels observed in this area generally worked within 100nm of the coast around 36 S, but have worked as far north as 28 S. In previous seasons they have worked as far south as SE Tasmania and up to Mooloolaba. They usually set one 19

20 longline per day. Generally lines are set during daylight hours, usually from first thing in the morning until ~10am, and "soak" for the remainder of the day. The vessel returns to the start of the set to begin retrieving after dark. However, setting times can vary depending on weather conditions. Between 550 and 1000 hooks are set on 60km of mainline during each shot. Bait consists of live bait (mackerel and yellow tail), fresh bait (rat tails) or frozen bait (mackerel, pilchards or squid plus glow sticks) depending on the latitude and the season. The vessels targeted yellowfin, bigeye and southern bluefin tuna depending on the season. There appears to be a potential for seabird interaction in the Bermagui area because lines are set sometimes during daylight and there can be large numbers of seabirds present (mostly shearwaters). Shearwaters, albatrosses and other seabirds have been observed following the vessels whilst shooting away. Shearwaters are the main species for potential interaction as they can, at certain times of the year, aggregate around the stern of the longliners during setting. Seabirds were observed flying and/or feeding during the setting of all lines observed, and varied between <10 to >100 birds. Four shearwaters (muttonbirds) were caught during the trips observed in this area, all during one haul in November. Given the small amount of fishing effort observed (only 2 vessels, 4 trips and less than 6,000 hooks), no useful inference can be made about seabird by-catch rate. The setting of lines during daylight appears to be in response to the presence of sharks, which can be a significant problem at times. Hooks are soaked during the day and winched up after dark to try to avoid the loss of hooked fish to sharks and minimise damage to fishing gear. The total observed catch of sharks was 13 in the Bermagui area. Mooloolaba The vessel working out of this port usually works a wider area than the main domestic fishery off Mooloolaba, generally in the area of the Morton Seamount. The vessel is equipped with a fuel bladder to enable it to work up to 150nm offshore. It aims to set one longline per day, and, in contrast to boats working in mores southern waters, sets its line immediately after dark. The longline soaks overnight, during which time the vessel returns to the start of the set to begin retrieving, usually starting at 7am. Between 500 and 1150 hooks are set on each shot. Depending on the month, three main commercial species are caught out of Mooloolaba yellowfin and bigeye tuna and broadbill swordfish. Bait consists of squid (Loligo spp.) aided by glow sticks. There appears to be less potential for seabird interaction in the Mooloolaba area because lines are usually set during the night (or very early morning), and there are generally fewer birds present in the area. Birds were recorded as flying and/or feeding during only 6 of the 17 shots observed. Shearwaters, albatross (very rare) and other seabirds have been observed following the vessel but in smaller numbers compared to the Bermagui area to the south. Again, shearwaters are the main species for potential interaction. No seabirds of any species were caught during the trips in this area. The total observed catch of sharks was 36 in the Mooloolaba area. 20

21 Discussion The small number of vessels in this study strongly constrains the conclusions that can be drawn about interactions between the domestic longline fleet and ecologically related species. Periodically, muttonbirds and other seabirds crowd the stern of boats working out of Bermagui, however, four muttonbirds were the only mortalities observed, and they were likely to have been short-tailed shearwaters, a species not listed as vulnerable or endangered. Anecdotal observations suggest that the presence of seabirds decreases to the north of Bermagui. Bird sightings were low off southern Queensland in comparison with waters further south. These results are consistent with previous observations from Australian domestic longline vessels, in which seabird by-catch rates in Queensland have been zero, and some seabirds have been caught off New South Wales (Brothers 1995; Polacheck 1995; Whitelaw 1995, 1997). Our observations show that ~6% of the longline catch is composed of sharks, and, as such, they suggest that the by-catch of sharks may not be insignificant. However, outside of a stock assessment context, it is not possible to evaluate the magnitude of any potential impacts. References Brothers, N. and Foster, A. (1995) Seabird catch rates: an assessment of causes and solutions in Australia s tuna longline fishery. CCSBT-ERS/95/19. Parslow, J. and Lyne, V. (1994) Development, application and evaluation of the use of remotely sensed data by Australian fisheries (FRDC project number 94/045) Polacheck, T. (1995) Summary tables of available information on seabird by-catch by Australian tuna longline vessels. CCSBT-ERS/95/40. Whitelaw, W. (1995) Some observations on seabird by-catch by Australian tuna longline fishing vessels. CCSBT-ERS/95/46. Whitelaw, W. (1997) Some observations on seabird by-catch from Australian longline fishing vessels CCSBT-ERS/97/. 21

22 Table 1. Summary of the number of cruises and shots observed in the Ocean Colour study between May 1997 and February Area Month No. of sets Total no. hooks Mooloolaba July Aug Oct Nov Feb Bermagui May Sept Nov Feb Total 9 cruises

23 Table 2. Summary of species caught by longliners involved in the Ocean Colour study between May 1997 and February Species Count % Albacore tuna Bigeye tuna Yellowfin tuna Southern bluefin tuna Black marlin Blue marlin Striped marlin Broadbill swordfish Lancet fish Manta ray Rudder fish Blue whaler shark Mako shark Ocean white tip shark Tiger shark Bronze whaler shark Unidentified shark species Others Total

24 APPENDIX 3 Pilot Seabird Bycatch Observer Program for Australian Domestic Longline Fisheries Design Guidelines Options and Recommendations Dennis Heinemann Jessica Farley Naomi Clear John Gunn Neil Klaer Wade Whitelaw 29 January 1999

25 2. FISHERIES DESCRIPTIONS 2.1 Tuna Fisheries Potential for seabird interactions The domestic and Japanese longline fisheries within the AFZ generally target the same species, fish the same areas and use the same fishing approaches. However, some features of the domestic fisheries suggest that they may have a lower seabird bycatch rate than the Japanese fishery. Those features generally include: 1) shorter mainlines and fewer hooks per set, 2) smaller vessels, which are lower to the water, 3) slower setting speeds, 4) the use of live bait in some cases, and 5) lack of offal discharge Frequency a Number of hooks per shot Frequency b Number of hooks per shot Figure 1. Number of hooks per set (shot) in the domestic (a) SBT (longline sector), and (b) non-sbt tuna fisheries, between January 1997 and June

26 However, other factors could produce higher bycatch rates, such as: 1) the use of monofilament mainlines (which sink more slowly than Kuralon mainlines), 2) weighting lines less, and 3) the lower prevalence and inconsistent use of mitigation measures such as night setting, bird lines, bait casters and bait thawing. Very few data are available from the domestic tuna fisheries to compare to the large body of bycatch statistics from the Japanese SBT fishery (Klaer & Polacheck 1995, 1997, Klaer & Heinemann 1998, Brothers et al. 1998a, b). What is available for domestic fisheries, has been collected since 1994 by CMS and Tasmania Parks and Wildlife Service observers on a largely ad hoc basis on a small number of longline fishing vessels. The results from most of these cruises, which are provided in Whitelaw (1997), Young et al. (1998), Brothers et al. (1998a, b), Brothers & Foster (in press), are summarised in Table 4. Table 4. Seabird bycatch rates in the domestic tuna fisheries on the east coast during summer and winter, combining data for Area Season Trips Sets Hooks (x10 3 ) Bycatc h (birds) Bycatch Rate (birds per 10 3 hooks) Northern Summer Queenslan 1 d Winter Southern Summer Queenslan 2 d Winter New South Wales Tasmania Summer Winter Summer Winter Cairns area, 2 Mooloolaba area For comparative purposes the range of bycatch rates for the Japanese fishery are provided in Table 5. No birds were caught on any of the 28 trips sampled in Queensland over 4 years. Within the Japanese fishery only two birds have been observed caught in that same area and period. 26