University of Otago, Dunedin, New Zealand
27- 29 November 2003
1. Introduction
The purpose of this workshop was to discuss technical issues related to the assessment and management of deepwater stocks. This report, prepared by session chairs, summarises discussions and considerations of possible ways forward.
2. Session 1 - The estimation of abundance
Presentations in this session covered aspects of trawl, acoustic and egg surveys; the use of catch per unit effort data; and tag and recapture data. The presentations referred to ongoing work in the northeast, northwest and southeast Atlantic, the Ross Sea and waters around New Zealand. Species covered included orange roughy, redfish, smooth oreo dory, Antarctic toothfish and a wide range of species from the northeast Atlantic.
The question arose in discussions as to what made abundance estimation of deepwater and deep-sea species special (or not). For some deepwater species, such as orange roughy, it was noted that they have low productivity, are highly aggregating, and often are found in association with underwater features but not exclusively. And, they react to approaching survey and fishing gear not only at the time of sonification or capture but also much earlier. The reasons for their aggregating behaviour (e.g. suitable conditions or learned behaviour) were discussed but no conclusions were reached. It was recognized that more work on fish behaviour is highly desirable. It was also noted that the low productivity in deepwater may not be universal. Some "deepwater" species (particularly those with long pelagic phases, strong diurnal migration patterns, or preferred depths above about 800 m) have moderate levels of productivity.
The utility of fish egg surveys were discussed but such surveys were considered unlikely to be a good means of estimating abundance for a variety of reasons. Problems with the use of CPUE as an index of abundance were noted (also in Session 3). Trawl and acoustic surveys were viewed as potentially the most useful methods for estimating abundance. Both could be used to create relative abundance indices although the use of acoustic methods is difficult even for relative abundance estimation when the target species is also associated with other species during the survey period. Both methods present problems with respect to the estimation of absolute abundance. For acoustics surveys, difficulties include determination of target strength (backscattering cross sections) and target species identification. For trawl surveys, estimating survey catchability, or vulnerability of fish to capture, is problematic.
The use of remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) was discussed. The potential to use such technology in its own right for abundance estimation, or in experiments to estimate catchability of trawls, was noted.
Most participants agreed that more technical work alone was not sufficient to solve many of the problems associated with abundance estimation. Rather, a greater understanding of fish behaviour (both natural and in response to fishing and research vessels and gear) is needed. In particular, further work is needed on factors influencing aggregating behaviour. ROVs and AUVs may offer opportunities for progress in this respect.
Other issues of concern included those relating to stock structure, distribution and movement. Obtaining some form of relative or absolute abundance estimates may be feasible, but their validity will depend on appropriate survey designs that take account of underlying distributions and movements.
In general, it was accepted that there is no one best way to estimate abundance of deepwater fish resources but rather a range of methods analysed individually or in combination would offer the best way forward. In some areas, trawl and acoustic surveys are in regular use and the estimates and indices derived are used in stock assessments with varying degrees of success - often depending on the availability and quality of other data.
The costs of surveys are high and it was recognised that the cost-benefit of surveys was an important consideration in deciding on best ways forward in different circumstance. Dedicated research cruises undoubtedly provide the best means of providing abundance estimates and can often undertake a wider range of associated work at the same time. However, the use of industry-based surveys (especially acoustic surveys) may also provide useful inputs for stock assessments at a much lower cost.
3. Session 2 - Biology, age and growth
This was a varied session, with nine papers covering a wide range of topics. These included biological characteristics of deepwater fish species in the North Atlantic, New Zealand and Chile, stock structure, age and growth, climate change effects, and the relationships between oceanographic features and fisheries. In addition, IFREMER researchers presented a video on an ROV cruise that examined aspects of catchability, i.e. vulnerability to capture, based on video observations and trawl catches.
Given the variety of presentations, and the time available, the discussion was limited and focused on the following critical gaps in knowledge.
4. Session 3 - Assessment of deep-sea fisheries
A total of seven papers were presented in this session; however, two of these were more closely related to the topic of Session 4 (below). Topics covered in the other five papers included hyper-depletion in orange roughy fisheries (the situation where commercial CPUE decreases at a faster rate than abundance itself), and assessment methodologies and results for Namibian orange roughy, Patagonian toothfish, New Zealand hoki and northeast Atlantic (ICES region) deepwater sharks.
Based on the presentations and the outcome from ensuing discussions, session participants identified a number of key data gaps and data needs for stock assessments of deepwater species. The three most important data needs, in order of priority were agreed as follows.
Other data needs that may be crucial for some stocks, and which almost always improve the accuracy and precision of assessments if available, include:
iv. relative or absolute estimates of recruitment
v. the relationship between stock size and recruitment and
vi. age data.
Although fish age information was considered essential for estimating population productivity, session participants concluded that it is less important to devote resources to ageing stocks for which age and growth information already exists for other stocks of the same species. Estimation of ages - which enables estimation of growth rates, natural mortality and, sometimes recruitment, was crucial for determining sustainable yields for orange roughy fisheries when they were first initiated. It was not until development of a validated methodology that it became evident that orange roughy is characterised by unusually low growth rates, low natural mortality, high age at maturity and high longevity. Ageing of other orange roughy populations has demonstrated some differences in these life history parameters, but such differences may not be sufficient to justify initiation of major research initiatives on ageing, particularly if resources are limited. It may make more sense to give higher priority to other data needs, such as the need for abundance indices and simply adopt the age-length keys, growth parameters and natural mortality estimates from a similar stock.
Finally, in order to satisfy wider objectives that are often mandated by international agreements or national policy, it may be necessary to augment existing, or to set up new, programmes to provide data on:
vii. Ecosystem considerations, such as bycatch species, associated species and the effects of fishing on habitat.
Session participants also briefly discussed the situation of multi-species fisheries for which it is extremely difficult to obtain species-specific data on catch and abundance. These may need to be assessed and managed as species assemblages with application of the precautionary approach with regards to setting catch or effort limits.
5. Session 4 - Management of deep-sea fisheries
Presentations in this session covered descriptions of management arrangements for high-seas orange roughy, deep-sea and deepwater fisheries in New Zealand; development of high-seas fisheries in the western Indian Ocean and frameworks for management advice including setting of reference points.
The time for discussion did not permit consideration of all issues. Some issues (e.g. the need for new legal instruments and the use of MPAs in fisheries management) were therefore intentionally deferred, as it was thought highly likely that they would receive much attention at the DEEP SEA 2003 Conference to be held the following week. Thus, discussions were focused on four main areas:
6. General discussion
The workshop considered the potential value of a hypothetical RFMO: "The Commission for the Conservation of Deepwater Fish Stocks". There was no discussion on the logistics of creating such an organization, but rather whether or not it could have merit from a scientific and management viewpoint. It was recognized that to have merit, such an organization would need to be global and that it would need to consider a carefully agreed set of stocks. Although such an organization would have no ability to manage stocks within national jurisdictions, it could serve a management purpose for high-seas fisheries by, for example, setting catch limits, determining data collection protocols, undertaking research planning and coordination and providing compliance regimes. It would also provide a forum for the better exchange of data, assessment technologies and management approaches. This would be highly advantageous given the lack of data or information on deepwater fish species globally, as it would enhance the ability of scientists working on such fisheries to exchange information and views.
A related proposal was presented during Session 3. It was suggested that a network be established for the investigation of deep-sea fisheries and resources among scientists belonging to APEC economies. Again, workshop participants generally supported the concept, but did not discuss the logistics of such an endeavour in detail.
Overall, whilst recognizing the wide variety of life histories of deepwater fish species, workshop participants emphasized the observation that many species have a low productivity-to-biomass ratio and will therefore also have low sustainable yields. As for all fisheries, the pressing need is for complete and accurate catch and effort information, ideally at a highly disaggregated level, together with valid biomass indices (relative at least and, ideally, absolute if possible). Abundance estimates may be based on suitably modelled commercial catch rates (CPUE), or on trawl, acoustic or possibly visual techniques. The integration of commercial- and research vessel-based data collection schemes needs further investigation. In addition to basic catch data and abundance information, early fishery and ongoing otolith sampling should be undertaken to give the potential of ultimately incorporating age information into assessments.
Whilst stock assessment or management procedures may be able to provide good bases for decision-making, the collection of appropriate ancillary biological data to be used in more comprehensive analyses may be crucial for elucidating patterns in population distribution and viability (e.g. contractions or expansions of spatial or temporal distribution).
The need for further work on stock structure was also identified as another important area of research.
7. Summary: Best ways forward
Workshop participants identified the following eight actions as the immediate priorities for improving the assessment and management of deep-sea resources:
i. formulate management objectives more explicitly
ii. incorporate biological reference points and, or, performance measures into management procedures
iii. implement management systems that promote data collection (e.g. adaptive management)
iv. conduct cooperative research with the industry and other stakeholders
v. implement management procedures that do not have high information needs (e.g. design decision "triggers" for opening and closing fisheries)
vi. integrate assessment and management (using, e.g. Management Strategies Evaluation (MSE) techniques)
vii. ensure use of collective experience world-wide (using, e.g. "meta-analyses") and
viii. adhere more closely to the precautionary approach.
8. Agenda - Workshop on the assessment and management of deepwater fisheries
Time |
Authors |
Title |
|
27 November |
|||
0900 |
Session 1 - Abundance estimation |
||
0900- 0930 |
John Annala |
Workshop and session introduction |
|
0930 - 1000 |
Malcolm Clark & Chris Francis |
Counting deepwater fish: some aspects of NIWAs experience with trawl surveys, egg surveys, and CPUE analyses of orange roughy |
|
1000-1030 |
George Rose & Stephane Gauthier |
Acoustic-trawl survey methods for redfishes (Sebastes spp.) off the Grand Bank of Newfoundland |
|
1100-1130 |
Pascal Lorance |
Abundance estimates of deepwater fish species in the northeast Atlantic |
|
1130- 200 |
Ian Doonan |
Measuring abundance of smooth oreo on the Chatham Rise New Zealand with acoustic surveys |
|
1200-1230 |
Dave Boyer & Ian Hampton |
Correction for the effects of bottom slope and transducer tilt on the dead zone in acoustic surveys of orange roughy Hoplostethus atlanticus off Namibia |
|
1230-1300 |
Kevin Sullivan |
Assessment of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea using a tag and recapture experiment. |
|
1300-1400 |
Lunch |
|
|
1400-1500 |
Discussion |
||
1500 |
Session 2 - Biology and age and growth |
||
1500-1515 |
Pamela Mace |
Session introduction |
|
1515-1545 |
John Gordon |
Biological characteristics of some deep-sea fish species from the Northeast Atlantic |
|
1545-1615 |
Break |
||
1615 -1645 |
Ron Thresher & Craig Proctor |
Otolith composition as a means of stock delineation in Orange Roughy and Oreos in Australia and New Zealand |
|
1645-1715 |
Nic Bax et al. |
Three factors affecting sampled age compositions for Australian orange roughy: place, schooling behaviour and time |
|
28 November |
|||
0830-0900 |
Raul Gili & Alejandro Zuleta |
Improvement of the growth parameters estimations of orange roughy (Hoplostethus atlanticus) in Chilean waters based on a Bayesian method |
|
0900-0930 |
Di Tracey et al. |
Longevity of New Zealand deep-sea fish |
|
0930-1000 |
Allen Andrews |
Radiometric age validation of long-lived fishes |
|
1000-1030 |
Mary Livingston & Jim Renwick |
Climate change and application to fisheries management |
|
1030 -1100 |
Break |
||
1100-1130 |
Vladimir Belyaev & V. Darnitsky |
Retrospective analysis of New Zealand area oceanography |
|
1130-1300 |
Discussion |
||
Lunch |
|||
1400 |
Session 3 - Assessment of deep-sea fisheries |
||
1400-1415 |
Malcolm Clark |
Session introduction |
|
1415-1445 |
John Annala & Malcolm Clark |
Issues in the management of high seas orange roughy fisheries in the Australia - New Zealand region |
|
1445-1515 |
Andre Punt & Richard Methot |
The impact of recruitment projection methods on forecasts of rebuilding rates for overfished marine resources |
|
1515-1545 |
Allan Hicks |
Hyper-depletion in orange roughy fisheries |
|
1545-1615 |
Break |
||
1615-1645 |
Doug Butterworth & Anabela Brandao |
Aspects of the Assessments of Orange Roughy off Namibia and Patagonian Toothfish off the Prince Edward Islands |
|
1645-1715 |
Chris Francis & Malcolm Clark |
The sustainability of orange roughy fisheries |
|
29 November |
|||
0830-0900 |
Kevin Sullivan |
Stock assessment of hoki (Macruronus novaezelandiae) in New Zealand |
|
0900-0930 |
Maurice Clarke |
Assessment of deepwater species: Problems encountered and lessons that can be learned, using the ICES assessments of deepwater sharks as examples |
|
0930-1030 |
Discussion |
||
1100 |
Session 4 - Management of deep-sea fisheries |
||
1100-1115 |
Kevin Stokes |
Session introduction |
|
1115-1145 |
Kate Graham, Charmaine Gallagher & Rob Tinkler |
The Fishery Management Process of Deepwater Fisheries in New Zealand: Now and in the Future |
|
1145-1215 |
Monde Mayekiso |
High Seas Resource management: some discussion of the Madagascar Ridge, western Indian Ocean |
|
1215-1245 |
Rudy Kloser |
Target and limit reference points for orange roughy fisheries - what is achievable? |
|
1315-1500 |
Discussion and workshop report |