CCAMLR

A reliable commercial tagging program is critical to the successful assessment and management by CCAMLR of a number of toothfish fisheries in Antarctica. The evaluation of the tagging programme relies on two key aspects (i) that the tagged fish have a good chance of survival and (ii) that the tagged fish are reliably detected when recaptured. Previous attempts to evaluate individual vessel tagging performance in relation to these two aspects has been thus far inconclusive because of confounding factors such as time and location of tagging and subsequent fishing effort, as well as size of fish tagged.

We propose that, by controlling for the spatial and temporal confounding factors using a case-control study design, we can derive meaningful indices of relative tagging performance of groups of fishing effort (e.g. vessel, vessel-trip). We developed indices to compare (i) the tag detection rate of recaptured fish and (ii) the tagging survival of released fish.

This method was applied to the toothfish tagging data in CCAMLR Subareas 88.1 and 88.2. Initial results show that the indices developed can provide evidence of significant differences in tagging performance between different groups of fishing effort. Preliminary investigation showed these indices are robust to the choice of the control group and the area included in the analysis. Subject to further checks, this method could be used to investigate the relative tagging performance of different components of the CCAMLR tagging program across all fisheries, and more generally the relative performance of spatially and temporally heterogeneous data sets.

At its 2011 meeting, the Scientific Committee agreed that a time series of relative recruitments from a well-designed survey could be a useful input into the Ross Sea stock assessment model and endorsed a proposal to carry out this work once the fishery had closed at the end of the 2011/12 season. The survey had two main objectives: (i) To establish the feasibility of developing a time series of longline surveys to monitor pre-recruit (<100 cm TL) toothfish in the south of SSRUs 881.J and 881.L in the southern Ross Sea using standardised gear in a standardised manner; and (ii) To carry out experimental depth-stratified fishing in 400–600 m depth adjacent to the survey boundaries to establish the most appropriate depth strata for future annual surveys.

The survey demonstrated it is possible to carry out a longline survey of pre-recruit toothfish from commercial fishing vessel in Ross Sea using standardised gear in a standardised manner. Based on a total of 45 sets in the three core strata (A12-C12) the survey had an overall c.v. of 9%, which met the target c.v. of 10%. The survey caught mainly 70–110 cm TL Antarctic toothfish. The survey provided new data on the depth distribution of pre-recruit fish in this area. Catch rates of pre-recruit toothfish were highest between 500 and 900 m and very low shallower than 450 m. The size distribution of toothfish was very similar between the four main strata suggesting no depth preference between 400 and 900 m. It is recommended that future surveys in this area should focus on depths greater than 500 m. The survey also demonstrated the feasibility of collecting samples for wider ecosystem monitoring.

Although the main aim of the 2012 survey was to monitor pre-recruit toothfish, the survey provided the opportunity to compare catch rates in 2012 with historical catch rates by San Aotea II and its sister ship Janas in earlier years of the fishery. The results of a standardized CPUE analysis suggest that there has been no significant change in catch rates in the southern Ross Sea over the past decade.

Currently the target tagging rate to be achieved by vessels fishing in the CCAMLR area is set in terms of the number of fish tagged per mass of fish caught thereby mixing “units” of measure. This note questions whether it is appropriate to set the tagging targets these terms and suggests that defining the target in terms of a percentage of the number caught may be more appropriate.

Using a modeling framework for toothfish population dynamics, fishing and data collection, this study investigated how the bias and precision of a CASAL assessment is influenced by various aspects of a tagging program, in particular the effects of the numbers of fish tagged, the duration of a tagging program, the size of tagged fish, and the type of auxiliary data used in the assessment.

The simulation study indicated that:

(1) A high tag size-overlap (at least 60%, better 100%) and high tagging numbers were important particularly in the early stages of an exploratory fishery to ensure some recaptures and maximise the likelihood of a robust assessment.

(2) Using catch-at-age data instead of catch-at-length data substantially improved all assessment estimates and was required for adequately estimate annual recruitment and year class strengths.

(3) For a simulated lightly fished stock, CASAL assessments with good quality tagging data had a low bias and reasonable precision for SSB₀ and annual SSB estimates, however the precision of SSB status estimates in the final assessment year was relatively low. Bias and precision of CASAL assessments were better for the lightly fished stock than for a heavily fished stock.

(4) This modeling framework appears to be useful for evaluating data sampling strategies, assessment approaches and management strategies.

Model used by WG-SAM-12/24

Using the simplest form of an abundance estimator using tag-recapture data, the Lincoln-Petersen equation, we summarise the processes that may occur during a tagging program that lead to difficulty in accurately estimating key parameters, and consequently introduce bias into an abundance estimate. We also review the methods that have been used in CCAMLR tag recapture to program to mitigate against this bias, or to account for their effects in assessment models. In nearly all cases, examples of at sea or model-based approaches are available from established toothfish tagging programs to reduce these biases. Estimates of post-capture mortality, tag detection rates and where it occurs, post-release depredation rates are a priority for new tagging programs and tag-based assessments. Due to the complexity of toothfish movements throughout their life cycle, as well as the spatial structure of release and recapture efforts by fishing and research vessels, development of spatially explicit modelling approaches is an important next step for toothfish assessments.

In order to reflect the level of confidence when linking a tag recapture to a tagging event, as well as an indication of the time and effort taken to make the link, the Secretariat introduced in 2011 a tag recapture link status code.  For the 2011 season, a total of 1433 tags have been returned; 50% provide an exact match with tag numbers held in the database, 22 % provide an exact match with tag numbers but had inconsistent ancillary data. For those tags that did not provide exact or unique matches only 109 (8%) could not be successfully linked using additional information. For the current season (2012), a total of 164 tags have been returned; 64% provide an exact match; 34% provided an exact match with inconsistent ancillary data; and less than 2% could not be successfully linked. An approach to developing thresholds for ancillary data to be used in allocating tag link status are provided for comment.

South Africa has played an active part in CCAMLR since its establishment in 1982 and has contributed to the scientific rationale for ecosystem management in a large area of the Southern oceans. Recently South Africa also initiated a new research plan within its EEZ around the Prince Edward Islands that acknowledges the objectives of the Commission for the responsible management of Antarctic Marine Living Resources.  The Koryo Maru 11 started with exploratory fishing in the CCAMLR Convention Area in 1996 and has completed a total of 47 trips to date.  Regions fished include Statistical Subarea 48.3 and 58.6 and 58.7 within the South African EEZ around the Prince Edward Islands and, more recently, research fishing in Subarea 48.6 and Division 58.4.2   The objectives for the 2012/13 season would be to start with the research in Subarea 48.6 and Divisions 58.5.2 and extend this into 58.4.3a later in 2013.  Research in this period will continue with specific focus on tagging within prescribed fine scale rectangles in these regions and on collecting detailed catch and effort and biological information on the target Dissostichus spp. and bycatch species.

In 2011 and 2012 in Subarea 88.3 Russian longliners “Sparta” and ‘Chio Maru 3” conducted research fishing for toothfish. Scientific program was carried out by scientific observers from VNIRO (Moscow, Russia) and YugNIRO (Kerch, Ukraine). Totally, during the work period 44 longlines were set at a depth from 625 to 2336 m. Total number of set hooks amounted 171096. In 2011 research fishing covered SSRU B, C and D. In 2012 ice conditions were much worse and longlines were set only in SSRU C. Collected from research fishing data contributes to the achievement of the main objectives of research - make estimation of toothfish quantity, as well as expand the knowledge about toothfish`s and by-catch species biology in this Subarea. (SC-CCAMLR-XXX/5, par. 2.26-2.29).

There are currently two sets of requirements for reporting data from vessels conducting fishing for research purposes (i.e. research fishing): (1) research fishing conducted under Conservation Measure 24-01 (scientific research) requires that catch, effort and biological data be reported on a haul-by-haul basis using the format used by research vessels (data form C4); and (2) research fishing under CM 41-01 (exploratory fisheries) requires that catch, effort and biological data be reported on a haul-by-haul basis using the formats used during commercial fishing by vessels (data form C2) and carrying scientific observers (cruise reports and logbooks).

This paper reviews the data collection and reporting requirements for research fishing. A harmonised approach is proposed to WG-SAM for consideration. The proposal would see fishing vessels use form C2 throughout their campaigns, with scientific observer continuing to use cruise reports and logbooks, and any supplementary data requirements for research fishing being reported on a separate form.

As of the end of May 2012, four longliners conducted research fishing in the exploratory fisheries in Subareas 48.6 and Divisions 58.4.1, 58.4.2 and 58.4.3a in 2011/12 (Table 1): Hong Jin No. 701 (Korea), Koryo Maru No. 11 (South Africa), Saint André (France) and Shinsei Maru No.3 (Japan). These vessels completed a total of 267 research hauls.

The four vessels deployed their research hauls within the fine-scale rectangles and buffer zones which had been assigned by the Secretariat in November 2011, prior to the start of the fishing season. During the course of research fishing, one vessel in SSRU 5841G did not meet the required ratio of 1 research haul to 3 commercial hauls.

All research hauls met the deployment criteria, i.e. fishing depths of 550 to 2200m, separation distance of at least 3 nmiles from any other research haul, between 3500 and 5000 hooks and soak times of at least six hours, except for the minimum separation distance in some sets in SSRUs 486D, 486G, 5841C, 5841E and 5842E. Limitations due to fishing depths and sea-ice in these southern SSRUs may have contributed to the concentration of research fishing effort.