CCAMLR Science, Volume 16 (2009)
‘POKER 2006’, a bottom trawl fish biomass survey, was conducted from September to October 2006 in the northern part of the Kerguelen Plateau (CCAMLR Statistical Division 58.5.1). The swept-area method was used in the depth range from 100 to 1 000 m with 207 random stratified stations. Estimates of biomass and abundance were produced for eight commercial species. The total biomass was 245 000 tonnes and Patagonian toothfish (Dissostichus eleginoides) accounted for half of the value (124 000 tonnes). The fish biomass was distributed between the shelf and the deep sea. However, this evaluation remains incomplete as four of the species (D. eleginoides, bigeye grenadier (Macrourus carinatus), Eaton’s skate (Bathyraja eatonii) and Kerguelen sandpaper skate (B. irrasa)) extend deeper than 1 000 m, the limit of the POKER 2006 survey. Some shelf and slope species (mackerel icefish (Champsocephalus gunnari) and marbled rockcod (Notothenia rossii)) exhibit low levels of biomass when compared to the results of previous surveys (SKALP surveys, 1987 and 1988). Other species (unicorn icefish (Channichthys rhinoceratus) and grey rockcod (Lepidonotothen squamifrons)) seem to have increased, even doubled, their biomass during the period between the two surveys. In addition to the commercial species, Zanclorhynchus spinifer was abundant on the shelf and Alepocephalus cf. antipodianus was abundant in the deep sea; the data on the latter are new. Data on the geographic and bathymetric distribution of the species provide evidence of geographically very stable species-specific concentrations. Distinct cohorts of some species (D. eleginoides and C. gunnari) were detected in some sectors. The survey has defined the distribution of species, commercial or not, that are important in the ecosystem and are of major interest for the management and conservation of fish populations in the area. |
The status of the toothfish resource in the Prince Edward Islands region is unclear because CPUE data suggest considerable depletion, whereas catch-at-length information indicates that past catches have had relatively little impact on abundance. A Management Procedure (MP) approach is proposed to provide a sound scientific basis to recommend future TACs in the face of this appreciable uncertainty. Four Operating Models (OMs) reflecting ‘Optimistic’, ‘Intermediate’, ‘Less Pessimistic’ and a ‘Pessimistic’ current status for the resource are developed which take account of the different selectivities of past longline and pot fisheries. These OMs are used for trials of a candidate generic MP which could provide future TAC recommendations for this resource. The MP uses two data sources: the recent trend in longline CPUE and the mean length of the catches made. An MP with control parameter values specified is proposed for implementation based on the results of the trials. Given the importance of an adequate catch rate for the economic viability of the fishery, the choice of control parameter values focused primarily on a reasonable probability of securing a catch rate increase, whatever the current resource status. MP performance is reasonably robust across a range of sensitivity tests, although it does deteriorate in conservation terms if the stock-recruitment curve steepness h is low. These tests also indicate that monitoring of future catch-at-length information would be necessary to guard against a change in selectivity towards greater catches of older fish. |
Exploratory fisheries for Dissostichus spp. have been operating off the coast of East Antarctica (30°E–150°E; FAO/CCAMLR Divisions 58.4.1 and 58.4.2) since 2003. An experiment run from 2005 to 2008 required the tagging of toothfish as a prerequisite for participation in the fishery, with only some Small-scale Research Units (SSRUs, consisting of 10° longitude divisions of the larger areas) being open to fishing. This paper reviews the results of this experiment and explores several methods for arriving at estimates of sustainable yields. Biological data suggest that there are two stocks in the area, one in Division 58.4.1 and one in Division 58.4.2, with the division between them being at about 90°E. The western stock may be centred around Prydz Bay, and appears to be of very low productivity. Estimates of average biomass were made by comparison of standardised catch rates with the Ross Sea, where an analytical assessment has been possible for several years, and through analysis of local depletion events. Results indicated SSRU vulnerable population sizes of about 100–1 000 tonnes per SSRU in the west (Division 58.4.2) and 1 000–1 700 tonnes per SSRU in the east (Division 58.4.1). Although 3 434 tags were released over the period 2003–2007, very few tags have been recaptured (only five where time at liberty was a year or more). These recaptures were inconsistent with expectations given known landed catches. Potential yields were calculated for each SSRU assuming a similar productivity and exploitation state to the Ross Sea, where sustainable yield is 5% of virgin vulnerable biomass. The estimated yield from all assessed SSRUs (260 tonnes) is much lower than the current total allowable catch (1 380 tonnes). |
A methodology for the initial stock assessment and adaption of catch limits and tagging rates is presented for new and exploratory stocks in the CAMLR Convention Area. The assessment methodology is designed to be able to accommodate mark–recapture data, catch (legal and illegal, unreported and unregulated (IUU)) and relative abundance data into an integrated assessment framework when more detailed data are not available – namely catch-at-length/age data and tagging data at-length/age. A simple algorithm, based upon the Petersen abundance estimator, is defined whereby catch limits and tagging rates can be adjusted together to define tagging levels that will produce an expected abundance estimate in the following year of a given precision whilst ensuring the sustainable exploitation of the stock as per the CCAMLR management procedure. The combination of the assessment and tagging rate adaption methods can then form the basis of an early management plan for exploratory fisheries. The accuracy of the catch limit and tag-rate adaption algorithm is tested using the assessment results for toothfish in CCAMLR Subarea 48.3 and the assessment method is applied to the catch (legal and IUU) and mark–recapture data for Patagonian toothfish (Dissostichus eleginoides) in Division 58.4.3a with catch limit and tag-rate recommendations being made given the assessment results and using the catch limit/tag-rate adaption algorithm. |
Age and growth of spiny icefish (Chaenodraco wilsoni) were investigated using counts of annual growth increments from sagittal otoliths. Samples were collected during research surveys by benthic trawl carried out off Joinville–D’Urville Islands (Antarctic Peninsula) in February–March 2006 and January 2007. A total of 218 specimens were selected for the study, consisting of 120 females and 98 males. The age of fish was estimated by counting annuli on transverse sections obtained by grinding and polishing whole otoliths embedded in epoxy resin in moulds. The precision of age estimates between readings was tested applying both the average percent error (APE) and the coefficient of variation (CV). Conversely, the accuracy of age estimates was not tested, so that present ageing data haveto be considered with caution. The estimated age range was 1–5 years for males and 1–4 years for females of C. wilsoni. Applying the von Bertalanffy (VB) growth function to the age–length data, a growth curve was obtained for each sex. The estimated values of VB growth parameters L∞ (cm) and k were respectively 32.7 and 0.81 for females and 32.7 and 0.68 for males. Age-at-sexual maturity was estimated to be about 2 years for females and 2.5 years for males. Like other icefishes, C. wilsoni exhibited a high growth rate until it reached sexual maturity, although it had a much shorter life span. The part of the population of C. wilsoni caught in the study area consisted mainly of adult individuals between 1 and 3 years of age, with very few older fish. |
Ten years of recent fine-scale haul-by-haul krill data were used to characterise the behaviour of the krill fishery. Analysis of distance between hauls in relation to their catch level revealed a distinct pattern. Mean between-haul distances were generally longer when catch levels fell below 10 tonnes/haul, and the travel distance decreased as the catch level increased; this pattern was most obvious for operations by Japanese fishing vessels. There were differences between statistical areas with longer distances moved between hauls in Subarea 48.1 compared to Subareas 48.2 and 48.3, reflecting the large number of fishing grounds within this area. The same patterns were observed for vessels from other nations, but were less clear. The study suggests the movement trends for Japanese vessels could form the basis for describing a generalised fishery model. Updates for some of the parameters for the krill fishery model suggested in the late 1980s are proposed based on the results from this study. These analyses demonstrate the need for high-quality year-round data on all vessels participating in the krill fishery to assist in interpreting the annual fishing patterns, which can best be collected by scientific observers. |
Penguin censuses on the Antarctic Peninsula are often subject to logistical challenges that preclude nest counts being conducted at the peak of egg laying. Additionally, the historical literature includes many census counts with non-standard timing. The challenge is, therefore, to correct ‘off-peak’ census counts to make them comparable with current standard methods. Census correction involves knowing (i) how the census is timed relative to the peak of egg laying, and (ii) how nest numbers change through the breeding cycle. In this paper the authors present an analysis relating to both these challenges. Clutch initiation dates for four penguin breeding sites are examined (Cape Shirreff, Admiralty Bay, Humble Island and Petermann Island) in relation to potential drivers of clutch initiation (e.g. temperature, precipitation, sea-ice etc.). It is found that mean October temperatures constitute the most consistent significant factor related to the timing of clutch initiation in all three of the penguin species examined (Adélie (Pygoscelis adeliae), gentoo (P. papua) and chinstrap (P. antarctica)). A statistical model for determining the peak of clutch initiation is presented and, along with a simple estimation of species-specific nest attrition rates, is used to illustrate the procedure for correcting off-peak census counts. |
A new South Georgia Bathymetric Dataset (SGDB) was compiled from a variety of primary sources including multi-beam swath bathymetry. Sea floor area (km2 <500 m depth) within CCAMLR Subarea 48.3 was calculated using this new dataset. Total sea floor area within the region closely matched existing estimates derived from nautical charts (and single-point sounding data). However, the reliability of existing sea floor area estimates was found to vary spatially and between different depth strata. The new dataset is considered the most accurate and reliable currently available and should be used for future assessments and for assisting with the stratification of surveys. |
CCAMLR adopted a new conservation measure in 2007 to ensure that significant adverse impacts of bottom fishing gear on Vulnerable Marine Ecosystems (VMEs) are avoided. Due to the high levels of uncertainty surrounding both the evidence of VME presence and the consequences of interaction with different types of gear, a risk-management framework is proposed, similar to that which has been used successfully to minimise the effects of longline fishing mortality on seabirds. Risk is broadly defined as the conditional probability of adverse impacts given particular bottom fishing activities multiplied by the consequences of those impacts. The aim of the risk-management framework is to avoid significant adverse impacts on VMEs from bottom fishing activities. The framework consists of four steps: (i) Risk analysis of current and proposed fishing activities; evidence of potential VMEs; scale of interactions between fishing activities and VMEs; impact of interactions on VMEs; and recovery potential of VMEs. (ii) Risk evaluation. Information on likelihood and consequences of interactions of bottom fishing gear with VMEs and associated uncertainties from risk analysis is combined to produce risk metrics. (iii) Risk elimination or mitigation. The spatial scale at which this framework operates should be related to the scale of VMEs, presently unknown. However, management at the level of fine-scale rectangles (0.5° latitude by 1.0° longitude) or smaller can be used in the first instance. Temporal scales must be matched to the recovery scale of VMEs, which are probably in the order of many decades or even centuries. Unacceptable levels of risk from bottom fishing activities to VMEs must be eliminated or reduced to acceptable levels through the use of management measures including, inter alia, closed areas around identified VMEs, open and closed management areas, by-catch limits for VME-forming organisms, gear modification or spatial distribution of fishing effort. (iv) Review. All of the above steps should be reviewed annually to ensure that all relevant or new information has been included, appropriate scientific research and data collection plans are in place and that risk mitigation measures are successful in their implementation. |
This paper presents a methodological framework to estimate the likely cumulative impact on fragile benthic organisms from bottom fishing activity. The approach has been designed to facilitate standardised application among various gear types and areas to allow comparisons between fisheries employing different bottom fishing methods. New Zealand implemented this approach in its preliminary assessment of bottom fishing impacts for the 2008/09 toothfish longline fishery. This paper illustrates the utility of the standardised approach and provides a methodological template for systematic impact assessment in fisheries using bottom impacting methods, to inform mitigation efforts and as a necessary component of a full ecological risk assessment. |
A previous study on the age and growth of Amblyraja georgiana in the Ross Sea suggested that these skates initially grow very rapidly for about five years, after which growth almost ceases (Francis and Ó Maolagáin, 2005). An alternative interpretation of age and growth in A. georgiana that is radically different from the published interpretation is presented. By counting fine growth bands in the caudal thorns instead of broad diffuse bands, growth curves have been generated that suggest much slower growth, greater ages-at-maturity (about 20 years compared with 6–11 years) and greater maximum ages (28–37 years compared with 14 years). Several pieces of circumstantial evidence support the new interpretation, but a validation study is required to determine which growth scenario is correct. |
Erratum and Addendum - Modelling catch and effort data using generalised linear models, the Tweedie distribution, random vessel effects and random stratum-by-year effects – CCAMLR Science, 11: 59–80 (2004) |