CCAMLR

At WG EMM-2013 the Working Group agreed that it would be useful to have a consolidated summary of information related to the krill fishery in a similar format to the fishery reports that are completed for finfish fisheries in WG-FSA (www.ccamlr.org/node/75667).

The Secretariat agreed to coordinate the preparation of a draft krill fishery report for consideration at WG EMM-14 that would be similar in content to a finfish Fishery Report.

Upon the recommendations from WG EMM-14 the report includes the same information provided in the previous report (i.e. an introduction on the background of the fishery, an inventory of catch and SISO data, including incidental mortality of marine mammals and seabirds as well as the CCAMLR approach to management of the krill fishery) with the addition of monthly catch maps for the last complete seasons (2014) and the current incomplete season (2015), an inventory of observer data effort since 2011 and a comparison bycatch occurrence in C1 and SISO data.

RV Tangaroa carried out a 42-day research voyage to the Ross Sea from 29 January to 11 March 2015. The main purpose of the New Zealand-Australia Antarctic Ecosystems Voyage (TAN1502) was to undertake ecological studies of Ross Sea marine foodwebs of importance to top predators. The work was centred on the feeding areas of cetaceans, primarily blue whales and humpback whales, and in the Ross Sea slope area, which is the main fishing ground for the Ross Sea toothfish fishery. Whales were located using passive acoustics and visual observations. Observations of prey species were collected with multifrequency echosounders with associated midwater and demersal trawling. Associated oceanographic and atmospheric observations were made while underway. Samples of prey species and whale tissue (from biopsy) were collected for trophic (stable isotope) studies. Weather conditions during the voyage were excellent and all five science objectives were successfully completed. The voyage was supported by funding from Antarctica New Zealand (ANZ), the New Zealand Ministry for Business Innovation and Employment (MBIE), Australian Antarctic Division (AAD), and the National Institute of Water and Atmospheric Research Limited (NIWA).

In this paper, we develop a candidate management system for the krill fishery suitable for achieving objectives for krill and its predators in local areas. We also indicate how this management system can be made operational in the early phases of a fishery in a local area, which can then be enhanced as the fishery develops, including testing future management procedures and in adapting them to a changing ecosystem. A local area decision rule is proposed for using krill biomass density and recruitment strength in a given year to determine an adjustment of the long-term annual catch for the area in the following year. This decision rule is designed to keep the probabilities of low reproductive performance by predators at acceptable levels in the long term. The process for undertaking the assessment and its application is demonstrated.

Vessels operating in the krill fishery in CCAMLR’s Convention Area are required to directly estimate the green weight of krill caught (Conservation Measure 21-03, Annex B). This requirements was introduced for the 2012/13 seasons, and the estimation methods were revised at WG-EMM-13 and WG-EMM-14. Estimates of green weight and parameter values are reported in each vessel’s haul-by-haul catch and effort data (C1 data).

Vessels fishing in 2014/15 used five methods for the direct estimation of the green weight of krill caught: codend volume, holding tank volume, flow meter (method 2), flow scale and meal conversion.

This paper provides a preliminary summary of the data reported so far in 2014/15 (to May 2015).

Annual acoustic trawl surveys for krill monitoring have been carried out by the Institute of Marine research, Norway near the South Orkney Islands since 2011. The survey has been conducted early in the fishing season (January/February), using two different krill fishing vessels as platforms. The vessels were equipped with similar Simrad echo sounder systems suitable for quantitative assessments, but the frequencies operated varied between vessels and years. In addition, the survey coverage has varied between years in particular due to ice. In order to allow for comparison of distribution and abundance of krill near the South Orkneys among years, we here attempt to generate a coherent series of krill density estimates from the 5 years of surveys. We follow the CCAMLR protocol for biomass estimation as far as practically possible, given that we work with unconventional sets of frequencies for target strength estimation and target identification. In order to avoid variability due to differences in coverage, we also define a stratum within the survey area on the north side of the islands with full coverage in all years except 2013. The results show that except from the year 2015, krill densities were high, in the range 100-300 g/m² based on the 120 kHz recordings, and a total estimated biomass of ca. 8 million tons of krill within the stratum in the peak year 2014. There were also consistently higher values of acoustic backscatter on the north side of the islands where the fisheries occur, than on the south side. Values were particularly high in the north-west shelf area associated with underwater canyons. In 2012, and particularly in 2015, low proportions of the acoustic backscatter were allocated to krill. The low proportions are probably caused by shortcomings in the krill identification techniques when other pairs of frequencies than combinations of 38, 120 and 200 kHz are used.

Between 2001 and 2013 the number of breeding pairs of Adélie penguins (Pygoscelis adeliae) at breeding colonies in the southern Ross Sea more than doubled from about 235 000 to more than half a million. It has been suggested that predation release of Antarctic silverfish (Pleuragramma antarctica) due to fishing of one of its predators, Antarctic toothfish (Dissostichus mawsoni), could have contributed to the increase in Adélie penguin numbers. This paper brings together information on the biomass, consumption rates and diets of toothfish and Adélie penguins over the Ross Sea shelf as a first test of the predation release hypothesis. In particular, the examination of 422 Antarctic toothfish stomachs showed that they consume only a small proportion of silverfish (1.9–5.1% by mass) over the southern Ross Sea shelf. These Antarctic toothfish were sampled over three years, between 2011/12 and 2013/14. The mass of silverfish estimated as being released from predation by fishing (577 tWW/y) was equivalent to about 2% of the amount of silverfish consumed annually by Adélie penguins in this region. This result was inconsistent with predation release of silverfish due to the toothfish fishery being responsible for recent increases in the number of Adélie penguins breeding in the southern Ross Sea. Mixed trophic impact (MTI) analysis was used to look for alternative indirect pathways through the food-web by which changes to toothfish could affect Adélie penguins in the Ross Sea. The MTI analysis found only a weak link between changes in toothfish biomass and changes to the biomasses of silverfish and Adélie penguins. Essentially, Antarctic toothfish and Adélie penguins were not assessed as having overlapping diets over the Ross Sea shelf: Antarctic toothfish consume mainly small, bottom-dwelling fishes (especially icefish, and Trematomus spp.) while Adélie penguins consume crystal krill and silverfish in the water column. The large-scale trophic connection between toothfish and Adélie penguins over the Ross Sea shelf is hence weak. We encourage the development of further specific hypotheses of mechanisms by which fishing could affect Adélie penguins in the Ross Sea.

We present definitive evidence, derived from two independent methods (satellite tagging and photo-identification), that TCKW undergo long-distance travel from the southern Ross Sea to New Zealand waters and into subtropical regions (31°-35°S). This not only establishes ecosystem connectivity between the Ross Sea and New Zealand, but also emphasises the urgent need to re-evaluate the profile of potential threats faced by, and capacity for resilience in, this top predator. Together with Weddell seals, TCKW have been identified as one of the two top predator species in the Ross Sea most likely to be affected by the Ross Sea fishery for Antarctic toothfish, Dissostichus mawsoni, but critical knowledge gaps regarding abundance, diet, foraging habitat, and movement patterns limit our ability to assess or manage risk to TCKW.

New results from satellite transmitters deployed on TCKW in Terra Nova Bay suggest that TCKW may use small-scale areas in this highly productive ecosystem intensely for a period of days to weeks, but also undergo rapid long-distance travel along a northward transect towards New Zealand and the Kermadec Trench. Dive records from these tagged TCKW (n=4) indicate that whales perform deeper dives while in Terra Nova Bay (100-455 m) than on the northbound journey. A preliminary analysis of photo-ID data indicates that TCKW show a high degree of seasonal site fidelity, with whales inter-annually returning to areas of ecological significance, including New Zealand waters north and east of East Cape, the Kermadec Trench region, and highly productive Antarctic areas providing access to silverfish and toothfish (or other, yet unidentified prey resources).

The unexpectedly complex movement patterns and extremely broad spatial scale of movement exhibited by TCKW have important implications for our understanding of the ecology of this key Ross Sea predator, and for the precautionary spatial management of the Ross Sea regions, including monitoring of the existing ASPA #173 Silverfish Bay and the establishment and ongoing monitoring of the proposed Ross Sea Marine Protected Area.  These research priorities would be best addressed by multi-national collaborative efforts coordinated through the frameworks of IWC SORP and CCAMLR.

An integrated assessment model for Antarctic krill in FAO Subarea 48.1 that incorporates catch and length-composition data from the krill fishery with biomass indices and length-compositions from research surveys has been developed. The model uses statistical fits to these data to estimate the effects of the fishery on the krill population. The model estimates parameters representing krill population biology and the fishery during the period with data (1976 to 2014 in these models) and then applies these parameter values to future projections (2015-2034) at pre-specified levels of future catches. The model can compare predicted krill spawning biomass expected with projected future catches to the CCAMLR decision rules. An alternative pair of decision rules to those currently employed by CCAMLR are also applied to the projections. The alternative rules are based on comparing krill spawning biomass expected under projected future catch levels to spawning biomass expected without any fishing during the same future period. The CCAMLR rules are based on comparisons to estimated pre-exploitation spawning biomass instead of to projections with no fishing. Catch levels that meet the various decision criteria are identified and compared. Arbitrary time-series of future annual recruitments may be supplied to the model. Example estimates of spawning biomass for different future levels of catch, assuming recruitment in the future will be the same as recruitment estimated during the period for which survey and fishery data were available, are reported. The effects of using different data sources and weightings on the estimates of stock status during the estimation period are explored.