Stock assessment of the Macquarie Island fishery for Patagonian toothfish (Dissostichus eleginoides) using data up to and including August 2014

[摘要] This paper presents results from an integrated stock assessment of Patagonian toothfish (Dissostichus eleginoides) at Macquarie Island using data collected up until and including August 2014. The assessment uses a spatial model that fits to data from the entire Macquarie Island toothfish fishery, and assumes a single reproductive stock, but takes into account spatial structuring of the population within the region. Two areas - northern and southern - are incorporated into the model, with movement of fish between areas, and recruitment to both areas. A single Total Allowable Catch (TAC) for the entire Macquarie Island region is calculated using the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) control rule.This assessment makes use of the Stock Synthesis assessment software v3.11b (MethotWetzel, 2013), and fits to data obtained from the tag-recapture program since 1995, to length composition information for the years 1994-2014, and to age-at-length data obtained from aged otoliths (1997-2013). It is an update of the final version of the 2014 assessment (Day et al., 2014). The assessments are based on a length-age structured model of fish population dynamics, with maximum likelihood and Bayesian methodsused to fit to the available data.The model designates five different fleets (Aurora Trough trawl, Northern Valley Trawl, Aurora Trough longline, and Northern and Southern Macquarie Ridge longlines). Fits to the length composition data are generally good. The fits to the age-at-length data appear to be reasonable, although larger fish are predicted to be older than they are observed to be (the model is growing older fish too slowly). The model fits the tag-recapture data well, with good accord between the total number of expected recaptures and those observed.The outcomes from the assessment are very similar to those in the 2014 assessment. The base case current female spawning biomass estimate is 69% of unfished (68% in 2014). The trend in spawningbiomass from 1990-2014 is almost identical to that estimated last year, but the estimated magnitude of spawning biomass is about 9% higher in each year, and about 7% higher than the spawning biomassseries from the 2013 assessment. The three new recruitment estimates are above average (2004-2006).The point estimate for the 2014 stock size in the northern area is estimated to be about six times larger than that in the south (female spawning biomass 2,008t and 322t respectively). The northern area is also estimated to be considerably less depleted than the southern area (78% and 40% respectively).Catch levels that satisfy the CCAMLR control rule have been calculated under ten alternative assumptions regarding how the catches will be allocated to fleet and region. The projected 2015/16 catch from these scenarios ranges from 460t to 530t.The new 2014 length frequency data include an additional 2216 fish in 62 hauls for Aurora Trough Long-line, 2570 fish in 70 hauls for Northern Macquarie Ridge Longline and 528 fish in 17 hauls for Southern Macquarie Ridge Longline. An additional 299 fish from the 2013 catch were aged and these were included as age-at length data for this assessment, with 200 females, 97 males and two unsexed newly aged fish.Updates to the tag recapture data include 55, five and 16 additional tag recaptures respectively by the Aurora Trough, North Macquarie Ridge and South Macquarie Ridge Longline fleets. This makes a total of 76 tag recaptures in 2014, all from fish tagged in previous years. Of these 76 recaptures, none involved recaptures of fish tagged in a different area. In addition there were 295, 499 and 33 new tag releases in 2014, with these releases respectively in the Aurora Trough, North Macquarie Ridge and South MacquarieRidge.

[发布日期] 2015-03-03 [发布机构] CSIRO

[学科分类] 地球科学(综合)