Stock Assessment of the Macquarie Island fishery for Patagonian toothfish (Dissostichus eleginoides) using data up to and including August 2015

[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 2015. 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 1994–2015, and to age-at-length data obtained from aged otoliths (1997–2015). It is an update of the final version of the 2015 assessment (Day et al., 2015). The assessments are based on alength-age structured model of fish population dynamics, with maximum likelihood and Bayesian methods used 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 dataare 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 2015 assessment. The base case current female spawning biomass estimate is 67% of unfished at the start of 2016 (69% in 2015). The trend in spawning biomass from 1990–2015 is almost identical to that estimated last year, 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 2016/17 and 2017/18 catches from these scenarios ranges from 420t to 500t. The new 2015 length frequency data include an additional 2950 fish in 84 hauls for Aurora Trough Long-line, 2739 fish in 96 hauls for Northern Macquarie Ridge Longline and 1985 fish in 62 hauls for SouthernMacquarie Ridge Longline. An additional 276 fish from the 2014 catch and 281 fish from the 2015 catch were aged and these were included as age-at length data for this assessment. This comprised 192 females, 82 males and two unsexed newly aged fish in 2014 and 205 females and 76 males in 2015. There were considerable revisions to the tag recapture history, with the exclusion of 297 historical recaptures for fish recaptured between 10 and 180 days of release, with 185 of these exclusions from recaptures in the period 1995–1997, with 27 in 2003 and another 54 in the period 2006–2007. New tag recaptures from the 2015 data included 75, nine and 47 recaptures respectively by the Aurora Trough, North Macquarie Ridge and South Macquarie Ridge Longline fleets. This makes a total of 131 tag recaptures in 2015 from fish tagged in previous seasons, with four of these tags recaptured in a differentarea to their release. One fish tagged in 1997 in the Aurora Trough was recaptured in 2015, which is the longest period between initial tagging and recapture for this fishery. In addition there were 354, 168 and 137 new tag releases in 2015, with these releases respectively in the Aurora Trough, North Macquarie Ridge and South Macquarie Ridge.

[发布日期] 2016-02-09 [发布机构] CSIRO

[学科分类] 地球科学(综合)