An assessment of beaked redfish (S. mentella and S. fasciatus) in NAFO division 3M (with an approach to the likely impact of recent 3M cod growth on redfish natural mortality)

65 páginas, 12 tablas, 10 figuras.-- Scientific Council MeetingThe 3M redfish assessment is focused on the beaked redfish, regarded as a management unit composed of two populations from two very similar species: the Flemish Cap S. mentella and S. fasciatus. The reason for this approach is the historical dominance of this group in the 3M redfish commercial catch until 2005. However a new golden redfish fishery (S. marinus) started on September 2005 on shallower depths of the Flemish Cap bank above 300m. This new reality implied a revision of catch estimates, in order to split recent redfish commercial catch from the major fleets on Div. 3M into golden (S. marinus) and beaked (S. mentella and S. fasciatus) redfish catches. An Extended Survivor Analysis (Shepherd, 1999) was used with the same framework of previous assessments and with the tuning of the 1989-2010 EU survey. Recent survey results suggest that the beaked redfish stock has not been able to hold its growth and sustain an above average level, suffering instead a severe decline on the second half of the 2000’s. For several reasons, the most likely hypothesis to justify this unexpected downward trend on stock size is an increase in mortality other than fishing mortality. From the sensitive analysis, carried out for a set of natural mortality options, a natural mortality of 0.4 (fixed for ages 4-6 through 2006-2010, and ages 7+ on 2009 and 2011) was adopted. This is the lowest possible level of natural mortality giving assessment results in line with the recent survey declines and at the same time with key diagnostics very close to the best ones, obtained with a higher natural mortality of 0.55. A 2011-2007 retrospective XSA was also carried out. When compared to previous assessments, these retrospective present more consistent trends namely as regards female spawning biomass and average fishing mortality, coupled with a non systematic bias signal. Very high fishing mortalities until 1996 forced a rapid decline of abundance, biomass and female spawning biomass. With lower fishing mortalities since then, the stock decline was halted. The weak 1991-1997 year classes kept the stock size at a low level till 2003, basically sustained by the survival and growth of the existing cohorts. Recruitment at age 4 increased from 2002 till 2006, when the 2002 year class was at an historical high, and from 2006 to 2008 fell as fast as it went up, still continuing to decrease on most recent years and being on 2010 just bellow average. Above average year classes coupled with fishing mortalities in the vicinity of F0.1 or even lower allowed a rapid growth of biomass and abundance since 2003 and sustained the stock at a high level on 2007-2008. However the stock decreased on the last couple of years despite low catch and, being still above average level, there are no signs that the present decline rate is slowing down. Female spawning stock component experienced a similar decline. Short and medium term stochastic projections were obtained for female spawning stock biomass (SSB) under Fstatusquo (average 2008-2010 fishing mortality), together with SSB and yield medium term probability profiles. Keeping fishing mortality at its present low level well below F0.1 will sustain on the short term the female spawning stock biomass above the SSB interval from where all the abundant year classes from the past decade where generated. But on the long term it will be natural mortality to determine the future of beaked redfish as a fishery resource. The average 2012-2013 Fstatusquo catch for beaked redfish will be 2 of 3,200 tons. According to 2008-2010 observed catch data from the Portuguese, Spanish and Russian National Sampling Programmes on board, a beaked redfish annual catch of 3,200 tons would correspond to an overall 3M redfish catch (including the shallower golden redfish catches) near 7,000 tons (6,840 tons)This assessment is part of a EU research project supported by the European Commission (DG XIV, Program for the collection of data in fisheries sector), IPIMAR, CSIC, IEO and AZT

An Assessment of Beaked Redfish (S. mentella and S. fasciatus) in NAFO Division 3M (With a Revised Approach to Quantify the Increase on Redfish Natural Mortality Determined by the Increase on Cod Predation Observed Over Recent Years, 2006-2012)

55 páginas, 13 figuras, 17 tablas.-- Scientific Council MeetingThe 3M redfish assessment is focused on the beaked redfish, regarded as a management unit composed of two populations from two very similar species: the Flemish Cap S. mentella and S. fasciatus. The reason for this approach is the historical dominance of this group in the 3M redfish commercial catch until 2005. However a new golden redfish fishery (S. marinus) started on September 2005 on shallower depths of the Flemish Cap bank above 300m, and the Flemish Cap cod fishery reopened in 2010. These new realities implied a revision of catch estimates, in order to split recent redfish commercial catch and by-catch from the major fleets on Div. 3M into golden (S. marinus) and beaked (S. mentella and S. fasciatus) redfish catches. An Extended Survivor Analysis (Shepherd, 1999) was used with the same framework of previous assessments and with the tuning of the 1989-2012 EU survey. Survey results suggest that the beaked redfish stock has not been able to hold its growth and sustain an above average level, suffering instead a severe decline on the second half of the 2000’s. The most likely hypothesis to justify this unexpected downward trend on stock size is an increase in natural mortality by cod predation. From the sensitive analysis, natural mortality at 0.4 was applied on ages 4-6 through 2006-2010, and extended to ages 7 plus on 2009 and 2010. It has been kept constant through all ages on 2011 and 2012, but with an overall decline to 0.125.This is the highest possible level of natural mortality giving assessment results in line with the recent survey trends and at the same time with key diagnostics very close to the best ones, obtained with the return on 2011-2012 to the “standard” redfish natural mortality of 0.1. A 2013-2009 retrospective XSA was also carried out, being this assessment very much in line with their immediate predecessors (2012-2011). Above average year classes coupled with low fishing mortalities allowed a rapid growth of biomass and abundance since 2003 that pushed the stock to a 2008-2009 high. Between 2009 and 2011 biomass and abundance of exploitable and 7 plus female stock went down for causes other than fishing. These declines were halted at well above average levels on the terminal year and, at least for biomass, there was some improvement on 2012. The recruitment at age 4 increased from 2002 till 2006 and was kept at a high level until 2009, with 2005 year class as the most abundant year class of the assessment interval. Recruitment to exploitable stock declined since then and is approaching the level of the weak year classes from the 1990’s. Short and medium term stochastic projections were obtained for female spawning stock biomass (SSB) under Fstatusquo , together with SSB and yield medium term probability profiles. As it was documented on the 2011 assessment F0.1 is an unacceptable management option at the current beaked redfish stock status. Keeping on 2014 and 2015 fishing mortality at its present low level will sustain on the short term a high level of female spawning biomass. But on the long term it will be natural mortality to determine the future of beaked redfish as a fishery resource.Peer reviewe

An assessment of beaked redfish (S. mentella and S. fasciatus) in NAFO Division 3M, from a biological based approach to recent levels of natural mortality (2011-2016)

69 pagesThe 3M redfish assessment is focused on the beaked redfish, regarded as a management unit composed of two populations from two very similar species: the Flemish Cap S. mentella and S. fasciatus. The reason for this approach is the historical dominance of this group in the 3M redfish commercial catch until 2005. However a new golden redfish fishery (S. marinus) started on September 2005 on shallower depths of the Flemish Cap bank above 300m, and the Flemish Cap cod fishery reopened in 2010. These new realities implied a revision of catch estimates, in order to split recent redfish commercial catch and by-catch from the major fleets on Div. 3M into golden (S. marinus) and beaked (S. mentella and S. fasciatus) redfish catches. The Extended Survivor Analysis assessment used as tuning file the 1989-2016 EU survey abundance at age matrix included in a revised input framework. Continuing pressure over Flemish Cap redfish stocks by cod predation, at levels higher, or much higher, than the levels prior to 2006 lead to higher natural mortalities since then. In order to include an independent approach to natural mortality in the sensitivity M framework, for the more recent years (2011-2016) natural mortality has been estimated from a number of different biological models, some size/age-independent and others size/age-dependent. These different estimates were arranged in two sets and tuned to survey at age data. A natural mortality of 0.1 on 2015-2016 and the natural mortalities adjusted on previous assessments were found to be the most suitable option to M input. A 2017-2013 retrospective XSA was performed, confirming the consistency of the present with preceding results as regards stock biomass, female spawning biomass and fishing mortality. Above average year classes and high survival rates allowed a rapid growth of biomass and abundance 2003 onwards, pulling the stock to a 2008-2010 high. Since 2009 abundance went down for causes other than fishing, being still above the 1990’s low in 2016. By the turn of the decade stock biomass and female spawning biomass (SSB) shown marginal declines as well, but reversed on 2011-2012. Individual growth of survivors and low fishing mortalities sustained stock biomass and SSB at high levels till 2015-2016. Recruitment at age 4 increased from 2002 till 2006 and was maintained at a maximum level till 2009. Recruitment declined since then and is kept on 2015-2016 at the low of the weak year classes from the 1990’s, while SSB is still well above the size that originated the high 2002-2006 recruitments. Despite the significant decline so far natural mortality has not flattened yet. If natural mortality and fishing mortality stay at their most recent levels, the actual high of female spawning biomass can hold on 2018-2019. But on the long term it will be natural mortality, namely over pre recruited ages, to determine the future of beaked redfish as a fishery resource. On 2015 STACFIS remind that projections are based in the assumption that natural mortality stay at its most recent level on the present year and at least on the two next coming years. And that, taking into account the uncertainty on the present and future level of natural mortality, its impact on female spawning stock biomass at the end of any projection is unknown. On 2017 these constraints are still in place, and therefore short and medium term projections are not presented.This assessment is part of a EU research project supported by the European Commission (DG XIV, Program for the collection of data in fisheries sector), IPMA, CSIC, and IEO.Peer reviewe