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)

Abstract

The 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. faThe 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.sciatus) redfish catches. 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.