REPORT OF THE STANDING COMMITTEE ON RESEARCH ... - Iccat

ICCAT REPORT 2008-2009 (I)8.12 SHK - SHARKSIn response to the Supplementary Recommendation by ICCAT Concerning the Conservation of Sharks caught inAssociation with Fisheries Managed by ICCAT [Rec. 06-10], an updated assessment of the stocks of blue shark(Prionace glauca) and shortfin mako (Isurus oxyrinchus) was conducted in 2008. Ecological risk assessments(ERA) were also conducted for nine additional priority species of pelagic elasmobranchs, for which availabledata are very limited (Isurus paucus; Alopias superciliosus; Alopias vulpinus; Carcharhinus longimanus; C.falciformis; Lamna nasus; Sphyrna lewini; Sphyrna zygaena; and Pteroplatytrygon violacea).Although both the quantity and quality of the data available to conduct stock assessments have increased withrespect to those available in 2004, they are still quite uninformative and do not provide a consistent signal toinform the assessment. Unless these and other issues can be resolved, the assessments of stock status for this andother species will continue to be very uncertain and our ability to detect stock depletion to levels below theConvention Objective level will remain considerably low.A summary of the Committee’s findings based on the assessment results is presented below. Although pelagicsharks are captured in the Atlantic Ocean with a wide variety of fishing gears, the largest volume of most of thespecies of major concern to ICCAT are captured by pelagic longline fisheries. The Committee assessed blue andshortfin mako sharks assuming the existence of three separate stocks: North, South and Mediterranean. However,the data available to the Committee for the Mediterranean were not considered sufficient to conduct quantitativeassessments for these species. The assessment results presented high levels of uncertainty due to data limitations.Therefore, increased research and data collection are required to enable the Committee to improve the advice itcan offer. A complete discussion on the uncertainties about stock structure, movements, life history andcharacteristics of some of the fisheries affecting these stocks can be viewed in the Detailed Report of the 2008SCRS Shark Stock Assessment Session (SCRS/2008/017).SHK-1. Fishery indicatorsEarlier reviews of the shark database resulted in recommendations to improve data reporting on shark catches.Though global statistics on shark catches included in the data base have improved, they are still insufficient topermit the Committee to provide quantitative advice on stock status with sufficient precision to guide fisherymanagement toward optimal harvest levels. Reported catches for blue shark, shortfin mako and porbeagle areprovided in SHK-Table 1. Given that catch reports to ICCAT are incomplete, the Committee attempted todevelop a more accurate estimate of shark mortality and capture related to the Atlantic tuna fleets on the basis ofthe expected proportions among tunas and sharks and in the landings of these fleets SHK-Figure 1, as well asusing shark fin trade data. These information sets were used to reconstruct plausible estimates of historic catchesused in blue shark and shortfin mako assessments.A number of standardized CPUE data series for blue shark and shortfin mako were presented in 2008 as relativeindices of abundance. The Committee placed emphasis on using the series that pertained to fisheries that operatein oceanic waters over wide areas. SHK-Figure 2 presents the central tendency of the available series for thefour stocks.Considering the quantitative and qualitative limitations of the information available to the Committee, the resultspresented below, as those of the 2004 assessments, are not conclusive.With regard to the species for which ERAs were conducted, the Committee understands that, in spite of existinguncertainties, results make it possible to identify those species that are more susceptible and vulnerable (basedonly on productivity) to prioritize research and management measures (SHK-Table 2). These ERAs areconditional on the biological variables used to estimate productivity as well as the susceptibility values for thedifferent fleets and thus may change in the future as new information becomes available.SHK-2. Blue sharkFor both North and South Atlantic blue shark stocks, although the results are highly uncertain, biomass isbelieved to be above the biomass that would support MSY and current harvest levels below F MSY . Results fromall models used were conditional on the assumptions made (e.g., estimates of historical catches and effort, therelationship between catch rates and abundance, the initial state of the stock in the 1950s, and various life-history142