Northeast Atlantic
Blue Sharks occurring in European waters are part of the wider North Atlantic stock that is exploited by fisheries from over 20 nations. Official Food and Agriculture Organization of the United Nations (FAO) statistics underestimate the true magnitude of catches: landings estimated from Blue Shark fin exports from the Atlantic Ocean alone are known to greatly exceed the reported catches from this area (Campana et al. 2006, ICCAT 2009). In the past decade since 2003, there has been a rise in catch landings reported to the FAO, particularly taken by Spain in the Northeast Atlantic. Catches of this shark increased by 62,000 tonnes globally with a large fraction of this taken from the Eastern Central Atlantic by Spain (Davidson et al. in press). This rise is likely to reflect increasing fishing pressure over and above increased reporting.

Demographic models, catch-rate analysis, age-structured models, food web and ecosystem models have been applied (or attempted) for this species, mainly in the North Atlantic and North and Central Pacific, and these yield a conflicting picture of Blue Shark status (West et al. 2004, ICCAT 2009). Increasing fin prices, further depletion of less productive sharks and lack of management (particularly on the high seas) will lead to greater pressure on Blue Shark stocks (Clarke et al. 2007) and for those population components occurring in European waters.

In the North Atlantic, different catch rate analyses of this species consistently show that it is declining but there is uncertainty as to the most likely decline rate. Analysis of logbook data from the U.S. pelagic longline fishery indicated that Blue Sharks declined by 60% between 1986 and 2000 (1.5 generation spans) (Baum et al. 2003), and Canadian standardised catch rate indices suggest a 5-6% decline per year since 1995 in the North Atlantic (Campana et al. 2006). Similarly, fishery-independent survey data indicate an 80% decline in males from the mid-1980s to early 1990s (Hueter and Simpfendorfer 2008). Cortes (2007) reports an 88% decline since 1986. Blue Shark standardized catch rates have decreased by 53% (CI: 38–64%) between 1992 and 2005 (Baum and Blanchard 2010). An analysis over a longer observation window (1950–2000) using multiple sources of data suggested that CPUE of Blue Shark declined by 30% (Aires-da-Silva et al. 2008). This overall 30% of decline comprised of two periods: an initial stage of stable abundance or even increase at the end of the 70s, and a second period of rapid decline. From recent catch patterns and these Western Atlantic surveys that these most recent declines have been the steepest. Note that these trend estimates end in the early 2000s prior to the recent increase in catches of Blue Sharks, particularly in the Eastern Central Atlantic (Davidson et al. in press).

In contrast, fisheries agency analyses for international waters of the North Atlantic suggest little change (ICCAT 2009), although it is acknowledged that catches vary considerably across fleets and that reported catches over time are known to represent only a portion of total removals of the species (ICCAT 2009). The ICCAT standardised catch per unit effort (CPUE) series showed that the relative catch rate of Blue Shark increased from 1994 to 1998, but declined from 1998 to 2006. The ICCAT assessments suggest the Blue Shark is neither overfished nor is overfishing occurring, however, these assessments are deeply at odds with independent population trajectory data, catch levels, and trade demand patterns.

In the Northeast Atlantic, there are no population trends specifically for Blue Shark in European waters that are inferred from effort-corrected catch rates of commercial fisheries. Blue Shark occurring in Irish and United Kingdom (UK) waters are near the northern extent of their range in the Northeast Atlantic and are summer migrants from core population areas further south, such as the Azores and Atlantic Iberian waters (Queiroz et al. 2012). Although not considered a population trend, the catch per unit effort index from the Irish recreational fishery based on data from >16,000 individual sharks caught shows a current decreasing trend. CPUE (Blue Shark per boat per day) varies annually, but generally increased between 1980 and 1997 with a steady decline in catches between 1998 and 2006 to about 50% of mean catch made prior to 1997 (Green et al. 2009). Declining trends in recreational fisheries that catch northerly migrating Blue Sharks in summer may signify range contractions.

Mediterranean Sea
In the Mediterranean Sea, the population trends have been inferred from an index appropriate for the species. Since the mid-20th century Blue Shark has declined in abundance by three to four orders of magnitude. It was regularly caught in the tuna trap of Camogli in small numbers, but none have been caught in the past six decades (Ferretti et al. 2008). Recent observations from the same gear confirm that no individuals were taken from 2006 to the present day (Cattaneo-Vietti et al. 2014). It was the most abundant of the large predatory sharks taken in pelagic fisheries, but catch rates in the Mediterranean Sea have declined considerably. In the northern Ionian Sea, there were significant declines in abundance and biomass over 21 years (1978–1999). In Spanish waters, catch rates in biomass declined steeply in 25 years (1979–2004) as well. Pelagic fishing pressure remains high and catches unregulated. Taking into consideration other local trend estimates in abundance and biomass, a meta-analytical estimate of these trend analyses suggested that the abundance of Blue Shark has declined around 78–90% over the last 30 years (i.e. three generation period).