MSFD Indicators and Reference Points for Data-Limited Stocks Rainer Froese GEOMAR EU-BON Workshop, Leipzig 18 February 2014 Some Terms • Maximum sustainable yield (MSY) is the maximum surplus production in numbers or weight (= ecosystem service) that an exploited population can provide forever • Biomass (B) is the size of a population in weight • Bmsy is the biomass that can produce MSY • Fmsy is the anthropogenic mortality rate that will result eventually in Bmsy MSFD Descriptor 3 1. The level of pressure of the fishing activity, measured either as fishing mortality F relative to the one associated with the maximum sustainable yield (Fmsy) or, if F is unknown, the ratio between catch and biomass, with a reference point that is compatible with Fmsy. 2. The spawning stock biomass SSB relative to the one that can produce the maximum sustainable yield (SSBmsy) or other suitable biomass indices. 3. The age and size distribution within the population, with the subindicators i. Proportion of fish larger than the mean size of first sexual maturation; ii. Mean maximum length across all species found in research vessel surveys; iii. 95 % percentile of the fish length distribution observed in research vessel surveys; iv. Size at first sexual maturation [relative to historic sizes], which may reflect the extent of undesirable genetic effects of exploitation. What is a Proxy for Fmsy? • Fmsy is the maximum mortality that may be inflicted by humans • Fmsy is known for less than ¼ of exploited fish stocks • Natural mortality M can be used as a proxy for Fmsy M as Proxy for Unknown Fmsy A fishing mortality rate F that equals the natural mortality rate M effectively - doubles the mortality rate that the species has evolved to withstand - reduces life expectancy and duration of reproductive phase by half - reduces the number of old, large, fecund fish M as Proxy for Unknown Fmsy There is a broad, longstanding agreement in fisheries science that sustainable rates of fishing F may not exceed Fmsy and shall not exceed M. Gulland 1971, Shepherd 1981, Beddington and Cooke 1983, Clark et al. 1985, Beverton 1990, Patterson 1992, Thompson 1993, Walters and Martell 2002, 2004, MacCall 2009, Pikitch et al. 2012. Thus, M can be used as a proxy for Fmsy What is a Proxy for Bmsy • Bmsy is the internationally agreed minimum size of exploited marine populations (UNCLOS 1982) • However, there are no agreed estimates of Bmsy for European stocks • A proxy for Bmsy can be derived from the biomass representing borderline of safe biological limits, which is available for many stocks 2 * Bpa as Proxy for Unknown Bmsy • Over the past two decades the border to safe biological limits Bpa was used as reference point in European fisheries • In fisheries textbooks, half of Bmsy is typically assumed as the borderline to unsafe stock status. • It follows that 2*Bpa is a reasonable proxy for Bmsy DATRAS: Millions of Survey Records http://datras.ices.dk SMALK: Length-Weight Needed to turn length into weight and biomass North Sea flounder: 25,609 observations of length and weight; 42 outliers were removed. Weight = 0.007 * Length3.16 [SMALK_Analysis_25.r] SMALK: Growth Needed to turn length into age North Sea flounder: 25,501 observations of length and age. Length-at-age = 48 * (1 – e-0.11 * (age – 2.8)) [SMALK_Analysis_25.r] SMALK: Length & Age at Maturity Needed for proxy recruits and spawners North Sea flounder: 10,814 observations of length, age, and state of maturity. Female length where 90% are mature is 23 cm, age is 2-3 years. [SMALK_Analysis_25.r] CPUE in Area 6 Average catch in numbers of North Sea cod resulting from one hour of trawling with standardized survey gears. The bold line represents a three-year moving average to reduce scatter and facilitate interpretation of trends. The dotted line indicates the mean catch of the time series. [MSFD_8.pdf] CPUE by Length a) c) b) d) North Sea dab. a)shows the raw data. The red line indicates individuals above 50% maturity; b) shows immature individuals as proxy for recruits; d) shows length converted to biomass of mature (red) and all fish (black); c) shows total mortality Z over the respective previous two years and scaled exploitation rate u+M, both as a proxies for F, with indication of M [MSFD_8.pdf]. CPUE by Length North Sea dab: preliminary stock-recruitment relationship based on CPUE in weight as proxy biomass of mature fish and number of young fish (= proxy-recruits) two years later, derived from length composition in standardized survey catches. A hockey stick was fitted by a rule-based procedure. The dotted vertical line indicates proxy SSBpa as the precautionary borderline to potentially compromised recruitment. [MSFD_8.pdf] CPUE by Length a) c) b) d) North Sea dab. a)shows the raw data. The red line indicates individuals above 50% maturity; b) shows immature individuals as proxy for recruits; d) shows length converted to biomass of mature (red) and all fish (black); c) shows total mortality Z over the respective previous two years and scaled exploitation rate u+M, both as a proxies for F, with indication of M [MSFD_8.pdf]. Peek Preview of Ongoing Research • For a population to sustain a history of output such as catch, it needs to have had a certain size and productivity • If you know the time series of annual production (biomass taken out for human use), and you know the productivity of the species, then you can calculate biomass and reference points Catch-MSY Revisited Martell & Froese 2013 Output of the Catch-MSY method showing “viable” pairs surplus production rate r and unexploited biomass k for North Sea cod. The red line indicates all r-k pairs that would result in the same estimate of MSY; the red circle indicates the geometric. While the estimate of MSY is robust, the geometric mean r = 0.24 depends on the lower bound for r. k Bmsy Bpa Icelandic cod: The black line shows the biomass predicted by the CMSY-method. The red line shows observed total biomass. The vertical blue lines show the prior biomass windows used as filters by the CMSY-method. The upper dashed line represents the unexploited biomass k, the middle dotted line represents Bmsy, and the lower dashed line represents Bpa. Exploitation Rate for Data-limited Stocks umsy Icelandic cod: exploitation rate catch/biomass as predicted by the CMSY method(black line) and as observed (red line). The dotted line represents a proxy for MSY-compatible exploitation. Conclusions • M is a good proxy for Fmsy and 2*Bpa is a good proxy for Bmsy • For most data-limited stocks in the ICES area, DATRAS contains sufficient information to estimate LWR, growth, maturity and relative abundance • Combining survey results with catch data leads to reasonable proxies for stock status and exploitation pressure • Length where 90% of the females reach maturity seems to be a reasonable lower limit reference point for mean length in commercial catches.