Objective

To come up with FMSY values, which are based on ecosystem functioning, for each of ICES data rich fish stocks. These FMSY values can be applied directly by ICES in its routine fisheries advice. The aim is to bridge the gap between the science available and management.

Problem addressed

The current FMSY values used by ICES are based on traditional single species consideration that ignores ecosystem functioning in terms of carrying capacity, density dependent population dynamics and species interactions. This generally means that ICES current FMSY values are severely biased in the new reality, where stocks are rebuilding. Ecosystem and multispecies modeling indicate that the bias in FMSY estimates could be as much as a factor of two. 

Context

Not bridging the gap between the science on ecosystem functioning available and management has the unfortunate consequence MSY is not reached, because the current FMSY values used are biased.

Meta-analysis and ecosystem/multispecies modeling in several ICES eco-regions, indicate that the foregone yield will be in the order of 40% less yield than by applying ecosystem based FMSY values (see e.g. Gislason 1999, Collie et al. 2003, Sparholt and Cook 2009, Fernandez and Cook, 2013, ICES 1989, 2008, 2012, 2013).  Figure 2.1 below illustrates this.

The North Atlantic countries are among the world leaders on fisheries biology, marine ecosystem understanding and fisheries management. Therefore, these countries are role models to the world and the current project will lead the way for similar approaches in other parts of the world. It must be noted, however, that fishing in many parts of the world are still in the situation, where overfishing occur. 

The approach suggested in this project is not a full multispecies approach, but focus on adding mainly density dependent growth, maturity and (mainly for cod) cannibalism, to the current single species way of estimating FMSY. Thus, managers need not consider the balance between species for using the proposed set of FMSY values.

There are four density dependent mechanisms in fish population dynamics that are important for Fmsy calculations. These are:

•       Density dependent recruitment

•       Density dependent individual fish growth

•       Density dependent mortality    

•       Density dependent maturity.                    

Currently, only the first one is taken into account in the Fmsy calculations. It is a mathematical fact that missing any one of these points will give an underestimate of Fmsy. The only exception to this is if the density dependent mechanism is “upside-down”, meaning for instance that recruitment increases exponentially with increasing stocks size. Such “upside-down” relationships must however be only temporary, because otherwise, the stock would keep increasing indefinitely or go extinct.   

The interaction between species need not be an integrated part of the calculations, if the new FMSY values are regarded as valid for only a limited time period, say 5 years. This is because the stock sizes can be considered reasonable constant within such a limited time period. However, if say, a predator stock increases quickly, as has been seen in the past for some cod stocks when fishing mortality is substantially reduced, newFMSY values might need to be calculated for its prey stocks before the end of the 5 year period, using a new set of natural mortality by age values.

Why has this not already resolved?

ICES have several times mentioned this problem with the current FMSY values to managers and the public (e.g. ICES 2012, 2013). This has proven very difficult for ICES to communicate in spite of many initiatives within the ICES system and encouragement from fisheries managers. Some of these ICES initiatives have been:

1.        Merging the former advisory committees ACFM (fisheries) and ACE (ecosystems), into one                       advisory committee ACOM;

2.       Many integrated assessment working groups like WGIAB (Baltic), WGINOR (Northeast Atlantic                 pelagic system), REGNS (North Sea);

3.       Establishing a benchmark process with workshops where environmental factors could be                       integrated into the ordinary assessment models;

4.       Establishing a new jobs position in the ICES Secretariat to facilitate this integration;

5.       Establishing and ACOM-SCICOM Steering Group on Benchmark in order to force improvements in the link between ICES science pillar and ICES advice pillar;

6.       Providing “pilot project”-type advice on multispecies management for the Baltic (ICES 2012 and 2013) and for the North Sea(ICES 2013);

Furthermore, The Nordic Council of Ministers (NMC) and ICES had in 2013 a project on “A Framework for Multispecies Assessment and Management” where five experts worked together to develop an ICES/NCM Background Document (Rindorf et al., 2013) giving guidelines to how multispecies and ecosystem functioning could be integrated into the advice and management. It included a one day Symposium at the Carlsberg Academy 23rd February 2013, with invited managers, stakeholders and scientists and “…all attendants agreed on the need to take multispecies interactions into account in advice and management”.

The ICES expert group on multispecies modeling was in 2008 requested by ACOM to review FMSY in a multispecies context. They concluded:

a)      The high yields predicted at low F by single‐species models are almost certainly unrealistic, as these will be ‘eroded’ by predation pressure and density‐dependent growth reductions.

b)      Multi‐species models indicate that the MSY is achieved at different fishing mortalities compared with single‐species approaches.

c)       It is impossible to attain the high yields predicted by single‐species models for all stocks                         simultaneously, because achieving BMSY for one species may result in stock declines for other species that are prey and/or competitors.

ICES gave advice on multispecies management for the Baltic (ICES 2012 and 2013) and for the North Sea(ICES 2013) as a kind of invitation to managers to go into a dialogue on what objectives they have for management in this regards. The FMSY values in the advice were about a factor of 1.6 larger than the single stocks FMSY.

Approach

In order to help ICES and managers to get unbiased FMSY values, the proposed project will develop an alternative set of FMSY values for ICES data rich fish stocks, which can be used directly in ICES annual assessment and advisory process.

The alternative set of FMSY values will be based on a meta-analysis of the very extensive amount of published science work on FMSY in multi-species and ecosystem models, including population dynamic characteristics of each stock in terms of growth, maturity and longevity parameters.  The scientists in the North Atlantic area (including the Baltic) should be world leaders in this research field based on four decades of intensive research where more than 200 peer review papers has been published, more than 1.5 million fish stomachs analyzed, hundreds of science person-years spend on fish evacuation experiments, and a multitude of models developed.  In the present project GLM models including e.g. life history parameters like Linf and K from the von Bertalanffy growth equation important for stock productivity (see e.g. Patrick et al., 2010), will be considered, in order to “expand” information from multispecies stocks to other stocks. 

Surplus production models will be applied to some selected data rich stocks, using estimated F time series as effort. The selection will be based on the dynamic range of F, so that only the best suited stocks for surplus production models will be analyzed. Surplus production models will give FMSY (and BMSY) as an integral part of the model. These are based on actual realizations over the past history of the stock and therefore implicitly includes ecosystem functioning in their FMSY (and BMSY) calculations.  Ricard et al. (2011) and Thorson et al. (2012) are the most prominent studies of this kind.   

Other ways of bridging the gap between the current single species advice and an ecosystem functioning approach will also be analyze. This could be the merits of using Fpa as a proxy for ecosystem based FMSY. It has often been claimed that preventing recruitment failure, like an Fpa approach will, is the most important issue for fisheries management and here this approach will be evaluated in details against the new FMSY values. One could for instance think of a GLM model with known ecosystem based FMSY as observations and Fpa as a parameter to obtain ecosystem based FMSY for other stocks.

Further exploration of the meta-analysis types used by Sparholt and Cook (2009) and Fernandez and Cook (2013), will be conducted. Their findings will be evaluated based on the new years of data points. It will be attempted to reveal the effect by new species groupings, and to include pelagic and industrial (sandeel, Norway pout etc. used for fish meal and oil) stocks in the analysis.

It will also be analyzed whether the current escapement approach ICES use for short lived stocks can be applied to long-lived stocks. Of course here not only the survival to the next coming spawning event will be relevant, but also the survival to future year’s spawning needs to be considered. 

The stocks to be included in the project are the so-called data rich stocks, which have long time series of catch, stock size, recruitment and fishing mortality.  About half of the annual catch taken in the Northeast Atlantic are from these stocks.