View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by OceanRep F I S H and F I S H E R I E S , 2004, 5, 86–91 Ghoti Ghoti papers Ghoti aims to serve as a forum for stimulating and pertinent ideas. Ghoti publishes succinct commentary and opinion that addresses important areas in fish and fisheries science. Ghoti contributions will be innovative and have a perspective that may lead to fresh and productive insight of concepts, issues and research agendas. All Ghoti contributions will be selected by the editors and peer reviewed. Etymology of Ghoti George Bernard Shaw (1856-1950), polymath, playwright, Nobel prize winner, and the most prolific letter writer in history, was an advocate of English spelling reform. He was reportedly fond of pointing out its absurdities by proving that ‘fish’ could be spelt ‘ghoti’. That is: ‘gh’ as in ‘rough’, ‘o’ as in ‘women’ and ‘ti’ as in palatial. Keep it simple: three indicators to deal with overfishing Rainer Froese Institute of Marine Sciences, Du¨sternbrooker Weg 20, 24105 Kiel, Germany Abstract Correspondence: Three simple fisheries indicators are presented: (i) percentage of mature fish in catch, Rainer Froese, Insti- with 100% as target; (ii) percent of specimens with optimum length in catch, with tute of Marine Sciences, Du¨sternb- 100% as target; and (iii) percentage of ‘mega-spawners‘ in catch, with 0% as target, rooker Weg 20, and 30–40% as representative of reasonable stock structure if no upper size limit 24105 Kiel, exists. Application of these indicators to stocks of Gadus morhua, Sardinella aurita and Germany Epinephelus aeneus demonstrate their usefulness. It is argued that such simple Tel.: indicators have the potential to allow more stakeholders such as fishers, fish dealers, +49 431 600 4579 Fax: supermarket managers, consumers and politicians to participate in fisheries +49 431 600 1699 management and eventually hold and reverse the global pattern of convenience E-mail: overfishing, which is defined here as deliberate overfishing sanctioned by official [email protected] bodies who find it more convenient to risk eventual collapse of fish stocks than to risk social and political conflicts. Received 18 July 2003 Accepted 10 Oct 2003 Keywords fisheries indicators, length at first maturity, longevity, optimum length, overfishing, sustainable fishing can replenish themselves (Sadovy 2001; Pauly et al. Introduction 1998; Christensen et al. 2003; Myers and Worm There is increasing evidence that global fisheries are 2003). This process is called overfishing and usually depleting natural resources much faster than these consists of two components: (i) diminishing the 86 Ó 2004 Blackwell Publishing Ltd Simple indicators R Froese ability of fish to reproduce, called recruitment- natural resources. I propose three simple and easily overfishing, and (ii) catching them before they can understood indicators that allow an effective assess- fully realize their growth potential, called growth- ment of status and trends in most fisheries by all overfishing. In response to the problem, fisheries concerned stakeholders including the general public. research over the past 100 years has developed increasingly complex stock assessment models that Description of indicators are incomprehensible to but a few experts. For example, the report of the International Council for Indicator 1 can be described as ‘Let them spawn!’ the Exploration of the Sea (ICES) Advisory Commit- and is measured as percentage of mature specimens tee on Fishery Management for eight fish species of in the catch. The target would be to let all (100%) the Southern Shelf (Celtic Sea, Western Channel, fish spawn at least once before they are caught to Bay of Biscay) in 2002 covers about 1000 pages. rebuild and maintain healthy spawning stocks. This This level of detail is requested by the regulatory may seem obvious, but for example an analysis of body (the Directorate General of Fisheries of the ICES (2002) data for the cod stock (Gadus morhua, European Commission, which makes proposals for Gadidae) of the western Channel area for 1994– decisions on this basis to the Fisheries Council 2001 (referred to below as ‘Western cod’) shows composed of the Fisheries Ministers of the currently that only 20–54% (mean 37%) fish in the annual 15 EU Member States). However, fishing quotas are catch were mature, or in other words: every year decided on the basis of political considerations, about two-thirds of Western Cod were excluded largely ignoring the scientific advice, and typically from reproduction. legalizing catches beyond safe levels. Other than Indicator 2 can be described as ‘Let them grow!’ ‘Malthusian overfishing’ (Pauly 1990) which is and is measured as the percentage of fish caught at driven by extreme poverty and lack of alternatives, optimum length, i.e. the length where the number of this deliberate overfishing is administered by official fish in a given unfished year class multiplied with bodies who find it more convenient to risk the their mean individual weight is maximum and where eventual collapse of fish stocks than to risk gener- thus the maximum yield and revenue can be ating social or political conflict. I therefore suggest obtained. Optimum length is typically a bit larger the label ‘convenience overfishing.’ As a result of than length at first maturity and can be easily such convenience overfishing, most stocks in the obtained from growth and mortality parameters or ICES area, and global stocks in general, are at empirical equations (Froese and Binohlan 2000). The historically low levels and continue to decline. target would be to catch all fish (100%) within, for One precondition of convenience overfishing is the example, ±10% of optimum length (see Fig. 1). An apparent lack of public involvement in fisheries analysis of the Western Cod data shows that only issues. The complexity of fishery models has made it 6–27% (mean 18%) of the fish caught were of that impossible for citizens outside the traditional institu- size. tions to bring their influence to bear on how Indicator 3 can be described as ‘Let the mega- humanity shall deal with responsible usage of aquatic spawners live!’ and is measured as percentage of 90 000 Lm Lopt Lmax 80 000 70 000 Optimum 60 000 size 50 000 40 000 Frequency Figure 1 Length–frequency data of 30 000 Western Cod landings from 1994 to 20 000 2001 in the Western Channel area, Mega- Juveniles Mature where Lm indicates length at first 10 000 spawners maturity, Lopt indicates the length 0 range where maximum yield could 0 20 40 60 80 100 120 140 be obtained and Lmax is the maxi- mum size reached during that time. Length (cm) Ó 2004 Blackwell Publishing Ltd, F I S H and F I S H E R I E S , 5, 86–91 87 Simple indicators R Froese old, large fish in the catch, i.e. fish of a size larger the prevalent practice of fisheries to remove large than optimum length plus 10%. Here the target specimens first and foremost. According to this depends on the management regime: the aim is to analysis, the Western Cod has very little resilience implement a fishing strategy that results in no (0%) against natural events such as recruitment failures mega-spawners being caught. If no such strategy is because of unfavourable combinations of environ- in place and thus the catch reflects the age and size mental parameters. structure of the stock, values of 30–40% mega- Two examples where the indicators have been spawners represent a healthy age structure and are applied to real world scenarios are given below. In desirable, whereas less than 20% will be a matter of Senegal, yields from pelagic resources were consid- concern. This attention to large specimens draws on ered satisfactory, whereas yields from demersal the increasing evidence that old fish play several species had declined in recent years (B. Samb, important roles in the long-term survival of a personal communication). Preliminary application population: (i) large females are much more fecund of our simple indicators to time series of length– because the number of eggs increases exponentially frequency data for the pelagic Round sardinella with length in most species; their eggs also tend to (Sardinella aurita, Clupeidae) and the demersal be larger, thus giving a greater chance of survival to White grouper (Epinephelus aeneus, Serranidae) larvae (Solemdal 1997; Trippel 1998); (ii) reaching resulted in Figs 2 and 3 (B. Samb and M.D. Barry, old age is usually a sign of overall individual fitness personal communication). For Round sardinella the and thus these mega-spawners are reservoirs and percentage of mature specimens in the catch was distributors of desirable genes; and (iii) extending above 90% since 1992, and the percentage of longevity and prolonging the reproductive phase specimens with optimum length has increased from can be viewed as a natural safeguard against about 50% in 1990 to about 80% in 2002. This subsequent recruitment failure (Craig 1985; would suggest a healthy stock and reasonable Beverton 1987). Such events are visible in respect- fishing regime, confirming the traditional assess- ive long-term time series and are a common cause of ment based on catch per effort (B. Samb, personal collapse in heavily fished stocks (Murphy 1967; communication). However, the percentage of mega- Longhurst 2002a,b). In other words, the percentage spawners in the catch is decreasing from 20–30% in of mega-spawners in a stock can be viewed as a the early nineties to around 10% from 1999 to simple proxy for resilience against random events. 2002, which is a matter of concern as this is not the An analysis of the Western Cod data shows that 2– result of an upper size limit and the erosion of the 7% (mean 5%) of the fish caught were mega- age-structure will reduce the resilience of the stock.