Ecological and evolutionary effects of harvesting: lessons from the candy-fish experiment

ICES Journal of Marine Science ICES Journal of Marine Science (2013), 70(7), 1281– 1286. doi:10.1093/icesjms/fst160 Food for Thought Ecological and evolutionary effects of harvesting: lessons from the candy-fish experiment Beatriz Diaz Pauli 1* and Mikko Heino 1,2,3 1 Department of Biology, University of Bergen, Box 7803, N-5020 Bergen, Bergen, Norway Institute of Marine Research, Bergen, Norway 3 International Institute for Applied Systems Analysis, Laxenburg, Austria 2 *Corresponding Author: tel: +47 5558 8137; fax: +47 5558 4450; e-mail: Diaz Pauli, B., and Heino, M. 2013. Ecological and evolutionary effects of harvesting: lessons from the candy-fish experiment. – ICES Journal of Marine Science, 70: 1281 – 1286. Received 1 July 2013; accepted 29 August 2013 Understanding the challenges of sustainable fisheries management is not easy for non-specialists, and even many specialists fail to appreciate the potential evolutionary consequences of harvest. We propose candy-fish experiments as a savoury approach to teaching and disseminating the key principles of applied ecology and evolution to students, practitioners and the general public. We performed a simple experiment where the resource was represented by fish-shaped candy of distinct colours and flavours (strawberry and liquorice). Typically, harvesting was neither ecologically sustainable (55% of the populations were extinct by the end of the experiment) nor evolutionarily sustainable (most surviving populations had liquorice fish only). This harvest-induced evolution went apparently unnoticed. Somewhat encouragingly, the harvest was most likely ecologically sustainable when a person spontaneously took the role of a stock manager. Keywords: candy-fish, dissemination, ecological sustainability, education, harvest-induced evolution. Introduction Managing wild fisheries is challenging, and the track record of fisheries management worldwide leaves plenty of room for improvement (Dankel et al., 2008; Worm et al., 2009; FAO, 2012). Superficially, the problem is easy to solve: it is generally accepted that reducing exploitation rate and bycatch, as well as maintaining relatively large fish stocks and low impact on ecosystems, are key issues for a sustainable fishery (Hilborn, 2007b). However, there is no consensus on how to achieve these objectives. A major challenge is that managing fish stocks is really about managing people (Larkin, 1988)—fishers in particular, but increasingly a much wider group of stakeholders too (Larkin, 1988; Hilborn, 2007a; McMullin and Pert, 2010). The situation is further complicated because the concept of success differs between ecologists, economists, policy makers, etc. (Hilborn, 2007a), and because fishery systems are characterized by uncertainty and ambiguity (FAO, 1995; Francis and Shotton, 1997; Moxnes, 1998). Fish resources are typically common property resources. If nobody controls exploitation, altruistic behaviours are not rewarded, and people tend to behave selfishly and overexploit the resource, as the costs of selfish actions are shared by all exploiters. This is commonly known as “the tragedy of the commons”, after Hardin’s (1968) seminal paper. Avoiding the tragedy requires closing the commons by restricting individual access and exploitation (Hardin, 1968; Basurto and Ostrom, 2009). However, the top-down practice of managing (fishers are told when, where and how to fish) is destined to fail (Hilborn, 2007a; Kraak, 2011), as it results in uncooperative behaviours and unexpected and creative ways to circumvent the rules (Hilborn, 2007a). Therefore, studying the behaviour of the exploiting agents, as well as their motivation and incentives, is the key to a successful fishery, complementing the study of ecological outcomes (Hilborn, 2007a). An additional challenge to sustainability is that fishing may drive unwanted evolution in fish populations. Fishing is purposely selective, commonly directed towards larger individuals. Fishing can also be directly selective for behavioural patterns, activity, sex, morphology and maturity (Nelson and Soulé, 1987; Smith, 1994; Heino and Godø, 2002). If a part of the phenotypic variation in selected characteristics is genetic, fishing drives genetic change (Law, # 2013 International Council for the Exploration of the Sea. Published by Oxford University Press. All rights reserved. For Permissions, please email: 1282 2000). There is increasing evidence that fisheries-induced evolution is contributing to the phenotypic changes commonly documented in fish stocks (Law, 2000; Jørgensen et al., 2007; Kuparinen and Merilä, 2007). This could have negative effects on the utility humans derive from fish stocks (Jørgensen et al., 2007), not least on the fisheries yield (Edley and Law, 1988; Conover and Munch, 2002). Given these challenges for developing appropriate management systems, we believe there is a need for better communicating the interplay of human behaviour and ecological and evolutionary feedbacks to both the general public and to students and practitioners in fisheries science and applied ecology. Traditional, lecture-based learning methods have been criticized for leading to low motivation, while active learning keeps the students involved and is more effective (Mitchell et al., 2014). Thus, games, as a form of active learning, have been developed for teaching purposes in a wide range of disciplines from health education, science, and technology to social change (Sherry, 2013). Learning through one’s own experience is powerful (Kolb, 1984; McCarthy and McCarthy, 2006), especially when relatively abstract phenomena like the tragedy of the commons and fisheries-induced evolution can be made tangible. Therefore, we designed a simple, easily repeated experiment to illustrate the key principles of applied ecology and evolution. We used a bowl of candy-fish as a resource, as we needed a model system where assessing the cause –effect relationships of exploitation would be both straightforward and rewarding. Specifically, we used the candy-fish system to test two main hypotheses: (i) exploitation is selective and leads to changes in populations’ genetic composition (clonal composition, in our particular case), and (ii), formal training in fisheries biology and management improves ecological, but not evolutionary sustainability. B. D. Pauli and M. Heino group could harvest. The groups were defined by coffee tables at three different working places (the University of Bergen, the Institute of Marine Research, and the Fisheries Directorate in Bergen, Norway). Each bowl contained two types of candy-fish, initially at the same frequency (total n ¼ 50). The two types of candy-fish were similar in size and appearance except for their colour and flavour: liquorice fish (black) and strawberry fish (red). Each bowl was accompanied by a note informing the group that the candy-fish will be available if harvested sustainably, and that the fish would reprodu (...truncated)