Niche Overlap Among Anglers, Fishers and Cormorants and Their Removals

Fisheries Research 238 (2021) 105894 Contents lists available at ScienceDirect Fisheries Research journal homepage: www.elsevier.com/locate/®shres Niche overlap among anglers, fishersand cormorants and their removals of fish biomass: A case from brackish lagoon ecosystems in the southern Baltic Sea Robert Arlinghaus a,b,*, Jorrit Lucas b, Marc Simon Weltersbach c, Dieter Komle¨ a, Helmut M. Winkler d, Carsten Riepe a,c, Carsten Kühn e, Harry V. Strehlow c a Department of Biology and Ecology of Fishes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587, Berlin, Germany b Division of Integrative Fisheries Management, Faculty of Life Sciences, Humboldt-Universitat¨ zu Berlin, Invalidenstrasse 42, 10115, Berlin, Germany c Thünen Institute of Baltic Sea Fisheries, Alter Hafen Süd 2, 18069, Rostock, Germany d General and Specific Zoology, Institute of Biological Sciences, University of Rostock, Rostock, Germany e Mecklenburg-Vorpommern Research Centre for Agriculture and Fisheries, Institute of Fisheries, Fischerweg 408, 18069, Rostock, Germany ARTICLE INFO ABSTRACT Handled by Steven X. Cadrin We used time series, diet studies and angler surveys to examine the potential for conflict in brackish lagoon fisheries of the southern Baltic Sea in Germany, specifically focusing on interactions among commercial and Keywords: recreational fisheries as well as fisheries and cormorants (Phalacrocorax carbo sinensis). For the time period Fish-eating wildlife between 2011 and 2015, commercial fisheries were responsible for the largest total fish biomass extraction Commercial fisheries (5,300 t per year), followed by cormorants (2,394 t per year) and recreational fishers (966 t per year). Com Human dimensions mercial fishing dominated the removals of most marine and diadromous fish, specifically herring (Clupea Conflicts Recreational fisheries harengus), while cormorants dominated the biomass extraction of smaller-bodied coastal freshwater fish, spe cifically perch (Perca fluviatilis) and roach (Rutilus rutilus). Pike (Esox lucius) as large-bodied freshwater fish was the only species where recreational fisheries were responsible for the major fraction of the annual biomass extraction. A strong trophic overlap and hence a similar foraging niche was documented among commercial fishers and recreational anglers and among non-resident and resident anglers, indicating that the aversion expressed by anglers against commercial fisheriesin a survey had an objective underpinning related to resource competition. By contrast, the foraging niches of cormorants and of both fishers and anglers differed strongly as evidenced by largely non-overlapping sets of species that were caught and removed by cormorants and by commercial as well as recreational fishers. However, for individual species of commercial and recreational in terest, specificallyperch, cormorants were responsible for a major fraction of total biomass extraction, suggesting that at the individual fishspecies level competition with fishersand anglers may still occur. In an angler survey, respondents expressed a preference for cormorant control, indicating the existence of conflict between fisheries and cormorants. We recommend that conflicts in the lagoon fisheries be proactively managed, e.g., through improved communication, zoning, predator control and outreach. Further research should clarify the population- level impacts of cormorants on target species of commercial and recreational fisheries as well as the relative impact of commercial and recreational fisheries on selected species of joint interest. 1. Introduction interference (Jacob and Schreyer, 1980). Accordingly, stakeholders may perceive reduced satisfaction attributed to somebody else‘s behavior, Conflicts in fisheries are well documented (Bavnick, 2005; Bishop which produces outcomes that conflict with their own expectations and Samples, 1980; Kearney, 2001, 2002; Spijkers et al., 2018). From a (Arlinghaus, 2005). For example, when two types of fishers, such as social science perspective, conflictamong stakeholders is caused by goal commercial or recreational fishers, target the same fish species (i.e., * Corresponding author at: Department of Biology and Ecology of Fishes, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587, Berlin, Germany. E-mail address: [email protected] (R. Arlinghaus). https://doi.org/10.1016/j.fishres.2021.105894 Received 9 December 2020; Received in revised form 26 January 2021; Accepted 28 January 2021 0165-7836/© 2021 Elsevier B.V. All rights reserved. R. Arlinghaus et al. Fisheries Research 238 (2021) 105894 have the same goal), elevated landings of a particular species by one Mixed commercial and recreational fisheries are present in many fishertype might be perceived by the other group as preventing reaching coastal waters (Ihde et al., 2011; Hyder et al., 2018). While commercial their own goals (e.g., expected catch) in the future. Conflicts do not fishers (Pauly et al., 1998) and recreational fishers (Donaldson et al., necessarily involve direct interactions and are often value-based 2011) may both desire the catch and harvest of adult upper trophic level (Arlinghaus, 2005; Boucquey, 2017; Loomis and Ditton, 1993). More predators, cormorants have been described as opportunistic foragers over, conflicts in fisheries are often asymmetric, i.e., they may only be that mainly target smaller-bodied, highly abundant species of lower felt by one party (Manning, 1979, 1999; Martinson and Shelby, 1992). trophic levels (e.g., Hansson et al., 2018; Keller, 1995; Suter, 1997). Conflictsmay be founded on the behavior or even the mere existence of However, in the coastal environment of the Baltic Sea there are also other people, groups, or animals. Well-documented examples in fisheries low-trophic level fish that are intensively targeted by commercial fish are the conflictaround fish-eatingwildlife (Brehens et al., 2008; Cowx, eries, e.g., herring (Clupea harengus) or cyprinids such as roach (Rutilus 2003; Steffens, 2010) or conflicts among resident and non-resident an rutilus), where impacts of cormorants may be economically relevant. ¨ glers that differ in values and behaviours (Aas and Skurdal, 1996). Work by Hansson et al. (2018) and Ostman et al. (2013) has suggested Solving conflicts typically requires some form of managerial interven that cormorants in the Baltic Sea exert their greatest impact on the more tion, including facilitation, communication and conflict resolution accessible coastal fish species rather than on those regularly using (Redpath et al., 2013). offshore habitats. Within the sector of fisheries, conflicts between commercial and The Baltic Sea is an example where commercial fishing for herring, recreational fisheriesare common in situations of co-exploitation of fish cod (Gadus morhua) and other marine species is prevalent, but where the stocks (Boucquey, 2017; Kearney, 2001, 2002; Loomis and Ditton, total removals of marine fish by recreational fishing are non-negligible 1993). Often, both groups blame each other for reduced access to fishing (Hyder et al., 2018; Radford et al., 2018). In the Baltic Sea cormorants grounds, interference during fishing, overfishing, damaging or stealing have increased strongly in abundance and may thus lead to competition ¨ of gears or illegal harvest (Dorow and Arlinghaus, 2012; Quinn, 1988; for fish, particularly in inshore coastal habitats (Ostman et al., 2013; Sullivan, 2003). Beyond competition for fish, fisher-angler conflicts Hansson et al., 2018; Mustamaki¨ et al., 2014; Veneranta et al., 2020). often have a root cause in different interpretation of value, e.g., is a fish We studied the lagoon fisheries around the Island of Rügen in the generating more value when captured by a recreational angler or a southern Baltic Sea in Germany as a model coastal European ecosystem commercial fisher, and general discussions about the moral appropri where commercial and recreational fisheries as well as cormorants are ateness of the use of fisheries resources by either fishers or anglers all abundant and jointly exploit a shared multi-species resource (Boucquey, 2017). composed of both freshwater and marine species. Pike (Esox lucius), Another common conflict in fisheries is, broadly speaking, intersec pikeperch (Sander lucioperca) and perch (Perca fluviatilis) are examples of toral when conservation and fisheriessectors collide (Arlinghaus, 2006; stenohaline freshwater fish that are common in the lagoon ecosystems Brehens et al., 2008; Hansson et al., 2018; Marzano et al., 2013; Steffens, around Rügen, and in many areas of the Baltic Sea under oligo- to 2010). For example, as a result of European bird conservation regula mesohaline conditions. These species are targeted by commercial fish ¨ tions, cormorants (Phalacrocorax carbo sinensis) have strongly increased eries with varying intensity (Ostman et al., 2013; Winkler, 1990), and in abundance in many areas of Europe, in some cases causing depletion they are also prime targets of recreational fisheries (Basan, 1988; Lars ¨ ¨ of local fish populations (Dieperink, 1995; Jepsen et al., 2019; Ostman son et al., 2015; Ostman et al., 2013; Weltersbach et al., 2021). Concerns et al., 2013; Rudstam et al., 2004; Skov et al., 2014; Veneranta et al., that fishing and other forms of predation might impact stock dynamics 2020). Protection of the cormorants in Europe has been elevated to a of freshwater predators in the Baltic Sea

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