We synthesize a large body of literature involving peer-reviewed work, grey literature and novel data analyses about the small-scale northern pike (Esox lucius) fishery in lagoon ecosystems in the southern Baltic Sea. Based on our comprehensive review that synthesizes ecological as well as social, economic and governance-related literature we derive implications for the management of mixed commercial-recreational fisheries in coastal areas. The interconnected shallow and biologically highly productive meso-to polytrophic lagoons (extension about 2000 km2) bordered by the peninsula of Fischland-Darss and the islands of Hiddensee, Rugen and Usedom in the southern Baltic Sea of Germany constitute an oligo-to mesohaline transitional habitat suitable for colonization by a range of freshwater fishes, including pike. In the Rugen area, pike successfully recruits in the mesohaline lagoons, but anadromous subpopulations and freshwater residents also exist in tributaries, forming a connected meta-population. The stock is co-exploited by a small-scale commercial fishery and a largely tourism-dominated recreational fishing sector that, depending on the angler type, values the pike for both consumption as well as for its trophy size. The recreational sector has risen in economic and social relevance since the German reunification in 1990 and today removes similar amounts of biomass than commercial fisheries. Pike is a prime target species of anglers, and recreational pike angling in the lagoons today generates a larger economic impact in terms of jobs created compared to the commercial pike fishing, where pike is typically one target among many freshwater fish. Stock assessments and stakeholder reports have revealed that the stock size and size of pike in the catch have been falling since 2010, fueling conflicts among fishers and anglers for space and fish. Reasons for the current decline of the pike stock involve multiple pressures operating jointly and possibly synergistically, such as local overharvest, loss of stock structure through past blocking of freshwater streams, eutrophication and macrophyte loss, predation mortality by natural predators, reduced availability of marine prey through declines of western Baltic spring-spawning herring (Clupea harengus), and poorly understood impacts of climate change. The

The northern pike (Esox lucius) is an iconic predatory fish species of significant recreational value and ecological role in the Baltic Sea. Some earlier studies indicate local declines of pike in the region, but a thorough spatial evaluation of regional population trends of pike in the Baltic Sea is lacking. In this study, we collate data from 59 unique time-series from fisheries landings and fishery-independent monitoring programs to address temporal trends in pike populations since the mid-2000′s in eight countries surrounding the Baltic Sea. In a common analysis considering all time-series in concert, we found indications of an overall regional temporal decline of pike in the Baltic Sea, but trends differed among countries. Individual negative trends in time-series were moreover found in several regions of the Baltic Sea, but predominantly so in the central and southern parts, while positive trends were only found in Estonia and northern Finland. The mix of data used in this study is inherently noisy and to some extent of uncertain quality, but as a result of the overall negative trends, together with the socioeconomic and ecological importance of pike in coastal areas of the Baltic Sea, we suggest that actions should be taken to protect and restore pike populations. Management measures should be performed in combination with improved fishery-independent monitoring programs to provide data of better quality and development of citizen-science approaches as a data source for population estimates. Possible measures that could strengthen pike populations include harvest regulations (including size limits, no-take areas and spawning closures), habitat protection and restoration, and an ecosystem-based approach to management considering also the impact of natural predators.

Information on catch and effort of recreational angling in mixed-use fisheries (co-exploited by commercial and recreational fishers) is often scarce, preventing the application of data-rich stock assessments typically performed for industrialized commercial fisheries. Here, we show how data-poor stock assessment methods developed for marine fisheries, particularly a class of models labelled as “catch-only” models (COMs), offer a possible solution. As a case study, we use COMs to assess a northern pike stock around the German Baltic island of Rügen. We fit multiple COMs to a time-series of total pike removals, and use their outputs as explanatory variables in superensemble models. We conclude that the stock is fully exploited and currently declining. Our study highlights the potential for using COMs to determine status of previously-unassessed coastal and freshwater stocks facing recreational fishing pressure, and demonstrates how incorporating recreational removals is crucial for achieving reliable insights into the status of mixed-use stocks.

A new approach for estimating the fishing mortality benchmark Fmsy (fishing pressure that corresponds to maximum sustainable yield) is proposed. The approach includes density-dependent factors. The analysis considers 53 data-rich fish stocks in the Northeast Atlantic. The new Fmsy values are estimated from an ensemble of data sources: (i) applying traditional surplus production models on time-series of historic stock sizes, fishing mortalities, and catches from the current annual assessments; (ii) dynamic pool model (e.g. age-structured models) estimation for stocks where data on density-dependent growth, maturity, and mortality are available; (iii) extracts from multispecies and ecosystem literature for stocks where well-tested estimates are available; (iv) the “Great Experiment” where fishing pressure on the demersal stocks in the Northeast Atlantic slowly increased for half a century; and (v) linking Fmsy to life history parameters. The new Fmsy values are substantially higher (average equal to 0.38 year−1) than the current Fmsy values (average equal to 0.26 year−1) estimated in stock assessments and used by management, similar to the fishing pressure in the 1960s, and about 30% lower than the fishing pressure in 1970–2000.

The recruitment and biomass of a fish stock are influenced by their environmental conditions and anthropogenic pressures such as fishing. The variability in the environment often translates into fluctuations in recruitment, which then propagate throughout the stock biomass. In order to manage fish stocks sustainably, it is necessary to understand their dynamics. Here, we systematically explore the dynamics and sensitivity of fish stock recruitment and biomass to environmental noise. Using an age-structured and trait-based model, we explore random noise (white noise) and autocorrelated noise (red noise) in combination with low to high levels of harvesting. We determine the vital rates of stocks covering a wide range of possible body mass (size) growth rates and asymptotic size parameter combinations. Our study indicates that the variability of stock recruitment and biomass are probably correlated with the stock's asymptotic size and growth rate. We find that fast-growing and large-sized fish stocks are likely to be less vulnerable to disturbances than slow-growing and small-sized fish stocks. We show how the natural variability in fish stocks is amplified by fishing, not just for one stock but for a broad range of fish life histories.

Throughout much of the world's oceans, life is organized around seasonal cycles of feast and famine. Here we seek to understand the life-history strategies by which marine organisms contend with seasonal variations through a range of adaptations and traits, including overwintering stages, dormancy, investment in reserves, and migration. Our perspective is broad, spanning across marine food webs, from unicellular plankton to whales, and covering all latitudes, from the equator to the poles. The analysis is organized around a simple mechanistic life history optimization model. The model generates several general hypotheses: (i) small organisms should cope with winters by making resting stages or by dormancy; (ii) medium-sized organisms should build reserves and perform seasonal vertical migration to reduce predation; (iii) large organisms should primarily employ latitudinal migrations to follow seasonal peaks in production. Subsequently, these hypotheses are tested against a large assemblage of observations and data reported in the literature. Body size, trophic level, and the intensity and duration of seasonal highs and lows appear to be closely related to seasonal strategies. Some, but not all of these hypotheses are borne out by our analysis of data. In particular, we find that organisms with a lifespan on the order of the seasonal length employ a multitude of strategies.

Global fisheries catches can be increased in a sustainable way after rebuilding of fish populations, if ecosystem functioning is considered. A central biological reference point for fisheries manag ...

Global fisheries catches can be increased in a sustainable way after rebuilding of fish populations, if ecosystem functioning is considered. A central biological reference point for fisheries manag ...

Global fisheries catches can be increased in a sustainable way after rebuilding of fish populations, if ecosystem functioning is considered. A central biological reference point for fisheries manag ...

Blue whiting 1 0.32 0.37 Cod Icelandic 2 -0.63 Cod W Scotland 3 0.17 -Cod Irish Sea 4 0.37 0.95 Cod (Gadus morhua) in divisions 7.e-k (western English Channel and southern Celtic Seas) 5 0.35 0.56 Cod North Sea 6 0.33 0.70 0.89 Cod Northeast Arctic 7 0.40 0.55 Cod Faroe Plateau 0.32 0.36 Cod Western Baltic Sea 0.26 0.62 Cod Eastern Baltic Sea --0.87 '000 t SSB according to

We recall here the entropy-like measure {S F } proposed in [1] and we compare it to our network entropy measure S. The results presented in [1] are substantially different from our achievements and the reason lies in the conceptual foundation of the two measures. We clarify their relation thank to a simple toy model. The “entropy of information flux distribution" {S F } is a single-node entropy measure, i.e. {S F } is a collection of entropy values, one for each node of the designed network (i = 1, ...N where N is the total number of nodes). This measure behaves similarly to the local disparity-heterogeneity index (or participation ratio PR) of weighted networks, and is defined as follows:

Currently applied fisheries models and stock assessments rely on the assumption that density-dependent regulation only affects processes early in life, as described by stock–recruitment relationships. However, many fish stocks also experience density-dependent processes late in life, such as density-dependent adult growth. Theoretical studies have found that, for stocks which experience strong late-in-life density dependence, maximum sustainable yield (MSY) is obtained with a small fishery size-at-entry that also targets juveniles. This goes against common fisheries advice, which dictates that primarily adults should be fished. This study aims to examine whether the strength of density-dependent growth in actual fish stocks is sufficiently strong to reduce optimal fishery size-at-entry to below size-at-maturity. A size-structured model is fitted to three stocks that have shown indications of late-in-life density-dependent growth: North Sea plaice (Pleuronectes platessa), Northeast Atlantic (NEA) mackerel (Scomber scombrus), and Baltic sprat (Sprattus sprattus balticus). For all stocks, the model predicts exploitation at MSY with a large size-at-entry into the fishery, indicating that late-in-life density dependence in fish stocks is generally not strong enough to warrant the targeting of juveniles. This result lends credibility to the practise of predominantly targeting adults in spite of the presence of late-in-life density-dependent growth.

During the 20th century, many large-bodied fish stocks suffered from unsustainable fishing pressure. Now, signs of recovery are appearing among previously overfished large-bodied fish stocks. This new situation raises the question of whether current fisheries advice and management procedures, which were devised and optimized for depleted stocks, are well-suited for the management of recovered stocks. We highlight two challenges for fisheries advice and management: First, recovered stocks are more likely to show density-dependent growth. We show how the appearance of density-dependent growth will make reference points calculated with current procedures inaccurate. Optimal exploitation of recovered large-bodied fish stocks will therefore require accounting for density-dependent growth. Second, we show how a biomass increase of large-bodied piscivorous fish will lead to a reverse trophic cascade, where their increased predation mortality on forage fish reduces forage fish productivity and abundance. The resulting decrease in maximum sustainable yield of forage fish stocks could lead to conflicts between forage and large-piscivore fisheries. Avoiding such conflicts requires that choices are made between the exploitation of interacting fish stocks. Failure to account for the changed ecological state of recovered stocks risks creating new obstacles to sustainable fisheries management.