Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

Casini, Michèle; Käll, Filip; Hansson, Martin; Plikshs, Maris; Baranova, Tatjana; Karlsson, Olle; Lundström, Karl; Neuenfeldt, Stefan; Gårdmark, Anna; Hjelm, Joakim

doi:10.1098/rsos.160416

Cited by 133 publications

(186 citation statements)

References 70 publications

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“…The higher levels of abundance (CPUE) and weight per occupied length group (MWPLC) in Western and Eastern Baltic cod at the latter parts of the time series, may not contradict the notion of a lower ecosystem productivity in the Baltic sea compared to the Öresund. The low condition (Casini et al., ) and the decline of the growth indices for Western and Eastern Baltic cod (this study) rather confirm the feeding restrictions.…”

Section: Discussionsupporting

confidence: 63%

Historic changes in length distributions of three Baltic cod (Gadus morhua) stocks: Evidence of growth retardation

Svedäng

Hornborg

2017

Ecology and Evolution

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Understanding how combinations of fishing effort and selectivity affect productivity is central to fisheries research. We investigate the roles of fishing regulation in comparison with ecosystem status for Baltic Sea cod stock productivity, growth performance, and population stability. This case study is interesting because three cod populations with different exploitation patterns and stock status are located in three adjacent but partially, ecologically different areas. In assessing stock status, growth, and productivity, we use survey information and rather basic stock parameters without relying on age readings. Because there is an urgent interest of better understanding of the current development of the Eastern Baltic cod stock, we argue that our approach represents partly a novel way of interpreting monitoring information together with catch data in a simplified yet more informative way. Our study reports how the Eastern and Western Baltic cod have gone toward more truncated size structures between 1991 and 2016, in particular for the Eastern Baltic cod, whereas the Öresund cod show no trend. We suggest that selective fishing may disrupt fish population dynamic stability and that lower natural productivity might amplify the effects of selective fishing. In support of earlier findings on a density‐dependent growth of Eastern Baltic cod, management is advised to acknowledge that sustainable exploitation levels for Eastern Baltic cod are much more limited than perceived in regular assessments. Of more general importance, our results emphasize the need to embrace a more realistic view on what ecosystems can produce regarding tractable fish biomass to facilitate a more ecosystem‐based fisheries management.

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Section: Discussionsupporting

confidence: 63%

Historic changes in length distributions of three Baltic cod (Gadus morhua) stocks: Evidence of growth retardation

Svedäng

Hornborg

2017

Ecology and Evolution

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“…In a subsequent paper, Caddy (2000) used several case studies (e.g., Black Sea, Baltic Sea) to illustrate how nutrient loadings and hypoxia affect fish populations. For example, hypoxia effects on the volume of reproductive habitat are one of several major factors implicated in a variety of analyses of Baltic Sea cod recruitment variability (Koster et al 2005;Margonski et al 2010;Tomczak et al 2012;Casini et al 2016). In another study, Huang et al (2010) estimated that an average 13% decline in harvest of brown shrimp in North Carolina estuaries was attributed to hypoxia.…”

Section: Communicated By Dennis Swaneymentioning

confidence: 99%

Modeling the Population Effects of Hypoxia on Atlantic Croaker (Micropogonias undulatus) in the Northwestern Gulf of Mexico: Part 1—Model Description and Idealized Hypoxia

Rose

Creekmore

Thomas³

et al. 2017

Estuaries and Coasts

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We developed a spatially explicit, individual-based model to analyze how hypoxia effects on reproduction, growth, and mortality of Atlantic croaker in the northwestern Gulf of Mexico lead to population-level responses. The model follows the hourly growth, mortality, reproduction, and movement of individuals on a 300 × 800 spatial grid of 1-km 2 cells for 140 years. Chlorophyll-a concentration, water temperature, and dissolved oxygen (DO) were specified daily for each grid cell and repeated for each year of the simulation. A bioenergetics model was used to represent growth, mortality was assumed stage-and age-dependent, and the movement behavior of juveniles and adults was modeled based on temperature and avoidance of low DO. Hypoxia effects were imposed using exposure effect submodels that converted time-varying exposures to low DO to reduced hourly growth, increased hourly mortality, and reduced annual fecundity. Results showed that 100 years of either mild or intermediate hypoxia produced small reductions in population abundance, while repeated severe hypoxia caused a 19% reduction in long-term population abundance. Relatively few individuals were exposed to low DO each hour, but many individuals experienced some exposure. The response was dominated by a 5% average reduction in annual fecundity of individuals. Under conditions of random sequences of mild, intermediate, and severe hypoxia years occurring in proportion to their historical frequency, the model predicted a 10% decrease in the long-term population abundance of croaker. A companion paper substitutes hourly DO values from a threedimensional water quality model for the idealized hypoxia and results in a more realistic population reduction of about 25%.

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“…Table 1). Thus, apart from such harmful effects of cyanobacteria blooms as degradation of recreational potential and increased water toxicity, this selfsupporting vicious circle (Vahtera et al, 2007a,b) counteracts nitrogen load reduction efforts and causes other ecosystem effects generated and sustained by hypoxia, including damage to cod reproduction and condition (MacKenzie et al, 2000;Casini et al, 2016). On the other hand, the cyanobacteria blooms stimulate summer production in the entire food web, from zooplankton and benthos to fish (Karlson et al, 2015;Svedén et al, 2016).…”

Section: The Vicious Circlementioning

confidence: 99%

“…Therefore, the priority should be given to weakening the vicious circle by substantial reduction of the marine phosphorus pool. Such reduction could eventually be achieved by continuing extensive (and expensive) measures decreasing terrestrial phosphorus loads (HELCOM, 2015(HELCOM, , 2017aMcCrackin et al, under revision), which would require decades of patiently tolerating the unpleasant effects of cyanobacteria blooms, from impaired recreation and toxicity to poor food and spawning conditions for cod (e.g., Casini et al, 2016). The reduction might be accelerated by geoengineering methods (e.g., Gustafsson et al, 2008;Rydin et al, 2017;Stigebrandt, 2018), but despite all the achievements in ecosystem modeling of the Baltic Sea (e.g., Meier et al, 2014;Tedesco et al, 2016) there are still no biogeochemical and ecosystem models capable of producing reliable long-term scenario simulations with the required engineering precision to assess these options.…”

Section: Management Considerationsmentioning

confidence: 99%

Large-Scale Nutrient Dynamics in the Baltic Sea, 1970–2016

Savchuk

2018

Front. Mar. Sci.

120

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The Baltic Sea is one of the world's marine areas well-covered by both long-term observations and oceanographic studies. It is also a large coastal area in which eutrophication had already been recognized half a century ago. While the mechanisms of eutrophication are largely understood, several features are less recognized and sometimes neglected, including: (a) natural and anthropogenic North-South and East-West nutrient gradients within the drainage basin and marine ecosystems; (b) the compensatory potential of the interconnectivity between the Baltic Sea basins; (c) long nutrient residence times and high buffer capacity of the system, resulting in slow responses to nutrient load reductions. Particularly important is the interaction of (d) naturally occurring saltwater inflows sporadically ventilating deep water layers and (e) a partly man-made intensification of biological oxygen consumption. Resulting redox alterations of biogeochemical nitrogen and phosphorus cycles are locked in a "vicious circle" that promotes cyanobacterial nitrogen fixation, thereby hindering nitrogen load reduction and sustaining an elevated trophic state. This tight coupling of natural environmental variation and human impacts complicates both scientific studies and management recommendations. Our primary objective is to describe all these features and mechanisms with the best available data on nutrient loads, and unique estimates of the basin-wide nutrient pools. These data are presented as both long-term time series and empirical nutrient budgets. The analysis is supplemented by results of biogeochemical modeling. A second, more practical objective is to make these time series available to the community.

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Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

Cited by 133 publications

References 70 publications

Historic changes in length distributions of three Baltic cod (Gadus morhua) stocks: Evidence of growth retardation

Historic changes in length distributions of three Baltic cod (Gadus morhua) stocks: Evidence of growth retardation

Modeling the Population Effects of Hypoxia on Atlantic Croaker (Micropogonias undulatus) in the Northwestern Gulf of Mexico: Part 1—Model Description and Idealized Hypoxia

Large-Scale Nutrient Dynamics in the Baltic Sea, 1970–2016

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