Understanding ontogenetic and temporal variability of Eastern Baltic cod diet using a multispecies model and stomach data

Kulatska, Nataliia; Neuenfeldt, Stefan; Beier, Ulrika; Elvarsson, Bjarki Þór; Wennhage, Håkan; Stefansson, Gunnar; Bartolino, Valerio

doi:10.1016/j.fishres.2018.11.023

Cited by 17 publications

(13 citation statements)

References 53 publications

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“…The Gadget implementation in the Baltic is a multispecies, multifleet, single area model representing the temporal development of the age-length structure of the eastern Baltic cod, central Baltic herring and Baltic sprat populations (see Kulatska et al, 2018, for more details on the model). The model includes an active and a passive fishery targeting cod and a pelagic fishery catching sprat and herring.…”

Section: Baltic Sea Modelmentioning

confidence: 99%

Comparing the steady state results of a range of multispecies models between and across geographical areas by the use of the jacobian matrix of yield on fishing mortality rate

Pope¹,

Bartolino

Kulatska

et al. 2019

Fisheries Research

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A B S T R A C TLike other fisheries models, multispecies models are subject to various sources of error. However, with regard to their use for ecosystem-based fisheries management (EBFM) between model errors are likely to be most important. As multispecies models are by definition many-dimensional, comparing them is potentially a complex task. The paper uses a simple approach. This is to calculate the Jacobian matrix of long term steady state catch by species with respect to the fishing mortality relative to status quo levels on all species. This enables the comparison of the relative strength of species interactions among models both within and between regions. This Jacobian matrix approach to comparing multispecies models is applied to available models for the North Sea, the Baltic Sea and from Icelandic waters. Moreover, this information is used to provide the basis for estimating a multidimensional quadratic yield surface for each model in the near field. Used this way it is possible to compare different model estimations of fishing mortality rate changes needed to approach yield-related management goals. The results suggest considerable variation between models in their detailed results but more coherence in suggesting directions for changing fishing mortality rate. Thus the approach is of considerable importance in specifying the confidence with which it is possible to make multispecies predictions for EBFM.

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Section: Baltic Sea Modelmentioning

confidence: 99%

Comparing the steady state results of a range of multispecies models between and across geographical areas by the use of the jacobian matrix of yield on fishing mortality rate

Pope¹,

Bartolino

Kulatska

et al. 2019

Fisheries Research

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“…The main distributional areas of the two cod stocks differ remarkably in oceanographic conditions and also in prey availability and composition. In the past decades the diet studies mainly focused on the role of EBC in the eastern Baltic food web (e.g., Casini et al, 2016;Dziaduch, 2011;Hüssy et al, 1997;Kulatska et al, 2019;Pachur & Horbowy, 2013). These studies revealed that currently EBC relies strongly on Clupeid prey species such as herring Clupea harengus and sprat Sprattus sprattus,…”

mentioning

confidence: 99%

The forgotten feeding ground: patterns in seasonal and depth‐specific food intake of adult cod Gadus morhua in the western Baltic Sea

Funk

Frelat

Möllmann

et al. 2020

Journal of Fish Biology

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This study presents the diet composition of western Baltic cod Gadus morhua based on 3150 stomachs sampled year-round between 2016 and 2017 using angling, gillnetting and bottom trawling, which enhanced the spatio-temporal coverage of cod habitats. Cod diet composition in shallow areas (<20 m depth) was dominated by benthic invertebrate species, mainly the common shore crab Carcinus maneas. Compared to historic diet data from the 1960s and 1980s (limited to depth >20 m), the contribution of herring Clupea harengus decreased and round goby Neogobius melanostomus occurred as a new prey species. Statistical modelling revealed significant relationships between diet composition, catch depth, fish length and season. Generalized additive modelling identified a negative relationship between catch depth and stomach content weight, suggesting reduced food intake in winter when cod use deeper areas for spawning and during peak summer when cod tend to avoid high water temperatures. The results of this study highlight the importance of shallow coastal areas as major feeding habitats of adult cod in the western Baltic Sea, which were previously unknown because samples were restricted to deeper trawlable areas. The results strongly suggest that historic stomach analyses overestimated the role of forage fish and underestimated the role of invertebrate prey. Eventually, this study shows the importance of a comprehensive habitat coverage for unbiased stomach sampling programmes to provide a more reliable estimation of top predator diet, a key information for food web analyses and multispecies models.

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“…Another possible mechanism behind the change in metabolism is changed in food quality rather than quantity. Analyses of cod stomach data suggest substantial changes in dietary composition of EBC during the time period from 1990 to 2013, including an increased proportion of sprat (Sprattus sprattus) and slightly decreased proportion of herring (Clupea harengus; Kulatska et al, 2019). Because the sprat abundance increased over the period while the herring stock declined, Kulatska et al suggested that EBC showed a strong preference for herring over sprat.…”

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confidence: 99%

Compensatory Feeding in Eastern Baltic Cod (Gadus morhua): Recent Shifts in Otolith Growth and Nitrogen Content Suggest Unprecedented Metabolic Changes

et al. 2020

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The productivity of the Eastern Baltic cod (EBC) has been severely reduced over the last 25 years, for reasons that remain unclear. The size distribution of EBC has become increasingly truncated, condition and health status have deteriorated, and sexual maturation has started to occur at increasingly smaller sizes. Despite an increasing trend in recruitment during this period, reduced growth or increased mortality rates after the recruitment phase have resulted in decreasing landing levels and low profitability in the cod fishery, whereas the scientific community has difficulties in disentangling the causes of the decline of EBC. We studied changes in metabolic status in EBC between the capture years of 1995 and 2015, by investigating two aspects of fish metabolism that can be extracted retrospectively from otolith (earstone) morphometry and nitrogen content. Changes in relative otolith size to fish size are related to the metabolic history of the individual fish, and the otolith nitrogen content reveals the level of protein synthesis and feeding rate. Because otoliths accrue continuously on their surface and are biological stable (inert), the chemical content of the otolith trajectory reflects the timeline of the fish. We measured the N/Ca ratio as a proxy for protein content in EBC otolith along distal radius traverses from the core to the edge of the otolith by using secondary ion mass spectrometry (SIMS). Here we show that the otoliths were similar or larger at a given fish size, and the ratio of N/Ca has increased over the studied period. These proxies reveal significant metabolic changes during the same period as the condition, and stock productivity has declined. We discuss potential mechanisms behind the metabolic changes, including elevated temperature and compensatory feeding due to nutrient deficiencies. Such changes in food quality may, in turn, relate to still unrecognized but on-going ecosystem shifts, where climate change could be the ultimate driver.

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Understanding ontogenetic and temporal variability of Eastern Baltic cod diet using a multispecies model and stomach data

Cited by 17 publications

References 53 publications

Comparing the steady state results of a range of multispecies models between and across geographical areas by the use of the jacobian matrix of yield on fishing mortality rate

Comparing the steady state results of a range of multispecies models between and across geographical areas by the use of the jacobian matrix of yield on fishing mortality rate

The forgotten feeding ground: patterns in seasonal and depth‐specific food intake of adult cod Gadus morhua in the western Baltic Sea

Compensatory Feeding in Eastern Baltic Cod (Gadus morhua): Recent Shifts in Otolith Growth and Nitrogen Content Suggest Unprecedented Metabolic Changes

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