Skinny cod and grey seal reveals troubling changes to food web in the Baltic Sea

JUNE 11, 2019

by Stockholm University

The prime predators of the Baltic Sea at the top of the food web are losing weight, according to a new study that links the deteriorating health of gray seals and cod with changes in bottom-living crustaceans, isopods and amphipods.

"It is important that you understand how the food web works when managing a fishery. It is not enough to manage how the fish and fisheries are changing. The availability and quality of food is at least as important," says Lena Bergström, researcher at the Department of Aquatic Resources at the Swedish Agricultural University.

In a collaboration between several universities, the authors of the study examined how the health and abundance of certain species has changed over two decades in the Bothnian Sea and the Baltic Proper. They investigated seal, cod, herring, sprat, isopods, amphipods and zooplankton, species that all occur at different levels in the Baltic Sea food web. The system is complex and several species can be both predators and prey. For example, herring eats zooplankton and some bottom fauna while the herring itself is eaten by cod and seal.

Shrinking habitats for bottom-living animals

The study primarily shows that there are links between the health of both cod and seal with the availability of bottom-living animals. Regarding the seals, the connection is indirect through that the herring it eats is influenced by the availability of the bottom-living animals. In both cases, there is a link to climate change and eutrophication.

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Increasing seal population will not harm largest fish stocks in the Baltic

Date:  December 10, 2018

Source:  Stockholm University

Seals feeding on fish does not decrease fish stocks of Baltic cod, herring and sprat the most -- climate change, nutrient load and fisheries do, shows a new study from Stockholm University.

It has long been debated whether the seal predation of fish play a major role in the fish decline in the Baltic Sea compared to human fishing. The debate escalated worldwide since conservation efforts to protect seals and fish-eating birds resulted in increased number of them.

A new study taking into account human pressures on the environment, shows that the seals are not the main problem on commercial fish stocks in the open water of the Baltic Sea.

"We currently have 30,000 grey seals in the Baltic Proper, but we can even have more than 100,000 seals and it will still not affect the amount of cod negatively as much as climate change, nutrient load and fisheries. The Baltic is very sensitive to human impact," says David Costalago, a former postdoctoral researcher at Department of Ecology, Environment and Plant Sciences, Stockholm University.

The cod population size for example, decreased more by environmental change and by human fishing, than the seals eating the fish. How much fish the seals eat is also affected by the climate and nutrient load.

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The first endemic Baltic Sea fish species received its name

Date:  July 11, 2018

Source:  University of Helsinki

Summary:

Researchers have discovered and named a new endemic fish species in the Baltic Sea, the 'Baltic flounder,' Platichthys solemdali.

The "Baltic flounder" Platichthys solemdali is the first fish species shown to be native only to the Baltic Sea, i.e. the first endemic fish described from the area and one of the only two known endemic species when considering any organism. The fact that a new vertebrate species is found and described from European waters, and especially from the species-poor Baltic Sea still after more than a century of biological research in the area, makes this finding significant.

"The reason why this species has not been recognized before is that it appears to be near to identical to the other flounder species, the European flounder, Platichthys flesus, also occurring in the Baltic Sea," says professor Juha Merila, one of the authors behind the article, from the Faculty of Biological and Environmental Sciences.

Currently the two species can be distinguished only with genetic methods, or by studying their eggs and sperm. The species also differ in their interaction with the environment: the newly described Baltic flounder lays sinking eggs on the sea floor in coastal areas while the European flounder spawns buoyant eggs in deep areas out in the open sea. The new species is more abundant in the Gulf of Finland while the distribution of the European flounder is centered to the central and southern Baltic Sea.

Read on

Seals, birds and humans compete for fish in the Baltic Sea

Date:  November 13, 2017

Source:  Stockholm University

In Sweden and in other parts of Europe there are concerns that seals and birds compete with humans for fish resources. For the Baltic Sea, an international study now shows that this competition is a reality.

"Because fish is nutrient-rich food and angling provides valuable recreation, the increased populations of seals and fish-eating birds in the Baltic have resulted in a sometimes contentious debate over the effects of these animals on the fish stocks. The debates are often based on assumptions, which is why I took the initiative to look at the problem from a scientific viewpoint," said Sture Hansson, Professor of Ecology, Environment and Plant Sciences at Stockholm University.

Together with four researchers from the Swedish University of Agricultural Sciences (SLU) and seven other colleagues from countries around the Baltic, Hansson has estimated birds' and seals' fish consumption. Seals are the primary fish-eating mammals, and their consumption is about the same as that of all birds together. Humans catch 3 to 4 times more fish than seals and birds combined.

Small-scale coastal fishing most impacted by wildlife

The fishing grounds most impacted by competition from wildlife are the coastal areas with species like perch, pike, pikeperch, brown trout, salmon, whitefish and vendace. Seals and cormorants consume similar amounts as humans. Because we know that these fish are impacted by human fishing activities, it's reasonable to conclude that they are also impacted by predation from seals and birds. Wildlife thus competes with humans for these fish resources.

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Young sea stars suffer more from ocean acidification than adults

Date:

September 26, 2014

Source:

Helmholtz Centre for Ocean Research Kiel (GEOMAR)

Summary:

Young sea stars from the Baltic Sea suffer more from the effects of ocean acidification than adults. In a laboratory experiment, scientists showed that younger animals already eat less and grow more slowly at only slightly elevated carbon dioxide concentrations.

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Darkened Fjord Waters Mean Fewer Fish, More Jellyfish

ScienceDaily (Nov. 19, 2012) — The seawater in the Baltic Sea, the North Sea, and Norway's coastal waters and fjords is gradually getting darker. Researchers are observing signs similar to those from overproduction of organic compounds. The result may be fewer marine areas with fish, and more jellyfish.

Marine biologist Dag L. Aksnes of the University of Bergen has analysed the impacts of the declining optical conditions in Norwegian coastal waters. The process has likely been taking place over many decades, and there is strong evidence that changes in weather and climate are causing it to accelerate. And it could prove difficult to reverse.

Coloured matter from fresh water causing problems

Fresh water from rivers and lakes flows into the sea, mixing with coastal seawater. "This fresh water contains far more coloured dissolved organic matter (CDOM) than marine water, so our coastal waters are darkening," explains Professor Aksnes.

His research project receives some of its funding from the Research Council of Norway's research programme on the Oceans and Coastal Areas (HAVKYST).

Major differences between fjords

For many years, Professor Aksnes and his colleagues have been studying two fjords, Lurefjorden and Masfjorden, in northern Hordaland county on Norway's western coast. The fjords are similar and located close to each other, but with one important difference: Masfjorden contains far more seawater than Lurefjorden, which contains lower-salinity coastal water all the way down to its seabed. The study shows that while Masfjorden still has an ecosystem dominated by fish, its darker neighbouring fjord is heavily populated by the jellyfish Periphylla periphylla.

Read on:  http://www.sciencedaily.com/releases/2012/11/121119093851.htm

Grey Seals in Baltic Sea Consume as Much Fish as the Fishing Industry Catches, Research Finds

ScienceDaily (Apr. 2, 2012) — The grey seals in the Baltic Sea compete for fish with the fishing industry. The seals locally eat about the same quantities of cod, common whitefish, salmon, sea trout and eel as those taken by fishermen. This is the conclusion from research carried out at the University of Gothenburg, Sweden.

Competing with the fishing industry

The grey seals in the Baltic Sea eat largely the same species and the same sizes of fish as those taken by the fishing industry. So even if the amount of fish eaten by seals is small relative to the total amount of fish caught in the Baltic Sea, the seals' dietary habits may have a major impact on the local availability of fish in the areas where they are common.

"If you compare the estimated consumption of fish by grey seals in their main range in Sweden, which is north of the Kalmar Sound, it is of the same order of magnitude as the total catch taken by Swedish professional and leisure fishermen in the same area," says scientist Karl Lundström.

Read on:  http://www.sciencedaily.com/releases/2012/04/120402112826.htm

Oceana Pushes to Protect 3,500 Km2 of the Baltic Sea

Crucial elements of the Baltic Sea's threatened marine biodiversity are completely unprotected

Oceana, the largest international marine conservation organisation has recently published a report on biodiversity and marine habitats, proposing nine areas totalling 3,500 km2 for inclusion in the current network of Marine Protected Areas (MPA) in the Baltic Sea. These areas, in Sweden, Finland and Denmark, identified during Oceana's extensive two month research expedition in the spring of 2011, all have specifically important biodiversity that must be protected from human activities, for the Baltic Sea to recover from its current critical state.

The nine proposed areas include offshore waters and host habitats, communities and species that are not sufficiently covered by the current network of MPAs. Some of the habitats documented by Oceana have not been described in the Baltic Sea before such as sponge aggregations and special types of coral gardens in the Kattegat and in the Sound. These habitats and communities are vulnerable to many human activities and in particular to bottom trawling.

"Biodiversity in the Baltic Sea is under enormous stress from pollution and destructive fisheries and the removal of sediments by dredging. The new areas proposed by Oceana represent elements of this biodiversity that are currently unprotected," says Niklas Zennström, Entrepreneur and founder of Zennstöm Philantrophies, one of the funders of Oceana's Baltic Sea project.

"Coupled with effective management of human activities, the establishment of MPAs is an important mechanism to support a healthier marine environment and as a consequence sustainable fisheries", added Anne Schroeer, Oceana Baltic Sea Project Manager.

Currently, 12 per cent of the Baltic Sea is covered by MPAs. To safeguard biodiversity, a minimum of 30 per cent of the Baltic Sea should be effectively protected. This means that besides legal protection, the areas must also be properly managed.. Many of these habitats can only recover with the immediate adoption of protective measures, which would benefit not only the benthic communities inside protected areas but also commercial fisheries with enhanced fish stocks.

http://www.prnewswire.co.uk/cgi/news/release?id=343538

Baltic seaduck take a dive

On Wednesday 1 December, a new report presenting the results of a census of wintering waterbirds in the Baltic Sea has been launched. The studies reveal that overall numbers have declined by more than 40% since the 1990s.

To read the full report Waterbird populations and Pressures in the Baltic Sea, please click here
Internationally coordinated counts were undertaken in 2007-2009 under the SOWBAS project (“Status of wintering waterbird populations in the Baltic Sea”), funded by the Nordic Council of Ministers. The total number of wintering waterbirds was estimated at 4.41 million, compared to 7.44 million during the last census in 1992-1993.

Of the 20 species covered, 11 decreased, including 7 that declined by more than 30%. The strongest declines were suffered by seaduck. Numbers of Long-tailed Duck, the most numerous wintering waterbird in the Baltic, declined by 65%, with similar declines recorded for Steller’s Eider (Vulnerable) and Velvet Scoter. Common Eider, Common Scoter and Red-breasted Merganser all declined by between 42% and 51%.

For some of these species, the Baltic is the most important wintering area in the world, holding the majority of their global populations. These declines are therefore of global concern, and could have implications for the species’ status on the IUCN Red List.

BirdLife has combined these results with available data from other parts of the world to review the species’ global status and propose appropriate changes. Detailed proposals are available for comment (until January 2012) on BirdLife’s Globally Threatened Bird Forums: http://www.birdlife.org/globally-threatened-bird-forums/

Most of these seaduck concentrate in the southern Baltic, but unlike some other waterbirds, no consistent climate-driven northward shift in their winter distribution was detected. However, climate change may be affecting them in other ways. Many of these species breed mainly in the Russian arctic or tundra, where they may be suffering from climate-induced ecosystem changes. Recent monitoring in autumn, as these birds arrive in the Baltic, has revealed worryingly low proportions of juveniles, implicating unsustainably low recruitment on the breeding grounds.

Other factors could also be involved, such as over-harvesting of certain species, or oil discharges from ships, which are known to cause significant extra mortality in some parts of the Baltic. Changes in nutrient loads could also be having an impact, and the report stresses the importance of eutrophication in determining food availability and thus the abundance and distribution of waterbirds. Finally, incidental bycatch in gill-nets has been reported in several Baltic fisheries, with diving species like seaduck being particularly susceptible.

Now that the trends of these species are known, the top priority is to diagnose and address the causes of their declines. Experience suggests that this is best achieved by bringing together key experts from across the species’ range to make progress in a coordinated and effective manner, at a flyway population scale and with international cooperation.

Discussions to organise a conservation planning workshop in 2012 have already begun, involving the IUCN-SSC/WI Duck Specialist Group, the Wildfowl & Wetlands Trust, BirdLife International, Wetlands International and the African-Eurasian Waterbird Agreement.

http://www.birdlife.org/community/2011/12/baltic-seaduck-take-a-dive/

Satellite spies vast algal bloom in Baltic Sea

A satellite image has revealed the scale of a vast algal bloom spreading in the Baltic Sea.

The potentially toxic bloom, covering 377,000 sq km, could pose a risk to marine life in the region, warn scientists.

They added that a lack of wind and prolonged high temperatures had triggered the largest bloom since 2005.

The affected area stretches from Finland in the north to parts of Germany and Poland in the south.

The image, captured earlier this month, was recorded by a camera on the European Space Agency's Envisat satellite.

Researchers monitoring the spread of the blue-green algae said such blooms had spread over the Baltic Sea each summer for decades.

They added that fertilizers from surrounding agricultural land were being washed into the sea and exacerbating the problem.

This has led to a process called eutrophication, in which the additional nutrients stimulate rapid growth of phytoplankton - microscopic free-floating marine plants.

This accelerated growth also reduces the amount of oxygen available to other plant and animal species in the affected area; raising fears that it could destabilise fragile marine ecosystems.

As well threatening certain species, blue-green algae can also pose a risk to human health, and officials are advising people not to bathe in areas where the algae is visible.

However, researchers said the current bloom would quickly break up with the arrival of strong winds, as the resulting waves would disperse the algae.

http://www.bbc.co.uk/news/science-environment-10740097