THIS IS WHAT MARINE SCIENTISTS THINK ABOUT THE OSLO FJORD

This is what marine scientists think about the Oslo Fjord.

Author: Bente Kjøllesdal.

The Ministry of Trade, Industry and Fisheries and the Ministry of Climate and Environment have proposals for a number of interventionist fisheries measures in the Oslo Fjord for consultation . 

The goals of the action plan are:

• The fjord must achieve good environmental status
• Important natural values ​​to be restored
• The biological diversity in the fjord must be safeguarded
• Active outdoor activities should be promoted

According to the consultation document, the proposed measures should also contribute to the following objectives:

• Building fish stocks and a well-functioning ecosystem

The Institute of Marine Research has carefully reviewed the proposed measures, and is now providing its input on whether these will contribute to meeting the objectives. Read the full consultation response here (PDF). 

Cod and shrimp failure 

In the Oslo Fjord, both demersal fish and shrimp populations have weakened.

“Demersal fish stocks, such as cod, are in poor condition. The stock has been reduced and few cod survive to grow large and old. Fisheries, climate change and the ecological state of the Oslo Fjord probably contribute to this,” says marine scientist Mette Skern-Mauritzen, who has led HI’s work on the consultation response.

For the shrimp population, the reasons for the decline are probably related to both the fishing pattern in the region and a failure in recruitment. Shrimp recruitment has been reduced over the past 15 years.

“To rebuild these stocks, it is crucial to take measures that contribute to reduced mortality in recreational and commercial fishing, as well as improving the habitat, environmental condition and ecological condition of the fjord,” says Skern-Mauritzen.

The condition of pelagic fish such as sprat is considered good in the Oslo Fjord.

Reduced impact from fisheries contributes positively

The proposed measures mainly affect recreational fishing, commercial shrimp and crayfish fishing with bottom trawls, as well as purse seine fishing for herring and sprat.

Recreational fishermen in the Oslo Fjord harvest demersal fish and migratory pelagic species such as mackerel.

Trawling for shrimp has a complex impact on marine ecosystems. It affects shrimp stocks – which are fished, it affects demersal fish stocks – as bycatch, and it affects seabed habitats.

Seine fishing for herring and sprat only affects these stocks, which are also important prey for bottom fish.

“By reducing the impacts from the various fisheries, the proposed measures can contribute to achieving the management goals for the Oslo Fjord,” says Skern-Mauritzen. 

The zero-fishing areas

The proposed zero-fishing areas in the inner Oslofjord, as well as for the Færder and Ytre Hvaler national parks in the outer Oslofjord, are expected to contribute to strengthening both the environmental and ecological condition, and the condition of shrimp and fish stocks.

At the same time, marine scientists emphasise that recreational fishing with a rod for mackerel and other migratory species has a significantly lower risk of negative effects on the ecosystem in the Oslo Fjord than fishing for local species.

“Recreational fishing can therefore be sustainable under given conditions and for some species in the current ecosystem. But this will require active management with associated control activities, as well as targeted competence building among recreational fishermen,” says Skern-Mauritzen.

Recommends further protection of Hvalerdypet

The researchers further recommend including the entire Hvalerdypet in zero fishing area 3, which overlaps with large parts of Ytre Hvaler National Park.

“New data confirms that Hvalerdypet is an important nursery area for shrimp. To safeguard this, an alternative is to expand the proposed no-fishing area or to protect the area with a trawl ban,” says Skern-Mauritzen.

Recommends gear regulation – rather than vessel length restrictions

In their consultation response, the marine scientists point out that the proposed technical regulations are also central to achieving the Oslofjord goals, by reducing direct impact on the stocks, including through bycatch, throughout the fjord.

One of the measures proposed is to limit fishing with shrimp trawls and crayfish trawls to vessels under 11 meters. According to marine scientists, the size of the vessel is not necessarily decisive for the extent of the bottom impact of fishing.

“What type of gear the vessels have, and how they use them, is more important,” says Skern-Mauritzen.

“Therefore, we also believe that it would be more targeted with measures based on gear type, such as a maximum weight on trawl doors or a ban on the use of more than a single trawl.”

Seine fishing for sprat and herring

In the Oslo Fjord, sprat fishing mainly focuses on two stocks: coastal sprat in the inner parts of the fjord and oceanic sprat in the outer parts.

HI considers it important to safeguard the local sprat population. The local sprat is an important prey for top predator fish that are in poor condition in the inner Oslofjord. In this area, the researchers therefore believe that a ban on fishing for sprat and herring will contribute positively.

In the outer part of the Oslofjord, sprat dominates.

“Still limited purse seine fishing for sprat in this area does not stand in the way of achieving the Oslofjord goals,” says the marine scientist.

Given the goal of safeguarding natural biodiversity in the areas covered by the national parks, zero fishing for sprat and herring should still be considered for these areas.

Starting in 2025, HI will also have a data base from the Oslo Fjord that will make it possible to set a separate quota for sprat in the Oslo Fjord.

Increased value creation in the long term

“In the short term, the measures are expected to result in somewhat reduced harvesting from the Oslo Fjord, but if the goals are achieved, it will provide a basis for increased harvesting and value creation in the long term,” the marine scientists write in the consultation response.

Marine scientists believe that the proposed measures reduce pressure on populations and ecosystems in the Oslo Fjord, and that they can help strengthen the fjord’s resilience to climate change.

They point out that it is still uncertain whether the bottom fish community will return to previous levels, as it is also uncertain who will be the climate winners in the coastal ecosystem in the Skagerrak.

Image: Erlend Astad Lorentzen, Heidi Gabrielsen / Institute of Marine Research

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