Dramatic decline in shrimp population

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Researchers estimate that the breeding population today is only about one eighth of what it was in 1908.

Norwegian shrimp fishing began in the Skagerrak and Oslo Fjord as early as 1899, when fisheries scientist Johan Hjort discovered large populations of shrimp in these areas.

Since 1908 shrimp catches have been recorded in Norwegian ports. However, most of this data is in old statistical directories, which makes it difficult to access.

Marine scientists have now for the first time digitized old data and created a continuous time series for shrimp landings in Norway, broken down by county, covering every year since 1908.

Using this data, they were also able to estimate the development of the North Sea and Skagerrak shrimp population during this period.

From the coast to the open ocean

“The time series shows how shrimp fishing, having started in eastern Skagerrak and Oslofjord in the late 19th century, spread west and north along the coast to over the following decades, developing into an important coastal fishery,” Guldborg Søvik, a researcher at the Institute for Marine Research (IMR), says.

In the 1920s and 1930s, fishermen began trawling shrimp further up the Skagerrak.

“The Second World War halted the growth of the fishery, but after the war the volumes landed increased rapidly. It was then that industrial fishing and deep-sea fishing developed in the Barents Sea and by Svalbard. Sometimes Norwegian fishermen have also fished shrimp near Jan Mayen and Greenland, and in international waters near Canada,” says Søvik.

The report was written by Katrine Wilhelmsen Melaa, who is doing a master’s degree at the University of Bergen, with support from Søvik and her IMR colleagues Fabian Zimmermann and Trude Hauge Thangstad.

Shrimp boat in the Langesund bat in 1925.

Large variations over time and between counties

Industrialization and the expansion of fishing grounds led to a significant increase in shrimp landings from around 1980: whereas annual landings were previously in the order of a few thousand tonnes, they reached more than 80,000 tons in the 1980s and early 2000s.

In recent decades, in particular, there have been large fluctuations, both in total landings and in the distribution between counties.

According to the researchers, these fluctuations are mainly explained by technological developments and economic factors, in other words the price.

“But the data also shows a drop in shrimp landings in western and central Norway, suggesting that shrimp fishing is disappearing or has already disappeared from these areas. It also suggests that the population itself is disappearing in several places,” says Søvik.

Shrimp landings by county in thousands of tons, 1908-2021.  “Other” (grey columns) includes landings abroad and at unknown locations.  Oslo is included in Viken here.

Shrimp landings by county in thousands of tons, 1908-2021. “Other” (grey columns) includes landings abroad and at unknown locations. Oslo is included in Viken here.

Landings of prawns by county in southern and western Norway 1908-2021.

Landings of prawns by county in southern and western Norway 1908-2021.

Less shrimp than before

In the shrimp fishery along the coast and in the Barents Sea, there are no catch quotas, only technical measures.

Fishing in the Skagerrak and the Norwegian Trough, on the other hand, is regulated by quotas, with the International Council for the Exploration of the Sea (ICES) giving the quota recommendations.

In the annual report released by the ICES Working Group on Shrimp earlier this year, researchers incorporated historical landings data into the stock assessment model used by ICES to provide quota recommendations. . The model estimates the size of the spawning stock based on survey and fishery data.

By putting the complete time series of landings from the Norwegian, Swedish and Danish shrimp fisheries into the model, the scientists were able to estimate the change in the stock between 1908 and today.

“This time series is longer than the ones we have for almost all other stocks,” says Søvik.

The time series shows a marked decline in the breeding population since the fishery began: researchers estimate that the breeding population today is about one-eighth its size in 1908.

“It’s quite a dramatic drop,” says Søvik.

Historical estimate of shrimp spawning biomass in the Skagerrak and Norwegian Trench.

Historical estimate of shrimp spawning biomass in the Skagerrak and Norwegian Trench.

Old data worth its weight in gold

Landings data is often the only source of data available for most of the time a fishery exists. According to Søvik and his colleagues, these data can therefore make an essential contribution to stock assessment and fisheries management.

“Time series of landings spanning the entire period of the fishery provide us with an important benchmark against which to compare the current status of the fishery and the stock,” she says.

In the new IMR report, the researchers recommend that all data on landings of all species should be made available in the highest possible spatial resolution.

“It will broaden our perspective on how fisheries have developed and can help ensure sustainable management of our marine resources,” she concludes.

Barents Sea prawn catches are sorted.

Barents Sea prawn catches are sorted.

References:

ICES. Joint NAFOICES Pandalus Assessment Working Group (NIPAG), ICES scientific reports, 2022. DOI: 10.17895/ices.pub.19692181.v1

Melaa et al. Historical Northern Shrimp Landings (Boreal Pandalus) in Norway – Data by county for 1908-2021, IMR report2022.