[ Back to EurekAlert! ] Public release date: 12-Dec-2007
[ | E-mail Share Share ]

Contact: Kira Paulli Pravato
kpp@ruc.dk
452-461-4096
Census of Marine Life

Ancient fish bones reveal impacts of global warming beneath the sea

Scientists discover that warm-water species that once thrived in Danish waters are returning

IMAGE: Part of the fishbones from 1m2 of the Maglemosegaard excavation. 48 percent of the 12,784 identified fish bones were from gadids, mainly cod. Each red bar segment on the scale...

Click here for more information.

Scientists studying ancient fish bones in Scandinavia have discovered that warm-water species like anchovies and black sea bream that once thrived in Danish waters during a prehistoric warm period are now returning. Some cold-water species, such as cod, were also abundant during this period, having benefited from a lower fishing effort.

Through the study of archaeological material, tax accounts, church registers and account books of monasteries, an international group of fisheries ecologists and fisheries/maritime historians have drawn a picture of marine life in the northern European seas (North Sea, Wadden Sea, Baltic Sea, and White Sea) as it looked in the past.

Their findings are presented in a special issue of Fisheries Research “History of Marine Animal Populations and their Exploitation in Northern Europe, ” 14 papers starting from ca. 7000 BC to present. The volume is edited by Henn Ojaveer and Brian R. MacKenzie.

New historical documentation is increasingly becoming available. Its interpretation is providing a broader basis for understanding processes and mechanisms that lead to variations in marine populations and ecosystems. The studies in this special issue are important contributions to the establishment of new baselines for management of marine ecosystems including conservation strategies for overexploited living resources. They were conducted under the auspices (or as part of) the History of Marine Animal Populations, a project of the international collaboration, the Census of Marine Life.

Fisheries Research “History of Marine Animal Populations and their Exploitation in Northern Europe Volume 87, Issues 2-3, Pages 101-262 (November 2007) http://www.sciencedirect.com/science/journal/01657836.

Overviews of three chapters follow:

IMAGE: Vertebrae of anchovy caught by the Stone Age people at Krabbesholm. Two connected vertebrae from a recent anchovy are shown for comparison. Scale 10 mm.

Click here for more information.

108,000 fish bones from 7000 BC predict the future: The Danish fish fauna during the warm Atlantic period (ca. 7000–3900 BC): Forerunner of future changes?

Global and regional climate models predict that air and sea temperatures will rise by approximately 3°C during the next 70–100 years. In order to understand some of the processes by which global warming might affect marine fish species near Denmark, researchers have investigated the fish fauna during one of the warmest prehistoric periods (the warm Atlantic period: ca. 7000–3900 BC).

A total of 108,000 fish bones were identified, and amongst them were bones of many species, for example, anchovy and black sea bream, which we usually consider to be typical of waters much farther south and warmer like the Bay of Biscay and the Mediterranean Sea. When temperatures cooled after the warm period ended, most of these species disappeared from the archaeological record, suggesting that local abundances declined. However, many of those same warm-water species have recently reappeared in waters around Denmark as temperatures have risen in the last 10–15 years. The archaeological information can be an indicator of which species may become common as climate change progresses and warms.

There were also thousands of cod bones present together with the warm-water species. That result was surprising because investigators knew that the increase in sea temperatures since the late 1980s to the early 1990s has reduced the survival of young cod in the North Sea. How can these two findings be reconciled? The researchers believe that the difference is due to the much lower fishing pressure in the archaeological period. The message from their work is that sustainable cod populations can be maintained in the North Sea even during the climate change expected in the 21st century, but the fish mortality needs to be lowered.

For further information contact: Inge B. Enghoff, Natural History Museum of Denmark (Zoological Museum), University of Copenhagen; email: IBEnghoff@snm.ku dk; tel: +45-3532-1086 or

Brian R. MacKenzie, Technical University of Denmark , Danish Institute for Fisheries Research, Charlottenlund, Denmark; email: brm@difres.dk; tel.: +45-3396-3403


IMAGE: Map of present day Limfjorden, with the breached Agger Tange in the west. Until 1825 the only entrance to the Limfjorden was from Kattegat at the town of Hals.

Click here for more information.

The climate influence the Gulf of Riga fisheries in during the 17th century: Gulf of Riga (Baltic Sea) fisheries in the late 17th Century

The exploited fish population in the Gulf of Riga was very different in the beginning of the 17th century from what is seen today. Archival evidence reveal that the timing of the fishing season, and species composition and, to an extent, the amounts of fish catches in the Gulf of Riga are strongly linked to climate dynamics.

The time-period 1675-1696 belongs to the coldest period of the Little Ice Age. During that time, fishing in the Gulf of Riga took place at more than 20 localities along the whole coast of the basin and was therefore an important livelihood at these times. Herring, flounder and eelpout (considered to be cold-tolerant species) formed the majority of the catch while the importance of species such as perch, pikeperch and various cyprinids, which prefer warm-water and are nowadays relatively widespread, was less than 1% of the catches.

Herring were in the coastal areas from the end of March to November. The highest catch was in today’s terms taken during the warm season - June and July. This should be considered as a direct effect of severe winters, due to which the ice-cover melted relatively late and therefore, massive herring migration to spawning areas near the coast was shifted later in the season.

During the period studied, two sub-periods were identified: 1675-1683 and 1685-1696. Winters were more severe during the second period, and as a result, herring fishing seasons started later due to a shift in the timing of herring spawning in the summer months. As a result, the window where fish were available for fisheries was a shorter period of time. This led to substantially lower herring catches, and this is direct evidence of a climatic impact.

For further information contact: Henn Ojaveer, Estonian Marine Institute, University of Tartu, Pärnu, Estonia;
Tel.: +3725158328; +3724434456; e-mail: henn.ojaveer@ut.ee


Why did the fishery collapse in the Limfjord in 1830?: A long-term (1667-1860) perspective on impacts of fishing and environmental variability on fisheries for herring, eel, and whitefish in Limfjord, Denmark

The Limfjord in northern Denmark is a shallow sound which has supported commercial fisheries for centuries. In the beginning of the 19th century, the fishery declined by 90%, and fishermen went bankrupt when all the fish disappeared. What happened to all the fish?

By reconstruction of historical data series for herring, eel and whitefish the question has now been answered. We now know that both nature and humans played a significant role in the collapse.

In 1825 a winter storm broke the narrow Agger Tange isthmus, which used to separate the Limfjord from the North Sea. That led to an increase of salinity in the western part of the Limfjord. The eel population declined due to the salt water intrusion, and resulted in a 15-year long crisis for the eel fisheries before it had fully recovered. The whitefish did not survive the salinity obstacle and has never returned to the area.

The commercially most important fishery was for herring. The collapse of the herring fishery was most likely due to unsustainable fishing practices, such as fishing on top of spawning areas, eventually destroying the production rate of new young herring. Today the herring have returned to the area, but not nearly in the same numbers as they were in the early 19th century.

The study of the Limfjord fisheries provides an example of how historical ecology may help ‘shift the baseline’ by revealing the previous existence of a marine ecosystem very different from that which is known from contemporary ecological research.

For further information contact: Bo Poulsen, Department of Environmental, Social and Spatial Change, University of Roskilde, Denmark Tel.: +45 4674 2726, e-mail: bopo@ruc.dk

###

History of Marine Animal Populations

HMAP: www.hmapcoml.org

History of Marine Animal Populations (HMAP) is a global inter-disciplinary project being conducted within the Census of Marine Life (CoML). HMAP is investigating historical changes in marine populations and ecosystems, and is encouraging the integration of natural and social sciences to understand the magnitude, causes and consequences of long-term changes in marine animal populations.

One of the main activities within HMAP is the identification, recovery and interpretation of new original datasets from both written (e. g., surveys, landings, tax records) and non-written sources (e. g., archaeological, paleo-oceanographic) that extend over long periods of time. The length of these datasets allows marine ecologists to develop new baselines of species abundances and distribution, and to investigate how exploitation and environmental variability have interacted over longer time scales and under different combinations of exploitation and environmental forcing.

Census of Marine Life

The Census of Marine Life is a global network of researchers in more than 80 nations engaged in a 10-year scientific initiative to assess and explain the diversity, distribution, and abundance of life in the oceans. The world’s first comprehensive Census of Marine Life—past, present, and future—will be released in 2010. (www.coml.org). The History of Marine Animal Populations is a component project of the Census.

The issue is also support by grants from the European Union:

INCOFISH (6th Framework Programme Specific Targeted Research Project on Integrating Multiple Demands on Coastal Zones with Emphasis on Aquatic Ecosystems and Fisheries), MarBEF (6th Framework Programme Network of Excellence on Marine Biodiversity and Ecosystem Functioning) and EUR-OCEANS (6th Framework Programme European Network of excellence for Ocean Ecosystems Analysis).



[ Back to EurekAlert! ] [ | E-mail Share Share ]

 


AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.