Cleaner water linked to smaller cockles that die younger
Cockles have been harvested along the coast of South Wales for centuries. The Burry Inlet and Loughor Estuary, near Swansea, is an important habitat for the popular and widespread common cockle (Cerastoderma edule).
Like other bivalve species, cockle populations are subject to change, either by sudden or gradual changes in the natural environment or by human activity.
The new research provides more insight into this variation and into long-term trends, helping to conserve and manage cockle stocks.
Swansea University bioscientist Dr Ruth Callaway conducted the study. She examined 64 Burry Inlet clam monitoring reports compiled between 1958 and 2009. With this she analyzed trends in the total number of cockles, their size and death rates, against the background of changes in weather, climate and wastewater treatment.
The overall message of the data varied widely over the 50-year period from 1958 to 2009.
Specific findings from the study were:
- Birth and death rates were both high during the first and last decades of the study, and variation was linked to the total number of clams in the population
- The larger the cockle population, the smaller the cockles – there was a significant relationship between the number of cockles and the average size of the specimens
- The size of cockles decreased in the late 1990s and the modernization of wastewater treatment was significantly related to this downward trend, suggesting that the changed nutrient regime in the estuary may have led to a reduced food supply for cockles
- The smaller the clams were, the higher their death rate: the average size of young clams was significantly related to their lifespan
- Environmental factors such as temperature were not significantly linked to dwindling clams
- The fishable cockle stocks have decreased in the last years of the study.
The study did not evaluate the impact of harvesting on cockle populations as monitoring reports do not include data on this, although fishing cannot be excluded as a contributing factor to cockle population variation.
However, changes in water treatment emerge from the data as an important factor. Prior to 1997, wastewater from seven sewage treatment plants was discharged into the estuary. It was modernized with two new installations using purification processes that disinfected the wastewater and removed the nitrogen. This meant cleaner, healthier water for humans, but less nutrients to sustain clams.
dr. Ruth Callaway of the University of Swansea, the bioscientist who conducted the study, says that “the data reveal further evidence that the 1997 change in wastewater treatment at the Burry Inlet reduced food availability for cockles, leading to smaller average cockle sizes.” , which in turn shortened their lifespan.”
“High water quality standards are essential. The challenge is to find ways to keep our water clean while keeping our cockle population strong.”
“To find a solution to any cockle stock problem, we first need as complete a picture as possible of its history and background variation. This is where the new research can help. It deepens our understanding of the relationship between wastewater management and bivalves, giving us greater insight into variation and long-term trends, which will help conserve and manage estuary and cockle populations.”
Spencer Williams of Gower Coast Seafood says: “I have personally observed clams getting smaller over the years. Not only did it affect clams, but in my experience mussels and sea worms also got smaller, which I think is related to the change in wastewater treatment.”
Byron Davies, Baron Davies of Gower, says: “I have personal memories of the cockles as a young boy in Gower, when they went up the northern Gower sands and came back with the shellfish. The cockle fishery provides a lasting heritage in the coastal communities .”
“As an MP, I regularly negotiated between fishermen, government organizations and researchers, and Ruth and I have been talking about changes in cockle populations for years.”
“These long-term data show the profound changes in fishable cockle stocks over the past decades, which may be natural or affected by human activities. The knowledge is vital for fisheries management, which should be supported in the long term.”
Andrea Winterton (Natural Resources Wales—Marine Services Manager) who is responsible for day-to-day cockle management in the Burry Inlet says that “our goal is to develop a thriving fishery that supports, protects and enhances the needs of the community, and the environment on which it depends.”
“This is a landmark document, providing evidence to help us better understand long-term trends in cockle populations over a 50-year period to 2009, when a number of factors influenced the population.”
“While there are ongoing challenges, fisheries management has improved in recent years, including better research methods and a new management plan. This provides much better information on stock distribution and population trends.”
“To build on this important paper, we hope to publish an overview of the most recent research data and evidence from 2010 to bring this story fully up to date.”
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Quote: Cleaner water linked to smaller clams that die younger (2022, September 21) retrieved September 21, 2022 from https://phys.org/news/2022-09-cleaner-linked-smaller-cockles-die.html
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