UK waters are home again to the bluefin tuna

Atlantic bluefin tuna have returned to UK waters and can once again be seen during the summer and autumn months.

Their numbers appear to be increasing, following a long period of absence linked to population decline, according to research led by Cefas and the University of Exeter.

Marine scientists in the UK and Ireland have analysed multiple datasets, spanning a 16-year period, to document the increase in bluefin, which arrive into the waters of the Celtic Seas and off South West England, the Scilly Isles, and North West Ireland to feed in late summer and autumn.

The research is part of the Defra-funded “Thunnus UK” research project.

Thunnus UK was established to improve knowledge of this species, as an essential first step in ensuring a positive future for Atlantic bluefin tuna around the UK.

Central to the project’s success has been a concerted effort to share and combine important data on where people have observed Atlantic bluefin tuna.

This will help to identify where and when these fish are found in UK waters.

Nearly 1,000 unique observations were recorded between 2013 and 2018 by citizen scientists, scientists, fishers and eco-tour leaders.

Researchers found that Atlantic bluefin tuna begin to arrive in May and stay as late as January.

However, peak numbers were recorded between August and October each year.

The research draws on five key data sources:

  • The general public: A total of 80 sightings recorded by the public and submitted to http://www.thunnusuk.org
  • Eco-tourism: three eco-tourism vessels collecting data on more than 1600 boat tours off the SW coast of England between 2008 and 2018.
  • Opportunistic scientific surveys: 40 days of surveys with >2500 km of effort conducted by Cefas and University of Exeter experts off the Northwest Coast of Ireland and SW England in 2016 and 2018.
  • Fisheries independent surveys: (1) data collected by MarineLife during the Peltic survey by Cefas between 2013 and 2015, and (2) data collected by the Irish Whale and Dolphin Group during the Irish Marine Institute’s Celtic Sea Herring Acoustic Survey between 2014 and 2018
  • Bycatch in commercial fisheries: Bluefin tuna were accidentally caught (bycatch) in the Irish commercial fishery for albacore tuna between 2003 and 2017.

Lead author Tom Horton, of the University of Exeter, said: “Atlantic bluefin tuna are once again a feature in nearshore waters off the UK and Ireland.

We’ve been able to document this story by using data from a wide variety of sources. We need to work together to ensure a future for Atlantic bluefin tuna, both in the UK and Ireland and more broadly throughout their range in the Atlantic Ocean. This is a really exciting study and the return of these fish suggest an important role in the UK’s ecosystem.

Scientists complete largest global assessment of ocean warming impacts

A group of international marine scientists has compiled the most comprehensive assessment of how ocean warming is affecting the mix of species in our oceans – and explained how some marine species manage to keep their cool.

Martin Edwards from the University of Plymouth along with other researchers from the UK, Japan, Australia, USA, Germany, Canada, South Africa and New Zealand analysed three million records of thousands of species from 200 ecological communities across the globe.

Reviewing data from 1985 – 2014, the team led by Michael Burrows of the Scottish Association for Marine Science (SAMS) in Oban showed how subtle changes in the movement of species that prefer cold-water or warm-water, in response to rising temperatures, made a big impact on the global picture. The findings, published in the journal Nature Climate Change [https://www.nature.com/articles/s41558-019-0631-5], show how warm-water species increase and cold-water marine species become less successful as the global temperature rises. However, the study also suggests that some cold-water species, and fish in particular, will continue to thrive by seeking refuge in cooler, deeper water.

Prof Burrows  further added:

“For the period from 1985 – 2014 we created the equivalent of an electoral poll in the ocean, showing swings between types of fish and plankton normally associated with either cold or warm habitats. As species increase in number and move into, or decline and leave, a particular ecological community, the make-up of that community will change in a predictable way. While this may not sound like a big change, it has a considerable impact on species that may already be on, or close to, their maximum temperature tolerance. A gradual temperature change like the one we are witnessing is not going to cause extinctions overnight but it is affecting the success of many species, not least zooplankton such as copepods, which are crucial to the ocean food web”.

Prof Edwards said the truly global study looked at data from the North Atlantic, Western Europe, Newfoundland and the Labrador Sea, east coast USA, the Gulf of Mexico, and the North Pacific from California to Alaska. While the global warming trend was widely seen, the North Atlantic showed the largest rise in average temperature during the time period. This area of the North Atlantic is routinely monitored by one of the world’s largest and longest marine biological surveys known as the Continuous Plankton Recorder (CPR) Survey which provided some key observational data in the global study. The changes observed have been driven by a seemingly small but ecologically significant rise in temperature of almost one degree Celsius in some parts of the ocean since 1985, a rapid change in just three decades. These changes are having huge implications for the abundance and distribution of plankton in our oceans.



Climate-related changes in fish and plankton communities shown by changes in Community Temperature Index values from 1985 to 2015.

New open access research paper on plankton biogeography in the North Atlantic

New research paper: Plankton biogeography in the North Atlantic Ocean and its adjacent seas: Species assemblages and environmental signatures

Loïck Kléparski, Grégory Beaugrand and Martin Edwards

Ecology and Evolution 2021; 00:1-15. DOI: 10.1002/ece3.7406

Plankton biodiversity is a key component of marine pelagic ecosystems. They are at the base of the food web, control the productivity of marine ecosystems, and provide many provisioning and regulating ecological services. It is therefore important to understand how plankton are organized in both space and time.

Abstract:

Here, we use data of varying taxonomic resolution, collected by the Continuous Plankton Recorder (CPR) survey, to map phytoplankton and zooplankton biodiversity in the North Atlantic and its adjacent seas. We then decompose biodiversity into 24 species assemblages and investigate their spatial distribution using ecological units and ecoregions recently proposed. Finally, we propose a descriptive method, which we call the environmental chromatogram, to characterize the environmental signature of each plankton assemblage. The method is based on a graphic that identifies where species of an assemblage aggregate along an environmental gradient composed of multiple ecological dimensions. The decomposition of the biodiversity into species assemblages allows us to show (a) that most marine regions of the North Atlantic are composed of coenoclines (i.e., gradients of biocoenoses or communities) and (b) that the overlapping spatial distribution of assemblages is the result of their environmental signatures. It follows that neither the ecoregions nor the ecological units identified in the North Atlantic are characterized by a unique assemblage but instead by a mosaic of assemblages that overlap in many places.

Spatial distribution of total
plankton taxonomic richness in the North Atlantic

Get the open access paper here: https://onlinelibrary.wiley.com/doi/10.1002/ece3.7406