The Role of Science in Canada's Sustainable Bluefin Tuna Fishery

Canada's bluefin tuna fishery is based on rigorous, up-to-date, and relevant science.

The total allowable catch of bluefin tuna in Canada's fishery is determined by an assessment of the western Atlantic Ocean stock. Scientists from member countries of the International Commission for the Conservation of Atlantic Tunas (ICCAT), which includes Canada, conduct this assessment. It is based on data that is collected by harvesters and recorded into logbooks to provide annually to ICCAT.

The assessment considers the number of spawning tuna that are 8-10 years of age, and older. It also reviews ‘indicators of abundance’ that are derived from commercial fishery observations and logbook data. For example, in 2008, bluefin tuna were abundant in Canada's southern Gulf of St. Lawrence fishery and at stable levels elsewhere in Canadian waters. Abundance indicators were mixed in other Atlantic Ocean locations. For example, the absence of larger older fish in US waters was a particular concern.

The bluefin tuna stock assessment also takes into consideration scientific research conducted on these tuna by ICCAT members. In recent years, Canada and its research partners in other countries have completed a number of these important studies:

Otolith Microchemistry

Otoliths are calcium carbonate balance organs found in the inner ear of bony fishes. They are continuously deposited through the lifecycle of a fish, so studies can determine age and growth information. Otoliths also carry certain trace elements that are in proportion to water chemistry, allowing researchers to determine their water locations.

Studies of otolith microchemistry reveal the origin of birth of fish caught in Canadian fisheries, and allow scientists to assess the extent of mixing between eastern and western bluefin stocks. This is important because severe overfishing taking place in the eastern Atlantic and Mediterranean Sea could be seriously impeding the health of western bluefin. Results to date indicate that Canadian fisheries almost exclusively rely upon bluefin tuna that were born in the Gulf of Mexico.

Bluefin Tuna Growth

Age-structured studies of bluefin tuna’s growth and mortality provide critical information for stock assessments. With an accurate measure of the age of bluefin tuna, related to size, fisheries managers and scientists can understand growth rate, better assess the abundance and productivity of adult stocks, and predict future numbers. Canadian research has shown that the growth of bluefin tuna is slower than expected using the growth model used by ICCAT.

Satellite Tagging

Canadian scientists and tuna harvesters have participated in satellite archival tagging studies for many years, often with American researchers. Satellite tags are tiny waterproof computers which are attached to tuna to record light levels, salinity and depth. After a pre-programmed time, the tags detach from the fish and float to the surface, where they relay their data to passing satellites. The data allow scientists to reconstruct the paths of the fish; the results of which support strong linkages of Canada’s bluefin tuna to the Gulf of Mexico.

Read More: Sustainable Tuna Stocks