Expanding Knowledge of Atlantic Mackerel Spawning Behaviour

This article was originally published in the Fall 2019 edition of the Union Forum Magazine, written by Dr. Erin Carruthers, FFAW-Unifor Fisheries Scientist.

For many years, Newfoundland fish harvesters have reported an abundance of young-of-the-year mackerel or “pencil mackerel”, which are 10 – 20 cm in length and approximately 2 to 4 months old. As it stands, the larval survey conducted by DFO is done in the southern Gulf and assumes that no significant spawning occurs outside the southern survey area. However, the abundance of these small mackerel elsewhere has led harvesters to question whether they were spawned in the southern Gulf.

Newfoundland mackerel harvesters are seeing an abundance of mackerel despite the declines in stock status shown at the assessment. Questions regarding additional mackerel spawning sites outside the southern Gulf of St. Lawrence (4T) – and whether the biomass estimates from the southern Gulf mackerel egg survey are still representative of the Canadian mackerel stock – have been repeatedly raised at assessment and management forums.

Not only do harvesters see an abundance of mackerel during the mackerel fishery but harvesters fishing in southern 3Ps fish have reported adult mackerel in the St. Pierre Bank area in May, June and July month. Mackerel spawn in May, June and July and water temperatures in southern 3Ps are suitable for mackerel spawning. The question is: Are mackerel spawning in 3Ps?

Over three dozen adult mackerel (greater than 26 cm in length) were collected from southern 3Ps in June and July by long-time fish harvester Keith Bath. Mr. Bath reported that adult mackerel were more common on the Bank in July this year, whereas last year they were getting mackerel in their nets in May. Adult mackerel samples were sent to DFO Science in Mont-Joli where their ear bones (otoliths) will be removed and their maturity stage will be assessed.

Our interest and commitment to mackerel research goes beyond sample collection. FFAW-Unifor has applied for funding to do otolith microchemistry research with DFO Science and academic researchers. Because the centre of the ear bone shows the chemical signature of the waters where mackerel were born, if northeast coast young-of-the-year mackerel were not born in the southern Gulf, their ear bones will show it.

Finally, harvesters have seen small mackerel in turr stomachs.  Fish harvesters from both Cape Freels and Fortune Bay reported seeing glass mackerel in turr stomachs when they were turr hunting. Taken together these observations suggest that mackerel are distributed in Newfoundland waters throughout their life cycle.

Our challenge is to systematically document when, where and what mackerel life stages are observed around the island. Secondly, we will need to collect more young-of-the-year or pencil mackerel this year. These mackerel are needed for the otolith microchemistry research.

The current egg survey in the southern Gulf of St. Lawrence is the basis for the Canadian assessment of this stock. Therefore, research on where mackerel were born could change our understanding of mackerel stock status.  More broadly, questions about where mackerel spawn are also questions about how fish distribution and behaviour might shift with changing marine environments. These broader questions are important ones for harvesters – and fisheries scientists who work with harvesters – to ask.