Spotted Mackerel Update

  • Spotted mackerel on a length measuring board
    Figure 1: Measuring the length of a spotted mackerel

Fisheries Queensland monitors key commercially and recreationally caught species to help assess the sustainability of Queensland's fisheries. Spotted mackerel (Scomberomorus munroi) has been monitored routinely since 2004, providing a long-term data series on the length, sex and age of fish being harvested.

The information collected through the monitoring program improves our knowledge of the harvest and increases our understanding of annual patterns and long-term trends in population characteristics. Fisheries Queensland uses these data sets, along with other information, to help assess the status of the spotted mackerel stock The most recent classification for spotted mackerel was sustainably fished.

Spotted mackerel is a species endemic to waters of southern Papua New Guinea and northern Australia. Multiple biological stocks are distributed across northern Australia from Rottnest Island on the west coast to Wollongong on the east coast.

Routine biological monitoring of spotted mackerel in Queensland focuses on the area south of Cairns to the Queensland - New South Wales border, where fish are known to belong to a single biological stock. This east coast stock undertakes annual migrations covering large distances. Schools move between spawning grounds in northern waters in winter/spring and southern feeding grounds in summer.

Fish length

More than 50% of spotted mackerel harvested are between 65 ¬and 75 cm long (Figure 2). Few fish longer than 95 cm are observed in the harvest (Figure 2). 

Small fish (60-70 cm) make up a higher percentage of the commercial catch than the recreational catch (Figure 2). This is a characteristic that has been observed throughout the history of the monitoring program.

  • Time series 2011-12 (top) to 2013-14 (bottom) financial years. Percentage of catch for  commercial (blue bars), and recreational catch (yellow bars) per length class
    Figure 2: Length structure of the spotted mackerel harvest showing the relative abundance (percentage) of fish caught within each length class for the commercial and recreational fishery sectors 2011-2012 to 2013-2014.

Fish age

Scientists can often estimate a fish's age from its ear bones (Figure 3). Spotted mackerel are fast growing and relatively short-lived predators; they reach maturity between 1-2 years of age and can live up to 8 years.
  • A photograph of an otolith (ear bone) as viewed using a microscope. Dots (in red) show the opaque bands. Copyright: DAF
    Figure 3: A spotted mackerel otolith (ear bone), after it has been removed from a fish’s head, as viewed using a microscope. Dots show the yearly bands (or periods of slower growth), similar to the growth rings of a tree.

One to five year-olds dominate the harvest of spotted mackerel (Figure 4). The oldest spotted mackerel aged in the monitoring program in 2013-2014 were 7 years old, the largest of which was 82 cm (approximately 3.3 kg). The largest fish aged in 2013-2014 was 103 cm and it was 6 years old.

  • Percentage of catch for  commercial (blue bars), and recreational catch (yellow bars) per age group - Copyright: DAF
    Figure 4: Age structure of spotted mackerel showing the relative abundance (percentage) of spotted mackerel within each age group for the recreational and commercial fishery sectors in 2013-2014. A similar pattern of age structure is observed throughout the history of the monitoring program.

How old is your fish?

It is possible to estimate the approximate age of a fish from its length. For spotted mackerel, females tend to grow faster than males so to obtain the best estimate of age, first identify the sex (mature male fish will have white testes, and mature female fish will have orange ovaries). Then measure the total length of the fish and use the graph below (Figure 5) to estimate its age
  • Estimate of the age (median) indicated by dot, with usual spread of ages (90%) shaded. Female data shown in pink, male data shown in blue for fish between 59 cm and 100 cm total length.
    Estimate of the age (median) indicated by dot, with usual spread of ages (90%) shaded. Female data shown in pink, male data shown in blue for fish between 59 cm and 100 cm total length.

Age-at-length graph for spotted mackerel. Measure the total length of your fish and estimate the age. For example a 70 cm male spotted mackerel would be on average 3 years of age.

Support and assistance

The monitoring team works closely with recreational and commercial fishers as well as fish wholesalers and retailers to collect biological information on spotted mackerel. Thank you to all these people and companies who have generously assisted with the monitoring of spotted mackerel by donating frames, providing length measurements or allowing Fisheries Queensland staff to measure their fish.

Want to find out more?

Phone 13 25 23, or email FisheriesMonitoring@daf.qld.gov.au

Additional information

Last updated 10 September 2015