Spanish Mackerel: East Coast update

Spanish mackerel (Scomberomorus commerson) is an important fish for both commercial and recreational fishers throughout Queensland.

Biological monitoring of Spanish mackerel in Queensland commenced in 1999. The program focuses on collecting information on the length, sex and age of fish caught by commercial and recreational fishers. Routine biological monitoring is conducted each year so that long-term trends in length, age and rate of total mortality can be monitored.

This page provides results for Spanish mackerel monitoring on the east coast of Queensland, summarised by financial year to match the management cycle of the east coast commercial fishery.

Fish Length

There are a similar range of sizes of Spanish mackerel caught by commercial and recreational fishers (Figure). In 2013-14, sampled fish ranged from 75 cm (legal size) to 164 cm. The largest fish sampled in the program was 191 cm.

  • Length frequency for the 2013-14 commercial and recreational catch.
    Percentage of Spanish mackerel in each length class for the recreational and commercial fisheries on the east coast during 2013-14.

Fish Age

A Spanish mackerel's age can be estimated  by examining its otoliths (ear bones) under a microscope. Seasonal variations in fish growth cause banding on the otoliths from which the age of the fish can be estimated.

  • Opaque bands on the ear bone of a Spanish mackerel.
    A Spanish mackerel otolith under the microscope with three annual bands marked by red dots.

The majority of Spanish mackerel caught by commercial and recreational fishers were between two and four years of age (see graph). 

However, an unusually large percentage of the 2013–14 catch consisted of one year-old fish, particularly in the recreational catch where they comprised 34% of the sampled catch. This is possibly an early indication that a strong cohort is recruiting into the fishery - a cohort that should be fully available to the fishery at 2 years of age. Strong cohorts are observed to come through this fishery periodically and are likely to be related to climatic conditions1. The oldest female sampled by the program since 1999 was 22 years and the oldest male was 26 years. However, it is very rare for Spanish mackerel to live longer than 18 years of age.

Welch, D, Saunders, T, Robins, J, Harry, A, Johnson, J, Maynard, J, Saunders, R, Pecl, G, Sawynok, B & Tobin, A 2014, Implications of climate change on fisheries resources of northern Australia, part 1, Vulnerability assessment and adaptation options, Fisheries Research and Development Corporation project 2010/565, James Cook University, Townsville.

  • Age frequency of the East Coast fisheries of Spanish mackerel. 2008-09 to 2011-12, peaks are usually in the 1 or 2 age group
    Percentage of Spanish mackerel in each age group for the commercial and recreational fisheries during four sampling years.

Determining sex

The sex of Spanish mackerel can be determined by examining their gonads (reproductive organs). Mature male fish will have white testes and mature female fish will generally have orange coloured ovaries (Figure). This distinction is less obvious in small fish.

  • Male gonads of Spanish mackerel appear pale and are solid inside, gonads from females are pink to orange, internally they are tubular and the presence of eggs makes the contents is looks granular.
    What sex is your fish? You can find out the sex of your fish by looking at its gonads, which are located towards the top of the gut cavity (near the backbone). Compare them with these photos of male and female Spanish mackerel. Note: The fish photographed have enlarged gonads as they were close to spawning when caught.

Fish Growth

Spanish mackerel have a rapid growth rate with females generally growing faster than males. Females will therefore tend to be younger than males of the same length.

  • Age-at-length graph for Spanish mackerel  on the East Coast of Queensland. Shaded sections show the 5th to the 95th percentile of male and female fish from each length category.  Points mark the median age for each sex. Sample sizes are 5424 females and 4956 males.
    How old is your fish? Estimate the age of east coast Spanish mackerel from total length using this graph. For example, a 110 cm male is typically four years old with a 90% likelihood of being between two and seven years. A female of the same size is typically three years old with a 90% likelihood of being between two and five. Note: due to small sample sizes males 140-159 cm and females 165-184 cm have been grouped.

How is the data used?

Fisheries Queensland has adopted several ways to monitor and assess the sustainability and impact of fisheries activities on fish stocks. Detailed (quantitative) mathematical models are used in periodic stock assessments of Spanish mackerel stocks using all available data sources. The biological data provided by the Fishery Monitoring program are crucial to many of these models. The most recent stock assessment indicates that Spanish mackerel is being sustainably fished on the east coast2.

A national stock status assessment framework is used to regularly determine the status of individual stocks of key fish species3. Fisheries information, including biological, catch and effort information and results from stock assessments, is collated and assessed against clearly defined criteria to determine the exploitation status of the stock. In 2014, the stock status of Spanish mackerel on Queensland's east coast was classified as 'Sustainable'4.

Support and assistance

Thank you to everyone who donates fish frames or assists with the collection of data for the Spanish mackerel monitoring program. This ongoing assistance helps to ensure that the collection of length, age and sex information is representative of the commercial and recreational fisheries during each fishing season.

Want to find out more?

Further information

Last updated 11 November 2015