Cuttlefish population survey

The annual spawning aggregation of Giant Australian Cuttlefish at Point Lowly is an iconic event for South Australia. Every year we assess the size of this population to help inform fishery management.

Population surveys are undertaken by the South Australian Research and Development Institute (SARDI) to estimate Giant Australian Cuttlefish abundance and biomass of the Point Lowly breeding group. This is done using the standard survey methodology described in Steer et al. (2013) (PDF 5.8 MB)

Cuttlefish population estimates for 2021 spawning season

Giant Australian Cuttlefish abundance remained variable, but relatively high, from 2015-2021, with annual estimates consistently exceeding 100,000 cuttlefish and the 2020 estimate of 247,146 Cuttlefish being the highest on record. Between 2020 and 2021, abundance decreased 56% to 107,847. The recent estimates of abundance indicate that the population has increased substantially from historic low observed in 2013. Giant Australian Cuttlefish abundance in 2021 remained relatively high and similar to the mean from 1998-2019 of 110,271 (Figure 1).

The biomass of the spawning aggregation remained above 70 t from 2015 to 2020, with peaks of 165.2 t in 2016 and 140.5 t in 2020 (Figure 1). The estimated biomass in 2021 was 63.1 t. Similar to 2017-2020, the average size (mantle length) of female (148 mm) and male (177 mm) cuttlefish in 2021 remained below the long-term averages of 172 mm and 196 mm, respectively (Figure 2). The sex ratio in 2021 remained dominated by males, with approximately 7 males for every 1 female (~14% females; Figure 2).

Discussion

The results show that greater emphasis is placed upon cuttlefish abundance as a population estimate rather than biomass, which is dependent on size records. Biomass estimates are considered less robust than abundance estimates because cuttlefish sizes are estimated in-situ by divers with varying levels of experience.

Giant Australian Cuttlefish population strength is linked to environmental processes that are highly variable and impact both development and growth.

This is reflected in the last 14 survey years where both abundance and biomass have fluctuated considerably over a short time.

Figure 1 graph results

Figure 1: Annual peak estimates (June survey) of total abundance and biomass (± SD) of Giant Australian Cuttlefish aggregating around Point Lowly during peak spawning from 1998 to 2020. * Population was heavily fished.  Historic data obtained from Hall and Fowler (2003).

Figure 2 graph results

Figure 2: The population sex ratio presented as the percentage of females (top). The average size of Giant Australian Cuttlefish (± SE) for males (middle) and females (bottom) from 1998 to 2020.  The red lines represent the overall average.

Page last reviewed: 20 Dec 2021

 


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