22 Jan Mulloway Tagging Update: Recent recaptures provide evidence of interstate spawning migrations
As we’ve reached the 12 month mark for the project, I thought it would be timely to provide a brief update on the Mulloway tagging work. The 3-year project is funded through the Victorian Fisheries Authority, by Recreational Fishing License Fees and is investigating broad-scale movement patterns of Mulloway across Victoria and interstate. Understanding the connectivity and movement patterns of Mulloway between estuarine nursery habitats and marine waters is particularly essential to interpreting population structures and obtaining a more complete picture of the species life history.
Since the project got underway, we have recruited the help of 68 anglers across Victoria and South East SA, who have collectively tagged over 260 Mulloway. To date, we have recorded 29 recaptures, which represents a recapture rate of 11%. Over half of these recaptures (14) were Mulloway tagged in the Glenelg River and later recaptured also in the Glenelg River, reflecting the significance of this local fishery. One of the highest growth rates observed in the estuary has come from a 65 cm Mulloway tagged in December last year, that was recaptured 6 months later at 75 cm. Distances travelled within the Glenelg River range from 1 km up to 14 km. Elsewhere in western Victoria, two Mulloway tagged in the Hopkins River were later recaptured in the same system, with one fish travelling 10 km upstream and growing 17 cm in approximately 10 months. Finally, two Mulloway tagged in the Yarra River were also recaptured in the same vicinity between 10 and 40 days later.
Perhaps the most interesting recaptures to date, are those Mulloway that have moved between estuaries and the marine environment. So far, we have recorded three Mulloway moving from beaches off Port MacDonnell in South East SA where they were tagged, into the Glenelg River. All three fish were tagged as sub-adults (<80 cm), and therefore their migration into the Glenelg River supports the knowledge that estuaries provide an important nursery area for Mulloway. It also confirms that important connectivity exists between western Victoria and South East SA, which further supports our genetic results.
Results from the biology project (which has now come to a close), showed that Mulloway do not reach sexual maturity in Victorian waters until they are approximately 80-85 cm. Those who fish the Glenelg and other waters in western Victoria, will know that over the past 6-12 months, a large proportion of the Mulloway in the estuaries have been approaching this length. I have been eagerly expecting to see some of these larger fish commence spawning migrations out to sea, in the lead up to the spring-summer breeding season. I was therefore very excited to hear of a tagged Mulloway being recaptured a week ago off a Port MacDonnell beach, that had been tagged in the Glenelg River back in November last year. It is likely that the Mulloway had moved to the coastal beach for breeding. The captured fish showed some pretty impressive growth, going from 59 to 75 cm during its 400 days at liberty. The fish was subsequently released, so hopefully it turns up again – perhaps back in the Glenelg River!
In central Victoria, a Mulloway tagged in the Patterson River (east of Melbourne) in May 2018, was recently recaptured at the entrance to the Yarra River. The fish was at liberty for 218 days, during which time it underwent a growth of 5 cm and travelled at least 40 km. This supports anecdotal evidence of Mulloway moving between the major river systems in Port Phillip Bay at different times of year. Hopefully a few more recaptures will help shed some light on the drivers behind these migrations.
Last but not least, our latest recapture confirms that Victorian Mulloway move west, presumably for breeding. In November 2017, not long after the project kicked off, Ray Bertrum tagged an 86 cm Mulloway from the Barwon River. It was recaptured by Craig Johnson a week ago on the 30th December 2018, north of the Tea-tree Crossing along the Coorong in South East SA. In the 399 days the fish was at liberty, it grew 8 cm and covered at least 700 km of coastline! It is likely that the fish migrated to the Coorong to breed, perhaps for the first time, this spring-summer. This significant recapture supports results from our genetics work, which show that Victorian Mulloway (as far east as Western Port Bay) are part of the same sub-population as Mulloway in South East SA. It also suggests that Victorian Mulloway stocks may be somewhat dependent on recruitment from interstate waters along the Coorong.
Anglers across Victoria and South East SA are again urged to be on the lookout for tagged Mulloway. It is encouraged to return recaptured tagged fish to the water to enhance the data we can collect. If you catch a Mulloway, please report the tag and recapture details (total fish length, location of capture) to the email or phone number provided on the tag. For more information, you can read the Tagging Newsletter No. 2, or follow the project via our Facebook page.
I’m sure you will agree the results we are now getting from this recapture study are illuminating and will have obvious positive impacts on Mulloway fishing and conservation in south-eastern Australia. A huge thank you to all the anglers that continue to dedicate their time to tagging Mulloway, and also those that have called up and reported a tagged fish.