A USC study into one of the ocean’s top predators – the great hammerhead shark – is seeking new insights into the impact of harvest and export levels on the declining species.
USC Lecturer in Animal Ecology Dr Bonnie Holmes has received a research grant from the Australian Academy of Science to gather detailed information on the ecology and biology of great hammerhead sharks (Sphyrna mokarran) in South East Queensland.
Dr Holmes is one of six Australian researchers to be awarded a 2021 Thomas Davies Research Grant, valued at $20,000, announced recently by the Academy.
Commercially fished worldwide for their valuable fins, the shark was last year globally listed as critically endangered. In Australia, it is estimated that both catch rates and overall size of this keystone predator has declined significantly over the past 50 years.
“More data on its biology, ecology and population structure is critically needed to set appropriate, sustainable harvest levels that could ensure the survival of this species and the health of our coastal ecosystems,” Dr Holmes said.
This study will be the first to explicitly assess great hammerhead movements across multiple ecosystems of South East Queensland, including its estuaries and oceanic waters, with particular focus on how the sharks utilise both Hervey Bay and Moreton Bay.
“From recent research, we now know that great hammerheads are important ecosystem regulators of other sharks and rays, putting them at the top of the marine food chain. Yet there is a critical lack of life history and habitat use data,” Dr Holmes said.
“Given that the species plays a vital influencing role in linking coastal food webs in east coast Australian waters, the ecological impacts caused by declining populations of this top predator can be far-reaching.”
Found in tropical and sub-topical Queensland waters, extending into northern New South Wales during the summer months, the great hammerhead is the largest of all hammerhead species, reaching over 4.5m in length and living for up to 40 years.
Overfishing is the species’ greatest threat.
“The shark’s oddly shaped head enhances its ability to hunt prey but also makes all sizes of the species, including juveniles, susceptible to becoming entangled in commercial gillnets,” Dr Holmes said.
“It is also vulnerable to being accidentally caught in beach protection programs that target large sharks in both Queensland and New South Wales.”
As part of the two year study, Dr Holmes will deploy satellite tags on great hammerhead sharks to track their distribution and movement patterns. Each time a shark’s fin breaks the water’s surface, the tag will transmit real-time location data to overhead satellites.
Tissue samples will also be collected to genetically assess their population structure across the broader Indo-West Pacific region.
“By correlating movements with fishery catch and location data, we can determine their susceptibility to fishing activities, and whether respective marine park management zones in our region afford adequate protection,” Dr Holmes said.
For details go to www.usc.edu.au/study
Uchunguzi wa USC juu ya moja ya wawindaji wakuu wa bahari - papa mkubwa wa kichwa cha nyundo - unatafuta ufahamu mpya juu ya athari za viwango vya mavuno na usafirishaji kwenye spishi zinazopungua. Mwalimu wa USC katika Ikolojia ya Wanyama, Dk Bonnie Holmes, amepokea ruzuku ya utafiti kutoka Chuo cha Sayansi cha Australia kukusanya habari za kina juu ya ikolojia na biolojia ya papa mkubwa wa kichwa cha nyundo (Sphynx mollusk) Kusini Mashariki mwa Queensland. Holmes ni mmoja wa watafiti sita wa Australia waliopewa ruzuku ya utafiti ya Thomas Davies ya 2021 yenye thamani ya $ 20,000, ilitangazwa hivi karibuni na Chuo. Mbwa huyo wa mwituni, ambaye samaki wake wa baharini wanawavutia watu wengi, amewekwa kwenye orodha ya wanyama walio hatarini sana kupotea. Katika Australia, inakadiriwa kwamba viwango vya uvuvi na ukubwa wa jumla wa mnyama huyu wa msingi umepungua sana katika miaka 50 iliyopita. "Hata hivyo, data zaidi juu ya biolojia, ikolojia na muundo wa idadi ya watu inahitajika sana kuweka viwango vya mavuno sahihi na endelevu ambavyo vinaweza kuhakikisha kuishi kwa spishi hii na afya ya mifumo yetu ya ikolojia ya pwani,"" alisema Holmes." Utafiti huu utakuwa wa kwanza kuchunguza harakati za nyundo kubwa katika mifumo mingi ya ikolojia ya Kusini Mashariki mwa Queensland, ikiwa ni pamoja na estuaries na maji ya bahari, na kuzingatia jinsi papa hutumia Hervey Bay na Moreton Bay. """Kwa utafiti wa hivi karibuni, sasa tunajua kwamba nyundo kubwa ni wasimamizi muhimu wa mazingira ya papa wengine na rays, na kuwaweka juu ya mlolongo wa chakula cha baharini." Hata hivyo kuna ukosefu mkubwa wa historia ya maisha na data ya matumizi ya makazi, <unk> alisema Dk Holmes. "Kwa kuwa aina hii ina jukumu muhimu katika kuunganisha mitandao ya chakula ya pwani katika maji ya pwani ya mashariki ya Australia, athari za ikolojia zinazosababishwa na kupungua kwa idadi ya mnyama huyu wa juu inaweza kuwa ya mbali. ""Kupatikana katika maji ya kitropiki na ya chini ya kitropiki ya Queensland, inayoenea hadi kaskazini mwa New South Wales wakati wa miezi ya majira ya joto, nyundo kubwa ni kubwa zaidi ya aina zote za nyundo." Uvuvi wa kupita kiasi ndio tisho kubwa zaidi kwa spishi hiyo. "Kichwa cha papa chenye umbo la ajabu huongeza uwezo wake wa kuwinda mawindo lakini pia hufanya ukubwa wote wa spishi, ikiwa ni pamoja na vijana, kuwa na uwezekano wa kuingiliana katika nyavu za kibiashara", alisema Dk Holmes. "Hiyo pia ni hatari ya kukamatwa kwa bahati mbaya katika mipango ya ulinzi wa pwani ambayo inalenga papa wakubwa katika Queensland na New South Wales. ""Kama sehemu ya utafiti wa miaka miwili, Dk Holmes ataweka alama za satelaiti kwenye papa wakubwa wa kichwa cha nyundo ili kufuatilia usambazaji wao na mifumo ya harakati." Kila mara fin ya papa inapovunja uso wa maji, lebo hiyo itatuma data ya mahali inapoelekea kwa satelaiti zilizo juu. Sampuli za tishu pia zitatolewa ili kutathmini kwa maumbile muundo wa idadi yao katika eneo pana la Indo-Magharibi ya Pasifiki. "Kwa kuhusisha harakati na data ya uvuvi na eneo, tunaweza kuamua uwezekano wao wa shughuli za uvuvi, na kama maeneo husika ya usimamizi wa mbuga za baharini katika mkoa wetu hutoa ulinzi wa kutosha, "Dakt. Holmes alisema. Kwa maelezo zaidi, angalia www.school.edu.au.