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Time for a catch up!!

By Jayson Semmens, 27th September 2013

Wow, how time flies. With the new field season rapidly approaching (it will be Christmas before we know it) I thought I would give you an update of the great progress we are making. Well, in May this year we completed another intensive summer/autumn field season monitoring chondrichthyans in the Pitt Water and Fredrick Henry Bay shark refuge areas in Tasmania, Australia. This included implantation of acoustic tags in multiple species. We have also downloaded data from acoustic arrays on multiple occasions, providing us with two years of data for examining fine- and broad-scale movement patterns of chondrichthyans in shark refuge areas.
Once again we captured large numbers of neonate school sharks in Pitt Water, with catch per unit effort very similar to that for last year and an order of magnitude higher than those in the early 1990’s. We are now gearing up for summer/autumn 2013/14, where we will determine if we get a third year of significantly increased school shark catches compared to the 1990’s. Three years of data would better support the idea of a recovery in the previously over-fished school shark population, although we will look to continue into 2014/15 in order to gain more conclusive evidence and also leverage federal funding. We will also tag more neonate school sharks in order to build up the numbers of individuals with long-life acoustic tags, such that we can examine migration routes and survival rates of these sharks outside of the nursery grounds. These data sets are incredibly important globally, as there is relatively little empirical evidence to date of overfished shark populations recovering and also very little empirical evidence that the protection of nursery areas can aid in this recovery. This study may serve as an excellent example of what can be done when a recovery plan is put in place (e.g. the School Shark Recovery Plan) and nursery areas are protected.
Fine-scale movement data indicates that there is a high degree of spatial overlap between species in Pitt Water and there is selection for deeper habitats suggesting that there may be some form of resource partitioning occurring to enable so many species to co-exist in a relatively small area. There also appears to be certain environmental conditions which influence fidelity to Pitt Water and the habitats in which individuals reside. Broad scale movement data shows that once individuals have left Pitt Water they move freely between different habitats in Frederick Henry Bay; however, most species depart the protection of the shark refuges during winter.
The use of ocean gliders fitted with a mobile receiver transiting Storm Bay has proven effective, with several of the chondrichthyans tagged in Pitt Water being detected throughout the year. The data from the acoustic receivers deployed off Tasmania’s East Coast has also been downloaded this year. Importantly, several of the sharks that we had tagged only a few months prior in Pitt Water were detected, including two neonate school sharks less than 6 months of age which were tagged in Pitt Water during March 2012 and had begun migrating up the east coast at the onset of winter.
It’s all very exciting and to add to that we have had some excellent recent papers and presentations that have arisen due to SOSF’s on-going support:

Journal Articles:
Stehfest, K.M., T.A. Patterson, A. Barnett & J.M. Semmens (In Press). Intraspecific differences in movement, dive behavior and vertical habitat preferences of a key marine apex predator. Mar. Ecol. Prog. Ser.
Barnett, A. & J.M. Semmens (2012). Sequential movement into coastal habitats and high spatial overlap of predator and prey suggest high predation pressure in protected areas. Oikos 121: 882–890.

Semmens et al (2013). Examining Chondrichthyan activity patterns within
an estuary. 2nd International Conference on Fish Telemetry, Grahamstown, South Africa, July 2013.

Semmens (2013). Where, when, how and why: Using acoustic telemetry to understand marine animal movement, behaviour and physiology. Invited Seminar Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth, UK.

Well, that’s it for now. Fingers crossed for a great 2013/14 summer field season and I’ll talk to you all soon. Cheers Jayson

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