Marine investigation:
the seasonal influx of tropical fish
at Seal Rocks, NSW, Australia
(currently self funded)
Statis Island
Statis Island snorkeling track
(1300 metres)
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Why examine these seasonal influxes?:
A recreational activity of regularly snorkeling out to Statis Island at Seal Rocks opened an opportunity to become familiar with marine fish of the area, and examine changes in these assemblages over time (i.e. study their dynamics). But what changes and why?
The regular seasonal (~January to May) influx of tropical fishes from the north causes the most notable changes in the fish assemblages and these are the focus of the investigation. Key understandings, predictions and weaknesses in knowledge in relation to these seasonal influxes are given here. Intentions of the investigation are given here in relation to the two key weakness.
UNDERSTANDING 1
There is strong evidence for the role of the East Australian Current in transporting tropical reef fishes southwards at a coastal scale (Booth et al. 2007)
WEAKNESS 1
However, there is little evidence that individual recruitment events are related to local increases in water temperature associated with the arrival of the EAC on the southern coasts (Booth et al. 2007).
INTENTION 1;
In respect to Weakness 1, it is the intention that regular repeated surveying (along the same snorkeling track out to Statis Island) during each influx season will provide evidence to link recruitment events with the arrival of the East Australian Current (EAC).
PREDICTION 1:
With the progression of climate change, it is predicted that the East Australian Current (EAC) will transport greater volumes of water from the Coral Sea southward to the Tasman Sea, resulting in higher ocean temperatures about south-eastern Australia (Hobday and Lough 2011)
PREDICTION 2
The strengthening and increasing southward extent of the EAC is already occurring with climate change, increasing the
potential for tropical species to move south
Click to see an image of the EAC in October 2016
WEAKNESS 2
There is negligible direct evidence for
climate-induced range shifts in Australian fish species (Booth et al. 2011). In 2011 a study of rocky shore fauna along south-eastern Australia (Poloczanska et al. 2011) claimed that there was little change over 60 years despite it being a period of rapid warming with increases in temperature of ~1.5oC
INTENTION 2
In respect to Weakness2, it is the intention that maintaining the repeated surveys over the long-term (i.e. multiple influx seasons) will incrementally provide evidence of the influence of climate change - mediated through the strengthening of the EAC - on the range of tropical marine fish.
The following up-to-date information is available:
Names and images of fish species which typically have a tropical distribution
Tropical species recorded so far
Changes in the number of tropical species
This across-assemblage variable is the total number of tropical species recorded across time. Data are provided for each influx season commencing in 2014-15
Changes in total abundance across all tropical species
This across-assemblage variable is the total abundance across all tropical species (excluding highly variable Cow-nosed rays and Striped catfish). Data are provided for each influx season commencing in 2014-15
Changes in the abundance of Indo-Pacific sergeants
Changes in the abundance of the Indo-Pacific sergeant is given. This species is frequently examined in marine fish range-extension studies. Data are provided for each influx season commencing with 2014-15; Photo courtesy of daveharasti.com
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Changes in the abundance of Australian cow-nosed rays
Changes in the abundance of the Australian cow-nosed rays are provided for each influx season commencing with 2013-14. Encounters with large flocks of these rays are unforgettable experiences, giving a similar elation when whales are closely encountered. Regionally this species has been recorded in large numbers to the south in Port Stephens (David Harasti pers. com.) and to the north off Forster (Suzanne Fiebig pers. comm.).
Other up-to-date marine data:
Changes in the abundance of Green turtles
Data are presented on the number of Green turtles appearing about Seal Rocks, NSW, a result of being transported south by the East Australian Current. The inclusion of this information here is for convenience and primarily relates to providing an information platform for a high conservation value species. Data are provided for each influx season commencing with 2013-14,
Changes in the abundance of Grey nurse sharks
Grey nurse sharks are found in both temperate and tropical waters, although in Australia primarily in the former . Their inclusion here is for convenience and primarily relates to providing an information platform for a high conservation value species. Data are provided for each season commencing with 2014-15,
Changes in the abundance of Humpback whales
Data on the number of Humpback whales appearing about Seal Rocks, NSW, during their southward migration (September to November) are presented. The inclusion of this information here is for convenience and primarily relates to providing an information platform for a high conservation value species. Data through six years are provided (2011-2016) as well as detailed across-season data for 2016 and 2017.
Changes in the abundance of
Fur Seals
Data on the number of Fur Seals appearing on Big Seal and Little Seal Islands out from the SugarLoaf Point Lighthouse are presented. This work started in the first half of 2024 and is the first systematic monitoring of fur seals in the area since the populations crashed in the 1970s
