The blue cod (Parapercis Colias) is a dominant character in the Tonga Island Marine Reserve. They are a generalist predator eating small fish, and invertebrates. Divers and snorkelers should look behind themselves, as that is where you will find the large males, trailing your every move looking for disturbed morsels kicked up by your fins. Blue Cod are not common outside the marine reserve, they prefer rocky habitat, but the bigger ones roam over the sand predating on all manner of prey. Some say the best bait for blue cod is blue cod! All blue cod start life as females, which are small and brownish. The male blue cod are larger and green or blue, they are the most aggressive and harass the females, keeping up the stress levels which in fact keeps them female. If I were to catch a blue cod, it would most likely be male, as he is generally the first to the bait. With him out of the way, the females will start to relax, and in one week the largest female will have turned into the male of the school. This hermaphrotism is actually quite common in fish. Some studies have shown that the blue cod have a range of only around several kilometres, this makes it very easy to fish an area out. It also makes Marine Reserves very effective at protecting stocks. As a result there are 40 times more blue cod per sq. km inside the Tonga Island Marine Reserve than outside. This is a graphic example of how recreational fishing can impact the marine ecosystems, as there is no commercial targetting of blue cod on the park’s coastline. This video was taken on snorkel in only a few metres of water. For more information about the Tonga Island Marine Reserve please read the latest ecological integrity report by Davidson and Freeman.
Marine reserves are important places for scientific research, as without this one, we would forget that blue cod should be common here, they are also incredible to experience and viewing these wet libraries is key to connecting people with healthy marine environments, which has profoundly impacted so many. Education is key, and here at Abel Tasman EcoTours, we support the work of Experiencing Marine Reserves, who educate the community on the importance of healthy marine ecosystems by getting people in the water.
Video and blog by Stew Robertson, Abel Tasman EcoTours