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\u201cThere\u2019s this perception that sharks are invading because there\u2019s warmer waters, but it\u2019s not. It\u2019s purely a seasonal movement from deep ocean water into the coastal shallows for food and for pupping.\u201d<\/p>\n
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Researcher Dr Riley Elliott says young sharks find their way around by instinct. Photo \/ NZME<\/p>\n
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Shallow coastal waters are a nursery ground for fish, and almost all fish species will use them, Elliott said.<\/p>\n
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\u201cSo everything from your snapper to your kingfish to your sharks come in to drop their pups or their eggs.<\/p>\n
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\u201cAnd you\u2019ve got, predominantly, bronze whalers, but also baby great whites and other species coming inshore.<\/p>\n
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\u201cThey\u2019re coming inshore to pup, coming inshore to mate, coming inshore to drop eggs \u2013 and also coming inshore to feed on all of those things that are coming inshore to do all that.\u201d<\/p>\n
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Their migrations back and forth mean they can be found around Stewart Island and elsewhere around the country during our summer, and then back to Tonga, Fiji, New Caledonia and Great Barrier Reef as we head back into winter, he said.<\/p>\n
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\u201cWe\u2019re starting to see some of those start to come back down now, just as the season is warming up.\u201d<\/p>\n
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The young sharks find their way around by instinct, he said. Their mothers birth them and then leave them, plus they do not spend time with their siblings.<\/p>\n
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\u201cIt\u2019s kind of built into their DNA. It\u2019s beyond comprehension, really.\u201d<\/p>\n
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Sharks are thought to use the bathymetry, the topography of the underwater environment, to find their way, Elliott said. They are also believed to do so visually and electromagnetically.<\/p>\n
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\u201cThey\u2019ll use the continental ridges where you\u2019ve got tectonic plates pushing together. It\u2019s also where ocean currents run along, so they can jump on them like finding Nemo does with the turtles.\u201d<\/p>\n
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Sharks also have certain behaviours that have been observed as they hang about the shallows. Elliott said they like to sit behind the surf break because the waves churn more oxygen into the water. This, along with the movement of the water under the waves, makes it easier for sharks to \u201cbreathe\u201d without having to swim as much.<\/p>\n
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The number of sharks around New Zealand is really pronounced during the El Nino phase of the El Nino-Southern Oscillation, Elliott said.<\/p>\n
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Riley Elliot regularly swims with sharks as part of his research. Photo \/ Amber Jones<\/p>\n
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\u201cEl Nino produces a lot of productivity. The water is colder because of westerly winds, and as it blows away from the shore, it creates upwelling in the ocean, it creates a lot of food.<\/p>\n
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\u201cThat\u2019s when we get really good numbers of kingfish, snapper, other pelagic fish, and with that comes the flow of the common sharks we have, the bronze whaler, the blue shark, the mako shark, and a little bit more recently, the great white seems more prevalent along the northeastern coast.\u201d<\/p>\n
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And as those sharks come inshore in summer, and as we head for the beach, we end up seeing more of them.<\/p>\n
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\u201cIt doesn\u2019t mean there are more fish or more sharks, it\u2019s just the distribution of them,\u201d Elliott said.<\/p>\n
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With more of them around, how should we react? Should we be worried? How do we keep ourselves safe?<\/p>\n
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Elliott said it was about respecting them as wild animals and respecting them as they went about their business.<\/p>\n
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\u201cIf you catch a shark while fishing, just cut the nylon as close as you can to the hook. You don\u2019t need to bash it with a club.<\/p>\n
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\u201cYou don\u2019t need to bring it on to the boat. And don\u2019t target them in the first place. You don\u2019t want to eat shark meat because it\u2019s filled with mercury, and most of them are threatened species.<\/p>\n
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\u201cAnd the other thing is, if you don\u2019t want to have an adverse interaction with one, never swim where you are overlapping with where people are fishing or disposing of fish or processing fish.\u201d<\/p>\n
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Elliott said it was \u201ccommon sense\u201d. If you see a shark, he said, \u201chonestly, just enjoy it\u201d.<\/p>\n
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