Shark tagging in the galapagos islands 2012Presentation Transcript
The Eastern Tropical Pacific Ocean Seascape Cocos Island (Costa Rica) Malpelo Island (Colombia) Galapagos Islands (Ecuador) Also Coiba & Las Perlas (Panama) Gorgona (Colombia) Isla de la Plata, Machalilla (Ecuador) 2.1 million km2
Why sharks? •Sharks are a key group in the marine ecosystem •Apex predators, drive natural selection processes •Distinct evolutionary group from bony fishes •Slow growth, late onset of sexual maturity, low fecundity – intrinsic characteristics which make sharks vulnerable. •Recent studies have shown declines in shark populations in almost every single population studied Internal reproduction and live young (mostly).
Focus: Research Species Sphyrna lewini Carcharhinus galapagensis Rhincodon typus
Migramar: a regional network www.migramar.org
Focus: Research Questions Nations encouraged to develop Shark Plans of Action to manage and conserve their shark populations • How to delimit stocks? • No baseline from which to follow trends Do hammerheads display residency at particular sites? Do hammerheads move between sites? Do they display synchronous behavior? Is their connectivity between MPAs on a regional scale? What are the mechanisms behind site preference and migrations?
Shark Tagging: ultrasonic coded tags VEMCO V16 coded tags. Emit train of pulses at 69 KHz. Tags are attached to darts and placed on pole spears. Free divers descend onto sharks and VEMCO VR2 listening stations insert tag behind the dorsal fin, at a distance (and temp logger), deployed not greater than 50 cm from the shark. on subsurface moorings
Shark tagging: Manual tracking
Shark tagging: Satellite tags
Shark tagging: Visual Census
Ultrasonic listening array in Galapagos Darwin Wolf Roca Redonda Marshall Point Cousins Gordon Leon Dormido Nameless Academy Bay Seamount 90
Overall animals tagged in Darwin & Wolf Species Ultrasonic SPOT/SPLASH PAT Tracking Hammerhead 149 14 - 7 Galapagos 23 4 12 1 Whale Shark 5 24 1 0 Silky 7 5 Blacktips 7 6
What have we learned so far? •Hotspots and site fidelity •Seasonal changes in abundance •Nocturnal foraging behavior •Movements between islands •Long distance migrations
Hotspots and site fidelity Tagging data showed the same preference for east coastCensus data showed greatest abundance in January, andalways on eastern side of Wolf
Hotspots and site fidelity Steel pompano Crevelle and green jacks Galapagos shark Scalloped hammerhead shark Bottlenose dolphin Snappers Yellowfin tuna The largest abundances of species were along the eastern coast of the island.
Manual Tracking The Galapagos shark patrols the entire island each day, never more than 200 m offshore, but it prefers the area between Shark Point and Rockfall The hammerhead hangs around Shark Point during the day, but heads out to sea at night, making deep dives (foraging?)… similar pathways each night… how does it navigate?
Hotspots and site fidelity N The Arch “hotspot” Proposed predominantFemale hammerhead left current directionDarwin Island 4 and Spent next threearrived at Wolf 7 Dec weeks between2008. Rockfall, Shark Point, and East Bay Detected at Elephant Rock (ER) at 1312 hrs and stayed within range of monitor for only 24 min
Regional Connectivity •Three sharks from Galapagos migrated to Cocos (one also returned) •Three sharks from Malpelo migrated to Cocos (one continued to Galapagos) •No apparent connection Galapagos north vs. Galapagos centre •Connectivity with coastal areas?
The next step – ontogenetic migration? Cocos ? Ecuador ? Mangrove bays?