In late August, Paul Rogers from Flinders University joined scientists from NOAA/NMFS' Large Pelagics Group to conduct an annual juvenile shark survey in the Southern California Bight, which included tagging a variety of sharks with TOPP tags. Paul was kind enough to write up a wonderful series of articles about this work, each of which is accompanied by stunning photographs. Rather than putting up a single, giant blog, I am going to be putting the pieces up individually over the next few weeks -- so stay tuned and check back often for updates!
Paul's Introduction begins here: The Large Pelagics Group at National Marine Fisheries Service has just completed its annual juvenile shark survey in the Southern Californian Bight for 2009. This pelagic longline survey was done onboard the commercial fishing vessel Southern Horizon which was skippered by John Gibbs and masterfully crewed by Lee, Famanu and Wayne. In 2009, the survey was completed as three separate legs and each had a different team including, NOAA/NMFS staff, affiliated students, interns and this lucky Australian scientist.
The researchers and crew of FV Southern Horizon worked together each day to set and retrieve the longline gear and to bring the sharks aboard for tagging and other forms of biological assessment. The Large Pelagics Group aimed to: conduct the annual abundance survey in a range of locations in the Southern Californian Bight, deploy standard tags on all sharks, electronic satellite tags on medium to large mako, common thresher and blue sharks, test rare earth metals as shark deterrents, collect oceanographic data, and deploy archival tags on broadbill swordfish. There were also some other awesome surprises along the way.
Previously, the survey has been undertaken from NOAA research vessel David Starr Jordan, which had a specially built shark tagging platform off its stern, but this year we used a different sling that was lowered into the water using a small crane and davit arm. This type of sling has been used in a previous survey and to tag salmon sharks, so we knew it was a winner.
When sharks were captured on the longline, we lifted them carefully onboard and took a small amount of their time to apply standard plastic spaghetti and roto fin tags and take some measurements. Animals were fitted with these tags and injected with an internal antibiotic fluorescent marker that will allow researchers to validate age estimates for recaptured sharks using colored stains on their vertebrae. There is still some uncertainty regarding previous age estimates of mako sharks and knowing the age, growth rates and age at sexual maturity has important implications for the future management of this awesome predator.
This year, 14 makos, 10 blue sharks, a common thresher, and a smooth hammerhead were tagged using various electronic tags. Other animals that were tagged with electronic tags included two broadbill swordfish and an oceanic sunfish. Of note, was that ‘spot’ and pop-up archival (PAT) satellite tags were deployed on some larger makos up to 2.5 m fork length (FL) this year, so it will be interesting to see if these large animals migrate out of the nursery area in search of large prey. Several Opah were also recorded on the first two surveys, which was awesome.