View Single Post
  #7  
Old 01-25-2013, 10:15 AM
ricki's Avatar
ricki ricki is offline
Administrator
Site Admin
 
Join Date: Jul 2004
Location: Florida
Posts: 8,700
Default

I communicated with graduate student Shari Tellman working under Professor Stephen Kajiura on the areal shark video survey. She told me that they have been performing a study of the blacktip shark population off Palm Beach County between February 2011 and March 2013. They hope to acquire baseline abundance data for comparison to findings in future studies to monitor environmental effects such as climate change on the distribution and relative numbers of this important apex predator.

She indicated that the blacktips, very similar to appearance to spinner sharks but still a different species, migrate south into Broward and Miami-Dade Counties in the fall. The sharks remain offshore in deeper water in the fall and early winter. This may account for the lower quantities of sightings spread out in deeper, sometimes turbid water. Then in the spring they migrate northward to Georgia and the Carolinas to breed. In their survey they have noticed sharks to be prevalent off Palm Beach county in late January into early March. So, the appearance of masses of sharks south of Lake Worth Inlet at this time of year isn't unusual.



A figure provided by Ms. Tellman showing the narrow shelf off Palm Beach County compared to points south.


Ms. Tellman indicated that the sharks follow and prey upon large schools of baitfish such as mullet which in large measure explains their distribution at various times of the year. She indicated that the narrow continental shelf off Palm Beach County serves to concentrate larger masses of sharks closer to shore. Adding in the better water visibility and influence of the Gulfstream under certain conditions, the sharks are even more noticeable than they might be spread out in more turbid waters in the two southern counties.

I had wondered about the appearance, disappearance and eventual reappearance of the shark aggregations off beaches in Palm Beach County. Specifically I was curious about significant factors influencing shark local distribution during the migration. She responded the nearshore distribution of the blacktips is patchy and speculated it may be attributable to food availability and sea state. In heavier seas the sharks may move to deeper water to where they may be less noticeable. Where there is an abundance of baitfish the sharks may be quite concentrated. I asked if they had impressions about the relative abundance of larger sharks such as bulls and tigers escorting and feeding upon the blacktip migration. She stated that their video imaging doesn't allow for identification of various shark species but that larger individuals were noted which might be bull and tiger sharks. I want to thank Shari Tellman for taking the time to provide detailed responses to my questions and wish them all success with their study and eventual publication.


What follows are some personal observations. So, the migration is on, have a care out there. Fatal shark attacks on kiters worldwide are infrequent. Certainly they are far less common that squall/wind related fatal kiting accidents. Then again, what percentage of the global kiter population ride in shark migrations for extended periods of time such as may be the case off here and now. By comparison, shark attacks on surfers are far more common particularly in Florida. I understand from other sources that our "taste" isn't to most shark's liking, not "fishy" enough. Blacktips may strike and then leave particularly in conditions of poorer visibility. Usually the injuries have been fairly minor with the smaller shark size and fleeting presence. Apparently we aren't on the favorites list with bulls or tigers either. The problem is a larger shark/bite radius the more damage that can be done. The location of the bite is also particularly relevant. Sharks may strike your thigh area to apparently disable locomotion, putting your femoral artery at risk as has happened in a number of severe attacks in various parts of the world. Multiple bites further compound the injury if such occurs.

Remember the sharks chasing the kiter after transitions. Also, if you bust a landing near a shark or slide off your strapless board it may strike out of impulse then move on or it may just ignore you entirely. It is fair to say, the odds of a negative encounter increase kiting during the migration, in areas with visible sharks, in areas with jumping bait and feeding birds and in my personal experience, near sunset. How much do they increase, who knows? For my part if there are visible shark signs of the migration, I will probably not go kiting at that location, at that time. It doesn't remove risk but it may serve to reduce it. It is worth thinking over.




Blacktip sharks
http://en.wikipedia.org/wiki/File:C._limbatus.JPG


.
__________________
FKA, Inc.

transcribed by:
Rick Iossi

Last edited by ricki; 01-25-2013 at 01:14 PM.
Reply With Quote