PIT 2006 Summary
PIT 2006 is now in the books. Over the course of three weeks, the team fished two areas of the lagoon and completed a census of the juvenile lemon sharks in Bimini Lagoon. Our efforts landed 235 lemon sharks in total and a wealth of new data was collected. Now we can begin to look at that data and see what it means. As we begin to clean, repair, and renew the equipment, the lab, and ourselves we can sit back and also reflect on what PIT means to each of us and how our experiences have affected us. A table and two graphs displaying some of the data collected this year can be found below, followed by a short discussion.
PIT means many things to many people, and to illustrate this point there is a sampling of personal contemplations by a small selection of the PIT team members. Finally, covering this project has been an amazing experience for me and one that I will never forget. I give myself one last indulgence, and have a personal endnote to express my review of this year's PIT project and give some kudos to everyone involved. Thank you for visiting this website and coming along on the journey with us. I hope we were able to share our experiences, and I hope you received as much enjoyment reading about our exploits as we did in making them.
PIT Data Table
Figure 1. Number of newborn, recaptured, and total sharks caught in the North Sound (A) and Sharkland (B) during each of the last five PIT sampling periods. Handling mortality was low in each year (mortality: 2002, 3.9%; 2003, 3.0%; 2004, 1.2%; 2005, 3.3%; 2006, 1.7%). Interestingly, 44% of newborn sharks originally tagged in the North Sound in 2005 that were later recaptured in 2006 had emigrated to Sharkland, whereas movement in the opposite direction never occurred (i.e. Sharkland to the North Sound). This could be due to newborns emigrating to more suitable sites, as the North Sound has suffered extensive anthropogenic impacts in recent years (i.e. construction of a resort/casino complex), or simply be a density-dependent effect (there were twice as many North Sound newborns in 2005 when compared to previous years).
SHORT DISCUSSION :
The data table shows a summary of shark catches in both parts of the lagoon, separated by sex. More sharks were netted in Sharkland than in the North Sound, which is traditionally the pattern (barring 2005 - discussed below). By collecting these data, we can tally the number of newborn sharks recruited into the lagoon and the number of recaptured sharks who are still living in the lagoon. The recaptures are particularly important, as we can make several calculations based on the census of recaptured individuals. We can compute mortality of last years newborns by seeing which sharks are captured the next year over total newborns from the previous year. Capturing and measuring the sharks from year to year allows us to calculate growth rates. Finally, recapturing a shark can give us some hint of movement patterns, as some sharks who are originally caught in the North Sound tend to migrate down the lagoon as they get larger. A glance at the table shows that more male sharks were caught than female sharks in every category in both parts of the lagoon. This is particularly interesting and somewhat puzzling. Usually, there is close to a one to one ratio for male to female offspring. The sex ratio for the newborns caught this year is roughly 1.5 males for every female - a very high ratio. Sex should not have a great effect on survivorship, so a similar amount of females and males should survive to the next year. The sex ratio for recaptures is also high at 1.3 males to every female. This may mean that last year's newborns were male dominated as well. These findings may need to be further looked at in greater detail.
The graphs show a breakdown of shark catches over the past five years as well as several general trends. For the North Sound, 2002-2004 are very consistent across all three categories of sharks. Last year, 2005, had a huge spike in newborns and total sharks. We suspect that at least one additional mother lemon shark pupped in this area of the lagoon. This may have been a new mother or one that dropped a litter two years in a row instead of in alternating years like most do. This year the total for the North Sound was a bit higher than the 2002-2004 levels. However, the number of newborns was comparable to 2002-2004, so the extra sharks are mainly due to the inflated number of newborns from last year that survived. It looks like 2005 was an anomaly and the shark populations are starting to stabilize and go back to their historical levels.
However, Sharkland shows a very different trend. The catches for Sharkland have shown a slow and steady increase over the past five years. This part of the lagoon also displays a consistent pattern of similar numbers of both newborn and recaptured sharks. 2006 shows this tendency as well, though with slightly elevated numbers than past years. This could mean the population is increasing. The next step is to look at where the sharks are coming from. Recruitment of newborns was strong this year, and there may be some immigration of North Sound sharks into the population. With the continued construction in the western edge of the lagoon, and its intrusion into the North Sound, more sharks may find Sharkland as more ideal habitat. We will have to continue to monitor the Sharkalnd population and see where the individuals are coming from to make more concrete assertions.
A powerful tool to answer these questions will be genetic analysis. We may be able to make some connection between the lemon sharks' reproductive strategies and the skewed sex ratios in the juveniles. Lemon sharks use a system of multiple paternity, where a female will mate with several males and therefore have a litter where different pups have different fathers. This is a strategy to optimize genetic diversity. We will be able to tell if additional lemon mothers pupped in the North Sound in 2005, causing the huge spike in the population numbers there. The genetic analysis will be indispensable to interpreting the data our hard work has earned us, and in the end, the DNA will help us tell the full story.
The PIT 2006 web journal has been a window to my thoughts throughout the course of the project. However, there were 21 individuals at the lab for the duration of the work, and therefore 20 other sets of experiences and perceptions. I would like to give you a quick sample of a few other perspectives from other members of the PIT team so that they can convey their viewpoints in their own words...
This year PIT was mainly run by Joey DiBattista, one of the three current PIs. Here is where the plot gets thicker though, as it wasn't only Joey's first PIT as the head honcho, but his first PIT in general.
"Coming into PIT 2006 I wasn't sure what to expect. I'd certainly heard stories from days gone by: unsettling storms, lightning strikes, armies of bugs, and many beautiful sharks. Now that all is said and done I can safely say that I've enjoyed the "PIT" experience. In fact, things ran like a well oiled machine, we had a wonderful group of volunteers who made the 12 days of fishing fly by. Everyone did their part and contributed to a fantastic final result of 235 total sharks captured, with minimal mortality. It was more of learning experience for me than anything else; this was my first PIT and so I knew little of the details and/or logistics of running such an operation. However, thankfully, we had a number of veteran staff members available for consultation prior to making important decisions in the field, which I believe was crucial to our successful campaign. I look forward to participating in future and hopefully working with many of the same volunteers in years to come."
Pretty soon I think the lab may have to institute a new rule that PIT cannot occur without Jo Imhoff. She has participated in PIT for four straight years and brings a wealth of experience to the table. This year was her first as a boat captain, one of three individuals who oversee a gillnet for all 12 nights of fishing. Jo tells us how this PIT experience compares to past years.
"Having participated in PIT four times from 2003 to 2006, I know that every PIT is different from the last. This year was different for me because it was my first time as a net boat captain. I was a little bit nervous to be a captain, but mostly excited to have the responsibility of running my own net. I have had both positive and negative experiences during PIT over the years and have learned a lot from the captains of crews that I was on, and once the nervousness wore off I felt pretty well prepared. My favorite part of being a captain, apart from getting to be out in the field every night, was explaining to newer volunteers and talking them through taking sharks out of the net until they felt more confident. I actually handled fewer sharks this year than I did in previous years. Overall, I would say that this has been my best PIT experience because of the great crew we had, especially a few volunteers that have been around for a while and made my first time as a net captain pretty low-stress and fun."
PIT is a hectic time and turns the lab's normal schedule on its ear. Kat Gledhill has been at the lab since January and is well versed in the day to day operations at the lab. This is her first PIT, and she comments on how PIT differs from "normal" life at the lab
"It's hard to believe that PIT 2006 has been and gone. Since my arrival in January, I heard so much about PIT. The thought of being part of the excitement of catching, tagging and releasing around 200 lemon sharks and being part of the longest running annual juvenile shark study known, inspired me to extend my original stay for 2 months until the end of June. It had obviously left an impression on many other past volunteers too, as the great majority of the people arriving were either PIT returnees or people who had volunteered at BBFS in the past.
The census definitely lived up to its expectations and beyond. The whole experience was amazing and very different to the usual routine at the lab. Never before in my time here had we dedicated our entire schedule and had every person in the entire lab working on one single project. Usually each day is different and there are several ongoing projects that the lab is divided up to work on. June was focused on PIT and only PIT. I probably gained as much experience gillnetting, handling and taking sharks out of nets in the 3 weeks of PIT, as I did during five months as a volunteer at BBFS. It was absolutely incredible to see and contribute to the science of so many beautiful little sharks.
All the staff and volunteers worked so hard not only during PIT but the months preceding. The work invested by all the volunteers leading up to PIT on building the pens, organizing and taking inventories on all the equipment definitely made the census run more smoothly and is greatly appreciated. We couldn't have done it without you guys too!"
This year we had the good fortune of having a very experienced crew. We usually get a few new volunteers who can be somewhat literally "thrown to the sharks". Wilson Hambrick is our sole rookie this year. He comments on how it feels to face the trial by fire that is jumping into the fieldwork.
"Three weeks have gone by and I can't believe that my first PIT has now flown by as a thing of the past. Along with this being my first PIT, I had only been at the lab a little less than 24 hours before PIT began and I am the only completely new member to the lab. I have to admit I was a little intimidated, not only at the large task at hand, but also by the amount of experience of those around me. I definitely sometimes played 'the rookie', as some of the instructions I was receiving seemed like Greek, but everyone here was always willing and able to sort me out in the right direction. Catching my first Lemon shark in the net was incredible; they're a lot stronger than their body size would lead one to believe. The nights can be long out on the nets for 12 hours straight, but with as many clowns (i.e. those from England) as we have here at the lab it usually ended up going by quite quickly. After hauling up my first Tiger Shark in the long-lines this week, I'm more than eager to see what else the waters of Bimini have in store."
The PIT 2006 Project was a resounding success. The team conducted the annual census of juvenile lemon sharks in Bimini lagoon in accordance with the tradition and methods employed by the Bimini Biological Field Station-Sharklab. Through the data obtained, we will be able to add another chapter to the story of the lemon shark. Along the way, we shared experiences and forged new friendships as we worked side by side. I am proud to have been involved with this project again this year and to count myself as a member of the PIT 2006 team. I would like to give a big thank you to everyone on the team for helping to make this a special experience for me personally. I thank Doc for having me and giving me the opportunity to photo-document the event. I thank the volunteers for all their hard work, the boat captains for their leadership, and last but definitely not least, I want to extend a special thanks to Grant and Katie. Their dedication, direction, and general love of Bimini influences the attitudes of everyone who passes through BBFS in a positive and productive manner.
As the lab settles back into its normal schedule, we attempt to collect our thoughts, memories, and pictures from the past few weeks. I hope that this website is a source of nostalgia for team members, of insights for others, and enjoyment for both. There have already been some goodbyes, and I will say my own very soon. Turnover is the way of life at the lab - as new crews continually find there way out to Bimini. I hope to return again soon - to see old friends and meet new ones, to continue to work towards BBFS research goals, or rise to new challenges. Most of all, I desire to have another set of unique experiences that only the Sharklab, and Bimini, Bahamas, can offer. I am already looking forward to PIT 2007...
- Matthew Potenski
June 26, 2006