Sharkland Gillnetting, Days 4-6
written by Janet Stalker
The 4th night of fishing in Sharkland was again fairly successful. Only 7 sharks were caught between all three nets, but that’s to be expected with the number of days already fished in the area. We’re expecting even more decreased numbers for the last two nights, which indicates we caught all the sharks in the nursery. A few nurse sharks were observed again last night, although only one small one was caught in the gillnet (and successfully released unharmed). The main pen now has 106 sharks in it, which can make for a interesting snorkel check in the middle of the night of the pen! Feeding the sharks is just as mesmerizing, as the sharks work themselves into such a frenzy over the fish they eat. Seeing so many sharks feeding at once is quite a sight, definitely an experience not many people will forget!
Only two nights left in Sharkland. Tonight we left a little later then usual (6:45PM), trying to play the tides right so we could set in the right amount of water. The nets were set about an hour later, and the sharks slowly trickled in through the night. By the time the nets were hauled four more baby sharks had been added to the main pen. The away team also saw a gorgeous sunrise this morning which needless to say was a nice treat at the end of the long night.
Sharkland had its last deployment of eager scientists out fishing for juvenile sharks tonight, and the night was a success, even though only two sharks were caught. This marks the end of the illustrious PIT project, and it's not hard to tell from the talk around the lab. With only a few days left here for many of the PIT volunteers, people are already beginning to feel like they don’t want to leave yet! In total the fishing in Sharkland resulted in 112 juvenile lemon sharks which were all tagged and will be released tomorrow morning. The last few days here for the PIT volunteers will be spent relaxing and having some fun, such as trips to “The Three Sisters” (a great snorkeling spot) and a shark dive. Several of the volunteers will be leaving on June 25th, with the remaining team resuming the regular schedule of research projects.
Summary of Sharkland Catches
Over the six nights of fishing in Sharkland, 112 juvenile lemon sharks were captured of which 51 were newborn (including two recaptured from North Sound), 47 were recaptured with PIT tags from previous years (including six recaptured from the North Sound, two of which were newborns) and 16 were untagged but not newborn. Of these 112 sharks 54 were females and 58 were males.
Of the 51 newborns, 20 were females and 31 were males with weight ranging from 0.5 kg to 1.4 kg averaging 1.1 kg. The total length ranged between 51.4 cm to 68.0 cm averaging 62.5 cm.
Of the 47 recaptured sharks, 26 were females and 21 were males with weight ranging between 0.9 kg to 5.9 kg with an average weight of 2.5 kg. The total length ranged between 60.4 cm to 105.8 cm averaging 78.5 cm.
Of the 16 untagged sharks that were not newborns, 9 were females and 7 were males with weight ranging from 1.4 kg to 6.6 kg averaging 2.2 kg. The total length ranged between 67.2 cm to 107.4 cm averaging 75.5 cm. It is possible that these sharks were previously marked and shed their PIT tag since prior analysis showed that over 5% lose their PIT tags over time. However the DNA sample will allow us to answer the question of prior capture.
Figure 1: Total catch in Sharkland pre-dredging (green bar) and post-dredging (red bar). The solid line is the moving average showing a decrease in total number of sharks caught in 2001 and 2002, the years with the most intensive dredging activity in the Bimini Lagoon.