Fall Collecting Trip #7: Seine and Night Diving

This morning we boarded a small motor boat and headed to shore for a special kind of collecting. Instead of diving with nets, we used a seine net – a long, fine mesh net with one end buoyed and the other weighted. Two pullers on each end of the net stretch it parallel to the beach about one hundred feet out. Perpendicular to the pullers is a line of beaters who stand evenly spread out from the pullers to the shore who splash furiously as the pullers bring the net in to keep fish from escaping out the sides. A snorkeler swims back and forth along the length of the net to untangle it from rocks and to let rays and sharks escape.

Beach Seining-101

Once the pullers reach the shore, everyone lines up on the net, gathers the sink-line to the float-line and walks back out into waist deep water to see what we got! Sarah worked her way from one end to another identifying fish (keep this, let that one go). We did three seines and were very successful; a couple of small barracuda, 25 needlefish, teeny tiny Sergeant Majors, and even two cowfish (one scrawled, one honeycomb)! [Seining is a regular institution on the dive trips. Click here to see how other groups fared!]

Captain John organizing our efforts during the seine (Photo Courtesy of Scott Bobek)

Needlefish from the seine, in the holding tank aboard the R/V Coral Reef II

During the seine, we encountered lots of Cassiopea xamachana (upsidedown jellyfish). Most jellyfish sting when their nematocysts (stinger cells) come in contact with another object. If that it is a prey item, they will have stunned or killed it and will start reeling it in to eat it. Cassiopea, on the other hand, release their nematocysts indiscriminately into the water. When the water gets into your wetsuit while you are, say, seining on the beach near these jellies, the little nematocysts go to work stinging away. It’s not a very potent venom, so it manifests itself as sort of an itchy rash. The only way to relieve it is a dip in nematocyst-free saltwater (freshwater makes it worse), so when we got back to the boat everyone jumped into the water – off the top deck. [Not the first time these Aquarium divers encountered these jellies. More here.]

Dave jumping off the top deck (photo courtesy of Scott Bobek)

Scott jumping off the top deck (photo courtesy of Dave Wedge)

Post jumpers enjoying the warm water.

Back on the boat, we motored out to a site called Frank and John’s for two dives in the afternoon. The site consisted of one long reef and several small surrounding reefs. Visibility was unlimited; it was like diving in a pool! Sam and I decided to do our first dive focusing solely on invertebrates (crabs, shrimp, sponges, etc.). It is amazing what you miss when you are looking for fish! When you focus on a smaller scale you can see all sorts of amazing little critters in the rocks – we got some arrow crabs, basket stars and cleaner shrimp (which had to be released because they were carrying eggs). There is a big crevasse in this reef where some of our expert collectors caught the elusive fairy basslets, and another trumpetfish.

After dinner we got to do something amazing – a night dive. About two thirds of the divers went down to collect cardinalfish which come out at night, but the last third of us went down simply to observe and enjoy the reef at night. Lit only by the moon and our flashlights we were surprised to see not a sleepy reef, but one full of life! Nocturnal animals like lobsters, squirrelfish and basketstars were in their glory. We brought back a big beautiful basketstar, and a gigantic Mythrax spinosissimus (Channel Clinging Crab) for Jeremy’s Blue Hole exhibit.

Divers descend into darkness. The green light hanging off the back of the boat helps us make our way back when the dive is over!

Usually I am fast asleep at this point in the night, but I am still amped from the dive. What an amazing trip so far!

-- Emily

1 comment:

  1. Sounds amazing! Can't wait to see them back at the Aquarium.


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