Friday, July 8, 2011

Day 31: Nekton monitoring

Upon arrival, I found the marsh teeming with.... scientists.

NPS coastal ecologist Patricia Rafferty had come to Rocky Point to train her crew in the use of throw traps to monitor marsh nekton, aka, swimming organisms. As Patricia explained, nekton are good indicators of  marsh health because unlike ground dwelling organisms, they can swim away if conditions aren't right. Throw trap surveys are employed before, during and after marsh restoration projects to track success.  Here's how it works. First, the trap location is selected, GPSed, and water temperature, salinity, and dissolved oxygen are recorded.

The three foot square trap is placed and any cover vegetation within the trap is identified. A rigid rectangular net is then swiped through.

Once the net is raised it's all hands on deck as the little fish flip about trying to escape. They're moved under the wet algae to keep moist (and still) until they can be tallied.

The fish are identified, counted, and the first 15 of each are species measured. This continues until three consecutive swipes come up empty.  It's precise and thorough work. The marsh is a nursery for juvenile fish, and at this size, it takes an expert eye to distinguish between species. From nose to tail, most are no longer than a pinky nail.

A horseshoe crab egg.

Atlantic silverside, Menidia menidia.

Striped killifish, Fundulus majalis

The crew found a number of sheepshead minnows, Cyprinodon variegatus, which Patricia noted are not commonly encountered in the nearby Jamaica Bay marsh islands.

The fish were all released back into the marsh. Check back soon for the results of the data the crew collected, which should shed light on how Rocky Point's fish population compares to that of other salt marshes.

Moving on to aerial organisms. The osprey pair visited twice, but my new mounting system was clearly not optimized for Nat Geo shots.

To make matters worse, some avian saboteur tilted the camera just four days into the camera trapping. Over 1,500 photos were subsequently captured of wind-blown twigs, 2x4s, and an ever-growing pile of bird excrement.

The culprit? A solitary fish scale stuck to camera gave it away. An osprey weighs only about three and a half pounds, but it apparently exerted enough force to dislodge one of the two screws holding the mount in place. Corrective measures have been taken.

Sadly, the marsh was bereft of willets today. Two pair had taken up residence since May. I saw breeding behavior on multiple occasions and a suspicious pile of downy gray feathers, but no chicks. Having failed to raise any young, the two pairs have likely moved on, although one lingered on the beach. The marsh feels empty without their incessant bleating and dive bombing. They will be missed. Here's wishing them a safe migration.

 In their place are the marauding skimmers. Not nearly as bold, but always a pleasure to watch.

I'll close with butterflies. Last weekend, biologist Steve Finn counted them at three Breezy Point locations: West Beach, Fort Tilden and Rocky Point marsh. Here's what he had to say about the marsh: "I used to include this area in the late 90's. I determined it was too difficult to access with all the accumulated flotsam (timber with nails, etc.). Now, not so bad." 
  1. Orange Sulfur- 3 (see photo below)
  2. Wood Satyr- 1 (Only specimen found in all three sites)
  3. Summer Azure- 1
  4. Clouded Sulfur- 1
  5. Northern Broken Dash- 3
  6. Cabbage White- 1
  7. Tiger Swallowtail- 1
  8. Common Buckeye- 3
  9. Eastern Tailed Blue- 1 
Impressive for a 15-minute survey.

butterfly photo courtesy Steve Finn

High of 92, max humidity 87%, average wind SW @ 8 MPH, 5.8 high tide @ 01:30 PM. Moon 34% visible.
*** marsh determined to flood at 5.9 inches.
Water level recorded at 7 inch mark.
Fish recorded in marsh: Mummichog, Fundulus heteroclitus; spotfin killifish, F. luciae; striped killifish, F. majalis; Atlantic silverside, Menidia menidia; sheepshead minnow, Cyprinodon variegatus
Birds seen in marsh: snowy egret, great egret, green heron, ? yellow and black warbler, black skimmer, least tern
Birds seen in bay: laughing gull, herring gull, willet, mallard, black duck, common tern, black skimmer, least tern

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