Townsend Cromwell
TC-99-04 Lobster Tagging
TC-99-04 Lobster TaggingMarch 24-April 21, 1999
April 12, 1999 Operations continue with lobster trap haul-back from 8:00 AM till
around 1:30 PM daily. We then run to a new location and reset the traps for an overnight soak. On the night of the 11th, we performed an Acoustic Doppler Current Profiler (ADCP) transect and bottom fished on the evenings of the 9th and 12th. During the ADCP transect, we measured the ocean currents off the west side of Necker Bank. The bottom fishing was conducted to capture juvenile onaga (pink snapper) which are highly prized in Hawaii's commercial fishing industry. Ehu (right) and onaga are both Hawaiian snappers found around the main Hawaiian Islands and NW Chain. They resemble one another in general body plan and in their bright red coloration. Onaga however have a deeply forked tail while the tail of the ehu is much less so. Ehu are also more common while onaga are more prized for their commercial value. Every once in a while, we catch more than what we want, like a sharks (below, left) that eat the fish we do want to catch. Their bright red coloration makes these fish highly visible near the surface. However, the little bit of sunlight that reaches the depth at which they live, contains no red light to reflect as the water has absorbed it all. Thus, on the ocean bottom, these fish appear black and thus hard to see. Ehu and onaga are both bottom predators, specializing in feeding on small fish and crustaceans. Ehu tend to prefer living at depths of 102-271 meters (334-889 feet) while onaga seem to prefer 183-256 meters (600-839 feet). They both tend to aggregate around steep drop-offs, ledges and pinnacles.
Although we haven't been successful with catching onaga, our spiny lobster tagging operations have been highly successful. When we first arrived on Necker bank, we trapped the southern portion of the reef. Our results were
about 70-75 spinys caught and tagged per day. After the first week, we worked our way to the north part of the reef (around Necker Island) and our catch rate increased to just over 200 spiny lobsters caught and tagged per day. On April
10th, we caught and tagged 427 spiny lobsters which is an "all time high" for us. As of today (April 12), we have tagged a grand total of 2,064 spiny lobsters, in addition to capturing 10 lobsters tagged the previous season. Wayne Haight, the Chief Scientist for this cruise, calculated we should recapture 10-15 tagged lobsters this trip. He calculated this by taking the estimated total lobster population and determining what percentage of that population consists of tagged lobsters. Our recapture rate should be comparable with the calculated percentage of tagged lobsters on the reef. So far our recapture of 10 lobsters is right in the ball park with his calculations. The assessment of the total population is extremely important as it is used in determining the allowable catch rates that lobster fisherman will be licensed for each season. The tagged lobster study appears to provide an indication that the overall lobster population assessment has been fairly accurate.
- For related information about lobster research, visit the Honolulu Laboratory's Kewalo Research Facility Lobster Research web pages.