Spawning Aggregation Evaluation. Utila January February 2009

Transcription

1 Spawning Aggregation Evaluation Utila January February 2009

2 Location Selection Selection considered fishermen and logistics Location 1: Joshua Swash Location 2: The Elbow The Elbow cancelled after January as NO fish Replaced with S.E. Bank Initially thought too deep but found exact location of shallowest part (35m EANx)

3 Surveys Schedule Full Moon New Moon January 11 th 13 th 24 th 26 th February 8 th -11 th 23 rd 25 th Two dives at each site each day Dawn (6am 8am) Dusk (4pm 6pm) Additional information: Gathered anecdotes from fishermen about catches Monitored Landings at the Fish Packing plant on Cayitos

4 Joshua s Swash 400m off North Shore of Utila A ridge of M. faveolatarunning ENE WSW Rises from 25m patches of sand and reef Drops steeply on North to 60m sand to 100m+ Groupers aggregate on sand behind ridge Located by old fishermen in boat with me Found active pots at site Reportedly the traditional spot for Nassau, Rockfish and tigers

5 Joshua s Swash Results January February Full Moon New Moon Full Moon New Moon AM PM AM PM Mean Mode Mean Mode Mean Mode Mean Mode Nassau AM PM AM PM Mean Mode Mean Mode Mean Mode Mean Mode Nassau Grouper Yellowfin < Black < 1 3 < 1 1 <1 <1 0 0 Tiger <1 1 Grouper Yellowfin <1 1 <1 1 < Black 0 0 < Tiger <1 3 <1 1 < Other < Dog Other Dog < < Snapper Yellowtail Mahog Snapper Yellowtail Mahog Other < Other <1 Grouper per dive. No significant Peaks. Average size of Groupers = 30cm Schools of resting Yellowtail, Goatfish and Mahogany Snapper (20cm)

6 Joshua s Swash Summary Very low grouper numbers Groupers that were seen were not large Evidence that site was an aggregation Fish pots at site Large school of pelagic Rainbow runners (Elagatis bipinnulata) and Jacks (Caranxlatus) seen in water column only around full moon. Behaviourof pelagic fish indicated they were expecting large fish to be ascending in water column Whaleshark seen near by Conclusion: Aggregation for Grouper Exhausted Site Still Important for resting Yellowtail and Mahogany

7 South East Bank 4 Km East of Utila Fishermen reported this site as BEST remaining site for Nassau and Rockfish Found site by locating a fishermen using pots on the site Found active fish traps at location Sea mound with top at 35m dominated by hard corals and barrel sponges with sand patches South East end of a ridge that runs NW to SE Most of area is 40m -60 m Difficult to monitor due to depth But thought to be most likely site still active near Utila

8 South East Bank Results January Collected data at the elbow: Total of 84fish of ALL species of Snapper and Grouper seen on 11 consecutive dives Max of 5 Tiger groupers were seen on one dive but all immature Average size of all groupers seen 25 cm Depletion of ALLreef fish very severe Decided to move to SE Bank Grouper Snapper February Full Moon New Moon AM PM AM PM Mean Mode Mean Mode Mean Mode Mean Mode Nassau < Yellowfin 2 4 < Black <1 1 Tiger Other Dog Yellowtail < Mahog Other Average 1-2 Groupers per dive No Significant Peaks Grouper size: 45cm

9 South East Bank Summary Large groupers seen at this site (45cm +) Only place to see this size of groupers Active Fish pots found during February full moon with Nassau groupers inside Fishing boat from La Ceibaseen in February new moon Conclusion: No aggregation formed here during February despite a few large groupers. Fishermen expected aggregation here

10 Overall Trends Grouper aggregations did not form during January or February at the sites chosen Water temperature has risen to 25 degrees C, so unlikely to form in rest of year (Grouper spawn at 24 degrees) Snapper Aggregations expected at same locations in March Data from fish landing indicate fishermen did not find many Rockfish or Nassau this year; indicating wider collapse. Worse year on record according to fish factory owner. Critical problem for fish populations around Utila OF CONCERN: Use of reef fish to bait fish pots increasing problem to other trophic groups

11 BIG PROBLEMS!!!