Assessment of Red Hind Breeding population structure and spawning habitat.
Completion Report for Grant #R-101-1-02
Submitted to:
University of Puerto Rico Sea Grant College Program
By Richard S. Nemeth, Ph.D.
Center for Marine and Environmental Studies, University of the Virgin Islands, St. Thomas. USVI 00802-9990. Tel: (340) 693-1381, Fax: (340) 693-1385, e-mail: rnemeth@uvi.edu
November 29, 2004
Completion Report for Grant R-101-1-02
November 2004
‘Assessment of red hind (Epinephelus guttatus) breeding population structure and spawning habitat’
ACCOMPLISHMENTS
Major Goals:
The primary research goals of this project were to 1) confirm the source area and movement patterns of red hind spawning within the MCD, 2) document the sex ratio, size and number of red hind spawning at this site, 3) characterize the physical and biological features of this essential fish habitat.
Accomplishments:
1. Documenting movement patterns and source of spawning red hind i. Tag and release program
A total of 1369 red hind were captured and measured on the spawning aggregation site from December 2002 through February 2003 using hook & line fishing and baited Antillian fish traps. Of these 1222 were successfully tagged and released. Following the spawning season in 2002/2003, 17 tags have been returned by fisherman. A total of 44 tag returns have now been obtained. These tag returns have significantly strengthened and broadened the known source area for red hind within the MCD spawning aggregation. The data indicate that many of the fish tagged at the spawning aggregation subsequently travelled 6 to 30 km westward and are normally resident in the region southwest of St. Thomas between Culebra, Vieques and Sail Rock, St. Thomas
ii. Identifying other potential spawning aggregation sites
During December 2003 and January-February 2004, searches for additional red hind spawning aggregations were carried out at 3 locations south of St. Thomas and St. John. In collaboration with the Division of Fish & Wildlife, St. Thomas, a drop video camera was utilised to determine the benthic cover at two potential sites, a mid-shelf reef and an elbow at the shelf edge. While the mid-shelf reef comprised extensive plate coral growth, there was no evidence of aggregating grouper at either site. The mid-shelf reef may, however, be an important staging area for grouper moving towards spawning aggregations.
An extensive area of deep plate-like corals south of St. John and close to the shelf edge is currently the most likely location for a further red hind aggregation. Four roving dives using scooters were conducted on this reef two days following the full moon in January. Although the benthic structure was very similar to the red hind aggregation within the Hind Bank MCD, there was no evidence of aggregating grouper. It may be hard to locate a spawning aggregation since this area has sustained heavy fishing pressure for many years and only the remnants of an aggregation may remain.
2. Determining sex ratio, size and number of spawning red hind i. Visual censuses
Scuba divers used enriched air nitrox to visually count the density of spawning red hind. A total of 99 visual transect surveys were conducted within the known boundaries of the spawning aggregation during the December 2002 – February 2003 spawning season. Some of the highest densities ever recorded were seen in January 2003 with peak densities reaching nearly 40 red hind per 100m2 Average densities over the 0.35 km2 spawning area during this month were nearly 25 red hind per 100m2 which translates to a spawning population size of 84,000 red hind.
ii. Size Frequency and Gender and Fecundity using Ultrasound technology:
A total of 1369 red hind were captured and measured from the MCD spawning aggregation site between December 2002 and February 2003. The average size of the red hind spawning population was 37.9 cm total length. The gender of a total of 820 fish was determined throughout the spawning season. Males and females showed a bimodal size frequency distribution with males being 6 cm larger than females (males: 42.3 ± 3.15 cm TL vs. females: 36.4 ± 3.42 cm TL).
Gender of red hind was determined using a laptop Terason ultrasound system and macro- and microscopic inspection of gonads. During December 2002 24 fish were transported live into the laboratory and were examined using ultrasound technology in an attempt to determine the gender. The ultrasound process was not successful with these fish as no differences between sexes could be determined and gonads were not clearly visible on the ultrasound images. Dissection of 12 sacrificed hind along with macro- and microscopic examination of gonads revealed that gonads of all fish were either immature or in resting phases and therefore the sex of individuals could not be determined. In January 2003 this process was repeated. Sixteen fish were transported live to the laboratory and scanned with ultrasound to determine gender. These fish were subsequently dissected to confirm gender. Accuracy at determining the gender of this sample of fish using the ultrasound was 100%. The ultrasound equipment was then used in the field the following day and all fish (Total 198 hind) which were captured and tagged were also scanned to determine sex. Equipment problems prevented use of the ultrasound on the boat during two days (15 & 16 January). A further 301 fish were scanned on 17and 18 January 2003. Analysis of these data showed that Female:Male sex ratio in January varied from 15:1 to 4:1 depending upon the day of the lunar cycle but in February the sex ratio remained around 1:1.
A model of female fecundity was constructed using ultrasound images to estimate ovarian volume together with samples of ovarian tissue to determine oocyte density. Twenty-seven females were scanned with the ultrasound and the length and width along four cross-sectional images of one ovary were recorded and saved to a digital video camera. Maximum and mean cross-sectional areas were subsequently calculated using Image Pro image analysis software. These fish were then dissected and total ovary volume (ml) was recorded by calculating the volume of water displaced when the whole ovary was added to a graduated cylinder filled with water. Step-wise regression analysis revealed that ovary volume could be best predicted using two variables: average ovary cross-sectional area (Aav) and total ovary length (L) Prediced ovary volume (V) therefore resulted in the following model: V = 3.805 Aav + 15.44L – 79.716 (r2 = 0.845). Cannular samples (0.1 ml of eggs) were taken from 24 females in January and February 2003, preserved in 10% formalin and counted using a dissection microscope. Fecundity was estimated by integrating predicted ovary volumes from model with oocyte densities from cannular samples.
Fecundity estimates for female red hind from the MCD spawning aggregation site indicated that 31 cm females had 199,840 eggs, 41 cm females had 1,566,120 eggs and the average sized female (36.4 cm) had 978,620 eggs.
3. Characterisation and assessment of benthic habitat
A total of 22 diver-operated digital video transects were conducted within the boundaries of the Marine Conservation District. Unfortunately 4 transects conducted at the western end of the aggregation and filmed between 5-6pm were too dark to accurately analyse. The remaining transects were carried out at the East (n=5), Centre (3) and West (3) ends of the aggregation boundaries and at an outer coral mound (n=7) located along the edge of the shelf. Topographic complexity or reef rugosity was also measured on each videoed transect using the chain method. All digital images were analysed using Photoshop software and Excel was used for calculating the benthic cover along these transects. Percent cover of benthic organisms and substrates include: live coral (25.5±9.1%), algae (54.4±7.4%), sponges (8.8±5.0%), gorgonians (0.02±0.1%), coralline algae (5.0±4.1%) and sand (5.3±5.6%). Some corals within the MCD also showed signs of bleaching (6.5±7.7%) and disease (1.4±3.4%).
Training and Development:
UVI undergraduate students which were involved in this research include Briana Smith, Devon Tyson, Alkin Paul.
Research technicians trained in technical nitrox diving during this program include Laurie Requa (accepted to graduate school at Cal. State Northridge), Steve Herzlieb (UVI alumni), Shaun Kadison, and Jeremiah Blondeau.
Post-doc fellow Elizabeth Whiteman received training in technical nitrox diving, use of ultrasound technology, and fishery techniques.
Dr. Cecil Jennings participated in our field research and served as technical advisor on the use of ultrasound. UVI faculty Dr. Richard S. Nemeth received training in technical nitrox diving and use of ultrasound technology.
Local fishermen Kenny Turbe received training technical nitrox diving to participate in this program and Captain Edmund Bryan and his boat and crew were hired to support our field research.
Dissemination of results, outreach:
Results were presented to the community at two fishery workshops on St. Thomas (R. Nemeth) and St. Croix (E. Kadison) hosted by NOAA’s National Marine Fisheries Service in May 2004, at the Caribbean Fisheries Management Council general meeting (R. Nemeth) and public forums (R. Nemeth), the St. Thomas/St. John Fisheries Advisory Committee (R. Nemeth), and at two UVI marine science seminar series in August (R. Nemeth) and October (S. Herzlieb) 2004 which were held on the St. Thomas campus but video-conferenced to the St. Croix campus.
The results of this research program were also disseminated locally through several newpaper articles (Daily News, St. Croix Avis), on-line newspaper (St Thomas Source) as well as on a radio talk show (Alex Randall’s Good News Program), and in several UVI Research and Public Service newsletters. Moreover, results of this research were also incorporated into the presentations of the Virgin Islands Marine Advisory Service, an outreach program partly funded by Puerto Rico Sea Grant.
Reward notices announcing the red hind tag and release reward program were advertised in local newspapers and hundreds of fliers in English and Spanish were distributed at local fish markets in St. Thomas, St. John, St. Croix the British Virgin Islands, and eastern Puerto Rico, Vieques and Culebra. Because of the importance of the area between western St. Thomas and eastern Puerto Rico for red hind leaving the MCD, additional effort was put into increasing the number of tag returns from this region. In late September 2003, R. Nemeth travelled to Culebra to distribute reward posters to the fisheries cooperative headquarters. In October 2003, the post-doc employed on this project (E. Whiteman) travelled to Puerto Rico and Vieques. This trip was scheduled to coincide with a regional meeting of port samplers and allowed presentation of the tagging program to port samplers, fishermen and staff at fish markets within the region. Reward posters were distributed at each location visited. The importance of fish markets in the coastal region of SE Puerto Rico was highlighted by the return of six tags from fish previously captured in the area.
PRODUCTS
Peer Reviewed Publications and Conference Proceedings: (federal support acknowledged)
Nemeth, RS. (2004) Population characteristics of a recovering red hind spawning aggregations following protection. Marine Ecology Progress Series. 284: (in press).
Whiteman, E. CA Jennings and RS Nemeth. (2004) Sex structure and potential female fecundity in a red hind (Epinephelus guttatus) spawning aggregations: applying ultrasound imaging. Journal of Fish Biology (in press).
Nemeth, R. S., S. Herzlieb, and J. Blondeau. (2004) Comparison of two seasonal closures for protecting red hind spawning aggregations in the US Virgin Islands. 10th International Coral Reef Symposium. June 27 – July 3, 2004, Okinawa, Japan.
Herzlieb, S., E. Kadison, and R. S. Nemeth. (2004) Comparative assessment of coral reef systems located along the insular platform of St. Thomas, US Virgin Islands and the Relative Effects of Natural and Human Impacts. 10th International Coral Reef Symposium. June 27 – July 3, 2004, Okinawa, Japan.
Presentations (federal support acknowledged):
Results of this project were presented at two scientific conferences by Dr. Richard S. Nemeth and Mr. Steve Herzlieb. These included:
Nemeth, R. S., S. Herzlieb, and J. Blondeau. (2004) Comparison of two seasonal closures for protecting red hind spawning aggregations in the US Virgin Islands. 10th International Coral Reef Symposium. June 27 – July 3, 2004, Okinawa, Japan.
Herzlieb, S., E. Kadison, and R. S. Nemeth. (2004) Comparative assessment of coral reef systems located along the insular platform of St. Thomas, US Virgin Islands and the Relative Effects of Natural and Human Impacts 10th International Coral Reef Symposium. June 27 – July 3, 2004, Okinawa, Japan.
Web site:
Some results are posted at www.marsci.edu
Networks and Collaborations:
A research collaboration was established with Dr. Cecil Jennings, USGS, Chief of the Georgia Cooperative Fish and Wildlife Research Unit, University of Georgia, Athens.
Technologies and Techniques.
The ultrasound technique for determining gender and estimating fecundity were developed for the red hind during this project and will be reported in Whiteman et al. 2004 as listed above.
Inventions:
None
Other Products
None
IMPACTS
The results of this project have provided some of the first information on the effects of marine protected areas on the recovery of a grouper spawning aggregation. These data will greatly facilitate the management of other red hind spawning aggregations by local and federal agencies in the Virgin Islands and by other resource managers throughout the Caribbean. The use and validation of ultrasound imaging in evaluating red hind spawning aggregations will greatly enhance future work since it eliminates the necessity to sacrifice hundreds of fish to determine gender or fecundity. This technique is currently being evaluated on larger grouper species (i.e. yellowfin and Nassau) which form spawning aggregations.
PARTICIPANTS
Note: All participants were non-Hispanic ethnicity and without disabilities so these categories were dropped and role of participant was added. All participants except undergraduate students worked more than 160 hours on project.
Name Sex Race Citizenship Role and Contribution
Richard S. Nemeth M W USA PI– all aspects of project
Cecil Jennings M B USA VI native Co-PI, technical advisor for ultrasound
Elizabeth Whiteman F W USA/ UK Post doc– all aspects of project
Steve Herzlieb M W USA Res. Tech – all field and lab work, data entry and analysis
Jeremiah Blondeau M W USA Res. Tech – all field and lab work, data entry and analysis
Elizabeth Kadison F W USA Res. Tech – all field and lab work, data entry and analysis
Laurie Requa F W USA Res. Tech – all field and lab work, data entry and analysis
Kenny Turbe M W USA VI native Master fisherman – all field and most lab work
Edmund Bryan M W USA VI native Captain
Mike M W USA VI native Deck hand
Brianna Smith F W USA
Undergraduate student helped in diver surveys
Devon Tyson M B USA VI native Undergraduate student helped in diver surveys and lab work
Alkin Paul M B USA VI native Undergraduate student helped in diver surveys and lab work
ADDITIONAL INFORMATION
none