Determining
the minimum size of fishery closures for protecting grouper spawning aggregations
Final Report
March 1, 2007 - August 31, 2008
Submitted to:
University of Puerto Rico Sea Grant College Program
By Richard S. Nemeth, Ph.D. Jeremiah Blondeau, M.S. and Elizabeth Kadison, M. S.
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
September 26, 2008
Final Report September 2008
A. Executive Summary
Project title: Determining the minimum size of fishery closures for protecting grouper spawning aggregations.
Date: September 26, 2008
Project Number: Grant/Project No. R-31-1-06
Investigators and affiliation: Richard S. Nemeth, Ph.D., Jeremiah Blondeau, M.S., and Elizabeth Kadison, M. S. 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.
Dates Covered: March 1, 2007 - August 31, 2008
Summary of Impacts and Contributions: 1. Objectives:
Objective (1) Determine habitat use and spatial distribution patterns of red hind, Nassau and yellowfin groupers during their spawning aggregations. This objective has been met. Strategic placement of acoustic receiver arrays over two spawning seasons allowed us to successfully determine small-scale distribution patterns of all target species. However, the full range of distribution of these species was limited to the area of receiver coverage.
Objective (2) Identify the daily, monthly, and seasonal patterns of movement of target species for the duration of the spawning season. This objective has been met. Successful tagging of target species prior to their spawning times and strategic placement of acoustic receivers enabled us to determine movement patterns during and between spawning events. Degree of movement varied by species size; with red hind being the smallest and most sedentary and yellowfin grouper being largest and most mobile. The majority of tagged yellowfin (63%) and Nassau (56%) also moved between the Grammanik Bank and the MCD on a regular basis.
Objective (3) Propose appropriate boundary closure areas to fully protect these three species on their spawning aggregations sites. This objective has been met. Based on results of this study we recommend that no change is needed to the Marine Conservation district (MCD) closure boundaries. The MCD is successfully protecting the red hind during migration to and from the spawning site as well as during the spawning events. Based on our acoustic data the existing Grammanik Bank closure (1.5 km²) provides limited protection for Nassau and yellowfin grouper. We propose to increase the size of the Grammanik
Bank closure from 1.5 km² to at least 7.5 km² or preferably 11 km² and extend its boundaries northward and westward so that it is contiguous with the eastern edge of the MCD. The expansion of the Grammanik Bank closed area would encompass the majority of the daily movements and migratory pathways of Nassau and yellowfin groupers.
2. Advancement of the Field:
Our acoustic receiver array design allowed us to determine the spatial extent of the Nassau and yellowfin groupers in a way that could be used as a rapid scientific assessment of an aggregation of these fishes for managers when planning closure boundaries. To our knowledge no other acoustic tagging studies of fish has deployed receivers in expanding coverage around a spawning site. This method is an effective use of technology for quantitatively determining the relationship between area (e.g. km²) and the amount of protection given to a particular species. Secondly, very little is known and very little is published about the biology and reproductive behavior of yellowfin grouper and nothing published on their migration patterns. This study provides some of the first pieces of evidence of the movement, behavior and timing of yellowfin at a spawning aggregation.
3. Problems encountered:
In this study, the size of the fish and the habitat type were key factors in the success of detecting an acoustic tag. The deep, offshore coral reef banks, where the study took place, are composed primarily of large, plating Montastraea annularis coral that form an extensive network of tunnels and crevices underneath the plates of coral (Herzlieb et al. 2006). This allows smaller fish, including red hind, to seek shelter and presumably travel considerable distances. We believe that red hind were able to utilize this reef structure to avoid predation and travel, at least some distances, within this network of tunnels and crevices resulting in the loss of tag detection by the acoustic receiver. Although thousands of detections were made by the receivers allowing us to determine general movement patterns and spatial extent of the red hind, some fish were still able to ‘sneak’ by receivers. We were able to overcome this by deploying receivers in multiple curtains, one closely surrounding the primary spawning site and another, double-curtain, to the west to catch the red hind in their migration to and from the spawning site. This was only possible due to the contribution of 20 additional VR2 acoustic receivers provided by new collaborators (see section 7 below). Unlike the red hind, the Nassau and yellowfin groupers are much bigger and probably less vulnerable to predation and therefore less likely (or able) to travel underneath the coral, making us confident that a Nassau or yellowfin would not be able to ‘sneak’ by an acoustic receiver.
4. Research Impacts:
The most important result of our study was to provide scientific data that quantified the degree of protection afforded to aggregating groupers by various
sized closed areas. We also found that the majority of tagged groupers of both species utilized regular migration pathways that connected the Grammanik Bank and MCD. Based on our acoustic data, the existing Grammanik Bank closed area (1.5 km²) protects Nassau and yellowfin groupers only 75% and 44% of the time during their spawning aggregations. By expanding the Grammanik Bank closure approximately 2 km north and 3 km west to be contiguous with the MCD’s eastern boundary we would enclose the primary migratory pathway of Nassau grouper. This larger closed area (7.5 km²) would increase the level of protection for Nassau and yellowfin groupers to 98% and 82%, respectively. Expanding the northern boundary an additional 1 km northward would increase the closed area to 11 km², enclose the primary migratory pathway of yellowfin grouper and increase the level of protection to as much as 99% for Nassau and 97% for yellowfin grouper during the spawning season.
5. Other import impacts or products:
Two students, Gaeton Gentius (pre-bachelor) and Steven Hitt (graduate student) supported this project as part of our dive team; frequently accompanying the research team in the field for receiver placement/retrieval. Gaeton also helped prepare the receivers for deployment by building concrete bases used to moor the receivers to the sea floor.
Conference presentations: 1 presentation was made at the 33rd Scientific conference of the Association of Marine Labs of the Caribbean and 2 presentations were given at the 11th International Coral Reef Symposium.
6. Indicate sources of matching funds:
Matching contributions of the University of the Virgin Islands’ Center for Marine and Environmental Studies for 2.5 year project
Category Description
Salary and fringe 6 of 9 months for PI: R. Nemeth
Major equipment
Boat use
Scuba facilities
Use of ultrasound imaging system and laptop computer
Use of 28’ R/V Hind Site and 30’ Garuppa for field work
Nitrox fills for scuba diving
Indirect costs 60% of PI salary and fringe
Matching amount (%)
$15,290 (66%)
$6,000 (100%)
$24,000 (75%)
$4,000 (50%)
$9,174 (21%)
Total $58,464 (41%)
7. New extramural funds in addition to match:
a. Characterization of deep water communities within the Marine Conservation District ($160,000), April 1, 2007 to April 30, 2008, Caribbean Fisheries Management Council. Primary contribution of this contract toward the Sea Grant project was training for 4 research divers and two sets of Megalodon
closed circuit rebreathers. This training and equipment greatly increased our ability to work in the deep waters (30 – 50 m) where groupers spawn.
b. Equipment grant ($30,000). Lana Vento Charitable Trust. One-time donation of funds to purchase two more sets of Megalodon closed circuit rebreathers for trained divers.
c. Effects of grouper spawning aggregations on spatial and temporal movements of sharks ($30,000). Ongoing research collaboration established with Mahmood Shivji (NOVA Southeastern University’s Guy Harvey Research Institute) and Brad Wetherbee (University of Rhode Island). Collaborators contributed 20 VR2 acoustic receivers which greatly expanded the extent of our acoustic array, boat fuel to deploy and maintain receiver array and salary and fringe of Drs. Shivji and Wetherbee.
8. List all the titles, funds duration and sponsors of all grants and contracts secured as a follow-up or adjunct to this Sea Grant project.
a. Physical and Biological Connectivity of Virgin Islands National Park, Virgin Islands Coral Reef National Monument and Buck Island Reef National Monument ($76,800). 6/01/2007 - 11/30/2010, USGS State Partnership Program. This project is examining the connectivity (ontogenetic movements and genetic) between the Nassau grouper spawning aggregation at the Grammanik bank and juvenile settlement and recruitment in near-shore waters around St. Thomas and St. John. Funds from this project will supplement the acoustic array funded by the Sea Grant project.
b. VI-EPSCoR program ($48,000) 10/1/08 – 6/30/13. Pending infrastructure grant from NSF would provide funds for 40 more acoustic receivers to supplement existing acoustic array.
9. Benefits:
This acoustic tagging study allowed us to understand the patterns of movement and migration of aggregating groupers and to use this information to recommend biologically relevant boundaries that maximize the protection of Nassau and yellowfin groupers during their spawning aggregations. This information will directly benefit the management of commercially important grouper species by providing useful guidelines for the Caribbean Fisheries Management Council and the Virgin Islands Division of Fish and Wildlife in designing more effective fishery protected areas. This approach and these data may also be applicable for defining boundaries useful for protecting these species in other locations or other species which form spawning aggregations.
B. Final Report Narrative
Statement of Problem: Reef fish spawning aggregations are unique life history events that occur at specific places and times. Once discovered by fishermen, these spawning aggregations are extremely vulnerable to over fishing and have been eliminated on many islands throughout the Caribbean. Nassau, yellowfin and red hind spawning aggregations have been severely depleted or extirpated throughout the Virgin Islands archipelago and other Caribbean islands (Sadovy 1992, Beets and Freidlander 1999, Olsen and LaPlace 1978, Sala et al. 2001). Today the grouper fishery, which dominated the Virgin Islands fin fish landings throughout the 1970’s and 1980’s (Sadovy 1992, Cummings et al. 1997), has been largely replaced by herbivorous fishes (Tobias 1997). Managers of fishery resources have found that the most effective management tool for protecting critical fish habitat or vulnerable life history periods such as spawning aggregations is through seasonal and permanent fishery closures (Sadovy 1994, Sluka et al. 1997, Bohnsack 1998). Although the approximate location of many spawning aggregations is known, little information is available for the area occupied by fishes during spawning or the migration or movement patterns associated with aggregating species. This lack of information often results in the closures being rejected by local fishermen on the grounds that the size of the proposed closure is inappropriate.
The most recent success of a closure improving a grouper fishery is the Red Hind Bank Marine Conservation District (MCD), which was implemented to protect a red hind (Epinephelus guttatus) spawning aggregation and associated habitat. During 10 years of seasonal protection (1990-2000) and 5 years of permanent closure (2000-2005) the red hind spawning aggregation within the MCD showed dramatic improvements in fish length, density, biomass and absolute abundance (Nemeth 2005). Unfortunately this positive scenario is not routinely observed since most marine protected areas are not implemented to their full extent (Appeldoorn and Lindeman 2003). In a recent survey of a seasonal closure on Lang Bank, St. Croix, USVI the red hind spawning aggregation has not shown the same improvements since its closure in 1995 as the MCD during a similar time period (Nemeth et al. 2006a). This study found that the red hind spawning aggregation site on Lang Bank was only about 600 m away from the closure boundary. In the MCD diver surveys found that between monthly spawning events the majority of the red hind spawning population moved at least several hundreds of meters off the spawning aggregation site to outlying patch reef and hard bottom habitats, presumably to feed (Nemeth 2005). This suggests that the red hind spawning on Lang Bank may actually move across the closure boundary during the spawning season and become vulnerable to fishing mortality. Zeller (1998) found that coral trout (Plectropomus leopardus) migrated from 0.25 to 5.2 km to the spawning aggregation site with males making multiple trips to the spawning site each season (Zeller 1998).
Although limited information exists on the approximate location of many spawning aggregations (Olsen and LaPlace 1978, Claro and Lindeman 2003), the area occupied by fishes during spawning or the migration or movement patterns associated with aggregating species is largely unknown but critical to the accurate placement of fishery closure boundaries. This lack of information often results in fishery closures being rejected by local fishermen on the grounds the size of the proposed closure are too large or inappropriately placed. In a recent example the National Marine Fisheries
Service and the Caribbean Fisheries Management Council proposed and implemented an interim three month seasonal closure of the Grammanik Bank south of St. Thomas to protect a multi-species grouper spawning aggregation site (Mycteroperca venenosa, M. tigris, and Epinephelus striatus). This site was found to contain a fledgling Nassau grouper spawning population that was being impacted as bycatch from fishermen who were targeting a yellowfin grouper spawning aggregation (Nemeth et al. 2006b). Three separate boundary areas for the closure were proposed but were disputed by the local fishermen’s association (Figure 1).
University of the Virgin Islands (1.5 km2)
Hind Bank closure (41 km2)
Caribbean Fisheries Management Council (25 km2)
Seasonal buffer recommended by Enforcement Agencies (100 km2)
Figure 1. Proposed alternative boundaries for the Grammanik Bank, a multi-species spawning aggregation site (modified from D. Olsen).
The largest boundary area in Figure 1 was proposed by the Enforcement agencies to simplify and facilitate enforcement of a fishery closure. The smaller square, recommended by the Caribbean Fisheries Management Council, was contiguous with the eastern edge of the MCD and provided for a potential corridor for migrating groupers. The smallest rectangle, recommended by University of the Virgin Islands scientists, provided protection for the spawning groupers along the Grammanik Bank with a 500 m buffer around the spawning bank based on divers surveys of the Grammanik Bank in 2004. Nemeth et al. (2006b) found that the three species of groupers utilized different parts of the reef during spawning and that daily, monthly and seasonal movement patterns
varied greatly. Based on this preliminary information an interim minimum-area closure was implemented for the grouper spawning season: February 1 to April 30, 2005. Although this is part of the normal political process, what is critically lacking in the final decision is detailed information on the movement and migration patterns of the species that are being protected during spawning. The spatial and temporal patterns of movement of groupers during spawning aggregations needs to be understood to implement biologically relevant closure boundaries and to justify these boundaries to the fishing community whose livelihoods are being impacted. These data will provide fishery managers critical data on the minimum area required for seasonal or permanent closures to protect groupers during spawning aggregations within the region. This is especially critical for the Gammanik Bank, which is the site of a small Nassau grouper spawning aggregation which may be recovering in the Virgin Islands.
Methods
Receiver Array – Prior to deployment of receivers and tagging of groupers we conducted an exercise to test the detection range of our receivers and transmitters. A receiver was deployed and the two transmitter types we used (V13 and V16P) were attached to a line that was secured to the research vessel. With vessel engines off, we drifted from 1000m upwind to 1000m downwind of the receiver location on three occasions. Based on these tests we decide to use a detection radius of 300m for the V13 and 400m for the V16 transmitters and subsequently based all array designs on these tests (Figure 2). All receiver graphics in this report will depict the calculated detection radii.
Vemco receivers (model VR2) were zip-tied in ~ 50-90 ft water depth to a polypropylene line that was attached to a 50lb concrete mooring block. Concrete blocks were used as mobile bases to ease repositioning throughout the study. Retrieving the receiver was performed by divers by replacing one receiver for another and then downloading the information on board the research vessel. Two separate arrays were deployed, one in the MCD for the red hind and another for the Nassau and yellowfin in and around the Grammanik Bank (Figure 2). We modified the arrays in both closures in the second year due to additional receivers added through an acquired collaboration.
Figure 2. Map of study site and location of the Marine Conservation District (MCD) and Grammanik Bank (top center), design of VR2 receiver array on the Grammanik Bank for both years (A),(C) and in the MCD for both years (B),(D). Size of yellow circles represent detection limits of Nassau and yellowfin grouper with V16 tags in Grammanik array (400 m radius) and red hind with V13 tags in MCD array (300 m radius). White
star represents location of red hind primary spawning site. Yellow star represents primary spawning site of yellowfin and Nassau grouper.
Tagging – In the Virgin Islands, red hind spawn within the MCD from December to February, the week before the full moon (Nemeth 2005). Yellowfin grouper spawn on the Grammanik Bank from February to April during the week after the full moon (Nemeth et al. 2006b). In the 1970’s, the historical Nassau grouper spawning aggregations located within the MCD formed from December to January during the full moon (Olsen and LaPlace 1978) which is similar to other sites around the Caribbean (Colin et al. 1987, Colin 1992, Tucker et al. 1993). The Nassau grouper recently found on the Grammanik Bank have been observed in greatest numbers from February to April, a pattern similar to yellowfin grouper (Nemeth et al. 2006b). Depending upon the month and species present (Nassau, yellowfin: February to April), target species were collected using hook and line or fish traps. Once onboard each fish was held in flowing seawater tanks and their airbladder deflated using a sterilized hypodermic needle. Each fish was anesthetized with MS-222 (recommended by Zeller 1999), measured (cm), tagged with numerically coded dart tags below the dorsal fin, and sexed using ultrasound (Whiteman et al. 2005). Vemco acoustic transmitters (model V16P, V16 for Nassau and yellowfin, model V13 for red hind), coated with antiseptic cream, was surgically implanted in the body cavity of each fish (Holland et al. 1993, Zeller 1999, Meyer et al. 2000). Incisions were closed using a light gauge surgical suture and cleaned with an iodine/water solution to prevent infection. The fish was allowed to recover before being released by divers to the sea floor in a specialized cage. This process continued until 5 males and 5 females of each species have been successfully tagged and released. Initially the acoustic receivers were retrieved after the first spawning period (approximately 2 weeks) and data downloaded to a laptop computer onboard the research vessel to verify their proper operation. After this initial trial, receivers were retrieved and redeployed once per month until the end of the spawning season. The transmitter identification code, date, time and depth (V16P only) were recorded and stored until the data was downloaded. These acoustic tags are designed with a battery life to last for two full spawning seasons.
Following the departure of the Grammanik Bank spawning aggregation, the receivers were retrieved and data downloaded. The receivers were redeployed in November within the Red Hind Bank MCD in an array to cover the entire red hind spawning aggregation site and adjacent reef and non-reef habitats along the closure boundaries. We began sampling the red hind spawning aggregation during the December full moon and continue until 5 male and 5 female red hind were tagged and released. After the red hind spawning aggregation has dispersed (late February 2007) the receivers were retrieved, downloaded and redeployed on the Grammanik Bank in advance of the Nassau and yellowfin grouper spawning season. During this second season, three (3) more males and females of each species were tagged and released to account for any fish which died or did not return to the spawning site. Thus a total of 8 males and 8 females of each species received acoustic tags during the two year project. Any previously tagged fish that was recaptured, notes on the external tags and condition of the incision will be recorded. This same procedure will be repeated on the red hind spawning aggregation the following winter.
Scuba surveys - During the spawning season scuba divers using nitrox and Megaladon closed-circuit rebreather conducted point counts, total population estimates, estimate fish length and made observations on habitat utilization, and fish behavior, including courtship and spawning. A Sony video camera in an underwater housing with lights was used to document and quantify these behaviors. Divers located groupers with the abdominal tags (i.e. fish with acoustic tags) and made detailed observations on the behavior of these individuals as well as randomly selected non-tagged fish to determine if tagging affects normal behavior patterns. Dives were conducted mostly in the afternoon hours near dusk to increase the probability of documenting spawning behaviors. Since diving depth at these two sites range from 120 to 135 feet (35 – 40 m), bottom time was limited to 20 to 30 minutes.
Data analysis - Data downloaded from the receivers were used to produce maps of grouper movements superimposed over the high resolution bathymetric data and habitat maps produced by NOAA and the Caribbean Fisheries Management Council (CFMC) for the MCD and Grammanik Bank. These maps provided detailed information on the daily, monthly and seasonal movement patterns around the spawning aggregation site, within the closure and in relation to the closure boundaries. The data will also document the dispersal and formation patterns of spawning aggregations of the 3 grouper species, interspecific patterns of movement and variations in movement associated with males and females before, during and after spawning.
Results and Findings
Temporal movement patterns, associated with spawning aggregations, of three commercially important grouper species, red hind (Epinephelus guttatus), Nassau (E. striatus) and yellowfin (Mycteroperca venenosa) were revealed using acoustic telemetry technology within two existing fishery closures. Spatial distribution patterns were also determined, but were limited to the extent of the acoustic receiver array. And although limitations existed, we were successfully able to determine the spatial extent utilized by a significant proportion of these grouper species. By determining these important distribution and movement patterns during spawning events, we were able to confirm the effectiveness of the MCD in protecting red hind during spawning. Our findings also allowed us to recommend appropriate boundaries for the Grammanik Bank fishery closure to fully protect yellowfin and Nassau groupers during spawning. Furthermore, the methods utilized to determine such boundary recommendations are applicable to other spawning aggregations of these species and could be used as a rapid, scientificbased, assessment tool by fisheries managers.
Red hind in the Marine Conservation District: The primary spawning site of the red hind is located in the southeast corner of the MCD, a 41 km² area closed year round to bottom fishing and anchoring. Eighteen red hind (10 female, 8 male) were tagged with acoustic transmitters over two spawning seasons and passively tracked by receiver arrays designed for the red hind in 2007 and then modified in 2008 (Figure 2, B and D). One female was observed being eaten by a large cubera snapper (Lutjanus cyanopterus) while
the fish was being returned to the reef and one transmitter (in a male) failed to signal, therefore our sample size was reduced to 16 fish (9 female, 7 male).
Based on our results, movement to and from the spawning site in 2007 and 2008 is from the west, supporting previous research using a traditional mark-recapture study (Nemeth 2005, Nemeth et al. 2007). Six of seven males and two of nine females were detected briefly on receivers west of the aggregation site soon after spawning ended, presumably migrating in that direction to home territories. An additional two females were resident or semi-resident, with detections logged on the receiver at the spawning site year round. No fish were detected on receivers to the east until March 2008, well after the red hind spawning season ending (see below).
Detection of tagged red hind during and between monthly spawning events was limited to approximately 2.1 km² surrounding the primary spawning site (Fig. 2 B and D), suggesting that the red hind are relatively sedentary while at the spawning location. Ninety-six percent of all detections (>150,000) were recorded over consecutive hours and days on the spawning site receiver. However, the detection of tagged red hind within the detection radius of receivers was apparently limited, presumably because fish were traveling within the network of tunnels and crevices underneath the extensive area of plating Montastraea corals. Eight red hind moved out of the primary spawning area and were detected by receivers 0.5 to 5.8 km to the west without being detected by the overlapping curtain of receivers surrounding spawning area. As a result, our assessment of movement during and between spawning events may be an underestimation. During the 2008 season, three out of four males tagged in 2007 returned to the spawning site. No females tagged in 2007 were detected in 2008 (with the exception of the resident). Gender information from recaptures of red hind on the spawning aggregation site using traditional Floy t-tags has been limited (Nemeth et al, 2006a) however these data suggests that females may not return to spawn every year but only return every other year. This supports Nemeth (2005) who suggested that most females return every other year and that odd numbered years (i.e. 2007) represent a large cohort. This also suggests that future studies be of longer duration and use tags that have a lifespan of at least 3 years.
Based on our data, the size and orientation of the MCD is adequate to provide protection during migration to and from the spawning site as well as between and during spawning events. Although it appears that very little movement takes place once fish reach the aggregation area, the orientation of the marine reserve to the west ensures protection for migrating fish, especially large males. December is traditionally a month that local fishermen target migrating red hind south of St Thomas (Robert Vante, personal communication) so the boundaries of the MCD play an important role in the success of the marine reserve.
Of additional note is the detection of three red hind five km east of the MCD in March and April of 2008. These fish were detected around the Grammanik bank spawning aggregation site during the weeks of yellowfin and Nassau grouper spawning. Detections were limited (5-6 per fish), indicating the red hind were probably moving through the area, however they were not detected on the surrounding curtain arrays.
Nassau and yellowfin groupers on the Grammanik Bank: The primary spawning site of the Nassau and yellowfin groupers is on the western end of the Grammanik Bank, a 1.5 km² fishery closure. A total of 18 Nassau (9 female, 9 male) and 17 yellowfin (9 female, 8 male) groupers were tagged and passively tracked by an acoustic receiver array designed for these two species on the Grammanik Bank (Figure 2, A and C). Like the red hind, migration to and from the spawning site seems to be from the west with at least 56% of Nassau and 63% of yellowfin migrating in this direction.
Both the Nassau and the yellowfin’s main spawning aggregation are located over sparsely colonized hard-bottom habitat. Actual spawning takes place at dusk and after sunset, 6-12 days after the full moon. Leading up to spawning, both species utilize high coral cover linear reefs to the east as well as an extensive reef to the north, spending very little time over the hard bottom. As daylight diminishes (~3-4 pm), fish begin to congregate over the hard bottom and over the nearest high coral cover reef 100 m to the north-northeast. On multiple dives we observed a grouper ‘highway’, with fish moving primarily from the high coral cover reef to the main spawning site. During these times the fish are inside the Grammanik Bank closure boundaries and receive protection. However, the dense congregation of fish disperses after spawning and moves beyond the Grammanik Bank boundaries leaving them vulnerable to fishing pressures.
Movement of the Nassau and yellowfin between and during spawning events extends well outside the protection of the closure boundaries (Figure 3, A and B). We observed daily movements of both species of, at least, 4.6 km to the west and 3.5 km to the north with yellowfin grouper showing more extensive and frequent movements than Nassau grouper. We also found that both Nassau and yellowfin grouper utilize two primary migratory pathways along deep linear coral reefs which run between the Grammanik Bank and MCD closures. Nassau uses a pathway closer to the shelf edge whereas the yellowfin use a route 2 km to the north.
MCD Closure Boundary
Figure 3. Distribution of acoustic detections at each receiver (Year 2 array) on the Grammanik Bank for all tagged A) Nassau (n = 18) and B) yellowfin (n = 17).
Only two tagged yellowfin returned to the spawning aggregation for the second year; and like the red hind, only tagged males returned. Of the ten Nassau grouper tagged
in 2007, three returned again in 2008 to the spawning aggregation. Unlike the red hind and the yellowfin, both male and female Nassau returned in the second year. Additionally, three Nassau were detected on the Grammanik Bank throughout the year suggesting that they are residents.
Divers estimated the total fish abundance for the yellowfin and Nassau at the spawning site. Spawning population was best estimated during dives later in the day when fish formed a more dense aggregation over the hard-bottom and nearby reef. We estimated that the reforming Nassau grouper spawning population to be a max of 100-125 individuals. And although we have not observed actual spawning rushes of the Nassau, we have observed and documented many Nassau in spawning coloration and in small groups within the larger aggregation of yellowfin at sunset indicating their readiness to spawn. Maximum number of yellowfin grouper at the spawning site was estimated to be 1,100 in 2007 and 600 in 2008.
Our results show that the existing Grammanik Bank closure (1.5 km² area) provides protection for Nassau and yellowfin grouper 75% and 44% of the time, respectively, during the spawning season. If the Grammanik Bank boundaries are increased to 7.5 km² (Figure 4) and extended to the north and west to include the Nassau migration route, the level of protection would increase to 98% for Nassau and 82% for yellowfin. If we extend the northern boundary another 1 km north (11 km²) and include the yellowfin migration route we increase protection of aggregating groupers to 99% for Nassau and 97% for yellowfin (Figure 4). Based on Nassau and yellowfin spatial and temporal patterns of distribution and migration route we propose that the boundary for the Grammanik Bank be extended north and west to meet the existing MCD boundary lines (Figure 4) to provide maximum protection for these two valuable commercial species during the spawning season (February, March and April) while minimizing the area closed to commercial fishing. By increasing the size of the Grammanik Bank closure from 1.5 km² to 11 km², Nassau and yellowfin grouper would receive maximum protection during movements associated with their spawning aggregations and be safe from fishing mortality while migrating to and from the spawning site.
Figure 4. Identification of closure boundaries are in figure legend. Proposed Grammanik boundary 1 (hatch marks) is 7.5 km2 and increases protection for Nassau from 75% to 98% and for yellowfin from 44% to 82%. Proposed Grammanik boundary is 11 km2 and increases protection for Nassau from 75% to 99% and for yellowfin from 44% to 97%.
Objectives accomplished or not and why
Objective (1) Determine habitat use and spatial distribution patterns of red hind, Nassau and yellowfin groupers during their spawning aggregations. This objective has been met. Strategic placement of acoustic receiver arrays over two spawning seasons allowed us to successfully determine small-scale distribution patterns of all target species. However, the full range of distribution of these species was limited to the area of receiver coverage.
Objective (2) Identify the daily, monthly, and seasonal patterns of movement of target species for the duration of the spawning season. This objective has been met. Successful tagging of target species prior to their spawning times and strategic placement of acoustic receivers enabled us to determine movement patterns during and between spawning events. Degree of movement varied by species size; with red hind being the smallest and most sedentary and yellowfin grouper being largest and most mobile. The majority of
tagged yellowfin (63%) and Nassau (56%) also moved between the Grammanik Bank and the MCD on a regular basis.
Objective (3) Propose appropriate boundary closure areas to fully protect these three species on their spawning aggregations sites. This objective has been met. Based on results of this study we recommend that no change is needed to the Marine Conservation district (MCD) closure boundaries. The MCD is successfully protecting the red hind during migration to and from the spawning site as well as during the spawning events. Based on our acoustic data the existing Grammanik Bank closure (1.5 km²) provides limited protection for Nassau and yellowfin grouper. We propose to increase the size of the Grammanik Bank closure from 1.5 km² to at least 7.5 km² or preferably 11 km² and extend its boundaries northward and westward so that it is contiguous with the eastern edge of the MCD. The expansion of the Grammanik Bank closed area would encompass the majority of the daily movements and migratory pathways of Nassau and yellowfin groupers.
Discussion of project impacts and products
Our acoustic receiver array design allowed us to determine the spatial extent of the Nassau and yellowfin groupers in a way that could be used as a rapid scientific assessment of an aggregation of these fishes for managers when planning closure boundaries. To our knowledge no other acoustic tagging studies of fish has deployed receivers in expanding coverage around a spawning site. This method is an effective use of technology for quantitatively determining the relationship between area (e.g. km²) and the amount of protection given to a particular species. Secondly, very little is known and very little is published about the biology and reproductive behavior of yellowfin grouper and nothing published on their migration patterns. This study provides some of the first pieces of evidence of the movement, behavior and timing of yellowfin at a spawning aggregation.
In this study, the size of the fish and the habitat type were key factors in the success of detecting an acoustic tag. The deep, offshore coral reef banks, where the study took place, are composed primarily of large, plating Montastraea annularis coral that form an extensive network of tunnels and crevices underneath the plates of coral (Herzlieb et al. 2006). This allows smaller fish, including red hind, to seek shelter and presumably travel considerable distances. We believe that red hind were able to utilize this reef structure to avoid predation and travel, at least some distances, within this network of tunnels and crevices resulting in the loss of tag detection by the acoustic receiver. Although thousands of detections were made by the receivers allowing us to determine general movement patterns and spatial extent of the red hind, some fish were still able to ‘sneak’ by receivers. We were able to overcome this by deploying receivers in multiple curtains, one closely surrounding the primary spawning site and another, double-curtain, to the west to catch the red hind in their migration to and from the spawning site. This was only possible due to the contribution of 20 additional VR2 acoustic receivers provided by new collaborators. Unlike the red hind, the Nassau and yellowfin groupers are much larger and probably less vulnerable to predation and therefore less likely (or able) to travel
underneath the coral, making us confident that a Nassau or yellowfin would not be able to ‘sneak’ by an acoustic receiver.
The most important result of our study was to provide scientific data that quantified the degree of protection afforded to aggregating groupers by various sized closed areas. We also found that the majority of tagged groupers of both species utilized regular migration pathways that connected the Grammanik Bank and MCD. Based on our acoustic data, the existing Grammanik Bank closed area (1.5 km²) protects Nassau and yellowfin groupers only 75% and 44% of the time during their spawning aggregations. By expanding the Grammanik Bank closure approximately 2 km north and 3 km west to be contiguous with the MCD’s eastern boundary we would enclose the primary migratory pathway of Nassau grouper. This larger closed area (7.5 km²) would increase the level of protection for Nassau and yellowfin groupers to 98% and 82%, respectively. Expanding the northern boundary an additional 1 km northward would increase the closed area to 11 km², enclose the primary migratory pathway of yellowfin grouper and increase the level of protection to as much as 99% for Nassau and 97% for yellowfin grouper during the spawning season.
This acoustic tagging study allowed us to understand the patterns of movement and migration of aggregating groupers and to use this information to recommend biologically relevant boundaries that maximize the protection of Nassau and yellowfin groupers during their spawning aggregations. This information will directly benefit the management of commercially important grouper species by providing useful guidelines for the Caribbean Fisheries Management Council and the Virgin Islands Division of Fish and Wildlife in designing more effective fishery protected areas. This approach and these data may also be applicable for defining boundaries useful for protecting these species in other locations or other species which form spawning aggregations.
Conference presentations
Kadison E. R. S. Nemeth, J. Blondeau (2007) Using hydro-acoustic tagging to determine the minimum size of fishery closures for protecting grouper spawning aggregations in the USVI. 33rd Association of Marine Labs of the Caribbean Scientific Conference. June 4-8, 2007, St. Thomas USVI.
Nemeth, RS, J. Blondeau, E. Kadison, J. Calnan, T. Smith (2008) Determining the appropriate size of closed areas for protecting spawning aggregations of large groupers using hydro-acoustics. International Coral Reef Symposium. July 7-12, 2008. Ft. Lauderdale, FL USA.
Kadison, E., R. S. Nemeth, J. Blondeau (2008) Red hind spawning aggregations: movement and migratory patterns. 11th International Coral Reef Symposium. July 7-12, 2008. Ft. Lauderdale, FL USA.
Upcoming conference presentation
Nemeth, RS, E. Kadison, J. Blondeau, (2008) Defining marine protected areas for yellowfin and Nassau grouper spawning aggregation sites. Gulf and Caribbean Fisheries Institute. Nov 10-14, 2008. Guadeloupe, FWI.
Manuscripts resulting from this research being prepared for publication
Nemeth, RS, J. Blondeau, E. Kadison (in prep) Defining marine protected areas for yellowfin and Nassau grouper spawning aggregation sites. Conservation Biology (expected submission date December 2008)
Nemeth, RS, J. Blondeau, E. Kadison (in prep) Movement patterns, habitat use and migration pathways of yellowfin and Nassau grouper during spawning aggregations. Journal of Fish Biology (expected submission date February 2009)
Nemeth, RS, J. Blondeau, E. Kadison (in prep) Movement patterns, habitat use and migration pathways of red hind during spawning aggregations. Coral Reefs (expected submission date March 2009)
Recommendations
The results of this project produced clear results directly applicable to the management of Nassau and Yellowfin grouper on the Grammanik Bank. We recommend expanding the area of the Grammanik Bank closure from 1.5 km2 to 11 km2 with the northern boundary line moved about 3 km northward and the western boundary moved westward to make the Grammanik Bank closure contiguous with the eastern end of the MCD during the three month (Feb-Apr) spawning season (see Figure 4).
Bibliography
Appeldoorn, R.S. and K.C. Lindeman. 2003. A Caribbean-wide survey of marine reserves: spatial coverage and attributes of effectiveness. Gulf. Carib. Res. 14:139-154
Beets, J. and A. Friedlander. 1999. Evaluation of a conservation strategy: a spawning aggregation closure for red hind, Epinephelus guttatus, in the U.S. Virgin Islands. Envir. Biol. Fish. 55:91-98
Bohnsack, J.A. 1998 Application of marine reserves to reef fisheries management. Austral. J. Ecol. 23:298-304
Claro, R., K.C. Lindeman. 2003. Spawning aggregation sites of snapper and grouper species (Lutjanidae and Serranidae) on the insular shelf of Cuba. Gulf Carib. Res. 14:91-106.
Colin, P.L. 1992. Reproduction of the Nassau grouper, Epinephelus striatus, (Pisces:Serranidae) and its relationship to environmental conditions. Envir. Biol. Fish. 34:357-377.
Colin, P.L., D.Y. Shapiro and D. Weiler. 1987. Aspects of the reproduction of two groupers Epinephelus guttatus and E. striatus in the West Indies. Bull. Mar. Sci. 40:220-230.
Cummings, N.J., M.L. Parrack, and J.W. Zweifel. 1997. The status of red hind and coney in the U.S. Virgin Islands between 1974 and 1992. Proc. Gulf Carib. Fish. Inst., p 354-397
Herzlieb, S., E. Kadison, J. Blondeau and R. S. Nemeth (2006) 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. Proc. 10th International Coral Reef Conference, Okinawa, Japan. 4:1144-1151.
Holland K.N., J.D. Peterson, C.G. Lowe, and B.M. Wetherbee. 1993. Movements, distribution and growth rates of the white goatfish Mulloides flavolineatus in a fisheries conservation zone. Bull. Mar. Sci. 52:982-992.
Meyer, C.G., K.N. Holland, B.M. Wetherbee, and C.G. Lowe. 2000. Movement patterns, habitat utilization, home range size and site fidelity of whitesaddle goatfish, Parupeneus porphyreus, in a marine reserve. Env. Biol. Fish. 59:235-242.
Nemeth, R.S. 2005. Population characteristics of a recovering US Virgin Islands red hind spawning aggregation following protection. Mar. Ecol. Prog. Ser. 286:81-97.
Nemeth, R.S., S. Herzlieb, S., J. Blondeau (2006a) Comparison of two seasonal closures for protecting red hind spawning aggregations in the US Virgin Islands. Proc. 10th International Coral Reef Conference, Okinawa, Japan. 4:1306-1313.
Nemeth, R.S., E. Kadison, S. Herzlieb, J. Blondeau and E. Whiteman (2006b) Status of a yellowfin grouper (Mycteroperca venenosa) spawning aggregation in the US Virgin Islands with notes on other species. Proc. 57th Gulf Carib Fish Inst. St. Petersburg, FL. 57:543-558.
Nemeth, R. S., J. Blondeau, S. Herzlieb and E. Kadison. (2007) Spatial and temporal patterns of movement and migration at spawning aggregations of red hind, Epinephelus guttatus, in the U.S.Virgin Islands. Environmental Biology of Fishes 78(4):365-381
Olsen D.A. and J.A. LaPlace 1978. A study of Virgin Islands grouper fishery based on a breeding aggregation, Proc. Gulf Carib. Fish Inst, 131:130-144
Sadovy, Y. 1994. Grouper stocks of the western Atlantic: the need for management and management needs. Proc. Gulf Carib. Fish Inst, p 130-144
Sadovy, Y. and M. Figuerola. 1992. The status of red hind fishery in Puerto Rico and St. Thomas, as determined by yield-per-recruit analysis. Proc. Gulf Carib. Fish Inst, p 23-38
Sadovy, Y., M. Figuerola, and A. Roman. 1992. Size and growth of red hind Epinephelus guttatus in Puerto Rico and St. Thomas. Fishery Bulletin 90:516-528.
Sala E., E. Ballesteros, R.M. Starr. 2001. Rapid decline of Nassau grouper spawning aggregations in Belize: fishery management and conservation needs. Fisheries 26:23-30
Sluka R, K.M. Chiappone, K.M. Sullivan, and R. Wright. 1997. The benefits of a marine fishery reserve for Nassau grouper Epinephelus striatus in the central Bahamas, 8th Inter Coral Reef Sym, p 1961-1964
Tobias, W. (1997) Three year summary report: Cooperative Fishery Statistics Program. Report No. SF-42 (NA27FT0301-01), National Marine Fisheries Service, St. Petersburg, FL, p 40
Tucker, J.W., P.G. Bush and S.T. Slaybaugh. 1993. reproductive patterns of Cayman Islands Nassau grouper (Epinephelus striatus) populations. Bull. Mar. Sci. 52:961-969.
Whiteman, E.A., C.A. Jennings and R.S. Nemeth. 2005. Reproductive characteristics of a red hind (Epinephelus guttatus) spawning aggregation: applying ultrasound imaging for population assessment. J. Fish. Biol. 66:983-995.
Zeller, D.C. 1998. Spawning aggregations: patterns of movement of the coral trout Plectropomus leopardus (Serranidae) as determined by ultrasonic telemetry. Mar. Ecol. Prog. Ser. 162: 253-263.
Zeller, D.C. 1999. Ultrasonic telemetry: its application to coral reef fisheries research. Fish. Bull. 97:1058-1065.