Presentation on theme: "Status of a Mutton Snapper (Lutjanis analis) Spawning Aggregation off St. Croix, U.S. Virgin Islands Barbara L. Kojis, Norman J. Quinn and Liam Carr Acknowledgements."— Presentation transcript:
Status of a Mutton Snapper (Lutjanis analis) Spawning Aggregation off St. Croix, U.S. Virgin Islands Barbara L. Kojis, Norman J. Quinn and Liam Carr Acknowledgements to Master Fisher – Gerson Nicky Martinez
Questions addressed by this study What is the status of the mutton snapper spawning aggregation? What are the some of the life history characteristics of the St. Croix mutton snapper Where and when do juvenile mutton snapper recruit on STX? How accurate were the habitat maps for the Mutton Snapper Closed Area? What corals and other invertebrates characterize the habitat? What types and how many fish were found in the different habitats in the Mutton Snapper Closed Area?
Background Mutton snapper, virgin snapper, or sama (Lutjanus analis) aggregate to spawn around the full moon in the spring in the southwest of St. Croix. Fishers traditionally targeted the spawning aggregation at night using handlines. Catches could be high - a fisher might harvest over 100 mutton snapper in a single night. Loss of a Nassau grouper spawning aggregation on St. Thomas focused fisher and management authority attention on protecting spawning aggregations. Local and federal agencies became concerned about the loss of the mutton snapper aggregation to fishing and implemented regulations to protect it.
Mutton Snapper Spawning Aggregation Protected The Mutton Snapper Seasonal Closed Area was established in 1993 by the Department of Commerce on the recommendation of the CFMC and 1994 by US VI government. All harvest of fish within the closed area was prohibited from 1 Mar – 30 Jun each year Mutton Snapper Closed Area
Further protection of the spawning aggregation Problems with Closed Area Enforcement of the closed area was difficult because the site was offshore and fishing occurred at night. Some fishers continued to fish within the closed area during the closure. Fishers also likely legally fished the aggregation by fishing just outside the closed area. Mutton snapper seasonal closure implemented Enacted 2005 (federal waters) and 2006 (territorial waters). Prohibits harvest and possession of mutton snapper and lane snapper from 1 April – 30 June each year. Mutton Snapper Closed Area
What is the status of the mutton snapper spawning aggregation protected by the CFMC and the VI Government? Can mutton snapper still be caught at traditional fishing sites in the closed area? What is the catch per unit effort at traditional fishing sites during the presumed peak spawning period – when the seasonal closure is in effect? Where do mutton snapper aggregate to spawn? How many and what size are the fish in the aggregation?
Fished within the MSCA to confirm the existence of the spawning aggregation and to obtain CPUE Relied on expert fishers who knew the best techniques for catching mutton snapper and knew where and when to catch them inside the Mutton Snapper Closed Area (MSCA). Fished the aggregation during April, May and June before and after the full moon using 50 – 100 lb line, generally without any weights, with single hooks and round robin (scad) for bait. Also, chummed periodically. Fishing usually commenced at sunset and continued for 4 – 6 hrs or until coolers were full or quota was met. Gerson Nicky Martinez
Success ! Expert fishers Maximiliano Valasquez and Liam Carr
Catch per Unit Effort (CPUE) – Mutton Snapper (MS) and all fish caught
Diving fishing sites to detect mutton snapper Fishing boat anchored at fishing site in late afternoon. Divers dived from boat just before and at dusk in April, May and June to search for spawning aggregations. A maximum of one or two mutton snapper were seen on each dive. On most dives no mutton snapper were seen. Visibility in 2009 was poor – Orinoco River Plume reached STX No spawning aggregations of mutton snapper seen.
Dedicated mutton snapper searches In 2009 and 2010, we dived the outer third of the shelf – within and adjacent to the Mutton Snapper Closed Area in May and June 2009 and May, June and July Diving was conducted in the mid to late afternoon primarily 1 – 5 days after full moon, the time of day mutton snapper spawned in Belize. None to a few mutton snapper were seen on the dives.
Possible reasons for not finding the aggregation. Mutton snapper aggregation forms only later in the lunar month. The aggregation forms in deepwater off the shelf. However, we dived to a depth of at least 95 ft and could see large fish to depths of at least 150 ft. So this is unlikely. Aggregation forms outside the Mutton Snapper Closed Area – most likely scenario. We visited a site that Martinez showed us that had large aggregations of fish of different species and which was geomorphologically similar to other known snapper spawning sites. Martinez had seen mutton snapper aggregating at this site in the past and he saw mutton snapper aggregating in the distance when we visited the site.
What is the reproductive status of the fish we caught? Fish were measured, weighed, and gonads removed, identified as to sex, and weighed.
What was the ratio of males to females caught in the MSCA? Sex ratio: 2.3 males to 1 female MonthMaleFemaleSex Ratio April May June Total Table 1.2 Ratio of number of male to number of female Lutjanus analis caught in Mutton Snapper Seasonal Closed Area during the area and seasonal closures in 2009.
Sizes of female and male fish caught in the Mutton Snapper Closed Area The total size range of males and females was similar. Males had a higher proportion of small individuals to large. Females had a larger proportion of large individuals. Size at L m50 (50% of fish are reproductive) was approximately 39 cm. Females appear to mature at a larger size than males. Reproductive females ranged in size from 39.3 – 63.5 cm Males from 36.7 – 66 cm.
Reproductive Index – Gonad Somatic Index Ratio of gonad weight to total fish weight Mean gonad somatic index (GSI) (gonad weight (g)*100/weight of fish (g)) with Standard Error bars.
Mutton snapper are batch spawners Confirmed by size distribution of eggs in ovaries
Evidence for batch spawning in mutton snapper Sample of eggs from an ovary showing size range of eggs. No hydrated eggs were observed. Size distribution of eggs from fish caught 11 May 09.
What does batch spawning mean? Batch spawners release eggs in batches over a period of days or months with only a portion of the yolked eggs spawned in each batch The fish can release eggs over a number of days during just one month of the spawning period. Or a fish may release eggs over a number of days each month and/or over several months of the spawning period. We know that mutton snapper are batch spawners, we dont know if an individual fish spawns in only one month of the spawning period or for more than one month.
Why is this important? If we want to estimate the size of the spawning population from counts of fish, we need to know the annual frequency of spawning. Do fish spawn only in one month each year? Then we can count fish each month in the spawning aggregation and add up all the months to estimate the number of reproductive fish aggregating at that location. Do individual fish spawn every month during the spawning season? Then we can count the fish during a single aggregation event and that should represent all the fish spawning at that aggregation site. However, it may be more complicated. Is there a size relationship that influences the number of months a fish spawns? Do large fish spawn more months than small fish? Do small fish only spawn once? We can use the sex ratio of catches from the aggregation to estimate the size of the female population.
Status of aggregation Fishing CPUE and analysis of gonads indicate that reproductively mature fish are still migrating to the SW of STX presumably to aggregate to spawn in the area. Observation of a spawning aggregation of mutton snapper at a reef outside the MSCA suggests that the fish are aggregating outside the closed area. The maximum size fish caught was 66 cm for males and 63.5 cm for females. Mutton snapper grow to at around 90 cm (SCRFA website). The maximum weight of the fish we caught was 5.85 kg for females and 5.73 kg for males. Mutton snapper can grow to 15 kg (SCRFA website). Our sample size was small (127 fish) but it appears that large fish are missing from the spawning population. Because we didnt find the aggregation we dont know the size of the aggregation.
Genetic analysis of mutton snapper from SW St. Croix (Gold pers. Com.) Tissue samples of mutton snapper caught from April – June 2009 were provided to John Gold of Texas A & M University for genetic analysis. He looked at the effective population size of mutton snapper at different locations. Effective population size (N e ) is defined as the average number of individuals in a population that actually contribute genes to succeeding generations. He found that the effective population size of mutton snapper on STX N e or 341 was below 500 or greater. This is the size needed to maintain adequate genetic variability in the population. S ITE NeNe L OWER 95% CI U PPER 95% CI St. Croix St. Thomas PR-East PR West Florida Keys Mutton snapper aggregation on STX is on the leeward side of the island. Leeward island sites tend to retain larvae and have less larval immigration from other sites. Limited larval immigration into St. Croix waters from outside could impede recovery if the spawning aggregation becomes depleted.
Where are the juvenile mutton snapper What habitats do the mutton snapper juvenile recruit to on St. Croix?
Are mutton snapper juveniles found in the backreef embayments in the East End Marine Park?
Juvenile lane, mahogony, yellowtail and schoolmaster snapper were observed in Chenay Bay and Robin Bay. No mutton snapper juveniles A few mutton snapper recorded in studies by Mateo and Tobias 2001 & 2004 and Adams and Ebersole 2002.
Large schools of snapper, primarily lane snapper were found in eroded beachrock habitat south of Frederiksted. No mutton snapper seen. St. Thomas – rocky shoreline Mutton snapper juvenile – Jan 2011 Lane snapper juvenile – Jun 2011 July Frederiksted
Conclusion The mutton snapper closed season which prohibits the harvest and possession of mutton snapper needs to remain in effect while the aggregation rebuilds. Compliance with regulations appears to be very good. Enforcement is much easier because it can be done on land. Mutton snapper likely do not aggregate within the closed area. Reverting to just the closed area will not protect the mutton snapper spawning aggregation. It protects any other mutton snapper aggregation on STX. The aggregation should be found and monitored on a regular basis.
ACKNOWLEDGEMENTS We relied heavily on the fishing knowledge of Gerson Martinez and Maximiliano Valasquez. We could not have accomplished this work without the competent boat handling, diving, and marine safety skills of Captain Gerson Martinez and Salvadore Martinez – Corcino. We would also like to thank Nicky Martinez, Jr. for his assistance on the boat and expert fishers: Carlos Farchette, and Edward Schuster. Funding from Caribbean Fisheries Management Council / Coral Reef Conservation Grant Program Division of Fish and Wildlife and NOAA NMFS are gratefully acknowledged for the research permit.