by
Fisheries Management Division
Southeast Regional Office
National Marine Fisheries Service
9450 Koger Boulevard
St. Petersburg, Florida, USA
Figure 1
INTRODUCTION
The Magnuson Fishery Conservation and Management Act provides for exclusive United States management authority over the fishery resources of the Gulf of Mexico (Figure 1), within a fishery conservation zone (FCZ) extending from the seaward boundary of the United States territorial sea (3 nautical miles for the Gulf of Mexico States of Louisiana, Mississippi and Alabama, and 9 nautical miles for Texas and the west coast of Florida) to a point 200 miles from shore. Responsibility for developing a shrimp fishery management plan for the Gulf of Mexico is vested in the Gulf of Mexico Fishery Management Council (GMFMC); and implementation and enforcement of any regulations pertinent to the management of fisheries within the FCZ are the responsibility of the Secretary of Commerce and the US Coast Guard.
One of the management strategies proposed in the plan was to reduce growth over-fishing 1 through closing selected areas to fishing. These closed areas were designed to increase the total weight and value realized from the shrimp fishery. This paper presents a discussion of the results obtained from two years of managing the shrimp resource.
THE GULF OF MEXICO
The Gulf of Mexico is a large embayment of the Atlantic Ocean that is almost surrounded by the United States and Mexico. The Gulf forms a huge ocean basin that covers nearly 700,000 square miles (1,800,000 square kilometres). It is 800 miles (1,300 kilometres) long on the north-south axis and 1,100 miles (1,770 kilometres) wide on the east-west axis. The Yucatan Channel connects the Gulf of Mexico with the Caribbean Sea and the Straits of Florida join it to the Atlantic Ocean.
The low level coastline of the Gulf of Mexico is about 3,000 miles (4,800 kilometres) long. It has hundreds of lagoons and many salty marshes bordered by sand bars. The water of the Gulf is deepest (12,700 ft or 3,871 m) near the coast of Mexico, while depths in other areas range upwards to about 10,000 ft (3,080 m). The Yucatan Channel and the Straits of Florida are not nearly so deep. The Gulf has many shallow areas with gently sloping beds formed by siltation.
THE FISHERY
Annual harvests of shrimp consistently lead the nation's fisheries in terms of ex-vessel value. In 1981, total US commercial landings for all fisheries were 5.98 billion pounds (heads on) valued at $463.4 million. The Gulf of Mexico shrimp fishery accounted for about 75.6 percent of the total shrimp landings. Shrimp landings in the Gulf amounted to about 16.8 percent of the total ex-vessel value for all US fisheries and 86.6 percent of total shrimp value.
The fishery is probably the most diverse in the nation. Harvesters include: (i) a large commercial fleet fishing the inshore, coastal and open Gulf waters, (ii) an undetermined (but large) number of recreational shrimpers, mainly fishing the inshore and nearshore Gulf waters, and (iii) a substantial number of bait shrimpers, mainly fishing the inshore waters. In all, about 9,000 boats and vessels participate in the fishery in the Gulf.
The fishery is based on six species occurring in the area of concern to the GMFMC, as well as in the adjacent territorial seas and associated bays, inlets and wetland areas. Species included are brown shrimp (Penaeus aztecus Ives), white shrimp (Penaeus setiferus Linnaeus), pink shrimp (Penaeus duorarum Burkenroad), royal red shrimp (Hymenopenaeus robustus Smith), seabobs (Xiphopeneus kroyeri Heller), and rock shrimp (Sicyonia brevirostris Stimpton). The latter three species are, for the most part, taken as incidental by-catch. The management plan addresses the fishery throughout its range; however, Federal regulations are implemented only in the FCZ.
None of the stocks appear to be biologically over-fished. Major concerns for the future are related to the preservation of adequate habitat, particularly for the estuarine-dependent brown, white and pink shrimps, which account for approximately 98 percent of the total annual shrimp harvest.
The biological characteristics which affect sustainable yields for penaeid shrimp are unique. They are an annual crop; very few individuals live a year and the majority harvested are less than six months old. There is no demonstrable stock-recruitment relation and recruitment over-fishing, given present fishing technology, may be unlikely. That is, it may not be economically or technically feasible to take so many shrimp that the supply for the following years is affected. Because of these characteristics, fishing mortality in one year does not determine yield in the following year. The maximum sustainable yield (MSY) in number for a given year is considered to be all the shrimp available to harvest, using current fishing technology.
Growth over-fishing is caused by taking the available recruits at too small a size. If growth over-fishing is occurring, allowing additional time for growth will permit taking a greater total yield in weight, although the total number of individuals will be less. Effort in the fishery has been increasing rapidly and it is probable that the total yield of penaeid shrimp could be increased if the average size taken were larger.
The abundance (number of recruits) and therefore yield and catch per unit effort vary greatly from year to year, depending on environmental conditions (especially temperature and salinity) in the estuarine nursery areas. This is evident when regression coefficients for different models are compared. For example, linear regressions of catch on effort showed that effort alone explained only 38 percent of the variation in catch of white shrimp off Louisiana and 57 percent of the variation in brown shrimp catch in the Gulf. Multiple regressions including environmental parameters explained 89 percent and 88 percent of the variation in catch, respectively. For brown shrimp, the environmental model predicts that, at a fishing effort of 100,000 units (essentially the record until 1976), annual catch would vary from 57 to 88 million pounds, provided temperature and salinity ranged within levels reported for the period 1963–1975. If environmental conditions were more favourable, a greater yield would be expected.
MANAGEMENT
The goal of the plan is to manage the shrimp fishery of the Gulf of Mexico to attain the greatest overall benefit to the nation, with particular reference to food production and recreational opportunities. Problems, objectives and management measures to achieve the goal of the fishery follow:
Problems:
Conflict among user groups as to area and size at which shrimp are to be harvested.
Discard of shrimp through the wasteful practice of culling.
The continuing decline in the quality and quantity of estuarine and associated inland habitats.
Lack of comprehensive, coordinated and easily ascertainable management authority over shrimp resources throughout their range.
Conflicts with other fisheries such as the stone crab fishery in southern Florida, the groundfish fishery of the north-central Gulf, and the reef fish fishery.
Incidental capture of sea turtles.
Loss of gear and trawling grounds due to man-made underwater obstructions.
Lack of basic data needed for management.
Objectives:
Optimize the yield from shrimp recruited to the fishery.
Encourage protection measures to prevent undue loss of shrimp habitat.
Coordinate the development of shrimp management measures by the GMFMC with shrimp management programmes of the several states, where feasible.
Promote consistency with the Endangered Species Act and the Marine Mammals Protection Act.
Minimize the incidental capture of finfish by shrimpers, when appropriate.
Minimize conflicts between shrimp and stone crab fishermen.
Minimize adverse effects of underwater obstructions to shrimp trawling.
Provide for a statistical reporting system.
Figure 2 Location of Tortugas Shrimp Sanctuary
Figure 3 Seasonal closure to shrimping off the State of Texas
In order to obtain the above objectives, the following management measures and recommendations were adopted:
Management measures:
Establish a cooperative permanent closure with the State of Florida and the US Department of Commerce of an area off Florida (Figure 2), to protect small pink shrimp until they leave the closed area where they generally have reached a size range larger than 69 tails to the pound.
Establish a cooperative closure of the territorial sea of Texas and the adjacent US FCZ (Figure 3), with the State of Texas and the US Department of Commerce, during the time when a substantial portion of the brown shrimp in these waters weigh less than a count of 65 tails to the pound (39 heads-on shrimp to the pound).
Consistent with the Stone Crab Management Plan, establish a seasonal closure of a portion of the Dry Tortugas shrimp grounds, in order to avoid gear conflicts with stone crab fishermen.
All statistical reporting requirements will be mandatory.
Management recommendations:
Recommend that all Gulf states consider establishing shrimp management sanctuaries in important segments of nursery grounds under their sole jurisdiction. The GMFMC has established an internal committee to review and assess the status of Gulf fishery habitats, with particular attention to those factors which might further stimulate “the downward trends in quality and quantity of fish habitats”.
The Gulf states are encouraged to adopt flexible management procedures which would provide regulation by administrative agencies of the shrimp resources in inland waters and territorial seas.
The Gulf states are encouraged to adopt reciprocal internal management decisions flexible enough to allow joint management of shrimp with other states and with the Department of Commerce.
Develop and implement educational programmes to inform shrimpers of the current status of sea turtle populations and of proper methods for resuscitation and return to the sea of incidentally captured sea turtles.
Encourage research on development of shrimping gear in order to reduce the incidental catch of finfish without decreasing the overall efficiency of shrimping or excessively increasing the cost of gear.
The GMFMC will attempt to reduce, where feasible, the loss of offshore trawlable bottom by establishing within their Council a committee to monitor and review construction of offshore reefs, with attention to the needs of the reef fish and shrimp user groups.
OPERATION
The ten management measures and recommendations which describe the management strategy were transposed into an operation plan to facilitate implementation and monitoring. Twenty-four actions were identified as being necessary in order to accomplish the stated goals. They involved actions in the broad areas of regulation, state cooperation, research, development, enforcement, data systems and habitat, and environment conservation. A time schedule for the actions was established, with some of the long-range research programmes requiring up to five years to accomplish.
DISCUSSION OF AREA CLOSURES
A major management objective is directed at reducing growth over-fishing. The strategy employed involved establishing a shrimp sanctuary off south Florida and a seasonal closure off Texas. The theory behind these closures was simply that, if the shrimp were protected from fishing mortality for some period of their lives, they would grow to a larger and more desirable size. The harvesting of these larger shrimp produces a greater weight, a higher catch per unit effort, and the value of the shrimp increases.
In determining the type of closures to invoke, several factors were considered. The fishery off Texas is a brown shrimp fishery, with recruitment and migration offshore occurring in a short predictable period of time, thus a 45 to 60 day seasonal closure was selected. In the area of the Northern Gulf, there is a strong market for small shrimp and a desire by fishermen to harvest those small shrimp; no closure was designed for that area. Recruitment of pink shrimp off Florida seems to fluctuate throughout the year and cannot be predicted, so the establishment of a permanent sanctuary was selected to provide the most benefit.
The establishment of the Tortugas shrimp sanctuary, a permanent closed area off south Florida, is presumed to have provided positive benefits, although several years of data will be necessary to fully evaluate the closure. Size and frequency distribution data collected within and around the closed area for a period of about one year generally demonstrate the utility of the closed area, because shrimp within the area are mostly too small (less than 103 mm) to optimize production.
However, analysis of the closure has surfaced a question concerning migration patterns which could have significant impact on evaluating the benefits of the closure. The scientific data which are available, although weak, indicate that shrimp migrate from the sanctuary into fishable areas. However, fishermen believe that shrimp migrating from a portion of the sanctuary mostly enter areas which are non-fishable because of coral and other obstructions and are thereby lost to the fishery. If these shrimp migrate into this non-fishable area, the benefits from the closure would be reduced.
To determine the migratory pattern of shrimp from this area of the sanctuary, a concentrated mark and recapture study was begun in November 1982. This study will last from one to two years and provide a major part of the information necessary for a thorough evaluation of the closure.
The seasonal closure of the FCZ off Texas has been in effect for two seasons and its impacts have been measured. This closure is designed to be concurrent with the closure of the Territorial Sea (water controlled by the State of Texas, from the beach out to nine nautical miles). The closure is usually in effect from 1 June until 15 July of each year; however, there is up to 15 days' flexibility on either end of the period. Thus, the actual period of the closure will range from 45 to 60 days. A sampling programme to determine the size of the shrimp within the internal waters of Texas is the basis for setting the period of closure for both the FCZ and the State Territorial Sea.
Texas has seasonally closed its Territorial Sea since 1959 but the seasonal closure of the FCZ has been in effect only in 1981 and 1982. In evaluating the impact of the closure, only the area in the FCZ was considered; although the closure of the Territorial Sea provides additional benefits, perhaps even greater than the closure of the Federal Zone.
In order to evaluate the effects of the closure, research vessels sampled shrimp populations in the closed area from May to July in 1981, to estimate the magnitude and size composition, as well as temporal changes, of the shrimp population in the closed area. In addition, data on fishery activities (catch, effort and location of fishing) were collected for the entire Gulf by interviewing dealers and selected fishermen. At-sea observers on shrimp vessels, in the course of other duties, collected data on magnitude and species composition of the incidental catch of fish in both closed and open areas. Finally, data were collected to measure the impact of the closure on shore facilities and processors. Both the impact on facilities outside the areas, from boats migrating elsewhere during the closed period, and also local impact upon opening the area were measured. The research was designed to answer a set of management questions formulated in consultation between fishery scientists and fishery administrators.
The topics covered and answers provided for the 1981 study follow:
Abundance of shrimp in the area during the time it was closed:
The closure was effective in protecting juvenile shrimp in the closed area. Recruitment to the FCZ closed area in 1981 was strong and shrimp in the area during the closed period are estimated to have increased in weight approximately 78 percent. Although recruitment to the area was strong, it does not satisfactorily account for the highly successful July-August fishery off Texas. In particular, observed catches and catch rates offshore of Texas were higher than would have been predicted from existing recruitment indices based on historical data.
Quantity and value of brown shrimp harvested by the regulated fishery compared with amounts that would have been taken had the fishery not been regulated:
Because of excellent Gulf-wide recruitment and protection of shrimp off Texas, catches in 1981 were at record levels. The June through August catch was 25 million pounds off Texas and 18 million pounds off Louisiana. In 1977, the best year of the 1976–80 period, catches were 19 million pounds off Texas and 18 million pounds off Louisiana. The closure is estimated to have increased the harvest in the Gulf offshore brown shrimp fishery from a probable 61 million with no closure to an actual catch of 65 million pounds with closure, a 4 million pound (7 percent) gain. The effect of the closure was valued at an increase of 9.4 million ex-vessel dollars.
Changes in fishing patterns and use of shore facilities that resulted from the closure:
The pattern of fishing effort in 1981 was significantly different from that observed in 1980. However, declines in catch rates resulting from this different distribution of fishing activity and from possible concentration of effort were not obvious.
The disruption of historic seasonal fishing patterns, resulting from the closure, had two effects on shore facilities - one anticipated and one unanticipated. The anticipated effect was that, because of the closure, some vessels which had historically fished in the area migrated into other areas in 1981. Although this migration was extensive and some of these vessels landed their catch in different ports, the shift in landings was not large enough to have any detrimental effect on shore facilities.
An unanticipated effect was the large amount of landings at Texas ports, after the area was opened, which resulted in difficulties in processing the catch. Vessels were delayed in unloading and, on several occasions, landings had to be trucked to other localities for processing. These difficulties occurred mainly near the opening of the fishing season and were exaggerated by bad weather that caused many of the vessels to land catches at the same time. After these initial problems, additional personnel were hired to process the larger catches and no major difficulties occurred.
Other possible effects on the resource and fishery (by-catch):
Cessation of trawling for 55 days followed by very intensive fishing conceivably could have affected the numbers of shrimp predators as well as the number of shrimp; however, no changes in the amount of fish taken incidentally were apparent.
Discarding of shrimp was not a major difficulty, although some were discarded from the catches when fishing resumed. This practice reportedly occurred because the crews could not process the large catches that were brought aboard the vessels, and the problem was quickly resolved by hiring additional persons to work on the vessels.
Conclusions from the 1981 study were that the Texas closure provided a benefit by increasing the overall yield and value of the brown shrimp fishery in the Gulf. The benefits were large because of the high level of recruitment experienced in 1981. It appears from the estimates that the overall economic gains substantially outweighed any losses resulting from price, a decline due to increased supply. Although not quantified, benefits undoubtedly resulted from increased employment in both the processing and harvesting sectors of the fishery. The change in fishing patterns clearly affected the density of shrimp populations; however, effects on organisms associated with shrimp, which probably occurred, were not obvious.
A study of the results of the second year of the closure (1982) presented a somewhat different picture. Again, for the 1982 season, a set of management questions were presented and a research and data collection system was designed to answer these questions. Following are the questions and their answers as defined by an analysis of the preliminary data.
What was the abundance of brown shrimp in the Northern Gulf of Mexico during the 1982 closure period compared to 1981?
Two factors made the impacts of the Texas closure much different in 1982 from those in 1981. The first was that recruitment was estimated to be 22 percent lower in 1982 than in 1981. The second factor was that shrimp did not migrate as far offshore in 1982 as they did in 1981. In 1982 recruits were distributed inside 20 fathoms off Texas, whereas in 1981 recruits extended out to 35 fathoms. Fewer shrimp were available for harvest in 1982, especially in the FCZ. Cruise surveys show that this low abundance was generally Gulf wide.
What was the catch upon opening the closed area?
Because of below average recruitment, catches in 1982 were much lower than in 1981. Offshore catches from the closed area during the period 15 July through August were down 45 percent from 1981.
What were the biological impacts of the 1982 closure?
Simulation models, yield per recruit models and catch data were analysed for 1982 to determine the impacts of the closure. The results of these studies were consistent and indicated that biological impacts were of a magnitude below detectable levels, given the precision of the modelling technique. Thus, the closure of the FCZ, with no consideration of the closure of the State's waters for 1982, provided no detectable benefit or loss. However, it appears that, if the closure of both the Federal and State waters were considered, positive benefits could have been detected. A study of the combined effects of the closure of both the Federal and State waters will be done in 1983.
What were the estimated economic benefits of the 1982 Texas Closure?
No detectable change in landings can be attributed to the closure; thus, no change in price or value is assumed.
Were there operational problems at Texas ports resulting from the closures in 1981 or 1982?
There was little or no discarding of shrimp reported in 1982. No market problems were reported in 1982. In 1981, as a result of very heavy production upon opening the area, some short-term gluts were reported by processors in Texas. There was no detectable shift in fishing patterns between States in 1982 from that experienced in 1981.
CONCLUSION
The shrimp fishery has been under management for about two and a half years. A complete evaluation of the management regime will require several more years. However, a major component of the management strategy is the seasonal closure off Texas, and some basic conclusions are evident from studies of the two closures to date. It appears that, because shrimp are an annual crop and their abundance is determined primarily by environmental conditions, the impact of a seasonal closure can range from very beneficial to non-detectable. During years of good recruitment, such as 1981, the seasonal closure provided excellent gains both in terms of number of pounds landed and value of the harvest. In years of low recruitment, such as 1982, benefits derived from the closure seem to be reduced. With several years of data, it may be possible to model the closure and predict those years in which benefits are expected. If this is possible, a more efficient closure can be established.
The seasonal closure, as well as all aspects of the shrimp management regime, will be continued for 1983, with its effects being monitored and refinements of management strategies made. In the short period of time that management has been in effect, major benefits have been observed with only minor losses being incurred.
Studies are currently being pursued to further evaluate the effects of closing the Tortugas Sanctuary off South Florida. Shrimp migratory patterns in this area are poorly defined, and could have considerable impact on the benefits derived from this permanent closure. Mark-recapture studies should provide insight into whatever modifications might be needed to improve the management strategy in this area.
