FI:TCP/BHA/4453 TECHNICAL COOPERATION PROGRAMME MANAGEMENT OPTIONS FOR THE THE BAHAMAS Terminal Statement the Food and Agriculture Organization of the United Nations Rome, 1998 |
FI:TCP/BHA/4453 TECHNICAL COOPERATION PROGRAMME MANAGEMENT OPTIONS FOR THE THE BAHAMAS Terminal Statement the Food and Agriculture Organization of the United Nations Rome, 1998 |
2.1 Assessment of the status of exploitation of the spiny lobster fishery
2.2 Minimum size determination
2.4 Proposed long-term spiny lobster stock assessment activities
Appendix DOCUMENTS PREPARED DURING THE PROJECT
Fisheries play an important part in the economy of the Bahamas and the Bahamian way of life. The fishing industry has a potential for growth if the natural resources available are efficiently utilized. In 1993, total earnings in the fishing industry were in excess of $B 57.8 million, of which $B 48.9 million were earned from exports, mainly of spiny lobster (Panulirus argus), which are abundant and among the principal categories of fishery resources. Since 1992, a steady increase in marine resources production, principally in the harvesting of lobster resources, has been observed. Currently, a fleet of approximately 320 vessels greater than 20 feet in overall length is engaged in commercial lobster fishing, annually landing over 5 million pounds of tails.
The Government of the Bahamas has announced policy initiatives to increase the level of employment in the fishing industry and to raise revenue earnings. However, a primary focus of these initiatives is the conservation and proper management of marine resources, with an emphasis on lobster fishery. The Government has already sought to implement strategies focusing on the importance of a rational approach to expansion in the fishing industry as a whole.
As part of its plans to expand the fishing industry, and thus the spiny lobster harvest, the Government decided that it was necessary to define a minimum size for the capture of spiny lobsters in order to maximize and sustain yield.
FAO assistance was therefore requested through the Technical Cooperation Programme to assist the Ministry of Agriculture and Fisheries to formulate a sound technical and scientific framework for fishery management of spiny lobster resources in the Bahamas and to identify the key issues in fisheries research for the long-term financing of comprehensive lobster resource assessments.
The "Management Options for the Spiny Lobster Fishery" project was scheduled to start in January 1995, with an FAO contribution of $US 95 000 and a scheduled duration of one year. The Project Agreement was signed on 6 January 1995. The Department of Fisheries (DOF) of the Ministry of Agriculture and Fisheries was designated the counterpart agency responsible for project implementation. The project began on 8 May 1995 and ended on 30 March 1996.
Technical assistance was provided by a fish population dynamics and fishery stock assessment specialist and a bioeconomist.
The objectives of the project were:
- to develop and recommend minimum-size management options for the spiny lobster fishery, based on several exploitation levels and their impacts on the potential yield of the spiny lobster;
- to update information on the cost of capturing and shipping spiny lobsters from outlying islands;
- to develop a proposal for a long-term plan to carry out comprehensive spiny lobster assessments;
- to train personnel at the DOF in simulation modelling, stock assessment, management strategies, sampling design and statistical analysis in order to continue to monitor the spiny lobster fishery.
Several activities were identified in response to the project objectives. These were the assessment of the status of exploitation of the lobster fishery, the definition of minimum lobster size, training, long-term spiny lobster stock assessment and a bioeconomic analysis of the lobster fishery.
In order to assess the status of exploitation of the spiny lobster fishery, the project made use of the wealth of historical statistical information on spiny lobster exports by commercial tail-weight categories available at the DOF. Since spiny lobster exports account for approximately 90% of total spiny lobster landings, this information was representative of the total tail-weight composition in the landings.
Data on catch and fishing effort by gear type (spear and condominium/hook), boat and vessel size, main fishing ground (Little Bahama Bank, Great Bahama Bank North, and Great Bahama Bank South) and month (August 1993 to September 1995) were also available. This information was used to assess the relative efficiency of vessel/boat and gear types and to produce estimates of the relative abundance of spiny lobsters in the different grounds and months. The results indicate that boats in the <20 ft length overall (LOA) and 20/35 ft LOA categories and the use of spiny lobster aggregating devices (condominium/hooks) are, respectively, 2.1 and 2.5 times more efficient than the boat selected as standard (<20 ft LOA and using spears). This is attributed to the deployment of the aggregating devices in areas which were easily accessible to these categories and to the fact that the devices were used in areas of increased densities of younger, and thus more abundant, spiny lobsters. However, vessels in the 35/60 ft and >60 ft LOA categories, using condominium/hooks, were only 1.35 and 1.62 times more efficient than the standard boat. This may be owing to the mechanisms of mothership operations among the largest vessel categories, which may not be fully represented in fishing effort declarations. These operational mechanisms may have an effect on the definitions of days at sea and effective fishing days, thus affecting relative efficiencies in these two categories. This is the case when larger vessels fish on various fishing grounds farther away from their landing ports and for protracted time periods, when effective fishing time is significantly less than the total trip time. This may account, at least in part, for the significantly lower efficiency observed between these two categories of vessels.
All categories of boats and vessels using spears were significantly less efficient than vessels and boats using aggregating devices, owing to lower fishing power. Boats using spears in the 20/35 ft LOA were approximately 1.05 times more efficient than the standard, while vessels in the 35/60 ft LOA were 1.07 more efficient and larger vessels in the >60 ft LOA category were 1.25 times more efficient.
Regional trends in relative average stock abundance estimated from spatio-temporal catch and effort data are indicative of general recruitment, abundance and migratory patterns of spiny lobster stocks in the main fishing grounds of the Bahamas. Their analysis shows the likelihood of significant seasonal abundance linkages between grounds in the Great Bahama Banks South and North. The results also indicate that recruitment processes in the Little Bahama Bank follow similar dynamics to those observed in the Great Bahama Bank South, but with significantly different intensities. If this is the case, future research should address important questions of fleet rotations and effort allocations to maximize spatio-temporal availability of the stocks to the fishery. For this purpose, general information systems should be used by the Government to integrate all existing data on stock spatial distributions.
Because of the inherent difficulties involved with aging spiny lobsters (and crustaceans in general), there was the need to develop stock assessment procedures that could make use of the valuable export data available at the DOF. The procedures developed were integrated in the following algorithm. The annual export statistics, in the form of tail-weight categories, were transformed to tail-length distributions by means of a computer software program developed for this purpose and data, collected by the project, on the tail-size compositions of each commercial tail-weight category declared in the export data. A total of 3 232 spiny lobsters was sampled by the project. The information was used to develop morphometric relationships between tail length, tail weight and carapace length according to sex. The resulting tail-length frequency estimates were then used to calculate annual total mortality rates using length-catch curves methods. Finally, the annual total mortality rates obtained were used as calibrating indices in a more robust stock assessment procedure (length-cohort analysis) designed to estimate stock abundance and fishing mortality rates.
The stock assessment algorithm was used in conjunction with a partial database collected by the project on size frequencies in commercial size categories in order to generate a preliminary evaluation of stock abundance and fishing mortality rates. The application corresponded to the last four years of available export data, and the estimated values corresponded to average spiny lobster stock abundance in weight and numbers.
The results indicated that the spiny lobster population was at a remarkably similar level of abundance in 1991, 1993, and 1994. The only departure was 1992, which showed a slightly lower abundance. These statistics differed significantly from the only existing standing stock abundance estimate of 14.9 million individuals in 1982. The latter estimate, however, did not represent the distributional range of the landings utilized in the present analysis.
Fishing mortality estimates were stable, averaging 0.194 and 0.245 for females and males, respectively. An average exploitation rate for females and males, estimated as simple ratios between fishing mortality and total mortality rates, resulted in 0.358 and 0.412 for females and males, respectively. These rates appear to be indicative of intermediate levels of stock exploitation, with males approaching the level of maximum exploitation (0.50) more quickly than females.
These preliminary assessments suggest that the spiny lobster fishery in the Bahamas is in a period of expansion between moderate to full levels of exploitation, with landings oscillating between 4.9 to 5.5 million pounds of tails and the population fluctuating between 15 and 21 million pounds of tails.
It is emphasized that the stock assessments performed by the project used data on tail-length frequencies at commercial size categories collected only during the period July-August 1995. It is essential that the DOF carry out a complete annual sampling of the morphometrics of tail distributions to corroborate that changes in length compositions corresponding to commercial size categories do not alter from one season to another. The stock assessment results in this report should thus be considered as preliminary until such data are collected and new assessments are made.
Determining an alternative minimum size that would optimize yield in the spiny lobster fishery entailed determining growth, natural and fishing mortality, the reproductive dynamics of the species and the value of the expected yield to fishermen. In the case of the spiny lobster fishery in the Bahamas, none of these aspects had previously been quantified. The project integrated the fishery data and biological information that most accurately reflected the exploited dynamics of spiny lobsters in order to develop new yield models for the fishery.
The results showed that maximum levels of yield-per-recruit were attainable when tail weight at first capture was about 5.5 ounces in females and 7 ounces in males. These figures correspond to the yield realized at levels of fishing mortality that will probably never be achieved, given the interactive nature of the condominium used in the fishery. At these tail sizes, and according to the growth and morphometric characteristics of the two sexes, females will have a carapace length (CL) of 3.13" (79.51 mm), a tail length (TL) of 5.56" (14.12 cm), and be approximately 2.03 years old, while males will have a CL of 3.54" (89.94 mm), a TL of 5.98" (15.18 cm), and be 2.85 years old. If the current fishing mortality level is considered to be the same as that in 1994, the minimum size generating maximum yield-per-recruit is attainable when tail weight at first capture is 4.5 oz in females and 6 oz in males. These minimum tail-weight sizes correspond to a CL of 2.96" (75.17 mm) in females and 3.37" (85.70 mm) in males. The corresponding TLs and ages are 5.2" (13.20 cm) and 1.29 years in females, and 5.68" (14.44 cm) and 2.55 years in males.
From a fishery management perspective, however, it is necessary to define a single minimum size applicable to both sexes. A minimum tail weight of 5 oz at first capture is regarded as practical since it is representative of the minimum commercial size category declared in all spiny lobster exports in the Bahamas. A 5-oz minimum tail weight represents approximately 5.38" (13.68 cm) TL and 3.05" (77.41 mm) CL in females and 5.35" (13.59 cm) TL and 3.19" (80.96 mm) CL in males. This minimum tail weight will generate slightly lower yield-per-recruit (61 versus 62 grams per recruit) among males at the current level of fishing mortality since the yield-per-recruit isopleths are vertical, indicating that almost no change in yield-per-recruit occurs with increases in minimum tail weight size within the 5 and 6.5-oz range.
This compromise on minimum tail-weight size at first capture is also important because, at that size, spiny lobsters will have similar tail sizes (5.38" in females and 5.35" in males). Thus the minimum size proposed facilitates enforcement, while appearing to be congruent with yield-per-recruit optimization based on the growth and mortality patterns of spiny lobsters and with the practices observed in the industry.
Generally, fishery management practices indicate that when exploitation drives spawning potential below 30% of that observed at the unexploited level (Spawning Potential Ratio or SPR), conditions of reduced recruitment may result in an increased risk of a fishery collapse. If a minimum tail weight at first capture of 5 oz is adopted for female spiny lobsters, the 30% SPR threshold could be reached if the fishing mortality rate exceeds 0.50. In other words, more than twice the present level of fishing mortality would need to be exerted by the fishery to drive the female stock to the 30% SPR. At current levels of exploitation, a minimum tail size of 5 oz or 5.38" would maintain the female stock above the 55% SPR level. The analyses indicate, therefore, that, within the level of uncertainty of the parameters and data used, it is biologically sound to adopt a minimum tail-weight size at first capture of 5 oz (or minimum tail size of 5.38"), since this allows a significant fraction of the stock to spawn even if future fishing mortality levels are higher than those now observed in the fishery.
The utility-per-recruit, defined as the value of yield-per-recruit, generates similar results to those found with yield-per-recruit, owing to the relative constancy of the price paid per pound of tails. Data on prices obtained by the project indicate that tails in the 5-8 oz categories were paid at $B 15.2/lb while those in the 16-20 oz range were paid at $B 14.23/lb and those in the largest size category (20-14 oz) were $B 14.10/lb. This slight price differential, which favours smaller tail sizes, results in a more conspicuous maximum of utility-per-recruit defined over a narrower range of minimum tail weights. Thus, the results of utility-per-recruit analysis corroborate the results already found for minimum size definitions using yield-per-recruit.
It can be concluded, therefore, that a minimum tail size of 5.35" to 5.38", corresponding to a 5-oz tail weight, will not compromise the future spawning potential of the stock at the current levels of exploitation, or within a rational expansion of the fishing effort if this important resource is fully exploited. Furthermore, the minimum TLs proposed are compatible with the minimum CL of 3" imposed in the United States spiny lobster fishery, thus making spiny lobster exports compatible with international market regulations.
Training in population dynamics and fishery modelling took place at the University of Miami. The training was scheduled in two periods, of 15 days each, during the months of May and July 1995, respectively. Training covered the principles of bootstrapping (intensive computer re-sampling), the applications of bootstrapping in FORTRAN, computer operations and the use of software such as dBASE, EXCEL, QPRO and text processors. This training complemented the abilities required in population dynamics to operate and understand the computer programs developed by the project.
Over 18 hours of formal training in stock assessment techniques and principles of fishery management were provided in June-August 1995.
These training efforts were significant, given the needs of the DOF to enhance its capabilities to generate stock assessments in support of fishery management.
Since the DOF is responsible for fishery research and development and the implementation of fisheries policies, it must efficiently manage the natural resources available to the sector. It thus needs to implement stock assessment work in order to draw conclusions on the status of exploitation of the lobster fishery and to develop appropriate management actions. During the project, a lobster stock assessment procedure was developed and implemented with existing data. In order to improve the existing knowledge on the status of exploitation of the lobster fishery, however, it will be necessary to refine the existing database used in the stock assessment algorithm.
The project developed a general framework suggesting the type and purpose of the new information required and showing how new information would enhance future spiny lobster stock assessment activities. Several important points emerged. First, it became clear that the DOF did not have the minimum critical mass needed to confront the level and complexity of the tasks to be performed in any lobster stock assessment programme. The framework therefore suggested modest initiatives to collect more accurate and precise data with minimum investments in new personnel. Second, it called for arrangements by the DOF to obtain temporal external technical assistance until at least two DOF officers were fully trained in existing lobster stock assessment procedures.
The proposal suggested that assessment activities take place once a year at the end of the lobster season. Data collections, however, should be implemented on a continuous basis throughout the fishing season. The requirements were reduced to collecting catch and effort data using the existing fishing trip reporting system, to assessing local lobster landings every few years through a properly designed census, and to completing the database on monthly size-frequency distributions according to commercial size categories, already started by the project.
If stock assessments were performed annually following the techniques and procedures suggested, the DOF would accumulate information on population abundance, recruitment trends and fishing mortality trends which, after a few years, would allow forecasts to be made. These forecasts would then permit more timely actions to be taken to manage the fishery.
During the project, some significant economic analyses were generated. First, a costs and earnings profile of the fishing fleet components was established based on data collected by the project. This allowed an analysis of fishing performances of three categories of boat/vessels: small open boats or dinghies operating in association with aggregating devices and hooka diving gear; vessels carrying out mothership-type operations using aggregating devices and dinghies; and vessels fishing with traps. The analyses show that dinghies operating independently provided an annual remuneration of $B 20 987 to each diver. The return to the owner's investment was $B 9 409. In the case of mothership vessels, remuneration to each diver and skipper was $B 21 493 and to each cook and deckhand $B 17 194. The return to the owner's investment was calculated as $B 91 010. The annual remunerations in the trap vessels were estimated at $B 20 543 for each crew member and $B 25 678 for the skipper and engineer. The return to the owner's investment was low, at $B 878.
Some financial disadvantages associated with operating from the outer islands were found. These were greatest for dayboats (dinghies), particularly for those operating from the Aklins and Crooked islands. These data must be considered, however, in the context of alternative employment opportunities and remuneration levels within these communities.
A preliminary bioeconomic analysis of the fishery was carried out, utilizing a model that showed how the analysis could be adopted to explore possible scenarios for fisheries development. The analysis indicated that if fishing effort was to increase, it should do so in relation to minimum cost. This could be achieved, for example, by increasing the number of working days per month. The least desirable way to achieve increased effort would be by allowing increased numbers of boats. Even at the present level of effort, the results showed that further increases as a result of an increase in boats would generate insufficient additional gross revenue to cover the additional fishery costs (not including labour costs). Even if the aim were to provide additional employment, the analysis showed that it would be cheaper for the existing fishermen to pay salaries directly to potential entrants, rather than allow them access to the fishery. Despite the practical difficulties of implementation, therefore, ways need to be identified to prevent the entry of additional boats.
The bioeconomic model developed by the project could be expanded to include not only more detailed financial aspects of the fishing operations but, more importantly, the economic mechanisms that control this important fishery.
Preliminary results from assessments of the lobster fishery show that moderate levels of exploitation are currently impacting the fishery. However, trends in fishing effort show a substantial increase in the use of aggregating devices. As these devices accumulate, the efficiency of daily diving operations will decrease more rapidly owing to the exponential nature of the interactions among the devices under fixed stock abundance. The negative economic impact will therefore be large, as more investment is required under increasingly diminishing returns. For this reason it is imperative that the Government improve the fisheries statistics of catch and effort, both in time and space, in order to keep track of the fishery developments and to allow more precise stock assessments to be performed with the new data.
It is recommended that the Government develop policies concerning the management of fishing effort entering the lobster fishery, so that strategies on the use of this important resource can be adequately defined and understood by all users. The biological database on size frequencies in commercial grades should also be improved in order to clarify the way in which seasonal effects on size frequencies may affect stock assessments.
The Government should perform annual stock assessments on a routine basis to accumulate abundance and fishing mortality estimates in order to generate fishery forecasts.
It is recommended that a minimum tail size of 5 oz, or its equivalent length of 5.35 to 5.38", be implemented in the fishery, since this size will optimize yield-per-recruit over a wide range of fishing mortality above the present levels of exploitation. This minimum size is also supported on biological grounds since reductions in spawning potential are above the 30% level, the minimum acceptable threshold if increases in the risk of recruitment overfishing are to be avoided.
It is recommended that the Government request temporary external assistance in stock assessment until DOF capabilities in this area are raised to levels of self-sufficiency. This external assistance should be viewed as an on-the-job training activity. The DOF should create a specifically-designed unit to take over responsibilities for stock assessment.
It is recommended that a thorough economic analysis of the fishery be undertaken. The analysis should include limited-entry schemes in the light of the potentially high rates of fishery development that the fishery may experience under present profit levels. The economic analysis should consider non-traditional surplus production models including nonlinear interactions between fishing effort units and catchability.
On the relative efficiency of spiny lobster fishing in the Bahamas. Field Document 1. N.M. Ehrhardt, V. Deleveaux, and C. Higgs, 1995.
Bahamas spiny lobster stock assessment algorithm. Field Document 2. N. Ehrhardt, 1996.
Alternative minimum size definitions for the spiny lobster, Panulirus argus, fishery of the Bahamas. Field Document 3. N. Ehrhardt, 1996.
A comprehensive long range stock assessment plan for the spiny lobster (Panulirus a--rgus)- fishery in the Bahamas. Field Document 4. N. Ehrhardt, 1995.
Analysis of the costs and earnings in the Bahamian crawfish fishery. Field Document 5. M.J. Sanders, 1995.
Bioeconomic analysis of the Bahamian crawfish fishery. Field Document 6. M.J. Sanders, 1995.