CHAPTER 1. INTRODUCTION

1.1 PROGRAMME OBJECTIVES
1.2 EFFORT OF INVESTIGATION
1.3 METHODS OF INVESTIGATION, INSTRUMENTS AND EQUIPMENT
1.4 FISH TAXONOMY

1.1 PROGRAMME OBJECTIVES

The general objectives of the programme as discussed and agreed at the planning meeting in Panama were as follows:

Describe the composition, distribution and abundance of the main components of the resources of small pelagic and demersal fish, squid and crustaceans on the shelf and slope for studies of the state and the potentials of the stocks.

Collect biological samples of the most important species for studies of growth, maturity etc.

Conduct taxonomic studies for the purpose of preparing a regional species guide.

Conduct oceanographic investigations and describe the oceanographical regimes and their ecological characteristics.

Prepare charts based on echo sounder observations of bottom character.

Provide data of catch rates for specific selected gears and areas including deep water shrimp and langostino on the slope and jigging for giant squid off the shelf.

As regards survey plan the time available during a two months coverage of the shelf between Colombia and Salina Cruz in Mexico would allow a mean of 15 nm between course tracks over the shelf leaving 10-12 hrs per day for fishing. The survey effort was, however, adjusted to the fish distribution with a denser coverage of areas of higher abundance. The survey plan was also amended in accordance with available information of the distribution of the fisheries and from previous survey programmes. As the programme developed the findings were discussed with the participating parties and the objectives and coverages adjusted as desirable.

1.2 EFFORT OF INVESTIGATION

The survey programme covered a period of one year from January to December 1987. The timing and number of days spent working in the waters of each country with distance steamed and number of fishing stations worked are set out for each survey in Table 1.2.1. The surveys generally covered the shelf from abt. 10 fathoms of depth to the shelf edge at abt. 200 m depth with some work also on the slope down to abt. 500 m depth and beyond the shelf when doing hydrographic profiles or testing for oceanic squid. The density of the course tracks are indicated as the ratio between the distance steamed and units of 100 nm² covered. Figure 1.2.1 shows an example of the course tracks and stations worked during a survey. The complete layout of the course tracks and the positions of the fishing stations are shown in the Data File, Annex 3. The total survey effort of the programme Comprised abt. 170 days of active research work with abt. 27 000 nm steaming and abt. 1 100 trawl stations.

Table 1.2.1 Details of investigational effort in the four surveys.
SURVEY	DAYS	DATES	DISTANCE (nm) TRAVELLED IN SURVEY AREA	SURVEY INTENSITY nm/100nm2	NUMBER OF FISHING STATIONS	NUMBER OF HYDROGR. STATION
I
PANAMA	10	4-14/2	1723	14.0	58	13
COSTA RICA	6	14-19/2	874	21.5	28	7
NICARAGUA	6	19-25/2	826	12.2	34	7
HONDURAS	1	25-26/2	55	13.7	7	7
SALVADOR	5	26/2-3/3	779	15.0	35	6
GUATEMALA	4	4-8/3	551	13.4	26	6
MEXICO	5	3-12/3	881	13.4	35	6
II
COLOMBIA	7	25/4-1/5	1218	21.7	30	8
PANAMA	13	1-13/5	2226	18.4	71	13
COSTA RICA	6	13-19/5	1141	28.0	13	5
NICARAGUA	7	19-25/5	963	14.3	40	9
HONDURAS	1	25-26/5	55	13.7	6	7
EL SALVADOR	6	28/5-2/6	720	13.9	34	6
GUATEMALA	5	3-8/6	516	12.5	32	7
MEXICO	5	8-13/6	834	12.7	37	10
III
COLOMBIA	5	6-11/8	785	14.1	29	8
PANAMA	10	11-21/8	2050	16.7	72	14
COSTA RICA	7	21-28/8	1075	26.4	49	6
NICARAGUA	10	28/8-6/9	1157	17.2	72	7
HONDURAS	1	6-6/9	55	13.7	7	7
EL SALVADOR	4	7-10/9	635	12.2	34	6
GUATEMALA	5	11-16/9	585	14.2	34	6
MEXICO	6	16-22/9	1215	18.5	42	12
IV
COLOMBIA	4	30/10-3/11	821	14.7	26	8
PANAMA	10	3-12/11	1546	12.6	55	11
COSTA RICA	5	12-17/11	926	22.7	46	6
NICARAGUA	6	17-23/11	1010	15.0	40	5
HONDURAS	1	23-23/11	55	13.7	4	7
EL SALVADOR	4	24-28/11	773	14.9	35	6
GUATEMALA	5	28/11-3/12	545	13.2	27	5
MEXICO	4	3-7/12	645	9.8	48	9

The scientific staff participating in the four surveys are shown in the following record:

Colombia: Guillermo Barreto, Hermes Mojica

Panama: Elvis Nieto, Ruben Salazar, Edwin Medina

Costa Rica: Hubert Araya, Mario Quiros, Carlos Rodriguez

Nicaragua: Manuel Perez, Rodolfo Sanchez, Leonel Martinez, Jose Villalobos

Honduras: Domingo Aguilar, Luis Morales

El Salvador: Mauricio Calderon, Juan Ulloa, Orlando Villatoro

Guatemala: Fernando Rosales, Antonio Salaverria, Herman Kinn, Anibal Rosales, Leonel Salaverria

Mexico: Armando Arias, David Mendizabal, Miguel Cisneros

FAO: Luis Villegas, Alvaro Abella, Gabriella Bianchi, Martina Schneider

IMR: T. Strømme, G. Sætersdal, J. Hamre, O. Alvheim, H. Ullebust, T. Haugland, I. Svellingen, Ø. Torgersen, E. Molvær, M. Dahl

1.3 METHODS OF INVESTIGATION, INSTRUMENTS AND EQUIPMENT

Acoustic instruments

Two SIMRAD scientific echo sounders, EK 400/38 kHz and EK 400/120 kHz were used during the survey for estimation of fish density. The EK 400/38 was coupled to a digital integrator QD as well as to an analog integrator QM. The performance of the instruments were checked by calibrations on a standard copper sphere in April, May, August and November 1987. The details of the instrument settings used and the results of the calibration experiments are shown in Annex 1.

Hydrography

Temperature, salinity and oxygen were sampled at standard depths with Nansen bottles. Oxygen was measured with the Winkler method and salinity determined with an inductive salinometer. Surface temperature was recorded at 4 m depth with a thermograph.

Fishing gear

Bottom trawl: High opening shrimp and fish trawl with net headline 31 m (float-line), foot-rope 47 m, gear with 12 cm diameter roller disks, estimated headline height 6 m and distance between wings during towing 18-20 m.

Pelagic trawl: Type “Harstad-trawl”, width about 30 m, vertical opening 10-15 m.

Cod ends of trawls with fine meshed inner lining. For trawl designs see Annex 1.

The pelagic schooling fish was investigated using acoustic integration technique combined with fishing with bottom and mid-water trawls for identification and sampling. Fish near the surface and very close to the bottom are not properly observed with this system. Horizontal ranging sonar was used to observe surface schooling fish, but such observations are not easily quantifiable in terms of measure of biomass.

The reliability of acoustic techniques in providing estimates of biomass is under continuous review by the scientific community. There is little direct information available on the acoustic target strength of fish species from low latitudes. For the pelagic fish biomass estimates are based on an assumption of a target strength similar to that of the European herring. Some observations on the dimensions and volumes of the swim-bladder of the main species of the region indicate that this assumption has not grossly biased the results. Another limitation is found in the incomplete coverage of inshore waters by the survey, since the parts of the shelf shallower than about 10 fathoms can not be navigated by the vessel.

The overall effects of these various limitations are thought to lead to an underestimation of the biomass.

The identification of the targets recorded by the acoustic integration system represents an important problem. The basis for this step is the composition of the catches in hauls with bottom and mid-water trawls together with an evaluation of the characteristics of the echo traces. Because the catchability offish is highly species and size dependent the catch data must be used with considerable reservations and in areas where many species occur in mixture identification can only be made by relatively broad groups. Some species occur, however, in distributional patches or in larger continuous aggregations and this facilitates the identification. The integrator values were allocated to the following groups:

Clupeids and anchovies;
Carangids, scombrids, barracudas etc.;
Demersal fish in mid-water.

The swept area trawl survey method carries with it a special problem of estimation viz. which value to assign to the catchability coefficient, q. We have used 1 which implies that all fish in the path of the gear are caught and contained in the catch. It seems, however, likely that part of the fish escape through the meshes and over or under the trawl and that this may exceed the herding effect of the sweep wires. The assumption q=1 thus probably results in underestimates of biomass.

The incomplete coverage of inshore waters caused by the vessel’s operational limitation of 10 fathoms also affects the results of the study of the demersal fish with bottom trawl. The inshore faunas of bottom fish may thus be incompletely sampled with possible underrepresentation of inshore forms. This is unfortunate since the inshore fauna often forms an important part of the resources for the artisanal fisheries.

The results of the fishing experiments also provide information on the composition and distribution of the resources both pelagic and demersal and to a limited extent the catch rates that can be expected. It must be noted, however, that most of the fishing with bottom trawl formed part of the programme for the swept area biomass estimation of demersal fish and for this purpose the trawl stations are positioned more or less randomly and with no intention of obtaining high catch rates. Pelagic types of fish sometimes formed substantial parts of the catches in these hauls. These data must, however, be interpreted with caution. The catchability of these gears are often highly species and size selective, large sized schooling clupeids such as thread herrings have for instance a very low catchability while anchovy, smaller carangids such as bumper and scads and more solitary species such as sierra and barracudas are more easily caught both at the bottom and in mid-water although the trawl is generally not an adequate gear for such pelagic fish.

The various types of shrimp resources could not be covered in an appropriate way within the trawl survey programme. This would have necessitated a concentration of effort both seasonally and in the various special shrimping grounds which would have precluded most of the other survey objectives. For the inshore shallow water penaeid shrimps the survey data only provide records of incidental catches. Combined with information on shrimp areas and seasons the total catch records may, however, represent an important source for shrimp by-catch studies. For shrimp at intermediate depth, like the crystal shrimp P. brevirostris, the survey results may for some areas give indications of catch rates and seasons. A similar consideration applies to the shrimps in deep water beyond 150 m, mainly kolibri shrimp (fidel) Solenocera agazissi and nylon shrimp (cabezon) Heterocarpus vicarius.

Among the other crustaceans, a special effort was made to cover the resources of langostino Pleuroncodes planiceps by area, season and depth.

All catches were sampled by species so that a total composition by weight and numbers could be estimated. Length frequencies were usually recorded for the most common species. Biological data were collected for some commercially important groups.

One should note that this type of resource surveys covers most shelf resources but not the more widely ranging tunas and other large sized pelagic schooling fish.

A record of the acoustic instruments and their calibration is presented in Annex 1 together with a description of the fishing gears.

1.4 FISH TAXONOMY

With assistance from this programme FAO has undertaken the preparation of a Species Identification Guide for the region. Special FAO consultants participated in the survey to collect material for this guide which is expected to be completed in 1990.

A total of about 650 species were identified and more than 200 photographs were taken of fishes and invertebrates. Also, as a result of the work on board, an annotated draft was prepared and this will form the basis for the preparation of the final document. Because of the shortcomings in the available taxonomic information, a large number of specimens were sent to specialized taxonomists throughout the world. Contacts have also been established with local fishery institutions to collaborate in compiling further data in occurrency, habitat, fisheries and vernacular names.