Fish Surveys

To collect fish we use electrofishing equipment complemented with a variety of fishing nets.  Depending on the size and characteristics of a river, the team consists of between 3 and 9 people the majority are normally volunteers.  Volunteers are essential to the work we do not only in practical and economic term, but because including local volunteers is part of the biomonitoring project´s environmental education objective.  It usually takes three to four hours to complete a sample. Fish are identified by species, counted, examined for illnesses, parasites and other anomalies before being returned to the water.
Based on the results of the sample, we calculate a score, or Index of Biotic Integrity (IBI) for each site. According to the score,  complemented by the knowledge and professional judgement of ANAI staff, a bioclass rating is assigned (Excellent, Good, Fair, Poor and Very Poor). The lowest possible score is 12. A score of 60 (Excellent) corresponds to a river that has not been altered by humans. Key aspect of the information used to determine the Index of  Biotic Integrity include:

  • Number of native species found
  • Trophic level (place in the food chain) of the species encountered
  • Habitat  requirements (where species  live in the aquatic system)
  • Tolerance of contamination

Since 2008 we have also been involved in development of a Visual Index of Biotic Integrity (IBIVI), calculated on the basis of instream inventories, using facemask and snorkel. This method greatly facilitates participation and eventual “ownership” of the biomonitoring process by rural communities.

Development and refinement of fish-based biotic indices for Talamanca, and the humid tropics in general, is an open-ended process in which the ANAI team occupies a leadership position.  In 2010 we concluded that we had accumulated a sufficient body of data to permit a more rigorous statistical analysis of much of our data.  This is reflected in recently revised indices, but further improvement is to be expected.


As a consequence of our concerns about hydro dam proposals in the Greater Talamanca region diadromous animal (those obliged to move between marine and fresh water environments in order to complete their life cycles) have become a major focus of conservation concern  in Bocas del Toro and Talamanca.  An inescapable conclusion is that barriers to diadromous behavior would cause massive damage to ecosystems and fisheries anywhere in the region.  This in turn places the role of rivers and streams as altitudinal biological corridors in the spotlight.  We have been able to derive reliable estimates of the relative importance of diadromous fish and shrimp at different sites without recourse to full-scale quantitative sampling, such as is necessary for calculation of IBI.

For the foreseeable future much of our work will focus on diadromy and conservation of riverine corridors.

Benthic Macroinvertebrate Monitoring

Monitoring of benthic (bottom dwelling) macroinvertebrates, chiefly insects, is the most traditional method of stream biomonitoring, based on identifying samples of benthic organisms and applying indices similar to those described above for fish.  Staff and volunteers normally carry out macroinvertebrate samples at each site monitored, applying the BMWP-CR index which officially establishes criteria recognized by the government of Costa Rica.  For a more detailed account of our macroinvertebrate monitoring methods, see

We are also working to refine our macroinvertebrate assessment methodology to more closely correspond to the special characteristics of the Talamancan environment.  An important emphasis at this time is the study of diadromous shrimp, which constitute a major component of the macroinvertebrate assemblage in most of our streams, but are little studied.