The types of information typically gathered from fishers or obtained from examining the catch include the following.
Fishery Catch Statistics
Of course, many fishery departments collect records and it is hoped that annual or monthly landings data are collected with a properly designed sampling program. It is critical that any sampling protocol is properly documented and consistently applied over time if the data are to be of value in assessing trends in a fishery. When referring to departmental records for historic datasets, it is important to refer carefully to the methodology applied to determine to what extent past and present data might be comparable. For example, often landings are collected with no reference to effort. Knowledgeable fishery officials could be consulted to determine whether important changes in effort might have occurred that could significantly have affected available data in departmental records. Ideally CPUE data should be used (but refer to Section IV.E.). If there is no reason to suppose significant changes in effort over time, landings data can still be useful.
Describing the method of take for the aggregation fishery is important and relatively easy. Common gear types include hook and line, fish traps, and speargun. In some cases nets (gill net or other) may be used. Each gear type has many variations so details are necessary to adequately describe the fishery. For example, hook and line fisheries can vary from a single hook 80 on a handline to a large vessel putting out miles of longline with thousands of hooks. Fish traps vary in size and design as well as methods for baiting, deploying and retrieving.
Record the type and size of boats that are fishing the aggregation. Information on what ports/villages the boats originate from is valuable as well as the place they offload their catch. Often aggregation fisheries are operated out of small boats (Fig. 54) making it difficult to monitor a large proportion of vessels involved. Nonetheless, as many boats as possible should be monitored, and the total number of boats known, to enable catch and effort to be estimated.
Figure 54. (Left) Handliner fishing from a small outboard boat capturing mutton snapper, Lutjanus analis, from a spawning aggregation. (Right) Catch of mutton snapper along with one grouper taken from the area of a spawning aggregation (MLD).
Sampling the Catch
Measurements taken from a random sample of fish being landed can provide biological and fishery information. Of course sampling can only be done with the permission of the fisher or buyer. Getting permission can be difficult when the fish are landed/shipped live. Even in these circumstances there may be mortalities that you will be allowed to examine. By examining gonads fish can be sexed and if gonad samples can be taken, data can be collected for gonadal somatic index (GSI) and ovaries can be examined for the presence of hydrated eggs and/or post ovulatory follicles (see Section IV.D.). Recording lengths and weights is important for converting numbers of fish caught to weight of catch. Although it is tempting to use these samples to characterize the aggregation (sex ratio, size frequency etc.) one must be careful to consider the possible selectivity of the gear (for size or sex of fish, for exampale).
Even crude estimates of catch and effort are better than no data. Information gathered simply from interviews can be used to estimate catch. Fishers may give rough numbers for how many fish they take per day or per year from the aggregation. Average catches per boat can be expanded by the number of boats known to be fishing to estimate total catch. The buyers may know the approximate biomass of the catch. More detailed catch and effort data are extremely valuable if they can be obtained. For example, CPUE expressed as a fish per unit gear (e.g. number/weight of fish per trap or per hook) or per unit time (number/weight fish caught per hour fished) can be obtained through observation and interview. These data are critical for documenting trends in the fishery. Below are specifics on collecting catch data.
Fish Market Surveys
Where there are just a few markets and all or the majority of the catch is landed at these markets, market surveys can provide a good indication of seasonality in landings (although as already noted above, landings can vary because of fisher behavior which can assessed by speaking to fishers directly). Regular visits to markets to carry out a pre-determined sampling protocol is advised but careful decisions need to be made concerning how many fish to sample, how many stalls or shops to sample, and how often and which species to sample. How will the data be organized and what is the objective of collecting the data? These are the kinds of questions that must be asked, and answered, in order to develop an appropriate sampling program. There are plenty of examples of this kind of sampling and it is not difficult to plan a program, but if there is no planning then the data may mean very little and much time, money and valuable information may be lost. CPUE data could be estimated by calculating the number of fishers and some measure of their effort such as number of days or hours they fish per day. Standardized forms should be developed so that different workers are sure to sample in the same way and over the long term. This means that forms should be clear and simple, with as little unnecessary detail as possible.
Some large and well-organized markets keep records of sales. These may or may not be useful depending on how they are taken and whether species are reliably and individually recorded (i.e., each fish is recorded to species level). Again, an estimate of fishing effort will be needed unless it can reasonably be assumed that effort is not changing over time. In some cases, market surveys might not be of any use for evaluating catches in local waters. For example, in Hong Kong, although all chilled fish caught by Hong Kong vessels must, by law, be sold through local markets, since Hong Kong vessels largely fish outside of local (Hong Kong) waters, market records tell us nothing about local Hong Kong catches (also, there is much fish sold outside of legal channels). Be aware when inspecting market records (as well as for other types of market surveys) what the numbers are actually telling you. For example, chilled, filleted and live fish may well be handled by different market sectors so be sure to check how your species of interest are marketed. Some might be sent directly to restaurants without ever passing through a retail market, for example, or culturally important species may go directly to the local community.
In some fisheries it is possible to sub-sample the catches of boats as they come into port. There are well-established methods for doing this and the usual considerations of which fish species to sample, how many boats and how often to sample, etc., must be made. As for any types of surveys, planning is essential and knowing your fishery is important. For example, port surveys have long been practiced in Puerto Rico, providing valuable fishery data. It was discovered, however, that a couple of species were under-sampled because they were particularly preferred by fishers and taken home to their families. These species had gone largely unrecorded in port-collected samples but, realizing the situation enabled suitably cautious interpretation of data.
Interviews of fishers can also provide valuable information on both catches and effort (see also Section III). Again, the basic questions of how many, how often and standardization of the approach are essential. It is also important to have some means of verifying responses. This 82 could be achieved by including, amongst survey questions, questions with answers known to the interviewer but not to the fisher. Often interviews can only be undertaken sporadically but even more qualitative information can provide useful indications of trends in catches within the year and over the long term and how and where a particular fishery is conducted. One particular advantage of fisher interviews is that questions can be asked regarding whether fish were releasing milt or eggs at capture, thereby identifying possible spawning aggregations.
In some fisheries, ship captains are required to keep logbooks and these can be used to determine catches for a known unit of time for a given vessel. Note, however, that it is essential that such logbooks be cross-checked periodically (for example by assigning on-board observers) and, in analyzing the data, it is essential that the resolution of the data is known. For example, it may be easiest for a captain to simply make an estimate of his monthly landings. This might provide a useful seasonal pattern of landings within an annual cycle but would not identify shorter-term patterns such as spawning aggregations that may occur for just a few days in a month. An interesting example of problems in interpretation occurred in the fishery of the coral trout, Plectropomus leopardus, on the Great Barrier Reef of eastern Australia. Logbooks provided monthly information that indicated an increase in catches during the known months of aggregation. However, the data were of insufficient resolution to detect whether the aggregations themselves were being specifically targeted during these months. Although reports by some fishers indicated that indeed aggregations were being targeted, the logbook data were used to suggest that there was no evidence of targeting of aggregations. This conclusion had consequences for the types of management measure subsequently considered. Again, as we have emphasized elsewhere, know your data and their limitations and interpret accordingly.
In some countries there is an important export trade in reef fish species that aggregate to spawn. Aggregations may provide particularly attractive bounties for exporters. If export records are complete enough they may be suggestive of seasonality in catches. This will depend very much on the local situation. Since exports are very likely to be an amalgamation of fish caught from many places and, moreover, only represent part of the catch, they may show little trend even when there may be seasonality in some of the fishing areas involved. However, if much of the catch of certain species is exported and mostly through one or two ports or airports, inspection of export records might be of value. This will only be the case, of course, if exports are noted by species and these identifications are reported accurately.
If restaurants are a major purchaser of certain fish species (often the higher value ones), then periodic restaurant surveys might provide an idea of seasonality, or at least indicate changes in the availability of such species.