Overviews of tuna baitfisheries were presented in the first session of the workshop. These were followed by aspects ofthe general biology of the species making
up the fisheries. The small fishes that form the basis of tuna baitfisheries in the
Indo-Pacific region comprise Engraulidae and Clupeidae (particularly Stolephorus and Spratelloides) and to a lesser extent Apogonidae, Atherinidae and
Caesionidae.
There are three main active pole-and-line tuna fisheries in the Pacific that
require a continuous supply of suitable live baitfish. The largest of these in Solomon Islands took about 2000 tonnes of baitfish in 1988. The baitfisheries of Fiji
and Kiribati are smaller but no less vital to the industry in each country. A smaIlscale pole-and-line fishery exits in Hawaii and relies on a regular supply of the
estuarine dependent Stolephorus purpureus. In the Indian Ocean Maldives has an
artisanal pole-and-line fishery that is vital to the nation's economy and likewise
needs an assured supply of baitfish. In other tuna fishing countries ofboth oceans
there has been a move away from pole-and-line fishing to purse-seining, largely for
economic reasons. The large Papua New Guinea pole-and-line fleet ceased operation in 1984. However, it is unlikely that the countries presently pole-and-line
fishing will cease such fishing in the near future. The pole-and-line method is
labour intensive, hence providing more jobs, produces higher quality fish, and
involves technologies more suited to certain developing countries.
Papers in the second session indicated that baitfish are also important for the
lucrative game-fishing industry in north eastern Australia. Anchovies ofthe genus
Stolephorus, the mainstay of Pacific tuna baitfisheries, form very important
coastal fisheries in India and Indonesia where they are used for human consumption.
The third session dealt with population dynamics and aging. Most baitfish
species live for less than a year. Historically, much ofthe research was conducted
on the now extinct Papua New Guinea fishery, with more recent work in Solomon
Islands, Maldives and Kiribati. Stolephorus and Spratelloides species have
received the most attention. Additional information on Stolephorus not used as
baitfish was given in papers from research in north eastern Australia, India and
Indonesia. Growth patterns based on length-frequency analyses using ELEFAN
showed broad agreement between areas, with K values of2.0 to 2.4 for Stolephorus
and 4.0 to S.O for Spratelloides. Growth curves were also generated from analyses
of daily growth rings in otoliths. The rings have been validated as daily in Spratelloides but experiments on Stolephorus have so far been inconclusive. Otolithic
aging ofSpratelloides species produced curves with K values of 4.0 to S.O, similar
to those generated by ELEFAN. Otolith data from Stolephorus from Solomon
Islands indicates a K value of4.0 to 5.0, and hence a much more rapid growth rate
than that generated by ELEFAN results. However, modal progression analysis of
length-frequency data from Stolephorus in India gave results closer to those from
the otolith analysis. Work is currently in progress to confirm the growth rate of
Stolephorus as this vitally affects interpretation ofthe population dynamics ofthis
most important baitfish.
The session on reproductive biology that followed showed that Stolephorus and
Spratelloides are continuous batch spawners in the tropics, with several spawning
peaks per year that vary according to site, time and geographical area. Such continuous spawning, with often ill-defined modes, may hamper length-frequency
analyses as following single cohorts is difficult. The spawning of both genera
appears to be driven by food availability and an array of environmental factors
(eg. moon phase, tidal phase, wind, rainfall and temperature), the influence of
7each ofwhich varies according to local conditions. The fish apparently maximise
spawning success by varying the intervals between spawnings to coincide with
favourable local conditions. Hence there is often no correlation between spawning
times, even at sites close to one another. Therefore, high local fishing effort should
not adversely affect the overall stock: fecundity, egg abundance in plankton and
commercial catch data indicate that commercial catches in a baitground are supported by immigration of baitfish from other grounds.
It is significant that in both sessions three and four that no direct evidence of
overexploitation was presented. Neither were there significant differences in the
biology and ecology of baitfish between fished and unfished sites that could be
attributed to fishing pressure.
Stock assessments of the Papua New Guinea baitfishery during its period of
operation indicated that it was at about MSY. Catch and effort data from Solomon Islands suggested the occurrence of short-term overfishing at one site during
a period ofhigh effort in 1987. In Hawaii the spawning stock biomass was directly
related to levels of exploitation.
Tuna baitfisheries do not exist in isolation. Thc pelagic target species form part
of the reef fish community and hence fishing effects on baitfish may alter such
communities, and possibly affect other fisheries. In the last session such interactions were discussed. In Solomon Islands a major concern was whether baitfishing
reduced numbers of baitfish sufficiently to impact on their natural predators
which form the basis of subsistence reef fisheries. In Solomon Islands, baitfish
comprised about 25% of the diet of 28 predatory species. In Maldives only 10
species ate baitfish. To simulate the subsistence fishery in Solomon Islands, fishing competitions (using droplining, spearfishing and trolling) were held. Droplining was the predominant technique and contributed most to overall catch.
Baitfish predators are primarily pelagic piscivores caught by trolling, A household
survey was carried out in Solomon Islands using a purpose-designed questionnaire in order to obtain information relating to the subsistence fishing activities of
rural communities. Results indicated that the lagoon areas near rural communities are most commonly used as fishing grounds and hand/droplinings is the
dominant technique. A close correlation was found between the results of the
survey and catch and effort data from the fishing competitions; the latter appear to
be an excellent means of rapidly assessing subsistence fisheries. Most fish caught
by the subsistence fishery in Solomon Islands do not eat baitfish. Unless there is a
marked increase in trolling, there is little evidence that the commercial baitfishery
in Solomon Islands has a direct trophic effect on the subsistence reef fishery.
Conversely in Maldives at least four major baitfish predators are important in the
developing reef fishery. Baitfish predators may become a significant proportion of
artisanal catches in Maldives in the future.
Another possible effect of baitfishing relates to the by-catch of non-target
species during baitfishing operations. These are primarily juveniles of reef
species. The problem only exists with night light fishing as practised in the Pacific.
Daylight baitfishing as used in Maldives catches few non-target species. In the
final paper an attempt is made to quantify the numbers ofjuvenile reeffish caught
in commercial catches in Solomon Islands. There was a seasonal pattern in the
numbers and species taken. However, the relative importance of the mortality of
juvenile reef fish caused by baitfishing remains unknown and requires further
investigation.
S.J.M. Dialler